bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental verification of the distortion overlap in alkali iodide systems
Authors: Pasternak M. , Shamai S. , Sonnino T.
Published: February 2003

Isomer shift systematics of 129I Mössbauer effect in the alkali iodides, solid-argon-matrix-isolated molecules, and crystals show unambiguously that no charge transfer (covalency) is present in these ionic species. The mechanism of distortion overlap is the only mechanism responsible for the enhancement of s-electron density along the metal–halogen bond. It is shown that the role of next-nearest-neighbors overlap present in the crystal is of prime importance and overwhelming in the case of LiI. The conclusions derived from the isomer shift and quadrupole coupling data suggest a larger intramolecular distance in the argon matrix as compared to the vapor phase.
Molybdenyl centers in NH4Cl single crystals
Authors: Radhakrishna S. , Chowdari B. V. R. , Viswanath A. Kasi
Published: February 2003

Molybdenyl centers are studied in single crystals of NH4Cl using a set of correlated experimental techniques like EPR, optical absorption, infrared absorption, conductivity, and dielectric loss. EPR studies on NH4Cl single crystals doped with (MoOCl5)2− are made over a wide temperature range. At room temperature the resonance due to even isotopes of Mo and the hyperfine interaction due to the odd isotopes are observed. At 77 K the ligand hyperfine interaction due to 35,37Cl is also observed. The spectra are analyzed using a suitable spin Hamiltonian. An LCAO–MO method is used to interpret all the results. In the optical absorption spectra the bands corresponding to the d–d transitions and charge transfer transitions are observed. Spin–orbit coupling constant is estimated using the EPR and optical results. Molecular orbital parameters are calculated taking into account the spin–orbit effects of the ligands also. The calculated bonding coefficients are correlated with the EPR results and the nature of binding in these complexes is discussed. The spin density on the ligand orbitals is estimated using the results of the ligand hyperfine interactions. The Mo–O stretching frequencies are observed in the infrared absorption spectrum. The evidence for the existence of the bound cation vacancies comes from the conductivity and dielectric loss experiments. The impurity–vacancy binding energy is also estimated.
Laser magnetic resonance of Hg (6 3P) atoms
Authors: Johns J. W. C. , McKellar A. R. W. , Riggin M.
Published: February 2003

The 3P1←3P0 transition within the 6s6p 3P excited state of atomic mercury has been detected and measured by the technique of laser magnetic resonance spectroscopy. The experiment involved flowing excited Hg atoms through an absorption cell located inside the cavity of a carbon monoxide laser operating on a line at 1767.3624 cm−1, and Zeeman shifting some components of the 3P1←3P0 transition into resonance with the laser. The 3P1–3P0 fine structure interval is determined to be 1767.2159±0.0007 cm−1, and to be independent of isotope number within this uncertainty.
Nonadiabatic interactions in unimolecular decay. II. Simplified formalism
Authors: Desouter-Lecomte M. , Lorquet J. C.
Published: February 2003

Simplified semiclassical formulas are derived for the study of the nonadiabatic transition probability between two electronic states. They are expressed in terms of the coupling function g (R) equal to the matrix element of the d/dR operator between adiabatic states. It is shown that if g (R) keeps the same sign for all values of R, the integration of the classical-trajectory equations in the adiabatic basis depends on a particular function T (S) only, which is the well-known Massey parameter. This function plays a role similar to the t (s) function introduced by Delos and Thorson in their ’’close coupling model.’’ The present method is an extension of the treatment suggested by Rosen and Zener and assumes that ΔE, the energy difference between adiabatic energies, can be considered as constant. The significance of this is investigated. In simple cases, the transition probability can be expressed in terms of an adiabatic parameter χ only, defined by Eq. (32). Formulas are given for the isotopic effect, and for the influence of the excitation energy on the transition probability. In a polyatomic molecule, different kinds of couplings must be distinguished, depending on the nature of the internal coordinates which vary along the nuclear trajectory.
Excitation of the E,F1Σ+g states of H2 by electron impact
Authors: Watson James , Anderson Richard J.
Published: February 2003

Optical excitation functions produced by low-energy electron impact excitation are reported for several rotational lines originating from the E,F1Σ+g and the H1Σ+g electronic states of neutral H2. The E1Σ+g→B1Σ+u, F1Σ+g→B1Σ+u, and H1Σ+g →B1Σ+u band systems are observed at an effective spectral slit width of ?2 Å, over an electron energy range 0–300 eV. The observed transitions are identified as originating from v′=2,3,4 vibrational levels of the E state, the v′=5 level of the F state, and the v′=2 level of the H state. Absolute emission cross section measurements are obtained at 200 eV electron energy and 30 mtorr H2 gas pressure through direct comparison with the λ=4686 Å (n=4→3) line of the He II spectrum. Analysis of the E→B (2,1) R0 rotational line intensity yields (1.0±0.3) ×10−18 cm2 as a lower-limit estimate of the E1Σ+g direct cross section at 200 eV.
Nomadic polarization in quasi-one-dimensional solids
Authors: Pohl Herbert A. , Pollak M.
Published: February 2003

The electrical polarization is examined which arises from the motion of mobile charges roving in quasi-one-dimensional domains which are long compared to lattice spacings or to interatomic bonds. Such polarizations can be quite large. Relative dielectric constants of up to 1 000 000 can result. The discussed polarization is marked by its ready saturation at low field strengths. Using a polaron model, the nomadic dielectric polarization magnitude and its ready saturation at moderate field strengths is calculated and the results of the model are found to be in reasonable agreement with experiment. Experimental precautions to be taken in ascribing and identifying nomadic polarization as the cause of high polarizability in a given solid are described.
Absorption spectra of Xe–rare gas mixtures in the far uv region (1150–1500 Å): High resolution analysis and first quantitative absorption measurements
Authors: Castex M. C.
Published: February 2003

In this paper we present a high resolution analysis of xenon–rare gas absorption spectra in the far uv region between 1150 and 1500 Å. We give also the first quantitative results on the pressure and temperature dependence of absorption. These results may be used to discuss the origin of the many satellite bands observed in the proximity of resonance and forbidden atomic xenon lines. Information on the lowest excited XeKr and XeAr potential curves is obtained from this work.
Inhomogeneous broadening of Morse oscillators in liquids
Authors: Dijkman F. G. , van der Maas J. H.
Published: February 2003

The approximate eigenfunctions of the Morse oscillator are used to obtain by first-order perturbation treatment the shifts of the transition frequency on intermolecular interactions. The results are shown to converge towards those obtained for the anharmonic oscillator within the limit of low anharmonicity. Subsequently, the obtained expression is used to compute the inhomogeneously broadened vibrational line shape for a number of diatomic molecules in a schematized solvent in the slow modulation limit. The agreement with experiment is fair in view of theoretical shortcomings and experimental errors.
Sodium chemiluminescence in the Na+N2O and Na-catalyzed N2O+CO reactions
Authors: Benson R. C.
Published: February 2003

The sodium chemiluminescence has been studied in low-pressure diffusion flames involving Na–N2O and Na–N2O+CO in a helium diluent. In the Na+N2O system, only the Na(3p) level is excited and a lower limit to the photon yield was determined to be ∼3×10−4. Two possible excitation mechanisms are proposed to explain the Na emission. Sodium particles were observed in the flow emanating from the sodium source and the implications of these particles on the measurements is discussed. In the Na-catalyzed N2O+CO system most of the emission is from Na(3p), although higher Na levels are populated and the distribution is statistical; the photon yield was determined to be ∼0.02. This low value for the photon yield implies that the direct production of electronically excited sodium followed by E–V transfer is not responsible for the vibrational pumping mechanism in the Na–N2O+CO chemical laser.
Far infrared reflection spectra of potassium tetrachloroplatinate (II)
Authors: Hiraishi Jiro , Tamura Tadao
Published: February 2003

The transverse and longitudinal vibrational frequencies of K2PtCl4 crystals are obtained from the classical dispersion analysis of the far infrared reflection spectra of the crystal. The values of the effective ionic charges of the ions are determined to be ZPt=0.5e, ZK=0.762e, and ZCl=−0.506e on the basis of the rigid ion model. The model well explains the frequencies observed in the infrared and Raman spectra.
Influence of intermolecular bonding on nuclear quadrupole interaction tensors in solid halogens
Authors: Coker Ayodele , Lee Taesul , Das T. P.
Published: February 2003

The role of intermolecular bonding in solid halogens is studied using the self-consistent charge extended Hückel procedure. It was found that the hybridization of s and d orbitals to p orbitals of the halogen plays a very important role in the intermolecular bonding. In particular it was found that the hybridization is stronger with (n+1) s and nd orbitals where n=3,4,5 for chlorine, bromine, and iodine than for ns orbitals. Using the ns, (n+1) s, np, and nd orbitals for the halogen atom and a number of its nearest neighbors, the wavefunctions of the interacting molecules have been calculated, and using these calculated wavefunctions, the field-gradient tensors have been evaluated for all three systems. The asymmetry parameters are found to be 0.06, 0.18, 0.23 for chlorine, bromine, and iodine, respectively. The quadrupole coupling constants were found to be −109.10, −779.31, and −1923.97 MHz for chlorine, bromine, and iodine. Relativistic corrections have been incorporated in the evaluation of the field gradient. The nature of the agreement between experiment and theory for both the quadrupole coupling constants and asymmetry parameters is discussed in detail.
The assignment of the Rydberg transitions in the electronic absorption spectrum of formaldehyde
Authors: Lessard C. R. , Moule D. C.
Published: February 2003

The electronic spectra of H2CO, D2CO, HDCO, and D213CO have been recorded between 1250 and 2000 Å and the vibrational fine structure associated with the n→3s, 3px, 3py, 3pz, 3d transitions assigned. The electronic origin bands in the Rydberg transitions show quite unusual isotope effects, with the ν (D2CO) –ν (H2CO) shift for the n→3d transition being somewhat smaller than the limiting value of the ion while the lower energy n→3s and 3py transitions have anomalously large values. As these effects cannot be accommodated by the changes in the totally symmetric in-plane frequencies on excitation, they are attributed to large differences in ν5 and ν6 in the upper and lower electronic states. Direct information concerning the reduction in ν6 on excitation comes from the identification of a series of low frequency bands in the n→3py system of D2CO which were assigned to quanta in ν6. The potential function which was derived from this data was found to be very anharmonic and could contain a double minimum. The reduction in V (Q6) at large Q6 was attributed to a coupling between the Rydberg 1A1(n, 3py) state and a second 1B2 state which lies at higher frequencies. An estimate of the coupling between these states lead to a value of 1480 cm−1 for the vibronic matrix element. While this value is entirely compatible with what would be expected for valence–valence coupling, it is somewhat larger than what would have been anticipated for vibronic coupling between Rydberg states.
Ion model and equilibrium configuration of the alkaline-earth dihalide dimers. The Mg2Cl4 molecule
Authors: Guido M. , Gigli G.
Published: February 2003

The polarized ion model has been applied in the study of the magnesium dichloride dimeric molecule (Mg2Cl4). The calculations predict as the equilibrium configuration for this molecule a planar structure with D2h symmetry with the outer Mg–Cl distance equal to 2.215 Å and the ring Mg–Cl′ distance equal to 2.36 Å. The angle Cl′–Mg–Cl′ in the ring is 105°.
Infrared spectrum of the water dimer in solid nitrogen. I. Assignment and force constant calculations
Authors: Fredin Leif , Nelander Bengt , Ribbegård Göran
Published: February 2003

The infrared spectra of all isotopic water dimers containing H, D, 16O, and 18O have been studied between 4000 cm−1 and 250 cm−1 in solid nitrogen. H-donating HDO has been observed. The assignment of Tursi and Nixon has been extended to HDO containing dimers. The assignment has been checked by force constant calculations.
Infrared spectrum of the water dimer in solid nitrogen. II. Temperature and irradiation effects
Authors: Fredin Leif , Nelander Bengt , Ribbegård Göran
Published: February 2003

The water dimer in solid nitrogen may exist in a stable and a metastable form. Transitions between the two forms are initiated by infrared radiation absorbed by the dimer fundamentals. The metastable form reverts to the stable form by a dark process. D-donating DOH may be transformed into H-donating HOD by infrared radiation. H-donating HOD is metastable and changes back to D-donating DOH by a dark (thermal) process.
Nonequilibrium velocity distribution and reaction rate in the hot 18F+H2 reaction
Authors: Koura Katsuhisa
Published: February 2003

The nonequilibrium velocity distribution and reaction rate in the hot 18F+H2 reaction are studied with the realistic cross sections by solving the time-dependent Boltzmann equation with the Monte Carlo simulation. The explicit time-dependent velocity distribution, temperature, rate constant, and yield from initial to steady states are obtained. The effects of the initial hot-atom velocity distribution, temperature, and the ambient temperature and the isotope effect on the rate constant are investigated. A high-temperature steady state does not exist.
Fluorescence lifetime studies of NO2. I. Excitation of the perturbed 2B2 state near 600 nm
Authors: Donnelly V. M. , Kaufman F.
Published: February 2003

A pulsed, tunable dye laser (0.05 or 0.005 nm FWHM) was used to measure NO2 fluorescence lifetimes in the 578–612 nm absorption region at pressures of 0.01 to 25 mtorr. When relatively strong absorption features at 585, 593, and 612 nm are excited, the decay of total fluorescence is highly nonexponential, even at pressures as low as 0.01 mtorr, with radiative lifetimes ranging about 20 to 260 μsec, as determined from biexponential fits. In more weakly absorbing regions at 578, 594, and 603 nm, the decays are nearly exponential, with lifetimes of about 200 μsec. Experiments with 0.005 nm bandwidth in the 593 nm region show that there is a one to one correspondence between strong features in the high resolution fluorescence excitation spectrum and the most highly nonexponential decays. These results are explained in terms of a single excited electronic state (2B2) variably vibronically coupled to upper vibrational levels of the ground state. States with a larger fraction of 2B2 parentage have shorter lifetimes and absorb more strongly. Their rotational structure overlaps that of the ubiquitous, more weakly absorbing, longer-lived states with less 2B2 character, so that when the laser frequency corresponds to a transition to one of the shorter-lived states, fluorescence is stronger and decays more nonexponentially. Based on published spectroscopic data, MC–SCF calculations, and density of states estimates, vibronic levels of the perturbed 2B2 states are expected to have lifetimes ranging from about 15 to roughly 100 μsec in the 600 nm region, in qualitative agreement with the experimental findings. These results are discussed in the context of earlier findings from this and other laboratories.
Deuteron line shape study of molecular order and conformation in the nematogens PAA and MBBA
Authors: Dong Ronald Y. , Tomchuk E. , Wade Chas. G. , Visintainer J. J. , Bock E.
Published: February 2003

The deuteron fast Fourier transform (FFT) spectra of the ring deuterated nematogens para-azoxyanisole (PAA-d8) and p-methoxybenzylidene p-n-butylaniline (MBBA-d8) have been studied as a function of temperature. An interpretation of the spectra is presented. It is based on the assumption of nonequivalent deuterons, a twist angle φ between the planes of the benzene rings, and an asymmetry order parameter δ in addition to the usual nematic order parameter S. The temperature dependences of δ and φ have been obtained.
Electron spin–lattice relaxation rates of octahedrally coordinated Yb3+ in Cs2NaYCl6
Authors: North M. H. , Stapleton H. J.
Published: February 2003

We have measured the electron spin–lattice relaxation rate of Yb3+ in the cubic host lattice Cs2NaYCl6 in the temperature interval between 1.75 and 4.5 K using a microwave frequency of 16.532 GHz. The T9 Raman relaxation rate was isotropic with a coefficient of 0.0203±0.0014 s−1K−9. The direct relaxation rate exhibited the expected angular anisotropy, varying with temperature and angle as [(3.20±1.0)+(50.6±4.0)u]coth(0.3967/T) s−1, where u=l2m2+m2n2+n2l2, and l, m, n are direction cosines of the magnetic field with respect to the cubic axes. The data were analyzed in terms of five models: the Newman superposition model, Buisson and Borg’s approach, and effective point charge models including, respectively, 1st, 1st, and 2nd, and 1st, 2nd, and 3rd nearest neighbors. The relaxation data are most consistent for the three effective point charge models, which are based upon the two known static crystal field parameters and two remaining variables: the effective charge for second order spherical harmonics, ‖Zeff(k=2) ‖=0.334±0.065 and vt, the transverse sound velocity, calculated from the data to be (1.97±0.12) ×105 cm/s.
Microwave spectrum and molecular structure of methylenimine (CH2NH)
Authors: Pearson Richard , Lovas Frank J.
Published: February 2003

The microwave spectra of five new isotopic species of CH2NH have been measured in the pyrolysis products of aqueous solutions of methylamine and 1,2-diaminoethane. Rotational constants and moments of inertia have been determined for 13CH2 14NH, 12CH2 15NH, 12CH2 14ND, 12CD2 14NH, and 12CD2 14ND. These data have been combined with previous measurements of 12CH2 14NH to give rs-coordinates for the C, N, and imine-H atoms, and the following structural parameters: r (CN) =1.273 Å, r (NH) =1.023 Å, and & HNC=110.5°. Methods for obtaining a complete structure, and uncertainties arising from the proximity of the C and N atoms to the principal a-axis are discussed. A pseudo-Kraitchman calculation constraining the CH distances to be equal gives the following (planar) structure: r (CN) =1.273 Å, r (NH) =1.021 Å, r (CH) =1.09 Å, & HNC=110.4°, & HCH=117.0°, and & NCHcis =125.1°.
The yield of N(2D) atoms in the dissociative recombination of NO+
Authors: Kley Dieter , Lawrence George M. , Stone Edward J.
Published: February 2003

The quantum yield or branching ratio of N(2D) atoms formed in the reaction e+NO+→N+O was measured to be 76±6%. Photoionization of buffered nitric oxide by a flash lamp was studied using time resolved atomic absorption. Atoms were produced both by direct photodissociation and by dissociative recombination, and these two effects were separated by means of SF6 as an electron scavenger.
High-precision electron paramagnetic resonance study of Gd3+ in single crystals of lanthanum ethyl sulfate nonahydrate near room temperature
Authors: Gerkin Roger E. , Rogers William J. , Tourek William J.
Published: February 2003

Stringent control of the angular orientation and temperature of single crystals of lanthanum ethyl sulfate nonahydrate containing Gd3+ as a dilute guest during X-band EPR measurements near room temperature has been attempted. A high precision value of the g factor of a standard polycrystalline sample of DPPH has been determined for use in analysis of the data. An order of magnitude improvement, relative to the best values previously reported, in determination of spin Hamiltonian parameters in this system has been achieved. Values of b02, b04, b06, and g∥ at 24.130 °C are specified, together with their temperature dependences over a 6° interval near room temperature.
Electron paramagnetic resonance of Fe3+ in diammonium indium pentachloride monohydrate
Authors: Misra Sushil K. , Sharp G. R.
Published: February 2003

Electron paramagnetic resonance of Fe3+ substituted for In ions in (NH4)2InCl5⋅H2O is measured at room temperature using an X-band spectrometer. Angular variation of the data for the magnetic field orientation in the ac plane clearly indicates overlapping spectra from ions occupying two inequivalent sites. The z principal axes of the g tensor for the two sites lie in the ac plane, making angles of ± (40.00°±0.25°) from the a axis; the x principal axes of the g tensor for the two sites are coincident. The resonance data for the two sites can be fitted with the same values (within experimental errors) of the spin Hamiltonian parameters. The individual values of all the parameters are deduced from the data, in particular gzz=2.014±0.003, gxx=2.016±0.003, gyy=2.014±0.004, b02=−4.570±0.008 GHz, b22=2.545±0.008 GHz.
Modulated molecular beam mass spectrometry: A generalized expression for the ’’reaction product vector’’ for linear systems
Authors: Chang H.-C. , Weinberg W. H.
Published: February 2003

A generalized expression is developed that relates the ’’reaction product vector’’, ε exp(−iφ), to the kinetic parameters of a linear system. The formalism is appropriate for the analysis of modulated molecular beam mass spectrometry data and facilitates the correlation of experimental results to (proposed) linear models. A study of stability criteria appropriate for modulated molecular beam mass spectrometry experiments is also presented. This investigation has led to interesting inherent limitations which have not heretofore been emphasized, as well as a delineation of the conditions under which stable chemical oscillations may occur in the reacting system.
Stochastic-molecular theory of spin–relaxation for liquid crystals
Authors: Freed Jack H.
Published: February 2003

The theory of spin relaxation for liquid crystals is examined with the objective of properly analyzing the statistical interdependence of the faster rotational reorientation of the individual spin-bearing molecules and the (slower) director or order-parameter fluctuations. The analysis is presented in terms of a composite Markov process including both types of motions. It is shown that one recovers a sum of spectral-density terms which, in lowest order in fluctuations, correspond to (1) reorientation of the molecule relative to the equilibrium potential of mean torque, (2) effects of director fluctuations, and (3) a negative cross-term between these two processes which bears a simple relation to (2). Detailed results are given for the particular models of director fluctuations in the nematic phase, quasicritical order fluctuations on either side of the isotropic–nematic phase transition, and slow fluctuations in the local structure. Effects of localized cooperative modes of molecular reorientation are also included. Explicit expressions for NMR and ESR relaxation and line shapes are given. The results obtained here clearly demonstrate some weaknesses in previous treatments which were presumed to be based on an assumption of the statistical independence of the different motional processes. Discussion is also given on how to formulate director fluctuations as a multidimensional Markov process, and on the applicability of motional narrowing theory in these cases where director fluctuations have very slowly relaxing components.
Stokes and anti-Stokes fluorescence of 1,12-benzoperylene in solution
Authors: Birks J. B. , Easterly C. E. , Christophorou L. G.
Published: February 2003

Extensive observations of the Stokes and anti-Stokes fluorescence spectra of 1,12-benzoperylene in n-heptane solution from −90 to +90°C are reported and analyzed. Corresponding absorption spectra over the same temperature range are used in the assignment of the vibronic states and transitions. The normal fluorescence spectrum has five bands, corresponding to the S01→S00, S10, S20, S30, S40 transitions (SVE refers to a singlet electronic state SE in a vibrational level V), which are the origins of symmetric ?5 vibrational progressions. Three bands beyond the S01→S00 transitions are identified as S11, S21, S31→S00 hot fluorescence and one band as S02→S00 fluorescene, and these are the origins of similar ?5 progressions. It is proposed that the S01→Sm0(m≠0), Sn1→S00 (n≠0), and S01→S00 transitions are induced by vibronic coupling to allowed Sm2→Sm0, S02→S00, and S12→S00 transitions, respectively. The S02→S00 fluorescence is partly directly excited and partly thermally excited from S01. Separation of these two components leads to an evaluation of the S02 lifetime (21±4 ps) and the S02→Sn1 internal conversion rate (4.8±0.8×1010 s−1).
A theoretical prediction of vibrational enhancement for dissociative charge transfer in the HeH2+ system
Authors: Preston Richard K. , Thompson Donald L. , McLaughlin Donald R.
Published: February 2003

A model has been developed to treat dissociative charge exchange occurring on excited-state surfaces in the weak adiabatic limit. This process is analogous to collisionally induced predissociation with the added feature that electronic as well as translational energy is used to effect the dissociation. The consequences of weak adiabaticity and the location of the avoided crossing seam are to require the consideration of tunnelling through a barrier in the dissociation curve. An appealing feature of the model is the reduction of a three-dimensional trajectory problem to one dimension by neglect of coupling of translation to vibration and rotation. Configuration interaction ground- and excited-state calculations have been performed in the vicinity of the curve crossing seam for He++H2→He+H++H. Use of the parameters derived from these ab initio results in the dynamics model yields cross section and rate coefficient values in qualitative agreement with experimental measurements. Vibrational excitation from the v=0 to v=1 states in H2 leads to an increase in cross section of approximately two orders of magnitude due to enhancement of the tunnelling.
Cation electric field gradients in perrhenates with the scheelite structure
Authors: Segel S. L.
Published: February 2003

The cation couplings have been measured in perrhenate salts with the scheelite structure. These include the ammonium, sodium, potassium, and rubidium salts. Values of the electric field gradient deduced from these couplings are, at 303 K, in units of 1019 V/m: 14N(NH4+), 21.7; 23Na, 4.95; 39K, 4.28; and 87Rb, 3.75. There appear to be no notable relationships between the values of the gradient and the scheelite lattice parameters.
Change of molecular configuration in crystalline decanoic acid as studied by infrared spectra and normal coordinate analysis
Authors: Umemura Junzo
Published: February 2003

Infrared spectra of a well-oriented crystalline film of decanoic acid were obtained in the range from room temperature to liquid-helium temperature. Many absorption bands due to the carboxyl group and a band progression due to the CH2 wagging modes appear as doublets. In each doublet, one component decreases in intensity with lowering temperature and disappears near liquid-helium temperature (type I), while another component increases in intensity with lowering temperature (type II). It is confirmed by normal coordinate analysis that the type I and II bands are ascribed to fundamental vibrations of the cis and trans isomers, respectively. The latter isomer would be produced from the former by double proton transfer in the decanoic acid dimer. From the temperature dependence of band intensities, the enthalpy and entropy differences between the two isomers are evaluated to be about 240 cal⋅mol−1 and 3.8 cal⋅mol−1⋅deg−1, respectively.
Raman evidence for thermally disordered energy states in various phases of ionic nitrates
Authors: Brooker M. H.
Published: February 2003

Detailed Raman studies of the symmetric stretching mode of a large number of nitrate salts have confirmed the presence of an anomalous second component not predicted by factor group analyses based on known crystal structures. Depolarization studies with oriented single crystals, decoupling studies with 18O-enriched samples, and temperature variation studies support previous suggestions that the new components are due to the presence of alternate sites which result from a dynamic disorder within the lattice. The alternate sites are present even for structures normally considered to be completely ordered and do not destroy the long-range interactions (correlation field coupling) of the ordered part of the lattice. Phase transitions may be precipitated by the increase in these impurity type disordered states until the long-range coupling of the ordered lattice can no longer be maintained.
Elementary finite order perturbation theory for vertical ionization energies
Authors: Born Gregory , Kurtz Henry A. , Öhrn Yngve
Published: February 2003

The analysis of ionization energies in Rayleigh–Schrödinger perturbation theory and in propagator theory, previously known separately through third order in electron interaction, are compared in detail using elementary algebraic methods and their equivalence is explicitly shown. Relaxation terms are identified as the ΔESCF contributions and appropriate rules are described for their construction from the electron propagator diagrams of arbitrary order. Correlation terms are obtained separately. The transition operator method is analyzed and found to differ from ΔESCF in third order, contrary to earlier claims.
Mixed quantum model for gas–solid energy transfer
Authors: Lin Y.-W. , Adelman S. A.
Published: February 2003

A new quantum close-coupling method for gas–solid scattering, the mixed quantum model (MQM), is proposed. A numerical application to gas–solid energy transfer for a six atom linear chain model solid is made. The MQM is based on a division of the solid into a primary zone containing those atoms directly struck by the gas atom and a heat bath which comprises the rest of the solid. The primary zone, a few particle system, is treated exactly within a coupled states framework. The heat bath, a many body system, is treated within a one-phonon truncation of a heat bath coupled states phonon expansion. The MQM reliably describes gas–solid energy transfer at both low and high gas energies Eg. In contrast, a single oscillator model for the solid breaks down at low Eg while the standard one-phonon theory breaks down at high Eg.
Vibrational spectra for t
r
a
n
s-dimethyldi azene-1,1,1-d3 (azomethane). Potential functions for t
r
a
n
s-dimethyldi azene and t
r
a
n
s-methyldiaz ene
Authors: Craig Norman C. , Ackermann Martin N. , MacPhail Richard A.
Published: February 2003

Gas-phase and matrix infrared spectra and gas-, liquid-, and solid-phase Raman spectra of trans-dimethyldiazene-1,1,1-d3 (CH3N=NCD3) have been recorded. A complete vibrational assignment has been secured for this molecule based on direct observation of 23 of the 24 fundamentals. Gas-phase Raman spectra have also been obtained for trans-dimethyldiazene-d0 and -d6, which supplement published infrared and Raman spectra. On the basis of these spectra and the assignment for the d3 isotopic species revised vibrational assignments for the d0 and d6 species are proposed. The valence-type potential function that was fitted to the d0 and d6 molecules by Pearce, Levin, and Harris has been confirmed and refined by including the frequencies of the d3 molecule in a normal coordinate calculation. This potential function has also been adapted to trans-methyldiazene (CH3N=NH). The potential energy distributions for these two simple diazenes correlate closely for many of the normal modes. For the methyl group torsional frequencies of trans-methyldiazene contributions of both kinetic and potential energy coupling are identified.
Collision-induced dissociation of CO+ in X 2Σ+ and metastable states in CO+–CO interactions
Authors: Moran T. F. , Wilcox J. B. , Abbey L. E.
Published: February 2003

Collision-induced dissociation of 0.65 to 3.2 keV CO+ has been examined in an apparatus with an extended flight path through which reactant ions take a long time to travel. Reactant ions were produced by electron impact ionization and the short-lived excited states decayed radiatively prior to ion–molecule interactions. The electronic and vibrational state distributions of reactant ions as functions of ionizing electron energy have been estimated from published spectroscopic data and the dissociation cross sections determined for CO+(X 2Σ+,υ) ions. A metastable ion state (or states) also contributes to the dissociative channels and the relative contribution of this metastable state becomes more important as the incident ion kinetic energy is lowered. A threshold of approximately 19.5±1.0 V has been measured for this long-lived state leading to C+ in dissociative collisions.
Nondissociative and dissociative permeation of gases through solids
Authors: Shupe Dean S.
Published: February 2003

By applying the quasiequilibrium approach of Langmuir, Richardson, and others to the permeation of gases through solids, limiting expressions for permeability P0 are derived that require no microscopic models for evaluation. The theoretical maximums thereby predicted agree satisfactorily with existing data for a multitude of gas–solid systems. An advantage of the approach is that it minimizes the use of atomic models and kinetics to the degree that rate expressions are obtained without assuming detailed kinetic models of the processes. The results are valuable for analyzing experimental permeation data, particularly in the absence of diffusivity and/or solubility data.
Configuration interaction calculation on the resonance states of HCl−
Authors: Goldstein E. , Segal G. A. , Wetmore R. W.
Published: February 2003

Configuration interaction and the stabilization method is used to compute potential energy curves for the resonant states of HCl−, an important example of electron–polar molecule scattering. Resonant states that dissociate to H−+Cl and Cl−+H are found as well as those that dissociate to H+Cl+e−. These curves provide an interpretation of the known experimental observations on this system.
Deuteron quadrupole coupling in molecules
Authors: Snyder Lawrence C.
Published: February 2003

Deuteron quadrupole coupling frequencies in molecules computed from ab initio wavefunctions in a ’’double-zeta’’ basis are reported. They exceed observed coupling frequencies by 20%. Charge on the deuteron and atom to which it is bonded account for 98% of the electric field gradient.
Calculation of dipole correlation factors in liquid crystals with use of a semiempirical expression for the internal field
Authors: Bordewijk P. , de Jeu W. H.
Published: February 2003

The internal field expression on a semiempirical basis in the preceding article, is applied in the generalization of the Kirkwood–Fröhlich theory for liquid crystals presented earlier by one of the authors. As an example correlation factors are calculated for two compounds in the nematic phase, and one in the smectic A phase.
The scalar-product expression of boundary free energy for long-range interacting systems
Authors: Kikuchi Ryoichi
Published: February 2003

The scalar-product formula of the excess free energy σ of a boundary between two phases (based on the lattice model) is proved for the case of interaction potential of the range longer than the nearest neighbor. The formula is exp(−Aσ/kT) =Σ[p(I)(ν1,ν2,...,νk) p(II)(ν1,ν2,...,νk)]1/2 exp[α(I)(ν1,ν2,...,νk)− α(II)(ν1,ν2,...,νk)], where A is the sectional area parallel to the boundary, νi is a configuration of an ith plane parallel to the boundary, p(I)(ν1,...,νk) is the probability that k consecutive planes in the bulk I phase take configurations ν1,...,νk, and the summation goes over all configurations ν1,...,νk. The variable α(I)(ν1,ν2,...,νk) is a Lagrange multiplier to guarantee continuity of p(I): Σμp(I)(μ,ν1,ν2,...,νk) = Σμp(I)(ν1,ν2,...,νk,μ). The expression is checked by two examples. The σ for the two-dimensional Ising model is calculated using a 3×2 cluster (i.e., a double square cluster made of six lattice points) with the ’’3’’-side perpendicular to the boundary, and is compared with the previous σ calculated with a 2×3 cluster (with the ’’3’’-side parallel to the boundary). The calculated σ’s agree well when the α terms are included. As a second example, surface tension σ of a liquid of a two-dimensional lattice gas–liquid model (in which the first, second, and third neighbor pairs are excluded, and the fourth and fifth neighbor pairs attract) is calculated. It is then compared with σ calculated by a sum method (which calculates the equilibrium state of a sandwich system made of the gas and the liquid phases with the boundary between them). The agreement between the two calculations supports the correctness of the proposed σ expression.
Lattice dynamical investigation of the rotator phase of n-paraffins
Authors: Kobayashi Masamichi
Published: February 2003

A lattice dynamical investigation was made in order to interpret the thermodynamical behaviors of the first-order solid-state phase transition of n-paraffins from the orthorhombic or monoclinic to the rotator phase. The internal energy, the entropy, and the Helmholtz free energy of the rotator phase were evaluated in variation with chain length, lattice dimension, and temperature, using a model of cooperative rigid rotation accompanied with a small translational fluctuation along the chain axis. The contribution of the molecular vibrations to the thermodynamic functions was estimated by a lattice dynamical calculation in the quasiharmonic approximation from the density of states obtained by the normal coordinate treatment. An orthohexagonal lattice with the dimension of a=31/2 b=8.31 Å was found to exhibit the minimum value of free energy at 300 K, as compared with the measured lattice dimensions of n-C19H40 (a=8.30 Å, b=4.79 Å) at 295.2 K. The calculated linear coefficient of thermal expansion αa (=αb) along the direction perpendicular to the c-axis (the chain axis) is 1.4–1.7×10−4 K−1 which is quite similar to the mean value of αa and αb of the orthorhombic polyethylene (o-PE) lattice at room temperature. The transition temperatures, the heat, and the entropy of transition were evaluated in variation with chain length. The theoretical transition points are 20–30°C higher than the observed ones. The calculated heat and entropy of transition are in good agreement with the experimental values.
Quantum dynamics in the effective system states basis. I. Mathematical structure and time-dependent perturbation theory
Authors: Ziv Alan R.
Published: February 2003

A molecule in the presence of a radiation field is described by a non-Hermitian reduced effective Hamiltonian and its eigenvectors, the effective system states. These states form a natural basis for the evaluation of spectroscopic properties; its use requires a generalized formulation of quantum dynamics. The mathematical structure of the vector space defined by those states is investigated; that vector space is found to be a Banach space which reduces to Hilbert space if the energies of the effective system states become real. Time reversal symmetry is found to be an important feature of the overall problem. The generalized time development operator and the Schrödinger equation which defines it are deduced, and the effect of that operator on the effective system states is discussed. The proper generalization of time-dependent perturbation theory in the interaction picture is then derived and its use in applications is discussed in general terms.
Satisfying certain matrix element formulas
Authors: Klein D. J. , DeVries Paul L.
Published: February 2003

Conditions are given for variational wavefunctions and energies to satisfy some formulas which exact wavefunctions and energies satisfy. The formulas include off-diagonal hypervirial, off-diagonal Hellman–Feynman, and sum rule formulas.
Dynamics of the reaction of oxygen atoms with carbon suboxide
Authors: Hsu D. S. Y. , Lin M. C.
Published: February 2003

The dynamics of the O(3P)+C3O2→3CO reaction (ΔH° =−115 kcal/mole) has been investigated by means of a CO laser resonance absorption technique. The reaction mixtures consisted of NO2 and C3O2, with He or SF6 dilution. The O(3P) atom was generated by the flash photolysis of the NO2 above 300 nm. The three CO’s formed in the reaction were found to carry vibrationally about 19% of the total available energy, with an apparent near statistical population distribution. The results of an 18O-labeled experiment, however, indicate that the two CO’s originating from the parent C3O2 molecule are vibrationally much colder (〈Ev〉? 4.2 kcal/mole) than that from the reaction of the O atom with the center C atom (〈Ev〉?15 kcal/mole). This result is attributed to the incomplete randomization of the reaction energy in the dissociating C3O3 complex. Possible reaction mechanisms are presented.
Measurement of HgXe excimer potentials
Authors: Lam L. K. , Gallagher Alan , Drullinger R.
Published: February 2003

The HgXe excimer band at 270 nm has been studied in fluorescence following optical excitation of the Hg 3P1 level. From the temperature dependence of the normalized fluorescence band shape, the potential curves of the 3O+ excimer state and the 1O+ ground state are inferred. A binding energy of 1400±100 cm−1 is found for the 3O+ state.
Resonance effects in the semiclassical theory of electronically nonadiabatic collision processes
Authors: Miller William H.
Published: February 2003

Significant advances in the theory of electronically nonadiabatic collision processes have been made in recent years by the advent of models that treat all the ’’heavy particle’’ degrees of freedom—i.e., translation, vibration, and rotation—by classical mechanics; only electronic degrees of freedom are treated quantum mechanically. The ’’surface hopping’’ model of Tully and Preston and the generalized Stuckelberg model of Miller and George are examples of this type of approach. There have, however, been questions as to whether or not such models are capable of describing resonance effects in electronic–vibrational energy transfer, e.g., A*+BC(v=0) →A+BC(v=1), with ΔEA?h/ωBC. This paper shows that these resonance effects are the result of interference of amplitudes for different classical trajectories that contribute to the transition. The Miller–George model, which incorporates interference and tunneling within the framework of classical S-matrix theory, thus describes resonance behavior, while the Tully–Preston model, which adds probabilities (rather than amplitudes) for the various trajectories, does not.
Dependence of radiationless relaxation in acridine on solvent using picosecond spectroscopy
Authors: Noe L. J. , Degenkolb E. O. , Rentzepis P. M.
Published: February 2003

We have studied by means of picosecond spectroscopy the solvent dependence of internal conversion, intersystem crossing, and quantum yield of intersystem crossing of acridine in hexane, acetonitrile, isopropanol, and ethanol by following the growth rate of the Tn ←T1 transient absorption. Solvent dependence of the measured lifetime of the lowest excited singlet and the quantum yield of intersystem crossing on solvent strongly indicates that the 1nπ*–1ππ* vibronic interaction, through a distortion of the lowest excited singlet state, is responsible for the unusual solvent dependent fluorescence behavior of this molecule.
Franck–Condon factors in studies of dynamics of chemical reactions. IV. Nonadiabatic collisions
Authors: Zvijac David J. , Ross John
Published: February 2003

We investigate the application of the Franck–Condon approach to nonadiabatic molecular scattering processes. Computationally simple, analytic formulas are developed to describe the energy dependence of quenching of electronically excited atoms by atoms and molecules. These formulas include the dependence of the Franck–Condon factors on the translational wavefunctions as well as the wavefunctions for the internal degrees of freedom. We use these formulas to evaluate the translational energy dependence of the fine structure transition cross sections for F(2P3/2)+X→F(2P1/2)+X, where X= Xe, H+, and H2. The cross sections generally increase as the initial translational energy increases. Our results agree semiquantiatively (or better) with those obtained from other theoretical techniques. In the case of F+H+ we find that the absolute cross section is sensitive to the analytic form used for the nonadiabatic coupling but our model gives the correct energy dependence. At the energies of our calculations we find only a small amount of vibrational excitation of H2. Finally, we use our expressions to interpret some trends of available experimental results on the quenching of Hg (3P2→3P1) by several molecules. We find that collisional excitation of the internal modes of the molecule becomes more important as the initial translational energy increases. However, these modes do not contribute to the quenching cross section in a statistical fashion.
The fluorescence excitation spectrum of the ArI2 van der Waals complex
Authors: Kubiak Glenn , Fitch Pamela S. H. , Wharton Lennard , Levy Donald H.
Published: February 2003

The van der Waals molecule ArI2 has been produced in a supersonic expansion of I2 in mixed argon–helium carrier gas, and its fluorescence excitation spectrum has been observed. Spectra of the complex are only observed when the iodine stretching vibration is exicted to v′?12 in the excited ? electronic state. Above this value the intensity of the van der Waals spectrum is observed to be an oscillatory function of the iodine vibrational quantum number. This behavior is attributed to competition between two decay channels in the excited state: vibrational predissociation with a cross section that increases monotonically with v′, and electronic predissociation with a cross section that oscillates with v′. The spectral linewidth provides a lower limit of 3×10−11 sec for the lifetime of the excited state involved in the 0–15 transition.
Linear nonequilibrium thermodynamic theory of glass transition kinetics
Authors: Berg James I. , Cooper Alfred R.
Published: February 2003

A phenomenological nonequilibrium thermodynamic theory of the glass transition is presented in a linear approximation and applied to glass transition kinetics. A linear relationship between ordering parameters and affinities is diagonalized so that each new affinity is proportional to the nonequilibrium portion of a corresponding single ordering parameter. It is shown that fictive temperatures defined for each of these new parameters can themselves serve as ordering parameters, and that the experimental fictive temperatures represent averaged ordering parameter values. A further transformation is made to uncouple the equations of motion, obtaining exponentially relaxing ordering parameters and affinities. The nonequilibrium portions of the dependent thermodynamic variables take the form of convolutions between linear response functions and the time derivatives of the independent variables. It is shown for the first time that the coefficients of expansion of the response functions into exponetials are not independent, but that coefficients for the entire set of 24 functions characterizing S, T, V, and P, with different dependent–independent variable pair combinations, can be expressed in terms of the coefficients for two properly chosen response functions.