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15 Jun 1994

Volume 100, Issue 12, pp. 8569-9278

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Microwave spectroscopy of hydroquinone: The rotational spectrum of the cis conformer

Walther Caminati, Sonia Melandri, and Laura B. Favero

J. Chem. Phys. 100, 8569 (1994); http://dx.doi.org/10.1063/1.466761 (4 pages) | Cited 16 times

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The microwave spectra of hydroquinone and of its O–D mono‐ and di‐deuterated species have been investigated in the frequency range 8–40 GHz. Only the cis rotamer, which possesses a permanent dipole moment, has been observed. For this conformer the rotational and quartic centrifugal distortion constants have been obtained and the dipole moment has been measured. No doubling due to internal rotation between the two equivalent minima of the hydroxyl groups has been resolved.
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33.20.Bx Radio-frequency and microwave spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Femtosecond electronic dynamics by time‐delayed four‐wave mixing with incoherent light: Iodine and azulene

Tzyy‐Schiuan Yang, Ruihua Zhang, and Anne B. Myers

J. Chem. Phys. 100, 8573 (1994); http://dx.doi.org/10.1063/1.466762 (17 pages) | Cited 25 times

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Two‐ and three‐pulse time‐delayed degenerate and nondegenerate four‐wave mixing (photon echo) experiments have been performed on I2 in the vapor and in hexadecane solution and on azulene in cyclohexane by using ‘‘incoherent’’ light from a broadband dye laser to achieve femtosecond time resolution. Detailed theoretical analyses, including the cases of both parallel and perpendicularly polarized excitation pulses, are presented along with the experimental data. In I2 vapor, the signals as a function of delay time τ between the two excitation pulses exhibit beats at a frequency characteristic of the spacing between vibrational levels of the B state near the center laser frequency. The rate of decay of the beats and the symmetry of the signals with respect to τ are consistent with partial rotational energy randomization during the 10–20 ns waiting time between excitation and probe pulses. This can be considered as a form of spectral diffusion in the gas phase. The solution phase data on both I2 and azulene are consistent with no significant inhomogeneous component to the solvent‐induced electronic spectral breadth on a time scale of several picoseconds or longer, but the theoretical signals from I2 are shown to be relatively insensitive to the partitioning of the breadth. The general utility of techniques based on incoherent light for examining femtosecond time scale dynamics in solution phase is evaluated.  
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

High resolution infrared spectroscopy of cyclobutane: A study of vibrational mode coupling involving large amplitude, low frequency modes

H. Li, C. Cameron Miller, and Laura A. Philips

J. Chem. Phys. 100, 8590 (1994); http://dx.doi.org/10.1063/1.466763 (12 pages) | Cited 13 times

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The high resolution IR spectrum of cyclobutane in a supersonic molecular beam was obtained for the region of 2981 to 2991 cm−1. The spectrum reveals four overlapping bands suggestive of vibrational mode coupling in the C–H stretching region. Ground state combination differences demonstrate that these bands originate from two different ground states, the symmetric and asymmetric ring puckering states. Evidence of vibrational mode coupling is present in all four bands. The coupling depends on both J and the symmetry of the puckering state. A model coupling scheme involving two qualitatively different types of couplings is developed to explain the observed spectrum. Symmetry restrictions and the interaction between molecular rotation and ring puckering qualitatively accounts for the dramatically different coupling behavior between the two ring puckering states.
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33.20.Ea Infrared spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Theory of natural circular dichroism in molecules oriented by photoselection

Diping Che, Robert A. Goldbeck, and David S. Kliger

J. Chem. Phys. 100, 8602 (1994); http://dx.doi.org/10.1063/1.466714 (12 pages) | Cited 4 times

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The polarization properties of light absorption by molecular chromophores partially aligned by photoselection are presented in complete form. Circular dichroism (CD) in a photoselectively oriented ensemble of absorbers arises from two types of magnetic dipole terms and, in systems of low symmetry, from electric quadrupole terms, the relative contributions of these depending on the polarization properties of the probe and actinic light beams. The anisotropic circular dichroism measured in such experiments may contain information about molecular moments that is not directly available from other spectroscopic techniques, although separation of the magnetic dipole and electric quadrupole contributions will be generally possible only in systems of C2 or D2 symmetry. Theoretical descriptions are presented of possible experimental configurations for measuring oriented CD by modulating circular polarization in the probe beam, exciting beam, or in dual beams. The possible effect of photoselection‐orientation on the time evolution of circular dichroism signals measured in laser flash‐photolysis experiments is discussed.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

Millimeter‐ and submillimeter‐wave spectroscopy of dibridged Si2H2 isotopomers: Experimental and theoretical structure

M. Bogey, H. Bolvin, M. Cordonnier, C. Demuynck, J. L. Destombes, and A. G. Császár

J. Chem. Phys. 100, 8614 (1994); http://dx.doi.org/10.1063/1.466715 (11 pages) | Cited 17 times

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Various isotopomers of the free dibridged disilyne molecule, Si(H2)Si, have been observed by millimeter‐ and submillimeter‐wave spectroscopy in a silane–argon plasma produced by an abnormal electric discharge. In order to make measurement of the weak absorption lines possible a novel computer processing treatment has been developed. From the molecular constants measured for 28Si(H2)28Si, 29Si(H2)28Si, 30Si(H2)28Si, and 28Si(D2)28Si an accurate substitution structure has been deduced with rs(Si–Si)=2.2154 Å, rs(Si–H)=1.6680 Å, and ∠(HSiSiH)=104.22°. The spectrum analysis and the structure determination have been aided by correlated level ab initio calculations resulting in accurate estimates of the equilibrium geometry and rotational constants, the cubic force field, the quartic and sextic centrifugal distortion constants, and the inversion barrier height of dibridged disilyne. The barrier to inversion of the ‘‘butterfly‐type’’ Si(H2)Si molecule must be relatively high as no splitting due to inversion could be experimentally observed.
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33.20.Bx Radio-frequency and microwave spectra
33.20.Ea Infrared spectra
33.15.-e Properties of molecules
31.15.V- Electron correlation calculations for atoms, ions and molecules

(σ3s) Rydberg states of cyclohexane, bicyclo[2.2.2]octane, and adamantane

Q. Y. Shang and E. R. Bernstein

J. Chem. Phys. 100, 8625 (1994); http://dx.doi.org/10.1063/1.466716 (8 pages) | Cited 10 times

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In this effort the effect of Rydberg electronic excitation on the structure of cyclic and polycyclic alkanes is investigated. Two‐photon resonant, one‐photon ionization, mass‐resolved excitation spectroscopy is employed to observe the (σ3s)←(σ)2 Rydberg transitions of cyclohexane, bicyclo[2.2.2]octane, and adamantane cooled in a supersonic jet expansion. Rydberg spectra of these three molecules display sharp, well‐resolved vibronic structure. Analysis of the spectra is assisted by isotopic substitution, circular/linear polarization, vibronic feature widths (rotational selection rules), as well as comparison to the ground‐state vibrational energies. A significant reduction of vibrational energies in the excited electronic state and a 381 cm−1 blue shift of the transition origin upon deuterium isotope substitution for cyclohexane are interpreted as due to the promotion of an electron from a σ‐bonding orbital to a nonbonding Rydberg orbital upon optical excitation. Extensive vibronic coupling is observed for both cyclohexane and adamantane in their excited (σ3s) Rydberg electronic states. Jahn–Teller splitting is small for adamantane but quite substantial for cyclohexane. This difference is attributed to the basic stability difference for the two different ring systems (mono‐ and tri‐cyclic). A progression in a nontotally symmetric mode is observed in the Rydberg spectrum of bicyclo[2.2.2]octane suggesting a change in the geometry of this molecule upon (σ3s)←(σ)2 excitation.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques

Spin–orbit autoionization and intensities in the double‐resonant delayed pulsed‐field threshold photoionization of HCl

Y.‐F. Zhu, E. R. Grant, Kwanghsi Wang, V. McKoy, and H. Lefebvre‐Brion

J. Chem. Phys. 100, 8633 (1994); http://dx.doi.org/10.1063/1.466717 (8 pages) | Cited 17 times

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State‐selected delayed pulsed‐field threshold photoionization spectra of HCl and DCl are recorded in double‐resonant transitions through the F 1Δ, E 1Σ+, and g 3Σ− states of the 4pπ Rydberg configuration. Comparison of observed rotational line strengths with calculated spectra, as well as with available time‐of‐flight photoelectron spectra, provides useful insight on the influence of spin–orbit and rotational autoionization on delayed pulsed‐field threshold photoionization of HCl. Spin–orbit and rotational autoionization are seen to dramatically reduce the ion rotational intensity associated with the upper spin–orbit level of the ion.
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33.60.+q Photoelectron spectra
33.70.Jg Line and band widths, shapes, and shifts
33.80.Eh Autoionization, photoionization, and photodetachment

Photoinduced absorption of conjugated polymer/C60 solutions: Evidence of triplet‐state photoexcitations and triplet‐energy transfer in poly(3‐alkylthiophene)

R. A. J. Janssen, N. S. Sariciftci, and A. J. Heeger

J. Chem. Phys. 100, 8641 (1994); http://dx.doi.org/10.1063/1.466718 (5 pages) | Cited 31 times

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We present spectral evidence of the efficient photogeneration of triplet‐state excitations in poly(3‐alkylthiophene), P3AT, solutions. The steady‐state photoinduced absorption spectra display a PIA band centered at 1.50 eV which is attributed to a dipole‐allowed triplet–triplet transition. Photoexcitation of P3AT solutions containing C60, results in an efficient energy transfer reaction and provides an estimate for the P3AT triplet‐state energy of 1.57–1.72 eV.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.38.-k Polarons and electron-phonon interactions

The influence of nonadiabatic rotational transitions on the line shapes of the rotational Raman spectrum of H2 in liquid argon

L. Xiao and D. F. Coker

J. Chem. Phys. 100, 8646 (1994); http://dx.doi.org/10.1063/1.466719 (10 pages) | Cited 38 times

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General expressions for time correlation functions of operators of a quantum subsystem being driven by a classical solvent are derived in the limit that the forces on the classical solvent from the quantal solute are independent of the state of the quantum subsystem [the zero back reaction (ZBR) limit]. These expressions are used to compute the rotational Raman spectrum of a quantal H2 rotor in liquid argon whose motion is described by nonadiabatic transitions between orientational sublevels resulting from solvent collisions. Line shapes computed in both the static and adiabatic limits are compared with those computed allowing for nonadiabatic transitions in an effort to understand the influence of these transitions on the spectrum.
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33.20.Sn Rotational analysis
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.70.Dk Environmental and solvent effects

Luminescence properties of Mn5+ in a variety of host lattices: Effects of chemical and structural variation

Ueli Oetliker, Markus Herren, Hans U. Güdel, Ute Kesper, Christa Albrecht, and Dirk Reinen

J. Chem. Phys. 100, 8656 (1994); http://dx.doi.org/10.1063/1.466720 (10 pages) | Cited 34 times

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The optical spectroscopic properties of Mn5+ doped into ten host lattices have been studied. The influence of both chemical variation [phosphates(V), arsenates(V), and vanadates(V)] and structural variation (spodiosites, apatites, and Li3PO4‐type salts) on the luminescence properties is studied in detail. By varying the host lattice, the position of the sharp luminescence band can be varied from 8300 to 8960 cm−1. Excited state splittings, luminescence lifetimes, and sideband intensities are correlated with the geometrical distortion of the MnO3−4 tetrahedron. In all the host lattices, the luminescence originates from the 1E excited state at all temperatures. It is essentially unquenched at room temperature in apatite and Li3PO4‐type lattices, whereas in spodiosites up to 90% of the luminescence may be quenched at room temperature.
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78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Vacuum ultraviolet laser/time‐of‐flight mass spectroscopy: Ion‐pair spectra of 79Br35Cl

S. S. Dimov, R. H. Lipson, T. Turgeon, J. A. Vanstone, P. Wang, and D. S. Yang

J. Chem. Phys. 100, 8666 (1994); http://dx.doi.org/10.1063/1.466721 (7 pages) | Cited 19 times

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A newly built vacuum ultraviolet (VUV) laser/time‐of‐flight mass spectrometer is described, which has been used to record the first vibrationally and rotationally resolved spectra of the E0+ ion‐pair state ←X0+ ground state transition of jet‐cooled bromine monochloride BrCl, near 145 nm. The mass resolution of the instrument (m/Δm≊1000) was sufficient to obtain single isotopomer data. Preliminary results for 79Br35Cl are reported. Like other interhalogens, BrCl vibronic band intensities vary widely in the VUV, presumably as a result of excited state perturbations. This scenario has been corroborated by the observation of an irregularly spaced vibrational progression, and the irregular behavior of the excited state rotational constants as a function of v′.
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33.20.Ni Vacuum ultraviolet spectra
33.15.Ta Mass spectra

Ultraviolet spectroscopy of the B 2A′ and C 2A″ states of FCO

M. Matti Maricq, Joseph J. Szente, Yi Su, and Joseph S. Francisco

J. Chem. Phys. 100, 8673 (1994); http://dx.doi.org/10.1063/1.466722 (8 pages) | Cited 5 times

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Gas phase uv spectra of FCO obtained from the flash photolysis of F2, or F2CO, in the presence of CO are presented. The spectrum consists of three prominent progressions assigned to the B and C states of FCO and a fourth, weaker, progression which may belong to the second excited 2A′ state. Analysis of the B 2A′ state progressions provides vibrational frequencies of ω1=1180±35 cm−1 and ω2=770±30 cm−1 and a zero point energy in the range 24 000<T0<27 000 cm−1. The spectrum of the C 2A″ state yields ω1=1458±6 cm−1 and ω2=651±5 cm−1 and a zero point energy of T0=28 500±25 cm−1. The electronic energies and vibrational frequencies are compared to recent ab initio calculations.
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33.20.Lg Ultraviolet spectra
33.20.Tp Vibrational analysis

Fourier transform infrared and tunable diode laser spectra of the 13C12CH6 ν12 torsion–vibration–rotation band: Frequencies, intensities, and barriers to internal rotation

Mark Weber, Dennis C. Reuter, J. Marcos Sirota, William E. Blass, and John J. Hillman

J. Chem. Phys. 100, 8681 (1994); http://dx.doi.org/10.1063/1.466723 (8 pages) | Cited 5 times

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High resolution spectra in the 12.2 μm region of the ν12 fundamental of the minor isotopomer 13C12CH6 have been recorded. Torsional Coriolis interaction of the excited v12=1 state with the close lying excited torsional v6=3 state leads to observed splittings of up to several tenths of cm−1 in ν12 near the crossing region at KΔK=−18. Torsional splittings measured with a high resolution tunable diode spectrometer (TDL) and more than 2200 lines measured with a Fourier transform spectrometer (FTS) have been analyzed in a global nonlinear least squares fit to a symmetric top Hamiltonian. The standard deviation of the overall fit is 5.5×10−4 cm−1. From 17 intensity measurements of individual lines, a square dipole moment of R2v=7.45(29)×10−4 D2 has been derived for the ν12 fundamental.
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33.70.Jg Line and band widths, shapes, and shifts
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Reactions of laser ablated Be atoms with O2: Infrared spectra of beryllium oxides in solid argon

Craig A. Thompson and Lester Andrews

J. Chem. Phys. 100, 8689 (1994); http://dx.doi.org/10.1063/1.466724 (11 pages) | Cited 10 times

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Pulsed‐laser ablated beryllium atoms codeposited with O2 in excess argon at 10 K yielded new beryllium–oxygen molecules. The initial reaction to make BeO is endothermic, but activation energy is provided by hyperthermal Be atoms. A strong band at 1572.9 cm−1 and a weak band at 398.9 cm−1 gave oxygen isotopic shifts consistent with a BeO diatomic molecule and are assigned to the O2–BeO complex analogous to the Ar–BeO complex. A sharp band at 1413.2 cm−1 exhibited an oxygen isotopic triplet with 16,18O2 and shifts appropriate for linear OBeO. A nearly coincident band at 1412.4 cm−1 gave an isotopic doublet and shifted in agreement with linear BeOBe. Quantum chemical calculations at the second‐order many‐body perturbation theory [MBPT(2)] level predict 3Σ ground states and ν3 fundamentals at 1422.5 and 1418.2 cm−1 for OBeO and BeOBe, respectively, in excellent agreement with the observed values. Three bands at 1131.2, 866.3, and 522.4 cm−1 increased together on photolysis, yielded isotopic triplets, and agreed with MBPT(2) calculations for rhombic Be2O2. A sharp photosensitive band at 988.6 cm−1 gave oxygen isotopic shifts consistent with another linear OBeO species and is tentatively assigned to the molecular anion. An intense band at 1465.1 cm−1 that appeared on annealing gave oxygen isotopic shifts in agreement with calculations for linear BeOBeO. Two bands at 1288.9 and 1264.1 cm−1 appeared on photolysis and gave isotopic triplets and shifts that are in excellent agreement with calculations for branched BeBeO2. Annealing produced bands at 871.8 and 436.1 cm−1 that decreased on photolysis and are assigned to BeO3.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Nr Association, addition, insertion, cluster formation
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Interatomic distances for some first row transition element dichlorides isolated in cryogenic matrices using x‐ray absorption fine structure spectroscopy

Ian R. Beattie, Mark D. Spicer, and Nigel A. Young

J. Chem. Phys. 100, 8700 (1994); http://dx.doi.org/10.1063/1.466725 (6 pages) | Cited 6 times

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X‐ray absorption fine structure (XAFS) data for several 3d transition metal dichlorides isolated in nitrogen, argon, or methane matrices have been collected and analyzed. The bond lengths obtained are in reasonable agreement with those from vapor phase electron diffraction. The results are briefly discussed with reference to Badger’s rule extended to triatomics.
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33.15.Dj Interatomic distances and angles
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Far infrared laser magnetic resonance detection of CHD (math 3A″)

J. Nolte, F. Temps, H. Gg. Wagner, M. Wolf, and T. J. Sears

J. Chem. Phys. 100, 8706 (1994); http://dx.doi.org/10.1063/1.466726 (7 pages) | Cited 4 times

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Far infrared laser magnetic resonance (FIR‐LMR) spectra of the CHD radical in its math3A″ electronic ground state were observed and assigned. The radicals were generated in the reaction of Na atoms with CHDBr2. LMR spectra were observed using seven laser lines at wavelengths around 100 to 200 μm. The spectra were assigned to six different rotational transitions and the molecular parameters of CHD were determined by a least squares fit. A number of additional transitions, observed using a laser line at λ=184.3 μm but not yet assigned in detail, were attributed to a coupling between the accidentally almost degenerate NKaKc=505 and 413 rotational levels induced by the ϵab term in the spin–rotation Hamiltonian and by the off‐diagonal components of the hyperfine coupling tensor.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques

Strong resonance enhancement of the CN two‐photon absorption B 2Σ+←X 2Σ+(3,0) by the A 2Πi, v′=4 level

John A. Guthrie, William R. Anderson, Anthony J. Kotlar, Yuhui Huang, and Joshua B. Halpern

J. Chem. Phys. 100, 8713 (1994); http://dx.doi.org/10.1063/1.467259 (7 pages)

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We have observed a strong two‐photon absorption in the B 2Σ+←X 2Σ+(3,0) band of CN by means of a resonant enhancement through the A 2Πi, v′=4 level. Many lines are seen in the two‐photon spectrum due to multiple single‐photon near resonances in the A 2Πi←X 2Σ+(4,0) band. The detuning of the laser from these resonances varies from less than one to hundreds of wave numbers, producing unusually large intensity variations in the two‐photon spectrum. This effect is not observed in two‐photon transitions far from resonance. Resonant enhancement is observed over a range from N=5 to 20. We know of no other molecular two‐photon transition in which a near resonance produces such dramatically varying intensities over a short range of rotational levels. A calculation of the line strengths for these transitions reproduces the major features of the spectrum.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Extension of the quasistatic far‐wing line shape theory to multicomponent anisotropic potentials

Q. Ma and R. H. Tipping

J. Chem. Phys. 100, 8720 (1994); http://dx.doi.org/10.1063/1.466727 (17 pages) | Cited 4 times

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The formalism developed previously for the calculation of the far‐wing line shape function and the corresponding absorption coefficient using a single‐component anisotropic interaction term and the binary collision and quasistatic approximations is generalized to multicomponent anisotropic potential functions. Explicit expressions are presented for several common cases, including the long‐range dipole–dipole plus dipole–quadrupole interaction and a linear molecule interacting with a perturber atom. After determining the multicomponent functional representation for the interaction between CO2 and Ar from previous published data, we calculate the theoretical line shape function and the corresponding absorption due to the ν3 band of CO2 in the frequency region 2400–2580 cm−1 and compare our results with previous calculations carried out using a single‐component anisotropic interaction, and with the results obtained assuming Lorentzian line shapes. The principal uncertainties in the present results, possible refinements of the theoretical formalism, and the applicability to other systems are discussed briefly.
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33.70.Jg Line and band widths, shapes, and shifts

Vibrational spectroscopy of NO and (NO)2 isolated in solid neon

R. Kometer, F. Legay, N. Legay‐Sommaire, and N. Schwentner

J. Chem. Phys. 100, 8737 (1994); http://dx.doi.org/10.1063/1.466728 (9 pages) | Cited 13 times

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By highly resolved infrared absorption spectra the dependence of aggregation of NO in neon on concentration, annealing, and deposition temperature is studied in recording the intensities of monomers in two sites (1874.54 and 1877.56 cm−1), of cis‐(NO)2 dimers in the symmetrical (around 1866 cm−1) and antisymmetrical (around 1780 cm−1) mode, of a special dimer around 1858 cm−1 and a series of monomer side bands shifted by about 0.3, 0.6, and 1.8 cm−1 due to coupling of molecules at different lattice sites. The dimer bands also exhibit a fine structure and a broad background caused by larger aggregates. The almost statistical size distribution at low concentration and condensation temperature changes to a preferential aggregation at higher concentration (≳2×10−3) and condensation temperature (≥7 K) and the irreversible aggregation by diffusion at elevated temperatures is followed on a time scale of hours. A reversible conversion of special dimers at 1778.67 and 1865.48 cm−1 to a dimer at 1857.93 cm−1 is accelerated by lowering the temperature and attributed to a martensitic hcp to fcc phase transition.
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33.20.Ea Infrared spectra

The forbidden predissociation of metastable H2(c 3Πu−) molecules studied by state specific lifetime measurements

Ch. Berg and Ch. Ottinger

J. Chem. Phys. 100, 8746 (1994); http://dx.doi.org/10.1063/1.466729 (9 pages) | Cited 4 times

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Using laser induced fluorescence detection of metastable H2(c 3Π−u, v=0–3, N=1–4) molecules in a beam at different distances from the source, the lifetime of resolved fine structure levels was determined. It was found to be much shorter for the F2 levels (∼150–10 μs for v=0–3, respectively) than for the F1 plus F3 components (several hundred to 70 μs). This is due to a forbidden (ΔN≠0) predissociation by the b 3Σ+u state, which operates preferentially on the F2 levels. Accurate bound–free Franck–Condon factor calculations reproduce the increasing trend of the predissociation rate in going from v=0–3. The absolute predissociation rates from previous theoretical work, however, can only be brought into agreement with the experimental results if they are multiplied with a common scale factor of 38.  
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33.70.Fd Absolute and relative line and band intensities
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Fluorescence spectra and torsional potential functions for trans‐stilbene in its S0 and S1(π,π∗) electronic states

Whe‐Yi Chiang and Jaan Laane

J. Chem. Phys. 100, 8755 (1994); http://dx.doi.org/10.1063/1.466730 (13 pages) | Cited 30 times

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The fluorescence excitation spectra and dispersed fluorescence spectra of trans‐stilbene have been recorded and analyzed. Vibrational assignments for the eight low‐frequency modes have been made for both the S0 and S1(π,π∗) electronic states, and these differ substantially from those of previous workers. Two‐dimensional kinetic and potential energy calculations were carried out in order to determine the potential energy surfaces for the two phenyl internal rotations ν37 and ν48. The function V(ϕ1,ϕ2)= 1/2V2(2+cos 2ϕ1+cos 2ϕ2)+V12 cos 2ϕ1 cos 2ϕ2 +V12′ sin 2ϕ1 sin 2ϕ2, with V2=1550 cm−1, V12=337.5 cm−1, and V12′ = 402.5 cm−1 for the S0 state and with V2=1500 cm−1, V12=−85 cm−1, and V12′ = −55 cm−1 for the S1(π,π∗) state fits the observed data (nine frequencies for S0 and six for S1) extremely well. The barriers to simultaneous internal rotation of both phenyl groups are given by twice the V2 values. The fundamental frequencies for these torsions are ν37=9 cm−1 and ν48=118 cm−1 for the S0 state and ν37=35 cm−1 and ν48=110 cm−1 for the S1 excited state. The third torsion ν35, which is the internal rotation about the C=C bond, was assigned at 101 cm−1 for the S0 state based on a series of overtone frequencies (202, 404 cm−1, etc.). For S1, ν35=99 cm−1 based on observed frequencies at 198, 396 cm−1, etc.
Kinetic energy calculations were also carried out for this mode, and a one‐dimensional potential energy function of the form V(θ)=1/2V1(1−cos θ)+1/2V2(1−cos 2θ)+1/2V4(1−cos 4θ) was utilized to reproduce the frequencies for the ground state. For the excited state, an additional V8 term was added in order to fit the data for the trans potential energy well. The data indicate that the trans→twist barrier for the S1 state is higher than 1400 cm−1. However, a somewhat revised frequency assignment would be compatible with a barrier of 1250 cm−1, which is close to the value of 1200 cm−1 determined from dynamics studies.
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33.50.Dq Fluorescence and phosphorescence spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Selective population of spin–orbit levels in the autoionization of a polyatomic molecule: Branching ratios and asymmetry parameters for the Tanaka–Ogawa Rydberg series in CO2

A. C. Parr, P. M. Dehmer, J. L. Dehmer, K. Ueda, J. B. West, M. R. F. Siggel, and M. A. Hayes

J. Chem. Phys. 100, 8768 (1994); http://dx.doi.org/10.1063/1.466731 (12 pages) | Cited 8 times

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The spin–orbit selectivity of angle‐resolved photoelectron spectra was used to provide new information on the electronic structure, symmetry, and decay dynamics of members of the autoionizing Tanaka–Ogawa Rydberg series in CO2. This represents the first time that spin–orbit selectivity has been used to obtain such information for a polyatomic molecule. The spin–orbit photoelectron branching ratios were used to show that the angular momentum quantum number λ of the excited Rydberg electron does not change upon autoionization. Furthermore, a consideration of the present results together with previous calculations of the relative intensities of the discrete and continuum ionization channels shows that the most probable electron configuration for the Tanaka–Ogawa Rydberg series is ...(πu)3(πg)4ndδg and that autoionization proceeds primarily via a dδg→ϵfδu process for the totally symmetric vibronic components of the ion. The asymmetry parameter β was determined for individual spin–orbit components of the various vibronic bands of the math 2Πg state and is discussed in terms of recent theoretical calculations. The Rydberg series appears to be well described by Ωcω coupling, even for relatively low principal quantum numbers. The general utility of this technique for autoionizing Rydberg states and its extension to multiphoton ionization of Rydberg states that lie below the first ionization threshold are discussed.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.70.Jg Line and band widths, shapes, and shifts
33.60.+q Photoelectron spectra

The electronic transition dipole moment of the B0+u→X0+g transition in iodine

M. Lamrini, R. Bacis, D. Cerny, S. Churassy, P. Crozet, and A. J. Ross

J. Chem. Phys. 100, 8780 (1994); http://dx.doi.org/10.1063/1.466732 (4 pages) | Cited 9 times

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The electronic transition dipole moment of the B0+u→X0+g transition in molecular iodine has been determined in the range 2.633≤Rcentroid≤6.035 Å. We have measured a decrease of ‖μe‖2 of about 4 orders of magnitude, perhaps the largest variation of ‖μe‖2 yet observed in a molecule.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.50.Dq Fluorescence and phosphorescence spectra
31.50.Df Potential energy surfaces for excited electronic states

N–O versus N–N bond activation in reaction of N2O with carbon cluster ions: Experimental and ab initio studies of the effects of geometric and electronic structure

Marianne Sowa Resat, Jason N. Smolanoff, Ilyse B. Goldman, and Scott L. Anderson

J. Chem. Phys. 100, 8784 (1994); http://dx.doi.org/10.1063/1.466733 (11 pages) | Cited 6 times

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We report a combined experimental and theoretical study of the reaction of small carbon cluster cations with N2O aimed at understanding the reaction mechanism and how it is affected by the electronic and geometric structure of the C+n reactants. Cross sections for reaction of C+n (n=3–12) with N2O were measured over a collision energy range from 0.1–10 eV, using a guided ion beam tandem mass spectrometer. Ab initio calculations were used to examine the structure and energetics of reactant and product species. Small clusters, which are linear, react with no activation barrier, resulting in either oxide or nitride formation. The branching between oxide and nitride channels shows a strong even–odd alternation, with even clusters preferentially forming nitrides. This appears to be correlated with an even/odd alternation in the ionization potential of the CnN. The larger, monocyclic C+n have activation barriers for reaction, and a completely different product distribution. Secondary reactions of the primary oxide and nitride products were studied at high N2O pressures. Products containing two O or two N atoms are not observed, but it is possible to add one of each. Possible reaction mechanisms are discussed and supported by thermochemistry derived from spin restricted ab initio calculations.  
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
36.40.-c Atomic and molecular clusters
31.15.V- Electron correlation calculations for atoms, ions and molecules

Accurate quantum mechanics from high order resummed operator expansions

Steven D. Schwartz

J. Chem. Phys. 100, 8795 (1994); http://dx.doi.org/10.1063/1.466734 (7 pages) | Cited 13 times

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In this paper we report new developments in the expansion and partial resummation of the evolution operator. Higher order resummations allow derivation of an effective one‐dimensional potential which accurately represents quantum dynamics for even strongly coupled low‐frequency modes. This allows a system bath approximation which can accurately reproduce multidimensional quantum mechanics. In addition the formulation presented in this paper should prove significantly easier to extend to many‐body problems than previous formulations we have derived. The accuracy of the method for even highly nonadiabatic applications, and the ease of implementation suggests that this approach will be useful in the calculation of the quantum dynamics of many dimensional systems.  
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34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)
03.65.-w Quantum mechanics
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