bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalized treatment of the quadrupole-quadrupole interaction of low symmetry molecules and its effect on the second dielectric virial coefficient
Authors: Hosticka C. , Bose T. K. , Sochanski Jerzy S.
Published: February 2004

The experimental dielectric virial coefficient data of ethylene as determined by Bose and Cole are reanalyzed. The quadrupole-quadrupole interaction energy of low symmetry molecules is calculated, and its effect on the second dielectric virial coefficient is determined by a Monte Carlo numerical integration. It is shown that taking into account the quadrupole-quadrupole interaction does not appreciably change the quadrupole moment value of ethylene. By combining the experimental results of dielectric and induced birefringence measurements, the quadrupole moment components of a low symmetry molecule can be estimated. The experimentally derived quadrupole moment components of ethylene, Θzz = 2.0 × 10−26 esu·cm2 and Θxx = 2.09 × 10−26 esu·cm2 and the existing theoretical values agree reasonably well.
Weak hyperfine structure measurement using the magnetic repolarization effect: Application to N = 1 v = 1 (1s 3d)1Σ level of H2
Authors: Melieres-Marechal Marie-Antoinette , Lombardi Maurice
Published: February 2004

The magnetic repolarization effect is studied in the case where the hyperfine structure (AI · J) of the considered excited atomic or molecular level is weaker than the natural width Γ. General expressions are given. It is shown that the amplitude of this effect varies as (A/Γ)2 and that its value permits the determination of A when one compares the magnetic repolarization and depolarization effects. Such an effect is experimentally studied in the N = 1, v = 1 (1s 3d)1Σ level of H2. A value of A = 1±0.17) MHz is deduced, corresponding to A/Γ = 0.15.
Dielectric properties of helium: The polarizability of diatomic helium
Authors: Fortune P. J. , Certain P. R.
Published: February 2004

Self-consistent field calculations of the dipole polarizability tensor of diatomic helium at four internuclear separations between 4a0 and 6a0 are reported. For larger separations, the calculations are shown to reduce to the point-dipole model of long-range polarizabilities. The computed polarizability is used in a companion paper to obtain estimates of the second dielectric constant virial coefficient, the Kerr constant virial, and the spectral moments for Raman scattering.
Dielectric properties of helium: Quantum statistical mechanics
Authors: Bruch L. W. , Fortune P. J. , Berman D. H.
Published: February 2004

Expressions for the second dielectric and Kerr virial coefficients and the first two moments of the associated spectral functions valid in quantum statistical mechanics are derived. Upper and lower bounds are derived for the second Kerr virial coefficient to enable an indirect evaluation when quantal effects are appreciable. Calculations of helium dielectric properties near 4 K are reported. The calculations incorporate approximations for the pair distribution function of gaseous helium and coupled Hartree-Fock results for the diatom polarizability. Structure factors calculated from the distribution functions and the calculated anisotropy moments are in good agreement with experiment. The calculated second dielectric virial coefficient at 4 K is in order-of-magnitude agreement with experiment and reflects an imprecise knowledge of the incremental mean polarizability of the helium diatom.
Nuclear magnetic resonance of glycine in aqueous solution
Authors: Tzalmona A. , Loewenthal E.
Published: February 2004

Relaxation time measurements as a function of the pH and the temperature are performed in 14N and 2D in an aqueous solution of glycine. Information about the nitrogen quadrupole interaction and the correlation times involved is obtained; the quadrupole interaction in NH2–CH2–COO− is 3.48 MHz and the correlation time τq=6.18×10−12 sec.
Intramolecular chain dynamics by forward depolarized scattering
Authors: Han Charles C.-C. , Yu Hyuk
Published: February 2004

Internal relaxation processes of two linear polymers are investigated by the quasielastic Rayleigh scattering in the forward depolarized configuration. The technique is shown to extract only the depolarized component of scattered light which arises solely from the intrachain dynamics without usual encumbrances due to the center of mass translational mode. The power spectrum obtained by direct Fourier transform of photocurrent which is an exact replica of the optical spectrum because of heterodyne-beating between the leakage component normal to the polarization direction of the incident light and the scattered light depolarized by the internal modes, is given by Lorentzian shape in which each mode contributes to the total spectrum with uniform weighting factor. The first polymer, poly(n -hexyl isocyanate), is chosen for its rodlike configuration in low molecular weight and the forward depolarized scattering (FDS) spectrum has been shown to be a single Lorentzian consistent with a unique rotatory relaxation process about the minor axes of the rod. The half-widths of FDS spectra are obtained at different concentrations and extrapolated to infinite dilution. The rod length calculated from the extrapolated half-width value is found to be in good accord with that from light scattered intensity measurement. For the second polymer, which is a linear flexible chain with optical anisotropy, isotactic polystyrene, M = 3.5×106, is selected. The FDS spectra at various concentrations are shown to be multiple Lorentzian, with the spacing of half-widths consistent with the Zimm model. The spectral half-width extrapolated to infinite dilution is in agreement with the prediction of Zimm's theory, but the precision of the terminal relaxation time is only within 30%. At higher molecular weight, the solutions of poly(n -hexyl isocyanate) are found to give multiple Lorentzian spectra and their half-width spacings are determined to be closer than that of the Zimm model. A qualitative rationale for the behavior is offered.
On transmission of low-energy electrons in alkane thin films
Authors: Huang Jan-Tsyu J. , Magee John L.
Published: February 2004

A phenomenological model for the transmission of low-energy electrons in organic thin films is presented and its applications to the photoinjection studies of Chang and Berry and the LEERS studies of Hiraoka and Hamill are discussed. Comparison and correlation of data obtained in both types of experiments are presented.
Vibrational transition probabilities in photoelectron spectra
Authors: Lee Ting Ho , Rabalais J. Wayne
Published: February 2004

Variations in photoionization cross sections, or transition moments, over the vibrational envelope of photoelectron transitions are investigated. Differential photoionization cross sections within the orthogonalized plane-wave approximation and Frank-Condon factors using Morse oscillator vibrational wavefunctions are employed to calculate vibrational transition probabilities of photoelectron transitions. It is shown that cross sections for vibrational bands are a function of the kinetic energy of the ionized electrons and the average normal coordinates associated with specific vibrational-photoelectron transitions. Calculated vibrational transition probabilities are compared to vibrational band intensities in the HeI(21.22 eV) and HeII(40.82 eV) photoelectron spectra of H2 and the HeI photoelectron spectrum of N2. The effect on the cross section of varying the kinetic energy of the photoelectron and the nuclear coordinates individually is investigated for H2, N2, and H2 O.
Nuclear magnetic resonance studies of 7Li ionic motion in alkali silicate and borate glasses
Authors: Hendrickson J. R. , Bray P. J.
Published: February 2004

Nuclear magnetic resonance (NMR) studies of 7Li ionic motion in four lithium and lithium-potassium silicate glasses of the R2O·4SiO2 and R2O·2SiO2 composition were made before and after heat treatment, and a newly developed equation was used for the analysis of the data. Other data from alkali borate glasses of the 3R2O·7B2O3 composition were reanalyzed using the equation, which eliminates the problem of a distribution of ionic relaxation times. It is shown how heterogeneities in the form of barriers to alkali ion motion in the glasses can be detected and studied by NMR. Although all glasses with higher alkali contents appear to be homogeneous, both the borates and silicates with lower alkali contents appear to be heterogeneous. These heterogeneities appear to be on a smaller scale in the borates than in the silicates. In addition to long-range 7Li ionic motion observed in homogeneous glasses (and intermediate-range motion in heterogeneous glasses), there is evidence of short-range motion within severely restricted regions in nearly all glasses studied. The data show that the long-range 7Li ionic motion in glasses proceeds by an interstitial process. The 7Li NMR data of several crystallized lithium silicate glasses in which polycrystalline lithium disilicate was formed reveal that the local atomic structure in the crystal differs from that of the glasses. A large difference found between the activation energies for 7Li long-range motion in glassy (0.648 eV) and crystalline (2.19 eV) lithium disilicate supports this conclusion. Changes of the 7Li activation energy in lithium borate glasses upon partial substitution of lithium-7 by other alkali species follow a trend in accord with an explanation of the mixed-alkali effect in glass previously proposed by the authors.
Droplet growth in a dilute vapor
Authors: Kelly G. E. , Sengers J. V.
Published: February 2004

When the mass flux Γ to a liquid droplet is expanded in terms of a parameter α which is the ratio of the droplet size to the mean free path (inverse Knudsen number), one obtains a series of the form Γ=Γ(0) +Γ(1)α + Γ(2)a2lna + ···. As shown in a previous paper, the coefficients in this series are determined by integrals associated with sequences of successive collisions among a number of vapor molecules and the droplet. For a droplet surrounded by its pure vapor, we have calculated the coefficient Γ(1) of the first inverse Knudsen number correction to the free molecular growth rate Γ(0) assuming that the vapor molecules can be treated as hard spheres. For most nonequilibrium conditions, the ratio Γ(1)/Γ(0) turns out to be positive, rather than negative, as heretofore was assumed in the literature. This result implies that the reduced growth rate Γ/Γ(0) will pass through a maximum as a function of the Knudsen number.
Simplified multiconfiguration self-consistent field theory for localized orbitals. III. Evaluation of operators and matrix elements
Authors: Schlosser Herbert
Published: February 2004

In this paper we continue our discussion of the simplified multiconfiguration self-consistent field theories for localized fixed and fluctuating orbitals. We obtain explicit expressions for the various orbital operators and matrix elements of orbital operators and of the Hamiltonian that are necessary to utilize the theory for numerical calculations. In addition we indicate how the theory may be further simplified by a particular choice of localization potential.
ESR study of paramagnetic centers in irradiated Ba(ClO3)2 · H2O · and Ba(ClO3)2 · D2O single crystals
Authors: Suryanarayana D. , Sobhanadri J.
Published: February 2004

ESR study of γ-irradiated Ba(ClO3)2 · H2O revealed three main centers which are identified as O3−, ClO2, and (ClO2–H2O) radicals, trapped at two distinct sites. The parameters of the spin Hamiltonian have been determined from single crystal and powdered samples. The principal values for O3− and ClO2 centers agree with those reported in other systems. The chlorine center having ``superhyperfine'' interaction with the two protons of water of crystallization has been identified as a (ClO2–H2O) radical. The principal values of the g tensor are gxx=2.0023, gyy=2.0065, and gzz=2.0150; those of the A tensor are axx=102.11, ayy=53.22, and azz=7.79 G. The parameters of the hyperfine coupling of 35Cl with the first proton are axx=8.6, ayy =5.0, and azz=5.0 G, with aiso=6.2 G, and those for the second proton are axx=2.5, ayy=1.2, and azz=1.2 G. The (ClO2–H2O) center is found to be bleached at temperatures (above 120°C), where the crystal loses its water of hydration. On exposing the irradiated crystal to uv light, the two chlorine centers ClO2 and (ClO2–H2O) are fully bleached, followed by an increase in the concentration of the O3− center.
Molecular structure of phosphabenzene: Analysis combining electron diffraction and microwave data
Authors: Wong T. C. , Bartell L. S.
Published: February 2004

The average (ra) structure of vapor phase C5H5P, the phosphorus congener of pyridine, was deduced. Vibrational corrections of diffraction data and rotational constants were made via a normal coordinate analysis based on an approximate quadratic force field. The heterocyclic molecule was found to be planar with principal structure parameters and uncertainties (2.5σ) of r g(C–P)=1.733± 0.003 Å, rg(C2–C3)=1.413± 0.010 Å, rg(C3–C4)=1.384± 0.012 Å, rg(C–H)=1.122± 0.015 Å, ∢ CPC=101.1°± 0.3°, ∢ PCC=124.4°± 0.7°, and ∢ C2C3C4=123.7°± 0.8°. Amplitudes of vibration were determined in the diffraction analysis as well as in the normal coordinate computation. A variety of different types of error matrices were computed to assess the effect of data correlations and the possible coupling, over and above scale factor shifts, between systematic errors in intensities and derived parameters. Conventional treatments of data correlations appear to lead to overoptimistic error estimates in the case of the longer internuclear distances. The structural characteristics of phosphabenzene are those expected for an aromatic molecule. Semiempirical molecular orbital calculations, adjusted to fit the experimental structure, suggest a small but significant involvement of phosphorus d orbitals in the π bonding.
Viscoelastic effect on the velocity autocorrelation function
Authors: Chow T. S.
Published: February 2004

The velocity autocorrelation function of a hard sphere moving in a simple fluid is derived from hydrodynamic fluctuation theory. The inertia effect causing slow decay at long times has been known. Now, the short time Enskog behavior can be explained adequately by including viscoelastic relaxation. The viscoelastic model so derived agrees well with the molecular dynamic calculations.
Evaluation of configuration coordinate parameters from high pressure optical data. II. Purine and pyrimidine bases and nucleosides
Authors: Okamoto B. Y. , Drickamer H. G.
Published: February 2004

High pressure optical absorption measurements have been made on a series of purine and pyrimidine bases and the corresponding nucleosides in the crystalline state, in neutral aqueous solution, in acidic solution, and in basic solution. The results are discussed in terms of the configuration coordinate parameters as developed in the previous paper. For the crystalline compounds, the purine bases exhibit a volume decrease (Δ) like that of phenanthrene upon excitation. The pyrimidines show slightly smaller contractions. The addition of the ribose group inhibits the volume decrease accompanying excitation. The coupling coefficients β are of the same order of magnitude as those for the crystalline hydrocarbons. In neutral aqueous solution larger volume changes occur upon excitation, and the ribose group is less inhibiting. The substituent effects are significant. In acidic solutions the magnitude of Δ is smaller and that of β is larger than in neutral solutions. The nucleosides show smaller changes from the neutral solution than do the corresponding bases. In basic solution one observed either a small negative Δ or a positive Δ. The ribose group again inhibits the change from neutral solution. Thymine and uracil exhibit very large blue shifts of the peaks with pressure. It is possible that they are doubly ionized.
Temperature dependence of de-excitation rate constants of He(23S) by Ne, Ar, Xe, H2, N2, O2, NH3, and CO2
Authors: Lindinger W. , Schmeltekopf A. L. , Fehsenfeld F. C.
Published: February 2004

Reaction rate constants for the quenching of the 23S state of helium by Ne, Ar, Xe, H2, N2, O2, CO2, and NH3 have been measured as a function of temperature between 300 and 900°K in a flowing afterglow. All of these rate constants increased with temperature. This finding offers an explanation for the discrepancies among recently published values for the reaction rate constant of He(23S) with these gases obtained in different experiments.
Raman studies of molecular reorientation in liquid perchloryl fluoride
Authors: Sunder S. , Hallin K. E. , McClung R. E. D.
Published: February 2004

The contour of the ν6 (E) Raman band of ClO3F liquid has been studied over the temperature range 133–350°K. Isotope splitting, vibrational and instrumental influences on the band shapes were taken into account, and reorientational and angular momentum correlation times were obtained by comparing the corrected Fourier transforms of the band contours with the reorientational correlation functions calculated using the J-diffusion limit of the extended rotational diffusion model. The correlation times are compared with those obtained in the nuclear relaxation study of ClO3F by Maryott et al.
Emission of microwaves by molecules excited by fast passage
Authors: Weatherly T. L. , Williams Quitman , Tsai Foch
Published: February 2004

The emission of microwave radiation associated with the NH3, 3,3 inversion transition and the OCS J = 2→1 rotational transition has been observed. The molecules were excited by a method analogous to fast passage in nuclear magnetic resonance. Details of the method and the nature of the molecular radiation are discussed.
Molecular inelastic neutron scattering: Computational methods using consistent force fields
Authors: Hudson Bruce , Warshel Arieh , Gordon Roy G.
Published: February 2004

Inelastic neutron scattering cross sections for vibrational transitions of molecules are calculated from a knowledge of the eigenvalues and eigenvectors of the vibrational motion which are, in turn, calculated from a knowledge of the molecular potential energy function. In this way, inelastic neutron scattering data may be used as a test of molecular potential energy functions, especially the small nonbonding terms which influence the low frequency motions. In this work the potential energy function of Lifson and Warshel is used in conjunction with the neutron scattering formalism of Zemach and Glauber to calculate neutron scattering spectra for several alkanes. A numerical procedure is used for the orientation averaging. The results are compared to the experiments of Strong and co-workers. It is demonstrated that reliable cross sections and frequencies can be obtained for the low frequency torsional modes of propane, n-butane, and cyclohexane without readjustment of the parameters of the potential function. Reasonable results are also obtained for the branched hydrocarbons isobutane and neopentane which represent an extension of the potential function beyond its original range of applicability. The utility of cross section calculations in vibrational assignments, refinement of the potential function, and prediction of neutron scattering experiments are illustrated. Approximate expressions for the cross sections are given and tested by comparison with the essentially exact numerical methods.
Intramolecular excimer formation in carbazole double molecules
Authors: Johnson G. E.
Published: February 2004

The emission properties of various carbazole ``double'' molecules in solution have been investigated. One compound in particular, namely 1,3-bis(N-carbazolyl) propane, a useful model coumpound for poly(N-vinylcarbazole), has been studied in detail. Both steady state and transient measurements are utilized to determine rate and thermodynamic parameters for the formation of intramolecular excimers. Results on other model coumpounds in which the carbazole groups are symmetrically or unsymmetrically attached to the 1,3 positions of a propane chain are used to offer qualitative insight regarding the geometry of the intramolecular excimer state.
Vibrational reduced partition function of the Morse oscillator
Authors: Ishida Takanobu
Published: February 2004

The anharmonicity correction factor for the vibrational reduced partition function of the Morse oscillator has been numerically evaluated. The effect of anharmonicity on the reduced excitation factor u/(1−e−u) opposes the effect of eux/4, the usual anharmonicity correction. At all levels of anharmonicity, the former correction exhibits its maximum effects near u=4, where its magnitudes are not negligible compared to that of the correction for the zero-point energy factor.
Reorientation of poly-γ-benzyl glutamate liquid crystals in a magnetic field
Authors: Filas Robert W. , Hajdo Leslie E. , Eringen A. Cemal
Published: February 2004

NMR was used to investigate the magnetic reorientation of a nematic mesophase composed of a racemic mixture of poly-γ-benzyl glutamate in dichloromethane. The results are explained quantitatively utilizing the theory of micropolar continuum mechanics as introduced by Eringen.
Molecular properties of excited electronic states: The ã 3A″ and Ã 1A″ states of formaldehyde
Authors: Garrison Barbara J. , Schaefer Henry F. , Lester William A.
Published: February 2004

Ab initio self-consistent-field wavefunctions and molecular properties have been calculated for the three lowest electronic states of H2CO. For the ground state, a variety of basis sets were used, the largest being an uncontracted Gaussian basis: C(11s 7p 2d), O(11s 7p 2d), H(6s 1p). For the excited states, the above basis was contracted to C(7s 5p 2d), O(7s 5p 2d), H(4s 1p). Ground state molecular properties agree well with the earlier theoretical study of Neumann and Moskowitz, and with available experimental data. The z components (along the CO bond axis) of the excited state dipole moments have been measured, and the present a priori predictions reproduce experiment rather closely. Other properties reported include quadrupole moments, octupole moments, and electric field gradients.
Calculation of the total energy in the multiple scattering-Xα method. I. General theory
Authors: Danese J. B. , Connolly J. W. D.
Published: February 2004

The multiple scattering-Xα method has been shown in previous work to be an accurate model for many properties of molecules and solids. However, in certain cases it has been found to be unreliable in determining total energies. This difficulty has been attributed mostly to the implementation of the multiple scattering part of the model rather than to the Xα approximation itself, since the multiple scattering equations are usually solved in the simplified ``muffin-tin'' form. In this paper, it is shown, in general, how one can calculate the error involved in this approximation by means of a procedure which is analogous to first-order perturbation theory and which establishes an upper bound to the exact Xα total energy. Expressions for the corresponding corrections to the one-electron eigenvalues are also derived.
Calculation of the total energy in the multiple scattering-Xα method. II. Numerical technique and results
Authors: Danese J. B.
Published: February 2004

In the previous paper (I) it was shown how in general the error caused by the muffin-tin approximation in the calculation of the Xα total energy could be estimated and could thereby establish an upper bound to the exact Xα energy of a molecular or solid state system. In the present paper (II) we describe the numerical techniques used to evaluate the non-muffin-tin correction to the muffin-tin Xα energy and give the results for two pilot calculations on the C2 and Ne2 molecules. It is found that the NMT correction results in a dramatic qualitative and quantitative improvement in the potential curves of these two molecules.
Rotation and vibration spectra for the H2O dimer: Theory and comparison with experimental data
Authors: Braun Charles , Leidecker Henning
Published: February 2004

The ground state binding energy (BE), rotational and vibrational energy levels, and line strengths for radiative transitions between some of these energy levels are calculated for the [H2O]2 molecule. These quantities are computed for three intermolecular potentials published for the [H2O]2 molecule, two of which were calculated by MO SCF techniques and one which was derived from an empirical point charge model for the water molecule. The value of BE calculated for two of the potentials is approximately 6 kcal/mole, and for the third is approximately 3 kcal/mole. The total concentration of [H2O]2 in equilibrium with H2O vapor is calculated for the sets of energy levels determined for these potentials. Results are compared with available experimental data. Using calculated values of line strengths and experimental data for the integrated absorptions for two rotational transitions, an independent value is deduced for the equilibrium concentration of [H2O]2 in fair agreement with values calculated from two of the intermolecular potentials. The theoretical calculations for BE and the equilibrium concentration of [H2O]2 are also compared with those obtained from analysis of experimental data for the second virial coefficient B2(T) of H2O vapor. The theoretical values for BE bracket the value of 3–4 kcal/mole obtained from analysis of the data for B2(T). A discussion of our results is presented, along with suggestions for experimental work to search for the spectrum of [H2O]2 in the absorption spectrum of H2O vapor.
Characteristic energy losses, luminescence spectra, and their lifetimes for RbI and KI under low energy electron impact
Authors: Huang Timothy , Hamill William H.
Published: February 2004

Evaporated thin films of RbI and KI have been examined at 25–300°K under low energy electron impact. The emission of RbI at 470 nm was excited at 3.8 to 5.4 eV electron energy as well as at the first optical exciton (5.7 eV) and above. The 395 nm band was excited at ≥5.1 eV and possibly below this energy. The lifetimes τ470 and τ395 at 40°K are both 10−5 sec at ≥5.4 eV electron energy while τ395 decreases to 3.5 × 10−7 sec in the range 4.0 to 4.7 eV. τ470 decreases below 5.4 eV to 10−7 sec at 4.4 dV, and is too weak to measure at <4.4 eV. The 400 nm band of KI was excited at 30°K in the range 4.2–5.4 eV as well as at and above the first optical exciton, 5.8 eV. The 294 nm band of KI and the 315 nm band of RbI were excited principally at and above the region of the step, 6.2 and 6.0 eV, respectively. The lifetimes of the 376 nm band of KI in the range 25–80°K were the same for 4.7 and 6.2 eV electron energy, below and above the first optical exciton energy. For each system the evidence indicates that the low energy emitters can be excited directly. The small Stokes shifts approximate those expected for cubic relaxation. Population of lower energy emitting states from other states lying below the first optical exciton may be responsible for lifetimes anomalies.
Semiclassical treatment of atom-asymmetric rotor collisions; rotational excitation of formaldehyde at low energies
Authors: Augustin Stuart D. , Miller William H.
Published: February 2004

The formalism necessary for the application of ``classical S-matrix'' theory to collisions of an atom with a rigid asymmetric rotor is derived. This is applied to rotational excitation of formaldehyde by H2 (taken to be spherically symmetric) at energies from 10 to 15°K. Classical Monte Carlo trajectory calculations were also carried out for the same system in the energy range 10–40°K. The results support the proposal of Townes and Cheung that a collisional mechanism is responsible for the 111 →110 anomalous absorption of formaldehyde in cool interstellar dust clouds.
Raman spectra of NH4Cl and NH4Br: Dependence of the librational and the internal modes of the NH4+ ion on volume and on nitrogen-halogen distance
Authors: Ebisuzaki Y.
Published: February 2004

The wavenumbers for the librational and the high frequency modes in the ``disordered'' NH4Cl and NH4Br were obtained from polarized Raman spectra with values for unresolved peaks determined by fitting the Raman intensity to damped uncoupled oscillators. The high frequency and the librational modes were studied isothermally (296 K) as a function of volume or of nitrogen-halogen distance over a decrease in distance of 4.4% in NH4Cl and 5.0% in NH4Br. The librational frequency increases with decrease in volume in both halides with anharmonicity being given by the Grüneisen constants (γ6): 1.30 (``disordered'' NH4Cl V); 0.29 (ordered NH4Cl IV); 0.72 (``disordered'' NH4Br II) and 0.46 (NH4Br V). The volume dependence of the librational motion does not show the behavior expected for a motion in a simple potential. The internal modes of the NH4+ ion are insensitive to phase transition in both halides but depend to a small degree on internuclear distance; for example, the Grüneisen constants for NH4Br are: γ1 =(negative); γ2=+0.022; γ3=−0.036; γ4(TO)=−0.044, and γ4(LO)=−0.065. These interesting results on the internal modes provide direct evidence that anharmonic effects which can be attributed to strong proton-halogen coupling or hydrogen bonding effects are present in NH4Cl and NH4Br.
Laboratory studies of negative ion reactions with atmospheric trace constituents
Authors: Fehsenfeld F. C. , Ferguson E. E.
Published: February 2004

A flowing afterglow system has been used to measure 296°K reaction rate constants and equilibrium constants for a number of negative ion reactions with atmospheric constituents. Three-body association reactions of O−, OH−, O2−, O3−, Cl−, CO3−, OH−(H2O), and O2−(H2O) with H2O have been measured and association rate constants for several ions with CO2 and SO2 have been measured. A number of binary reactions for these ions and their hydrates have been measured with H2O, CO2, SO2, NO2, O3, and NO. Some equilibrium constants for negative ion hydration and some equilibrium constants for solvent (H2O, CO2, and SO2) exchange to several negative ions are reported.
On symmetry properties of reaction coordinates
Authors: Metiu Horia , Ross John , Silbey Robert , George Thomas F.
Published: February 2004

We discuss relationships between reaction coordinates, normal coordinates, and symmetry coordinates, defined at an arbitrary point on an adiabatic energy surface. Using simple group theoretical arguments, we prove that the points representing nuclear configurations with symmetry elements other than the identity element are located in valleys (or on ridges or shelves; all abbreviated as BGV) of the adiabatic electronic energy surface. We illustrate with examples complexities such as the bifurcation of a BGV or a transition from a valley into a ridge, for which motion along the reaction coordinate is not totally symmetric at every point, nor is the symmetry of nuclear configuration necessarily conserved during the reaction.
Vacuum ultraviolet fluorescence from photodissociation fragments of O2 and N2
Authors: Lee L. C. , Carlson R. W. , Judge D. L. , Ogawa M.
Published: February 2004

The vacuum ultraviolet fluorescence from the atomic photofragments of O2 and N2 produced by extreme ultraviolet excitation has been investigated and their production cross sections measured. The processes were studied using synchroton radiation, in the λλ175–780 Å region, to excite the gases. The nature of the fluorescence spectrum in the wavelength range λλ1050–1800 Å was studied by using a combination of optical and gaseous filters. The dependence of the intensity of the fluorescence radiation on the gas pressure was studied in order to determine the relative contributions from direct excitation and photoelectron excited emissions. Direct excitation processes were verified to be the primary contributor, particularly at low pressures. In the incident wavelength range λλ200–350 Å, the cross sections for the production of fluorescence for each gas shows a broad band, which is presumably produced by dissociative ionization processes. In the longer wavelength region, discrete structure was observed at the positions of known Rydberg series. These features are the result of the interaction of dissociation continuum states with bound states. Photodissociation continua were also observed in the λλ400–780 Å region.
Theoretical studies in photoelectron spectroscopy: Use of angular distribution data to deduce molecular orbital parameters. II. Calculation the angular distributions for electrons ejected from molecules of selected symmetries
Authors: Ritchie Burke
Published: February 2004

The theory of the angular distribution for molecular photoionization resulting in ejection of energetic electrons, previously formulated for the case of linear, nonpolar molecules, is extended to the case of molecules of any geometry. Calculations are performed for the angular distributions of electrons ejected from molecules of the following symmetries: C3ν (distorted CH4 as an example of a nonlinear, polar molecules), D3h (planar CH3 as an example of a nonlinear, nonpolar molecules), and Td (CH4 as another example of a nonlinear, nonpolar molecules). The initial molecules orbitals are represented as symmetry orbitals in the LCAO form, re-expanded about the carbon atom. These orbitals are in parametrized form such that the features of the angular distributions can be related to selected parameters. The ejected electron is assumed to move in a multicenter screened Coulomb field, and the set of coupled differential equations which describe its motion relative to the distance from the carbon atom is solved by consecutive use of the distorted-wave Born and Coulomb-Born approximations. At this level of approximation the effects of the molecular ionic field on the motion of the ejected electron are calculated to first order in perturbation theory, where the zeroth order motion is motion in the Coulomb potential of unit strength relative to the carbon atom. The features of the angular distribution are found to be quite sensitive to the symmetry of the molecule and therefore to molecular orbital parameters and multiplet splittings.
Light scattering of spheroids. II. Angular dispersion and dissymmetry of light scattering
Authors: Nakagaki M. , Heller W.
Published: February 2004

The angular variation of spheroid scattering is investigated as a function of spheroid volume (or molecular weight), axial ratio, and relative refractive index using equations given recently by the authors. On using visible radiation, the limiting largest dimension of spheroidal bodies is defined by 1500–2000 Å. This corresponds to a molecular weight of 106–108, the pertinent order of magnitude depending on the axial ratio of the spheroids. Results are given for the σσ, ππ, and πσ=σπ components of polarized light. Regularities for unpolarized light can easily be computed using previously given relations. The dissymmetries of light scattering are discussed for the same components. Several methods are proposed for the utilization of the results in order to determine simultaneously the volume of rigid compact particles—or the molecular weight of macromolecules—and the physical dimensions parallel and perpendicular to the symmetry axis of prolate or oblate spheroidal bodies.
Semiclassical collision theory. Multidimensional integral method
Authors: Kreek H. , Marcus R. A.
Published: February 2004

Numerical results on the integral expression for the semiclassical S matrix are compared with exact quantum results for a multidimensional problem. The collision of a rigid rotor with an atom is treated. The integral method proves to be easy to apply. Within its range of maximum validity (no sign changes in the pre-exponential factor of the semiclassical wavefunction) the agreement was typically within 20%. When sign changes occurred, the agreement was about a factor of 2 or better. Conditions affecting sign changes are described.
The application of time correlation functions to chemical kinetics and vibrational relaxation
Authors: Kutz H. Douglas , Oppenheim Irwin , Ben-Reuven Abraham
Published: February 2004

Linear response theory is used to obtain an expression for the chemical relaxation rate in terms of the time integral of a correlation function. The important quantity is the time derivative of the progress variable. This expression is evaluated in the finite-temperature Green function representation. The familiar cross-section expression for the rate constants is obtained. A similar theory for vibrational relaxation in dilute gases is presented.
Semiclassical three-dimensional inelastic scattering theory
Authors: Sorensen Gert Billing
Published: February 2004

A semiclassical theory, which does not involve the use of complex trajectories or multidimensional root-searching, is presented. For a linearly forced harmonic oscillator the number of coupled equations to be solved is halved. The rotation-vibration coupling term is discussed and taken into account.
A theoretical evaluation of the effect of photoselection on the measurement of the circular polarization of luminescence
Authors: Steinberg I. Z. , Ehrenberg B.
Published: February 2004

The orientation of molecules excited by a beam of light is not isotropic as a rule. If rotatory Brownian motion is not fast during the lifetime of the excited state the polarization properties of the light emitted from the excited molecules will depend as a rule on the mode of photoselection of the molecules by the excitation beam. A general theoretical method is developed for proper weighting in the process of summing of the contributions of the various photoselected molecules to the emitted light when Brownian rotational motion is frozen. A formula is obtained for the calculation of the probabilities of emission of light of a specified polarization from the photoselected system. To use this formula average values of multiples of elements of the Euler matrix are to be evaluated first; the polarization properties of the emitted light are then obtained by insertion of the components of the electric and magnetic transition dipole moments characterizing the absorption and emission of light by the molecule under discussion. By use of this formula, the Perrin-Jablonski formula for the linear polarization of emitted light is derived in a simple fashion. It is shown that for asymmetric molecules the degree of circular polarization of the emitted light is affected by photoselection if the electric transition moments responsible for absorption and emission are not parallel. It is of much interest that under such circumstances the angle between the emitting electric and magnetic dipole moments can in principle be obtained.
Electron reactions in EG/H2O glass. Temperature dependence
Authors: Steen Harald B.
Published: February 2004

The decay of x-ray-induced et− in glycol-water glass and the reduction of G(et−) by various scavengers have been studied as functions of the temperature. The decay of et− was independent of temperature from 77 to 113 K as expected if the reaction occurs primarily by electron tunneling. The reduction of G(et−), however, decreased significantly with increasing temperature in the same region, the temperature dependence being larger for less efficient scavengers. The results are qualitatively accounted for by the assumption that a significant fraction of the electrons react prior to formation of stable traps, viz. from shallow, transient traps.
On the mechanism for collisional deactivation of vibrationally excited singlet molecular oxygen
Authors: Parker J. G. , Ritke D. N.
Published: February 2004

In order to study in more detail the mechanism involved in the collisional deactivation of singlet molecular oxygen excited to the first vibrational level by means of laser irradiation, measurements of both amplitude and phase of the resultant acoustic pressure signal were measured as a function of frequency for 35 atm pure oxygen and a mixture containing 1 atm He and 34 atm O2. All significant features of the experimental data may be explained theoretically by assuming that the only significant deactivation paths are (a) a vibrational deactivation O2(1Δg) (ν′ = 1→0) followed by an electronic deactivation O2(1Δg) (ν′=0) → O2(3Σg−) (ν=0); and (b) an electronic deactivation O2(1Δg) (ν′=1) → O2(3Σg−) (ν=1) followed by the vibrational step O2(3Σg−) (ν=1→ 0).
Far-infrared relaxation in the isolated formic acid dimer molecule: Possibility of fast proton tunneling in a hydrogen bond
Authors: Rothschild Walter G.
Published: February 2004

The band contours of the far-infrared hydrogen bond stretching fundamental of the low-pressure vapors of the ring dimer molecules of (HCOOH)2 and (HCOOD)2 were measured and Fourier inverted. The resulting dipole correlation functions decay appreciably faster than those of the vibrational fundamentals not directly involved in hydrogen bonding, such as the C–H stretching and deformation modes of the molecules. However, it is shown conclusively that proton tunneling in the hydrogen bonds of the isolated dimer molecule is not the cause of the band broadening and, if proton tunneling occurs at all, it must have an inversion rate considerably slower than 1012 sec−1.
Determination of solute properties by vapor pressure measurements of the solvent in dilute solutions
Authors: Amdur S.
Published: February 2004

Minor decreases in the vapor pressure of water in solution were accurately determined using a newly established method. The decreases were found to be linear with solute concentration in the range 0.02–0.1 molal. A slope for the decrease of vapor pressure for one molal solutions based on single particles was calculated and compared with the slope generally expected according to Raoult's law. The differences were found to be proportional to the charge and radius of the solute particles. An experimental rule was formulated. It provides a good fit for electrolytes, nonelectrolytes, and polyelectrolytes. The results are interpreted according to a standard state, P°i, for the vapor pressure of each solution at 10−3 molal. It is assumed that the solution obeys Raoult's law in the range 10−3−10−1 molal, substituting P°i for the vapor pressure of water. P°i is smaller than P° by about 0.2% for electrolyte and 1.5% for polyelectrolyte solutions.
Deuterium isotope effects in zero-field splittings of oriented triplet states of 1,2;5,6-dibenzanthracene, phenanthrene, and naphthalene
Authors: Cullick A. S. , Gerkin Roger E. , Thorsell David L. , Winer Arthur M.
Published: February 2004

Changes in the zero-field splitting parameters of phosphorescent 1,2;5,6-dibenzanthracene, phenanthrene, and naphthalene oriented in single-crystal hosts have been determined at temperatures near 77°K upon perdeuterating the phosphorescent molecules, the host molecules, or both. Through control and determination of appropriate experimental variables these changes have been shown to arise strictly from the isotopic substitution. For the naphthalene-biphenyl and phenanthrene-biphenyl systems readily measurable changes were observed upon isotopic substitution of either guest or host molecules. The data support the distinction of ``guest'' and ``host'' isotopic effects for zero-field splitting parameters, but definitive analysis of the origin of these effects awaits further work.
Reactions between isotopically labeled N2+ and N2 for primary ion energies below 45 eV
Authors: Maier William B.
Published: February 2004

Apparent cross sections for electron transfer between N2+15 and 14N2 and for the reactions (1) N2+ + N2 → N3+ + N, and (2) N2+ + N2 → N+ + N + N2 have been measured, with the primary ion and target molecules isotopically labeled. The laboratory kinetic energies E of N2+ are between 3 and 45 eV. The effect of excited states of N2+ is studied. Reactions (1) and (2) proceed both by processes which involve dissociation of the primary N2+ and by processes which involve dissociation of the target N2. Processes which involve dissociation of the primary ion are favored, and even more so when the primary N2+ is excited by ∼8.5 eV to unidentified, long-lived states. The isotopic composition of the reactants influences Reactions (1) and (2) significantly; these isotopic effects may be caused by kinematic phenomena. It is suggested that Reaction (1) proceeds via stripping processes which convert most of the reactants' kinetic energy into internal energy of the N3+ and/or N products. Reaction (2) may proceed either through the formation and disintegration of excited N3+ or through some unidentified mechanism. A survey of the available information on N2+ suggests that the production and lifetimes of the various states of N2+ may now be well-enough known to permit detailed comparisons between theory and experiment.
Molecular beam electric resonance study of the molecular Zeeman spectrum of lithium chloride
Authors: Freeman Richard R. , Johnson David W. , Ramsey Norman F.
Published: February 2004

A high resolution study of the molecular Zeeman spectrum of lithium chloride in the first rotational state (J = 1) and various isotopic and vibrational (ν) states has been performed using a molecular beam electric resonance apparatus which includes an external electromagnet for the resonance region. By fitting the observed resonance lines to an appropriate molecular Hamiltonian, the values of the rotational magnetic moment (gJ), the nuclear shielding anisotropies for chlorine (σTCl) and lithium (σTLi), and the molecular magnetic susceptibility anisotropy (ξT) were determined for each state. The values of these constants obtained are as follows (numbers in parentheses are the uncertainties in the final figures): Molecule (state)gJ (nuclear magnetons)σTCl (ppm)σTLi (ppm)ξT (10−30erg/G2)Li7Cl35 (J = 1, ν = 0):+ 0.100419(31)− 184(27)− 36(14)+ 2.52(25)Li7Cl35 (J = 1, ν = 1):+ 0.100642(80)− 301(83)− 42(52)+ 2.04(27)Li7Cl37 (J = 1, ν = 0):+ 0.101336(40)− 253(100)− 74(37)+ 3.13(30)

The resonances were obtained in the low electric field limit by making explicit use of the motional electric field experienced by the molecules in the magnetic field of the resonance region. The motional field Stark shift is also used to calibrate the velocity selection properties of the quadrupole state selectors.
Vibrational relaxation in the A1A′(1B1) electronic state of 4-methyl-1,2,4-triazoline-3,5-dione
Authors: Pocius Alphonsus V. , Yardley James T.
Published: February 2004

The fluorescence decay rate from selected vibronic levels of the A1A′(1B1) excited electronic state of 4-methyl-1,2,4-triazoline-3,5-dione has been examined as a function of added inert gas pressure. A simple, physically reasonable model is presented from which vibrational relaxation rates may be explicitly determined. The relaxation rate constants have been found to be 6.3×105 Torr−1 sec−1 for collisions with helium, 7×105 Torr−1 sec−1 for argon, 2.5×106 Torr−1 sec−1 for CCl4, 15×105 Torr−1 sec−1 for O2, and 75×105 Torr−1 sec−1 for cyclohexane.
Forbidden transitions in the emission spectrum of atomic aluminum
Authors: Wei P. S. P. , Tang K. T. , Hall R. B.
Published: February 2004

The emission spectra of species evaporated by a laser pulse from an alumina surface in air have been studied. In addition to the well-known spectrum of Al, several groups of weak and forbidden lines are identified. The spatial distribution of line intensity and the Stark shifts have been measured. The results are discussed in connection with the plasma shielding effect in laser-solid coupling and the reduction of aluminum by a high-temperature method. A weak doublet of lines is tentatively attributed to a transition involving the 3s 3p2 2D state.