bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution electron scattering from chemisorbed oxygen on the ruthenium (001) surface
Authors: Thomas G. E. , Weinberg W. H.
Published: February 2003

Inelastic electron scattering spectroscopy has been used to measure energy-gain as well as energy-loss transitions of oxygen chemisorbed on the Ru(001) surface. The relative intensity of the energy-gain to the energy-loss transition was found to follow the expected Boltzmann distribution. The intensities of the inelastic peaks relative to the elastic peak were observed to increase with temperature. The temperature dependence and sources of experimental error are explained within the context of an approximate theory for the scattering of electrons from adsorbates on metal surfaces.
Energies and widths of quasibound levels (orbiting resonances) for spherical potentials
Authors: Le Roy Robert J. , Liu Wing-Ki
Published: February 2003

Various methods for calculating the energies and widths of quasibound levels (orbiting or shape resonances) for spherical potentials are critically compared. A derivation for the previously-proposed Airy function boundary condition method is presented, and a Weber function boundary condition method for locating resonances which lie above the potential barrier maximum is derived, tested, and found wanting. It is shown that the Weyl m-function method of Hehenberger et al. [J. Chem. Phys. 65, 4559 (1976)] yields results in essentially exact agreement with the time-delay maximum method of Le Roy and Bernstein [J. Chem. Phys. 54, 5114 (1971)]. An improved semiclassical method of calculating these resonance widths, suggested by M.S.Child, is presented and shown to be reliable even for levels lying right at a potential barrier maximum.
On scaling theories of polymer solutions
Authors: Kosmas Marios K. , Freed Karl F.
Published: February 2003

We present a rigorous derivation of a scaling theory of the thermodynamics of polymer solutions at finite concentrations. The derivation proceeds directly in 3(2, 4, etc.) dimensions from the expression for the partition function for a solution of monodisperse continuous Gaussian chains with excluded volume. There is no need for the use of renormalization group methods or for the extrapolation of results from calculations near four-dimensions. Nethertheless, the importance of four dimensions emerges directly from the scaling theory as does a proof that only the binary excluded volume parameter appears in the equation of state, average chain dimensions, etc., in the limit of long enough chains. The irrelevance of the range of the binary segment interaction and the sufficiency of the two parameter theory is thus established by the scaling theory in a straightforward and elementary fashion. We demonstrate that the power law dependence, ν in 〈R2〉∝L2ν, of the mean square end-to-end distance 〈R2〉 on the chain length L in good solutions can be calculated directly in three (two, etc.) dimensions from the scaling relations. Applications are presented to good solutions at finite concentrations, to confined chains in good solvents, and to the properties of solutions of block copolymers.
Effect of excluded volume on the cluster model of condensation
Authors: Swaminathan P. K. , Poland Douglas
Published: February 2003

The effect of excluded volume is incorporated into Fisher’s physical cluster model for the gas–liquid phase transition using the Percus–Yevick approximation for a mixture of spherical clusters to treat excluded volume. The resultant formalism is in terms of coupled nonlinear equations in terms of the densities of the various clusters. The equations can be solved as fugacity series using an exact recursion relation. The analytic properties of the model are easily obtained using an expansion in terms of a variable containing the fugacity and the pressure. The condensation point is found to remain an essential singularity of the fugacity series as in Fisher’s model, the effect of excluded volume being to strengthen the cause of this singularity. The effect of excluded volume is to make the radius of convergence in the fugacity series greater than unity. The critical point no longer occurs when the surface free energy per unit area of a cluster is zero, but rather at a value that favors the surface making the assumption of spherical clusters at the critical point invalid. The unrealistic assumption of spherical clusters near the critical point gives the incorrect results that the critical point is an essential singularity with no critical exponents.
The regularities observed in the second order hyperpolarizabilities of variously disubstituted benzenes
Authors: Dulcic A. , Sauteret C.
Published: February 2003

Second order hyperpolarizabilities of a group of para-disubstituted benzenes have been determined from the measurements of the dc electric field induced second harmonic generation in liquid samples. Four donor groups and four acceptor groups were used to provide different combinations of donor–acceptor disubstitution. The results show clearly that it is possible to establish a sequence of donors (acceptors) with increasing donating (accepting) effectiveness of each other. It has been observed that the increase of the second order hyperpolarizabilities is followed in general by a red shift of the first electronic absorption peak. The interpretation in terms of the intramolecular charge transfer has been presented.
Phase separation in fluid systems by spinodal decomposition. II. A molecular dynamics computer simulation
Authors: Mruzik Michael R. , Abraham Farid F. , Pound G. M.
Published: February 2003

Spinodal decomposition is observed in a simulated Lennard-Jones fluid using molecular dynamics, and the results are in agreement with the predictions of a recent microscopic theory. An initial exponential growth of supercritical density fluctuations is found and supports the linear approximation of the generalized diffusion equation for the initial phase separation.
The OH stretching region infrared spectra of low density amorphous solid water and polycrystalline ice Ih
Authors: Bergren Michael S. , Schuh Daniel , Sceats Mark G. , Rice Stuart A.
Published: February 2003

The transmission spectra in the intramolecular stretching region have been measured for thin films of H2O and D2O polycrystalline ice Ih and amorphous solid water. The data have been reduced to obtain the complex refractive index in this region via an iterative procedure designed to account for reflection and interference losses. Details of this procedure are described. The values which result from this analysis are converted to give the imaginary part of the dielectric permittivity as a function of wavelength for each sample. In this form the spectra are examined and compared to one another, with regard to recent experimental and theoretical studies. We conclude that it is difficult to obtain detailed structural information for the amorphous solid from an analysis of the OH (OD) stretching vibrational spectrum alone.
A theoretical study of the OH stretching region of the vibrational spectrum of ice Ih
Authors: McGraw Robert , Madden William G. , Bergren Michael S. , Rice Stuart A. , Sceats Mark G.
Published: February 2003

We describe a theoretical interpretation of the OH stretching region of the vibrational spectrum of ice Ih derived from a study of extended models. The principle conclusions are the following: (i) The breadth and distribution of vibrational modes, and of intensity in the Raman and infrared spectra, are dominated by the influence of strong intermolecular coupling. The intermolecular coupling is comparable in strength to the intramolecular coupling. Long range couplings between molecules not directly hydrogen bonded mainly serve to make the features of the spectrum more diffuse than they would otherwise be, but have no great influence on the spectral distribution. (ii) The intramolecular OH stretch-OH stretch coupling in ice Ih is of opposite sign to that in the gas phase. (iii) The vibrational modes of ice Ih are found to be complex mixtures of molecular motions, so identification of regions of the Raman or infrared spectra with particular isolated molecule modes is not useful. Rather good agreement is obtained between the Raman and infrared spectra predicted and those observed. Some deficiencies of the model, associated with residual discrepancies between theory and experiment, are discussed.
Deuterium magnetic resonance of some polymorphic liquid crystals: The conformation of the aliphatic end chains
Authors: Hsi Shan , Zimmermann Herbert , Luz Zeev
Published: February 2003

Deuterium magnetic resonance measurements of four members of the homologous series p-alkoxybenzylidene-p-alkylaniline (no⋅m), perdeuterated in their alkoxy chains, are reported. The compounds studied were 40⋅7, 50⋅7, 60⋅7, and 70⋅7. For 50⋅7 various isotopic species specifically deuterated in the alkoxy chains, as well as in the benzylidine moiety, were prepared and their DMR studied. These measurements allowed a complete assignment of the resonances from the alkoxy chain. The spectrum of all four compounds was studied over their whole mesomorphic regions. In most phases well resolved spectra were obtained yielding the various quadrupole splittings and in many cases also the dipolar interactions within the methylene and methyl groups. Using double quantum spectroscopy dipolar splitting between different methylene deuterons could also be resolved. The methylene quadrupolar splittings and the dipolar interaction within the methylene groups decrease along the chain towards the methyl end in a characteristic stepwise manner. This behavior is attributed to chain reorientational freedom and is quantitatively interpreted in terms of two structural factors: (i) Fast dynamical equilibrium between the all-trans conformation of the alkoxy chains and chain conformations involving one or more kinks, and (ii) a molecular model in which the aliphatic chain axis is inclined with respect to the molecular long axis. The characteristic pattern of the splitting can then be reproduced by assuming a monotonically increasing kink probabilities along the chain towards its methyl end. This interpretation is used to estimate the kink probability distribution in the alkoxy chains in the various compounds and mesophases. No significant effect of the mesophase structure on the kink statistics was found.
Multiplicity and stability of concentration waves. Analysis of a model autocatalytic system
Authors: Pismen L. M.
Published: February 2003

Conditions of existence and stability of propagating wave solutions are investigated for a model multicomponent autocatalytic system with piecewise-constant kinetics. A variety of behavioral patterns is generated by appropriate mapping of kinetic domains and allowing for diverse length and velocity scales associated with different components. The described phenomena include instability of wave fronts, multiple propagating solutions, stable steady inhomogeneities, and persisting spatial oscillations in kinetic systems which do not exhibit homogeneous limit cycles.
Surface roughness and the enhanced intensity of Raman scattering by molecules adsorbed on metals
Authors: Moskovits M.
Published: February 2003

Greatly enhanced Raman scattering from monolayers of pyridine adsorbed on silver has been reported by several authors. I propose that the anomalous intensity arises from preresonant or resonant excitations of conduction electron resonances in adsorbate covered metal bumps on the surface. The bumps form a two-dimensional colliodlike layer which displays a collective resonance at a frequency which depends on the bump density. The model can account for the disparate excitation functions reported by two groups in terms of varying degrees of roughness. The apparent lack of enhancement with metals other than Group Ib is also explained.
Core excitons and the dielectric response of polystyrene and poly(2-vinylpyridine) from 1 to 400 eV
Authors: Ritsko J. J. , Bigelow R. W.
Published: February 2003

The complete spectra of valence and core electronic excitations of atactic polystyrene, PS, and poly(2-vinylpyridine), PVP, from 1 to 400 eV were measured by electron energy loss spectroscopy. Energy losses of 80 keV electrons transmitted through 1000 Å thick films were measured with a resolution of 0.1 eV. The spectrum of PS contains several previously unreported broad peaks between 9 and 20 eV which coincide with structure observed in gas phase benzene spectra and which have been attributed to Rydberg states, but which are described here as valence molecular orbital excitations. The dielectric response function of PS and PVP from 1 to 100 eV is computed from energy loss data. The calculated reflectivity and refractive index are in excellent agreement with recent optical measurements. The spectrum of carbon core electron excitations above 285 eV consists of a series of sharp peaks due to transitions to empty molecular states (core excitons) followed by transitions to a free-electron-like continuum of states. The core exciton spectrum is quantitatively described in a model based on a molecular orbital ground state calculation (CNDO/S). The results show that such spectra provide a measurement of the distribution of empty molecular orbitals. In addition, shifted exciton peaks are observed which correspond to inequivalent core electron binding energies due to differences in net atomic charge.
Dynamics of growth or dissolution of a gas bubble
Authors: Tao L. N.
Published: February 2003

The paper is concerned with the dynamics of growth or dissolution of a gas bubble in an infinite liquid, subject to arbitrarily prescribed initial and boundary conditions. The isothermal growth or dissolution is assumed to be by diffusion without convection. During the diffusive process, the effect of surface tension on the moving boundary is included in the study. It is found that the exact solutions of the problem can be established which are applicable to either growth or dissolution of a gas bubble in a supersaturated or undersaturated liquid. The convergence of the series solution is considered and proved. A numerical example of the solution is given and it is compared to some known approximate solutions. The position of the gas–liquid interface is of the order t1/2 as t→0, when the initial concentration of the gas at the interface is discontinuous, and it is of an order other than t1/2 when the initial concentration is continuous. Also, in problems of growth of a bubble in a supersaturated liquid, no solution could exist when the initial concentration at the interface exceeds a certain value. This establishes a necessary condition for the existence of the solution. On the other hand, the solution for a gas bubble in an undersaturated liquid always exists. The result of the lifetime of a gas bubble is also established.
The classical path approximation in time-dependent quantum collision theory
Authors: Augustin Stuart D. , Rabitz Herschel
Published: February 2003

Time-dependent treatments of molecular collisions have frequently employed the combination of quantum equations for the internal degrees of freedom (i.e., vibration, rotation) with a classical description of the translational motion. In this paper, it is shown how energy-conserving classical path equations may be derived from first principles, thereby obtaining quantum correction terms of arbitrary order. These expressions have interesting implications for the question of how the classical limit is approached. If the translational degree of freedom is assumed to be described by a very narrow wave packet, the correction term to first order in h/ is purely imaginary and therefore non-Hermitian. These techniques can be generalized to a classical treatment of other degrees of freedom, and the case of rotation in an atom–vibrotor collision is explicitly considered. For both the translational and rotational examples, the full series of corrections takes on an interesting and suggestive exponential form. The failure of classical path methods to satisfy microscopic reversibility is ascribed to a difficulty with the boundary conditions for the translational motion.
Infrared photodissociation of fluorinated ethanes and ethylenes: Collisional effects in the multiple photon absorption process
Authors: Quick C. R. , Wittig C.
Published: February 2003

The ir photodissociation of fluorinated ethanes and ethylenes produces vibrationally excited HF via collisionless molecular elimination. Monitoring of the time resolved HF fluorescence is used as a probe to examine the effects that collisions with inert gas molecules have on the ir photodissociation process. The addition of inert gas is shown to enhance the dissociation yield. Mechanisms which may be responsible for this enhancement are discussed. An example of consecutive dissociation events within the same laser pulse is presented. The energy absorbed in excess of the minimum required for dissociation, the absorption cross section, and the energy absorption rate of highly vibrationally excited vinyl fluoride are estimated.
Orientational ordering and tunneling states in solid CH2D2 as deduced from low temperature heat capacity and neutron cross section measurements
Authors: White M. A. , Lushington K. J. , Morrison J. A.
Published: February 2003

Heat capacity measurements have been performed on isotopically purified solid CH2D2 over the temperature range 0.12⩽T<2.7 K to characterize a large Schottky anomaly. In addition, the total neutron cross section of condensed CH2D2 was measured over the temperature range 0.75⩽T⩽100 K. While a change in neutron cross section consistent with conversion between nuclear spin symmetry species was observed in the region T<4.2 K, no measurable thermal relaxation was encountered in the calorimetric experiments. On the basis of the latter result and of the magnitude of the entropy at the lowest temperatures, it is argued that conversion probably does not occur in this methane. It seems probable that the results should be interpreted as indicating incomplete orientational ordering of the CH2D2 molecules in phase III. A model is developed for the manifold of low-lying tunneling states.
On the role of the distortion energy in the a
b i
n
i
t
i
o calculated dimerization energy of formic acid
Authors: Smit P. H. , Derissen J. L. , van Duijneveldt F. B.
Published: February 2003

It is shown that the use of experimental geometries in ab initio calculations of the dimerization energy of formic acid can lead to unrealistic results. This is caused by errors in the molecular energy difference between the free molecule and the distorted molecule as it occurs in the dimer. A method is suggested that overcomes this difficulty, and it leads to a value of about 3.5 kcal/mole for this molecular energy difference.
Vibrational and rotational relaxation of CDCl3 in nonpolar solvents
Authors: Arndt R. , McClung R. E. D.
Published: February 2003

Vibrational and reorientational correlation functions and correlation times for the ν1 band of CDCl3 in the pure liquid and in solutions in carbon tetrachloride, n-hexane, and carbon disulfide have been obtained using spontaneous Raman scattering, and reorientational correlation times have been obtained from deuterium spin relaxation measurements. The concentration dependence of the reorientational correlation times in the CDCl3/CS2 and CDCl3/n-hexane solutions closely paralleled the solution viscosity, while in CDCl3/CCl4 mixtures, the correlation time exhibited little concentration dependence. These features reflect differences in the anisotropy of the intermolecular potential experienced by the CDCl3 molecules in these solutions. The reorientational correlation functions for the pure liquid exhibited time dependences different from that of the extended rotational diffusion models and a stochastic second-order memory function model. The temperature dependence of the vibrational relaxation times and vibrational second moments of ν1 in CDCl3 liquid is not consistent with Kubo-type dephasing models. The vibrational relaxation data indicate that collisional dephasing (Fischer–Lauberau model) is the probable mechanism of relaxation, but do not rule out contributions from energy relaxation via independent binary collisions. In CDCl3/CS2 mixtures, the band frequency and the bandwidth exhibit concentration dependence in accord with microscopic concentration fluctuations in the solution.
The chemisorption of CO on clean and oxidized Ir(110)
Authors: Taylor J. L. , Ibbotson D. E. , Weinberg W. H.
Published: February 2003

The chemisorption of CO on clean and oxidized Ir(110) has been investigated under ultra-high vacuum conditions with thermal desorption mass spectrometry, contact potential difference measurements, Auger electron spectroscopy, and LEED. On both surfaces, adsorption is nondissociative under all conditions examined, i.e., temperatures between 90 and 1300 K and pressures below 10−6 torr. Two LEED patterns, p (2×2) and (4×2) disordered ones in the [001] direction, form on the clean surface. A (2×1) p1g1 structure forms on the oxidized surface. Thermal desorption spectra from the clean and oxidized surfaces exhibit three and two features, respectively. The desorption energy and pre-exponential factor in the Arrhenius equation describing the desorption kinetics have been measured as functions of surface coverage. The compensation effect occurs on both surfaces. In the limit of zero coverage, the desorption energies are 37 and 31 kcal/mole for clean and oxidized Ir(110), respectively. The adsorption kinetics are identical for both surfaces. At 90 K, the sticking probability is unity until the surface coverage nears saturation. At 300 K, the adsorption kinetics display second-order behavior with an initial sticking probability of unity. The saturation coverage is about 1015 molecules/cm2 for both surfaces at 90 and 300 K. Upon adsorption, the work function increases for both surfaces, but is larger for the clean surface and at lower temperatures. A model developed to fit the change in work function with coverage and temperature indicates that binding sites between the topmost rows of surface atoms are preferred energetically.
The radiative and nonradiative decay of the triplet state of F2 centers in KCl and KBr
Authors: Farge Y. , Ortega J. M. , Silsbee R. H.
Published: February 2003

The temperature variation of the decay time of the triplet state of the F2 center in KCl and KBr has been measured from 4 to 240 K using the linear dichroism technique. These results are interpreted in terms of several mechanisms. At low temperature, a radiative process is competing with a nonradiative one, while at high temperature, a thermally activated one (level crossing process) competes with the nonradiative one. The radiative mechanism can be calculated assuming a spin orbit mixing of the 3Σu ground triplet state with a 1Πu singlet state and the result is in good agreement with experiment. The nonradiative decay can be roughly accounted for by the mixing of non-pure-spin Born–Oppenheimer singlet and triplet states (spin–orbit mixed) by the nonadiabatic terms of the potential; this theory gives a satisfactory description of the temperature behavior of the triplet decay time and an order of magnitude quantitative prediction of the rate.
Semiconducting behavior in simple and complex charge-transfer salts of tetracyanoquinodimethane with substituted pyridinium donors
Authors: Lane J. E. , Fico T. R. , Lombardo A. , Blakemore J. S.
Published: February 2003

A series of eight anion–radical salts has been prepared, each with tetracyano-p-quinodimethane (TCNQ) as the acceptor and a substituted pyridinium ion as the donor. Four species of donor substitution were made as follows: placement of a CN group at either the 3 or 4 position on the pyridinium ring, and use of either N-methyl or N-benzyl substituents. The simple (1:1) and complex (1:2) salts were crystallized for each species. Compaction conductivity measured between 100 and 300 K showed that the simple salts are weakly conducting semiconductors, of activation energy ≳0.3 eV. Single crystal conductivity data for two of these showed essentially isotropic conduction, compatible with alternating stack structures. The four 1:2 salts are all semiconductors, with considerably enhanced conductivity and with activation energies ?0.15 eV. Single crystal data for one of these showed the large conductivity anisotropy characteristic of structures with segregated TCNQ stacks.
Perturbation calculation of molecular correlation energy using Gaussian-type geminals. Second-order pair energies of LiH and BH
Authors: Adamowicz Ludwik , Sadlej Andrzej J.
Published: February 2003

The second-order pair energies of LiH and BH are calculated using Rayleigh–Schroedinger perturbation theory. The first-order perturbed pair functions are expanded in terms of explicitly correlated Gaussian functions. The nonlinear parameters entering the Gaussian geminals are optimized with reference to crude SCF functions according to the method proposed previously. The final values of the second-order pair energies are then calculated using accurate SCF orbitals. At this final stage only the linear parameters are reoptimized. The calculated second-order correlation energies of LiH and BH are compared with recent diagrammatic many-body perturbation theory results. The basis sets composed of two optimized Gaussian geminals for each spin-adapted pair function are shown to give quite reliable second-order correlation energies. The results obtained with four geminals for each pair function are superior to the most accurate many-body perturbation theory data. It is stressed that the nonlinear parameters of Gaussian geminals can be given a simple physical interpretation which facilitates their reasonable guess. The first-order pair functions represented in terms of Gaussian geminals have a very attractive compact and simple form. If properly optimized they can also provide highly accurate values of the second-order molecular correlation energies.
Optical properties of organic dye monolayers by surface plasmon spectroscopy
Authors: Pockrand I. , Swalen J. D. , Santo R. , Brillante A. , Philpott M. R.
Published: February 2003

The spectroscopic properties of dye monolayers on silver films were determined by using the technique of attenuated total reflection (ATR). The dyes N,N′-di(methyloctadecyl) squarylium and N,N′-dioctadecyloxacarbocyanine were deposited on silver films by the Langmuir–Blodgett monolayer technique. From a least squares fit of the experimental ATR curves to the exact reflection formula, the dielectric function of the dye monolayers was determined in the visible wavelength region. It was found that squarylium forms ordered layers with a regular array of molecules and a film thickness equal to the length of the molecule (2.66 nm). These films were characterized by a strong absorption band at λs=530 nm (dimer band) and were highly anisotropic, the transition dipole moment lying in the plane of the monolayer film. Undiluted cyanine dye films on silver, on the other hand, showed a thickness less than that expected from the length of the molecule and a high degree of disorder. Increasing regularity in arrangement and growing thickness were observed when the cyanine dye was diluted with cadmium arachidate. For both the pure and diluted cyanine dye monolayers, two absorption bands have been measured in the visible region (a monomer band at λs=500 nm and a dimer band at λs=464 nm) and it was confirmed that their relative intensities depended on the mixing ratio of cyanine dye to Cd–arachidate.
Infrared absorption intensities of methyl acetylene
Authors: Kondo Shigeo , Koga Yoshinori
Published: February 2003

The infrared absorption intensities of the fundamental bands of CH3CCH, CD3CCH and CH3CCD were measured in the gas phase by the pressure broadening technique. Out of 32 possible sign combinations of (∂p/∂Qi) for each of a1 and e species, only one combination was selected for both species, utilizing the isotopic data, Coriolis information, and the CNDO calculation. Thus, the polar tensor and the effective charges were obtained, as well as the dipole moment derivatives with respect to primitive coordinates. Comparison of these parameter values with those of other molecules suggests that the methyl hydrogens in methyl acetylene resemble those in methyl halides rather than those in saturated hydrocarbons, while the acetylenic hydrogen seems to retain the property in acetylene molecule itself. On the other hand, the CNDO method was not found very successful in this molecule as in propane, cyclopropane, or benzene. In particular, its capability to predict intensity parameter values concerned with the acetylenic group of this molecule was found fairly poor.
Hydrodynamic boundary conditions at the surface of an ablating material
Authors: Vaslow Dale F.
Published: February 2003

The boundary conditions for a vapor at the surface of an ablating or vaporizing material are obtained. The vapor pressure, temperature, and mass flow rate are obtained when the initial state of the solid or liquid material and power absorbed at the phase transition layer are specified. These boundary conditions are derived from the hydrodynamic jump conditions and one equation from the thermodynamics of irreversible processes for a single component system. The results show that, for small mass flow rates, the vapor temperature rise is linearly proportional to the mass flow rate and the pressure drop varies as the square of the mass flow rate. These dependencies are the reversal of Vulliet’s results. Two application examples are considered: the ablation of iron, and the ablation of condensed hydrogen. It is shown that these boundary conditions for the ablation of condensed hydrogen are useful in studies of the refueling of present-day tokamak plasmas by injection of hydrogen pellets.
Radiative lifetimes and two-body deactivation rate constants for Ar(3p5, 4p) and Ar(3p5,4p′) states
Authors: Chang R. S. F. , Setser D. W.
Published: February 2003

The radiative lifetimes and two-body deactivation rate constants of the Ar(3p54p and 4p′) levels have been measured by a time-resolved laser-induced fluorescence technique in a flowing afterglow apparatus. The flowing afterglow produced the Ar(3p54s,3P2) metastable atoms, which subsequently were pumped by the pulsed dye laser. The measured radiative lifetimes are in excellent agreement with the calculated transition probabilities based upon intermediate-coupling theory. Radiative branching ratios of these states also were measured in order to assign the transition probabilities and the absorption oscillator strengths of the transitions between the 4s and 4p levels. The two-body deactivation rate constants range from 1×10−10 to 2×10−11 cm3 atom−1 sec−1. Specific product states from the two-body collisions between Ar(4p and 4p′) atoms and Ar were identified from the laser-induced emission spectra and rate constants for individual product states were assigned for each level. Our results show that two-body collisions do not necessarily result in cascade down the p and p′ manifold, and for the Ar(4p and 4p′) levels more than 50% of the atoms are directly converted to the Ar(4s and 4s′) manifold.
Molecular distortion in the pyrazine triplet state. Analysis in terms of the MIDP experiments under polarized light
Authors: Matsuzaki Kazuo , Azumi Tohru
Published: February 2003

The distortion of the pyrazine molecule in its triplet excited state, as revealed by the appearance of the group theoretically forbidden bands in the sublevel phosphorescence, is analyzed in terms of the polarization of the originally forbidden bands in the sublevel phosphorescence. The experimental results together with some theoretical estimates lead to the conclusion that the pyrazine triplet state is distorted to C2h[C2(y)] due to the pseudo Jahn–Teller type vibronic coupling involving b2g(ν4) vibrational mode.
Scattering of thermal He beams by crossed atomic and molecular beams. I. Sensitivity of the elastic differential cross section to the interatomic potential
Authors: Keil Mark , Kuppermann Aron
Published: February 2003

The ability of diffraction oscillations in atomic beam scattering experiments to uniquely determine interatomic potentials for highly quantal systems is examined. Assumed but realistic potentials are used to generate, by scattering calculations and incorporation of random errors, differential cross sections which are then treated as if they were ’’experimental’’ data. From these, attempts are made to recover the initial potential by varying the parameters of assumed mathematical forms different from the original one, until a best fit to the ’’experimental’’ results is obtained. It is found that the region of the interaction potential around the van der Waals minimum is accurately determined by the ’’measured’’ differential cross sections over a range of interatomic separations significantly wider than would be expected classically. It is also found, for collision energies at which the weakly repulsive wall is appreciably sampled, that the SPF–Dunham and double Morse–van der Waals types of potentials lead to accurate determinations of the interatomic potential, whereas many other mathematical forms do not. Analytical parameterizations most appropriate for obtaining accurate interatomic potentials from thermal DCS experiments, for a given highly quantal system, may depend on the collision energy used.
Proton and deuteron magnetic resonance study of single crystals of diamminesilver dinitroargentate, [Ag(NH3)2]Ag(NO2)2
Authors: Maurer H. M. , Weiss Alarich
Published: February 2003

Proton and deuteron NMR spectra of single crystals of diamminesilver dinitroargentate, [Ag(NH3)2]Ag(NO2)2 and [Ag(ND3)2]Ag(NO2)2, were studied at room temperature. Rapid reorientational motions of the ammine groups around their C3 axes were found. The orientations of the C3 rotation axes within the crystal coincide (deviation=0.9°) with the directions Ag–N in the diamminesilver ions as found by an x-ray crystal structure determination of the compound. A small deviation from linearity of the bond angle N–Ag–N within the ion [H3NAgNH3]+ found röntgenographically is supported by the NMR experiments. The deuterium quadrupole coupling constant e2qQh−1 at room temperature is 71.6±0.5 kHz. A comparison of this value with the data reported for solid ND3 supports the assumption of only small changes in the geometrical and electronical structure of the ammonia molecule by the coordination to the silver ion.
Observations on O(1D→3P) and O2(b 1Σg+ →X 3Σg−) following O2 photodissociation
Authors: Lee L. C. , Slanger T. G.
Published: February 2003

Time-resolved studies have been made on the energy transfer process O(1D)+O2→O(3P)+O2(b 1Σg+)v. O(1D) was generated by O2 photodissociation at ?1600 Å, using an H2 laser, and observed by its emission at 6300 Å. Only the v=0 and 1 levels are produced in O2(b1Σg+) by energy transfer, in the ratio k1/k0=0.7. The quantum efficiency of converting O(1D) electronic energy into O2(b 1Σg+) is 0.77±0.2, in agreement with the most recent determination. O2(b 1Σg+)v=1 is quenched very rapidly by O2, with a rate coefficient of 2.2×10−11 cm3 molec−1 s−1. This is almost six orders of magnitude faster than O2 quenching of O2(b 1Σg+)v=0 and accounts for the weakness of emission from the v=1 level in the terrestrial airglow.
Photodissociation dynamics of small polyatomics: Isolated molecule behavior and collision induced effects
Authors: Heller Donald F. , Elert Mark L. , Gelbar William M.
Published: February 2003

We outline a conceptually simple theoretical approach to the study of photodissociation of small polyatomics at low pressures. In this approach, we employ a realistic Hamiltonian and solve numerically for the ensuing dynamics. Formaldehyde is treated as a prototype, and the results of calculations are given and compared with recent experiments. Several conclusions are drawn about the photodissociation mechanism. In particular, our calculations suggest that the barrier to products lies above the first few vibrational levels of S1. Hence, both the experimentally determined nonradiative decay of S1, and the much slower CO appearance rate, must be collision induced. We expect similar time-lag behavior to be evinced in other small polyatomics and we suggest that collisional effects often may persist to very low pressure.
ENDOR evidence of noncubic distortion in Cs2NaYCl6:Ce
Authors: Fish G. E. , Stapleton H. J.
Published: February 2003

We have measured the ligand hyperfine coupling of 23Na and 133Cs nuclei nearest to paramagnetic Ce3+ ions in sites of octahedral symmetry in Cs2NaYCl6 using ENDOR. For 133Cs (I=7/2), an isotropic three line pattern was seen. The center line, at the free 133Cs resonance, arises from distant nuclei; the other lines could be fit by a spin Hamiltonian ℋs =AsI⋅S with As= (49.7±3.0) kHz, S=1/2. The 23Na (I=3/2) spectrum exhibited a bulk sodium resonance and an additional pattern with (1) an anisotropic splitting ∼4 times larger than that expected on the basis of point dipolar coupling between the nearest nucleus and paramagnetic electron and (2) a slight departure from the axial symmetry expected from the room temperature cubic crystal structure of Cs2NaYCl6 and previous low temperature measurements. We believe this indicates a slight noncubic distortion of the crystal lattice, at least near the Ce3+ substitutional impurity.
Vibrational relaxation and small ’’bubble’’ spectroscopy of the NO 3sσ (A 2Σ+) Rydberg state in solid rare gases
Authors: Goodman J. , Brus L. E.
Published: February 2003

The 1933 Å ArF excimer laser has been used to excite NO 3sσ Rydberg fluorescence in solid rare gases. A comparison of Rydberg and valence spectra indicates that Rydberg fluorescence is particularly sensitive to the nature of the local environment. The data demonstrate the limits of a continuum host approximation in the small ’’bubble’’ model. All observed emission is vibrationally relaxed. The relaxation rates appear to be many orders of magnitude faster than observed for ground state diatomics with equivalent vibrational quanta.
Theory of ir continua with polarizable hydrogen bonds. I. Aqueous solutions of strong acids
Authors: Hayd A. , Weidemann E. G. , Zundel G.
Published: February 2003

The wavenumber dependence of the continuous ir absorbance of strong aqueous acid solutions is calculated on the basis of SCF calculations on H5O2+. The two strongly coupled modes (νOH and νOO stretching vibrations) of the hydrogen bond in H5O2+ are treated exactly. A distribution of the local electrical field strength is taken into account since the hydrogen bond is easily polarizable. Furthermore, a distribution of OO bond lengths is used with these calculations. The calculated continua—wavenumber dependence, the absolute intensity, and the structure—are in close agreement with the ir continua observed with aqueous solutions of strong acids. The intensity of the calculated continuum decreases with increasing strength of the mean local electrical field at the polarizable hydrogen bonds, and it is independent of temperature over a very large temperature range, both of which are in very good agreement with experiment. The influence of the hydrogen bond lengths is studied, considering the system as a model for short, medium, and long hydrogen bonds. Relatively short polarizable hydrogen bonds show continua only below 1500 cm−1. With relatively long polarizable hydrogen bonds, the continuum is much more intense in the region 3000–1600 cm−1. Medium long polarizable hydrogen bonds show a continuous absorption in the whole region below 3400 cm−1. The results demonstrate that the electrical field as well as the bond length distributions are necessary conditions for the occurrence of ir continua. The continua occur in the whole range below 3400 cm−1 when the OO distribution includes the typical double minimum case with a moderate barrier.
Photoluminescence of ArO and KrO in doped rare-gas matrices
Authors: Taylor R. V. , Walker W. C.
Published: February 2003

Photoluminescent emission and excitation spectra of matrices of Ar and Kr doped with O2 and N2O and excited by uv radiation between 200 and 110 nm are reported. To our knowledge, the normalized excitation spectrum of Ar:O2 provides the first measurement of the relative quantum yield for the photodissociation of O2 into O(3P)+O(1S). The differences between matrix isolated XeO, ArO, and KrO spectra are discussed. A simple model to explain the results is proposed.
Orientational order and tricritical behavior in the trans-p-n-alkoxy-α-methyl-p′-cyanophenyl cinnamate (n-OMCPC) series of liquid crystals
Authors: Fernandes J. R. , Venugopalan S.
Published: February 2003

The temperature dependence of the orientational order parameter S has been evaluated from their infrared spectra for six homologues of the n-OMCPC (trans-p-n-alkoxy-α-methyl-p′-cyanophenyl cinnamate) series of liquid crystals with n = 7–12, where n is the number of carbon atoms in the end alkyl chain. The even–odd effect of the S values in the nematic phase is rather weak for homologues 7–10. In homologues 10–12, the changes of S at the transitions have been correlated with their thermodynamic behavior. The smectic A–nematic (A–N) and nematic–isotropic (N–I) transitions in several binary mixtures of 11 with 8, 10, and 12 have been studied by differential scanning calorimetry. With decreasing average alkyl chain length in the mixtures, the nematic range becomes extended and the enthalpy of the A–N transition is found to decrease. We deduce that the tricritical point in the A–N transition occurs when the reduced temperature TR=TAN/TNI=0.94±0.005. The triple point between A, N, and I phases has also been observed in an 11–12 mixture at the mole percent ratio of ∼27:73.
Infrared spectra of AlCl2Br, AlClBr2, and AlBr3 in solid argon
Authors: Pong Richard G. S. , Shirk Amy E. , Shirk James S.
Published: February 2003

We report the ir spectra of AlCl2Br, AlClBr2, and AlBr3. It is pointed out that the vibrational spectra of AlCl2Br and AlClBr2 can provide a novel and sensitive test for small deviations from planarity of AlCl3. The observed spectra imply a planar D3h structure for each of these trihalides.
Scattering of thermal He beams by crossed atomic and molecular beams. III. Anisotropic intermolecular potentials for He + N2, O2, CO, and NO
Authors: Keil Mark , Slankas John T. , Kuppermann Aron
Published: February 2003

Differential scattering cross sections are measured for He + N2, O2, CO, and NO, using the crossed molecular beams technique. These data, which are sensitive to the van der Waals attractive minima and adjacent regions of the intermolecular potentials, are analyzed in terms of both central-field and anisotropic models. Little evidence is found for quenching of the observed diffraction oscillations, and anisotropic contributions are determined to be small:The spherical averages of these anisotropic potentials are indistinguishable, within experimental error, from the potentials obtained by a central-field analysis. This study thus provides a quantitative, empirical validation of the central-field assumption for molecular scattering in weakly anisotropic systems.
Theoretical Compton profile anisotropies in molecules and solids. V. Lithium and sodium bromide diatomics
Authors: Matcha Robert L. , Pettitt Bernard M. , Ramirez B. I. , McIntire William R.
Published: February 2003

Anisotropies associated with momentum distributions along vectors parallel and perpendicular to bond axes in alkali bromide molecules are computed and analyzed. An attempt is made to relate these to charge cloud deformations accompanying molecular formation. Our analysis indicates that the parallel profile associated with the valence pi orbital is the dominating factor determining the relative shapes of the total profile anisotropies in the low momenta regions pz ?0.5.
NMR test of extended diffusion with internal rotation
Authors: Bull T. E.
Published: February 2003

The nuclear magnetic relaxation times for the ring and methyl deuteriums in mesitylene-d12 and for the fluorine and deuterium in methyltrifluorosilane-d3 have been measured as a function of temperature. These results together with the literature values for the chlorine and deuterium relaxation in tert-butylchloride-d9 [D. E. O’Reilly, E. M. Peterson, C. E. Scheie, and E. Seyfarth, J. Chem. Phys. 59, 3576 (1973)] have all been analyzed in terms of the theory of extended diffusion for symmetric top molecules with internal motion. These three cases are examples of low, intermediate, and high internal rotation barriers, respectively. For the intermediate and high barrier cases, the data are in good agreement with the predictions of the internal M diffusion theory for molecules with the corresponding barrier heights. However, for mesitylene-d12 (V∼58 J/mole), the methyl deuterium correlation times are smaller than those predicted by the theory for this barrier, but are consistent with the predictions for the internal M diffusion theory with zero barrier height. This discrepancy is due to breakdown in treating the internal rotor with classical mechanics. When the more correct, quantum mechanical treatment is used, these data are also consistent with the internal M diffusion model.
High resolution photoelectron spectra of deuterated ethylenes
Authors: Cvita? T. , Güsten H. , Klasinc L.
Published: February 2003

The high resolution Hei photoelectron spectra of ethylene and five of its deuterated derivatives (CH2CHD, CH2CD2, cis- and trans-CHDCHD, and CD2CD2) have been recorded and the vibrational bands in the first systems of the molecular ions have been assigned. The anomalous deuterium shifts have been explained by Fermi resonance between ν2 and ν3 levels in CH2CH2 and cis-CHDCHD. The PE spectra of cis- and trans-CHDCHD were found to be different supporting the D2 symmetry of the molecular ion.
Collisional quenching of BaCl (C2Π) by He, Ar, and N2
Authors: Edelstein S. A.
Published: February 2003

The quenching cross section of Bacl (C2Π) by He, An, and N2 have been measured by time-resolved laser-induced fluorescence decay method.(AIP)
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o effective core potentials including relativistic effects. III. Ground state Au2 calculations
Authors: Lee Yoon S. , Ermler Walter C. , Pitzer Kenneth S. , McLean A. D.
Published: February 2003

SCF calculations have been carried out for the ground 1Σ+g(0+g) state of Au2 using a variety of ab initio effective core potentials (EP). The effective core potentials studied both include a two-component relativistic EP (REP) that includes spin–orbit effects and also averaged relativistic EP (AREP) and a nonrelativistic EP (NREP). All-electron nonrelativistic calculations were also performed. The values of spectroscopic constants obtained from these calculations indicate that relativistic effects account for a decrease in Re of over 0.3 Å and an increase in the bond energy of the order of 1 eV. Various intercomparisons indicate the general validity of effective potential methods, properly applied, but also show certain limitations. In particular, the NREP results agree well with the all-electron, nonrelativistic calculations. Also, various relativistic effective-potential methods agree for SCF calculations provided both the basis sets and the EP are carried to sufficiently high order in angular quantum number. The bond distance calculated relativistically agrees very well with experiment.
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o effective core potentials including relativistic effects. IV. Potential energy curves for the ground and several excited states of Au2
Authors: Ermler Walter C. , Lee Yoon S. , Pitzer Kenneth S.
Published: February 2003

The ground and excited states of Au2 are studied using ab initio averaged relativistic effective core potentials (AREP) and MCSCF–CI procedures. Spin–orbit effects are included in the excited states derived from 2S1/2+2D3/2 and 2S1/2+2D5/2 atomic states using an empirical procedure. The ground state dissociation energy is calculated to be 2.27 eV as compared to the experimental value of 2.31 eV. The calculated energies for the two spectroscopically allowed 0+g to 0+u transitions and other molecular parameters also agree reasonably well with experiment.