bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Rydberg transitions. VI. t
r
a
n
s-Dibromoethylene. The relation between vacuum ultraviolet and photoelectron spectroscopy
Authors: Wittel K. , Felps W. S. , Klasinc̆ L. , McGlynn S. P.
Published: February 2003

The vacuum ultraviolet absorption spectrum of trans-dibromoethylene is reported. Most of the extensive structure is assigned to four different Rydberg series, one of which converges on the first ionization limit, two of which converge on the second ionization limit and one of which converges on the fourth ionization limit. Much of the vibrational fine structure is associated with the first Rydberg series. The discussion focuses on the geometries of Rydberg and corresponding cationic states, on some aspects of the series fitting procedures, on the meaning of quantum defect values, and on selection rules.
Generalized Langevin equation approach for atom/solid–surface scattering: Numerical techniques for Gaussian generalized Langevin dynamics
Authors: Doll J. D. , Dion D. R.
Published: February 2003

General numerical techniques suitable for the treatment of Gaussian generalized Langevin dynamics are developed. The specific problem considered is that of gas/solid–surface collisions. The basic result is that minor modifications of the methods commonly utilized in classical-mechanical trajectory approaches allow their use in generalized Langevin studies. Sample numerical results are presented for the Ne/W and Ar/W systems.
Immobilized radicals. III. Anisotropic saturation of semiquinones in protic solvents
Authors: Hales Brian J.
Published: February 2003

The nonuniform saturation behavior of semiquinones was investigated as a function of temperature, solvent, and ESR microwave frequency levels. Results from these studies show that this effect occurs only in protic solvents at temperatures equal to and below the solvents’ freezing point. This phenomenon is theorized to be due to the strong hydrogen bonds experienced by semiquinones in these solvents. Apparently, the radical’s relaxation behavior along the direction of the hydrogen bonds is significantly different from the relaxation along the remaining two principal axes. The nonuniform saturation behavior is, therefore, an anisotropic relaxation phenomenon.
Multiple stationary states and hysteresis in a chemical reaction
Authors: Creel C. L. , Ross John
Published: February 2003

Multiple stationary states have been observed experimentally in a homogeneous chemical reaction which is maintained far from equilibrium in a closed system by energy flow across the boundaries. The reaction studied is the gas phase, reversible, dimerization of NO2, 2NO2?N2O4, under the constraint of constant external temperature. The system is illuminated with visible light of a wavelength which is absorbed by the NO2, but is not adsorbed by the N2O4. Multiple stationary states result from the nonlinear positive feedback due to the coupling between the light input, the temperature of the system, and the NO2 concentration. These multiple stationary states are evidenced by the hysteresis they produce in NO2 concentration with respect to changing light intensity, which is in good agreement with the predictions of some simple deterministic equations describing the system. The different states of the system are characterized by different values of NO2 concentration as determined from the light absorption by the NO2 and the NO2 fluorescence emission. Some qualitative information on the fluctuations in the regime of multiple stationary states can be deduced from the experimental data, which indicates that the system exhibits large fluctuations which induce transitions between stable states prior to the transition predicted by the deterministic equations.
Quenching rate constants for metastable argon, krypton, and xenon atoms by fluorine containing molecules and branching ratios for XeF* and KrF* formation
Authors: Velazco J. E. , Kolts J. H. , Setser D. W.
Published: February 2003

The flowing afterglow technique was used to study the reactions of Xe(3P2), Kr(3P2), and Ar(3P2) metastable atoms with small fluorine containing molecules. Fluorides from Groups III through VIII (XeF2) were examined. Although all the fluorides have large quenching rate constants, only F2, XeF2, some interhalogen fluorides, and small molecules with the OF or NF bond have high branching ratios for XeF* or KrF* excimer formation. The branching ratio measurements were made via comparison to the XeCl* and KrCl* emission intensities from reaction of Xe(3P2) and Kr(3P2) with Cl2, which were adopted as reference reactions. Within experimental error, the branching ratios are unity for Kr(3P2) and Xe(3P2) with Cl2, F2, and OF2. Increasing the argon pressure from 1–40 torr gives extensive vibrational relaxation but no electronic quenching of the lowest energy excimer state of XeF*, XeCl*, KrCl*, or KrF*. Increasing pressure also reduces the intensity of the secondary emission system of KrCl* and XeCl* which implies collisional transfer from the (2Π3/2) to the 2Σ+ excimer state. The occurrence of vibrational relaxation suggests a spontaneous radiative lifetime of ∼50 nsec. A higher energy excimer state (2Π1/2) was identified for XeF*, XeCl*, XeBr*, XeI*, KrF*, and KrCl*. Discussion is presented regarding the chemical dynamics and chemiluminescence of these reaction systems.
Isotope effects in the molecular spectrum of plutonium hexafluoride
Authors: Kugel R. , Williams C. , Fred M. , Malm J. G. , Carnall W. T. , Hindman J. C. , Childs W. J. , Goodman L. S.
Published: February 2003

The first evidence for an isotope shift in the near infrared region of the spectrum of an actinide molecule, PuF6, is reported. Using samples of 239PuF6 and 242PuF6, isotope shifts were found in the absorption region near 8000 Å. Shifts of 0.3 to 1.2 cm−1 were observed. The data are interpreted as indicating that some of the absorption bands in this region are vibronically induced electronic transitions which result from coupling of one or more quantum changes in the asymmetric ν3(F1u) and ν4(F1u) vibrations to electronic states of the nonbonding 5f electrons in the molecule.
An ENDOR Study of the δ proton hyperfine interaction in x-ray damaged 2,5-piperazinedione
Authors: Helms H. A. , Miyagawa Ichiro
Published: February 2003

ENDOR studies of x-ray irradiated crystals of 2,5-piperazinedione were conducted. The structure of the primary radical reported in the previous ESR studies [I. Miyagawa, Technical Report of the Institute for Solid State Physics, Ser. A, No. 27, University of Tokyo, Tokyo, Jpana, October 1961; W. C. Lin and C. A. McDowell, Can. J. Chem. 41, 9 (1963)] was confirmed, but analysis of the δ proton is correct. The present results indicate that practically all of the spin density must bew in the vicinity of the α carbon.
Electron paramagnetic resonance of Fe3+ in guanidinium aluminum sulfate hexahydrate
Authors: Misra Sushil K. , Sharp G. R.
Published: February 2003

The electron paramagnetic resonance spectrum of Fe3+ substituted for Al3+ in guanidinium aluminum sulphate hexahydrate, C(NH2)3 Al(SO4)2⋅6H2O, is measured at X-band frequencies at room, liquid nitrogen, and liquid helium temperatures. The measurements are made for various orientations of the magnetic field. The values of all the parameters are deduced from the data using a rigorous least-squares fitting procedures, in a simultaneous fitting of the data corresponding to several orientations of the magnetic field. The zero-field splitting parameter b02, as determined from liquid helium data, is found to have a negative sign. In particular, the following values for the g tensor and b02 are found. At 295 K, for site I gzz=2.001±0.003, gxx =2.004±0.003, b02=−8.622 ±0.008 GHz; for site II gzz=2.002±0.003, gxx=2.002±0.003, b02=−8.499±0.008 GHz. At 1.61 K, for site I gzz =1.994±0.003, gxx=1.992±0.003, b02=−8.931 ±0.008 GHz; for site II gzz=1.996±0.003, gxx =1.997±0.003, b02=−8.808±0.008 GHz.
Excition transport in impure molecular crystals. II. Local defect scattering
Authors: Greer William L.
Published: February 2003

We derive an exact formula for the exciton propagator in a linear, nearest neighbor coupled molecular crystal containing a single arbitrary local imperfection. This imperfection modifies both the molecular energy (diagonal scattering) as well as the energy transfer between the imperfection site and its nearest neighbors (off-diagonal scattering). It may be an impurity molecule, a locally misaligned molecule or a local lattice compression. This calculation provides an exact extension of earlier work on single site scattering and of perturbation theory of diagonal and off-diagonal scattering. For special values of the scattering parameters we also present simplified formulas for the propagator. In all cases however, even in the general exact case, the results are reduced to practical forms, requiring only a simple integration for numerical applications.
Nuclear magnetic resonance spectroscopy in cholesteric liquid crystals. I. Orientational order parameter measurements
Authors: Collings Peter J. , McKee Terrence J. , McColl James R.
Published: February 2003

NMR spectroscopy is utilized to measure the ’’nematic’’ orientational order parameter ? in a pure cholesteric liquid crystal for the first time. The character of the 19F NMR spectra in our sample of cholesteryl m-fluorobenzoate, and its o-isomer, is determined by anisotropic chemical shifts, dipolar splittings, random domain alignment, and fast self-diffusion. The temperature dependence of ? and its value of 0.32 near the transition to the isotropic phase in both compounds closely resemble the behavior of nematic liquid crystals. This may suggest that similar ordering mechanisms are at work in both steryl and nonsteryl liquid crystals.
Dielectric relaxation in substituted propanes in the liquid state
Authors: Roy S. K. , Gupta K. Sen , Ghatak A. , Das A.
Published: February 2003

Complex dielectric permittivities of 1,3-propanedithiol and 1,2,3-tribromopropane in the liquid state have been evaluated at 0.85, 1.25. 1.62, 3.17, and 3.49 cm in the microwave regions at different temperatures. The activation energies for dielectric relaxation and viscous flow have been determined. The dipole moments of both molecules have been calculated. The distribution parameter in 1,3-propanedithiol was found to increase with increase in temperature, and a possible explanation is given.
Contact interaction between 129Xe and nitric oxide
Authors: Jameson Cynthia J. , Jameson A. Keith , Cohen Sheila M.
Published: February 2003

The chemical shift of 129Xe in nitric oxide gas has been observed as a function of temperature and density of NO. The derivative of the frequency with respect to density gives the second virial coefficient of chemical shielding of 129Xe in nitric oxide, σ1(Xe–NO) = −0.6840 + 1.5516 × 10−3τ − 1.3142 × 10−5τ2 +7.2769 × 10−8τ3 ppm amagat−1, in which τ=T−300, and T goes from 220 to 380 K. The results are compared with the Xe in oxygen gas and the contact contribution to σ1(Xe–NO) is determined. By using Ar as the diamagnetic counterpart of an NO or O2 molecule, empirical values of the integral ℱρspine−V/kTdx3 are obtained for the Xe–NO and the Xe–O2 interaction. The empirical values of this integral are greater for the Xe–NO pair than the Xe–O2 pair. Both exhibit a slight temperature dependence.
Second virial coefficient of 129Xe chemical shielding in mixtures of Xe with spherical top molecules CH4, CF4, and SiF4
Authors: Jameson Cynthia J. , Jameson A. Keith , Cohen Sheila M.
Published: February 2003

129Xe chemical shifts in mixtures of Xe with CH4, CF4, and SiF4 as a function of temperature and density have been obtained by pulsed Fourier transform NMR spectroscopy. The low densities of gases used and the previously determined 129Xe shifts in pure xenon enable the determination of the chemical shielding contribution which is linear in density for Xe–CH4, Xe–CF4, and Xe–SiF4 molecular pairs, with a high degree of precision. An approximate reduced second virial coefficient of chemical shielding for 129Xe in Xe interacting with other molecules can be defined, which leads to superposition of Xe–Xe and Xe–Kr curves over a large part of the reduced temperature range for which data is available. Estimates of well depths for Xe–Ar, Xe–CH4, Xe–CF4, Xe–SiF4, and Xe–HCl have been obtained by this method.
Differences in fluid dynamics associated with an atomic versus a molecular description of the same system
Authors: Olmsted R. D. , Snider R. F.
Published: February 2003

A fluid of diatomics is usually described entirely in terms of the motions of the molecules themselves. On the other hand, since the molecules are composed of atoms, a purely atomic description of the fluid is also possible. This paper explores the relationships and differences between these descriptions. Thus atomic mass, momentum, and energy densities, as well as the atomic momentum flux and heat flux, differ from their molecular counterparts. While some of these differences vanish in the Navier–Stokes regime (small spatial inhomogeneities), others do not. In particular, the atomic pressure tensor is necessarily symmetric while the natural molecular pressure tensor has an antisymmetric component.
Symmetry of the pressure tensor in macromolecular fluids
Authors: Olmsted R. D. , Snider R. F.
Published: February 2003

For molecules possessing internal angular momentum, irreversible thermodynamics shows that the relaxation of the internal angular momentum occurs via the antisymmetric component of the pressure tensor. Yet it is common in fluid dynamics, even for fluids of orientable molecules, to assume that the pressure tensor is symmetric. An attempt to clarify this anomaly for solutions of macromolecules was made by Curtiss, Bird, and Hassager [Adv. Chem. Phys. 35, 31 (1976)]. They found in their kinetic theory treatment, that after making several approximations common in polymer theory, the pressure tensor is symmetric. The purpose of this paper is to show that within the usual question of uniqueness, their conclusion regarding the symmetry of the pressure tensor depends on only two things: (i) that the interatomic (between ’’beads’’) potential is spherical and (ii) that the fluid’s densities (of mass and momentum) are localized at the bead points. If instead, the densities are localized at the polymer center of mass, there arises an inherently antisymmetric component of the pressure tensor. This localization is considered to be more in keeping with the molecular nature of such systems.
Studies in statistical mechanics of Coulombic systems. I. Equation of state for the restricted primitive model
Authors: Larsen Bjo/rn
Published: February 2003

Thermodynamic properties for a system consisting of charged hard spheres are investigated in the liquid state. A Padé type approximant which satisfies certain known limiting features of this model is fitted to Monte Carlo calculated internal energies previously reported. Other thermodynamic properties are derived from this energy equation of state and compared with experimental results for some molten alkali halides. It is found that the primitive model system shows a thermodynamic behavior that is remarkably similar to a typical alkali halide in the liquid phase. This similarity is explained in terms of the similar basic properties of the pair potential, namely the short range repulsion and the long range Coulomb contribution which are sufficient for a typical molten salt structure to be formed.
Infrared absorption intensities: Transferability of electro-optical parameters
Authors: Gussoni M. , Abbate S.
Published: February 2003

In this paper the electro-optical theory of valence is reanalyzed and its advantages are described with respect to other methods developed for the study of the absorption intensities in the infrared spectra. A particular attention is paid to the transferability of electro-optical parameters to other molecules (isotopic derivatives or chemically similar molecules).
The electronic spectra of thieno[3,2,-b]thiophene
Authors: Bertinelli F. , Brillante A. , Palmieri P. , Taliani C.
Published: February 2003

The uv spectrum of thiophthene is investigated in the vapor and crystal phase. Two intense absorption systems in the region 36 000–40 000 cm−1 are assigned to two allowed electronic transitions to Bu excited states, while a very weak absorption observed in the crystal spectrum at 34 394 cm−1 is assigned to a single–triplet transition allowed by spin-orbit interactions. Ab initio CI computations of the energies of the excited states and relevant singlet–triplet spin-orbit matrix elements provide support for the assignment. The vibrational analysis of the first intense absorption system suggests that the molecule has a distorted geometry in the first excited electronic state. An explanation is offered of the very different vibrational structure of the vapor and crystal spectra.
Carbon isotope effects in photodissociation of phosgene. I. Photocatalyzed carbon isotope exchange between phosgene and carbon monoxide
Authors: Vukmirović Zorka B. , Ribnikar Slobodan V.
Published: February 2003

The exchange reaction 12COCl2+13CO?13COCl2+ 12CO is theoretically expected to have a separation factor of 1.04 at 60°C, and of 1.07 at −35°C. Pure COCl2 and a series of COCl2–CO gaseous mixtures were irradiated either with the 253.7 nm mercury line or the light of a medium pressure mercury lamp (above 200 nm). The 13C distribution in the photostationary state has shown separation factors ranging from 1.092 at 60°C to 1.170 at −35°C for the 253.7 line and from 1.059 at 60°C to 1.067 at 25°C at irradiation with the medium pressure lamp. The increase of the factors above the theoretically predicted values is attributed to differences in the fine structure of 12COCl2 and 13COCl2 predissociation spectra. The possibility of improving the selectivity of the separation process is analyzed.
Concentration and temperature dependence of viscosity in the critical mixing region of aniline–cyclohexane
Authors: D’Arrigo G. , Mistura L. , Tartaglia P.
Published: February 2003

Measurements of shear viscosity as a function of molar composition ? and temperature T near the consolute point of the binary system aniline–cyclohexane are reported. The results are analyzed in terms of the mode coupling theory. The needed dependence of the correlation length on ? and T is established using a scaling equation of state. The agreement between experiments and theory is quite good.
On the application of the method of interval normalization to neutron diffraction data from molecular liquids
Authors: van Tricht J. B.
Published: February 2003

A new method of normalization applied to thermal neutron diffraction data on molecular liquids, called interval normalization, is proposed. The method consists of fitting the scattering by the free molecules to the corrected intensity distribution within a limited interval of wave number transfer. The method has been applied to the tetrachlorides of carbon, silicon, titanium, and tin in the liquid state at room temperature. Besides the pursued normalization, the intramolecular interatomic distances and mean amplitudes of vibration are obtained. These intramolecular parameters follow without applying Fourier transform techniques.
Infrared rotatory dispersion of binary cholesteric mixtures
Authors: Korte E. H.
Published: February 2003

The optical rotation exhibited by mixtrues of cholesteryl chloride and myristate was measured in the infrared region. Scanning the temperature while observing at a given wavenumber, was found three anomalies, each of which has a shape similar to a Cotton effect curve. The results, especially the cause and the H sign of the anomalies, are discussed on the basis of the de Vries theory.
Energy loss of electrons in random motion
Authors: Magee J. L. , Helman W. P.
Published: February 2003

A subexcitation electron (energy range 1–6 eV or so) in a molecular medium losses energy in the excitation of molecular vibrations or phonons. One of the loss mechanisms involves the transient electric field generated by the motion of the electron and this paper presents an investigation of such energy loss. Ensembles of random tracks generated by a Monte Carlo procedure are considered. The Fourier transform of the electron displacement of each track is obtained by a fast Fourier transform (FFT) algorithm and the ensemble-averaged square of this transform provides a frequency spectrum which determines the average energy loss of the electron. Two mechanisms are considered as examples: the loss to dipolar relaxation in water, and the loss to infrared-active vibrations in benzene and polyethylene. The rate of energy loss to dipolar relaxation in water is in the range of 1013 eV/sec and the rate of loss to infrared-active vibrations in hydrocarbons is less by perhaps a factor of 3 or more. The relationship of this classical model to a more rigorous quantum mechanical treatment and the numerical methods are discussed in the Appendices.
On the functions associated with the Burrau approximation for the hydrogen molecular ion and analogous molecules
Authors: McKinney Paul Caylor
Published: February 2003

The Schrödinger equation for the Burrau-like molecular species (A-B)ZA+ZB−1 is (−h/2/2me) ∇2 ψ + [−ZAe2/rA−ZBe2/rB +ZAZBe2/RAB]ψ = Eψ. After separation using prolate spheroidal coordinates, the mathematical analysis of this equation can be reduced to the investigation of the ordinary differential equation (d/dx) { (1−x2)[dP (x)/dx]} + {[−m2/(1−x2)] + 2αβx + α2x2 + σ} P (x) =0, where m is an integer, α and β are molecular parameters expressed as elements of the real number set, and σ is the eigenvalue of the equation which is dependent on two numbers κ and m related to the quantum numbers found in the discussion of the hydrogen atom as well as α and β. The solutions for the function P (x) where m is replaced by μ and μ is any number are expanded in power series of various kinds, in series of Legendre functions, and confluent hypergeometric functions to give three term recursion relations. The recursion relations are used to generate continued fractions which allow convenient numerical calculation of the eigenvalues and they are also helpful in the derivation of asymptotic expressions of the eigenvalues and eigenfunctions in terms of their dependent variables. Integral equation solutions are given for the two intervals x∈[−1,1] and x∈[1,∞]. For β=−(ν+μ+1) or β=ν+μ+1, where ν∈{0} UN, it is possible to generate polynomials solutions.
Nuclear quadrupole coupling effects in the microwave spectrum of dichlorodifluoromethane
Authors: Su Chun Fu , Beeson E. L.
Published: February 2003

The nuclear electric quadrupole hyperfine structures in the microwave rotational absorption spectra of C 35Cl2F2 and C 35Cl 37ClF2 have been investigated. The quadrupole coupling constants of 35Cl in C 35Cl2F2 have been found to be (in MHz) χaa=−43.42±0.16, χbb=4.70 ±0.20, χcc=38.71±0.22. Measurements of hyperfine spectra for C 35Cl 37ClF2 agree with the ratio Q37/Q35=0.788. The second-order perturbation has been used to determine the off-diagonal element χab, which has been found to be −56±4 MHz.
Radiation-induced oxidation and reduction of nitromethyluracil
Authors: Box Harold C. , Potienko George , Budzinski Edwin E.
Published: February 2003

ESR–ENDOR measurements were made on single crystals of 5-nitro-6-methyluracil x-irradiated at 4.2 K. The primary oxidation and reduction products were characterized and identified. The reduced species has a large spin density localized on the nitrogen atom of the nitro group. The hyperfine and quadrupole coupling tensors of the 14N nucleus were determined from ENDOR measurements. The oxidized species is the cation formed by removal of an electron from the uracil ring.
Infrared radiative decay constants for the vibrational levels of CO  (a 3Π)
Authors: Marcoux P. J. , Piper L. G. , Setser D. W.
Published: February 2003

The decay of the CO  (a 3Π,v′=0–3) levels have been studied in a flowing-afterglow apparatus. The vibrational distribution was monitored by observing the CO  (a 3Π→X 1Σ+) emission intensity. The results were interpreted to obtain 52.5, 77, and 178 sec−1 for the infrared radiative decay constants for the v′=1, 2, and 3 vibrational levels of CO  (a 3Π). The data also establish that the upper limit to the rate constant for vibrational relaxation of CO  (a) by collision with He is ?6×10−17 cm3 molecule−1 sec−1, corresponding to a collision probability of ?1.5×10−7.
New radioluminescence effects of aqueous HgI2 solutions after high energy electron irradiation
Authors: Fujita S. , Horii H. , Mori T. , Taniguchi S.
Published: February 2003

Pulse radiolysis studies of aqueous solutions of HgI2 are reported. Radioluminescence corresponding to new luminescent species has been observed.(AIP).
Absolute total elastic cross sections for collisions of He with Ne, Ar, Kr, and Xe
Authors: Pirani F. , Vecchiocattivi F.
Published: February 2003

The total elastic cross sections for collisions of He with other rare gases are reported and discussed in terms of potentials in the ESMSV form. (AIP)
Quantum vibrational transition probabilities from real classical trajectories: Symmetric diatom–diatom collisions
Authors: Skodje Rex T. , Gentry W. Ronald , Giese Clayton F.
Published: February 2003

Our previous theory of vibrationally inelastic atom–diatom collisions, which is based on an approximate correspondence between the classical and quantal equations of motion, is extended here to the problem of translational–vibrational and vibrational–vibrational energy transfer in collisions of two identical diatoms. Parameters describing the quantal motion of harmonic oscillators subject to an interaction potential which includes only terms linear and bilinear in the two oscillator coordinates are evaluated from exact classical trajectories for the full potential. The formalism makes it possible to distinguish between the vibrational–vibrational and translational–vibrational energy transfer modes and to isolate the intermode coupling terms. The validity of approximations based on a reduced state basis is easily evaluated. The model results are in generally excellent agreement with exact fully quantal calculations, and they reproduce well the dependence of the transition probabilities for collinear H2+H2 collisions on the assumed form of the interaction potential.
A study of hydrogen bonding in methanol vapor by measurement of thermal conductivity
Authors: Renner T. A. , Kucera G. H. , Blander M.
Published: February 2003

The thermal conductivity of methanol vapor was measured in a modified thick hot-wire cell between 307 and 345 K at pressures ranging from approximately 50 torr up to a maximum of 1 atm. Analysis of the experimental data indicates that a tetrameric species is the principal source of the observed enhancement of the thermal conductivity of the vapor due to association reactions. Equilibrium constants for the reaction 4CH3OH? (CH3OH)4 were determined from the thermal conductivity data. The enthalpy of formation of the methanol tetramer is −23.73 kcal/mole and the entropy of formation is −80.92 cal/mole K.
Theory of nonradiative decays in the non-Condon scheme
Authors: Fujimura Y. , Kôno H. , Nakajima T.
Published: February 2003

Without invoking the so-called Condon approximation, a theory is developed for the nonradiative decay rate constant in molecules. The electronic coupling matrix elements obtained by using adiabatic electronic wavefunctions are expressed in terms of commutators [p2, η], where p is the nuclear momentum operator and η is a function of nuclear coordinates. Evaluating commutator [p, η] at a fixed nuclear configuration, we obtain the rate constant within a Condon-like approximation. Assuming harmonic and displaced potential energy surfaces, the rate constant of the nonradiative decays where the promoting mode has a displacement is derived in the low temperature limit. The dependences of the non-Condon correction factors on the vibronic coupling constant γ, the displacement Δ, and the energy gap E are examined by performing model calculations. The correction factors decrease with increasing γ owing to the resonance effect near the potential surface crossing. The calculations also show that the rate constant in the non-Condon scheme exceeds that obtained invoking the Condon approximation by about two orders of magnitude. Finally, a simple upper bound to the decay rate constant is derived by applying a Condon-like approximation to the electronic coupling matrix elements. It is shown that in the weak coupling situation the evaluation of the electronic coupling matrix elements by the use of a Q-centroid method gives an upper bound to the rate constant.
Reactivity bands in atom–molecule collisions. II. X+HX on the collinear SSMK surface
Authors: Wright James S. , Tan K. G.
Published: February 2003

The collision of X+HX on the collinear SSMK surface is studied by classical trajectory calculations for masses X=1.008(H), 2.014(D), 3.016(T), and 10.000. Total reactivity maps are given as plots of vibrational phase angle versus relative kinetic energy (range 0.3–2.0 eV). A clear relationship between the maps for different mass combinations is shown. The total reaction probability for T+HT and 10+H−10 shows a range of kinetic energy above the threshold where all trajectories are unreactive, followed by reactive ranges at higher energy. Threshold energies and reactivity maps are discussed in terms of skewed coordinate axes. Product vibrational energy distributions show patterns which are closely related to the total reactivities. The results are interpreted in terms of single and multiple collisions.
A group–dipole interaction model of the molecular polarizability and the molecular first and second hyperpolarizabilities
Authors: Sundberg Kenneth R.
Published: February 2003

The group–dipole interaction model is generalized to treat the molecular polarizability and the molecular first and second hyperpolarizabilities. A molecule is divided in groups; each group is characterized by a polarizability and by first and second hyperpolarizabilities, and it resides in an internal molecular electric field. The internal field is thought to arise from any charges or permanent moments within the molecule, and it is characteristic of the system being studied. In the point dipole approximation, all the dipole–dipole interactions are treated exactly, and all the molecular results are written in terms of only those quantities needed to calculate the molecular polarizability. Several approximate theories are considered, and the additivity of group polarizabilities and hyperpolarizabilities is discussed. Special formulas are derived to treat an assembly of interacting isotropic atoms.
The internal state distribution of CN free radicals produced in the photodissociation of ICN
Authors: Sabety-Dzvonik M. J. , Cody R. J.
Published: February 2003

Laser-induced fluorescence has been used to measure the vibrational–rotational (υ″, N″) product state distributions of CN  (X 2Σ+) radicals produced in the photodissociation of ICN in two spectral regions. Intermolecular energy transfer studies of CN  (X) produced by photolysis at λ?145 nm indicate that near resonant collision-induced energy transfer from the υ′=0 and υ′=1 vibrational levels of the A 2Πi state populated the υ″=4 and υ″=5 levels of the X state. The observed X state υ″ level population inversions, viz., Nυ″=0?Nυ″=1∼ Nυ″=2≲Nυ″=3<Nυ″=4≳ Nυ″=5 (0.38:0.28:0.25:0.32:1.00:0.17) confirm the presence of CN  (A 2Πi) in υ′=0 and υ′=1. Time resolved laser-induced fluorescence studies indicate that A state CN is a primary product with a calculated lower limit to the vibrational temperature of ∼1450 K. Photolysis of ICN in the low energy Ã state continuum at λ?220 nm produces primarily CN  (X 2Σ+) with little vibrational excitation. The measured X state vibrational ratio Nυ″=1/Nυ″=0 yields an initial vibrational Boltzmann temperature of ∼750 K. Furthermore, the X state CN radicals are observed to be rotationally excited. The rotational level distributions can be fit by a theoretical function that is the sum of two Boltzmann functions with temperatures of ∼400±50 K and 2700±400 K. The observed rotational distributions are discussed with emphasis upon the symmetry and geometry of the excited ICN molecule. Furthermore, the observation that X state CN is produced with little vibrational excitation is discussed in reference to several conflicting theoretical and experimental investigations by others.
PNO–CI and CEPA studies of electron correlation effects. IV. Ionization energies of the first and second row diatomic hydrides and the spectroscopic constants of their ions
Authors: Rosmus P. , Meyer W.
Published: February 2003

Near equilibrium potential curves for the ground states of the diatomic hydride ions LiH+ to HCl+ have been calculated from highly correlated PNO–CI and CEPA wavefunctions. The spectroscopic constants derived from the CEPA potential curves are in very good agreement with the known empirical values. Several new constants are given: re=1.203±0.001 Å, ωe=2530±20 cm−1, Δ G1/2=2401±20 cm−1 for BH+; ωe=2851±20 cm−1 for CH+; re=1.070±0.001 Å, ωe=3059±20 cm−1 for NH+; ωe=1695±20 cm−1, Δ G1/2=1544±20 cm−1 for AlH+; ωe=2376±20 cm−1 for PH+. The polarization minima of the potential curves of the LiH+ and NaH+ ground states are calculated deep enough to allow for several vibrational levels. The correlation contributions to the proton affinities of the first- and second-row atoms have been calculated to range from −0.47 eV (for B) to +0.13 eV (for S) with expected uncertainties of about ±0.05 eV. Combination of the proton affinities with experimental atomic data and dissociation energies of the neutral hydrides yields dissociation energies of the ions with uncertainties of about ±0.05 eV and first adiabatic ionization energies with uncertainties of about ±0.1 eV. The corresponding experimental values show larger error bounds in many cases. New values are recommended for the dissociation energies (D0) of XH+ and the first adiabatic ionization energies of XH, respectively, in the cases of X being Li(0.12,7.7), N(3.50,13.5), O(5.00,13.0), Na(0.12,6.9), Mg(2.00,6.9), Al(0.65,8.4), P(3.30,10.2), and S(3.70,10.2) (all values in eV).
Interaction site cluster series for the Helmholtz free energy and variational principle for chemical equilibria and intramolecular structures
Authors: Pratt Lawrence R. , Chandler David
Published: February 2003

The interaction site cluster series is derived for the Helmholtz free energy of a molecular mixture in which molecules can interconvert by chemical reactions. This series expresses the free energy as a functional of the single-molecule (intramolecular) distribution functions. Variations of this functional are studied. It is shown that when the total numbers of atoms in the mixture are fixed, the free energy functional is a minimum with respect to variations of the intramolecular distribution functions. Further, this variational principle is shown to be equivalent to the cluster series formulas derived earlier [J. Chem. Phys. 65, 2925 (1976)] for chemical equilibrium constants and intramolecular distribution functions of nonrigid molecules in condensed phases.
Temperature dependence of pressure broadened linewidths in the microwave region
Authors: Srivastava G. P. , Kumar Devendra , Kumar Anil
Published: February 2003

Self-broadened linewidths of OCS, BrCN, CH3Br, and HCHO have been measured at various temperatures from −40 to 75 °C using a double modulation microwave spectrograph. The linewidths have also been calculated using Anderson–Tsao–Curnutte theory and the extension by Murphy and Boggs. Within the temperature range investigated the linewidth decreases with temperature both experimentally and theoretically in an identical manner.
Physical clusters in an imperfect vapor
Authors: Gillis H. P. , Marvin Dean C. , Reiss H.
Published: February 2003

We examine the general problem of calculating the equation of state in terms of physical clusters, and direct attention to the two main components of the problem: (i) formulating a satisfactory definition of the physical cluster concept; (ii) developing a method to account for interference between clusters and to assess the importance of interference. For (i) we use Stillinger’s definition, which is based on the distance between molecular centers. To account for interference, we treat the clusters in a one-dimensional vapor as a mixture of hard rods, each of which assumes its most probable length. We find that neglect of interference induces errors in the second virial coefficient down to a very low temperature, which depends on the strength of the pair attraction. Thus, we conclude that interference between clusters can never be neglected in a calculation of the equation of state when ordinary dispersion forces operate between molecules.
Physical clusters in nucleation theory
Authors: Gillis H. P. , Marvin Dean C. , Reiss H.
Published: February 2003

We examine the general problem of calculating from microscopic principles the equilibrium distribution of physical clusters demanded by the theory of homogeneous nucleation. We direct attention specially to the effect of interference between clusters. In a one-dimensional fluid where interference is accounted for by the ’’most probable length’’ approximation developed earlier, we show that the effect is negligible under conditions corresponding to nucleation experiments. Also in one dimension, we show that cluster partition functions appearing in the theory are numerically very well approximated by calculations based on the definition of Lee, Barker, and Abraham (LBA). We therefore argue that in three dimensions the distribution of clusters for nucleation theory can be obtained from the familiar mass-action law, in which cluster partition functions are calculated by the method of LBA.
The radiation-induced formation of hydrogen and deuterium compounds in silica as observed by Raman scattering
Authors: Hartwig Charles M.
Published: February 2003

Radiation-induced compound formation in vitreous silica has been observed with Raman light scattering. The compounds were observed to form in silica samples that were impregnated with hydrogen (deuterium) gas and irradiated with gamma rays. Neither impregnation nor irradiation alone produced Raman-active compounds. The combination, however, did produce compounds that were identified as silicon hydrides (deuterides) and hydroxyls (deuteroxyls). In addition, the hydroxyl (deuteroxyl) band shapes differed between as received and impregnated/irradiated samples and among the different impregnated/irradiated silica samples. The principal band features were found to be due to light scattering from at least three independent modes, each of which appear to result from a different hydroxyl (deuteroxyl) genus. In contrast, the hydride (deuteride) bands behave as though they were due to scattering from a single vibrational mode.
Angular resolution and isotope studies for inversion relaxation in NH3
Authors: Williams J. R. , Kukolich S. G.
Published: February 2003

Inversion relaxation cross sections for the J=3, K=2 upper state of NH3 were measured using a beam maser spectrometer. Scattering gases were NH3, ND3, HCl, and H2O. For NH3–NH3 scattering the angular resolution was varied from 1.5° to 0.2° with little effect on cross sections. Cross sections for NH3 and ND3 as scattering gases were equal within experimental error. The result that beam maser cross sections are relatively independent of angular resolution is discussed. Calaculated angular resolution corrections are compared with values of beam attenuation cross sections and total cross sections obtained from the present data. Comparison is made between our pure state (σ1) and superposition state (σ11) cross sections and recent gas-cell data.
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o studies of the β−-decay in OHT, NH2T, CH3T, and 14CH4
Authors: Ikuta Shigeru , Iwata Suehiro , Imamura Masashi
Published: February 2003

The T→He+ β−-decay in OHT, NH2T, and CH3T, and the 14C→N+ β−-decay in 14CH4 are theoretically studied by ab initio SCF-MO calculations. The ground and excited state daughters and the transition probabilities from the parent to these daughters are calculated with the basis set of the double zeta quality. The potential energy curves of these daughter ions, OHHe+, NH2He+, and CH3He+, are obtained by an ab initio SCF approximation. The correlation of the excited state daughters with the states of XHn + ions is also discussed on the basis of the conservation of the orbital symmetry. In T→He+ β−-decay, the transition probabilities to the ground state daughters are about 0.61 for all of the parents studied. The main products in the β−-decays of OHT, NH2T, and CH3T are found to be OH+, NH2+, and CH3+, respectively. The calculated results in CH3T are qualitatively in agreement with the experimental one, but quantitatively the calculation underestimates the production yield of the CH3 + ion. In 14CH4 decay, the transition probabilities to the ground state daughter are larger than those in T→He+ β−-decay, and those to the excited state daughters are different from the values calculated by Raadschelders-Buijze et al.
Sodium NMR and the phase transition in NaN3
Authors: Jeffrey Kenneth R.
Published: February 2003

The sodium nuclear quadrupole interaction has been used as a microscopic probe of the static and dynamic behavior of the crystalline lattice near the phase transition in NaN3 at 293 K. The phase transition from a rhombohedral to monoclinic structure is very evident in the experimental measurements of the quadrupole coupling constant e2qQ/h and asymmetry parameter η. These measurements were facilitated by the use of the nuclear quadrupole echo and pulsed Fourier transform techniques. In the rhombohedral phase e2qQ/h is nearly independent of temperature and equal to 130 kHz while η is zero, which is consistent with the crystal structure. Below Tc, e2qQ/h is larger and η is nonzero. As the temperature approaches Tc from below, both parameters become smaller and the rate increases rapidly near Tc. A simple point charge model calculation indicates that η is a measure of the order parameter squared for the phase transition. The sodium spin–lattice relaxation rate 1/T1 is proportional to T2 throughout the temperature region investigated and shows no effects due to the phase transition. The relaxation is a result of the quadrupolar spin–phonon interaction. Because the relaxation rate shows no Arrhenius-type temperature dependence, molecular reorientation of the N3 ion is thought not to be a factor in the dynamics of the phase transition.
Endothermic reactions of uranium ions with N2, D2, and CD4
Authors: Armentrout P. B. , Hodges R. V. , Beauchamp J. L.
Published: February 2003

An ion beam apparatus is employed to study the reactions of uranium ions with N2, D2, and CD4 at laboratory energies up to 335 eV. The endothermic reaction of U+ with nitrogen leads to the product UN+ for which a bond dissociation energy D (UN+) =4.7±0.2 eV is determined, corresponding to ΔHf(UN+) =272±7 kcal/mole. Endothermic reactions of U+ with D2 and CD4 lead to formation of UD+ with D (UD+) =2.9±0.1 eV and ΔHf(UD+) =254±6 kcal/mole. The dependence of experimental reaction cross sections on relative kinetic energy is discussed in terms of simple models for reaction. The proton affinity of uranium is determined, P.A.(U) =238±5 kcal/mole, and this exceptionally high value is compared to other atomic and molecular base strengths.
Neutron diffraction study of the crystal structure of ethylene oxide deuterohydrate at 80°K
Authors: Hollander F. , Jeffrey G. A.
Published: February 2003

A single crystal neutron diffraction study of 6 C2H4O⋅46 D2O at 80 °K has confirmed the higher symmetry space group Pm3n and has provided more precise structural data relating to the hydrogen bonding in this clathrate hydrate. The four unique hydrogen-bonding interactions which form the edges of the polyhedra of involve three bonds with D...O lengths of 1.726, 1.757, and 1.761 Å and three longer bonds of 1.797, 1.802, and 1.818 Å. The three longer bonds form the edges of hexagons, while the shorter ones occur only in the pentagons. There is a definite trend for the longer bonds to be associated with shorter covalent O–D distances and greater deviations from O–D...O linearity. The scattering density of the ethylene oxide guest molecule was best fitted by a model with 24-fold disorder, more consistent with small barriers to reorientation than with free rotation. A residual scattering density was also observed within the dodecahedra, corresponding to approximately 0.4 mole per unit cell of occluded air.
Note on the specific heat of microcrystallites
Authors: DuBose John
Published: February 2003

The specific heat of microcrystallites is computed according to a method used by Kothari and Singal. Their work is extended to a full range of microcrystallite size, and a bulk specific heat prediction allows comparison with experimental excess specific heat due to small particle size. Agreement is surprisingly good and offers a possibility for a practical and reasonably accurate approach to calculations of small particle specific heat.
On the location of the lowest triplet excitation in ammonia
Authors: Johnson Kenneth E. , Lipsky Sanford
Published: February 2003

Electron impact spectra of NH3 at Θ=0° and Θ=90° for incident electron energies E=20–50 eV are reported. The spectra provide evidence for a low-lying states in ammonia.(AIP)
Photoelectron spectroscopy of liquids up to 21.2 eV
Authors: Nemec Ladislav , Gaehrs Hans Jasper , Chia Lucille , Delahay Paul
Published: February 2003

Photoelectron spectroscopy of liquids is investigated at variable photon energies up to 10 eV and with rare-gas resonance lines at 11.7 (ArI), 16.8 (NeI), and 21.2 (HeI) eV. Seven liquids are studied: N-methylaniline, N,N′-dimethyl-p-toluidine, formamide, hexamethyl phosphoric triamide, tetraglyme, ethylene glycol, and n-decanol. Energy distribution curves display at the higher photon energies a band structure matching the sequence of bands in the corresponding gas-phase photoelectron spectra. The bands are attributed to emission of unscattered electrons (no loss of kinetic energy to the liquid) whereas the underlying background is ascribed to scattered (in the liquid) electrons. Quantitative treatment based on this interpretation agrees with experiment. Energies characterizing either bulk or surface photoionization are determined within ±0.1 eV. The gas–liquid red shift (0.9 to 1.4 eV) and bulk–surface blue shift (0.5 to 1.3 eV) in photoionization energies are interpreted in terms of electronic polarization of the liquid medium. This is, to our knowledge, the first investigation of liquids by ultraviolet photoelectron spectroscopy above 10 eV.
MCSCF+CI wavefunctions and properties of the X 2Π and A 2Π states of ClO
Authors: Arnold J. O. , Whiting E. E. , Langhoff S. R.
Published: February 2003

A multiconfiguration, self-consistent field plus configuration-interaction calculation has been performed on the X 2Π and A 2Π electronic states of ClO. The values of certain molecular properties computed from the wavefunctions agree well with those from experiment. The sum of the squares of the computed electronic transition moments between the X 2Π and A 2Π states at 3.07 bohr is 1.75 a.u., which corresponds to the experimental result of 1.58±0.20 a.u. The computed ground state dipole moment at the experimental equilibrium separation is 1.232 D, which compares well with two experimental results of 1.18±0.12 and 1.239±0.010 D. The value of the computed dissociation energy is 2.75 eV, which agrees well with the experimental value of 2.803±0.001 eV.
Molecular beam study of the reactions of K and Cs with UF6, WF6, MoF6, TeF6, and SeF6
Authors: Annis B. K. , Datz S.
Published: February 2003

The reactions of K and Cs with UF6, WF6, MoF6, TeF6, SeF6, and SF6 at thermal energies have been investigated using crossed molecular beams. Except for SF6, these hexafluorides have remarkably high electron affinities. In fact, the electron affinities of MoF6, WF6, and UF6 exceed the ionization potentials of K and Cs so that spontaneous ion pair formation is energetically possible. In no case was a significant ion current observed. Instead, exchange reactions to form MF (and possibly MAF5) are observed. The measured product angular distributions were in all cases found to be consistent with the model of complex formation. However, substantial differences in the nature of the complex disintegration were noted.