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15 Jun 1976

Volume 64, Issue 12, pp. 4815-5322

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Temperature and pressure dependence of the NMR transition frequencies of 27Al in LiAl(SiO3)2, spodumene

S. F. Harley, C. D. Williams, and R. F. Tipsword

J. Chem. Phys. 64, 4815 (1976); http://dx.doi.org/10.1063/1.432136 (6 pages) | Cited 2 times

Online Publication Date: 28 August 2008

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Equations have been developed, correct to second order in the normal‐mode amplitudes for lattice vibration, which describe the constant‐volume temperature dependence of the NMR transition frequencies for a spin 5/2 nucleus located at a site of arbitrary asymmetry parameter. These equations indicate that an analysis of the temperature dependence of the transition frequencies will not yield rigorously the temperature dependence of the quadrupole coupling constant or asymmetry parameter unless all the transition frequencies are measured. The temperature and pressure dependences of two of the NMR transition frequencies of 27Al in LiAl(SiO3)2 have been measured over a temperature range of 4.2–300 K at atmospheric pressure, and a pressure range of 0–7 kbar at 195, 273, and 298 K. From these measurements, as well as from measurements of the volume expansion coefficient and the compressibility, the temperature dependence of the transition frequencies at constant volume was calculated. An analysis of these results indicates that, with the assumption of three vibrational modes of characteristic temperatures of approximately 150, 675, and 2600 K, there is reasonable agreement between experiment and a simplified form of the theory.
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76.60.Es Relaxation effects
76.60.Gv Quadrupole resonance

Effective Hamiltonian methods for the semiclassical treatment of molecular collisions

Stuart Augustin and Herschel Rabitz

J. Chem. Phys. 64, 4821 (1976); http://dx.doi.org/10.1063/1.432137 (11 pages) | Cited 21 times

Online Publication Date: 28 August 2008

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Effective Hamiltonian theory has previously been applied in a quantum mechanical framework, where the computational savings resulted from the reduced number of coupled equations. The present paper shows how effective Hamiltonian theory can be combined with classical S‐matrix theory. In this case the computational difficulty is reduced by lowering the number of degrees of freedom that must be semiclassically ’’quantized’’ via root‐searching techniques. It is shown, for example, that a full classical S‐matrix calculation for collisions of two rigid diatoms would require root searches in a four‐dimensional space while an effective potential calculation would need only two‐dimensional root searches. This can represent a substantial decrease in computational effort. A modified effective potential and the centrifugal decoupling method are formulated for application to classical S‐matrix theory. Also included is a description of the rotational coordinates and momenta needed for the semiclassical treatment of an arbitrary, nonreactive bimolecular collision.
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34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Microwave spectrum, structure, and dipole moment of 3,3‐difluorocyclopropene

K. R. Ramaprasad, Victor W. Laurie, and Norman C. Craig

J. Chem. Phys. 64, 4832 (1976); http://dx.doi.org/10.1063/1.432138 (4 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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The microwave spectra of four isotopic species of 3,3‐difluorocyclopropene have been investigated in the region from 18–40 GHz. Structural parameters obtained are r (C1C2) =1.321±0.001, r (C1C3) =1.438±0.007, r (CH) =1.075±0.001 , r (CF) =1.365±0.005 Å, &FCF=105.5±0.5°, &C1C3C2=54.6±0.4°, &HC1C2=148.4±0.1°. From the Stark effect the dipole moment has been determined to be 2.98±0.02 D.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Dj Interatomic distances and angles

Proton modulation of the electron spin echo envelope in a Nd3+:aquo glass

W. B. Mims and J. L. Davis

J. Chem. Phys. 64, 4836 (1976); http://dx.doi.org/10.1063/1.432139 (11 pages) | Cited 26 times

Online Publication Date: 28 August 2008

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The electron spin echo envelope has been measured at 4.2 °K for a frozen solution of NdCl3 in water and alcohol. Measurements were made at a frequency of 9.134 GHz and at Zeeman field settings of 2400, 3200, and 4000 G. At all these field settings the electron spin echo envelope showed a deep modulation associated with frequencies in the vicinity of ωI and 2ωI, where ωI is the free proton precession frequency. The components at ?ωI were clearly visible in the early portion of the envelopes, but components ? 2ωI tended to predominate towards the end. These results have been interpreted by means of a model in which it is assumed that the protons lie on one or more concentric spheres about the Nd3+ ion. In the simplest form of calculation based on this model the proton distribution was taken to be uniform over each of the spherical shells, and the envelope modulation function was calculated by summing contributions weighted according to the area of elements on the surface and the number of protons in the shell. In an alternative approach, the coordinating protons were assumed to be added in a random and uncorrelated manner on the surface of the sphere (or spheres) and a product formula was used to derive the result. Although the main qualitative features of the modulation envelope could be explained in this way, neither form of calculation was sufficiently exact to interpret the data to within the limits of experimental accuracy. The approximation on which the linear sum calculation is based breaks down in the magnetic field regime concerned here. The product calculation is on the other hand inherently inaccurate because of the assumption regarding the random placement of successive protons. We obtain a best value r1= 3.0 ±0.1 Å for the radius of the first proton shell in the Nd:aquo complex. A more accurate value could probably be obtained by working with a higher microwave frequency and higher values of H0. The significance of these results in relation to the design of electron spin echo experiments in organic and biological materials is discussed.
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76.30.Kg Rare-earth ions and impurities
81.05.Kf Glasses (including metallic glasses)
61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)

Brillouin–Rayleigh scattering studies of polypropylene glycol. III

C. H. Wang and Y. Y. Huang

J. Chem. Phys. 64, 4847 (1976); http://dx.doi.org/10.1063/1.432140 (6 pages) | Cited 17 times

Online Publication Date: 28 August 2008

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A comprehensive Brillouin scattering experimental study of polypropylene glycol (PPG), average molecular weight of 1025, 2025, and 4000, has been carried out. The hypersonic velocity, attenuation coefficient, the modulus of elasticity, and the Landau–Placzek ratio have been obtained as a function of temperature for each polymer. The PPG 425 data reported earlier are also included for comparison. For all the quantities measured, only the Laudau–Placzek ratio (below ambient temperature) is molecular weight dependent; the hypersonic velocity, attenuation coefficient, and elastic modulus are found to be independent of molecular weight in the present 425–4000 weight range. The differences in the Landau–Placzek ratio between the different polymers are attributed to different degree of frozen‐in density fluctuations due to the difference in the medium’s viscosity; the mechanism of structural relaxation is not sufficient to explain the increase of the Landau–Placzek ratio of each polymer below ambient temperature. All polymers display the velocity dispersion and sound attenuation maximum. However, contrary to that observed in the ultrasonic frequency region, the maximum of the hypersonic attenuation coefficient appears to lie close to the beginning of the velocity dispersion curve and not its middle. The present results on the sound velocity and attenuation can be satisfactorily fit to a theory developed by Isakovich and Chaban, who have modeled the highly viscous liquid as a microinhomogeneous medium.
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81.40.Tv Optical and dielectric properties related to treatment conditions
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Infrared and Raman spectra of the M+Cl3− ion pairs and their chlorine–bromine counterparts isolated in argon matrices

Bruce S. Ault and Lester Andrews

J. Chem. Phys. 64, 4853 (1976); http://dx.doi.org/10.1063/1.432141 (7 pages) | Cited 11 times

Online Publication Date: 28 August 2008

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The argon matrix reactions of alkali chloride salts with Cl2 have been investigated through infrared and Raman spectra. In each infrared experiment, an intense product band was observed between 327 and 375 cm−1 and assigned to the antisymmetric stretching vibration ν3 of the Cl3− anion in the ion pair M+Cl3−. Raman spectra of these reaction mixtures yielded the same ν3 bands and, in addition, new signals between 253 and 276 cm−1 which are assigned to the symmetric stretching vibration ν1 of Cl3− in the M+Cl3− species. The observation of two stretching modes in the Raman spectra indicates that the Cl3− ions are asymmetric in these ion pairs. Bromine counterparts and the mixed chlorine–bromine anions were also formed, and used to verify that the anion in the M+X3− species contains three halogen atoms, with the metal ion beside the anion in an asymmetric ’’T’’ shaped structure.
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33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Temperature dependent activation energy for electron transfer between biological molecules

Joshua Jortner

J. Chem. Phys. 64, 4860 (1976); http://dx.doi.org/10.1063/1.432142 (8 pages) | Cited 473 times

Online Publication Date: 28 August 2008

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This paper considers electron transfer between biological molecules in terms of a nonadiabatic multiphonon nonradiative decay process in a dense medium. This theoretical approach is analogous to an extended quantum mechanical theory of outer sphere electron transfer processes, incorporating the effects of both low‐frequency medium phonon modes and the high‐frequency molecular modes. An explicit, compact and useful expression for the electron transfer probability is derived, which is valid throughout the entire temperature range, exhibiting a continuous transition from temperature independent tunneling between nuclear potential surfaces at low temperatures to an activated rate expression at high temperatures. This result drastically differs at low temperatures from the common, semiclassical, Gaussian approximation for the transition probability. The experimental data of De Vault and Chance [Biophys. J. 6, 825 (1966)] on the temperature dependence of the rate of electron transfer from cytochrome to the chlorophyll reaction center in the photosynthetic bacterium Chromatium are properly accounted for in terms of the present theory.
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87.15.ag Quantum calculations
82.20.Pm Rate constants, reaction cross sections, and activation energies

Variational localized‐site cluster expansions. I. General theory

D. J. Klein

J. Chem. Phys. 64, 4868 (1976); http://dx.doi.org/10.1063/1.432143 (5 pages) | Cited 10 times

Online Publication Date: 28 August 2008

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Cluster expansions in terms of general sites (which may be spin orbitals, spin‐free orbitals, shells, component atoms in a molecule, etc.) are developed for electronic wavefunctions. Emphasis is placed upon the potential simplification of such expansions in the case that the sites are localized. Formulas for both diagonal and off‐diagonal matrix elements for such cluster expanded wavefunctions are given, and approximations to these general formulas are discussed.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

Variational localized‐site cluster expansions. II. Trees and near trees

D. J. Klein and M. A. Garcia‐Bach

J. Chem. Phys. 64, 4873 (1976); http://dx.doi.org/10.1063/1.432144 (5 pages) | Cited 5 times

Online Publication Date: 28 August 2008

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Cluster expanded wavefunctions involving localized‐site states and only pair excitations between nearest neighbor sites are considered. In the case that the bonds connecting these nearest neighbor sites form a tree graph (without rings), exact matrix element formulas are obtained in terms of the inverse of a modified type of topological matrix associated with this tree graph. The treatment of some near‐tree cases, without any touching rings, is also discussed.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

Simulation of molecular spectra: A linear equation solving method

Ronald W. Golland, Arthur E. Stillman, and Robert N. Schwartz

J. Chem. Phys. 64, 4878 (1976); http://dx.doi.org/10.1063/1.432145 (3 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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The difficulties in using diagonalizing algorithms in the calculation of molecular spectra are discussed. An alternative method is proposed in which the complex matrix equation is solved directly. The inherent inefficiency of this method is largely bypassed by first reducing the matrix into Hessenberg or triangular form by means of similarity transformations. This method is found to yield accurate line shapes even for matrices for which many diagonalizing algorithms fail.
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33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.xh Group-theoretical methods
33.20.-t Molecular spectra

MCSCF potential energy surface for photodissociation of formaldehyde

Richard L. Jaffe and Keiji Morokuma

J. Chem. Phys. 64, 4881 (1976); http://dx.doi.org/10.1063/1.432126 (6 pages) | Cited 27 times

Online Publication Date: 28 August 2008

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The ground state potential energy surface for the dissociation of formaldehyde H2CO→H2+CO is calculated with the ab initio MCSCF method with an extended (4–31G) basis set. The location, barrier height, and force constants of the transition state are determined and the normal coordinate analysis is carried out. The calculated barrier height is 4.5 eV. Based on the calculated quantities, the detailed mechanism of the photochemical dissociation is discussed.
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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
82.50.Hp Processes caused by visible and UV light

Determination of the proton affinity from the kinetics of proton transfer reactions. VI. The relative proton affinities of N2, Xe, and CO2

F. C. Fehsenfeld, W. Lindinger, H. I. Schiff, R. S. Hemsworth, and D. K. Bohme

J. Chem. Phys. 64, 4887 (1976); http://dx.doi.org/10.1063/1.432127 (5 pages) | Cited 10 times

Online Publication Date: 28 August 2008

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The position of equilibrium was investigated with the flowing afterglow technique for the proton transfer reactions N2H++Xe?XeH++N2 at 297, 378, and 800°K, N2H++CO2?CO2H++N2 at 700 and 798°K, and XeH++CO2?CO2H++Xe at 800°K. The equilibrium constants measured at each temperature provided values for the proton affinity differences PA(Xe)−PA(N2) =0.63±0.19 kcal mole−1 and PA(CO2)−PA(Xe) =9.7±1.5 kcal mole−1. Rate constants were also determined for the three reactions proceeding under nonequilibrium conditions.
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82.20.Pm Rate constants, reaction cross sections, and activation energies

Absolute rate parameters for the reaction of atomic hydrogen with hydrazine

L. J. Stief and W. A. Payne

J. Chem. Phys. 64, 4892 (1976); http://dx.doi.org/10.1063/1.432128 (5 pages) | Cited 18 times

Online Publication Date: 28 August 2008

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Absolute rate parameters for the reaction of atomic hydrogen with hydrazine H+N2H4→H2+N2H3 have been determined in a direct manner using flash photolysis of dilute mixtures of hydrazine in helium and time dependent observation of H via resonance fluorescence. By measuring the H‐atom decay under pseudo‐first‐order conditions, the bimolecular rate constant k1 was obtained over the temperature range 228–400°K. The data were fitted with good linearity to the Arrhenius expression k1= (9.87±1.17) ×10−12 exp(−2380±100/RT) cm3 molecule−1⋅sec−1. The data were shown to be free of any contributions from secondary reactions involving H as a reactant or product. A comparison of the present results with those from previous studies employing discharge flow methods is presented.
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82.20.Pm Rate constants, reaction cross sections, and activation energies

Normal vibrational modes resulting from the lifting of degeneracies in anisotropic crystals: The internal optic modes of K2SO4

Guo‐Jen Wu and Roger Frech

J. Chem. Phys. 64, 4897 (1976); http://dx.doi.org/10.1063/1.432129 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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The vibrational normal coordinates of internal optic modes originating in molecular normal modes whose degeneracies have been lifted through site group effects are discussed. The normal mode frequencies are calculated in a molecular dipole formalism. The coupling between different Cartesian components of a phonon mode is described with particular attention to the symmetry based sufficiency condition for that coupling to occur.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

The adsorption of neon on graphitized carbon in the submonolayer and multilayer region between 1.5 and 30°K

A. A. Antoniou

J. Chem. Phys. 64, 4901 (1976); http://dx.doi.org/10.1063/1.432130 (11 pages) | Cited 6 times

Online Publication Date: 28 August 2008

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Heat capacities and heats of adsorption (calorimetrically measured) together with equilibrium pressures are reported for coverages up to three monolayers. The data indicate that neon remains localized up to 30°K in the submonolayer region. Phase transitions of the adsorbed neon were observed in the temperature and coverage range of this investigation. The regions in which these transitions take place are shown in a coverage vs temperature plane. In region II of this plane, a phase transition takes place which results in excess heat capacities in the submonolayer region. In region III, a transition of a different nature takes place which resembles the ’’melting’’ process. The ’’two‐dimensional gaslike’’ phase could only appear at temperatures higher than those attained in this work. In region I, the adatoms behave as highly localized oscillators, and those at the high energy sites contribute a major portion to the heat capacity below 3°K. The residual entropy was calculated for the two submonolayer coverages and was found to be equal to zero within the experimental error. The Ne–solid interaction energy is 2990 J/mole at 24°K and 2770 J/mole at 29°K. The integral heat of adsorption at 0°K was calculated in the submonolayer and multilayer region, and the difference between the first and subsequent monolayers is found to be more than 700 J/mole. The integral adatom–adatom interaction energy of adsorbed neon in the submonolayer region at 24°K varies almost linearly with coverage and is approximately equal to 290 J/mole at the completion of the first monolayer. The monolayer capacity of the adsorbent for neon depends on temperature and the coefficient of the thermal expansion of the first monolayer in the xy plane is estimated to be about 0.002 deg−1 in the temperature range 24–29°K. For higher coverages a substantially higher coefficient is observed, and this is attributed to a phase change which takes place in the structure of the film. Finally, the degree of homogeneity of graphitized carbon, Spheron 6, i.e., the ratio of the high energy sites to the planar sites of graphitized carbon, is found to be approximately equal to 0.1.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.60.Fa Heat capacities and heats of phase transitions

Theoretical investigations on the light scattering of spheres. XVII. Angular and spectral location of intensity maxima and minima

W. Heller and M. Nakagaki

J. Chem. Phys. 64, 4912 (1976); http://dx.doi.org/10.1063/1.432131 (9 pages) | Cited 3 times

Online Publication Date: 28 August 2008

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Comprehensive data were collected on the angular location of the various types of maxima and minima of Mie scatterers within the m range 1.050–1.333. Detailed comparison with the extrema calculated for the simple Rayleigh–Gans–Debye case of (m−1) →0 led to a relatively simple correction equation which allows one to calculate with fairly good accuracy the angular location of Mie extrema quickly and easily and within a wide range of α and m values the limits of which are defined. Application of the results is discussed for fast particle size determinations in monodisperse systems of isotropic homogeneous spheres.
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42.25.Dd Wave propagation in random media
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Graph theory and molecular orbitals. XV. The Hückel rule

I. Gutman and N. Trinajstić

J. Chem. Phys. 64, 4921 (1976); http://dx.doi.org/10.1063/1.432132 (5 pages) | Cited 16 times

Online Publication Date: 28 August 2008

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The topological analysis of the Hückel (4m+2) rule is carried out and shows its dependence on the structural features of conjugated systems. The proof of the validity of the Hückel rule for a given molecule is also presented.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
02.20.Bb General structures of groups

Chemistry of nuclear recoil 18F atoms. VIII. Mechanisms and yields of caging reactions in liquid phase 1,1‐difluoroethane and 1,1,1‐trifluoroethane

Ronald G. Manning and John W. Root

J. Chem. Phys. 64, 4926 (1976); http://dx.doi.org/10.1063/1.432133 (13 pages) | Cited 6 times

Online Publication Date: 28 August 2008

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New procedures are reported for the specification of caging yields in nuclear recoil chemistry experiments. All five hot 18F substitution channels in CH3CF3 and CH3CHF2 exhibit caging at large density. The respective total caged yields at 195 °K are 4.0%±0.6% and 5.6%±0.6%, and the total yields of stabilized substitution products are 8.9%±0.4% and 8.6%±0.6%. The simplest plausible caging mechanism involves primary Franck–Rabinowitsch radical recombination of 18F atoms with aliphatic radicals. Density‐variation results cannot be used for the qualitative detection of caging reactions unless excitation‐stabilization complications have been shown to be unimportant.
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82.30.-b Specific chemical reactions; reaction mechanisms
82.20.Hf Product distribution

Electronic structure of the luminescent centers in rare earth oxysalts doped by bismuth

Bernard Jacquier

J. Chem. Phys. 64, 4939 (1976); http://dx.doi.org/10.1063/1.432134 (13 pages) | Cited 5 times

Online Publication Date: 28 August 2008

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A cluster model is assumed for the luminescent centers in Y2O3:Bi, BiOCl, and LnOCl:Bi (Ln=La,Y). A semiempirical self‐consistent charge and configuration molecular orbital theory has been used to determine valence MO energies and populations. Including spin orbit and configuration interactions, we compute the pattern of the excited levels. Changing the number and the nature of the ligands in the cluster, one can see the variation of the localized charge with respect to the constitution and symmetry of the several environments. Dependence of the electronic levels on distance indicates a large substitution effect comparing with presently available experimental data. The results confirm the presence of allowed electronic excited states with strong oscillator strength in the near uv range, and trap levels. One of the latter always is the lowest electronic level and thus suggests an interpretation of the luminescent processes similar to that proposed for the La2O3:Bi phosphor.
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78.55.-m Photoluminescence, properties and materials
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
31.15.xr Self-consistent-field methods

Electrical properties of KF‐doped hexagonal ice

Joseph J. Inchackal and A. H. Weber

J. Chem. Phys. 64, 4952 (1976); http://dx.doi.org/10.1063/1.432135 (5 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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KF doped ice single crystals were grown between platinum electrodes from water of about 5 MΩ cm resistivity and their electrical ac conductance Gac and capacitance C measured over a temperature range of −10 to −90 °C and a frequency range of 50 to 20×103 Hz using a Wayne–Kerr B 641 ac bridge. The activation energy Eσ for ac conduction was determined from the plot lnG vs 1000/T (concentration range of KF, 10−6 to 10−3 N). The dielectric relaxation time τ was obtained from the Debye dispersion relation and the activation energy Eτ of dielectric relaxation found from the plot lnτ vs 1000/T. For the same KF ice, Eσ was 5.9 kcal/mole and Eτ was 4.06 kcal/mole. In KF ice Eσ was always found to be greater than Eτ. Direct current conductivity Gdc obtained from plots of ϵm″ω vs f2 also showed a temperature dependence and hence an activation energy Eσ (determined from the plot lnσdc vs 1000/T) implying that it is unnecessary to invoke the mechanism of quantum mechanical tunneling for dc conduction. The static dielectric constant ϵs for KF ice was found to decrease with decreasing temperature, the values ranging from 15 to 50×102 for the temperature range −90 to −13 °C. The experiments indicate that the predominant mechanism for ac conduction is that of propagation of Bjerrum defects and that the dopant (F− ions, KOH, or HF) is incorporated into the ice lattice substitutionally.
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72.80.Jc Other crystalline inorganic semiconductors
61.72.S- Impurities in crystals
77.22.Gm Dielectric loss and relaxation

Electron scattering by nitrogen molecules: Theory and application to elastic scattering and rotational excitation at 30–75 eV

Maynard A. Brandt, Donald G. Truhlar, and F. A. Van‐Catledge

J. Chem. Phys. 64, 4957 (1976); http://dx.doi.org/10.1063/1.432146 (11 pages) | Cited 42 times

Online Publication Date: 28 August 2008

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An effective potential model applicable to electron scattering by small or large molecules, including rotational and vibrational motions, is developed for electron scattering by N2. The INDO/1s method is used to calculate the static potential at a large number of distances and a simple model is used for the polarization potential. The rotational and vibrational matrix elements of these potentials are accurately calculated and the scattering is treated by a truncated close‐coupling expansion. With no adjustable parameters, calculated electronically and vibrationally elastic scattering cross sections are in reasonable agreement with experiment for angles 40°–50° and less at energies 30–75 eV. The rotational excitation cross sections have never been measured for N2 but are predicted to be large (as large as half the pure elastic cross sections when integrated over scattering angles and larger than the pure elastic differential cross sections at a range of large scattering angles at each energy).
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34.80.Gs Molecular excitation and ionization
34.80.Bm Elastic scattering

Lamb dip studies of the nuclear quadrupole coupling and dipole moment in an excited vibrational state of NH2D

E. W. Van Stryland and R. L. Shoemaker

J. Chem. Phys. 64, 4968 (1976); http://dx.doi.org/10.1063/1.432147 (5 pages) | Cited 2 times

Online Publication Date: 28 August 2008

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The hyperfine structure of two transitions in the ν2=0→1 vibrational band of the asymmetric rotor NH2D is resolved. These spectra represent the first direct observation of 14N nuclear quadrupole splittings in the optical region. The transitions were observed using Lamb dip spectroscopy in which a Stark field is used to tune the spectral components through resonance with a CO2 laser. Splittings of less than 1 MHz are resolved, and the nuclear quadrupole coupling constants in the excited vibrational state are determined to be χaa=2.52±0.24, χbb=1.46±0.36, χcc=−3.98±0.29 MHz. In addition, we find μc=1.09±0.04 D for the excited state permanent dipole moment. These values differ significantly from the ground state values, and some discussion of their physical implications is presented.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.25.+k Nuclear resonance and relaxation
33.15.Pw Fine and hyperfine structure

Mode to mode energy transfer in OCS directly pumped by a CO2 laser

Donald R. Siebert and George W. Flynn

J. Chem. Phys. 64, 4973 (1976); http://dx.doi.org/10.1063/1.432148 (11 pages) | Cited 25 times

Online Publication Date: 28 August 2008

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Laser‐induced fluorescence has been observed from all the modes of OCS after pumping the 0→2ν2 overtone transition with the P (22), 9.6 μ line of the Q‐switched CO2 laser. In pure OCS approximately 145 collisions are required to equilibrate the laser pumped bending modes (ν2=520 cm−1) with the antisymmetric stretching mode (ν3=2062 cm−1), while approximately 915 collisions are required for ν2–ν1 (ν1=859 cm−1) equilibration. The overall equilibration of the vibrational degrees of freedom with the translational/rotational degrees of freedom (deactivation of ν2) determined in these experiments corresponds to 7800 collisions for pure OCS, in excellent agreement with ultrasound results. The behavior of this relaxation process in OCS–rare gas mixtures suggests that very little vibrational energy is transferred directly into rotational degrees of freedom during deactivation of ν2 as might be expected for a molecule like OCS with no light atoms such as H or D. Simple calculations of the V–T relaxation probability using a short range repulsive force model are in unexpectedly good agreement with the experimental data, particularly for pure OCS. On the other hand, a long range attractive potential, dipole–dipole calculation which emphasizes the large electrical anharmonicity of the OCS bending modes appears to be in good agreement with the experimentally observed ν2–ν3 V–V energy transfer probability.
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34.50.Ez Rotational and vibrational energy transfer
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)

Solution for bound state wavefunctions and matrix elements by the piecewise analytic method

Alan M. Dunker and Roy G. Gordon

J. Chem. Phys. 64, 4984 (1976); http://dx.doi.org/10.1063/1.432149 (11 pages) | Cited 24 times

Online Publication Date: 28 August 2008

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The solution of multidimensional bound state problems in quantum mechanics by the piecewise analytic method introduced by Gordon is discussed in detail. The numerical techniques necessary to calculate the wavefunctions and matrix elements are presented. An efficient least squares method for fitting the potential energy function to spectroscopic frequencies is described. Tests of the accuracy of the piecewise analytic method have been performed and the results are given. The techniques presented here are especially advantageous for systems in which the motion along the several coordinates is strongly coupled (beyond the perturbation theory limit).
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03.65.Ge Solutions of wave equations: bound states
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Variational time‐dependent Hartree–Fock calculations. II. Six‐electron molecules

D. K. Watson, R. F. Stewart, and A. Dalgarno

J. Chem. Phys. 64, 4995 (1976); http://dx.doi.org/10.1063/1.432150 (5 pages) | Cited 20 times

Online Publication Date: 28 August 2008

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The time‐dependent Hartree–Fock equations are solved variationally for the six‐electron molecules Li2, BH, and CH+. The values obtained for excitation energies, oscillator strengths, and other properties are in harmony with the available accurate comparison data. The calculations demonstrate the presence of bound excited states and resonances due to transitions from inner shells.
Show PACS
31.15.xr Self-consistent-field methods
31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates
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