bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of excited-state vibrations on fragment state distributions: The photodissociation of NOCl on T1(1 3A″)
Authors: Qian C. X. W. , Ogai A. , Iwata L. , Reisler H. 
Published: July 2002

NO V,R distributions are reported following photodissociation of jet-cooled NOCl from selected vibrational levels of the T1(1 3A″) state. By varying the photolysis wavelength while monitoring selected rovibrational levels of NO, a photofragment yield spectrum showing the same diffuse vibrational structure as the absorption spectrum is obtained. NO rotational distributions are obtained at photolysis wavelengths corresponding to peaks in the absorption spectrum. We find that the NO stretching vibrations of T1 evolve adiabatically into NO vibrational excitations [i.e., excitation of v1 quanta of the T1 NO stretch yields predominantly NO(v″=v1) ]. The NO rotational distributions depend only on the number of T1 bending quanta, v3. The shapes of the distributions reflect the number of nodes in the bending wave functions, and similar rotational distributions are obtained following excitation of vibronic levels with equal number of ν3 quanta, but different number of ν1 quanta (v1=0–2).
We also find that the excited NO(2Π3/2) state is much more populated than the lower NO(2Π1/2) state, and the widths of the absorption features increase with increasing number of ν3 quanta, but decrease with increasing ν1 excitation. The results are explained in terms of a model in which the bending and NO stretch motions in the excited state are largely uncoupled. In order to explain the multimodal rotational distributions, we calculate separately the components of the NO rotational excitation that derive from the angular momentum inherent in the bending wave function and the angular anisotropy in the potential-energy surface. We find, using the momentum representation of the harmonic oscillator, that the rotational distributions map the bending wave functions and exhibit minima for v3&gt;0. In addition, a unidirectional torque generated by the angular anisotropy in the potential causes shifts in the distributions calculated by the pure Franck–Condon model that are bending level dependent. The observation that the absorption linewidth decreases with increasing NO stretch excitation in the parent T1 state may be a manifestation of the energy mismatch between the frequency of the NO stretch in NOCl and free NO; the increased mismatch with increasing stretch quantum number results in slower dissociation.
Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4: Another case of arrested growth of hydrogenated silicon particles
Authors: Mandich M. L. , Reents W. D. , Kolenbrander K. D. 
Published: July 2002

Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4 are observed in the ion cell of a Fourier transform mass spectrometer. Clustering occurs either by addition of SiD2 or SiH2 accompanied by loss of D2 or H2, or by the formation and stabilization of the bimolecular adducts. All of the clustering reactions are highly inefficient and lead to bottleneck structures at small silicon cluster sizes containing two to four silicon atoms. Rates are measured for both the addition and association products for each step of the reaction. Back reaction rates are monitored via silicon-29 isotope exchange. Ab initio electronic structure calculations of the reaction pathways including intermediates, transition states and products have been performed by Raghavachari and are presented in his companion paper. The overall reaction mechanisms are similar for each reaction step. First an intermediate complex is formed between the ion and neutral which is strongly bound by a bridging deuterium or hydrogen atom.
Collisional stabilization of this complex leads to formation of the observed bimolecular adduct products. These bimolecular adducts do not react further with SiD4 (SiH4) on the time scale of our experiments. Elimination of D2 or H2 leading to the SiD2 (SiH2) addition products occurs via a thermoneutral transition state. Sequential growth by addition of SiD2 (SiH2) arrests at Si3D+7 (Si3H+7). Ab initio calculations find that this occurs because Si3D+7 (Si3H+7) assumes a highly stable cyclic structure. Phase space theoretical modeling of the experimentally measured reaction rates is performed to quantitatively test energies of the reaction intermediate complexes and transition states calculated by Raghavachari. Excellent agreement within 0.13 eV is obtained between the phase space and ab initio energies. Phase space derived kinetic isotope effects on the reaction rates of protiated and deuterated species also correspond well with experiment. Reaction rates at typical temperature and pressure conditions in silane plasmas are also calculated. These results strongly suggest that sequential clustering of SiH+3 with SiH4 does not lead to formation of the deleterious hydrogenated silicon dust observed in silane plasmas.
Vibrational dynamics of the bifluoride ion. III. F–F (ν1) eigenstates and vibrational intensity calculations
Authors: Epa V. C. , Thorson W. R. 
Published: July 2002

This paper concludes a theoretical study of vibrational dynamics in the bifluoride ion FHF−, which exhibits strongly anharmonic and coupled motions. Two previous papers have described an extended model potential surface for the system, developed a scheme for analysis based on a zero-order adiabatic separation of the proton bending and stretching motions (ν2,ν3) from the slower F–F symmetric-stretch motion (ν1), and presented results of accurate calculations of the adiabatic protonic eigenstates. Here the ν1 motion has been treated, in adiabatic approximation and also including nonadiabatic couplings in close-coupled calculations with up to three protonic states (channels). States of the system involving more than one quantum of protonic excitation (e.g., 2ν2, 2ν3 σg states; 3ν2, ν2+2ν3 πu states; ν3+2ν2, 3ν3 σu states) exhibit strong mixing at avoided crossings of protonic levels, and these effects are discussed in detail.
Dipole matrix elements and relative intensities for vibrational transitions have been computed with an electronic dipole moment function based on ab initio calculations for an extended range of geometries. Frequencies, relative IR intensities and other properties of interest are compared with high resolution spectroscopic data for the gas-phase free ion and with the IR absorption spectra of KHF2(s) and NaHF2(s). Errors in the ab initio potential surface yield fundamental frequencies ν2 and ν3 100–250 cm−1 higher than those observed in either the free ion or the crystalline solids, but these differences are consistent and an unambiguous assignment of essentially all transitions in the IR spectrum of KHF2 is made. Calculated relative intensities for stretching mode (ν3, σu symmetry) transitions agree well with those observed in both KHF2 [e.g., bands (ν3+nν1), (ν3+2ν2), (3ν3), etc.] and the free ion (ν3,ν3+ν1). Calculated intensities for bending mode (ν2, πu symmetry) transitions agree well with experiment for the ν2 fundamental in the free ion and KHF2(s), and for a πu transition in KHF2 which we assign to ν2+2ν3, but are far too small to explain the prominence of progression bands (ν2+nν1) and especially the strong overtone 3ν2 in the spectrum of KHF2(s). Intensity of the progression bands (ν2+nν1) in KHF2 can be explained by hydrogen bonding between adjacent FHF− ions; in NaHF2(s) where such interaction is absent, the band (ν2+ν1) is 50–100 times weaker, in agreement with calculations.
The relatively high intensity of the 3ν2 band, which also appears strongly in NaHF2(s), remains the major unexplained feature of the bifluoride spectrum in these solids. Suggestions are made for further experiments on the FHF− and FDF− systems which could test predictions of this dynamical analysis.
On the electronic structure and dynamical aspects of the predissociation of the A 2ΠΩ states of MgCl. A rigorous quantum mechanical treatment incorporating spin–orbit and derivative coupling effects
Authors: Parlant Gérard , Rostas Joëlle , Taieb Guy , Yarkony David R. 
Published: July 2002

The nonadiabatic electronic structure and decay mechanisms of the spectroscopically analyzed A 2Π state of MgCl are studied using a unique combination of rigorous ab initio electronic structure and quantum dynamics techniques. The electronic structure treatment is based on ab initio multiconfiguration self-consistent field/first order and second-order configuration interaction wave functions [ΨaJ(r;R)] for the 1,2 2Π adiabatic electronic states. These wave functions are used to determine rigorous diabatic state wave functions using the derivative coupling matrix elements, gaJ,I(R)=〈ΨaJ(r;R) ‖(∂/∂R)ΨaI(r;R)〉r, and approximate diabatic state wave functions using a diabatization procedure based on diagonalizing the dipole moment operator suggested by Werner and Meyer [J. Chem. Phys. 74, 5802 (1981)]. Near its equilibrium geometry the A 2ΠΩ state is well characterized as a regular diabatic state corresponding to Mg+(2P)-Cl−(1S).
The higher vibrational levels of this state are significantly perturbed (predissociated) by the interaction with a second inverted, dissociative, diabatic state of the same symmetry corresponding to Mg0(1S)Cl0(2P). Because the fine structure splitting, E(2 2Π3/2)–E(2 2Π1/2), of the predissociating state is comparable to the vibrational spacing of the predissociated state, relativistic, spin–orbit, effects must be incorporated into the treatment of the predissociation. These relativistic effects are treated using the full microscopic Breit–Pauli spin–orbit (that is spin–orbit and spin–other–orbit contributions) operator. The coupled diabatic state representation incorporating relativistic effects is used as the basis for semiclassical and fully quantum mechanical treatments of the predissociation lifetimes and energy shifts of the A 2Π3/2,1/2 vibrational states. By correctly taking into account the mixing of the regular and inverted 1,2 2Π states the coupled state quantum scattering calculations are able to reproduce the observed ‘‘anomalous’’ dependence of the fine structure splitting factor Asov.
Quasielastic neutron scattering measurements of n-butane in its crystalline, plastic, and liquid phases
Authors: Bradley K. F. , Chen S.-H. , Brun T. O. 
Published: July 2002

We report here measurements of quasielastic neutron scattering from n-butane at temperatures of 90, 115, 125 and 190 K and in a momentum transfer range of 0.8–2.4 Å−1. These measurements confirm that between 115 and 125 K butane forms a plastic crystal in which the centers of mass of the butane molecules form a crystalline structure, but the individual molecules are free to rotate. At these two intermediate temperatures, there exists both an elastic peak, characteristic of a solid structure, and quasielastic components arising from the rotational motions of the butane molecules. At 90 K, the butane scatters neutrons only elastically, while at 190 K, the butane scatters neutrons only quasielastically. In both the plastic and the liquid phases, the presence of at least two quasielastic processes must be assumed in order to explain the measurements. In the plastic crystal, we associate a broad Lorentzian component with intramolecular reorientations about the central carbon–carbon bond and a second, relatively narrow, Lorentzian component with whole molecule rotations.
The latter process gives rise to a rotational quasielastic peak having a width of 400 μeV, which is constant to within the instrumental resolution of 70 μeV at both temperatures and at all measured momentum transfers. In a continuous diffusion model, this width corresponds to a rotational diffusion constant of 0.277 rad2/ps, a value which is about 3.5 times larger than one extracted from a molecular dynamics simulation of n-butane in the plastic phase recently published by Refson and Pawley [Mol. Phys. 61, 669 (1987); 61, 693 (1987)]. On the other hand, the first process, which corresponds to the carbon–carbon reorientation peak, is about 16 meV wide, indicating that this reorientation occurs on a time scale of about 0.1 ps. The absence of this broad peak in the solid butane at 90 K indicates that this fast carbon–carbon reorientation is coupled to an aspect of the structure or dynamics of the plastic phase. In the scattering from liquid butane at 190 K, there is a third, narrow quasielastic peak which also has a Lorentzian energy distribution. This peak width is about 200 μeV and corresponds to a translational diffusion constant of 0.23 Å2/ps, a result in rough agreement with a recent molecular dynamics simulation of liquid butane by Ullo and Yip. [J. Chem. Phys. 85, 4056 (1986)].
Ab initio potential and variational transition state theory rate constant for H-atom association with the diamond (111) surface
Authors: de Sainte Claire Pascal , Barbarat Philippe , Hase William L. 
Published: July 2002

High-level ab initio calculations were performed to determine accurate analytic potential energy functions for interactions a gas-phase H-atom has with H-atoms attached to the diamond (111) surface and with C-atom radical sites on this surface. The nonbonded potential between the gas-phase H-atom and H-atoms attached to the surface was determined from coupled-cluster ab initio calculations, including single, double, and perturbatively applied triple excitations [CCSD(T)], with the 6-311++G(2df,p) basis set. The resulting nonbonded potential is nearly identical to that found previously from both theory and experiment for interactions between H-atoms on different hydrocarbon molecules. In the ab initio calculations, a C-atom radical site on the diamond surface is represented by a constrained tert-butyl radical. Radial and small-displacement angular potentials for a H-atom interacting with this radical were determined from unrestricted quadratic configuration interaction calculations, with single, double and perturbatively applied triple excitations [UQCISD(T)], with the 6-31G** basis set. UQCISD(T) calculations were performed on the H+CH3→CH4 reaction system with both the 6-31G** and 6-311++G(3df,3pd) basis sets to calibrate the accuracy of the 6-31G** basis set results for the H-atom plus constrained tert-butyl radical.
The above information was used to construct an analytic potential energy function for H-atom association with a radical site on the (111) surface of diamond, which was then employed in a canonical variational transition state theory (CVTST) calculation of the association rate constant. The resulting rate constant is 1.8–2.1×1013 cm3 mol−1 s−1 for the 1000–2000 K temperature range. It is insensitive to the gas-phase H-atom/surface H-atom nonbonded potential and the potential for the diamond lattice. The H+diamond (111) CVTST rate constant is used to estimate a rate constant of 4×1013 cm3 mol−1 s−1 for H+tert-butyl association at 298 K. The UQCISD(T)/6-31G* calculations give a H—C(CH3)3 bond dissociation energy which is only 1 kcal/mol lower than the experimental value.
Coherent states of the real symplectic group in a complex analytic parametrization. II. Annihilation-operator coherent states
Authors: Quesne C. 
Published: July 2002

In the present series of papers, the coherent states of Sp(2d,R), corresponding to the positive discrete series irreducible representations 〈λd+n/2,..,λ1+n/2〉, encountered in physical applications, are analyzed in detail with special emphasis on those of Sp(4,R) and Sp(6,R). The present paper discusses the annihilation-operator coherent states, i.e., the eigenstates of the noncompact lowering generators corresponding to complex eigenvalues. These states generalize the coherent states introduced by Barut and Girardello for Sp(2,R), and later on extended by Deenen and Quesne to the Sp(2d,R) irreducible representations of the type 〈(λ+n/2)d〉. When λ1,...,λd are not all equal, it was shown by Deenen and Quesne that the eigenvalues do not completely specify the eigenstates of the noncompact lowering generators.
In the present work, their characterization is completed by a set of continuous labels parametrizing the (unitary-operator) coherent states of the maximal compact subgroup U(d). The resulting coherent states are therefore of mixed type, being annihilation-operator coherent states only as regards the noncompact generators. A realization in a subspace of a Bargmann space of analytic functions shows that such coherent states satisfy a unity resolution relation in the representation space of 〈λd +n/2,...,λ1+n/2〉, and therefore may be used as a continuous basis in such space. The analytic functions and the differential operators representing the representation space discrete bases and the Sp(2d,R) generators, respectively, are found in explicit form. It is concluded that the annihilation-operator coherent state representation provides the mathematical foundation for the use of differentiation operators with respect to the noncompact raising generators in symbolic expressions of the Sp(2d,R) generators. This is to be compared with the habit of replacing a boson annihilation operator by a symbolic differentiation with respect to the corresponding creation operator, accounted for by the Bargmann representation of such operators.
Plasma wave equations of state
Authors: Amendt Peter 
Published: July 2002

A systematic description of wave equations of state is presented for three categories of plasma waves distinguished by superthermal, subthermal, and superluminous phase velocities. Each class entails the formulation of a distinct Vlasov fluid model where only the first coincides with well-known covariant fluid modeling. An investigation of the linearized version of this standard model is first undertaken. A complete, lowest-order, warm fluid model is derived without the drawbacks that characterize previous models such as the generation of spurious modes and the absence of a Bernstein wave spectrum. The improved fluid model is obtained by avoiding a premature truncation of the hierarchy of linearized moment equations near cyclotron and acoustic resonance and is applied to representative types of waves in a warm, magnetized plasma. Relativistic corrections and anisotropic properties of the corresponding dispersion relations are used to illustrate the utility and rigor of the theory.
The conspicuous absence of a subthermal wave within this improved model motivates the subsequent derivation of a novel fluid model with associated moments that involve averages of derivatives of the electron distribution function. The first moment equation reproduces the Boltzmann relation while succeeding equations in the hierarchy provide constraints on the spatial dependence of the distribution function. A linearized analysis yields the ion-acoustic mode together with an isothermal equation of state in the long wavelength limit. The key distinction with previous work is the complete avoidance of a pressure and an appropriate (third) moment representation for temperature in the collisionless, subthermal regime. A relativistic analog to this unusual approach is developed for the case of ultrarelativistic electron plasma waves. This requires the formulation of a noncovariant near-thermal equilibrium fluid modeling with associated moments that are not relativistically dilatated. An isothermal equation of state is recovered in tandem with the adoption of a third fluid moment definition for relativistic temperature. This definition of effective temperature differs from the relativistic thermodynamic version which follows from an assumed form invariance of the defining equations of nonrelativistic thermodynamics in the relativistic regime. The introduction of these two latter models is intended to provide a more general notion of equation of state without recourse to an assumption on the form of the stress-energy tensor.
Abstinent chronic crack‐cocaine and crackcocaine/alcohol abusers evidence normal hippocampal volumes on MRI despite persistent cognitive impairments
Authors: DI SCLAFANI VICTORIA , TRURAN DIANA L. , BLOOMER COURTNAY , TOLOU‐SHAMS MARINA , CLARK H. WESTLEY , NORMAN DAVID , HANNAUER DAVID , FEIN GEORGE 
Published: July 2002

AbstractWe measured hippocampal volumes and cognitive functioning in crack‐cocaine and crack‐cocaine/alcoholdependent subjects (abstinent approximately 10–12 weeks) compared to age‐matched controls. Cognitive function was evaluated using the computerized MicroCog Assessment of Cognitive Functioning (which includes tests of explicit, declarative memory subserved by the hippocampus). The hippocampal volumes were quantified on T1‐weighted MRIs and were expressed as a proportion of intracranial vault volume. Both subjects and controls showed the larger right versus left hippocampal volume expected in normal anatomy, but we found no differences in hippocampal volume between any of the groups. However, both abstinent cocaine‐dependent subjects and abstinent cocaine/alcohol‐dependent subjects showed persistent cognitive impairments, including deficits in explicit memory. Our results suggest that either: (1) the hippocampus is resistant to structural volume loss in young and middle‐aged cocaine or cocaine/alcohol‐dependent subjects, (2) the hippocampal volume loss suffered by young and middle‐aged cocaine or cocaine/alcohol‐dependent subjects resolves after approximately 3 months of abstinence, or (3) hippocampal atrophy is obscured by the process of gliosis. Further, the cognitive impairments persisting in these abstinent cocaine and cocaine/alcohol‐dependent samples may (1) be unrelated to hippocampal function or (2) be associated with abnormal hippocampal function that is not reflected in MRI measures of overall hippocampal atrophy.
Two C‐Terminal Variants of NBC4, a New Member of the Sodium Bicarbonate Cotransporter Family: Cloning, Characterization, and Localization
Authors: Pushkin Alexander , Abuladze Natalia , Newman Debra , Lee Ivan , Xu Gouping , Kurtz Ira 
Published: July 2002

AbstractWe report the cloning, characterization, and chromosomal assignment of a new member of the sodium bicarbonate cotransporter (NBC) family, NBC4. The NBC4 gene was mapped to chromosome 2p13 and is a new candidate gene for Alstrom syndrome. Two variants of the transporter have been isolated from human testis and heart, which differ in their C termini. NBC4a encodes a 1137‐residue polypeptide and is widely expressed in various tissues, including liver, testis, and spleen. NBC4b is identical to NBC4a except that it has a 16‐nucleotide insert, creating a C‐terminal frame shift. NBC4b encodes a 1074‐residue polypeptide and is highly expressed in heart. Amino acids 1‐1046 are common to both NBC4 variants. NBC4a has two protein‐interacting domains that are lacking in NBC4b: a proline‐rich sequence, PPPSVIKIP (amino acids 1102‐1110), and a consensus PDZ‐interacting domain, SYSL (1134‐1137). NBC4b lacks the stretch of charged residues present in the C terminus of NBC4a and other members of the NBC family.Unlike other members of the NBC family, both NBC4a and NBC4b have a unique glycine‐rich region (amino acids 440‐ 469). In comparison with other members of the bicarbonate transport superfamily, NBC4a and NBC4b are most similar structurally to the electrogenic sodium bicarbonate cotransporters (NBC1).