bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser excited Raman spectrum of 1,1,1-trifluoro-2,2,2-trichloroethane
Authors: Krishnaji  , Kumar Laloraya Rajendra
Published: February 2004

Laser excited Raman spectra of 1,1,1-trifluoro-2,2,2-trichloroethane have been studied in detail using laser sources, and new data have been obtained. The spectra show eight new Raman bands. Out of these eight bands one band at 659 cm−1 (ρ≃0) has been assigned as the CF3 deformation fundamental vibration of species A1. The other bands at 61, 92, 202, 232, 287, 476, and 518 cm−1 have been interpreted as combinations of the assigned fundamentals. The Raman band at 61 cm−1 (ρ≃0.43), being interpreted as 2×ν6=61 cm−1 (A1), predicts a value of 30.5 cm−1 for the torsional frequency of this molecule, which corresponds to a cosine potential barrier of aproximately 1260 cal/molecule.
Gaussian basis configuration interaction calculations on twenty electronic states of H3+. A bound Σu+3 excited level
Authors: Schaad L. J. , Hicks W. V.
Published: February 2004

Configuration interaction calculations with a Gaussian basis were carried out on the lowest five states of each symmetry 1A′, 3A′, 1A″, and 3A″ for H3+. All geometries with bond lengths between 1.2 and 3.6 a.u. were examined. Other than the ground state, only the 1 3A′ surface contained a stable state. This is a linear symmetric Σu+3 level with energy equal −1.11422 a.u. and bond lengths of 2.457 a.u. It is stable by only 6.47 kcal/mole with respect to dissociation to H2+ (X2Σg+)+H(1s). The state is computed to have vibrational frequencies of 1191 cm−1 (symmetric stretch), 683 cm−1 (asymmetric stretch), and 775 cm−1 (degenerate bend).
Laser magnetic resonance study of the gas phase reactions of OH with CO, NO, and NO2
Authors: Howard Carleton J. , Evenson K. M.
Published: February 2004

A laser magnetic resonance spectrometer has been used in combination with a discharge-flow system to measure the gas phase reaction rates of the OH radical with CO, NO, and NO2 at 296°K and over a pressure range 0.4–5 torr. For the bimolecular reaction OH + CO → CO2 + H we measure a rate constant, k = 1.56×10−13 cm3/molecule·sec. For the termolecular reactions OH + NO + M → HNO2 + M, M = He, k = 4.0×10−31 cm6/molecule2·sec; M = Ar, k = 4.4×10−31 cm6/molecule2·sec; M = N2, k = 7.8×10−31 cm6/molecule2·sec. For the reaction OH + NO2 + N2 → HNO3 + N2, k = 2.9×10−30 cm6/molecule2·sec. Laser magnetic resonance detection of radicals is shown to be extremely sensitive, linear, and versatile. A complete description of this technique is presented with a discussion of its potential in the study of the reactions of free radicals.
Raman spectrum of HDO in rare earth perchlorate solutions
Authors: Gutierrez L. , Mundy W. C. , Spedding F. H.
Published: February 2004

Raman data were obtained of the OD stretching vibrations of HDO at 23.0±0.5°C in nine or 10 concentrations of aqueous La(ClO4)3, Gd(ClO4)3, and Lu(ClO4)3 solutions in which the total water content was about 5 mole% D2O. The rare earth salt concentration was varied from approximately 0.25 to 4.0 or 4.5m. A differential analysis technique, previously reported, was used to identify and to correlate changes in the frequency distribution of the OD band with water molecules that are being diversely affected by the rare earth salt ions. At least four general types of water molecules are discernible in solution at various salt concentrations. In dilute solutions, cation-affected, anion-affected, and unaffected free water molecules are clearly distinguished, whereas at high perchlorate salt concentrations water molecules associated with ion pairs are also identified. In addition, results are presented to indicate that the La3+ cation affects water somewhat differently than do either the Gd3+ or Lu3+ cations, and this is interpreted as reflecting a difference in the hydration number between these RE3+ cations.
Normal coordinate analysis of potassium and rubidium fluoaluminates
Authors: Soga T. , Ohwada K. , Iwasaki M.
Published: February 2004

Infrared absorption spectra of alkali fluoaluminate crystals MAlF4 (M: K and Rb) have been measured in the frequency region from 4000–30 cm−1. Both the intramolecular vibrations such as the Al–F bond stretching and the F–Al–F bending vibrations and the lattice vibrations due to the interaction between the inner complex and the outer ions have been observed in the frequency regions of 800–160 cm−1 and below 160 cm−1, respectively. A normal coordinate analysis of the crystal as a whole has been carried out on the basis of a simple valence force field. The force constants of the Al–F stretching, F–Al–F bending, and M · · · F interaction have been obtained and discussed in relation to the interatomic distances. It has also been found that the simple valence force field assumed here is adequate for these complex fluorides.
Improved potentials for Ne + Ar, Ne + Kr, and Ne + Xe
Authors: Ng C. Y. , Lee Y. T. , Barker J. A.
Published: February 2004

Improved interatomic potentials for Ne-rare gas pairs have been obtained by fitting a multiparameter potential to low energy differential cross sections, second virial coefficients, and diffusion coefficients. All asymmetric Ne-rare gas potentials have narrower attractive wells than those of the symmetric rare gas pairs. The values of rm and ε for Ne+Ar, Ne+Kr, and Ne+Xe are 3.43 Å, 71.9°K; 3.58 Å, 74.5°K; and 3.75 Å, 75.0°K, respectively.
Restrictions on the potential and cross section for collisions between rigid rotors
Authors: Biolsi Louis
Published: February 2004

A restricted distorted-wave treatment of the total cross section when two rigid diatomic molecules with orbital and nuclear spin angular momenta collide is examined. There are certain restrictions on the intermolecular potential and on the possible combinations of the various quantum numbers. These restictions are examined for the lowest order nonspherical elastic and the lowest order inelastic contributions to the total cross section. The effects of degeneracy averaging and of collisions between indistinguishable molecules are also briefly examined.
Analysis of autoionizing Rydberg states in HI and CH3I. Comments on Rydberg electron wavefunctions
Authors: Tsai Bilin P. , Baer Tomas
Published: February 2004

Three Rydberg series, n s, n p, and n d, converging to the 2E1/2 and 2Φ1/2 states of CH3I+ and HI+, respectively, are identified on the basis of their photoionization spectra. Splittings observed in the Rydberg peaks of CH3I are attributed to an interaction of the Rydberg electron with the quadrupole moment and polarization of the ionic core. Three one-electron wavefunctions for the Rydberg orbital were investigated to determine the effect of the quadrupole moment on the Rydberg energy levels.
Merging beams studies of Na, K, and Mg collisions with atmospheric ions
Authors: Rol P. K. , Entemann E. A. , Wendell K. L.
Published: February 2004

Ion-molecule reactions between Na, K, and Mg and some atmospheric molecular ions have been studied at relative energies between 0.05 and 10 eV using a merging beams apparatus. In all cases the exothermic reactions proceed via stripping mechanisms and the endothermic reactions proceed via rebound mechanisms. The absolute cross sections for some of the reactions have been measured. It was possible to determine D°0 (Na+−O) = 0.8 ± 0.3 eV and D°0 (K+ − O) = 0.3 ± 0.3  eV from the energy dependence of the cross sections for the reactions of Na and K with CO+. Some details of the merging beams technique are discussed.
Analytical Hartree-Fock functions for positive ions from lithium to xenon
Authors: Roetti Carla , Clementi Enrico
Published: February 2004

Analytical wavefunctions in the Hartree-Fock approximation are computed with Slater type functions for the ground state of the lowest electronic configuration for the first positive ions from Li+ (Z = 3) to Xe+ (Z = 54). Only the computed total energies are reported here and discussed (however, the basis sets, the expansion coefficients, and the orbital energies are made available elsewhere).
Far infrared ring puckering vibration of 3,3-difluoroxetane: Effect of fluorine substitution on the ring puckering potential
Authors: Pringle Wallace C. , Meinzer A. L.
Published: February 2004

The far infrared spectrum of the ring puckering vibration of 3,3-difluoroxetane has been observed and the potential determined to be V(Z) = 0.644×104Z2 + 0.425×106Z4 cm−1, where Z is in angstroms. The reduced mass for the vibration is 151 amu. From the vibrational dependence of the rotational constants, the dynamics of the ring vibration are found to shift from 1.5 times more bending about the C–O axis in trimethylene oxide to 1.5 times more bending about the C–C axis in difluoroxetane. An analysis of the changes in the barrier to inversion in cyclobutane, 1,1-difluorocyclobutane, trimethylene oxide, and difluoroxetane is based on the assumption of a model potential. The model potential for the ring puckering vibration is approximated as the sum of angle deformations and torsions about the ring bonds with a ``torsional strain'' parameter included which is analogous to the angle strain contribution to the deformation. Using literature values for the unstrained threefold contribution to the potential, the torsional strain contribution is found to decrease by 1.9±0.1 kcal mole−1 with difluoro substitution on both cyclobutane and trimethylene oxide.
``Quantization'' in macroscopic chemical systems
Authors: Hanson M. P.
Published: February 2004

Open spherically symmetric systems of chemical reactions are shown under appropriate conditions to exhibit time independent inhomogeneous concentration profiles. The form of the concentration profiles is characterized by a set of five ``quantum'' numbers and the radius of the system. The first four quantum numbers are analogues of the quantum numbers of a hydrogen atom electron. The fifth quantum number is new. The effect of varying the radius of the system for two different sets of conditions is examined. An analogy with mitotic cell division is drawn for one of the sets of conditions.
CI calculations for the inversion barrier of ammonia
Authors: Stevens Richard M.
Published: February 2004

CI calculations have been performed for the planar and pyramidal forms of ammonia using a near-Hartree-Fock basis set of STO's. Full single and double excitation valence Cl shows that the correlation energy for the barrier is small, less than 0.5 kcal/mole, a result in agreement with experiment. Several more approximate methods were found to yield similar results; however, the first-order wavefunction method gave a result of 2.5 kcal/mole for the correlation energy of the inversion barrier. Fully optimized SCF and CI calculations were also performed for minimum basis sets: In this case it was found that the CI results were much worse than the SCF.
van der Waals interactions of carbon dioxide
Authors: Pack Russell T
Published: February 2004

van der Waals C6 coefficients for the interaction of CO2 with CO2, He, Ne, Ar, Kr, Xe, H2, N2, O2, H, Li, Na, K, Rb, and Cs are calculated using Padé approximants and experimental frequency-dependent polarizabilities α(ω). The tightness of the error bounds and accuracy of the results is increased dramatically by treating the infrared contributions to α(ω) of CO2 separately. The use of formulas involving finite linewidths (damping factors) is discussed and found to be useful in fitting the infrared terms to α(ω) but to have negligible effect on the C6 coefficients.
Measurements of ion-molecule reactions of He+, H+, and HeH+ with H2 and D2
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2004

A drift tube-mass spectrometer apparatus has been used to determine the rate coefficient, energy dependence, and product ions of the reaction He+ + H2. The total rate coefficient at 300 K is (1.1±0.1)×10−13 cm3/sec. The reaction proceeds principally (80%) by dissociative charge transfer to produce H+, with the small remainder going by charge transfer to produce H2+ and by atom rearrangement to produce HeH+. The rate coefficient increases slowly with increasing ion mean energy, reaching a value of 2.8×10−13 cm3/sec at 0.18 eV. The corresponding reaction with deuterium, He+ + D2, exhibits a value (5±1)×10−14 cm3/sec at 300 K. The reaction rates for conversion of H+ and HeH+ to H3+ on collisions with H2 molecules are found to agree well with results of previous investigations.
Electron repulsion integral approximations and error bounds: Molecular applications
Authors: Jafri J. A. , Whitten J. L.
Published: February 2004

In a previous study of Coulombic potential energy integrals, an approximation theory was discussed which led to rigorous error bounds on the difference between exact integrals and proposed approximations. The simple structure of the bound provides a favorable context for introducing approximations of two-particle electron repulsion integrals which occur in molecular structure theory. Studies of the ethylene and pyridine molecules are reported in an investigation of the utility of the approximations. Comparisons of exact and approximate integrals and theoretical error bounds and analysis of entire integral distributions are presented. Ground state SCF total energies, orbital energies, and molecular orbitals show excellent agreement with the results of computations using exact integrals.
Measurement of a continuous distribution of spherical particles by intensity correlation spectroscopy: Analysis by cumulants
Authors: Bargeron C. B.
Published: February 2004

This paper presents the measurement and analysis of a continuous distribution of spherical particles by intensity correlation spectroscopy. The method of cumulants is used for the analysis. The first three cumulants are calculated and compared for Gaussian and rectangular distributions of particle sizes. The method is used to characterize a continuous distribution of polystyrene latex spheres (PSL). The results of these light scattering measurements are compared to electron microscope data for the same sample of PSL. The results agree with each other to within the experimental error.
Ion-atom interchange reactions using isotopic species
Authors: Fehsenfeld F. C. , Albritton D. L. , Bush Y. A. , Fournier P. G. , Govers T. R. , Fournier J.
Published: February 2004

Isotopically labeled species, D+, 15N+, and 18O+, have been used to study ion-atom interchange reactions at room temperature and, the case of D+, at lower temperatures. The use of isotopes permits the investigation of interchange reactions involving otherwise identical atoms. The implications of these measurements for reaction kinetics are discussed.
Equilibrium OH− + C2H2 ⇄ C2H− + H2O and the determination of Δ H°f,298 (C2H−)
Authors: Bohme D. K. , Mackay G. I. , Schiff H. I. , Hemsworth R. S.
Published: February 2004

The kinetics of the proton transfer reaction OH− + C2H2 ⇄ C2H− + H2O have been investigated at 296°K with the flowing afterglow technique. The rate constants were determined to be kforward = (2.2±0.4) × 10−9 cm3 molecule−1 sec−1 and kreverse = (9.3±3.7) × 10−15 cm3 molecule−1 sec−1. The ratio of rate constants, kf/kr = (2.4±1.0) × 105, was found to be in agreement with the equilibrium constant, K = (2.5±1.0) × 105, determined from equilibrium concentrations. The best estimate of the true value of K corresponds to a standard free energy change, ΔG°296, of −7.3±0.2 kcal mole−1. An estimate of the standard entropy change, ΔS°298, of +3.6 cal deg−1 mole−1 leads to a standard enthalpy change, ΔH°298, of −6.2±0.5 kcal mole−1 and a value for ΔH°f,298 (C2H−) = 71.5±1.1 kcal mole−1. O− was observed to react rapidly with C2H2, k=(2.0±0.4) × 10−9 cm3 molecule−1 sec−1, principally by associative detachment and proton transfer. The reaction of O2− with C2H2 was observed to be slow, k ≤ 1 × 10−12 cm2 molecule−1 sec−1.
Improved modified wavenumber approximation applied to elastic collision
Authors: Nanbu K.
Published: February 2004

A method to improve the usual modified wavenumber result is applied to an elastic collision problem. For an exponential repulsive potential, simple expressions for the phase shift are obtained. The partial cross sections obtained by this improved modified wavenumber approximation agree qualitatively with those of the exact numerical solutions. The total cross sections agree very well with the exact results.
Fine structure of the metastable a3Σu+ state of the helium molecule
Authors: Lichten W. , McCusker M. V. , Vierima T. L.
Published: February 2004

We have measured the spin—spin, electronic fine structure of the a3Σu+ metastable state of He2 by means of a molecular beam, magnetic resonance apparatus, with the flowing afterglow of a pulsed, helium discharge as the source. The zero field separations in the N=1 and N=3 rotational levels, probably in the ν=0 vibrational state, are (in MHz) N=1; J=0 ↔ J=1:2199.968 ± 0.01, J=1 ↔ J=2: 873.668 ± 0.0007; N=3: J=2 ↔ J=3: 1323.911±0.006, J=3↔J=4: 964.992±0.006, where the errors quoted are three standard deviations of the mean. From these measurements and from a separate determination of the level order, the interaction constants for these states are the following (in MHz): spin—spin: λ:−1098.773 ±0.005(N=1), −1096.803±0.004(N=3), spin-rotation: γ: −2.421±0.003(N=1), −2.414±0.001(N=3), where the errors are 3σ.
Relation between self-diffusion coefficients and interdiffusion coefficients in methanol-carbon tetrachloride and ethanol-carbon tetrachloride systems
Authors: Oishi Y. , Kamei Y. , Sumie H.
Published: February 2004

Darken's binary diffusion equation was tested between interdiffusion coefficient and self-diffusion coefficients for thermodynamically nonideal methanol-carbon tetrachloride and ethanol-carbon tetrachloride systems in which molecular association of the alcohols is known to occur. When the thermodynamic factor was calculated from equilibrium vapor pressures, Darken's equation did not hold for the two systems, but the thermodynamic factor approximately calculated from the mean degree of association of the alcohol better satisfied the equation for the systems within the low alcohol concentration range. Self-diffusion coefficients of the respective components necessary for the present testing were measured for the methanol-carbon tetrachloride system at 25°C. By assuming Darken's relation, mean degrees of association of the alcohols were reversely calculated for the high alcohol concentration range of the two systems.
Depolarized Rayleigh scattering in liquids. Molecular reorientation and orientation pair correlations in a nematic liquid crystal: MBBA
Authors: Gierke T. D. , Flygare W. H.
Published: February 2004

The spectrum and intensity of depolarized light scattered from binary solutions of the nematic MBBA and carbon tetrachloride have been measured. The results are interpreted in terms of pair correlations in the orientation of MBBA molecules. A systematic approach to the study of the orientational structure in nematic liquid crystals is proposed.
Zero field magnetic resonance of photoexcited triplet state species in naphthalene crystals and proton hyperfine structure
Authors: Hutchison Clyde A. , Scott Gary W.
Published: February 2004

We have investigated the microwave magnetic resonance absorption spectra produced at zero external magnetic field and ∼1.7°K by Hg–Xe arc irradiation of host naphthalene-d8 crystals with and without added guest naphthalene-h8 and also by irradiation of host naphthalene-h8 crystals with and without guest naphthalene-d8. We have measured the values of the zero field energy splittings of the three components of the lowest energy triplet states for the naphthalene-h8 guest molecule in naphthalene-d8 host, for naphthalene-h8 X-traps in naphthalene-h8 host crystals with and without added naphthalene-d8 guest, and for naphthalene-d8 X-traps in naphthalene-d8 host crystals with and without added naphthaplene-h8 guest. We have determined the zero field line shapes and proton hyperfine structures for these various triplet species and find them to be in excellent quantitative agreement with our exact calculations for these systems. We have given a detailed discussion of our identification of the various triplet state species reported here.
Calculation of electric field gradients, electric fields, diamagnetic shieldings, dipole moment, second moment, and diamagnetic susceptibility of BH3NH3
Authors: Dixon Maurice , Palke William E.
Published: February 2004

The electric field gradient tensors at each of the four distinct nuclei of BH3NH3 have been calculated from ab initio LCAO MO SCF wavefunctions constructed from a minimal basis set of STOs. In total 22 geometries have been examined of which 11 were eclipsed and 11 were staggered. From the equilibrium geometry the B–N bond length was expanded by 0.1 and 0.2 bohr, the B–H and N–H bond lengths were expanded and contracted by 0.1 bohr, and the ∠BNH and ∠HBN bond angles were increased and decreased by 5°. The values of 0.249 a.u. at HB, 0.387 a.u. at HN, 0.194 a.u. at B, and −0.765 a.u. at N have been calculated for the largest component of the electric field gradient tensor in the principal axis representation. The electric field, the diamagnetic shielding, the dipole moment, second moment tensor, and the diamagnetic susceptibility have been calculated as well.
Off-diagonal contribution to the hyperfine anisotropy of vanadyl and chromyl complexes
Authors: Narayana P. A. , Gogan N. J.
Published: February 2004

The off-diagonal contribution involving the central ion and ligand orbitals to the hyperfine anisotropy for vanadyl and chromyl complexes is calculated. The calculations indicate that this contribution is approximately 10% of the diagonal contribution.
Analysis of the transient EPR signals in the photoexcited triplet state. Application to porphyrin molecules
Authors: Levanon Haim , Vega Shimon
Published: February 2004

Anomalous EPR line intensities observed in the photoexcited triplet state of porphyrins at 100°K are discussed. A kinetic model consisting of the singlet ground state and the first excited triplet state is developed. The EPR signal intensities are expressed in terms of the kinetic rate constants and are given as linear combinations of two exponents. With these expressions the transient effects on the line intensities can be explained. Experimental results for two porphyrin molecules H2TPP (tetraphenyl porphyrin free base) and H2(PF)TPP (pentafluorotetraphenyl porphyrin free base) are presented and compared with the theory. From the analysis we evaluated the spin lattice relaxation rate W, the depopulation rate constants kp and the ratio between the population rate constants Ap: For H2TPP, kx =(6±2)×102 sec−1, ky =(3±1)×102 sec−1, kz =(1.5±0.5)×102 sec−1, Ax:Ay:Az≃1:0.6:0.2, and W =3.3×103 sec−1. For H2(PF)TPP, kx =(5±2)×102 sec−1, ky =(1.4±0.4)×102 sec−1, kz =(1.0±0.3)×102 sec−1, Ax:Ay:Az≃1:0.2:0.3, and W =1.7×104 sec−1.
Contribution of relaxation and chemical shift results to the elucidation of the structure of the water-DMSO liquid system
Authors: Tokuhiro Tadashi , Menafra Luis , Szmant H. Harry
Published: February 2004

Proton spin-lattice relaxation times (T1) of water and dimethyl sulfoxide (DMSO) in H2O–DMSO (I), H2O–DMSO-d6 (II), and D2O–DMSO (IV) systems at 9.8, 18.7, 29.9, and 41.4°C exhibited minima near 0.65 mole fraction of water (XH2O). The depth of the minimum, relative to T1 values at higher and lower XH2O, increased as the temperature was lowered. The intramolecular contribution to the relaxation of DMSO protons was always greater than the intermolecular DMSO–DMSO contribution and the former showed a minimum at XD2O≈0.6 as compared with the latter's minimum at XD2O≈0.4–0.6. There is almost no contribution to water proton T1 from the interaction of water protons-DMSO protons in the DMSO-rich mixtures, while this contribution is rather significant in the DMSO-poor mixtures. The proton chemical shifts of water with reference to DMSO protons (over a temperature range of −60−45°C) moves to higher fields with rising temperatures, and this temperature dependence is affected considerably by the changes in composition. All these experimental results suggest the presence of strong intermolecular interactions between water and DMSO molecules that contribute to the ``structuring'' of this binary mixture. The structure of this liquid system is very sensitive to composition and temperature.
Scattering of alkali halides by electrons. II. CsCl
Authors: Becker W. G. , Fickes M. G. , Slater R. C. , Stern R. C.
Published: February 2004

Scattering of CsCl by 0.47–15.7 eV electrons has been measured using the molecular beam recoil technique. Center of mass differential cross section models are adjusted to the scattering after transformation to apparatus space. Absolute total cross sections, approximately equal to the first Born approximation point dipole prediction at 15.7 eV, fall to one-fourth of the theory at 0.47 eV. Momentum transfer cross sections are dramatically smaller than the theory at low energies.
Magnetic properties of verdazyl free radicals. VII. π-Bridged verdazyl biradicals with triplet ground state
Authors: Azuma Nagao , Ishizu Kazuhiko , Mukai Kazuo
Published: February 2004

Magnetic susceptibilities of two π-bridged verdazyl biradical solids have been measured in the temperature range 1.8−300°K. Paramagnetic Curie constants of 1.0±0.1 and 0.90±0.05 K·emu/mol have been found in 1,4-bis(1,5-diphenyl-3-verdazyl)benzene (P-verdazyl) and 1,3-bis(1,5-diphenyl-3-verdazyl)benzene (M-verdazyl), respectively. Both Curie constants suggest the presence of the triplet ground state. The intramolecular positive exchange integrals, J/k, of these biradicals are much greater than 300°K. The susceptibility of P-verdazyl exhibits a maximum at 19±1°K, which implies a negative exchange interaction between the triplets, its magnitude being estimated to be about 7°K.
Reduction of macroscopically derived dispersion forces to two-body interactions
Authors: Nir S.
Published: February 2004

It is shown analytically and illustrated numerically that the magnitude of dispersion forces per unit area is the same according to two different methods of calculation, the Lifshitz macroscopic theory and the microscopic pair summation of London-Hamaker, for a geometry of two semi-infinite slabs separated by a thin film. Consequently, if the macroscopic approach is accepted, then at least for the given geometry and distances of separation studied, dispersion forces between bodies or particles may be obtained by a sum over pairs. This result may be useful in calculation of dispersion forces for geometries where lack of symmetry makes macroscopic derivations unworkable. Calculations on several systems in the framework of the Lifshitz theory illustrate that in most cases dispersion forces alone can account for the major part of van der Waals forces between macroscopic bodies at close distances of separation. An exception to this rule is exhibited in the case of the system water-benzene-water.
Quantum kinetic theory of chemical recombination
Authors: Snider R. F. , Lowry J. T.
Published: February 2004

A quantum kinetic theory for monomer-dimer dilute gas mixtures is specialized to the case of homogeneous isothermal mixtures. The resulting expressions for the termolecular recombination rates (with either a monomer or a dimer being the third body) is compared with standard chemical expressions. This involves the use of a novel exact decomposition of the termolecular transition superoperator, through which both energy-transfer and bound-complex mechanisms are identified.
Electron momentum distribution in NH3
Authors: Van Hise James R. , McDonald Dennis N.
Published: February 2004

We have calculated the electron momentum distribution in the N–H bond of the ammonia molecule using a valence-bond wavefunction. Included in the calculation were the positron wavefunctions on the nitrogen and hydrogen atoms. The results are compared with experimental data and a calculation of the momentum distribution using a SCF molecular orbital.
On the structure of the smectic H phase
Authors: de Vries Adriaan
Published: February 2004

On the basis of theoretical considerations and experimental evidence it is proposed that in the smectic H phase of TBBA all molecular planes are essentially parallel to the direction of tilt. It is shown that this model does not fit the data on the smectic H phase of BBEA, and so for this phase the previously suggested herringbone packing is retained. A theoretical model is developed for the forces governing the packing in these smectic H phases. This model combines the dipole model of McMillan with interactions between neighboring phenylene groups. The model predicts a parallel arrangement for TBBA and a herringbone arrangement for BBEA, in agreement with the conclusions reached in the first part of the paper.
Design of a high density atomic hydrogen source and determination of Balmer cross sections
Authors: Walker James D. , St. John Robert M.
Published: February 2004

A high density beam of atomic hydrogen was obtained from a Wood discharge and utilized in the measurement of electron-hydrogen atom collision cross sections. Balmer optical excitation cross sections were determined from observations of crossed electronic and atomic beams. In order to choose Wood discharge parameters to obtain a high degree of dissociation under conditions of a high gas throughput, the differential equations relating the production, loss, and flow of hydrogen atoms and molecules were formulated and solved. The solutions show that recombination of atoms on the metal electrodes greatly reduces the degree of dissociation in large diameter tubes. They further show that this effect can be nearly eliminated by placing short small diameter tubes, called constrictions, between the electrodes and the main tube. A Wood tube 2 cm in diameter and 2 m in length with these constrictions was constructed which produced an atomic to molecular density ratio of 11 at a throughput of 1000 mtorr · liter/sec. The atoms and molecules from the Wood tube were passed through a nozzle and formed into a beam which was crossed with a monoenergetic electron beam. In the crossed beam volume the atomic density was approximately 5.6×1012 cm−3 and the background molecular density was approximately 3.3×1013 cm−3. Optical excitation data were obtained by observation at 90° to the crossed beams with a monochromator and photomultiplier detection system. The ratio of the atomic density with the Wood discharge on to the molecular density with the Wood discharge off in the crossed beam volume was determined from molecular light intensity measurements and a derived relation. Combining this ratio with Balmer optical excitation data with the Wood discharge on and off gave the ratio of the atomic and molecular Balmer cross sections. Absolute molecular Balmer cross sections were measured in a static gas apparatus for use in determining the absolute atomic Balmer cross sections. The atomic Balmer cross sections (in units of 10−20 cm2) for Hα, Hβ, Hγ, Hδ, and Hε at 200 eV thus determined are 229.0, 72.4, 22.5, 12.9, and 6.5, respectively. All of these cross sections are within 23% of the theoretical optical cross sections determined under zero electric field conditions.
vuv absorption spectra of mercury atoms trapped in solid inert gases
Authors: Malo Salvador A.
Published: February 2004

The photoelectrically obtained vuv absorption spectra of Hg-doped rare-gas matrices are shown. The main features observed are correlated with those of the 1P1–1S0 transition of Hg in its gaseous phase: These are shifted and show fine structure. Matrices of Ar, Kr, Xe, and Ne were used. Spectra were also obtained under different experimental conditions, and the results are compared with previous work.
Vibronic magnetic rotational strengths in the B2u state of benzene
Authors: Rosenfield Joan Samour , Moscowitz Albert , Linder Robert E.
Published: February 2004

The vibronic magnetic circular dichroism (MCD) spectrum of the electronically forbidden 260 nm 1A1g→1B2u transition in benzene is analyzed in terms of e2g vibrational modes. The negative MCD progression is aasigned to the e2g 608 cm−1 and 1596 cm−1 modes and the positive progression to the e2g 1178 cm−1 and 3056 cm−1 modes. Experimental MCD and absorption spectra of benzene and benzene-d6 in solution at room temperature and liquid nitrogen temperature are reported. Magnetic rotational strengths and oscillator strengths associated with each of the four e2g vibrations in benzene and benzene-d6 have been calculated by two different methods: a perturbation treatment involving the π electrons only, and a CNDO calculation for a geometry in which the nuclei are distorted along a normal coordinate. The results of the two calculations agree reasonably well with each other and with experiment. Two terms that dominate the magnetic rotational strengths are identified.
Hydrogen bonding between neon and hydrogen fluoride
Authors: Losonczy M. , Moskowitz J. W. , Stillinger F. H.
Published: February 2004

Hartree-Fock calculations have been carried out to characterize the potential energy surface for interaction of a neon atom with a molecule of hydrogen fluoride. The results exhibit formation of a linear hydrogen bond. Although this bond is weak (0.234 kcal/mole), its strength exceeds that found earlier for the neon-water hydrogen bond.
X-ray scattering by a tunnel-model liquid
Authors: Lund L. H.
Published: February 2004

The x-ray scattering by a tunnel-model liquid is calculated and the resulting expression for the intensity inverted to give the liquid radial distribution function based on such a model. These functions are presented for liquid argon at 91.8 and 84.4°K and agree well with those obtained by the usual inversion method, but with increased peak resolution.
Intersystem crossing and internal conversion in propynal vapor
Authors: Thayer C. A. , Yardley James T.
Published: February 2004

A kinetic model that describes the energy flow through a propynal molecule which is initially excited to the 1A″ state has been proposed. Eight decay rates contained in this model have been determined from Stern-Volmer plots, quantum yields, and integrated absorption coefficient measurements in the pressure region from 0.05 to 1 torr. Only forward rates were considered, and all pathways were found to be significant. In particular, both intersystem crossing and internal conversion from the 1A″ state were observed under both collisional and collision free conditions. However, intersystem crossing appears to predominate in each case. A model previously proposed to describe collisional quenching in propynal must be slightly modified in order to be consistent with these observations.
Infrared laser enhanced reactions: O3 + SO
Authors: Kaldor Andrew , Braun Walter , Kurylo Michael J.
Published: February 2004

Vibrationally excited ozone, O3†, produced by CO2 laser radiation was found to react with SO significantly faster than thermal ozone via the chemiluminescent reaction process O3+SO→SO2(1B1) +O2(3Σg). The vibrational rate enhancement of this reaction was 2.5±0.6 at 300 K. This represents the utilization of 27% of the available vibrational energy to promote the reaction based on a model assuming involvement of a single vibrational mode. The laser enhanced chemiluminescence measured from 260 to 450 nm was found to exhibit a 630±200 cm−1 blue shift. This is interpreted as a partitioning of the available vibrational energy of O3† in the vibrational manifold of the SO2(1B1) product.
Direct measurements of energy transfer between triplet states of molecules in liquids using picosecond pulses
Authors: Anderson R. W. , Hochstrasser R. M. , Lutz H. , Scott G. W.
Published: February 2004

We have measured the buildup and decay rates of triplet-triplet absorption of triplet donor solute molecules dissolved in acceptor solvents following picosecond excitation of the first excited singlet state of the solute at room temperature. We have used harmonic pulses from a mode-locked Nd+3 /glass laser for exciting (3545 Å) and probing (5300 Å) the samples. We report buildup (k) and decay rates (kQ) for the following solutions: benzophenone in cis -piperylene (k−1=7 psec, kQ−1=9 psec) and trans -piperylene (k−1=7 psec, kQ−1=11 psec), benzophenone in 1-methylnaphthalene (k−1<10 psec, kQ−1=20 psec), and 1-nitronaphthalene in cis-piperylene (k−1=8 psec, kQ−1=678 psec). We discuss our results in terms of a model of triplet-triplet energy transfer which depends on good overlap of donor and acceptor energy levels with large Franck-Condon factors. This model indicates that energy may compete with vibrational relaxation particularly for the benzophenone in piperylene systems, but that thermally assisted energy transfer will be required for 1-nitronapthalene in cis -piperylene. These predictions are in good agreement with our experimental results. We also report a novel technique of measuring the position of t =0 and the laser pulse duration for calibrating the type of experimental apparatus we use.
Potential energy surfaces related to the ion-molecule reaction C+ + H2
Authors: Liskow Dean H. , Bender Charles F. , Schaefer Henry F.
Published: February 2004

The C+ + H2 ion-molecule reaction has been studied by several experimental groups and appears likely to become the focal point of much experimental and theoretical activity. Ab initio self-consistent-field and configuration interaction calculations have accordingly been carried out for this system. A double zeta basis set of contracted Gaussian functions was employed and as many as 648 configurations included. For isosceles triangle configurations (C2V point group) the 2A1, 2B1, and 2B2 potential surfaces were considered, while for linear geometries (C ∞V) the 2Σ+ and 2Π surfaces were studied. For general (Cs) geometry, the lowest 2A′ potential surface was considered. Properties reported include minimum energy paths and energy profiles for the various processes considered. The intuitive correlation diagram of Mahan and Sloane is given qualitative reliability. Pathways to CH2+ complex formation are shown to depend crucially on the Cs potential surface.
Averaging of transverse relaxation times of scalar coupled nuclei under spin lock conditions
Authors: Vold R. L. , Vold R. R.
Published: February 2004

The response of a scalar coupled spin system to a train of closely spaced 180° pulses is analyzed by means of an effective Liouville operator from which terms involving chemical shifts are omitted. It is shown that the resulting equations of motion for the spin density matrix are most easily solved in a basis for which the spin coupling part of the Hamiltonian is diagonal. Transverse relaxation behavior for each line in the spectrum may then be calculated by transforming to the basis in which the entire time independent Hamiltonian is diagonal. The analysis shows that under spin lock conditions produced by rapid nonselective pulses, the existence of scalar coupling causes all transitions of the same symmetry to exhibit identical transverse relaxation behavior. For two coupled nuclei of spin 1/2 all four transitions are shown to decay with the same single exponential, and the relaxation time is the average of relaxation times expected for each spin in the absence of scalar coupling. Experimental results demonstrating this averaging effect are reported for the protons in neat 2,3-dibromothiophene.
A theoretical study of the lithium fluoride molecule in water
Authors: Watts R. O. , Clementi E. , Fromm J.
Published: February 2004

Monte Carlo results are reported for the structure of molecular clusters consisting of a lithium fluoride ion pair surrounded by 50 water molecules at temperatures of 298 and 500 K using Hartree-Fock interaction potentials that include some three-body terms. It is shown that when separated by distances of between 3 and 4 Å each ion is surrounded by a nearest-neighbor shell of four atoms, hydrogen in the case of the fluoride ion and oxygen in the case of the lithium ion. There is evidence of both secondary hydrogen atom and secondary oxygen atom structure around the ions but there is no evidence of any larger hydration shell. It is tentatively concluded that the coordination number of 4 for each ion is responsible for the behavior of lithium and fluoride ions as ``structure makers.''
Potential curves from emission continua. IV. The upper state of the vacuum uv continua of Ar2
Authors: Michaelson R. C. , Smith A. L.
Published: February 2004

Photoelectric spectra of weak pulsed discharges in argon (4 < P < 20 torr, 125 < T < 200°K) show that the red-degraded first continuum of Ar2 begins at 1074 Å and exhibits oscillatory structure out to 1500 Å, this structure being due to interference effects in the energy dependence of bound-continuum transitions from high vibrational levels. A semiclassical procedure previously used for He2 is employed to derive the upper state potential curve for 2.0 < R < 3.2 Å from the oscillatory structure and different assumed lower (repulsive) potentials. Vibrational levels in this well are computed numerically; comparison of their spacings with those observed by Tanaka and Yoshino in the absorption spectrum of Ar2 show that the radiating state is a high vibrational level (ν = 22±2) of the 0u+ state (dissociation limit 3P1 + 1S0), populated by a collision-induced curve crossing in a collision of Ar(3P2) + Ar(1S0). Spectroscopic constants of the 0u+ state, which depend somewhat on the lower potential assumed, are D′e = 6000±600 cm−1, ω′e = 310±30 cm−1, ωex′e = 2.5±0.5 cm−1, and R′e = 2.32±0.10 Å. These constants agree well with those computed by assuming that Ar2(0u+) is a Rydberg state with configuration [Ar2+ (X 2Σu+)]4s σg. Calculations of the position of the maximum of bound-continuum emission from ν = 0 of the 0u+ state confirm that it is also the upper state of the second continuum, which peaks at 1270 Å. The kinetics of formation of the 0u+ state are briefly discussed.
Negative ion formation from energetic collisions of cesium with CO2, CS2, and COS
Authors: Tang S. Y. , Rothe Erhard W. , Reck Gene P.
Published: February 2004

An experiment is described in which cesium atoms, with kinetic energies in the range 10–350 eV, collide with CO2, CS2, and COS. The measured products are negative ions from charge exchange (NICE). The parent anions, CO2−, CS2−, and COS− are observed, as are other fragment ions. Intensity ratios for the various anions are measured as a function of cesium atom energy. The electron affinity of CO2, determined from crude threshold measurements, lies in the range −2.1 to −1.1 eV, with a precision of about ±0.25 eV.
Polarized two-photon studies of biphenyl and several derivatives
Authors: Drucker Ronald P. , McClain W. M.
Published: February 2004

The two-photon absorption spectrum of biphenyl dissolved in CCl4 is reported, using both the absolute two-photon absorption technique and the two-photon excited fluorescence technique. Polarization methods were used which permit the strong two-photon absorptions to be assigned without resort to any subsidiary vibrational analysis. We find that the lowest singlet of biphenyl is a B state (in group D2, with twisted rings); its band stretches from about 33 000–36 000 cm−1, well to the red of the lowest strong one-photon transition. We also find clear evidence of an A state hidden to one-photon spectroscopy in the 42 000–45 000 cm−1 region. Other A states are also possibly present. Two-photon spectra of 4,4′ dichlorobiphenyl, 4,4′ difluorobiphenyl, 2,2′ bipyridine, 2,2′ difluorobiphenyl, and terphenyl are also given and discussed.
Modified free energy averaged potential for complex polar fluids
Authors: Malik A. K. , Varshneya N. C.
Published: February 2004

Free energy averaged potential for low density simple polar fluids used by Danon et al. has been modified for complex polar fluids like water and ammonia by introducing a dipole-quadrupole interaction term in Stockmayer angular dependent potential. The resulting temperature dependent effective pair potential is used for calculation of second virial coefficient and specific heat of water vapor at 1 and 10 atm pressure. Comparison of results shows an improvement of new potential over DA potential.
Vibrational relaxation times for HF due to collisions with He
Authors: Smith Kenneth , Ormonde S. , Davies A. R. , Torres B. W.
Published: February 2004

Calculations of HF vibrational relaxation times in He have been performed using a theoretical model which treats the HF molecule as a simple harmonic oscillator and approximates the He–HF interaction as a separable product of a Lennard-Jones function of the intermolecular distance and an empirical exponential function of the internal molecular coordinate. When the two state formula for the relaxation time is used, the results agree with the experimental values of Bott and Cohen near 2600 °K but have a slightly greater slope.
Depolarized light scattering from Ar, Kr, CH4, SF6, and C(CH3)4 at pressures around 1 atm
Authors: Watson Richmond C. , Rowell Robert L.
Published: February 2004

An apparatus for measuring the density dependence of the depolarization ratio for Ar, Kr, CH4, SF6, and C(CH3)4 at pressures around 1 atm is described. The results are compared to theoretical values based on DID theory and to results of other experimental techniques for investigating collision-induced light scattering. The discrepancy between theory and experiment for the large molecules provides further evidence of the inadequacy of the point-dipole approximation of DID theory.
Charge transfer in the Mn–O bond as determined by ESR of MnO42− in BaSeO4
Authors: Ezzeh C. , McGarvey B. R.
Published: February 2004

The ESR of MnO42− has been studied at 4°K in single crystals of BaSeO4. The principal values of g and A tensors are gxx=1.9572, gyy=1.9633, gzz=1.9848, Axx=126.2×10−4 cm−1, Ayy=84.1×10−4 cm−1, and Azz=16.8×10−4 cm−1. The x and z axis of g and A are found to differ by 4°. It is shown that the ground state is dz2 with a 2% admixture of dx2−y2 similar to that of MnO42− in BaSO4 but different than the ground state of MnO42− in K2CrO4. It is further shown that the difference in principal x and z axes for the g and A tensors is attributable to the admixture of the dyz orbital with the dxy orbital which is estimated to be 0.03% from the angular separation of the axes. An MO analysis of the ESR data for MnO42− in BaSeO4 and BaSO4 is done which shows that the d orbitals occupied by the unpaired electron are those of a +2 charged ion. Further the analysis reveals more σ charge transfer and less π charge transfer when MnO42− replaces the smaller SO42− ion than when it substitutes for the larger SeO42− ion.
Hypernetted chain solutions for the classical one-component plasma up to Γ=7000
Authors: Ng Kin-Chue
Published: February 2004

The hypernetted chain equation has been solved numerically for the classical one-component plasma in a uniform background up to Γ=7000, where Γ=(Ze)2/kTa and a is the ion-sphere radius. Numerical results are presented. The distribution functions and thermodynamical quantities obtained are in good agreement with the Monte Carlo results in the fluid region. The average potential energy Ū/NkT is in error by less than 0.8% for 20≤Γ≤160 and approaches −0.8995Γ as Γ approaches infinity. The pressure and the free energy calculated do not show any evidence of a phase transition. However, the distribution function g(r) for Γ ≳ 1500 has an unusual behavior between 2.5<r<4.0, resembling somewhat that of a hcp crystal. If we assume the sum of the bridge diagram to be of the form B(r)=−λΓ/r where λ=0.6 erf (0.024Γ), the distribution function calculated agrees to within about ±0.02 with the Monte Carlo g(r) in the whole fluid region.
Kinetics of homogeneous nucleation on many-component systems
Authors: Hirschfelder Joseph O.
Published: February 2004

Reiss's classical treatment of the kinetics of homogeneous nucleation in a system containing two chemical components is extended to many-component systems. The formulation is analogous to the pseudostationary state theory of chemical reaction rates with the free energy as a function of the composition of the embryo taking the place of the potential energy as a function of interatomic distances.