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15 Dec 1976

Volume 65, Issue 12, pp. 5033-5540

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A classical trajectory study of inelastic scattering in the system He+H2

M. D. Pattengill

J. Chem. Phys. 65, 5033 (1976); http://dx.doi.org/10.1063/1.433064 (4 pages) | Cited 18 times

Online Publication Date: 28 August 2008

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The classical trajectory study method has been used to investigate inelastic scattering in the system He+H2 using previously developed collision models. The calculations spanned the total energy range E=0.403 eV to E=1.900 eV. For all cases studied, H2 was initially in the ground vibrational–rotational state. Despite the fact that over half the energies employed were above the threshold (Eth?0.8 eV) for vibrational excitation of H2, the scattering was found to populate only the lowest two allowed rotational levels of the vibrational ground state. The classical cross sections obtained are compared with those from previous exact quantal (close‐coupled), effective potential, and coupled states calculations.
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34.50.Ez Rotational and vibrational energy transfer

The effect of porous barriers on the molecular composition and total flux of a reactive gas mixture

Pirooz Mohazzabi and Alan W. Searcy

J. Chem. Phys. 65, 5037 (1976); http://dx.doi.org/10.1063/1.433065 (7 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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When a gas mixture that is governed by a pressure dependent equilibrium is passed through a porous barrier, the exit molecular fluxes are functions of the equilibrium constant and the atomic concentrations at the exit face of the barrier rather than of the molecular weights and impingement pressures as has been tacitly assumed for Knudsen flow conditions. It is shown that whether or not molecules of the gas react with each other, the ratio of the total atomic escape flux of each elemental constituent to the total atomic impingement flux of that element for Knudsen flow should be a/l, where l is the barrier thickness and a is the same constant, of the order of the average diameter of barrier pores for each element in the gas mixture. The equilibrium prediction is confirmed for the sodium chloride monomer/dimer equilibrium mixture passed through alumina barriers with pores of the order of 1–10 μ diameter and various thicknesses. Measured dimer fluxes are reduced by the barriers to less than 10−3 times the dimer fluxes in conventional effusion; yet the measured fluxes agree to within about 30% with predictions from the measured monomer fluxes and the monomer/dimer equilibrium constant. The prediction that total atomic flux reductions for different vapors have the same dependence on a/l is confirmed by measurement with sodium chloride vapor and zinc vapor. The influence of porous barriers on the apparent heats of vaporization of monomers and dimers and the possibility of significant influence of surface diffusion on the experimental measurements are discussed.
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47.56.+r Flows through porous media
47.70.Fw Chemically reactive flows

Dynamics of the reaction of N+ with H2. IV. Reactive scattering at relative energies above 6 eV

Bruce H. Mahan and W. E. W. Ruska

J. Chem. Phys. 65, 5044 (1976); http://dx.doi.org/10.1063/1.433066 (8 pages) | Cited 9 times

Online Publication Date: 28 August 2008

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Product velocity vector distributions for the reaction N+(H2,H)NH+ and its isotopic variants have been determined in the range of relative energies above 6 eV. The reaction is direct, and there is a critical relative energy above which the spectator stripping peak disappears and is replaced by a double intensity lobe structure. Some evidence of the reaction of electronically excited metastable ions, probably N+(1D), is found. The results are compared with the predictions of the sequential impulse model of reactive scattering. The agreement is generally good, except that more very large angle scattering is observed, particularly for the N+(HD,H)ND+ case, than is predicted by the model.
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34.50.Lf Chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Laser‐induced rate processes in gases: Dynamics of polyatomic systems

Myron F. Goodman, James Stone, and David A. Dows

J. Chem. Phys. 65, 5052 (1976); http://dx.doi.org/10.1063/1.433067 (10 pages) | Cited 54 times

Online Publication Date: 28 August 2008

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A model is proposed to describe the collision‐free dynamics of a polyatomic molecule driven by an intense laser field. The evolution in time of stable and quasistable (chemically reactive) energy level populations driven on and off resonance are given, and analytic estimates are derived for the effects of dynamic power broadening (a–c Stark effect), mode and level degeneracies, and rapid unimolecular decay on the efficiency of laser pumping.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
42.62.-b Laser applications

A model for laser isotope separation in SF6

James Stone, Myron F. Goodman, and David A. Dows

J. Chem. Phys. 65, 5062 (1976); http://dx.doi.org/10.1063/1.433068 (6 pages) | Cited 48 times

Online Publication Date: 28 August 2008

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We propose a model for the effect of CO2 laser radiation in decomposing and separating isotopes of SF6. Analytic expressions for oscillator strengths are derived for discrete‐to‐discrete, discrete‐to‐continuum, and continuum‐to‐continuum energy level transitions. Loss in oscillator strength as the system is driven up the manifold is compensated for by a cooperative power broadening that contains an explicit dependence on level degeneracies. Isotope selectivity and yield at low pressures are computed as a function of laser intensity, and a threshold in yield is found at approximately 14 MW/cm2.
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32.10.Bi Atomic masses, mass spectra, abundances, and isotopes
42.62.-b Laser applications

Some aspects of electron–phonon interaction in the thermal modulation spectra of molecular crystals

B. H. Loo, A. H. Francis, and K. W. Hipps

J. Chem. Phys. 65, 5068 (1976); http://dx.doi.org/10.1063/1.433069 (8 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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The details of the temperature dependent intensity and linewidth of zero‐phonon bands in molecular crystal absorption and emission spectra are considered in relation to the line shape functions observed in thermal modulation spectra. Theory suggests and experiment confirms that in the limit of the Condon and adiabatic approximations for linear electron–phonon coupling, the extraordinary temperature dependence of zero‐phonon bands may be utilized to separate them from diffuse background absorption or emission. Qualitative consideration of line broadening from quadratic electron–phonon coupling utilizing a configuration coordinate model suggests that even when these terms dominate the linear interaction, increased resolution may be obtained in a thermal modulation spectrum. The theoretical considerations are illustrated with several experimental examples and some applications of the technique are discussed.
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63.20.K- Phonon interactions
78.40.Ha Other nonmetallic inorganics

Electron–phonon interaction in the spectra of p‐benzoquinone in chemically mixed crystals

B. H. Loo and A. H. Francis

J. Chem. Phys. 65, 5076 (1976); http://dx.doi.org/10.1063/1.433070 (7 pages) | Cited 5 times

Online Publication Date: 28 August 2008

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Phonon sidebands of unusual sharpness and number are observed in the phosphorescence spectrum of p‐benzoquinone in chemically mixed crystals with p‐dichlorobenzene and p‐dibromobenzene. Phosphorescence–Microwave Double Resonance (PMDR) and thermal modulation spectroscopy are used to examine the role of localized phonon modes in the phosphoresence spectrum. Localized phonons are shown to be active in both distributing as well as inducing radiative intensity in the 3Blg→1Ag transition observed in phosphorescence. Some comments on the excited state geometry of p‐benzoquinone are offered in view of our experimental results and recent results from other laboratories. JCP
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63.20.K- Phonon interactions
78.40.Ha Other nonmetallic inorganics

Kinetic energies and angular distributions of oxygen atom photofragments produced by photodissociation of O2 and N2O in the vacuum ultraviolet

E. J. Stone, G. M. Lawrence, and C. E. Fairchild

J. Chem. Phys. 65, 5083 (1976); http://dx.doi.org/10.1063/1.433071 (10 pages) | Cited 22 times

Online Publication Date: 28 August 2008

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A gas phase chemi‐ionization process is used to detect O atoms produced by photodissociation of O2 and N2O. For the photon energies used here the accessible O atom states are within the ground 3P levels and the metastable 1D and 1S levels. Kinetic energies of the O atom photofragments are determined using an atomic beam time‐of‐flight technique, and the O atom angular distributions are determined by varying the angle between the direction of the photon beam and the atomic beam flight path. Dissociative transitions within the Schumman–Runge continuum of O2 and the principal vacuum ultraviolet absorption continuum of N2O yield results in agreement with previous predictions. For the dissociation of O2 at wavelengths of 120 and 124 nm, the principal dissociation products are O(3P)+O(1D); and, at these wavelengths, the O atom angular distribution is consistent with previous conclusions that predissociation is important. Using existing theories of photofragment angular distributions, an asymmetry parameter having a value of (−0.61±0.05) is obtained for predissociation in O2 at the 10.0 and 10.3 eV absorption features.
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82.50.Hp Processes caused by visible and UV light
82.33.Tb Atmospheric chemistry

Electronic and magnetic properties of metal diiodides MI2 (M=V, Cr, Mn, Fe, Co, Ni, and Cd) from 129I Mössbauer spectroscopy

J. M. Friedt, J. P. Sanchez, and G. K. Shenoy

J. Chem. Phys. 65, 5093 (1976); http://dx.doi.org/10.1063/1.433072 (10 pages) | Cited 12 times

Online Publication Date: 28 August 2008

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The hyperfine interaction parameters at the iodine site in various metal diiodides (M=V, Cr, Mn, Fe, Co, Ni, and Cd) were measured using the 27.8 keV Mössbauer transition in 129I. Charge densities in the valence orbitals are deduced from an interpretation of isomer shift and quadrupole coupling constant values. Magnetic hyperfine interactions transferred at the originally diamagnetic iodine ion in the magnetically ordered phases of the compounds allow one to determine the unpaired spin densities in the valence orbitals. Information relative to the magnetic structures is obtained from the number and intensities of magnetically nonequivalent sites and from the relative orientation between the transferred field and the electric field gradient axes. The Mössbauer spectra of 129Xe impurities created by β− decay of 129I in the NiI2 lattice reveal the absence of bonding of xenon atoms in this matrix.
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76.80.+y Mössbauer effect; other γ-ray spectroscopy

Rotationally resolved resonance scattering from a predissociating molecule: Ammonia‐d3 excited at 2139 Å and 2144 Å

P. A. Hackett, R. A. Back, and S. Koda

J. Chem. Phys. 65, 5103 (1976); http://dx.doi.org/10.1063/1.433049 (7 pages) | Cited 7 times

Online Publication Date: 28 August 2008

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Rotationally resolved resonance scattering spectra of ND3 excited within the 0000←00+00 and 0100←01−00 bands of the ?←? transition have been photographed. The quantum yield of this emission has been measured (1×0.5×10−5) and is in agreement with that predicted for simple ’’fluorescence.’’ However, the spectra show evidence for excitation of rovibronic levels up to 20 cm−1 off of resonance with the exciting line, and rotational lines within a single vibrational band obey ’’Raman’’ selection rules. Thus the position of rotational lines gives information about ground state energy levels only. Information about excited state energy levels is contained in the relative intensity of vibrational progressions in the emission spectra.
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33.20.Ni Vacuum ultraviolet spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)

Pressure‐broadened linewidths of nitric oxide

G. D. T. Tejwani, Bruce M. Golden, and Edward S. Yeung

J. Chem. Phys. 65, 5110 (1976); http://dx.doi.org/10.1063/1.433050 (5 pages) | Cited 21 times

Online Publication Date: 28 August 2008

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N2‐broadened linewidths of NO in the 5.4 μ band have been measured. This provides a means of determining the quadrupole moment of NO, which has been poorly measured so far. Using the Anderson–Tsao–Curnutte theory of line broadening, and this new value, 2.4×10−26 esu⋅cm2, for the quadrupole moment of NO, self‐broadened and foreign‐gas (N2 and O2) ‐broadened linewidths of NO at 300°K for all important infrared transitions are calculated. In the self‐broadening calculations, dipole–dipole, dipole–quadrupole, quadrupole–dipole, quadrupole–quadrupole, induced, and dispersion interactions were taken into account. For the case of foreign‐gas broadening, dipole–quadrupole, quadrupole–quadrupole, dipole–hexadecapole, quadrupole–hexadecapole, induced, and dispersion interactions were considered. Air‐broadened linewidths of NO have also been computed at 200, 250, and 300°K.
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33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

HFClF: Structure and bonding

Stewart E. Novick, Kenneth C. Janda, and William Klemperer

J. Chem. Phys. 65, 5115 (1976); http://dx.doi.org/10.1063/1.433051 (7 pages) | Cited 51 times

Online Publication Date: 28 August 2008

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The structure of the complex formed between HF and ClF has been determined by molecular beam electric resonance spectroscopy. The molecule HFClF is a slightly asymmetric prolate top. The spectroscopic constants determined from K=0 spectra of several isotopic species are as follows: The atomic arrangement in the complex is HFClF with the three heavy atoms collinear. The proton is off axis by 55°. The FCl van der Waals bond length is 2.76 Å. Comparison of the structure of HFClF with that of (HF)2 shows striking similarities. It appears that the bonding in both complexes is quite similar.
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33.15.Dj Interatomic distances and angles
33.15.Fm Bond strengths, dissociation energies
34.50.Lf Chemical reactions

Semiclassical calculations of cross sections for fine‐structure transitions in Rb (62P) and Cs (82P) colliding with rare gas atoms

J. Pascale and P. M. Stone

J. Chem. Phys. 65, 5122 (1976); http://dx.doi.org/10.1063/1.433052 (11 pages) | Cited 13 times

Online Publication Date: 28 August 2008

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Calculations of cross sections for fine‐structure transitions in the second and third excited 2P state of rubidium and cesium, respectively, have been carried out using a semiclassical theory for collisions with ground state He, Ar, and Xe atoms. The primary difference from previous theories for the first 2P state of an alkali is the full formulation of the semiclassical theory in terms of molecular states of the alkali–rare gas atom complex. The molecular states are consistent with the interaction potential and both radial and rotational coupling are explicitly included in the calculations. In the collision energy range investigated (from threshold to 0.3 eV) the cross sections are found to have an undulatory structure, especially prominent for the Rb–Ar system. Except for the Cs–He system, the thermally averaged cross sections agree with experiment within a factor of 1.4–2.8. For cesium, these results reduce considerably the large discrepancy between previous calculations of Nikitin and Reznikov (1971) and experiment.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Determination of T2/T1 for inversion transitions in NH3 by analysis of power‐broadened line shapes

T. Amano and R. H. Schwendeman

J. Chem. Phys. 65, 5133 (1976); http://dx.doi.org/10.1063/1.433053 (5 pages) | Cited 21 times

Online Publication Date: 28 August 2008

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A computer‐coupled microwave spectrometer has been used to record the line shapes of 14 inversion transitions in 15NH3 at several pressures under conditions of low and moderate microwave powers. From the low‐power line shapes, values of Δν/p= (2πpT2)−1 have been determined and used as input data for the analysis of the power‐broadened line shapes from which values of T2/T1 have been obtained. The T2/T1 results generally increase with J and K and range from 1.11±0.06 for the (J,K) = (1,1) transition to 1.58±0.09 for the (5,5) transition. The data appear to imply that the ratio of the rate constant for adiabatic collisions to that for diabatic collisions is about 0.35 in NH3.
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33.20.Bx Radio-frequency and microwave spectra
33.70.Jg Line and band widths, shapes, and shifts

Vibrational relaxation and energy gap law breakdown in the X 3Σ− state of NH and ND in solid argon

V. E. Bondybey

J. Chem. Phys. 65, 5138 (1976); http://dx.doi.org/10.1063/1.433054 (3 pages) | Cited 31 times

Online Publication Date: 28 August 2008

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The lifetimes of the v=1 levels in the ground electronic states of NH and ND were measured. It is shown that the rate of vibrational relaxation in NH is faster by at least a factor of 150, contrary to the predictions of the energy gap law. This is due to the localized rotational mode being the energy acceptor and to the larger amplitude of center of mass motion in the hydride. The absolute rates are considerably slower than the corresponding rates in the excited A 3Π state owing to the lower polarizability and lower barrier to free rotation in the ground electronic state.
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82.20.Rp State to state energy transfer
31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates

Electron correlation in small metal clusters. Application of a theory of self‐consistent electron pairs to the Be4 system

Clifford E. Dykstra, Henry F. Schaefer, and Wilfried Meyer

J. Chem. Phys. 65, 5141 (1976); http://dx.doi.org/10.1063/1.433055 (6 pages) | Cited 83 times

Online Publication Date: 28 August 2008

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A knowledge of the properties of small metal particles is essential to the understanding of catalysis on a molecular level. In this regard, one particularly important property is the rate at which the dissociation energy of a small metal cluster approaches the bulk cohesive energy. The present research concerns the effect of electron correlation on the dissociation energy of a particularly stable beryllium cluster, the tetrahedral Be4 system. A contracted Gaussian basis set of size Be(9s 4p/5s 2p) was adopted in conjunction with the recently developed theory of self‐consistent electron pairs (SCEP). Several new theoretical and computational wrinkles are discussed, including the incorporation of the SCEP/coupled electron pair approximation (SCEP/CEPA). The Be4 results provide strong evidence for the reliability of the Hartree–Fock approximation for alkaline earth cohesive energies. As suggested earlier the Be4 dissociation energy appears to be ∼40 kcal/mole. Analogous studies of the Be2 molecule are reported.
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36.40.-c Atomic and molecular clusters
31.15.V- Electron correlation calculations for atoms, ions and molecules
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Homogeneous nucleation in associated vapors. I. Acetic acid

Richard H. Heist, Kevin M. Colling, and Calvin S. DuPuis

J. Chem. Phys. 65, 5147 (1976); http://dx.doi.org/10.1063/1.433056 (8 pages) | Cited 23 times

Online Publication Date: 28 August 2008

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Homogeneous nucleation measurements on acetic acid vapor are reported. The presence of the relatively stable association clusters tends to stabilize the vapor with regard to homogeneous nucleation. The variation of the critical supersaturation with temperature for acetic acid vapor was found to agree well with the predictions of the Katz–Saltsburg–Reiss theory for nucleation in associated vapors.
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82.60.Nh Thermodynamics of nucleation

Optimized diatomics‐in‐molecules potential energies for H3 and H4

Charles W. Eaker and Christopher A. Parr

J. Chem. Phys. 65, 5155 (1976); http://dx.doi.org/10.1063/1.433057 (6 pages) | Cited 23 times

Online Publication Date: 28 August 2008

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Several variants of diatomics‐in‐molecules (DIM) theory are used to calculate the potential‐energy hypersurfaces (PEH) for H3 and H4. The minimum basis set calculations yield qualitatively incorrect PEHs for these systems. Extension of the basis set to include the excited 2S∗ state or ionic states of hydrogen can result in a good ’’optimized’’ DIM PEH for H3, but the H4 energies remain poor. Extension of the theory to include triatomic contributions explicitly does not correct the H4 energies in the minimum basis set application.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions

Three‐dimensional quantum mechanical studies of the H+H2 reactive scattering

B. H. Choi and K. T. Tang

J. Chem. Phys. 65, 5161 (1976); http://dx.doi.org/10.1063/1.433058 (20 pages) | Cited 43 times

Online Publication Date: 28 August 2008

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A three‐dimensional quantum mechanical study is made of H+H2 reactive scattering. The differential and total cross sections as well as the S‐matrix elements are obtained from the adiabatic distorted wave model and the Porter–Karplus semiempirical potential surface. With the initial molecule in the ground rotational state, the energy dependence, rotational state dependence, and other properties of the reaction probabilities and of the cross sections for transitions to all possible states of the product molecule are determined. The reactive scattering from the threshold to 0.5 eV is predominantly backward. The 0→0 rotational transition contributes only a small fraction to the total reactive cross section; however, most product molecules prefer rotational states that are considerably lower than the highest one allowed by energy conservation. The reaction probability is found to be a smoothly decreasing function of the total angular momentum of the system. These results are very similar to our previous results for the D+H2 reaction except the threshold energy for the H+H2 is higher and the magnitude of the cross section for the reaction of the D+H2 is larger. A systematic study of the effects of the Pauli exclusion principle on cross sections of the scattering of three identical particles shows that in order to obtain the ’’observable’’ cross sections, the unsymmetrized results of the H+H2 and D+D2 reactions have to be multiplied by various ’’strange’’ numerical factors. These observable cross sections are compared with three different sets of close coupling results on the same potential surface. Our results are in close agreement with those of Kuppermann and Schatz and are in substantial disagreement with those of Wolken and Karplus. Our results near the threshold and at 0.5 eV are similar to those of Elkowitz and Wyatt but there are significant differences in energy dependence in the intermediate region. The present results are also compared with the three‐dimensional classical trajectory results. The most significant quantum effect is caused by the spin statistics. Dynamically, there are excellent qualitative and quantitative agreements in many respects between the quantum and classical results, although the present quantum cross sections rise above the classical values at incident energies greater than 0.4 eV.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions

Studies of reactions of importance in the stratosphere. I. Reaction of nitric oxide with ozone

John W. Birks, Brian Shoemaker, Thomas J. Leck, and Deborah M. Hinton

J. Chem. Phys. 65, 5181 (1976); http://dx.doi.org/10.1063/1.433059 (5 pages) | Cited 15 times

Online Publication Date: 28 August 2008

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The rate constant for the reaction NO+O3→NO2+O2 has been measured by the fast flow method over the temperature range 203–361 K. Loss of ozone in a large excess of nitric oxide was detected by molecular beam sampling into the electron impact ion source of a quadrupole mass spectrometer. The resulting Arrhenius expression is k=2.34±0.23×10−12 exp(−1450±50/T) cm3 molecule−1 s−1 which predicts k298=1.80×10−14 cm3 molecule−1 s in excellent agreement with previous determinations. Our results suggest a slight curvature in the Arrhenius plot, the activation energy increasing with increasing temperature.
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82.33.Tb Atmospheric chemistry
82.20.Pm Rate constants, reaction cross sections, and activation energies

Viscosity of multicomponent mixtures of four complex gases

J. Kestin, H. E. Khalifa, and W. A. Wakeham

J. Chem. Phys. 65, 5186 (1976); http://dx.doi.org/10.1063/1.433060 (3 pages) | Cited 13 times

Online Publication Date: 28 August 2008

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In a series of earlier papers it has been established that the viscosities of the pure gases CH4, CO2, CF4, and SF6 as well as those of their binary mixtures conform to the extended law of corresponding states formulated by Kestin, Ro, and Wakeham. In this paper, the kinetic‐theory expressions for multicomponent gas mixtures are used in conjunction with the law of corresponding states and the appropriate binary scaling parameters σij and ϵij to generate the viscosities of several ternary and quaternary mixtures of these gases. The calculated viscosities are compared with direct measurements (accuracy ±0.2%) performed in an oscillating disk instrument in the temperature range 25–200°C. The comparison reveals that the generated data depart from the measured viscosities by a maximum of 0.5% and that the standard deviation is only 0.25% which is comparable with the experimental uncertainty. The validity of the calculation scheme presented for predictive purposes is thereby confirmed. It is emphasized that the calculation is based exclusively on previously published information and that it does not in any way utilize the data on multicomponent mixtures. Thus the calculation can be described as a true ’’prediction.’’
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51.20.+d Viscosity, diffusion, and thermal conductivity

Measurement of the rate coefficients for the bimolecular and termolecular de‐excitation reactions of He(23S) with Ne, Ar, N2, CO, CO2, and CH4

F. W. Lee and C. B. Collins

J. Chem. Phys. 65, 5189 (1976); http://dx.doi.org/10.1063/1.433061 (9 pages) | Cited 39 times

Online Publication Date: 28 August 2008

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This work reports the measurement of second and third order excitation transfer reactions of metastable 23S helium atoms with Ne, Ar, N2, CO, CO2, and CH4. In this study He  (23S) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 3889 Å, 23S→43P, helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharge. Data have been obtained as functions of helium pressure over the range from 800 to 2000 torr and as functions of the partial pressure of reactant from 14 to 200 mtorr. From this data pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from second order, bimolecular, and third order, termolecular, components. The bimolecular components have been found to agree with tabulated values appearing in the literature. The sensitivity of the method has been sufficient to detect termolecular components as small as 0.3×10−30 cm6/sec and values were found to range from this threshold value for Ne to 8.3×10−30 cm6/sec for CO2. The size of these termolecular rates suggests the general importance of such third order reactions in higher pressure plasmas and afterglows such as those found in e‐beam lasers.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Vibrational relaxation of DCl (v=1) by Cl and Br atoms and of HBr (v=1) by Br atoms

R. Glen Macdonald and C. Bradley Moore

J. Chem. Phys. 65, 5198 (1976); http://dx.doi.org/10.1063/1.433062 (3 pages) | Cited 8 times

Online Publication Date: 28 August 2008

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The rates of vibrational relaxation of DCl (v=1) by Cl and Br are measured as (5.5±1.6) ×10−12 and (2.3±0.7) ×10−13 cm3 molecule−1⋅ sec−1, respectively. DCl is relaxed somewhat less rapidly than HCl in both cases. The rate for HBr (v=1) relaxed by Br atoms is found to be (2.6±1.0) ×10−12 cm3 molecule−1⋅ sec−1.
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34.50.Ez Rotational and vibrational energy transfer
82.20.Rp State to state energy transfer

ESR studies of nearest neighbor Cr3+ pairs in MgO

J. Marguglio

J. Chem. Phys. 65, 5201 (1976); http://dx.doi.org/10.1063/1.433063 (3 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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Nearest neighbor Cr3+ pairs in MgO have been studied by ESR techniques. The spectrum associated with the S=2 spin state was observed. The appropriate spin Hamiltonian for the system is H=βH⋅g⋅S + Ds{S2z−1/3 S (S+1) }, where the z axis is along 〈110〉. The axially symmetric D tensor was measured to be 0.182±0.009 cm−1, 0.206±0.009 cm−1, and 0.231±0.009 cm−1 for the S=2 spin state. In addition, the temperature dependence of Ds was obtained and was attributed to thermal expansion of the crystal lattice.
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76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Multiphoton molecular dissociation in intense laser fields

Shaul Mukamel and Joshua Jortner

J. Chem. Phys. 65, 5204 (1976); http://dx.doi.org/10.1063/1.433073 (22 pages) | Cited 104 times

Online Publication Date: 28 August 2008

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In this paper we advance a model for multiphoton photofragmentation of an ’’isolated,’’ collision‐free, polyatomic molecule on the ground state potential surface. The molecular energy levels are separated into three regions. In the low energy range the level structure is sparse and only dynamic Stark shifts will be exhibited. In the intermediate energy range the density of bound vibrational states is high and the level structure can be described in terms of mixed (zero‐order) states. We argue that in this energy range intrastate anharmonic scrambling may be of central importance in the excitation process, but that intrastate vibrational relaxation and energy redistribution is not encountered for medium‐sized molecules. In the high energy region dissociative channels open up and reactive intramolecular decay is handled in terms of resonance theory. The time evolution of a multilevel system, whose highest energy levels are metastable, and which is driven by an intense laser field, is handled by the effective Hamiltonian formalism. Explicit expressions are derived for the photofragmentation yields and their dependence on the molecular parameters and on the field parameters. Specific applications to two distinct model systems are presented. First, we treat the quasidiatomic model, which disregards level scrambling in the intermediate energy range, whereupon near‐resonant radiative coupling prevails between the states of a truncated anharmonic oscillator. Second, we have considered the two‐ladder model where in the low energy range near‐resonant radiative coupling occurs within an anharmonic ladder, while in the intermediate energy range resonant radiative coupling between mixed states prevails. We present numerical simulations of the photofragmentation yields and their dependence on the molecular parameters, such as the diagonal anharmonicity, the molecular dissociation energy, the predissociative widths, and the isotopic shift. We have also explored the dependence of the photofragmentation yields on the pulse parameters, such as the off‐resonance energy, the field intensity, and the pulse duration. The quasidiatomic model seems to overestimate the power onset for photodissociation and the power required for the onset of saturation effects, while the two‐ladder model is quite adequate to account for the gross features of coherent multiphoton molecular photofragmentation.
Show PACS
82.50.Hp Processes caused by visible and UV light
32.80.Rm Multiphoton ionization and excitation to highly excited states
32.80.Wr Other multiphoton processes
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