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15 Dec 1994

Volume 101, Issue 12, pp. 10211-11087

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Theoretical study of rotational‐echo double‐resonance and related experiments

Yan Li and Jeremy N. S. Evans

J. Chem. Phys. 101, 10211 (1994); http://dx.doi.org/10.1063/1.467901 (6 pages) | Cited 4 times

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This paper discusses the theory of the rotational‐echo double‐resonance (REDOR) and related experiments by using a different approach than that used by previous researchers. The theory has been used to discuss the REDOR, rotational‐echo double‐resonance total sidebands suppression (REDORTOSS), and interrupted REDOR experiments. In the case of REDORTOSS experiment, an analytical solution has been derived which ensures that the quantification of the dipolar coupling constant and therefore the measurement of the distance between two anisotropic heteroatoms can be made. An alternative REDOR method for situations in which anisotropy is a problem is also proposed, called the interrupted REDOR. © 1994 American Institute of Physics.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
76.60.Lz Spin echoes
76.20.+q General theory of resonances and relaxations

Near‐dissociation expansions and dissociation energies for Mg+–(rare gas) bimers

Robert J. Le Roy

J. Chem. Phys. 101, 10217 (1994); http://dx.doi.org/10.1063/1.467902 (12 pages) | Cited 43 times

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This paper describes the use of fits to near‐dissociation expansions (NDE’s) for performing optimum vibrational level energy extrapolations to determine diatom dissociation energies, together with realistic estimates of the uncertainties due to model‐dependence. The imposition of extended near‐dissociation theory constraints on the leading deviation from limiting near‐dissociation behavior is introduced and applied for the first time. Fits of recently determined vibrational energies for Mg+–Ar, Mg+–Kr, and Mg+–Xe to near‐dissociation expansions yield improved estimates of the dissociation energies and realistic predictions for the total number and extrapolated energies of upper vibrational levels for both the A 2Π and X 2Σ+ states. A combined analysis of the data for the A 2Π1/2 and 2Π3/2 states, and of the vibrationally‐dependent spin–orbit splittings, yields particularly compact internally consistent results for these systems. © 1994 American Institute of Physics.
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34.20.Cf Interatomic potentials and forces
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

Further observations on the nitrogen orange afterglow

Lawrence G. Piper

J. Chem. Phys. 101, 10229 (1994); http://dx.doi.org/10.1063/1.467903 (8 pages) | Cited 9 times

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We have extended earlier observations on the nitrogen orange afterglow that results from the excitation of N2(B 3Πg,v′=1–12) in the energy transfer reaction between N2(A 3Σ+u) and N2(X,v≥4). Spectral observations out to 1550 nm show that N2(B,v′=0) accounts for about 38% of the total N2(B) excitation. This makes the rate coefficient for N2(B) excitation in the energy‐transfer reaction between N2(A) and N2(X,v≥4) equal to (4±2)×10−11 cm3 molecule−1 s−1. Experiments involving 14N2(A) and isotopically labeled 15N2(X,v) show 15N2(B) is the principal product. This demonstrates that the mechanism involves electronic energy transfer from the N2(A) to the N2(X,v). The vibrational distributions of N2(B,v≥4) are qualitatively similar whether 15N2(v) or 14N2(v) is excited although the magnitude of 15N2(B,v≥4) excitation is about 20% larger. These distributions can be characterized roughly as a 5200 K Boltzmann distribution. In contrast, the vibronic levels of 14N2(B,v=0–2) are substantially more excited than are those of 15N2(B,v=0–2). Interestingly, the overall excitation rates for both 14N2(X,v) and 15N2(X,v) are the same to within 20%. Adding 14N2(X) to the mixture of N2(A) with 15N2(X,v) results in quenching of 15N2(B) and the concomitant excitation of 14N2(B). The rate coefficient for this electronic energy exchange reaction is (8±2)×10−11 cm3 molecule−1 s−1, about 2.5 times greater than the rate coefficient for N2(B) removal by N2. © 1994 American Institute of Physics.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Characterization of silicon–carbon clusters by infrared laser spectroscopy: The ν3(σu) band of linear Si2C3

A. Van Orden, T. F. Giesen, R. A. Provencal, H. J. Hwang, and R. J. Saykally

J. Chem. Phys. 101, 10237 (1994); http://dx.doi.org/10.1063/1.467904 (5 pages) | Cited 25 times

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The ν3(σu) fundamental vibration of 1Σ+g Si2C3 has been observed using a laser vaporization‐supersonic cluster beam‐diode laser spectrometer. Forty rovibrational transitions were measured in the range of 1965.8 to 1970.9 cm−1 with a rotational temperature of 10–15 K. A least‐squares fit of these transitions yielded the following molecular constants: ν3(σu)=1968.188 31(18) cm−1, B″=0.031 575 1(60) cm−1, and B′=0.031 437 4(57) cm−1. These results are in excellent agreement with recent Fourier transform infrared (FTIR) measurements of Si2C3 trapped in a solid Ar matrix [J. Chem. Phys. 100, 181 (1994)] and with ab initio calculations [J. Chem. Phys. 100, 175 (1994)] which suggest cumulenic‐like bonding for Si2C3, analogous to the isovalent C5 carbon cluster. © 1994 American Institute of Physics.
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36.40.-c Atomic and molecular clusters
33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

The Ω=1 van der Waals and Ω=0+ double well potentials of Xe 6s[3/2]01+Kr 1S0 determined from tunable vacuum ultraviolet laser spectroscopy

Charles D. Pibel, Kaoru Yamanouchi, Jun Miyawaki, Soji Tsuchiya, Bhavani Rajaram, and Robert W. Field

J. Chem. Phys. 101, 10242 (1994); http://dx.doi.org/10.1063/1.468483 (10 pages) | Cited 15 times

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The laser induced fluorescence spectrum of jet‐cooled XeKr has been measured in the vicinity of the Xe 6s[3/2]01–1S0 atomic transition at 68 045.663 cm−1. The spectrum consists of two band systems, corresponding to transitions to the Ω=0+,1 electronic states from v″=0 of the ground electronic state. By using the observed band positions and intensities, we have constructed model potentials for both excited electronic states. The Ω=0+ state has a double minimum potential [inner well, re′ = 3.09(3) Å, De′ = 624(3) cm−1; outer well, re′ = 5.1(2) Å, De′ = 101(1) cm−1] while the Ω=1 state potential has only a shallow van der Waals potential [re′ = 5.24(4) Å, De′ = 52.2(7) cm−1]. The double minimum potential for the Ω=0+ state and the difference between the potentials for the Ω=0+ and Ω=1 states are understood in terms of the dominance of two different types of bonding interactions over different ranges of the internuclear distance. At long range, the interaction is dominated by weak dispersion and overlap repulsion between the closed shell Kr atom and the excited Xe atom, giving rise to shallow minima at r≊5 Å in both states. At short range, the XeKr interaction is better described by a XeKr+ ion‐core with an excited 6sσ Rydberg electron.
The Ω=0+ state is associated with the strongly bound 2Σ+1/2 XeKr+ ion‐core, while the Ω=1 state corresponds to the weakly bound 2Π3/2 XeKr+ ion‐core. The dual nature of the bonding which gives rise to the double minimum potential in the Ω=0+ state is similar to the bonding seen in excited states of HgAr and HgNe [Duval et al., J. Chem. Phys. 85, 6324 (1986); Okunishi et al., ibid. 98, 2675 (1993); Onda et al., ibid. 101, 7290 (1994); Onda and Yamanouchi, ibid. (submitted)] or the long range s–s, short range d–d bonding seen in the ground state of Cr2 [Casey and Leopold, J. Chem. Phys. 97, 816 (1993)], but is different from some double minima states seen in other diatomics, such as H2 (E,F 1Σ+g) [Davidson, J. Chem. Phys. 35, 1189 (1960); Kolos and Wolniewicz, ibid. 50, 3228 (1968)], Na2 (4 1Σ+g) [Tsai et al., J. Chem. Phys. 101, 25 (1994)], and Cl2 (1 1Σ+u) [Yamanouchi et al., Chem. Phys. Lett. 156, 301 (1989); Tsuchizawa et al., J. Chem. Phys. 93, 111 (1990)] which arise from curve crossings between ionic and covalent diabatic states. © 1994 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
34.20.Cf Interatomic potentials and forces
32.80.-t Photoionization and excitation
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Electronic absorption spectroscopy of matrix‐isolated polycyclic aromatic hydrocarbon cations. II. The phenanthrene cation (C14H10+) and its 1‐methyl derivative

F. Salama, C. Joblin, and L. J. Allamandola

J. Chem. Phys. 101, 10252 (1994); http://dx.doi.org/10.1063/1.467905 (11 pages) | Cited 37 times

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The ultraviolet, visible, and near infrared absorption spectra of phenanthrene (C14H10), 1‐methylphenanthrene [(CH3)C14H9], and their radical ions [C14H+10; (CH3)C14H+9], formed by vacuum‐ultraviolet irradiation, were measured in neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed. The oscillator strengths were calculated for the phenanthrene ion and found lower than the theoretical predictions. This study presents the first spectroscopic data for phenanthrene and its methyl derivative trapped in a neon matrix where the perturbation of the isolated species by its environment is minimum; a condition crucial to astrophysical applications. © 1994 American Institute of Physics.
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33.20.-t Molecular spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Three‐dimensional nuclear dynamics on conically intersecting potential energy surfaces of O+3 (2A1–2B2)

H. Müller, H. Köppel, and L. S. Cederbaum

J. Chem. Phys. 101, 10263 (1994); http://dx.doi.org/10.1063/1.467906 (11 pages) | Cited 17 times

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Three‐dimensional calculations of the nuclear dynamics of the ozone cation have been performed involving the vibronically coupled 2A1–2B2 electronic states and using the results of large‐scale ab initio computations of Schmelz et al. [Chem. Phys. Lett. 183, 209 (1991)]. Anharmonic (diabatic) potential surfaces are employed and the vibronic coupling term is taken to be a linear function of the asymmetric stretch coordinate. These calculations are compared to the first and second bands of the experimental photoelectron spectrum. Most features of its peculiar shape can be correctly reproduced and interpreted in this way. The band maximum for zero temperature is assigned to the fourth peak and the first peak of the experimental spectrum is interpreted as a hot band (vibronic temperature ≊275 K). In addition the properties of a quadratic model Hamiltonian are investigated and compared to the afore mentioned calculations. It is found that the model Hamiltonian is suitable to reproduce the full three‐dimensional computations. As a by‐product of this work the vertical ionization potentials (IP) of the interacting states are determined to be IP(2A1)=12.78 eV and IP(2B2)=13.02 eV. © 1994 American Institute of Physics.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.50.Df Potential energy surfaces for excited electronic states
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Hyperfine structure of first negative system (B 2Σ+u–X 2Σ+g) of 14N+2 and 15N+2 from laser‐induced fluorescence measurements

K. Boudjarane, J. Lacoursière, and M. Larzillière

J. Chem. Phys. 101, 10274 (1994); http://dx.doi.org/10.1063/1.467907 (9 pages) | Cited 8 times

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In this work, we present a study of the hyperfine structure of the (1,2) band of the first negative system (B 2Σ+u–X 2Σ+g) of 14N+2 and 15N+2 using laser‐induced fluorescence with the fast ion beam laser spectroscopy technique. The hyperfine structure of 14N+2 and 15N+2 have been observed in 30 rotational lines (5≤N″≤19) of the (1,2) band of this system. The Fermi‐contact (bF′,bF″) and dipolar (t′,t″) hyperfine parameters are given with their evolutions versus the vibrational quantum numbers. Furthermore, the hyperfine structure of 15N+2 led to the revision of the preliminary spin–rotation (γ′,γ″) constants. The hyperfine parameters for the (1,2) band in the B 2Σ+u–X 2Σ+g system have been determined for the first time. © 1994 American Institute of Physics.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.50.Dq Fluorescence and phosphorescence spectra

Time‐resolved two‐photon induced anisotropy decay: The rotational diffusion regime

Chaozhi Wan and Carey K. Johnson

J. Chem. Phys. 101, 10283 (1994); http://dx.doi.org/10.1063/1.467908 (9 pages) | Cited 14 times

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Two‐photon excitation (TPE) of randomly oriented chromophores in solution generates an anisotropic distribution. In a previous paper [Chem. Phys. 179, 513 (1994)], the polarization dependence of the TPE signal probed by a secondary spectroscopic transition (fluorescence or transient absorption) was determined. In this paper, the time dependence of anisotropic two‐photon induced fluorescence or transient absorption signals due to rotational diffusion is treated in spherical tensor formalism. The two‐photon signal in general contains isotropic (orientation independent) and anisotropic (orientation dependent) contributions. The latter decay with up to five exponential components. Four time‐dependent anisotropy parameters can be defined and measured, allowing additional information, not available in conventional one‐photon fluorescence depolarization measurements, to be determined. The special case of one‐color TPE is discussed in particular. It is shown that by measurement of the linear and circular anisotropies r1(t) and r2(t), more than one rotational correlation time can be determined in many cases, providing information on rotational diffusion parameters not readily determined by analogous one‐photon methods and leading in some cases to resolution of rotational motion about the principal diffusion axes of the molecule. © 1994 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
36.20.Kd Electronic structure and spectra
31.70.Dk Environmental and solvent effects

Excitonic interaction in the fluorene dimer

John Wessel, Steven Beck, and Clark Highstrete

J. Chem. Phys. 101, 10292 (1994); http://dx.doi.org/10.1063/1.467909 (11 pages) | Cited 1 time

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The fluorene van der Waals dimer exhibits a complex origin spectrum. This region has been studied by resonance two‐photon ionization and by fluorescence excitation spectroscopies. The spectra can be interpreted on the basis of intermediate strength exciton coupling, in which the electronic interaction is comparable to the van der Waals vibrational energies. The spectra are reasonably well described by two distorted adiabatic potential surfaces, which correspond to the two excitonic components of the origin system. A single Franck–Condon active intermolecular mode provides a reasonable description of the system, however the potentials have significant cubic and quartic contributions. Non‐Born–Oppenheimer nuclear momentum coupling is present and intermodal (IVR) interactions are observed, even for intermolecular modes as low as v=1. The results are remarkably different from prior observations of excitonic structure in other systems, providing a detailed picture of coupling between electronic and intermolecular motion in a van der Waals dimer. © 1994 American Institute of Physics.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.80.Eh Autoionization, photoionization, and photodetachment
33.50.Dq Fluorescence and phosphorescence spectra
34.20.Gj Intermolecular and atom-molecule potentials and forces

Electronic energy‐level structure and correlation crystal‐field effects of Er3+ in Cs3Lu2Br9

Markus P. Hehlen, Hans U. Güdel, and John R. Quagliano

J. Chem. Phys. 101, 10303 (1994); http://dx.doi.org/10.1063/1.467910 (10 pages) | Cited 12 times

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Single crystals of Cs3Lu2Br9:1% Er3+ were grown using the Bridgman technique. From highly resolved polarized absorption and luminescence measurements at 15 and 4.2 K, respectively, 101 crystal‐field levels from 27 different 2S+1LJ(4f11) multiplets of Er3+ in C3v symmetry were assigned. A Hamiltonian including 16 atomic and 6 crystal‐field parameters was fitted to a set of 87 crystal‐field levels and gave a rms standard deviation of 23.84 cm−1. Inclusion of one freely varying correlation crystal‐field (CCF) parameter lowered the overall rms standard deviation to 19.25 cm−1 and provided a dramatic improvement of the calculated crystal‐field splittings of specific CCF‐sensitive J multiplets. © 1994 American Institute of Physics.
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78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.55.Hx Other solid inorganic materials
71.70.Ch Crystal and ligand fields
42.55.-f Lasers

Two‐photon time‐of‐flight spectra of Xe2

S. S. Dimov, J. Y. Cai, and R. H. Lipson

J. Chem. Phys. 101, 10313 (1994); http://dx.doi.org/10.1063/1.467911 (10 pages) | Cited 22 times

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Resonantly enhanced multiphoton ionization (REMPI) spectra of jet‐cooled Xe2 are presented, covering the spectral region between ≊74 627 and 80 849 cm−1. Dimer ions produced by (2+1) REMPI excitation were mass selected in a linear time‐of‐flight (TOF) mass spectrometer. The vibrational and isotopic structure of several band systems dissociating to Xe∗ 5p56p and 5p55d asymptotes have been analyzed, many unambiguously for the first time, and molecular constants derived. Equilibrium bond lengths were estimated from Franck–Condon calculations. Insight into excited state predissociation was also obtained by recording atomic TOF excitation spectra. © 1994 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ta Mass spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Gj Diffuse spectra; predissociation, photodissociation

Inhomogeneous broadening of optical spectra in mixed crystals: Basic model and its application to Sm2+ in SrFClxBr1−x

R. Jaaniso, H. Hagemann, and H. Bill

J. Chem. Phys. 101, 10323 (1994); http://dx.doi.org/10.1063/1.467912 (15 pages) | Cited 14 times

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We have developed a model to describe the inhomogeneous broadening of optical spectra in the substitutionally disordered crystals. The comparison with the experimental f–f fluorescence spectra of SrFClxBr1−x:Sm2+ (0≤x≤1) allowed to establish, in a very detailed manner, the relationship between the inhomogeneous spectral distribution and the crystal structure around the Sm2+ impurity. © 1994 American Institute of Physics.
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78.55.Hx Other solid inorganic materials

1.7 GHz electron spin echo envelope modulation due to 29Si in gamma‐irradiated fused quartz

V. V. Kurshev, H. A. Buckmaster, and L. Tykarski

J. Chem. Phys. 101, 10338 (1994); http://dx.doi.org/10.1063/1.467913 (5 pages) | Cited 4 times

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Gamma‐irradiated fused quartz has been investigated at 290 K using 1.7 and 9.8 GHz electron spin echo spectroscopy. Three pulse stimulated echo sequences were used in this study because the electron spin echo signal decay was too fast using two‐pulse echo sequences. It was found that no electron spin echo envelope modulation could be observed at 9.8 GHz but that a small relative amplitude envelope modulation signal could be observed at 1.7 GHz if the time interval between the first and second pulses was 1.0 or 3.0 μs but not for 2.0 μs. It was concluded that this modulation is due to the magnetic dipole interaction between the E′1 centers and 29Si nuclei. The natural abundance of this isotope of silicon is 4.7%, I=1/2, and μ=−0.5553 μN. Unsuccessful attempts were made to model this modulation signal assuming that the E′1 center was located at oxygen and silicon vacancies in the hexagonal lattice of quartz. It was concluded that the E′1 center behaves as if it does not interact with the nearest‐ or next‐nearest‐neighbor 29Si nuclei. Acceptable agreement was obtained if this electron center is located at a silicon vacancy and only interacts with all nuclei located outside a 0.5 nm radius sphere. This implies that the point charge model may not be applicable because the electron appears to be delocalized within this spherical volume. © 1994 American Institute of Physics.
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76.30.Lh Other ions and impurities
61.80.Ed γ-ray effects

Laser‐induced fluorescence spectroscopy of the math 1Πu–math 1Σ+g transition in jet‐cooled C3

Walter J. Balfour, Jianying Cao, C. V. V. Prasad, and Charles X. W. Qian

J. Chem. Phys. 101, 10343 (1994); http://dx.doi.org/10.1063/1.467914 (7 pages) | Cited 24 times

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C3 radicals have been produced in a plasma of rhenium with methane doped in helium and cooled in a supersonic free jet expansion. More than 50 vibronic bands in the laser induced fluorescence spectrum of the math 1Πu–math 1Σ+g electronic transition have been recorded in the region 370–415 nm at 0.4 cm−1 resolution. The observations include bands identified by Gausset et al. (1965) and many bands not previously characterized. Rotational analyses have been made for a majority of the bands and the number of located Renner–Teller levels of the math state has been considerably extended. The (002) level is tentatively identified. A comparison of the experimentally determined energy level pattern in the math state with theoretical predictions has suggested a number of revisions to previous assignments and evidence is presented to contradict suggestions from earlier work that the (020) level of the math state is perturbed. © 1994 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Sn Rotational analysis

Microwave spectrum of the HNCN radical in the math 2A″ ground electronic state

Satoshi Yamamoto and Shuji Saito

J. Chem. Phys. 101, 10350 (1994); http://dx.doi.org/10.1063/1.467915 (4 pages) | Cited 6 times

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The rotational spectral lines of the HNCN radical are observed in the millimeter‐wave and submillimeter‐wave regions. The radical is produced in a glow‐discharge plasma of a gaseous mixture of CH4 and N2 at the room temperature. Rotational constants, centrifugal distortion constants, and spin–rotation interaction constants with their centrifugal distortion corrections are precisely determined from observed frequencies of 43 a‐type R branch transitions with N=12−11 to N=18−17 and Ka=0 to Ka=3. From the observed spin–rotation interaction constant, ϵaa, the energy of the math 2A′ electronic state is estimated to be 12 000 cm−1, which is comparable to the energy of the corresponding electronic state (math 2A1) for the NH2 radical. A preliminary radioastronomical search for the HNCN radical is carried out toward the Galactic center without success. © 1994 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
52.80.Hc Glow; corona
98.38.Bn Atomic, molecular, chemical, and grain processes

Luminescence of atomic magnesium in inert low temperature solids. I. Argon and krypton

John G. McCaffrey and Geoffrey A. Ozin

J. Chem. Phys. 101, 10354 (1994); http://dx.doi.org/10.1063/1.467916 (12 pages) | Cited 8 times

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Absorption and luminescence spectra have been recorded in the 200–700 nm range for atomic magnesium isolated in solid Ar and Kr at 12 K. Strong absorptions occurring in the near UV at 285 nm, showing a threefold splitting, are identified as the solid phase equivalent of the gas phase 3p 1P1←3s 1S0 Mg atom transition. Evidence of multiple site trapping of Mg atoms in Ar and Kr matrices formed at 12 K has been obtained from annealing studies in absorption, but especially in luminescence spectroscopy. The single emission band of Mg/Ar, centered at 297.6 nm, exhibits a radiative lifetime of 1.12 ns and is thereby assigned as singlet 3p 1P1→3s 1S0 Mg atom fluorescence. The luminescence exhibited by the Mg/Kr system is more complex than the Mg/Ar system in that a weak visible band at 472 nm occurs as well as several bands in the UV having nanosecond lifetimes. The richness of the Mg/Kr UV spectra has been examined with annealing and time‐resolved measurements and identified as arising from multiple trapping site effects, with at least three spectrally distinct sites identified. Efficient resonant radiative energy transfer is demonstrated to be occurring between two of these sites and an average separation between the sensitizor and activator sites is calculated to be 60 nm at a Mg:Ar dilution ratio of 3:104. Annealing of Mg/Kr samples to 45 K was found to remove all but one site which exhibits emission at 297.6 nm and a very weak band at 472.6 nm. The former, having a radiative lifetime of 1.25 ns, is assigned as 3p 1P1→3s 1S0 Mg atom fluorescence; the latter with a radiative lifetime of 8.9 ms, is assigned as 3p 3P1→3s 1S0 Mg atom phosphorescence. © 1994 American Institute of Physics.
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32.30.Jc Visible and ultraviolet spectra
32.50.+d Fluorescence, phosphorescence (including quenching)

Theoretical study of the S1↔S0 spectroscopy of anthracene

Daniel Gruner, An Nguyen, and Paul Brumer

J. Chem. Phys. 101, 10366 (1994); http://dx.doi.org/10.1063/1.467917 (16 pages) | Cited 16 times

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Dispersed fluorescence spectra for S0 to S1 vibronic transitions in anthracene are computed using the semiempirical QCFF/PI approach plus corrections resulting from fits to experimental spectral intensities. Extensive comparisons are made with the experimental jet spectra. The nature and assignment of low lying levels are clarified within the normal mode picture, whereas higher energy spectra are shown to be considerably broadened by low order anharmonic corrections. © 1994 American Institute of Physics.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.50.Dq Fluorescence and phosphorescence spectra
03.65.Sq Semiclassical theories and applications

Analysis of long range dispersion and exchange interactions between two K atoms

Warren T. Zemke, Chin‐Chun Tsai, and William C. Stwalley

J. Chem. Phys. 101, 10382 (1994); http://dx.doi.org/10.1063/1.467918 (6 pages) | Cited 17 times

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This paper critically surveys the best available spectroscopic data for the two lowest electronic states (X 1Σ+g and a 3Σ+u) of K2. Since both states are known up to dissociation, they can be used to determine Coulomb and exchange contributions to the intermediate and long range interaction potentials. The multipolar expansion representation of the Coulomb (dispersion) energy at long range (−ΣnCnR−n) and the exponential representation of the exchange energy (Ae−αR) as well as a variety of theoretical calculations are compared with these empirical results. Finally, dissociation energy values are discussed and improved dissociation energies for the X 1Σ+g (De=4449.1±1.0 cm−1) and the a 3Σ+u state (De=252.9±1.1 cm−1) proposed. © 1994 American Institute of Physics.
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34.20.Cf Interatomic potentials and forces
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

Electron–ion recombination rate in high‐mobility liquids

A. Mozumder

J. Chem. Phys. 101, 10388 (1994); http://dx.doi.org/10.1063/1.467919 (5 pages) | Cited 6 times

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An analysis of electron–ion recombination rate in high‐mobility liquids is presented from the viewpoint of fractal diffusion (mean‐free path effect), followed by a repeated encounter formulation of partially diffusion‐controlled reaction of the final step. Good agreement is achieved with experiments in liquid methane, liquid argon, and liquid krypton with an encounter reaction probability of 0.567, 0.060, and 0.383, respectively. The corresponding ratio of the fractal scale parameter ‘‘d’’ to the mean‐free path is found to be approximately 2.0, 4.0, and 1.0, respectively. For liquid methane the experimental variation of the recombination rate with the mean‐free path agrees fairly well with theoretical calculation using the same value of the reaction probability. Other theoretical models and their limitations are briefly discussed. © 1994 American Institute of Physics.  
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.-w Chemical kinetics and dynamics

Classical S‐matrix theory for chaotic atom–diatom collisions

Ampawan Tiyapan and Charles Jaffé

J. Chem. Phys. 101, 10393 (1994); http://dx.doi.org/10.1063/1.467920 (11 pages) | Cited 15 times

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The extension of classical S‐matrix theory to chaotic scattering systems is considered. It is shown that if the fractal structure of the chattering region is understood then the contribution to the S‐matrix elements and the transition probabilities can be expressed as a sum over the infinite number of contributing trajectories and that by using the scaling laws of the fractal that this sum can be evaluated. It is shown that if the transition is classically forbidden then the contribution from the chattering region is significant. © 1994 American Institute of Physics.
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05.45.-a Nonlinear dynamics and chaos
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

Dissipative vibrational dynamics in a curve–crossing system

O. Kühn, V. May, and M. Schreiber

J. Chem. Phys. 101, 10404 (1994); http://dx.doi.org/10.1063/1.467921 (12 pages) | Cited 60 times

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The density matrix theory is utilized for the description of ultra fast optical properties and related vibrational wave packet dynamics of molecular systems in condensed media. As an example, optically induced vibrational wave packets in the so‐called curve–crossing system are considered. Such a system goes beyond the standard treatment of optical phenomena since the vibrational wave packet moves in a double well potential and is subject to environmental influences like wave function dephasing and relaxation. The complete theoretical description has been carried out in a representation of the vibrational wave functions of the diabatic states which refer to the two coupled vibrational surfaces. Solving the corresponding density matrix equations by numerical methods allows us to incorporate the static coupling between the crossed surfaces in a nonperturbative manner. Standard projection operator technique is used to treat environmental contributions up to the second order. For the case of a bilinear coupling between the molecular system and the environment we determine the time development of an initially prepared Gaussian wave packet. Corresponding time‐resolved spectra of a pump–probe configuration are also derived. The developed formalism is finally applied to the system of the coupled electronic states c′ 1Σ+u and b′ 1Σ+u of the N2 molecule. © 1994 American Institute of Physics.
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31.70.Dk Environmental and solvent effects
31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates
78.47.-p Spectroscopy of solid state dynamics

Time‐dependent quantum mechanical study of the photodissociation of HOCl and DOCl

Alison R. Offer and Gabriel G. Balint‐Kurti

J. Chem. Phys. 101, 10416 (1994); http://dx.doi.org/10.1063/1.467922 (13 pages) | Cited 44 times

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The results of time‐dependent quantum mechanical calculations on the photodissociation of initially nonrotating HOCl and DOCl molecules are presented. Two photodissociation processes, 1 1A″←math 1A′ and 2 1A′←math 1A′, are considered. The dynamics are treated in a two dimensional model with a fixed O–H distance and the dissociation process is followed in a rotating body‐fixed frame with total angular momentum of J′=1. The total photodissociation spectra and product rotational distributions resulting from dissociation of HOCl and DOCl originating in a number of different vibrational states are presented over a continuous range of incident photon wavelengths in the range 140–440 nm. It is found that, for HOCl, the physically more correct treatment with J′=1 leads to a qualitatively different OH product rotational distribution than that resulting from the more usual model treatment in which both initial and excited states are assumed to possess zero total angular momentum. © 1994 American Institute of Physics.
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82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
03.65.-w Quantum mechanics

Experimental and theoretical studies of the (C 1s−1,π∗)3Π state of CO: Momentum transfer dependence and vibrational structure

J. T. Francis, N. Kosugi, and A. P. Hitchcock

J. Chem. Phys. 101, 10429 (1994); http://dx.doi.org/10.1063/1.467923 (7 pages) | Cited 18 times

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The intensity of the X 1Σ+→(C 1s−1,π∗)3Π transition of CO has been measured by electron energy loss spectroscopy using a range of scattering angles (0°–45°) and impact energies (376 to 1806 eV) in order to investigate the momentum transfer dependence of a spin forbidden inner‐shell excitation. A Franck–Condon factor analysis of the vibrational structure of the singlet and triplet (C 1s−1,π∗) states was used to quantify differences in the potential energy curves of these states. Ab initio self‐consistent field configuration interaction (SCF‐CI) calculations were carried out to generate the potential curves of the 1Π and 3Π(C 1s−1,π∗) states. The electronic and vibrational energies and Franck–Condon factors are in good agreement with the experimental results. The calculations indicate that the difference in the 1Π and 3Π potential curves are related to differences in relaxation of both the (active) π∗ and other (passive) valence electrons. © 1994 American Institute of Physics.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.20.Tp Vibrational analysis
31.15.V- Electron correlation calculations for atoms, ions and molecules

Vibrational energy transfer from resummed evolution operators

Steven D. Schwartz

J. Chem. Phys. 101, 10436 (1994); http://dx.doi.org/10.1063/1.467861 (6 pages) | Cited 13 times

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This paper describes the application of our recently derived infinite order evolution operator expansion and resummation technique to the problem of vibrational energy redistribution in molecules. For a standard mass tensor coupled model of a linear hydrocarbon we show how the resummation technique allows the derivation of an approximate evolution operator that in a single time step accurately reproduces vibrational dynamics for over 25 fs in hydrocarbons. This single time evolution operator can be calculated efficiently enough so that long time dynamics with multiple time steps seem to now be within reach. In addition, the structure of the theory is such that longer chain hydrocarbons can be efficiently ‘‘built up’’ from shorter chain molecules. The theory starts with an adiabatic approximation which describes coupled vibrational degrees of freedom by uncoupled but guage shifted evolution operators. A modified version of this adiabatic approximation shows promise for application to molecules of a size too large to be handled exactly. © 1994 American Institute of Physics.  
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
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