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8 Feb 1997

Volume 106, Issue 6, pp. 2055-2556

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Magneto-infrared spectra of matrix-isolated NiH and NiH2 molecules and theoretical calculations of the lowest electronic states of NiH2

S. Li, R. J. Van Zee, W. Weltner, Jr., M. G. Cory, and M. C. Zerner

J. Chem. Phys. 106, 2055 (1997); http://dx.doi.org/10.1063/1.473342 (5 pages) | Cited 13 times

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Two vibronic transitions, 2Δ3/2(v = 0)←2Δ5/2(v″ = 0) and 2Π3/2(v = 0)←2Δ5/2(v″ = 0) at 923 and 2560 cm−1, respectively, were observed for NiH in solid argon (and krypton) at 4 K. These Ω=3/2←Ω=5/2 transitions were shifted and broadened by magnetic fields of up to 4 T. Also, its ground state vibrational frequency has been observed in neon, argon, and krypton matrices. Bands in the 600–2000 cm−1 region were assigned as frequencies of the NiH2 (NiD2, NiHD) molecule. Contrary to earlier ab initio calculations, this assignment implies that the molecule is strongly bent in its ground electronic state. This discrepancy was explored theoretically by considering the lowest triplet (linear) and singlet (bent) states of NiH2. The relative energies of the two states have not been satisfactorily resolved, but the calculated structural and vibrational properties of the singlet state are in good agreement with the observations. © 1997 American Institute of Physics.
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33.20.Ea Infrared spectra
33.57.+c Magneto-optical and electro-optical spectra and effects
33.70.Jg Line and band widths, shapes, and shifts
31.50.Df Potential energy surfaces for excited electronic states
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Optical detection of yttrium dicarbide, a “T-shaped” molecule

T. C. Steimle, A. J. Marr, J. Xin, A. J. Merer, K. Athanassenas, and D. Gillett

J. Chem. Phys. 106, 2060 (1997); http://dx.doi.org/10.1063/1.473343 (7 pages) | Cited 7 times

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The yttrium dicarbide molecule, YC2, has been identified in the reactions of laser-ablated yttrium with methane and other small hydrocarbons under supersonic jet-cooled expansion conditions. A parallel-polarized electronic band system with origin at 12 889.5 cm−1 has been tentatively identified as an A1–math 2A1 transition of a “T-shaped’’ isomer where the Y atom is bonded to the side of a C2 molecule. Weak vibronically induced perpendicular bands, representing Δυ3=odd transitions, are also present. Extensive vibrational progressions in the excitation and the resolved fluorescence spectra have been analyzed to give the two lowest vibrational frequencies of the two electronic states: math 2A1, ν2 (a1) = 561.1(±2.8 cm−1), ν3 (b2) = 369.6 (±1.7 cm−1); excited A1, ν2=494.5(±5.0 cm−1), ν3=331.6(±2.2 cm−1). No bands involving the C–C stretching vibration (ν1,a1) have been found. The frequency of the ν3 vibration in the ground state indicates that the barrier to internal rotation of the C2 group against the Y atom is quite high, but large anharmonic coupling between the ν2 and ν3 vibrations suggests that internal rotation is facilitated by excitation of the Y–C2 stretching vibration. © 1997 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Kf Visible spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.50.Df Potential energy surfaces for excited electronic states
33.20.Tp Vibrational analysis
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Collision-induced double transition effects in the 3ν3 CO2 band wing region

N. N. Filippov, J.-P. Bouanich, C. Boulet, M. V. Tonkov, R. Le Doucen, and F. Thibault

J. Chem. Phys. 106, 2067 (1997); http://dx.doi.org/10.1063/1.473140 (6 pages) | Cited 2 times

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IR absorption beyond the head of the 0003–0000 (3ν3) band of CO2 near 7000 cm−1 has been analyzed. This absorption is found to consist of two comparable intensity contributions, namely, the allowed band wing and a collision-induced absorption (CIA) band. The band wing profile has been described by using a non-Markovian theory and the rotational perturbation densities for CO2–CO2 collisions, which was previously calculated from the intensity distribution in the high-frequency wing of the 0001–0000 CO2 band. The CIA component has a typical shape of CO2 CIA bands with the maximum at the double transition (0001+0002)–(0000+0000) frequency. The integrated binary coefficient of this CIA band was estimated to be B2 = (1.0±0.6)×10−5 cm−2 Amagat−2. The CIA spectral moment theory has been used for the intensity calculation, which takes into account for the first time the collision-induced vibrational force field in CO2 pairs. By comparing the calculated and measured intensity for the double transition, the polarizability anisotropy matrix element for the 2ν3 band has been estimated as β20=0.26±0.08 a.u., value in reasonable agreement with an independent estimation from previous results of polarizability matrix elements of CO2. © 1997 American Institute of Physics.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.50.-s Scattering of atoms and molecules
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra

Molecular beam optical Zeeman spectroscopy of iridium mononitride

T. C. Steimle, A. J. Marr, S. A. Beaton, and J. M. Brown

J. Chem. Phys. 106, 2073 (1997); http://dx.doi.org/10.1063/1.473141 (5 pages) | Cited 7 times

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The Zeeman effect on the F-1/2←3/2 hyperfine component of the R(0) line in the (0,0) band of the A1Π–X1Σ+ transition of iridium mononitride, IrN, was investigated using a supersonic molecular beam optical spectrometer. The magnetic gJ-factor for IrN in the A1Π state was determined to be 0.96±0.05. The general applicability of Zeeman measurements is described and the gJ-factor which is determined is related to plausible molecular orbital descriptions for IrN in the A1Π state. © 1997 American Institute of Physics.
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33.57.+c Magneto-optical and electro-optical spectra and effects
34.50.Lf Chemical reactions
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

First-, third-, and fifth-order resonant spectroscopy of an anharmonic displaced oscillators system in the condensed phase

Yoshitaka Tanimura and Ko Okumura

J. Chem. Phys. 106, 2078 (1997); http://dx.doi.org/10.1063/1.473099 (18 pages) | Cited 28 times

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We have obtained Nth-order response functions for a two-level system described by displaced anharmonic potential surfaces coupled to a heat bath. The anharmonicity of the potentials has been taken into account as a perturbation of harmonic potentials. The heat-bath was assumed to be an ensemble of harmonic oscillators. Coupling between the two-level system and the bath was assumed to be bilinear. The calculations were done analytically using the Liouville-space generating functional, which had been obtained by way of the path-integral approach. The response functions have been defined in terms of line-shape functions with these line-shape functions being expressed in terms of the bath spectral density and the temperature. We have carried out model calculations of the first-, third-, and fifth-order optical processes for various parameters of anharmonicity to show that anharmonicity plays a minor role in linear absorption, impulsive pump–probe, and photon echo experiments, but plays a major role, in some cases, in fifth-order two-dimensional resonant spectroscopy which is proposed in this paper. © 1997 American Institute of Physics.
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78.20.Bh Theory, models, and numerical simulation

One-dimensional nutation nuclear quadrupole resonance spectroscopy for measurement of the electric field gradient tensor-asymmetry parameter

H. Robert and D. Pusiol

J. Chem. Phys. 106, 2096 (1997); http://dx.doi.org/10.1063/1.473142 (5 pages) | Cited 7 times

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A novel one-dimensional nuclear quadrupole resonance experiment to measure the asymmetry parameter of the electric field gradient tensor in polycrystalline specimens using nutation spectroscopy is reported. The complete data set, necessary for the reconstruction of the powder nutation lineshape, is recorded in a single scan provided by a train of short and intense on-resonance radiofrequency pulses. A modified scheme is presented to deal with multiple well-resolved resonances to provide a frequency selective nutation method. The technique is successfully demonstrated for the two 35Cl resonances in cyanuric chloride. A reduction of 1 or 2 orders of magnitude in the data acquisition time, relative to the usual two-dimensional method, is achieved. © 1997 American Institute of Physics.
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76.60.Gv Quadrupole resonance
71.70.Ch Crystal and ligand fields
71.70.Jp Nuclear states and interactions
61.50.-f Structure of bulk crystals
07.05.Hd Data acquisition: hardware and software

Spectroscopy of mass-selected rhodium dimers in argon matrices

Huaiming Wang, Hanae Haouari, R. Craig, Yifei Liu, John R. Lombardi, and D. M. Lindsay

J. Chem. Phys. 106, 2101 (1997); http://dx.doi.org/10.1063/1.473344 (4 pages) | Cited 21 times

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The absorption (scattering depletion) spectrum and Raman spectra for Rh2 in an argon matrix prepared by the mass selected ion deposition technique have been obtained. The absorption spectrum in the visible region shows a single broad transition centered near 495 nm Resonance Raman spectra obtained by exciting with eight visible lines (457.9–514.5 nm) of an argon ion laser give a single, sharp progression with up to four Stokes transitions. These data give ωe = 283.9(18) cm−1 with ωexe=1.83 (33) cm−1, leading to an experimental dissociation energy of 1.4±0.3 eV. The Raman results are discussed in the context of previous theoretical predictions for the dimer. © 1997 American Institute of Physics.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Fm Bond strengths, dissociation energies
33.20.Kf Visible spectra

Bounds on spin dynamics and the design of multiple-pulse NMR experiments

Colan E. Hughes and Stephen Wimperis

J. Chem. Phys. 106, 2105 (1997); http://dx.doi.org/10.1063/1.473783 (13 pages) | Cited 5 times

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The “universal bound on spin dynamics’’ proposed by Sørensen is examined in detail and shown to be of great assistance in the design of novel multiple-pulse NMR experiments. The efficiency of coherence transfer between all possible states of a spin system, including populations, single-quantum coherences, and multiple-quantum coherences, is investigated. Examples are drawn from coherence transfer processes in quadrupolar coupled spin I=1 and 3/2 nuclei and weakly J coupled systems of two and three spin I=1/2 nuclei. It is found that many of the most commonly used NMR pulse sequences fail to achieve the maximum coherence transfer efficiency when applied to spin I=3/2 or to three spin I=1/2 nuclei. However, it is shown that, with knowledge of the universal bound, novel multiple-pulse NMR experiments that achieve optimal efficiency can be easily derived using computer optimization. The application of the universal bound to two-step coherence transfer experiments presents a number of conceptual difficulties. In particular, examples are presented where the product of the universal bounds on the two individual coherence transfer coefficients is larger than the universal bound on the overall transfer from the initial to the final state. These difficulties are resolved and explained in terms of the presence of a “residue’’ that is created together with the intermediate state. The universal bound is used to examine the conditions under which the effect of this residue can be suppressed and the constraints that this places on the design of optimal multi-step coherence transfer NMR experiments. © 1997 American Institute of Physics.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
75.30.Ds Spin waves
76.60.-k Nuclear magnetic resonance and relaxation

Time-resolved infrared diode laser spectroscopy of the ν1 band of the iron carbonyl radical (FeCO) produced by the ultraviolet photolysis of Fe(CO)5

Keiichi Tanaka, Kouichi Sakaguchi, and Takehiko Tanaka

J. Chem. Phys. 106, 2118 (1997); http://dx.doi.org/10.1063/1.473143 (11 pages) | Cited 15 times

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The infrared spectrum of the iron carbonyl radical FeCO generated by the 193 nm excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved diode laser spectroscopy. The 85 lines, mostly observed as triplets split by the electron spin-spin interaction, were assigned to the ν1 (CO stretch) band of FeCO. The electronic ground state of FeCO was confirmed experimentally to have 3Σ− symmetry. Molecular constants in the ground and ν1 vibrational states were derived from an analysis of the infrared spectrum combined with pure rotational lines in the lowest spin component Ω=0 observed by Fourier transform microwave (FTMW) spectroscopy. The rotational and centrifugal distortion constants in the ground state were determined as B0 = 4364.266(55) MHz and D0 = 1.378(25) kHz, where the figures in parentheses are standard errors to be attached to the last digit. The spin-spin and spin-rotation coupling constants are λ0=663.1(40) GHz and γ0=−974(27) MHz, respectively. The origin of the ν1 vibrational band determined is 1946.470 60(12) cm−1, which is consistent with the value derived from photodetachment spectroscopy of the FeCO− anion. The collisional quenching rate of FeCO by Fe(CO)5 was measured to be 1.13(4)×10−10 cm3 molec −1 s−1 by a kinetic study. © 1997 American Institute of Physics.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Molecular theory of electronic spectroscopy in nonpolar fluids: Ultrafast solvation dynamics and absorption and emission line shapes

M. D. Stephens, J. G. Saven, and J. L. Skinner

J. Chem. Phys. 106, 2129 (1997); http://dx.doi.org/10.1063/1.473144 (16 pages) | Cited 87 times

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We present a theory of time- and frequency-domain spectroscopy of a dilute nonpolar solute in a nonpolar liquid or supercritical fluid solvent. The solute and solvent molecules are assumed to interact with isotropic pair potentials. These potentials, together with the solute and solvent masses, are the only input in the theory. We arrive at expressions for the absorption and emission line shapes, which include the possibility of motional narrowing, and for the time-resolved fluorescence and transient hole-burning observables, by assuming that the solute’s fluctuating transition frequency describes a Gaussian process. These expressions depend only on the average and variance of the transition frequency distributions in absorption and emission and on the normalized frequency fluctuation time-correlation functions. Within our formalism the former are obtained from the solute-solvent and solvent-solvent radial distribution functions, which are calculated using integral equations. The time-correlation functions involve the time-dependent solute-solvent Green’s function. Its solution depends upon the solute and solvent diffusion constants, which in turn are determined from the radial distribution functions. The theory compares favorably with computer simulation results of the same model. We then investigate the dependence of the various spectroscopic observables on the solvent density, the temperature, and the difference between the ground- and excited-state solute’s pair interaction with the solvent molecules. For example, since our theory for the time-correlation functions captures both their short- and long-time behavior, we can see how the crossover from inertial to diffusive dynamics depends on these variables. Our results are similar to a variety of experiments on solutes in both nonpolar and polar solvents. © 1997 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
82.30.Nr Association, addition, insertion, cluster formation
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.55.Bq Liquids
31.50.Df Potential energy surfaces for excited electronic states
31.70.Dk Environmental and solvent effects
33.70.Jg Line and band widths, shapes, and shifts
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
34.20.Gj Intermolecular and atom-molecule potentials and forces
61.20.Gy Theory and models of liquid structure

Resonant ion-dip infrared spectroscopy of benzene–(methanol)m clusters with m=1–6

R. Nathaniel Pribble, Fredrick C. Hagemeister, and Timothy S. Zwier

J. Chem. Phys. 106, 2145 (1997); http://dx.doi.org/10.1063/1.473784 (13 pages) | Cited 43 times

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Resonant ion-dip infrared spectroscopy has been employed to record cluster-size-specific spectra of C6H6–(CH3OH)m with m=1–6 in the OH stretch fundamental region. The comparison of the spectra with the results of ab initio calculations on the pure methanol clusters enables the assignment of the hydrogen-bonding architecture in the clusters. In all cases, the methanol molecules aggregate together in a single subcluster. With m=1, a single infrared transition is observed, redshifted from that of a free methanol momomer by 42 cm−1 due to π hydrogen bonding between benzene and methanol. The m=2 spectrum features two strong transitions at 3506 and 3605 cm−1. The lower frequency peak is redshifted from the free monomer value by 175 cm−1 and is assigned to the proton donor in the methanol dimer subcluster. The proton acceptor, which would be a free OH stretch in the absence of benzene, is redshifted by 76 cm−1 due to a strengthened π hydrogen bond. In benzene–(CH3OH)3, three sharp OH stretch transitions are observed at 3389, 3435, and 3589 cm−1. The comparison of these absorptions with ab initio calculations and with experiments on the pure methanol trimer leads to a structure for benzene–(CH3OH)3 which incorporates a π hydrogen-bonded methanol trimer chain, confirming the earlier assignment based on its ultraviolet spectrum. The 3589 cm−1 transition, due to the π hydrogen bond of the terminal methanol, is redshifted from the free monomer by 93 cm−1, a value approaching that of the donor methanol in methanol dimer (−107 cm−1). The lower frequency transitions in the m=3 spectrum arise from the donor–acceptor and donor OH stretches in the methanol trimer chain. The spectral characteristics change when m=4. The OH stretch transitions are all located in a region around 3320 cm−1 and are significantly broadened compared to the smaller clusters. By comparison with ab initio calculations, the methanol tetramer structure in benzene–(CH3OH)4 is deduced to be a cyclic methanol tetramer. The spectra for m=5 and 6 are slightly redshifted but similar to m=4 and point toward cyclic structures as well. © 1997 American Institute of Physics.
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33.20.Ea Infrared spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
33.70.Jg Line and band widths, shapes, and shifts
33.15.Fm Bond strengths, dissociation energies

Exact six-dimensional quantum calculations of the rovibrational levels of (HCl)2

Yanhui Qiu and Zlatko Bačić

J. Chem. Phys. 106, 2158 (1997); http://dx.doi.org/10.1063/1.473139 (13 pages) | Cited 31 times

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Results of comprehensive full-dimensional (6D) quantum calculations of the rovibrational levels of (HCl)2, for total angular momentum J = 0,1 are presented. The calculations employed two 6D potential energy surfaces (PES)—the ab initio PES of Bunker and co-workers, and the semiempirical PES of Elrod and Saykally. This 6D study provides the first rigorous, approximation-free description of the bound state properties of (HCl)2, including the dissociation energy, tunneling splittings and their J, K dependence, frequencies of intermolecular vibrations and associated J = 0→1 spacings, and quantum number assignments of the 6D eigenstates. Detailed comparison with 4D bound state calculations (for fixed HCl bond length) was made in order to assess the importance of including the intramolecular vibrations of the two HCl subunits for accurate calculation of various spectroscopic properties of (HCl)2. Comparison of the 6D results with experimental data, while confirming that the ES1 PES is substantially more accurate than the ab initio PES, shows that there is room for further refinements, preferably using 6D bound state calculations. © 1997 American Institute of Physics.
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31.15.A- Ab initio calculations
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.Ez Rotational and vibrational energy transfer

Spectroscopic characterization of the 3Δ(4d), 3Π(4d), 3Σ+(4d), and 3Π(5p) Rydberg states of the MgAr van der Waals molecule

Steven Massick and W. H. Breckenridge

J. Chem. Phys. 106, 2171 (1997); http://dx.doi.org/10.1063/1.473673 (11 pages) | Cited 12 times

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The Mg(3s4dσ 3DJ)⋅Ar(3Σ+), Mg(3s4dπ 3DJ)⋅Ar(3Π), Mg(3s4dδ 3DJ)⋅Ar(3Δ), and Mg(3s5pπ 3PJ)⋅Ar(3Π) Rydberg states have been characterized via Resonance Enhanced Two-Photon Ionization (R2PI) spectroscopy of transitions from the long-lived Mg(3s3pπ 3PJ)⋅Ar(3Π0+,0−) metastable states of the MgAr van der Waals molecule. The 4dπ, 4dδ, and 5pπ states are all strongly bound (D0 = 1230±50, 1200±40, 1270±50 cm−1, respectively). These bond energies are very similar to that of the ground-state MgAr+ “core’’ ion (D0 = 1240±40 cm−1), indicating very effective penetration of transversely aligned, diffuse Rydberg electron clouds on the Mg atom by the Ar atom, even for the low-lying n = 4,5 Rydberg states. The Mg(3s4dσ 3DJ) ⋅Ar(3Σ+) state was substantially less bound, D0 = 800±40 cm−1, showing there is still some residual Mg(4dσ)/Ar(3pσ)2 electron–electron repulsion preventing penetration of the axially aligned Mg(4dσ) Rydberg electron cloud by the Ar atom. Successful computer simulations of the rotational structure of several of the vibrational transitions to the 4dΔ and 4dΣ states, assuming Hund’s case “b’’ upper-state character, resulted in R0′ values of 2.80±0.04 Å and 2.90±0.05 Å, respectively (compared to R0 = 2.82±0.01 Å determined previously by others for the MgAr+ ion). Because the 4dπ and 5pπ states have similarly large bond strengths as well as similar asymptotic Mg(4d 3DJ) and Mg(5d 3PJ) atomic energies, they have “mixed’’ 4dπ/5pπ character. © 1997 American Institute of Physics.
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33.20.Lg Ultraviolet spectra
31.50.Df Potential energy surfaces for excited electronic states
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Electronic structure of vanadium cluster anions as studied by photoelectron spectroscopy

Masako Iseda, Tetsuya Nishio, Sang Yun Han, Hiroyuki Yoshida, Akira Terasaki, and Tamotsu Kondow

J. Chem. Phys. 106, 2182 (1997); http://dx.doi.org/10.1063/1.473785 (6 pages) | Cited 22 times

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Photoelectron spectra of vanadium cluster anions, Vn− (3⩽n⩽100), were measured at a photon energy of 3.49 eV (355 nm) by using a magnetic-bottle-type photoelectron spectrometer. The electronic density-of-state profiles and the photoelectron spectra of V4− and V3− were calculated by the spin-polarized DV (discrete variational)-Xα method for several plausible geometrical structures. The most plausible structure was determined so that the calculated photoelectron spectrum based on this structure well reproduces the observed one. The calculation showed that V4− has a square planar geometrical structure and a charge distribution of D4h symmetry. On the other hand, V3− was found to possess an equilateral triangle geometrical structure, but C2v symmetry for the charge distribution. The electronic states in the vicinity of the Fermi energy were found to consist of 3d atomic orbitals. The population differences between the minority and the majority spins per atom turned out to be 4.6 and 1.7 for V4− and V3−, respectively. The result implies that the d-electron spins are coupled ferromagnetically in these cluster anions. In addition, the size-dependence of the electron affinity of Vn was explained by a spherical conducting droplet model in the n≳9 range. © 1997 American Institute of Physics.
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33.60.+q Photoelectron spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Wa Charged clusters
31.15.xt Variational techniques
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Mobility of atomic hydrogen in solid krypton and xenon

J. Eberlein and Martin Creuzburg

J. Chem. Phys. 106, 2188 (1997); http://dx.doi.org/10.1063/1.473786 (7 pages) | Cited 40 times

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Atomic hydrogen is produced in xenon and krypton matrix by in situ x-ray induced photolysis of the dopants water, butane, acetone, or methane and trapped interstitially forming the “caged hydrogen” with characteristic VUV absorption bands. Their thermal bleaching as investigated between 8 K and 45 K cannot be described by a first-order process. A random walk model is introduced considering the hydrogen atoms to move in a thermally activated diffusive motion to traps where they become “invisible.’’ The temperature dependence of the mean trapping time is Arrhenius-type and characteristic only for the matrix. Infrared experiments have confirmed a partial recovery of the dopant molecule only in krypton. Annealing-induced IR absorption bands are assigned to a new complex which involves two hydrogen atoms. © 1997 American Institute of Physics.
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32.30.Jc Visible and ultraviolet spectra
32.30.Bv Radio-frequency, microwave, and infrared spectra

NaK D1Π electric dipole moment measurement by Stark level crossing and e–f mixing spectroscopy

M. Tamanis, M. Auzinsh, I. Klincare, O. Nikolayeva, A. V. Stolyarov, and R. Ferber

J. Chem. Phys. 106, 2195 (1997); http://dx.doi.org/10.1063/1.473145 (10 pages) | Cited 9 times

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The paper presents the first permanent electric dipole moment dp measurements for NaK D1Π state rovibronic levels. Two different methods were applied to obtain dp values. Stark effect induced level crossing registered as the changes of fluorescence linear polarization P(E) with external electric field E yielded from one fit both the electric dipole moment value and the Λ-doubling splitting between e,f substates of an individual rotational state. Another method consisted of obtaining the ratio ΔefJ/dp from E-dependence of the forbidden line appearing in fluorescence as a result of e–f Stark mixing, along with direct ΔefJ measurement by RF – optical double resonance. The respective dipole moment values obtained are 5.9 – 6.4 D for the state v = 7, J = 23, as well as 4.5 – 4.8 D for v = 12, J = 7, the typical errors being ca. 12%–20%. The dp value for the latter state reflects dp diminution expected due to the admixture of the d3Π state caused by intramolecular interaction. Signal simulation and data fitting have been accomplished using direct Hamiltonian diagonalization accounting for Stark interaction within rotational states J±ΔJ,ΔJ = 0,1 and 2 in the initial, excited and final state. © 1997 American Institute of Physics.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.20.Sn Rotational analysis
33.80.Be Level crossing and optical pumping
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
33.20.Vq Vibration-rotation analysis

Spectroscopy and ultrafast dynamics of the 2A1 state of Z-hexatriene in gas phase

W. Fu\S, T. Schikarski, W. E. Schmid, S. A. Trushin, P. Hering, and K. L. Kompa

J. Chem. Phys. 106, 2205 (1997); http://dx.doi.org/10.1063/1.474080 (7 pages) | Cited 17 times

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As in longer polyenes, the strong 1A1→1B2 band in the UV spectrum of 1,3Z,5-hexatriene (Z-hexatriene) has a weak precursor, the 1A1→2A1 transition. It was measured in this work by a conventional spectrometer. Whereas the wave number of the 0–0 transition is by 5400 cm−1 lower than that of the 1B2 origin, the vibrational contour indicates that the vertical transitions of thetwo bands nearly coincide. From the fast decay of the rotational anisotropy in the time-resolved measurements we conclude that this band is perpendicularly polarized. We measured the lifetime of the 2A1 state after pumping it directly by 250 fs pulses and probing the excited molecules by ionizing it by delayed pulses. The lifetimes decreased from several ps to 730 fs, when the excess energy was increased from near 0 to 4000 cm−1 and more. From the temperature dependence we infer a barrier of about 170 cm−1 (2 kJ/mol). © 1997 American Institute of Physics.
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33.20.Lg Ultraviolet spectra
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
31.50.Df Potential energy surfaces for excited electronic states
33.80.Be Level crossing and optical pumping

Time–frequency theory of pump-probe absorption spectroscopy

Yi Jing Yan, Weimin Zhang, and Jianwei Che

J. Chem. Phys. 106, 2212 (1997); http://dx.doi.org/10.1063/1.473146 (13 pages) | Cited 7 times

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A variation of density matrix formulation based on the nature of field–matter interference in a mixed time–frequency domain is developed to study molecular pump-probe absorption spectra in condensed phases. Considered are both the integrated probe transmitant signals and the frequency-dispersed transient absorption coefficients for molecular systems with either two or three electronic surfaces involved. The present formulation is exact and applicable to any field with arbitrary timescale and shape, and it is valid when the pulses are overlapped as well as separated. The dual temporal-spectral effect of both the excitation and detection fields can be clearly elucidated via a transformation that preserves causality. The resulting field–matter interference picture of transient absorption in the correlated time-frequency domain is conceptually natural and physically transparent. The molecular dynamics, and the field–matter temporal/spectral coherence and interference phenomena can all be clearly demonstrated. © 1997 American Institute of Physics.
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33.20.-t Molecular spectra
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

An adiabatic exponential perturbation theory for rotationally inelastic scattering

E. Curotto and R. J. Cross

J. Chem. Phys. 106, 2225 (1997); http://dx.doi.org/10.1063/1.473147 (6 pages) | Cited 1 time

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We develop a perturbation theory to treat rotationally inelastic scattering using an adiabatic basis set. The results for Ar+N2 are twice as accurate as those using a diabatic basis set. The theory can be trivially extended to include closed channels. It can also be simply recast into the exact integration of a set of semiclassical coupled equations. In this mode it agrees to better than 1% with the exact quantal results. © 1997 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
03.65.Sq Semiclassical theories and applications
03.65.Ge Solutions of wave equations: bound states

Photodissociation of binary metal metallocarbohedrenes

B. D. May, S. E. Kooi, B. J. Toleno, and A. W. Castleman

J. Chem. Phys. 106, 2231 (1997); http://dx.doi.org/10.1063/1.474118 (8 pages) | Cited 5 times

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The 532 nm photodissociation of the three singly substituted, binary metal containing Metallocarbohedrenes, Ti7MC12+ (M=Y, Zr, or Nb), is investigated. The photofragments are identified through energy analysis of the fragment ions in a reflectron time-of-flight mass spectrometer, a new technique in photodissociation studies that results in a more accurate identification of the photofragment mass than what would normally be achievable through mass analysis using time-of-flight determinations. The findings reveal that the dominant mechanism proceeds through the loss of neutral Ti atoms for all clusters studied. © 1997 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Ta Mass spectra
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
36.40.Qv Stability and fragmentation of clusters

Rotationally resolved photoelectron spectra from vibrational autoionization of NO Rydberg levels

Hongkun Park and Richard N. Zare

J. Chem. Phys. 106, 2239 (1997); http://dx.doi.org/10.1063/1.473148 (9 pages) | Cited 15 times

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Rotationally resolved photoelectron spectra from vibrational autoionization of individual rotational levels of the nlR (v=1, 11⩽n⩽15, 0⩽lR⩽3) Rydberg states of NO are measured by combining two-color double-resonance excitation via the NO A 2∑+ (vi=1, Ni=19) state with time-of-flight photoelectron spectroscopy. The photoelectron spectra show that both even-l and odd-l continuum partial waves are generated by the autoionization events, and thus provide evidence for angular momentum exchange between the outgoing electron and the molecular-ion core. We interpret these observations as caused by the multipolar interactions between the outgoing electron and the vibrating nuclear core, which appear to be brought about both by the dependence on internuclear distance of the electron-ion-core electronic interaction and by Rydberg-valence state couplings. © 1997 American Institute of Physics.
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33.60.+q Photoelectron spectra
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
31.50.Df Potential energy surfaces for excited electronic states
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants

Scattering dynamics in HF+He, Ne, and Ar: State-to-state cross sections, Dopplerimetry, and alignment measurement via direct infrared laser absorption in crossed supersonic jets

William B. Chapman, Miles J. Weida, and David J. Nesbitt

J. Chem. Phys. 106, 2248 (1997); http://dx.doi.org/10.1063/1.473787 (17 pages) | Cited 20 times

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Absolute state-to-state cross sections are reported for rotationally inelastic scattering in crossed jets of HF with He, Ne, and Ar at mean center-of-mass collision energies of 480, 390, and 350 cm−1, respectively. HF seeded in Ar diluent gas is cooled into the J=0 ground rotational state in a pulsed supersonic expansion, followed by single collision rotational excitation with rare gas atoms from a second pulsed supersonic jet. The column-integrated densities of HF in both the initial and final scattering states are probed in the jet intersection region via direct absorption of light from a narrow bandwidth (0.0001 cm−1), continuously tunable, color center laser. Total inelastic cross sections for collisional loss out of J=0 and collisional excitation into J>0 states are determined in absolute units from the dependence of infrared absorption signals on collider gas concentration. Full close coupling scattering calculations are performed on several ab initio and empirical potential energy surfaces for each of the three HF+rare gas systems. Agreement for He+HF and Ar+HF integral cross sections is remarkably good, but significant discrepancies are noted for the less accurately determined Ne+HF surface. Photoelastic polarization modulation of the IR laser is used to probe for rotational alignment in the scattered HF flux; the measurements set an upper polarizance limit for collisionally populated J=1 HF molecules [probed on P(1)] of ∣P∣<2%. High resolution IR laser Dopplerimetry reveals velocity structure in the collisionally excited J=1 Doppler profiles, which is in excellent qualitative agreement with theoretical predictions of rainbow features in the J=1←0 state-to-state differential cross section. © 1997 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Translational to vibrational and rotational (T→V,R) energy transfer and reactive exchange collisions of H(D)+HF(DF) in the energy range from 1 to 2 eV by time-resolved Fourier transform spectroscopy

Jörg Lindner, James K. Lundberg, Christopher M. Lovejoy, and Stephen R. Leone

J. Chem. Phys. 106, 2265 (1997); http://dx.doi.org/10.1063/1.473149 (12 pages) | Cited 6 times

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The product state distributions for hot atom collisions of H(D) with HF(DF) with a broad range of collision energies between 1.2  eV and 2.3 eV are measured with time-resolved Fourier transform spectroscopy and rotational resolution under multiple collision conditions. In most cases the vibrational distributions of reactive and nonreactive channels can be distinguished. All rotational distributions have a similar appearance with a maximum at J = 5 and an additional pronounced higher component, which cannot be described by a single Boltzmann distribution. The results are compared with recent three dimensional quasiclassical trajectory calculations (accompanying paper by Schatz) by applying a multiple collision model for both the H(D) atom slowdown and the rotational and vibrational relaxation. The rotational distributions can also be interpreted by a three dimensional asymmetric breathing ellipsoid model. © 1997 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
34.50.-s Scattering of atoms and molecules
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
33.20.Ea Infrared spectra
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Quasiclassical trajectory studies of H(D)+HF(DF) collisions at 2 eV

George C. Schatz

J. Chem. Phys. 106, 2277 (1997); http://dx.doi.org/10.1063/1.473088 (9 pages) | Cited 3 times

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This paper presents a quasiclassical trajectory study of nonreactive and reactive (F transfer) collisions involving H+HF, D+HF, H+DF, and D+DF, with emphasis on comparisons of product vibration/rotation distributions with those in an accompanying paper by Lindner, Lundberg, Lovejoy, and Leone. We find that the nonreactive rotational distributions for each isotope and each vibrational state are composed of a large peak at low J plus a long tail that extends to high J. These results are in general agreement with experiment. The low J peak arises from direct collisions of H with the F atom in HF, while the high J tail is due partly to failed reactive (F-exchange) collisions, and partly to collisions of H with the H atom in HF. The calculated reactive rotational distributions are controlled by the kinematic propensities expected for a heavy–light–heavy mass combination and a nearly isotropic potential. This result does not appear to match experiment, although limitations in the data preclude a detailed comparison. © 1997 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Fd Collision theories; trajectory models
82.20.Hf Product distribution

Stabilization of localized states in dissipative tunneling systems interacting with monochromatic fields

Nancy Makri

J. Chem. Phys. 106, 2286 (1997); http://dx.doi.org/10.1063/1.473345 (12 pages) | Cited 21 times

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We study the dynamics of an initially localized symmetric two-level system coupled to high-temperature dissipative environments and driven by a strong time-periodic force which corresponds to high-frequency monochromatic light. Qualitative arguments based on the quantized representation of the radiation field predict a wealth of intriguing behaviors which are confirmed and quantified via accurate numerical path integral calculations. With the exception of very strong friction we find that high-frequency driving always helps stabilize localized states. At intermediate friction the delocalization rate approaches a “universal’’ limiting value which is largely independent of the parameters of the environment and of the specifics of the driving force, depending only on its overall strength. This robust behavior implies that localized states can be stabilized in these systems without much finetuning of external conditions. In the weak friction regime the interplay between phase interference and dissipation results in nonmonotonic variation of the decay rate with friction and driving frequency. The path integral results are compared to those obtained earlier via analytical treatments. © 1997 American Institute of Physics.
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78.70.-g Interactions of particles and radiation with matter
73.40.Gk Tunneling
42.50.Ct Quantum description of interaction of light and matter; related experiments
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