bluuebunny/crossref_metadata_2025 huggingface dataset:
Positron studies of metal hydrides
Authors: Huang W. F. , Burton L. D.
Published: February 2003

Angular correlation of the two photons emerging from positron annihilation in LaH2.71, YH2.36, EuH2.0, and EuH2.73 have been measured. By comparing with other published data it can be concluded that all heavy rare earth hydrides at high hydrogen concentrations exhibit almost triangular shaped angular correlation curves with an exceptionally large Gaussian component. Results are consistent with charge transfer to the hydrogen site and contribution from interference between the metal and hydrogen atoms. Mixed valency is believed to play a role in europium hydrides.
Matrix-isolation triplet (T1) state IR spectroscopy of acridine and phenazine
Authors: Mitchell Mark B. , Smith George R. , Guillory William A.
Published: February 2003

The matrix-isolated infrared (IR) spectra of the lowest triplet (T1) states of acridine and phenazine have been obtained by direct measurement. Population of T1, sufficient for IR detection, is achieved by pulsed indirect pumping with an Ar+ laser source. The ground and triplet state IR spectra were 180° out of phase, providing unambiguous indentification of the excited metastable state absorptions. Approximate T1 vibrational assignments are made on the basis of analogous experimental and theoretical results for ground state acridine, phenazine, and anthracene.
Microscopic surface tension down to molecular dimensions and microthermodynamic surface areas of molecules or clusters
Authors: Sinanoğlu Oktay
Published: February 2003

Surface tension, surface energy, and entropy of small droplets, n clusters, and of cavities in liquids for sizes down to a single molecule are obtained. Rigourous relations are derived that relate microsurface properties to the usual handbook properties of bulk liquids. The microvalues and their dependence on the ratio of the cluster, droplet, or cavity size to the average liquid molecular size are given for common solvents, polar and nonpolar, including alcohols, water, hydrocarbons, rare gas liquids, and liquid (or solid) metals. Microscopic values are less than bulk-planar values by around 40% for nonpolar liquids, and greater for polar liquids by around 60%. The n-cluster (or cavity) sizes ? at which the microsurface properties approach the bulk values within a desired percentage, e.g., 5%, are given. The ordinary, bulk thermodynamic properties of liquids are also related to new useful quantities: ’’microthermodynamic surface areas’’ of molecules from which, using the equations given, ’’experimental’’ geometric (van der Waals) surface areas of molecules are calculated. The molecular surface properties introduced in the theory of ’’solvophobic forces’’ by this author earlier are finding applications presently in areas like HPLC (’’high pressure liquid chromatogrphy’’), multicomponent adsorption from solution phase (e.g., purification of waters from trace carcinogens), large ion association, protein structure, and drug–biopolymer binding, as well as the earlier ones for the prediction of rates and equilibria in diverse solvents in physical organic chemistry. The microsurface properties given now apply also to the convex case, e.g., the n clusters in nucleation and in metal cluster phenomena.
Determination of the 14N electric field gradient tensor in the nitro group: A single crystal nuclear double resonance study of p-nitrotoluene
Authors: Hiyama Yukio , Brown Theodore L.
Published: February 2003

The 14N electric field gradient tensor in single crystalline p-nitrotoluene has been determined at room temperature via proton–nitrogen double resonance in the rotating frame. The major principal (Z) axis of the tensor lies along the C–N bond axis. The quadrupole coupling constant (1340 kHz) and asymmetry parameter (0.408) determined from analysis of the rotation patterns are in excellent agreement with the values measured in a zero field double resonance experiment on powdered p-nitrotoluene.
Laser light scattering from concentrated solutions of polystyrene latex spheres: A comparative study
Authors: Trotter C. M. , Pinder D. N.
Published: February 2003

Quasielastic light scattering was used to measure the mutual diffusion coefficient of polystyrene latex spheres over the concentration range 0.004 to 4.46 g per 100 ml. Measurements were made at 25.0 °C in solutions of 0.01 and 0.001 M sodium chloride, with several low sphere concentration measurements also being made in triply distilled water. The diffusion coefficient was found to be ionic strength dependent over the entire concentration range studied. Solutions of polystyrene spheres at moderate concentrations exhibit the phenomenon of multiple scattering. The available literature on multiple scattering is reviewed and criteria adopted for the reliable extraction of data from these solutions. The diffusion coefficients so obtained show substantial agreement with the macroscopic capillary penetration results of Anderson et al. The conclusion reached in this work is that quasielastic light scattering is able to provide a measure of the macroscopic mutual diffusion coefficient at moderate sphere concentrations and moderate ionic strengths. This conclusion is seen to be in accord with earlier QELS studies on cyanomethemoglobin and Bovine Serum Albumin, provided that a reassessment of available macroscopic diffusion data on these systems is undertaken.
Investigation of HgBr* excitation by x-ray sustained discharge in Xe/HgBr2 mixtures
Authors: Degani J. , Rokni M. , Yatsiv S.
Published: February 2003

The excitation kinetics and luminescence of HgBr* are investigated in Xe/HgBr2 mixtures, under x-ray irradiation as well as under x-ray sustained low current discharge. The discharge characteristics are studied for mixtures containing variables amounts of HgBr2. A value of 8.4×10−11 cm3 sec−1 is measured for the attachment rate of slow electrons to HgBr2, by observing the decay of the electron current following a 30 nsec x-ray radiation pulse. From the dependence of the intensity of the HgBr B→X transition on the mercuric bromide density, the quenching rate of HgBr* by HgBr2 is determined. The dependence of the emitted radiation intensity on the applied electric field is investigated and its spatial distribution is studied. The formation kinetic processes conforming with the experimental results are discussed.
Theory of thermal unimolecular reactions at high pressures
Authors: Troe J.
Published: February 2003

A simplified version of a statistical adiabatic channel model for unimolecular simple bond fission and the reverse radical association reactions is presented. The pattern of threshold energies for individual channels is analyzed and expressed empirically. High pressure rate constants for thermal dissociation and recombination are given in explicit form and applied to practical examples. The present theory interpolates between rigid and loose activated complex theory in a simple way with an account for angular momentum couplings. The interpolation parameter is the ratio α/β of the Morse parameter β and the looseness parameter α.
An interpolation method for forcing SCF convergence
Authors: Camp R. Nicholas , King Harry F.
Published: February 2003

A continuous path connecting two SCF trial functions can be defined in a variety of ways. We introduce one which is, in a sense, the minimal path between these states. Corresponding occupied and virtual orbital pairs are defined. Variation of the SCF energy along the minimal path is fitted by a cubic polynomial using information supplied by the normal SCF calculation. The cubic fit is usually found to be an excellent approximation to the true energy function. Interpolation, or extrapolation, along the path effectively overcomes problems due to use of a poor initial trial function, and always converges. The final approach to convergence can be slow. Various acceleration methods, applicable to the end-game problem, have been proposed in the literature. Our interpolation method insures convergence when combined with almost any of these alternative methods for the closed-shell problem.
The contracted density product (CDP) concept as a new way to simplify molecular orbital calculations
Authors: Hug W. , Mascarello F.
Published: February 2003

It is shown that invariant MO–CI schemes, approximate in the sense that they neglect part of the electron–electron interaction, can be derived in a systematic way from rigid ab initio methods. Two electron integrals over basis functions can be divided into independent groups on account of the number of centers over which they and the individual electron densities extend. Entire such groups can be neglected, retained as they are, or retained in space averaged form by contracting their corresponding products of density matrices. For irreducible tensors as basis functions, full contraction distinguishes integrals which have a vanishing space average up to 3p orbitals from integrals with a nonvanishing space average. The latter can be replaced by a set of four parameters, three of which are linearly dependent wherever the Coulomb and exchange terms are interdependent in the unified atom limit.
Spontaneous pattern formation in spherical nonlinear reaction–diffusion systems: Selection rules favor the bipolar ‘‘mitosis’’ pattern
Authors: Hunding Axel , Billing Gert Due
Published: February 2003

It is shown analytically, by means of bifuration theory, that the bipolar mitosis prepattern may arise directly from the homogeneous state.(AIP)
Observation and quantitation of light emission from cytochrome c using Soret band laser excitation
Authors: Champion P. M. , Perreault G. J.
Published: February 2003

We have observed relaxed emisson from the S1 (Q band) of ferrocytochrome c following laser excitation into S2 (B band). The quantum yield for this process is found to be φBQ = 5.0×10−7. A simple kinetic analysis is employed in order to deduce intermanifold branching ratios of the ferrocytochrome. Assumptions regarding the variability of the nonradiative decay rate within the Q manifold are also discussed.(AIP)
SF6 in a xenon matrix: Vibrational energy relaxation
Authors: Abouaf-Marguin L. , Boissel P. , Gauthier-Roy B.
Published: February 2003

Measurements of the vibrational relaxation of SF6 isolated in a Xe matrix are reported. The relaxation measurements were done at 7 K and the relaxation time measured is in the microsecond range.(AIP)
Asymptotic form of first-order density matrix for atoms and molecules
Authors: March N. H. , Pucci R.
Published: February 2003

The asympototic form of the first-order density matrix for atoms or molecules is considered.(AIP)
Two-photon excitation of xenon atoms and dimers in the energy region of the 5p56p configuration
Authors: Gornik W. , Kindt S. , Matthias E. , Schmidt D.
Published: February 2003

Two-photon excitations from the xenon ground state into the region of the 6p configuration were measured with frequency-doubled light of a tunable pulsed dye laser. Experimental two-photon transition probabilities for the J = 0 and 2 states are compared with theoretical estimates. For atomic transitions populating the 6p‖1/2‖0, 6p‖3/2‖2, and 6p‖5/2‖2 states the following pressure shift parameters β/N were found: −(2.5±0.2)×10−9, −(2.7±0.2)×10−9, and −(2.8±0.2)×10−9 s−1 cm3, respectively. In addition to atomic two-photon transitions, molecular absorptions were observed. Two vibrational v′ progressions converging towards the 5d‖7/2‖3 dissociation limit could be identified. The energy difference of (19.4±1.0) cm−1 coincides with known values for the ground state vibrational separation ΔG(1/2).
A self-consistent semiclassical approach to the inelastic scattering of atoms from solid surfaces
Authors: Kumamoto D. , Silbey R.
Published: February 2003

A self-consistent semiclassical theory of inelastic scattering is developed using a boson Hamiltonian and a time-dependent Hartree solution. The quality of the self-consistent solution is shown to be dependent on the choice of initial state. Two choices of initial state are compared for a simple choice of interaction potential. The results of this analysis are applied to the inelastic scattering of atoms from metal surfaces considering either the electron–hole pair or the phonon models of energy dissipation. The calculation of sticking probabilities is considered.
Rigorous results for branched polymer models with excluded volume
Authors: Klein D. J.
Published: February 2003

It is pointed out that on taking excluded volume into account for branched polymers there are modifications to previous work, such as that of Cayley and Polya on isomer enumeration. Indeed, it is argued that the classical Cayley–Polya count overestimates the corrected count by an arbitrarily large factor. Further, some limited rigorous results concerning the asymptotic behavior of isomer counts and of counts for polymer conformations are established.
Excluded volume effects for branched polymers: Monte Carlo results
Authors: Seitz W. A. , Klein D. J.
Published: February 2003

As a simple model of randomly branched polymers, we consider the different ways that N-bond trees may be self-avoidingly embedded on a lattice. A general Monte Carlo approach is developed and applied. The mean square radii of gyration of the conformations with a given N are found to vary with N as Nν, where ν?1.23 and ν?0.92 in two and three dimensions. The critical importance of volume exclusion for branched structures is discussed.
The healing process at polymer–polymer interfaces
Authors: Prager Stephen , Tirrell Matthew
Published: February 2003

When two pieces of the same amorphous polymer are brought into contact at a temperature above the glass transition, the junction surface gradually heals until, at very long contact times, it is indistinguishable from bulk polymer. We have developed an analysis of this welding process based on the reptation picture of polymer dynamics due to de Gennes. The theory predicts the number of bridges (pieces of polymer chain) per unit area spanning the original junction surface as a function of time. At fixed time the number of bridges (σ) also depends on the molecular weight (M) of the chains. If the initial contact is between surfaces which have been equilibrated against a gas phase, we find that σ∼t1/2M−3/2. Alternatively, if the contacting surfaces contain many chain ends, such as may be found at brittle fracture surfaces in glassy polymers, we find that σ∼t1/4M−1/4 at short times. The theory may be compared to available measurements on strength development in healing interfaces leading to the conclusion that the model reproduces several aspects of the observed phenomenon.
Improved calculation of the cross section for excitation of the asymmetric stretch of CO2 by electron impact
Authors: Thirumalai Devarajan , Truhlar Donald G.
Published: February 2003

Our previous calculations for excitation of the 001 state of CO2 by electron impact at 10 eV are corrected for breakdown of the vibrational sudden approximation. This reduces the calculated differential cross sections at scattering angles of 1° and 3° by 41% and 6%, respectively, and the calculated integral cross section by 14%.
Measurement of relative Penning excitation rates for the individual Zn(II) and Cd(II) states by Ne metastable atoms
Authors: Inaba S. , Goto T. , Hattori S.
Published: February 2003

The relative penning excitation rates and cross sections for the individual Zn (II) and Cd (II) states are reported. The excitation was achieved by collisions of Cd and Zn with metastable Ne atoms. (AIP)
Correlated prolate–spheroidal wave function containing no adjustable parameters for two-electron diatomic systems
Authors: Aubert-Frécon M. , Ceyzeriat P. , Lesech C. , Jorus A. M.
Published: February 2003

The total energy of the following states of H2 and He22+:X 1Σ+g[(1sσg)2], 1,3Σ+g(1sσg, 2sσg), 1,3Σ+u(1sσg, 2pσu), and 1,3Σ+g(1sσg, 3dσg), has been investigated from a correlated prolate–spheroidal wave function with no adjustable parameters. Results of reasonable accuracy are obtained for the ground state of H2 and He22+ as well as for the excited states of He22+ but unsatisfactory results are displayed for excited states of H2. (AIP)
Laser initiated chain reactions: A generalized extension to complex chemical chain systems
Authors: Nesbitt David J. , Leone Stephen R.
Published: February 2003

We present a generalized extension of the detailed kinetic and experimental analysis for studying rapid gas phase chemical chain reactions initiated by short pulse laser photolysis. The key ingredients of the technique are pulsed laser initiation of the chain by dissociation of a small fraction of a precursor molecule to produce radicals (Cl2→hνCl⋅+Cl⋅), followed by time resolved, infrared chemiluminescence detection of product HCl(v) emission from the propagation steps (Cl⋅+RH→k1 R⋅+HCl(v), R⋅+Cl2→k2Cl⋅+RCl). This laser initiated chain reaction technique is now extended to encompass a far wider range of chain kinetic rates, mechanisms, and product state distributions. Three prototypical systems are investigated which demonstrate distinctly different facets of the extended technique: (1) Cl2/HBr—a slow chain reaction system, (2) Cl2/CH3SH—a multiple chain reaction system, and (3) Cl2/H2—a slow starting chain reaction system in which the product emission appears after an intital induction period. Quantitative rate data are obtained for several chain propagation steps: Br⋅+Cl2→Cl⋅+BrCl, k = 2.4(±0.2)×10−15 cm3 molecule−1 s−1; Cl⋅+CH3SH→⋅CH2SH+HCl(v), k = 4.3(±1)×10−12 cm3 molecule−1 s−1; ⋅CH2SH+Cl2→Cl⋅+ClCH2SH, k = 2.6(±1)×10−13 cm3 molecule−1 s−1. The results illuminate a more general approach to precise kinetic and mechanistic studies of complex chain reactions under nearly ideal psuedo-first-order laboratory conditions.
Theoretical computation of the binding energy of BH3NH3, a difficult case
Authors: Zirz Constantin , Ahlrichs Reinhart
Published: February 2003

The reaction energy ΔE for BH3+NH3→BH3NH3 is investigated by means of large scale ab initio calculations using extended basis sets and highly correlated wave functions. The results for ΔE as obtained in the usual way or by the counterpoise method reveal serious basis saturation problems if an accuracy of 1 kcal/mol is desired for ΔE.
A theoretical study of core and valence ionization in ClF
Authors: Ewig C. S. , Sur A. , Banna M. S.
Published: February 2003

The core and valence binding energies of ClF have been obtained by SCF and MCSCF/CI calculations respectively using a Gaussian basis set. Numerical Dirac–Fock ’’ΔSCF’’ calculations have been performed on Cl, Cl−, Cl+, F, F−, and F+. These make possible a good estimate of the Cl ls binding energy of ClF, a quantity that has not been measured experimentally. The calculations of the valence ionization potentials make possible an unambiguous assignment of the ionic states. The underlying reasons for the calculated ordering are discussed in light of our results.
Comparison between experimentally and theoretically determined potential curves of the Ar2* lowest states
Authors: Castex M. C. , Morlais M. , Spiegelmann F. , Malrieu J. P.
Published: February 2003

Accurate potential curves have been determined for the (3p54s)Ar*+(1S0) Ar excimer, with extended basis sets, large CI and the Cohen–Schneider spin–orbit coupling scheme. Using the synchrotron radiation, measurements of the quantitative absorption temperature dependence of the wings of the 3P1 and 1P1 lines have been made and parts of the potential curves have been derived through the quasistatic treatment. The theoretical work shows that the complex and detailed shapes of the curves result from the action of various physical phenomena (electronic correlation, van der Waals dispersion forces, R−3 resonance interaction, and spin–orbit coupling); however a sufficiently accurate calculation and analysis allows a state by state comparison with absorption and emission experimental results and an attempt to gather and clarify the present knowledge.
Theoretical studies of the benzene molecule: Magnetic susceptibility and nuclear shielding constants
Authors: Lazzeretti Paolo , Zanasi Riccardo
Published: February 2003

Coupled Hartree–Fock perturbation theory is employed to evaluate the magnetic susceptibility, proton and carbon shielding constants, and their gauge dependence in benzene within the framework of an LCAO approach retaining 198 CGTO’s as the basis set. The magnetic properties are rationalized by analyzing the orbital contributions: the theoretical results indicate that an important role is played by π electrons, which largely contribute to the determination of the bulk of magnetic susceptibility and shieldings. The basic soundness of the ring current model for benzene seems to have been confirmed, but our findings demonstrate that also local electron circulations provide significant deshielding effects on the proton chemical shift and a relevant contribution to the in-plane susceptibility.
A Kerr effect and dielectric study of α, ω-dibromoalkanes
Authors: Khanarian G. , Tonelli A. E.
Published: February 2003

We report the molar Kerr constants mK and dipole moments squared <μ2≳ of the α, ω-dibromoalkanes Br(CH2)n−1Br (n−1 = 3–20) in cyclohexane. We calculate the average mK and <μ2≳ on the basis of the rotational isometric state theory with nearest-neighbor interactions and the optical valence scheme. The dipole moments at each end of the alkane chain are assumed to be (a) along the C–Br bond only, (b) the sum of a moment along the C–Br bond and an induced moment along the adjoining C–C bond. We obtain good agreement between calculated and experimental mK and <μ2≳ by assuming that the gauche states of the first and last rotatable bonds are φg± = ±80° to ±100° and not ±120°. Better agreement with experimental results is obtained by using assumption (b) for the dipole moment. We calculate the effect of dipole–dipole interactions between the C–Br dipoles on mK and <μ2≳ and find them to be negligible. Finally we use Onsager’s theory of the reaction field to calculate solvent effects on mK and <μ2≳ and find the theory to be inadequate.
Further development of the approach of Peralta and Zwanzig. II. The drag on a sphere as a function of density
Authors: Keyes T. , Morita Terumitsu
Published: February 2003

Our modification of the method of Peralta and Zwanzig for the calculation of the drag on a sphere is applied at high and low bath densities. We obtain Stokes law at high density and 0.82 times the exact result at low density. Thus, our theory gives a unified framework for calculation of the drag as a function of density.
The electrostatic potential and field in the surface region of lamina and semi-infinite point charge lattices
Authors: Heyes David M. , van Swol Frank
Published: February 2003

General and readily adaptable equations are derived for the Coulomb potential in the surface region of infinite lamina and semi-infinite point charge lattices using the Bertaut method. The expressions which resemble the Ewald formulas used for comparable bulk lattices are cast in terms of charge spreading functions of arbitrary analytical form and are evaluated at real and reciprocal space lattice sites. The significance of the zero reciprocal space vector term is discussed. The convergence behavior of a modified direct summation scheme over the lattice charges compares favorably with that of the Bertaut method.
Nucleation, spinodal decomposition, and interface motion in the van der Waals fluid
Authors: Varea C. , Robledo A.
Published: February 2003

We discuss the predictions of the phenomenological theory of Metiu, Kitahara, and Ross for the most probable evolution of density fluctuations in the van der Waals fluid model. The knowledge of the exact (nonlocal) form for the grand potential functional Ω permits a precise study of the kinetics of phase change under strongly nonuniform conditions. It is shown that for every subcritical temperature and chemical potential in the spinodal region there exists an infinite family of periodic stationary states in addition to the usual uniform ones. The stability analysis of these states provides a description of spinodal decomposition in its intermediate and later stages. It is also shown that fluctuations separated in space are correlated through the nonlocality of Ω and that they cooperate in the nucleation process with an additional term absent in the classical and gradient theories. The solitary wave motion which describes condensation–evaporation processes is obtained from a perturbation on the thermodynamic conditions for phase equilibrium.
A theoretical study of the resonant multiphoton ionization from a molecular system: Relaxation effects
Authors: Fujimura Y. , Lin S. H.
Published: February 2003

Effects of the vibrational and electronic relaxations on the resonant two-photon ionization from molecules are theoretically studied. Taking into account the relaxations in the resonant state, an expression for the ion current is derived by using the master equation involving zero-, one-, and two-photon processes in the Markoff approximation. The resultant ion current is expressed by the time-dependent and -independent terms. The time-dependence of the ion current is originated from the longitudinal relaxation, and on the other hand the time-independent term consists of both the coherent interaction of molecules with laser fields, and the elastic interaction between the molecules and the heat bath. Approximate expressions for the ion current for the slow and fast vibrational relaxation rates compared with the optical transition rate are also derived by using the matrix perturbation method. Model calculations of the ion current are performed to demonstrate the longitudinal relaxation effect for a model system characterized by the two-level resonant state.
Evidence of a phase transition in the rotator phase of the odd-numbered paraffins C23H48 and C25H52
Authors: Doucet J. , Denicolo I. , Craievich A. , Collet A.
Published: February 2003

We present here a study of the ’’rotator phase’’ displayed by the odd-numbered paraffins CnH2n+2 with n = 23 and n = 25. From x-ray and D.S.C.(differential scanning calorimetry) experiments we show that the so-called rotator phase of these compounds exhibits a phase transition from a pseudohexagonal symmetry modification to a hexagonal symmetry modification when increasing the temperature. The corresponding phase transition seems to be a weak, first order transition.
The millimeter wave spectra of NaH and NaD
Authors: Sastry K. V. L. N. , Herbst Eric , De Lucia Frank C.
Published: February 2003

Utilizing a glow discharge absorption cell, we have detected the v = 0, 1, 2, and 3, J = 0→1 transitions of NaH and the v = 0, 1, 2, and 3, J = 1→2 and v = 0, J = 2→3 transitions of NaD in the millimeter and submillimeter regions of the spectrum. The derived Dunham constants (MHz) are                           A significant breakdown of the Born–Oppenheimer approximation has been observed.
Structural properties of macromolecular solutions
Authors: Giordano R. , Maisano G. , Mallamace F. , Micali N. , Wanderlingh F.
Published: February 2003

We report measurements of viscosity and light scattering in an aqueous solution of BSA. Like the lysozyme solutions, previously investigated, the BSA solutions show thixotropic properties. Optical measurements of both elastic and inelastic light scattering indicate the existence of a structure in which the BSA molecule tends to clusterize, each cluster being correlated to the others. A k-dependent diffusion coefficient D(k) is found. The static structure factor deduced from the values of DL(k) agrees well with the indications given by the elastically scattered intensity 𝒥(k). Also, the statical properties of scattered light appear to be consistent with the proposed model. A qualitative explanation, in terms of a dominant component in the fluctuations of concentration, is briefly sketched.
Analysis of torsional spectra of molecules with two internal C3v rotors. XXI. Analysis of the torsional spectra of dimethylsulfide-d0, -d3, and -d6
Authors: Durig J. R. , Jalilian M. R. , Sullivan J. F. , Compton D. A. C.
Published: February 2003

The Raman spectrum of gaseous dimethylsulfide-d6 has been recorded between 100–300 cm−1 with a resolution of 2 cm−1. The far infrared spectrum has been recorded from 100–250 cm−1 with a resolution of 0.25 cm−1. Considerable torsional data are reported and used to characterize the torsional potential function of (CD3)2S based on the semirigid model. Previous assignments of the torsional transitions in dimethylsulfide-d0 and -d3 have been revised. The average effective V3 for the dimethylsulfides was found to be 748 cm−1 (2139 cal/mol). A strong correlation was found between the V03 and the cosine–cosine coupling term (V33). The effective barriers obtained for all three isotopic species are comparable to the results obtained from the most recent microwave study.
Nascent product vibrational state distributions of ion–molecule reactions: The H+F−→HF(v)+e− associative detachment reaction
Authors: Zwier Timothy S. , Weisshaar James C. , Leone Stephen R.
Published: February 2003

The nascent product vibrational state distribution is obtained for the thermal energy associative detachment reaction H+F−→HF(v?5)+e−, ΔH = −57.0 kcal/mol. The relative vibrational populations are as follows: Nv = 10 = 0.00±0.06; Nv = 20 = 0.23±0.04; Nv = 30 = 0.27±0.03; Nv = 40 = 0.29±0.03; and Nv = 50 = 0.21±0.03. Arguments are presented that suggest that Nv = 00 = 0. The average fraction of the total energy deposited in product vibration is <fv≳ = 0.64±0.03. The release of the very light electron as one of the reaction products places severe angular momentum constraints on the reaction system. A simple kinematic model predicts a highly non-Boltzmann HF rotational state distribution which increases with increasing J up to some cutoff level. The high degree of vibrational excitation in the HF product has been accounted for by theoretical calculations of Gauyacq using the zero-range potential approximation.
Observation of collisional relaxation from HD v = 5 and v = 6 by direct overtone pumping and photoacoustic detection
Authors: Rohlfing Eric A. , Gelfand Jack , Miles Richard B. , Rabitz Herschel
Published: February 2003

We present here the first detailed measurement on the mechanism of collisional relaxation from the upper vibrational states of HD. Preliminary results are given in which we have measured collisional relaxation following the direct overtone pumping of HD into v = 5 and v = 6 with a pulsed visible wavelength dye laser. These time-resolved photoacoustic data indicate that the vibrational to transitional (V–T) and vibrational to vibrational (V–V) relaxation rates for collisions with ground state molecules become equal near v = 5.
Collisional deactivation of PH(b 1Σ+) by rare gases
Authors: Margani A. , Xuan C. Nguyen , Di Stefano G. , Lenzi M.
Published: February 2003

The deactivation rate constants of PH(b 1Σ+, v = 0) by rare gases are reported. A correlation of these constants with molecular parameters has been attempted through a semiclassical treatment by long range interaction of the collision induced transition between two discrete vibrational levels of two distinct electronic states. A correlation according to Parmenter’s theory has also been considered.
Photoionization study of CO2, N2O dimers and clusters
Authors: Linn S. H. , Ng C. Y.
Published: February 2003

Photoionization efficiency data for (CO2)+2–4 and (N2O)+2 in the region 600–1020 Å have been obtained using the molecular beam method. The ionization energies (I.E.) of (CO2)2, (CO2)3, (CO2)4, and (N2O)2 were measured to be 13.32±0.02 eV (930.5±1.5 Å), 13.24±0.02 eV (936.5±1.5 Å), 13.18±0.02 eV (941±1.5 Å), and 12.35±0.02 eV (1004±1.5 Å), respectively. Using these values, the known I.E.’s for CO2 and N2O, and the estimated binding energies for (CO2)2 and (N2O)2, the dissociation energies for CO+2⋅CO2, (CO2)+2⋅CO2, (CO2)+3⋅CO2, and N2O+⋅N2O were deduced to be 11.8±1.0, 3.3±1.4, 2.8±1.4, and 13.1±0.9 kcal/mol, respectively. The ion–molecule half reaction N2O+⋅N2O→N3O+2+N was observed. The analysis of the photoionization efficiency curves for (CO2)+2 and (N2O)+2 suggests electronic predissociation or direct dissociation might be important dissociation mechanisms for the CO*2(n)⋅CO2 and N2O*(n)⋅N2O excited Rydberg dimers.
A comparison of the l-average coupled states, corrected coupled states, and close coupling results for a model system
Authors: Fitz D. E. , Khare V. , Kouri D. J.
Published: February 2003

Calculations are reported for a model collision system using the l-average coupled states [CS(lav)] approximation. These results are compared against exact close coupling and corrected centrifugal sudden (CCS) results of McLenithan and Secrest. The uncorrected CS(lav) results are found to be more accurate for the McLenithan–Secrest model than the CCS results. (AIP)
Reinvestigation of Brillouin’s theorem in open-shell SCF theory by means of constrained orbital variation
Authors: Morikawa Tetsuo , I’Haya Y. J.
Published: February 2003

The orthonormality-constrained variation (ONCV) method is compared with the usual variation methods with respect to the so-called Brillouin’s theorem. Within the restricted open-shell Hartree–Fock approximation, the ONCV method yields a modified form of Brillouin’s theorem which is not in a form such that one bra–ket vanishes, together with the well-known forms of Brillouin’s theorem. Brillouin’s theorem for the excited singlet state constructed from nonorthogonal spatial orbitals is examined using a parameter representation of the ONCV variation and is found to be not in a typical form. What has caused these results is discussed in some detail.
Theoretical study of the H3− cluster
Authors: Rayez J. C. , Rayez-Meaume M. T. , Massa L. J.
Published: February 2003

Calculations at the ab initio level with an extended basis set including polarization functions have been performed in order to study the possible existence of ion–induced dipole clusters like H3− in the interstellar medium. Configuration interaction calculations have shown that the interstellar diffuse bands observed by astronomers and not attributed till now can be explained by the presence of such clusters in the ground state and excited states 1Σ0+ and 1Π.
Collisions of excited Na atoms with H2 molecules. I. A
b i
n
i
t
i
o potential energy surfaces and qualitative discussion of the quenching process
Authors: Botschwina Peter , Meyer Wilfried , Hertel Ingolf V. , Reiland W.
Published: February 2003

Potential energy surfaces have been calculated for the four lowest electronic states of Na (3 2S, 3 2P)+H2(1Σ+g) by means of the RHF–SCF and PNO–CEPA methods. For the so-called quenching process of Na (3 2P) by H2 at low initial translational energies (E–VRT energy transfer) the energetically most favorable path occurs in C2v symmetry, since—at intermediate Na–H2 separation—the ? 2B2 potential energy surface is attractive. From the CEPA calculations, the crossing point of minimal energy between the ? 2A1 and ? 2B2 surfaces is obtained at Rc = 3.57 a.u. and rc = 2.17 a.u. with an energy difference to the asymptotic limit (R = ∞, r = re) of −0.06 eV. It is thus classically accessible without any initial translational energy, but at low initial translational energies (∼0.1 eV) quenching will be efficient only for arrangements of collision partners close to C2v symmetry. There is little indication of an avoiding crossing with an ionic intermediate correlating asymptotically with Na+ and H2− as was assumed in previous discussions of the quenching process. The dependence of the total quenching cross sections on the initial translational energy is discussed by means of the ’’absorbing sphere’’ model, taking the initial zero-point vibrational energy of the hydrogen molecule into account. New experimental data of the product channel distribution in H2 for center-of-mass forward scattering are presented. The final vibrational states v′ = 3, 2, 1, and 0 of H2 are populated to about 26%, 61%, 13%, and 0%, respectively. The observed distributions in H2 (and D2) may be rationalized by simple dynamic considerations on the basis of the calculated surfaces.
First-order model for the surface properties of liquid metals: Electroneutrality conditions and interionic correlations
Authors: Amokrane S. , Badaiali J.-P. , Rosinberg M. -L. , Goodisman J.
Published: February 2003

A previously presented model for simple liquid metals, in which the electron–ion pseudopotential is treated in first order, is used to calculate some surface properties. The electron density profile is obtained by minimization of the surface energy of a reference sysytem and the ionic profile is taken as a step function. In the surface, we write the ion–ion distribution function in a form which reduces to the bulk radial distribution function in the interior, while satisfying the local electroneutrality condition as well as other necessary constraints. The bulk distribution function is that for neutral hard spheres. Calculated energies are of the right size for most of the metals considered, in spite of the fact that the components are sometimes an order of magnitude larger than the surface energy itself. The sensitivity of the surface energy to the approximations in the model are discussed. The classical Fowler contribution of the Coulombic interaction of the ions is found to be markedly reduced by the modification demanded by the electroneutrality condition. Some directions for future improvements are indicated.
The nature of the phase transition observed for monolayers of azulene on Pt(111)
Authors: Dahlgren David , Hemminger John C.
Published: February 2003

A model is presented for the reversible phase transition observed for azulene monolayers on Pt(111). Below the transition temperature the overlayer LEED pattern consists of (3×3) aligned with the substrate and (3×3) rotated by 30°. Above the transition temperature the LEED pattern is a (3×3) aligned with the substrate. The model attributes the phase transition to an order–disorder transition of the rotational orientation of azulene molecules with the molecular plane parallel to the surface. (AIP)
Rotational analysis of congested spectra: Application of population labeling to the BaI C–X system
Authors: Johnson Mark A. , Webster Christopher R. , Zare Richard N.
Published: February 2003

The rotational analysis of the congested spectra of the BaI radical is carried out by optical–optical double resonance method by exciting fluorescence. (AIP)
A note on the transition dipole moment of alkali dimers
Authors: Woerdman J. P.
Published: February 2003

A correlation is observed between the dipole moment D and the frequency ν of the Li2 and Na2 X → A and X → B transitions: the product D2(R)ν(R) is. independent of the internuclear separation R. This is used to predict D(R) for the X → A and X → B transitions of K2. (AIP)
ESR of GdF3 and related molecules at 4 °K
Authors: Baumann C. A. , Van Zee R. J. , Zeringue K. J. , Weltner W.
Published: February 2003

The pyramidal (C3v) GdF3 molecule was trapped in neon and argon matrices at 4°K and its ESR spectrum measured in the X-band region. In neon the spectrum exhibited several off-principal-axis transitions which were sensitive to the assigned magnetic parameters. It was shown to be a S = 7/2 molecule (ground state 8A1) with g∥ = 1.995, g⊥ = 1.990, and ‖ D ‖ = 0.433 cm−1. The 19F hfs was unresolved and therefore <∼10 G. Only the mS = +1/2 ↔ −1/2 transition of GdH3 was observed, yielding ‖ D ‖ = 0.7 to 1.3 cm−1, and it is inferred to be a planar (D3h) molecule (ground state 8A1′). Weak spectra of GdCl3 (8A1) and GdF2 (9A1) were also observed, yielding ‖ D ‖?0.36 and 0.20 cm−1, respectively.
UV and visible emission produced from S2Cl2 in the rare gas flowing afterglow
Authors: Tsuji Masaharu , Murakami Isao , Nishimura Yukio
Published: February 2003

The energy transfer reactions of metastable Ar(3P0,2), Ne(3P0,2), and He(2 3S) atoms with S2Cl2 have been studied by optical spectroscopy in a flowing afterglow apparatus. In the Ar(3P0,2)+S2Cl2 reaction, ArCl*, S2(B–X), and Cl*2 emissions were observed, whereas S i and Cl*2 emissions were detected in the Ne(3P0,2)+S2Cl2 reaction. The He(2 3S)+S2Cl2 reaction produced a new extensive S+2 (A 2Πu–X 2Πg,r) emission in the 350–700 nm region, in addition to S i, Cl i, and Cl*2 emissions. Vibrational analysis of the S+2(A–X) band system provided molecular constants of the S+2(A, X) states. By using these constants, Morse potential Franck–Condon factors and r centroids of the S+2(A–X) transition have been calculated. The relative electronic transition moments and vibrational populations of S+2(A) have also been determined. The vibrational populations for 0⩽v′⩽6 were nearly exponential with an effective vibrational temperature of 1020±50 K.
Electron-impact excitation of autoionizing states in xenon
Authors: Mathur Deepak , Frost David C.
Published: February 2003

High-sensitivity single-ionization efficiency functions of Xe have been measured using a computer-controlled beam of electrons monoenergetic to ∼45 meV FWHM. Well-defined structure detected in the energy range 12.2–13.5 eV is attributed to the excitation of neutral Xe Rydberg states converging on XE+(2P1/2) followed by autoionization. Some of the structure appears to correspond to parity forbidden s–p′ transitions. A sharp increase in ionization is observed at the 2P1/2 threshold.
Multiphoton ionization spectroscopy of organometallics: The Cr(CO)6, Cr(CO)3C6H6, Cr(C6H6)2 series
Authors: Fisanick G. J. , Gedanken A. , Eichelberger T. S. , Kuebler N. A. , Robin M. B.
Published: February 2003

The multiphoton ionization (MPI) spectra of the title compounds have been studied in the 3533–6000 Å region in an effort to elucidate the fragmentation and ionization pathways. At wavelengths longer than 4000 Å, the compounds dissociate more rapidly than they are ionized, thereby forming Cr(I) which then can be ionized in a (2+1) resonant process. The resonance wavelengths are identical in the three compounds, and only Cr+ is observed in the MPI-produced mass spectra. At wavelengths shorter than 4000 Å, both Cr+ and CrO+ appear in the mass spectra of Cr(CO)6 and Cr(CO)3C6H6. Surprisingly, however, no ionization of the unbound ligands was observed in any of the complexes studied. Electron time-of-flight measurements in Cr(CO)6 show that at wavelengths shorter than 4000 Å ionization of the parent–molecule resonant state and fragmentation to neutrals with eventual ionization of Cr(I) are important ionization paths. The observation of severe ac Stark broadening of the Cr(I) MPI resonances implies that a rate-equation approach to ion production will be inadequate, except at very low flux. Additionally, the exclusive production of Cr+ indicates extremely rapid dissociation of the intermediate molecular fragments. The breakdown of the rate-equation approach leads to effective power exponents which are smaller than those required by the known Cr+ mass-spectrometric appearance potentials; this indeed is found experimentally. The branching ratios for production of various excited states of Cr(I) are dependent upon the precursor molecule and the incident laser flux.
High pressure study of viscosity and temperature effects on tetracyanobenzene EDA complexes
Authors: Thomas Michele Moisio , Drickamer H. G.
Published: February 2003

High pressure fluorescence studies from 0–10 kbar have been performed on electron donor–acceptor (EDA) complexes of s-tetracyanobenzene (TCNB) with a series of aromatic hydrocarbons. Four solvents were used: 2,2,4,4,6,8,8-heptamethylnonane (HMN), methylcyclohexane (MCH), 2,6,10,14-tetramethylpentadecane (TMPD), and a mixture of MCH and HMN. A viscosity range from 0.006 to 10 000 P was covered at two temperatures: 0 and 25 °C. As pressure (viscosity) increased the fluorescence spectrum shifted from one dominated by emission from the equilibrium (EQ) excited singlet state to one dominated by Franck–Condon (FC) singlet emission. Lifetime measurements for the complexes of o-xylene and p-xylene with TCNB yielded the two radiative rates (kEQ and kFC) as well as the rate of relaxation from FC to the EQ excited state (kRE). kRE was found to correlate well with viscosity and to be independent of temperature at constant viscosity, indicating that the relaxation process is diffusion controlled.
Relaxation parameters for power-broadened microwave line shapes. I. Anderson theory
Authors: Peterson Keith L.
Published: February 2003

A model is developed for the calculation of collisional cross sections for all spherical tensor orders. The model is based on the Anderson low-power linewidth theory. General expressions are derived for the cross sections and then evaluated for the case of multipole–multipole interaction potentials. Motivated by application to power-broadened microwave line shapes, the dependence of the cross sections on tensor order is discussed. It is shown that for the typically dominant case of dipole–dipole potentials, many of the cross sections are independent of tensor order. The order dependence for other potentials is discussed.
Isotopically decoupled vibrational spectra and proton exchange rates for crystalline NH3 and ammonia hydrate
Authors: Thornton Cynthia , Khatkale M. S. , Devlin J. Paul
Published: February 2003

Codeposits of NH3 with ND3 or D2O have been prepared at liquid nitrogen temperatures in the absence of proton exchange. Vibrational data for the anhydrous cubic crystalline ammonia, containing isolated NH3 or ND3, confirm that, relative to water ice, intermolecular coupling in ammonia ice exerts a relatively minor influence on the infrared and Raman spectra. Nevertheless, sizeable decoupling shifts, particularly for ν1, have been observed and attributed to a combination of factors including correlation field and Fermi resonance effects. The Raman polarization data has also affirmed long standing assignments of ν1 and ν3 for ammonia ice. Warming of the ammonia thin films resulted in limited isotopic scrambling at 130 K, apparently possible only through the agency of trace concentrations of water. The vibrational coupling pattern for the resultant NHD2 and NH2D molecules suggest that proton (deuteron) migration away from the exchange centers is impossible at temperatures up to 150 K. By contrast, isotopic scrambling was rapid and complete at 140 K for amorphous ammonia hydrate films (∼35% NH3, ∼65% D2O) which were also prepared without exchange at ∼90 K. The proton (deuteron) exchange rate is much greater for the amorphous ammonia hydrate at 140 K than for pure water ice. Such exchange requires both ion-pair defect formation and proton mobility. Since the NH3 suppresses the H3O+ concentration via formation of NH+4, a suppression the likes of which has been shown to stop proton exchange in water ice, the evidence strongly suggests that NH4+ in ammonia, like H3O+ in water, is an effective proton transfer agent, probably acting through a tunneling mechanism (i.e., H3N+–H⋅⋅⋅NH3→H3N⋅⋅⋅H–N+H3 etc.) to render the proton mobile in the ammonia hydrate. This mobility combined with the greater NH4+ concentration, relative to the H3O+ concentration in H2O ice Ic, results in isotopic scrambling at the reduced temperature.
Absorption and circular dichroism line shapes of a molecular dimer in the strong electronic coupling limit
Authors: Friesner Richard , Silbey Robert
Published: February 2003

We have derived approximate analytical expressions for the absorption and circular dichroism line shapes of a molecular dimer composed of two identical molecules (each with a single excited electronic state and single vibrational mode) in the strong electronic coupling limit. These are compared with numerical results and yield excellent agreement. We compare our approach to other theories and discuss experimental applications and possible extensions of this work.