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15 Jun 1981

Volume 74, Issue 12, pp. 6539-6999

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The rotational and hyperfine spectrum of Ar–HF

T. A. Dixon, C. H. Joyner, F. A. Baiocchi, and W. Klemperer

J. Chem. Phys. 74, 6539 (1981); http://dx.doi.org/10.1063/1.441113 (5 pages) | Cited 82 times

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The radio frequency and microwave spectrum of Ar–HF has been remeasured by molecular beam electric resonance spectroscopy. Analysis of the data yields a revised value for the HF nulear spin–spin constant S, which in turn provides information about the vibrationally averaged geometry of the complex. Rotational and hyperfine constants and the dipole moment have also been measured for Ar–DF:               The average structures and estimated harmonic force constants are shown to be consistent with those observed for other Ar–HX complexes. Comparison of the two hyperfine constants for Ar–DF indicates that the average charge distribution around the deuterium is only weakly perturbed by the argon atom.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Pw Fine and hyperfine structure
33.15.Mt Rotation, vibration, and vibration-rotation constants

CO2–HF: A linear molecule

F. A. Baiocchi, T. A. Dixon, C. H. Joyner, and W. Klemperer

J. Chem. Phys. 74, 6544 (1981); http://dx.doi.org/10.1063/1.441114 (6 pages) | Cited 90 times

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The results of microwave and radio frequency spectroscopy of the weakly bound complexes of hydrogen fluoride with carbon dioxide and carbonyl sulfide are presented. The following spectroscopic constants are determined:                           A nearly linear hydrogen bonded equilibrium structure with an O–H bond length of ∼1.9 Å is consistent with all the experimental data. The stretching force constant, estimated from the distortion constant to be ks = 0.021 mdyne/Å for CO2–HF, appears anomalously small for such a short bond.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants

The structure of N2O–HF

C. H. Joyner, T. A. Dixon, F. A. Baiocchi, and W. Klemperer

J. Chem. Phys. 74, 6550 (1981); http://dx.doi.org/10.1063/1.441115 (4 pages) | Cited 75 times

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The rotational spectra of four isotopes of the weakly bound complex N2O–HF have been measured by molecular beam electric resonance spectroscopy. The following spectroscopic constants and structural parameters were derived from the observations:                               In the average structure, the N2O axis makes an angle of ∼47° with a line rc.m. drawn between the centers of mass of the two submolecules. HF is hydrogen bonded toward the oxygen on N2O to form an angle of ∼31° with the center of mass line.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Dj Interatomic distances and angles
33.15.Fm Bond strengths, dissociation energies

Laser‐excited emission spectra of In atoms trapped in Kr and Xe matrices

L. C. Balling and J. J. Wright

J. Chem. Phys. 74, 6554 (1981); http://dx.doi.org/10.1063/1.441116 (2 pages) | Cited 2 times

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The first measurements of the fluorescence spectra of In atoms trapped in Kr and Xe matrices are reported. The In atoms were trapped at 4 °K and the fluorescence was excited by a pulsed dye laser tuned to the matrix‐isolated In absorption bands. The results are compared with the previously reported emission spectra of matrix‐isolated Tl atoms.
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32.50.+d Fluorescence, phosphorescence (including quenching)

Far infrared laser magnetic resonance spectrum of NF(a 1Δ)

P. B. Davies and F. Temps

J. Chem. Phys. 74, 6556 (1981); http://dx.doi.org/10.1063/1.441117 (4 pages) | Cited 12 times

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The NF radical in its a 1Δ metastable state has been detected by far infrared laser magnetic resonance spectroscopy at 513 μm. The spectrum arises from the J = 7→8 rotational transition, and yields an accurate measurement for this spacing of 19.55172 cm−1.
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33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)

Theory of resonance Raman scattering beyond the Condon approximation for a system with two modes of different symmetry

W. H. Henneker, W. Siebrand, and M. Z. Zgierski

J. Chem. Phys. 74, 6560 (1981); http://dx.doi.org/10.1063/1.441118 (20 pages) | Cited 20 times

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A theoretical study is presented of resonance Raman excitation profiles and depolarization dispersion curves for a molecule with two Raman‐active normal modes of vibration and three electronic states. The modes are taken to be of different symmetry, one totally and the other non‐totally symmetric. The three electronic states are the ground state and a pair of excited states coupled through the non‐totally symmetric mode. The energy gap separating the pair is allowed to vary from zero (Jahn–Teller limit, strong coupling) to large values (Herzberg–Teller case, weak coupling). The totally symmetric coordinate is allowed to assume different equilibrium values not only between the ground state and the resonant state, but also between the two coupled excited states. As a result, the effective coupling depends indirectly on the totally symmetric coordinate, causing breakdown of the Condon approximation. The effect of this breakdown is demonstrated by calculating excitation profiles for all one and two quantum transitions involving the two modes. The profiles show progression of the totally symmetric mode with or without superimposed non‐totally symmetric quanta. If the Condon approximation breaks down, the intensity distribution in these progressions generally depends on the presence of such quanta. For weak coupling, the effect should be most readily observable in combination bands. For strong coupling, it should also be observable in totally symmetric fundamentals and overtones. Special attention is given to systems with resonance–preresonance interference and to intermediate‐coupling systems.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Magnetic resonance study of Mo5+ in Ca1−xYxMoO4

M. Greenblatt, P. Strobel, and J. H. Pifer

J. Chem. Phys. 74, 6580 (1981); http://dx.doi.org/10.1063/1.441119 (4 pages) | Cited 2 times

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The ESR of MoO3−4 has been studied at 4.2 K in single crystals of Ca1−xYxMoO4 (x<0.01). The g values and Mo hyperfine constants are gx = 1.8925, gy = 1.8753, gz = 1.9780, Ax = 38.6×10−4 cm−1, Ay = 42.8×10−4 cm−1, and Az = 22.2×10−4 cm−1. The resonances show an isotropic superhyperfine splitting due to a nearby charge compensating yttrium ion. The ground state of the d1 electron is dz2 as expected for the MoO4 tetrahedron which is distorted to D2d symmetry by a c axis compression in this host. Crystal field parameters are calculated by fitting the ESR data to equations assuming xz mirror symmetry at the Mo5+ site.
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76.30.He Platinum and palladium group (4d and 5d) ions and impurities (Zr-Ag and Hf-Au)
71.70.Ch Crystal and ligand fields

Halogenated benzene radical cations and ground state degeneracy splitting by asymmetric substitution

V. E. Bondybey, C. R. Vaughn, Terry A. Miller, J. H. English, and R. H. Shiley

J. Chem. Phys. 74, 6584 (1981); http://dx.doi.org/10.1063/1.441120 (8 pages) | Cited 5 times

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The absorption and laser induced fluorescence of several halogenated benzene radical cations were studied in solid Ne matrices. The spectra of 1,2,4‐trifluorobenzene, 1,3‐dichloro‐5‐fluorobenzene, and 1‐chloro‐3,5‐difluorobenzene radical cations are observed and analyzed. Studies of fluorescence polarization and a photoselection technique were used to examine the splitting of the degeneracy of the benzene cation ground state by asymmetric subsitution.
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33.20.Kf Visible spectra
33.50.Dq Fluorescence and phosphorescence spectra

Fluctuations in optical activity: A probe of fast reactions using light scattering

T. G. Dewey, Douglas H. Turner, and Mark G. Sceats

J. Chem. Phys. 74, 6592 (1981); http://dx.doi.org/10.1063/1.441105 (11 pages)

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Theory is presented for light scattering from a liquid where there is a change in optical activity of the molecules upon chemical reaction. The results indicate that the difference spectrum for 90° scattering between right and left circularly polarized input is dominated by the reactive component through the cross term which couples fluctuations in the dielectric permittivity and the optical activity. The feasibility of the technique is illustrated by calculations for a unimolecular reaction.
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82.53.-k Femtochemistry
78.20.Ek Optical activity
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Coriolis interactions and infrared intensities in fluoroform

Shigeo Kondo and Shinnosuke Saëki

J. Chem. Phys. 74, 6603 (1981); http://dx.doi.org/10.1063/1.441106 (9 pages) | Cited 13 times

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Infrared intensities of the fundamental bands of the CHF3 molecule were remeasured. The Coriolis interaction between ν3 and ν5 bands as well as that between ν6 and ν5 bands was analyzed to determine the sign of the perturbation. As a result, the relative signs of all the (∂p/∂Qi)’s in this molecule have been determined without using the CNDO/2 method or an ab initio calculation. An empirical rule on the sign of the CF bond intensity parameters is proposed by the name of ’’CF‐bond criteria’’, according to which a negative dipole moment is enhanced in the direction of the displacements of the F atoms in both the CF stretching and CF deformation modes. Further, a possibility is suggested to extend this rule to all halogen atoms.
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33.20.Ea Infrared spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Intramolecular vibrational relaxation in jet‐cooled phthalocyanine

Pamela S. H. Fitch, Christopher A. Haynam, and Donald H. Levy

J. Chem. Phys. 74, 6612 (1981); http://dx.doi.org/10.1063/1.441107 (9 pages) | Cited 41 times

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We have observed the dispersed fluorescence spectrum of free base phthalocyanine cooled in supersonic free jet. The spectrum consists of a single strong feature and some weaker red shifted structure. The frequencies of the single strong feature and the red shifted structure change only slightly as a function of the exciting frequency. This indicates that the potential surface does not change greatly upon electronic excitation and that the strong fluorescence transitions are Δv = 0. For excitation at frequencies greater than 720 cm−1 above the origin, the features in the fluorescence spectrum are broadened although the absorption features remain narrow. This is taken to indicate a mixing of background vibrational levels leading to intramolecular vibrational relaxation that is fast compared to the fluorescence lifetime. The intramolecular vibrational relaxation in phthalocyanine is compared to that observed in a recent series of experiments on alkylbenzenes.
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34.50.Ez Rotational and vibrational energy transfer
33.50.Dq Fluorescence and phosphorescence spectra

Dynamic NMR in liquid crystalline solvents—ring inversion of s‐trioxane

Z. Luz, R. Naor, and E. Meirovitch

J. Chem. Phys. 74, 6621 (1981); http://dx.doi.org/10.1063/1.441108 (10 pages) | Cited 8 times

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The proton magnetic resonance spectrum of s‐trioxane in nematic liquid crystalline solvents was studied over a wide range of temperatures. The spectra exhibit striking line shape variations with temperature which are attributed to the ring inversion of s‐trioxane. At high temperatures (≳100 °C) the spectra correspond to an average Hamiltonian due to the two fast interconverting chair forms of the molecule. As the temperature is lowered the resonance lines undergo selective broadening due to incomplete averaging of the two conformers. In order to obtain quantitative kinetic results the line shape theory for dynamic NMR in anisotropic liquids is formulated and is used to calculate theoretical spectra for s‐trioxane undergoing ring inversion. Comparison of the experimental and theoretical spectra yields kinetic parameters for the reaction in the temperature range at which the liquid crystalline solutions were studied, i.e., −20 to +110 °C. The proton NMR of s‐trioxane was also studied in the isotropic solvent freon in the temperature range −80 to −40 °C. Analysis of these spectra yield essentially the same kinetic parameters as in the anisotropic solvents. The final overall results are ΔH≠ = 11.2 kcal/mole, ΔS≠ = +3.1 e.u., and 1/τ (300 °K) = 2.0×105 sec−1. The advantages and limitations of dynamic NMR in liquid crystalline solvent are discussed.
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33.25.+k Nuclear resonance and relaxation
33.70.Jg Line and band widths, shapes, and shifts

Infrared emission spectroscopy of the products of UV‐dissociated chloroethylenes

Mary G. Moss, Mark D. Ensminger, and J. D. McDonald

J. Chem. Phys. 74, 6631 (1981); http://dx.doi.org/10.1063/1.441109 (5 pages) | Cited 33 times

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The chloroethylenes are known to undergo dissociation under ultraviolet light to form chloroacetylenes. We report here the infrared emission spectra of the products of 193 nm dissociation of vinyl chloride, trans‐ and cis‐dichloroethylene, vinylidene chloride, and trichlorothylene. The spectra reported here represent molecules that have undergone from four to 40 collisions. The most prominent features of these spectra are that the products are very highly vibrationally excited. The energy partitioning possibilities that are consistent with these results are discussed.
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33.20.Ea Infrared spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation

The high temperature generation and ESR investigation of ScH2, YH2, and YD2 radicals in rare gas matrices: A nonequilibrium vaporization technique for solid samples

L. B. Knight, M. B. Wise, T. A. Fisher, and J. Steadman

J. Chem. Phys. 74, 6636 (1981); http://dx.doi.org/10.1063/1.441110 (8 pages) | Cited 16 times

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The ScH2, YH2, and YD2 radicals have been generated from metal hydride powders at high temperatures by a nonequilibrium vaporization technique. The MH2 radicals were isolated in rare gas matrices at 12 K and investigated by electron spin resonance (ESR). The vaporization procedure has potential applications for the production of other vapor species which are difficult to generate by conventional means. The electronic structure, geometry, and ground state of these dihydride radicals were estimated from the ESR results and compared with recent theoretical conclusions. The metal ’’d’’ electron was found not to participate significantly in the M–H bond. These findings for MH2 are compared with recent results for ScF2 and YF2. The magnetic parameters for ScH2 are g∥ = 1.980 (1), g⊥ = 1.987 (1), A∥(45Sc) = −212 (2) MHz, A⊥(45Sc) = −128, ‖Aiso‖(H) = 12 (2). For YH2, g⊥ = 1.991  (1), A⊥(89Y) = −40 (10) MHz, ‖A⊥‖ (H) = 13 (2) MHz.
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81.20.-n Methods of materials synthesis and materials processing
76.30.Rn Free radicals

A simple interpretation of Raman excitation spectra of metalloporphyrins

J. A. Shelnutt

J. Chem. Phys. 74, 6644 (1981); http://dx.doi.org/10.1063/1.441111 (14 pages) | Cited 24 times

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A simple treatment of vibronic coupling in metalloporphyrins is described. Electronic degeneracy in the excited states is treated to arrive at simple expressions for the Raman excitation spectra and the absorption spectrum. The expressions are simple analogs of the usual A and B term expressions for the scattering tensor and are easily programmed for a small computer. They are only applicable in the weak vibronic coupling limit, but are nevertheless suitable for interpretation of the spectra of most biologically relevant porphyrin systems, at least as a starting point. They allow a simple discussion of a number of interference phenomena that influence the Raman intensity distribution in the excitation profiles of metalloporphyrins and other molecular systems. Some of these phenomena are consequences of electronic degeneracy in the resonant excited state. Nonadiabatic coupling contributions are also included in the expressions. Experimental Raman excitation spectra are discussed in light of this simple model.
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36.90.+f Other topics in exotic atoms and molecules; macromolecules; clusters (restricted to new topics in section 36)
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Absorption and dispersion in the O2 microwave spectrum at atmospheric pressures

Earl W. Smith

J. Chem. Phys. 74, 6658 (1981); http://dx.doi.org/10.1063/1.441112 (16 pages) | Cited 78 times

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Calculations are performed for absorption and phase dispersion at various frequencies within the 60 GHz band of O2 from low pressures where the spectral lines are isolated, to atmospheric pressures where they merge to form a continuum band. A perturbation theory proposed by Rosenkranz was tested and found to be valid for pressures up to 100 kPa (1 atm). The ’’line coupling coefficients’’, which describe the transfer of excitation from one radiating state to another, are also studied and various methods for evaluating these coefficients are analyzed and compared with experimental data. It is found that dispersion measurements are extremely sensitive to these coefficients and an experimental procedure for systematically measuring them is outlined; it is shown that such measurements can provide a very sensitive test for theoretical calculations of inelastic transition amplitudes.
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33.20.Bx Radio-frequency and microwave spectra
33.70.Jg Line and band widths, shapes, and shifts

Time resolved study of rotational energy transfer in A 2Σ+(ν′ = 0) state of OH in a flame by laser induced fluorescence

D. Stepowski and M. J. Cottereau

J. Chem. Phys. 74, 6674 (1981); http://dx.doi.org/10.1063/1.441121 (6 pages) | Cited 41 times

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Time resolved study of rotational transfer in the A 2Σ+(ν′ = 0) state of OH in a flame is performed by analyzing the fluorescence spectra scanned at different delays after the short exciting laser pulse. The conditions under which a three level model apply are discussed. Then comparison between this kinetic model and experiment provides direct total transfer rate out of the J′ = 7 1/2 excited level: The specific transfer cross sections derived are 70 Å2 for N2 and 18 Å2 for Ar. The fluorescence spectra show a strong propensity for spin conservation upon rotational transfer. As the delay increases, the rotational population distribution among the upper state tends to a Boltzmann distribution.
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33.50.Dq Fluorescence and phosphorescence spectra
34.50.Ez Rotational and vibrational energy transfer
82.33.Vx Reactions in flames, combustion, and explosions

Vibrational dephasing in liquid ethane‐d6

Richard E. Wilde and Ta‐Chau Chang

J. Chem. Phys. 74, 6680 (1981); http://dx.doi.org/10.1063/1.441122 (6 pages) | Cited 2 times

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The spontaneous Raman spectrum of liquid C2D6 has been obtained. The ν2 and ν3 isotropic bands have been analyzed by a memory‐functions procedure. The analysis suggests that the vibrational dephasing arises from rotation about the symmetry axis. The tumbling of the symmetry axis is much slower, and in the case of the ν3 band leads to ’’homogeneous narrowing.’’ The 2ν2 overtone bandwidth was found to have a first‐power dependence on the vibrational quantum number. The depolarization ratio of the ν3 band is 0.14; the ν2 band has a depolarization ratio less than 0.02.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
78.30.C- Liquids
33.70.Jg Line and band widths, shapes, and shifts

Theoretical study of shape resonances in the partial photoionization cross sections for the b 4Σg− and B 2Σg− states of O2+

G. Raşeev, H. Lefebvre‐Brion, H. Le Rouzo, and A. L. Roche

J. Chem. Phys. 74, 6686 (1981); http://dx.doi.org/10.1063/1.441123 (6 pages) | Cited 37 times

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Using the single‐center static‐exchange approximation, the 3σg photoionization cross section of O2 is calculated. The R‐averaged results are obtained for the production of O+2 in the b 4Σ−g and B 2Σ−g states. Shape resonances, a few electron volts wide, are found at 3 and 2.5 eV from the threshold for these two states, respectively. We find reasonable agreement with the experimental cross sections for the B 2Σ−g state and with the β values for the b 4Σ−g state. For this last state, comparison between theory and experiment leads us to a possible interpretation of the data, but a definite answer can not be given without taking into account the autoionized Rydberg states.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.70.Jg Line and band widths, shapes, and shifts

Multiphoton ionization mass spectroscopy of deuterated analogs of acetaldehyde: Evidence for deuterium scrambling

G. J. Fisanick and T. S. Eichelberger

J. Chem. Phys. 74, 6692 (1981); http://dx.doi.org/10.1063/1.441124 (8 pages) | Cited 7 times

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Fragmentation patterns as a function of laser flux are obtained for CD3CHO using a quadrupole mass spectrometer for excitation at the origin of the two‐photon resonant n→3s Rydberg transition at 55 138 cm−1. Extensive fragmentation is found with product ion branching ratios showing a strong dependence on laser flux. Fragments such as CDO+ appear, indicating that bond rearrangement occurs. In the case of the CD+3, CD2H+ ion pair, the CD2H+ scrambled product dominates, although in no case does the scrambling reach the statistical limit obtained by assuming that all hydrogen species are equivalent. The individual ion signal data can be fit with a rate equation model. Isotopic selectivity for mixtures of CD3CDO/CH3CHO is demonstrated; no partially deuterated products are found, indicating that the scrambling in CD3CHO is not collisionally induced.
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82.50.Hp Processes caused by visible and UV light
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Collision dynamics of three interacting atoms: Vibrational–rotational excitation in atom–diatom hyperthermal collisions

Lyntis H. Beard and David A. Micha

J. Chem. Phys. 74, 6700 (1981); http://dx.doi.org/10.1063/1.441125 (9 pages) | Cited 14 times

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We describe atom–diatom collisions at hyperthermal energies within the theory of three‐body scattering. We show how one can treat angular momentum coupling and rotational excitation to low order in a multiple‐collision expansion. The emphasis here is in the use of accurate two‐atom transition amplitudes and form factors, and on impulse and peaking approximations with simple interaction potentials. We present results for differential cross sections as functions of final rotational quantum numbers jf for Li+–CO and Li+–N2 at several center of mass angles in the eV region of collision energies. Form factors are also shown for varying jf, and are discussed in terms of simple overlap models in momentum space.
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34.50.Ez Rotational and vibrational energy transfer

Monte Carlo trajectory calculations of the energy of activation for collision‐induced dissociation of H2 by Ar as a function of rotational energy

Normand C. Blais and Donald G. Truhlar

J. Chem. Phys. 74, 6709 (1981); http://dx.doi.org/10.1063/1.441126 (4 pages) | Cited 10 times

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Rate constants and activation energies for selected initial rotational levels, thermally averaged over vibrational states and translational energies, are calculated for Ar+H2→Ar+H+H by the Monte Carlo quasiclassical trajectory method. The results show that activation energies for high rotational quantum numbers exceed those estimated from centrifugal barrier heights. To characterize the rotational‐level model of diatomic dissociation, we tabulate rate constants, activation energies, and other properties of dissociative collisions as functions of initial rotational quantum number j for conditions of thermal vibrational and translational degrees of freedom at 4500 K. Under equilibrium conditions, dissociation from a given j level is shown to occur primarily from the topmost v state of that j level.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
82.20.Fd Collision theories; trajectory models

On a model ecosystem showing competitive phenomena

Kazutoshi Iwamoto and Manabu Senō

J. Chem. Phys. 74, 6713 (1981); http://dx.doi.org/10.1063/1.441127 (5 pages)

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Competition within an ecosystem consisting of two similar subsystems is studied in detail. The procedure for analysis is based upon a multiplicity of steady states, and it was developed for the investigation of competition in a model chemical system. A spruce budworm system is analyzed as an example. Our results are quite different from those of a well‐known ecological theory of L. B. Slobodkin.
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82.20.Wt Computational modeling; simulation
89.60.-k Environmental studies

The classical limit of the quantum mechnical expressions for the kinetic theory cross sections

C. F. Curtiss

J. Chem. Phys. 74, 6718 (1981); http://dx.doi.org/10.1063/1.441128 (7 pages) | Cited 6 times

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The integral expressions for the various kinetic theory cross sections describing collisions between nonvibrating diatomic molecules, based on the generalized phase shift development of molecular scattering theory, which were developed in a previous paper are considered further. It is shown that in the classical limit the expressions can be written in forms similar to the usual expressions for the special case of spherical molecules. The spherical harmonic Yl(χ,0) where χ is the angle of deflection, which appears in the expressions for the spherical case, is replaced by a properly coupled sum of products of three spherical harmonics and additional integrations over two sets of Euler angles arise.
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51.10.+y Kinetic and transport theory of gases
34.90.+q Other topics in atomic and molecular collision processes and interactions (restricted to new topics in section 34)
03.65.Nk Scattering theory

Intermolecular and intramolecular V→V transfer in the vibrational predissociation of some polyatomic van der Waals molecules

J. A. Beswick and Joshua Jortner

J. Chem. Phys. 74, 6725 (1981); http://dx.doi.org/10.1063/1.441129 (9 pages) | Cited 28 times

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In this paper we present a theoretical study of vibrational predissociation (VP) on the ground state potential surface of van der Waals complexes consisting of polyatomic molecules. The intermolecular interaction was represented by separate contributions of atom–atom interactions, which were expressed in terms of Morse potentials. The VP process was handled utilizing the distorted wave approximation to describe a zero‐order Hamiltonian, which is separable in the intramolecular and in the intermolecular motion, while the residual interaction, which induces the reactive process, corresponds to the deviations of the intermolecular interaction from its value at the frozen intramolecular equilibrium configurations of the two constituents. Model calculations of the VP dynamics were performed for the He⋅⋅⋅N2O complex and for the (N2O)2 dimer, where the N2O unit is initially excited to the (001) vibrational state. These calculations were performed for the linear configuration as well as for the T‐shaped configuration of the complexes. We have considered three VP channels; (1) the V→T process, (2) the intramolecular V→V+T process and (3) the intermolecular V→V+T process. For He⋅⋅⋅N2O channels (1) and (2) prevail, while for (N2O)2 all three channels are open. For collinear He⋅⋅⋅N2O a second‐order process of type (2) dominates the VP, while for the T‐shaped He⋅⋅⋅N2O complex the first‐order process (1) is not efficient. In both cases the VP lifetimes, τ is τ∼10−5–10−6 sec. For the collinear (N2O)2 dimer a V→V+T process of type (2) dominates, with τ∼10−2–10−3 sec, the inefficiency of this process being attributed to a large mass effect. For the T‐shaped (N2O)2 dimer the most effective VP channel involves simultaneous intermolecular and intramolecular V→V+T process with low ΔE = 355 cm−1 translational energy, which is characterized by τ∼10−5–10−6 sec. These results provide guidelines for the analysis of the infrared spectra of the (N2O)2 complex.
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34.50.Ez Rotational and vibrational energy transfer
33.20.Ea Infrared spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
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