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15 Jun 1982

Volume 76, Issue 12, pp. 5659-6456

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Frequency dependence study of the proton spin relaxation in the re‐entrant nematic phase

Ronald Y. Dong

J. Chem. Phys. 76, 5659 (1982); http://dx.doi.org/10.1063/1.442984 (3 pages) | Cited 9 times

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Proton T1 measurements are reported for two 60CB/80CB mixtures as functions of temperature and Larmor frequency. The frequency and temperature dependences of T1 support that different relaxation mechanism is responsible for spin relaxation in the nematic and in the re‐entrant nematic phase. While the molecular self‐diffusion is effective in the nematic phase, the orientational order director fluctuations play a dominant role in the re‐entrant nematic phase.
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76.60.Es Relaxation effects

Bond shift kinetics in cyclo‐octatetraene by dynamic NMR in liquid crystalline solvents

R. Naor and Z. Luz

J. Chem. Phys. 76, 5662 (1982); http://dx.doi.org/10.1063/1.442985 (3 pages) | Cited 9 times

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A complete line shape analysis of the dynamic NMR spectra of cyclo‐octatetraene dissolved in nematic liquid crystalline solvents is presented. The analysis involves simulation of the dynamic NMR spectra in the presence of the bond shift reaction. This is performed using a newly developed group theoretical method. Comparison of the simulated and experimental spectra yield the following kinetic parameters for the bond shift process in cyclo‐octatetraene: 1/τ (0 °C) = 2.3×102 s−1; ΔE = 10.62 kcal/mol; ΔH≠ = 10.0 kcal/mol; ΔS≠ = −9.7 e.u.
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33.25.+k Nuclear resonance and relaxation
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.20.-t Molecular spectra

X‐ray absorption studies of Cu(en)2+2 exchanged Y zeolite

T. I. Morrison, G. K. Shenoy, L. E. Iton, Galen D. Stucky, and Steven L. Suib

J. Chem. Phys. 76, 5665 (1982); http://dx.doi.org/10.1063/1.442986 (4 pages) | Cited 5 times

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X‐ray absorption studies have been performed on Cu(en)2+2 exchanged Y zeolite. The copper EXAFS shows that there is little change in the equatorial copper‐ligand bond lengths, but the XANES is indicative of axial distortions. Both the EXAFS and XANES can be interpreted to show that the complex remains intact upon exchange and that it is structurally and electronically similar to the bis(ethylenediamine) copper (II) complex in solutions.
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78.70.Dm X-ray absorption spectra
61.90.+d Other topics in structure of solids and liquids; crystallography (restricted to new topics in section 61)

Beam maser spectroscopy on CH3CCD and CD3CCH

C. D. Cogley, L. M. Tack, and S. G. Kukolich

J. Chem. Phys. 76, 5669 (1982); http://dx.doi.org/10.1063/1.442987 (3 pages) | Cited 6 times

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The J = 1→0 transition frequencies in CH3CCD and CD3CCH were measured using a beam maser spectrometer. Hyperfine structure from deuterium quadrupole coupling was well resolved. The measured deuterium quadrupole coupling tensor components along the symmetry axis are eQqaa = 228±2 kHz for CH3CCD and eQqaa = −55.0±0.5 kHz for CD3CCH. The coupling strength along the bond direction for CD3CCH is eQqzz = 174±6 kHz. These results are compared with the other deuterium quadrupole coupling values. Measured rotational constants are B = 7 778 170±1 kHz for CH3CCD and B = 7 355 767±1 kHz for CD3CCH.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Pw Fine and hyperfine structure

The fluorescence and the absorption spectra of 1,8‐diphenyl‐1,3,5,7‐octatetraene. The origin of the transition moments and the interpretation of anomalous intensity distribution

Takeshi Ikeyama and Tohru Azumi

J. Chem. Phys. 76, 5672 (1982); http://dx.doi.org/10.1063/1.442988 (6 pages) | Cited 18 times

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The fluorescence and the fluorescence excitation spectra of 1,8‐diphenyl‐1,3,5,7‐octatetraene in octane are observed at 77 K. Special effort has been devoted to obtain the correct absorption spectrum from the fluorescence excitation spectrum. The fluorescence and S1←S0 absorption spectra consist of progressions of totally symmetric C = C and C–C stretching vibrations built on the 0–0 band. These spectral features together with the appearance of the 0–0 band indicate that the molecule is distorted from the C2h point group. No mirror image relationship is observed between the S1←S0 absorption and the fluorescence. Especially, the vibronic band in the absorption involving one quantum of the C = C stretching vibration is observed to be anomalously intense. Such anomalous intensity distribution of the S1←S0 absorption and the lack of the mirror image relationship are analyzed in terms of a mechanism in which both the Herzberg–Teller and Born–Oppenheimer vibronic coupling terms contribute to the transition moment. For the 0–0 and all of the vibronic bands in the absorption and fluorescence, the largest contribution to the transition moment comes from the zeroth order term in the expansion in the nuclear coordinate (i.e., nonvibronic) which is ascribed to the reduction of molecular symmetry. In the fluorescence, the Herzberg–Teller vibronic coupling term contributes destructively with the zeroth order term, whereas the Born‐Oppenheimer vibronic coupling term contributes only negligibly. In the absorption, on the other hand, the Born‐Oppenheimer vibronic coupling term contributes constructively with the zeroth order term, whereas the Herzberg–Teller vibronic coupling term contributes only a little. The anomalous intensity distribution and the lack of mirror image relationship are mainly ascribed to the difference in sign in the two major terms in the transition moment.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Ea Infrared spectra
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry

Na2(A 1Σ+u→X 1Σ+g) fluorescence accompanied by a continuous spectrum

Hajime Katô, Tooru Matsui, and Chifuru Noda

J. Chem. Phys. 76, 5678 (1982); http://dx.doi.org/10.1063/1.442989 (6 pages) | Cited 17 times

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A suitably adjusted single‐mode line of the krypton ion laser at 5682 Å has been found to excite Na2 to the single level A 1Σ+u(v′ = 34, J′ = 50). Then, a series of resonance fluorescence to different vibrational levels of the ground state X 1Σ+g have been observed up to the point of convergence. A continuous spectrum with banded diffraction structure has been contiguous to it and extended toward the small wave number region. The spectrum has been quantitatively accounted for by quantal calculations.
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33.50.Dq Fluorescence and phosphorescence spectra
42.62.-b Laser applications

Electronic excitations of magnesium tetraphenylporphyrin in supersonic expansions

Uzi Even, Yaacov Magen, Joshua Jortner, and Haim Levanon

J. Chem. Phys. 76, 5684 (1982); http://dx.doi.org/10.1063/1.443012 (9 pages) | Cited 16 times

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In this paper we report the results of our experimental study of the fluorescence excitation spectrum of Mg tetraphenylporphyrin (MgTPP) seeded in supersonic expansions of He. The spectra of the ’’isolated,’’ internally cold, bare MgTPP molecule reveal a well‐resolved vibrational structure for the S0→S1 transition (the Q band), as well as for the S0→S2 transition (the Soret, B band). The vibrational structure in the S1 state reveals low‐frequency, large amplitude motion, giving rise to two distinct even‐parity vibrational progressions, with frequencies ω1 = 14.5 cm−1 and ω2 = 24.5 cm−1. Higher vibrational excitations in the S1 manifold of MgTPP are in good agreement with the fundamental frequencies of chlorophyll a. The spectroscopy of the Soret band of MgTPP provided information regarding the dynamics of interstate radiationless relaxation of low‐lying vibrational excitations of the S2 state, which decay on the ps time scale.
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33.20.Lg Ultraviolet spectra
33.50.Dq Fluorescence and phosphorescence spectra

Resonant nonlinear optical mixing using the phase conjugate configuration: Spectroscopic studies

H. Souma, E. J. Heilweil, and R. M. Hochstrasser

J. Chem. Phys. 76, 5693 (1982); http://dx.doi.org/10.1063/1.442990 (10 pages) | Cited 23 times

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We introduce the phase conjugate configuration for the study of ultrashort relaxation processes of the excited states of molecules having complex electronic spectra. This three beam configuration allowed us to distinguish between the optical and thermal portions of the four‐wave nonlinear mixing in the frequency domain, and the typical characteristic features of the third‐order nonlinear susceptibilities for all of the interesting difference frequency regions. The dispersive characteristics of the third‐order nonlinear susceptibility, χ(3)(ωi = 2ω1−ω2) were interpreted by using a three‐level model including spectral cross relaxation with which we discuss the various relaxation pathways and rates associated with the excited electronic states of cresyl violet and rhodamine 6G in ethanol.
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42.65.-k Nonlinear optics
33.20.Kf Visible spectra

Shape‐resonance‐induced non‐Franck–Condon effects in the valence‐shell photoionization of O2

P. M. Dittman, Dan Dill, and J. L. Dehmer

J. Chem. Phys. 76, 5703 (1982); http://dx.doi.org/10.1063/1.442965 (7 pages) | Cited 38 times

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Non‐Franck–Condon effects in the valence‐shell photoionization spectrum of O2 are studied using the multiple scattering model. Calculations for the 3σg, 1πu, and 1πg levels indicate that the enhanced sensitivity of dipole strengths to internuclear separation, induced by shape resonances, reduces and broadens the resonant cross section; nonresonant channels are negligibly affected. The resulting cross sections and asymmetry parameters show fair overall agreement with line and continuum source measurements.
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33.80.Eh Autoionization, photoionization, and photodetachment

Ab initio vibrational‐rotational spectrum of potassium cyanide: KCN. II. Large amplitude motions and rovibrational coupling

Jonathan Tennyson and Ad van der Avoird

J. Chem. Phys. 76, 5710 (1982); http://dx.doi.org/10.1063/1.442966 (9 pages) | Cited 23 times

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The ten lowest vibrational states of KCN have been obtained ab initio using the close‐coupling method of Le Roy and Van Kranendonk. Fundamental vibrations are found to lie at 114.7 (bending) and 293.0 cm−1 (K–CN stretch). Comparison is made with previous results obtained using the Watson Hamiltonian for nonlinear molecules and separating the rotations and vibrations. It is found that this model breaks down for the higher librations near and above the barrier to inversion. For these states the average geometry of the KCN molecule shifts towards the linear isocyanide (KNC) structure. Properties of the vibrational states and the rotational spectrum are analyzed.
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33.20.Vq Vibration-rotation analysis
33.20.Ea Infrared spectra

Triplet exciton transfer and fusion in isotopically mixed molecular crystals

R. Brown, J.‐P. Lemaistre, J. Megel, Ph. Pee, F. Dupuy, and Ph. Kottis

J. Chem. Phys. 76, 5719 (1982); http://dx.doi.org/10.1063/1.442967 (8 pages) | Cited 14 times

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We present experimental results on triplet energy transfer from traps to super‐traps and on triplet exciton fusion in substitutionally disordered naphthalene crystals, monitored by the phosphorescence and by the delayed fluorescence of the traps and of the super‐traps. The concentration dependence of these emissions at fixed temperatures has been discussed abundantly by other authors. In this work, we present new results on their dependence on temperature and on the source of excitation, which have, respectively, been little or not at all reported on before. Comparison of experiments done with selective and with nonselective excitation of the traps shows that the results depend on the method of preparation of the trap excitons. The existence of threshold temperatures for these emissions is interpreted as evidence of phonon assisted processes, for which mechanisms are proposed. A significant drop in transport efficiency at high temperatures is observed for trap concentrations from 4% to 8%. This drop with trap concentration is discussed in relation to the random distribution of traps and to the likely importance of clusters of ’’conducting’’ sites for energy transport in random systems.
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78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena
31.70.Ks Molecular solids

Higher excited vibrational states of polyatomic molecules

Izo Abram, Antonello de Martino, and Robert Frey

J. Chem. Phys. 76, 5727 (1982); http://dx.doi.org/10.1063/1.442968 (12 pages) | Cited 31 times

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The overtone bands in the vibrational specturm of methane can be accounted for on the same footing as the fundamentals by use of a simple vibrational Hamiltonian and the application of conventional symmetry considerations and radiative selection rules. This approach gives a rough map of all stretch vibrational states up to ∼24 000 cm−1, by fitting the states of the appropriate symmetry to the observed overtone spectrum. All vibrational states are described in terms of anharmonic symmetrized internal coordinate (SIC) states which are very close to the eigenstates of the Hamiltonian. The one‐quantum SIC states are identical to the normal modes while some multiquantum SICs present features analogous to the ’’local modes’’ conventionally used in the interpretation of overtone spectra. The discrete structure of the vibrational state–space obtained from this treatment is in conflict with the symmetryless quasicontinuous structure of state–space postulated to explain IR multiphoton absorption in polyatomic molecules. At the same time, it suggests that this process might take place mainly through an equidistant ladder of states, as is found in molecules with several identical bonds.
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33.20.Ea Infrared spectra
31.50.Df Potential energy surfaces for excited electronic states
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.20.-t Molecular spectra

Triplet state Stark spectroscopy above the phosphorescence origin of 2,4,5‐trimethylbenzaldehyde

I. C. Winkler and D. M. Hanson

J. Chem. Phys. 76, 5739 (1982); http://dx.doi.org/10.1063/1.442969 (7 pages) | Cited 7 times

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The electric field effect on several of the bands in the phosphorescence excitation spectrum of 2,4,5‐trimethylbenzaldehyde, isolated in a durene single crystal at 4.2 K, was measured. While the weak origin of the first triplet state at 4140 Å was sufficiently narrow (∼1 cm−1) to resolve the Stark splitting, the intense bands in the region previously assigned to the second triplet state near 4060 Å were broad (∼10 cm−1). A selective laser excitation technique was developed to determine the Stark splitting of these bands. It was found that the most intense peaks in the 4060 Å region have the same dipole moment difference vectors, within the measurement uncertainties, as the T1 origin. This result is unexpected since the first triplet state is known to be ππ∗ in character, while the second is thought to be nπ∗. An explanation of these observations in terms of coupling of the T2 (nπ∗) state to a set of nearby T1(ππ∗) vibronic states is proposed.
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78.55.Kz Solid organic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Theory of ESR parallel‐edge lines of slowly tumbling molecules

Daniel Kivelson and Sook Lee

J. Chem. Phys. 76, 5746 (1982); http://dx.doi.org/10.1063/1.442970 (9 pages) | Cited 25 times

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For each hyperfine component we have examined the sharp feature, called the ’’parallel‐edge line,’’ which is observed at the limit of the ESR rigid powder and slow‐tumbling spectra associated with those molecules in a liquid which have their symmetry axes oriented nearly parallel to that of the applied field. The parallel‐edge linewidths are well determined in the second derivative ESR spectra. The motional broadening and shift of the parallel‐edge lines which arise from the rotational modulation of the anisotropic molecular magnetic parameters can be separated from motionally narrowed inhomogeneous effects by taking the difference of parallel‐edge linewidths and shifts of two hyperfine components. These differences in linewidths and shifts of two parallel‐edge hyperfine lines are predicted to vary as τ2−1/2, where τ2 is the rotational correlation time. An analysis of the parallel‐edge lines enables us to estimate slow tumbling times from ESR spectra without carrying out full‐scale line shape simulations, which require an exact knowledge of motionally narrowed inhomogeneous linewidths.
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33.35.+r Electron resonance and relaxation
33.70.Jg Line and band widths, shapes, and shifts

Importance of initial and final states as intermediate states in two‐photon spectroscopy of polar molecules

Bernhard Dick and Georg Hohlneicher

J. Chem. Phys. 76, 5755 (1982); http://dx.doi.org/10.1063/1.442971 (6 pages) | Cited 80 times

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Two‐photon transitions may proceed via a mechanism not involving virtually excited intermediate states. For some examples, it is shown numerically that this mechanism may account for the largest contribution to the two‐photon cross section in polar molecules, if the dipole moment strongly alters with excitation. Possible consequences for the two‐photon detection of ’’forbidden’’ states in polar polyene systems are discussed.
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33.20.Lg Ultraviolet spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Wz Other multiphoton processes

Proton magnetic resonance study of classical reorientations and tunneling in LiNH4SO4

E. C. Reynhardt, A. Watton, and H. E. Petch

J. Chem. Phys. 76, 5761 (1982); http://dx.doi.org/10.1063/1.442972 (6 pages) | Cited 6 times

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Nuclear magnetic resonance studies have been made of the protons and lithiums in LiNH4SO4 at temperatures below 285 K. The proton line shape at 4.2 K has shown that tunneling rotation of the NH+4 ion around one of its C2 axes is favored over the others. Additional tunneling around threefold axes is also present. The ground torsional level structure of the NH+4 ion has been determined. The classical reorientations of the two nonequivalent NH+4 groups can be described as simultaneous two and threefold reorientations with estimated activation energies ranging from 1.0 to 1.6 kcal/mol. Slight differences in activation energies have been observed during cooling and heating cycles below 133 K. The 7Li relaxation time is determined to a large extent by the reorientations of the NH+4 ions. Evidence has been found that the phase transition at 133 K is accompanied by a slight rearrangement of the Li–O–S skeleton.
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76.60.Es Relaxation effects

Infrared spectra of the hydrogen‐bonded pi complex C2H4–HF in solid argon

Lester Andrews, Gary L. Johnson, and Benuel J. Kelsall

J. Chem. Phys. 76, 5767 (1982); http://dx.doi.org/10.1063/1.442973 (7 pages) | Cited 25 times

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The hydrogen‐bonded pi complex C2H4‐‐HF has been prepared by codeposition of C2H4 and HF with excess argon at 12 K. Isotopic substitution in both submolecules identified the complex and provided assignments to νs at 3731 cm−1, νl at 424 and 396 cm−1, and ν7c at 973 cm−1. The observation of a substantial perturbation on the out‐of‐plane bending mode of the C2H4 submolecule in the complex without a perturbation on the in‐plane bending mode indicates that H–F is bonded to the pi electron system perpendicular to the plane of the molecule. The positions of νs and νl indicate a hydrogen bond of intermediate strength and the splitting in νl is characteristic of the anisotropy in the hydrogen bonding interaction with a π system.
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33.20.Ea Infrared spectra
33.15.Fm Bond strengths, dissociation energies

Raman study of the temperature and pressure dependence of vibrational relaxation in propyne

T. W. Zerda, S. Perry, and J. Jonas

J. Chem. Phys. 76, 5774 (1982); http://dx.doi.org/10.1063/1.442974 (7 pages) | Cited 3 times

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The Raman isotropic band shapes of the ν3 (C≡C stretch) vibration of propyne complexed with acetone have been measured as a function of temperature and pressure. The experimentally determined correlation functions 〈ω(0)ω(t)〉 have been calculated. It is shown that these functions have a long‐time tail which is negative. This effect is explained in terms of a slowly relaxing rotational motion which causes the environment of the scattering propyne molecule to change on a time scale comparable to the vibrational relaxation time. The short‐time portion of the 〈ω(0)ω(t)〉 function is shown to be dominated by collisional effects. The isotropic band shapes of the ν3 vibration have also been measured for solutions of propyne in inert solvents (tetramethylsilane and carbon disulfide). The analysis of the band shapes suggests that, in these cases, the band broadening is in the ’’motionally narrowed’’ limit.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts

Fourier transform infrared study of the polymer‐dopant interaction in polyacetylene

J. F. Rabolt, T. C. Clarke, and G. B. Street

J. Chem. Phys. 76, 5781 (1982); http://dx.doi.org/10.1063/1.442975 (4 pages) | Cited 15 times

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Fourier transform infrared (FTIR) measurements of AsF5 doped (CH)x with dopant concentrations which vary over three orders of magnitude have been obtained in both the mid (4000–400 cm−1) and far (400–15 cm−1) infrared. The bandwidths of the strong bands characteristic of the doped polymer have been observed to be invariant with dopant concentration. However, the frequency positions of these new IR bands are found to be a sensitive function of the dopant level. In the far infrared, no evidence of the predicted soliton pinning mode was found for any of the dopant concentrations studied. The consequence of these results, in view of current theoretical models of the polymer‐dopant interaction, is discussed.
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78.30.Jw Organic compounds, polymers
72.80.Le Polymers; organic compounds (including organic semiconductors)

Infrared study of electron‐molecular vibration interactions and phase transitions in the organic conductors (TMTTF)2X (X = BF−4, ClO−4, and PF−6) and TMTTF‐bromanil

Renato Bozio, Moreno Meneghetti, and Cesare Pecile

J. Chem. Phys. 76, 5785 (1982); http://dx.doi.org/10.1063/1.442976 (11 pages) | Cited 11 times

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The infrared (4000–200 cm−1) absorption spectra of powder samples of (TMTTF)2X (X = BF−4, ClO−4, and PF−6) and of TMTTF‐bromanil at temperatures 300 ≳T≳15 K are investigated. Polarized absorption spectra of oriented polycrystalline films of the bromanil complex in the same temperature range are also reported. Spectral features originated by the electron molecular vibration (EMV) interactions involving some totally symmetric modes of TMTTF are identified for all the compounds. For the case of the (TMTTF)2X salts, the intensity of the broad vibronic absorptions has been related to the degree of dimerization of the donor stacks. Analysis of their temperature evolution and comparison with the known behavior of the magnetic and electrical properties suggest that these systems may be viewed as strongly correlated magnetic semiconductors. The role of the commensurate anion sublattice in opening the semiconducting gap and suppressing the (4kF) Peierls instability is stressed. Possible similarities between the electronic properties of the TMTTF salts and of the bromanil complex are discussed. Analysis of vibronic absorptions of (TMTTF)2BF4 according to a ’’dimer charge oscillation model’’ yields semiquantitive estimates of the linear EMV coupling constants of TMTTF which result to be substantially similar to those previously reported for unsubstituted TTF.
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78.30.Jw Organic compounds, polymers
71.38.-k Polarons and electron-phonon interactions
71.30.+h Metal-insulator transitions and other electronic transitions

A spectroscopic study of CH3F isolated in rare gas matrices

V. A. Apkarian and Eric Weitz

J. Chem. Phys. 76, 5796 (1982); http://dx.doi.org/10.1063/1.442977 (16 pages) | Cited 21 times

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The hindered rotational/librational motion of symmetric top molecules isolated at substitutional sites in rare gas matrices is considered. It is shown that the dominant perturbation of the free rotor states is due to the reorientational forces of the cage atoms. An electrostatic model for symmetric top molecules trapped in octahedral fields that hinder the molecular tumbling motion is developed. The model is successfully applied to the qualitative interpretation of experimentally observed line shapes, linewidths, and spectral shifts of the ν3 mode of CH3F isolated in rare gas matrices. Exact quantitative predictions are not made due to the many model parameters, however, the spectra are compatible with a minimum barrier to tumbling of approximately 80 cm−1 and are compatible with free spinning motion. A complete analysis of the spectra requires the consideration of dynamic perturbations as well as possible sources of dynamic line broadening. The role of rotation‐translation coupling is also explored. Experimental studies have provided a direct measure of the ν3 intergrated absorption coefficient from which a radiative lifetime of τ = 82±10 ms is obtained. Direct observation of 2ν3 yields the first anharmonicity constant ωeχe = 8.05±0.05 cm−1. Studies of matrices ’’capped’’ with pure rare gas have provided an insight as to the dynamics of aggregation with the conclusion that aggregation occurs at surfaces and grain boundaries. An absorption at 1034 cm−1 is assigned to molecules trapped in these locations. Implications with respect to energy transfer processes in these systems are also discussed.
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31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates
33.70.Jg Line and band widths, shapes, and shifts
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.20.-t Molecular spectra

Collision‐induced transitions between electronic states B→A and C→B of laser‐excited Li2 molecules

G. Ennen and Ch. Ottinger

J. Chem. Phys. 76, 5812 (1982); http://dx.doi.org/10.1063/1.442978 (8 pages) | Cited 16 times

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Nonradiative transitions between the Li2 (C 1Πu, B 1Πu, A 1Σ+u) states have been studied using monochromatic laser excitation. In a cell experiment under single‐collision conditions, the B–A transfer was induced by rare gas atom collisions. With argon, the cross section is 240 Å2. B→A and C→B transfer by Li atom collisions was observed with cross sections of 1200 and 330 Å2, while C→B transfer is not measurably induced by argon collisions. The final state rotational‐vibrational level population distribution is very broad and non‐Boltzmann.
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33.50.Hv Radiationless transitions, quenching
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Inclusion of frequency shifts with electronic excitation in the calculation of multiple‐order resonance Raman profile line shapes from optical absorption data

D. L. Tonks and John B. Page

J. Chem. Phys. 76, 5820 (1982); http://dx.doi.org/10.1063/1.442979 (7 pages) | Cited 34 times

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A previously discussed exact relation which allows one to compute first‐order resonance Raman intensity profile line shapes directly from optical absorption data within well‐defined assumptions is generalized to approximately include vibrational frequency shifts with electronic excitation and is extended to profiles of higher order. For a large class of optical absorption line shapes and sufficiently small frequency shifts and temperatures, the generalization is found to be quite simple. We demonstrate its usefulness and the importance of including frequency shifts by using optical absorption data to compute first‐, second‐, and third‐order profile line shapes for the KClO4:MnO−4 impurity system and comparing the results with measured profiles.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Kf Visible spectra
33.70.Jg Line and band widths, shapes, and shifts

Determination of the rate parameters and products for the reaction of hydroxyl radicals with nitric acid

J. L. Jourdain, G. Poulet, and G. Le Bras

J. Chem. Phys. 76, 5827 (1982); http://dx.doi.org/10.1063/1.442980 (7 pages) | Cited 8 times

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The discharge flow‐EPR technique has been used to measure the rate constant and the product distribution for the reaction of OH with HNO3, which is important for stratospheric modeling. The rate constant is found to be (7.3±2)×10−15 exp[876±85)/T] cm3 molecule−1 s−1 in the range 251–403 K. Besides, the in situ titration of NO3 by NO has shown that the reaction of OH with HNO3 only produces NO3 and H2O at room temperature.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.33.Tb Atmospheric chemistry

Photoacoustic study of a UV initiated solid‐state polymerization

A. Prock, M. L. Shand, and R. R. Chance

J. Chem. Phys. 76, 5834 (1982); http://dx.doi.org/10.1063/1.442981 (4 pages) | Cited 4 times

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We report a detailed photoacoustic study of a highly exothermic solid‐state reaction, the photopolymerization of diacetylene crystals. Both the amplitude and the phase shift of the photoacoustic signal are monitored during the course of the polymerization at various UV excitation wavelengths and various chopping frequencies. A one‐dimensional heat‐diffusion model employing impedance boundary conditions is shown to fit the experimental data quite adequately. We conclude from the theoretical interpretation of the results that the quantum yield for photopolymerization is very high (∼100) and that the polymer acoustically couples much more effectively to the gas than does the monomer.
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82.35.-x Polymers: properties; reactions; polymerization
82.80.-d Chemical analysis and related physical methods of analysis
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