bluuebunny/crossref_metadata_2025 huggingface dataset:
A complete energy transfer map for COF2
Authors: Ahl J. L. , Bohn R. K. , Casleton K. H. , Rao Y. V. C. , Flynn George W.
Published: February 2003

Fluorescence from the ν1, ν4, ν6, and ν3/ν5 states has been observed following Q-switched CO2 laser excitation of the ν2 C–F stretch mode of COF2. A kinetic model is presented which is consistent with the observed fluorescence lifetimes. Following excitation of the ν2 mode, 2ν2 is rapidly pumped by ladder climbing collisions. The 2ν2 states are collisionlessly coupled to the ν1 mode by Fermi resonance leading to the creation of a steady state between the ν1 and ν2 manifolds within 30 gas kinetic collisions. Subsequently, the ν2 state decays to the ν6 mode in 800 collisions, and also fills the ν4 mode in 2000 gas kinetic collisions. The ν4 level rapidly equilibrates with the near resonant states 2ν3, 2ν5, and ν3+ν5 after about 25 collisions, and these states rapidly decay to the ν3 and ν5 fundamentals in less than or about 100 collisions. The ν6 state relaxes to the ν3/ν5 states, in approximately 190 collisions, while vibration-translation/rotation relaxation of ν3 and ν5 to the ground state occurs on a time scale of 1200 collisions.
Fast and exceptionally slow vibrational energy transfer in acetylene and phenylacetylene in solution
Authors: Zinth W. , Kolmeder C. , Benna B. , Irgens-Defregger A. , Fischer S. F. , Kaiser W.
Published: February 2003

The excitation of the CH-stretching mode (ν3) of C2H2 in CCl4 leads to fast population (<2 ps) and very slow depopulation (240 ps) of the symmetric CC-stretching mode (ν2). The long lifetime of ν2 is due to the absence of anharmonic interaction to neighboring states (symmetry forbidden). The corresponding CC-stretching mode of C6H5–C2H has a lifetime of 15 ps. The phenyl group relaxes the symmetry restrictions and introduces new decay channels.
The collisional flow of vibrational energy into surrounding vibrational fields within S1 benzene
Authors: Tang Kenneth Y. , Parmenter Charles S.
Published: February 2003

Vapor phase fluorescence spectra are used to determine the absolute rate constants for the collisional transfer of vibrational energy from initial single vibronic levels of S1 benzene into the surrounding S1 vibronic field. 11 initial levels are probed with vibrational energies ranging to 2368 cm−1 where the level density is about 10 per cm−1. CO, isopentane, and S0 benzene are the collision partners. Benzene rate constants are three to four times gas kinetic for all levels, and electronic energy switching between the initial S1 molecule and the S0 collision partner probably makes important contributions. Isopentane efficiencies range from one to two times gas kinetic. Most of the transfer from low S1 levels occurs with excitation of vibrational energy within isopentane. These V–V contributions decline to only about 10% for the high transfer. CO-induced transfer is by V-T,R processes for all levels. The CO efficiency rises from about 0.1 for low regions to about unity for levels above 1500 cm−1. The CO efficiencies retain significant sensitivity to initial level identity even in the higher regions. Propensity rules derived from collisional mode-to-mode transfer among lower levels of S1 benzene are used to calculate the relative CO efficiencies. The calculated efficiencies agree well enough with the data to suggest that it may be meaningful to model vibrational equilibration with the use of propensity rules. The rules suggest that only a small number of levels among the thousands surrounding a high initial level contribute significantly to the total relaxation cross section and that this number is rather independent of the level density. While CO and isopentane have comparable efficiencies for relaxation of a high S1 level, CO is much less efficient for inducing full thermal equilibration. CO, which uses V-T,R processes only, becomes a relatively poor transfer partner once low levels are reached during the equilibration, whereas V–V transfer sustains isopentane’s large efficiency for all levels.
Remarks on semiclassical quantization
Authors: Pechukas Philip
Published: February 2003

Semiclassical quantization in the basic, or ‘‘primitive,’’ version often predicts a simpler, more highly degenerate energy level spectrum than is observed. This point is illustrated by remarks on two-dimensional systems with threefold and higher rotational symmetry and on perturbations of such systems. For example, according to semiclassical quantization essentially all energy levels of a C3 system are at least doubly degenerate. Such ‘‘incorrect’’ degeneracy predictions are to be interpreted as predictions of coalescence of levels in the semiclassical (ℏ→0) limit, coalescence which may manifest itself in real spectra as an excess of near degeneracies. Finally, a consideration on degeneracy rules out one possible solution to the problem of semiclassical quantization of ergodic systems.
An orthogonality constrained generalization of the Weizsacker density functional model
Authors: Nyden Marc R.
Published: February 2003

An exact density functional theory for two orbital systems (such as Hartree–Fock beryllium) is extended to give a density functional model for first-row atoms. The new model is related to the Weizsacker model but it includes additional terms which arise from orthogonality constraints. Two approximate methods based on this model are tested numerically.
Natural bond orbital analysis of near-Hartree–Fock water dimer
Authors: Reed Alan E. , Weinhold Frank
Published: February 2003

We have carried out a natural bond orbital analysis of hydrogen bonding in the water dimer for the near-Hartree–Fock wave function of Popkie, Kistenmacher, and Clementi, extending previous studies based on smaller basis sets and less realistic geometry. We find that interactions which may properly be described as ‘‘charge transfer’’ (particularly the n-σ*OH interaction along the H-bond axis) play a critical role in the formation of the hydrogen bond, and without these interactions the water dimer would be 3–5 kcal/mol repulsive at the observed equilibrium distance. We discuss this result in relationship to Klemperer’s general picture of the bonding in van der Waals molecules, and to previous theoretical analyses of hydrogen bonding by the method of Kitaura and Morokuma.
Monte Carlo simulation of solvent effects on vibrational and electronic spectra
Authors: Herman Michael F. , Berne Bruce J.
Published: February 2003

Solvent effects on vibrational states are treated in the Born–Oppenheimer approximation. A Monte Carlo procedure is devised for simulating a system in which the vibrations are treated as quantum degrees of freedom and all other degrees of freedom are treated classically. The key to this method is the use of a restructured perturbation theory for solving the vibrational Schrödinger equation at each of the solvent configurations sampled. This method also is used to compute Franck–Condon factors. The methods developed are applied to two different problems. First, solvent effects on vibrational transitions in the ground electronic state are considered. It is found that the frequency shift from the gas phase frequency is to the red at low solvent densities, but to blue at high solvent densities. Secondly, the heterogeneous electronic absorption and emission line shapes are simulated in a variety of model solute–solvent systems and the results are discussed in terms of a simple theoretical model.
Reactive and inelastic processes involving I2(D 1Σ+u) with the collision partners CH4, CH3Cl, CF3Cl, and CF4
Authors: Donovan Robert J. , O’Grady Barry V. , Lain Luis , Fotakis Constantine
Published: February 2003

Fluorescence from the D 1Σ+u state of I2, and from other ion-pair states populated as a result of inelastic collisions with the molecules CH4, CH3Cl, CF3Cl, and CF4, was studied throughout the 200–510 nm region. I2(D 1Σ+u) was optically pumped using an ArF laser (λ=193 nm) and the above spectral region recorded with single laser shots by employing an optical multichannel analyzer. The physical quenching of I2(D 1Σ+u) was found to involve an electronic cascade, through intermediate states, terminating in the lowest ion-pair state I2(3Π2g). The presence of reactive channels was identified by the reduction in I2 fluorescence following successive laser shots. Fluorescence from I2(D 1Σ+u) was also studied following excitation with a cw mercury lamp (λ=185 nm) and Stern–Volmer analysis of these data yielded total removal rate constants (reactive+inelastic channels), viz; k(CH4)=(7.9±0.3)×10−10, k(CH3Cl)=(21.0±1.0)×10−10, k(CF3Cl)=(7.1±0.4)×10−10, k(CF4)=(6.0±1.0)×10−10 (all in cm3 molecule−1 s−1 units). The presence of reactive channels was confirmed using end-product analysis techniques and it was shown that the lowest ion-pair state I2(3Π2g) also reacts with CH4 and possibly with CF3Cl.
Luminescence of the excited mercury diethylamine complex. Attachment by ligand exchange
Authors: Callear Anthony B. , Devonport Colin P.
Published: February 2003

The possibility of molecular attachment to excited atoms in gases by ligand exchange has been examined. It was first confirmed that mixtures of mercury vapor and diethylamine Et2NH give negligible luminescence when subject to irradiation with the 2537 Å mercury resonance line. The emission was then examined from mercury vapor with added amine up to 100 Torr, in the presence of an excess of NH3. With NH3 alone, a strong emission was observed due to HgNH*3, a complex of Hg(3P0) and NH3, with λmax∼3500 Å. The addition of Et2NH gave rise to a second band to the long wavelength, extending throughout the visible region, with λmax∼5140 Å; the ratio of the intensity of the long wavelength member to the residual emission in the 3500 Å region was found to be proportional to the amine pressure. For various [Et2NH] and fixed [NH3], the set of normalized spectral profiles are isosbestic, corresponding to the superposition of just two basic functions. From the cw experiments, it was adduced that the addition of quite small pressures of Et2NH,∼1 Torr, to NH3 at 1 atm pressure effectively extinguishes the HgNH*3 luminescence by a fast ligand exchange reaction HgNH*3+Et2NH→Hg(Et2NH)*+NH3. The two basic functions which comprise the spectra are due to Hg(Et2NH)* and the dimer Hg(Et2NH)*2, which is the carrier of the long wavelength component. This scheme was confirmed using the resonance flash technique to time resolve the exchange of ligands; the rate coefficient is ∼2×10−10 cm3 molecule−1 s−1 for the above reaction. The radiative lifetime of the Hg(Et2NH)* monomer is 1.15 μs. The large red shift and broadening associated with attachment of the second ligand arises because the emission is from an upper state which belongs to the Hg(3P1) asymptote, and which is more strongly bound than the state which correlates with Hg(3P0).
Competing dissociation channels in the infrared multiphoton decomposition of ethyl vinyl ether
Authors: Huisken F. , Krajnovich D. , Zhang Z. , Shen Y. R. , Lee Y. T.
Published: February 2003

Infrared multiphoton decomposition of ethyl vinyl ether (EVE) has been investigated by the crossed laser-molecular beam technique. Competition is observed between the two lowest-energy dissociation channels: (1) EVE → CH3CHO+C2H4, and (2) EVE → CH2CHO+C2H5. Center-of-mass product translational energy distributions were obtained for both dissociation channels. The products of reactions (1) and (2) are formed with mean translational energies of 31 and 5 kcal/mol, respectively. The branching ratio shifts dramatically in favor of the higher energy radical producing channel as the laser intensity and energy fluence are increased, in agreement with the qualitative predictions of statistical unimolecular rate theory.
Matrix elements for Morse oscillators
Authors: Vasan V. S. , Cross R. J.
Published: February 2003

We have derived exact analytic expressions for the following matrix elements for a Morse oscillator: 〈m‖exp[γ(r−r0)]‖n〉, 〈m‖(r−r0)exp[−a(r−r0)]‖n〉, and 〈m‖(r−r0)exp[−2a(r−r0)]‖n〉, where a is the Morse range parameter and γ is an arbitrary constant. We have found that several of the commonly used expressions for various diagonal matrix elements of the Morse oscillator involve considerable roundoff error. Due to near cancellation of terms the result may be many orders of magnitude lower than any of the terms. We obtain simple yet accurate asymptotic approximations for the diagonal elements which avoid these problems. These approximations are obtained for 〈m‖(r−r0)‖m〉, 〈m‖(r−r0)2‖m〉, and the cases mentioned above.
Vibrational energy transfer efficiency in a three-channel thermal unimolecular system. Temperature dependence
Authors: Krongauz V. V. , Rabinovitch B. S.
Published: February 2003

Thermal isomerization in the three-channel cyclopropane-1t1-2,2d2 system was studied at 823 and 973 K in the presence of Kr and CO2 bath gases. It was found that CO2 is more efficient in energy transfer from the hot cyclopropane than Kr, which is more efficient than He. For the stepladder model of energy transfer, the average energy removed per collision from energized cyclopropane-1t1-2,2d2 by a bath gas 〈ΔE〉 for Kr is 780±90 cm−1 at 823 K and 520±70 cm−1 at 933 K; while for CO2 it is 1220±90 cm−1 at 823 K and 800±70 cm−1 at 973 K. The relative collision efficiency of both bath gases β̄ω also declines with temperature rise. For Kr, β̄ω is 0.17 at 823 K and 0.07 at 973 K; for CO2, β̄ω is 0.40 at 823 K and 0.17 at 973 K. Comparison is made with earlier results. A T−γ(γ∼5.5) temperature dependence fits the existing data for He/cyclopropane sytems and is in accord with the computational deductions of Tardy and Rabinovitch (Ref. 17). For stronger colliders, e.g., Kr and CO2, the temperature dependence of β̄ω should be less than He. A value of ≊1 kcal/mol for the activation energy difference for T and H migration during cyclopropane-1t1-2,2d2 isomerization was confirmed.
Vibrational relaxation of gaseous CO(v=1) and N2(v=1) from 300 K to liquid temperatures: A comparison with liquid state relaxation
Authors: Gregory Eric A. , Maricq M. Matti , Siddles Robert M. , Wickham-Jones C. T. , Simpson C. J. S. M.
Published: February 2003

The V–V energy transfer rate constants are reported for the deactivation of both CO(v=1) and N2(v=1) by O2 and CH4 in the temperature range 300 to 80 K. The results are obtained by an infrared fluorescence technique. In order to study the relaxation of N2(v=1), a small amount of CO is added to the gas mixture to function both as a pump and a probe. The probability vs temperature curves obtained are approximately parallel for the deactivation of CO(v=1) as compared to that of N2(v=1). This temperature dependence is found to resemble that for the V-T deactivation of CO at low temperatures. This is due to the large mismatch for these V–V energy transfer processes. The rate constants at liquid N2 temperatures are compared with rate constants measured by other researchers for relaxation of the same systems in the liquid phase. The results show that the relaxation rate constants, expressed in terms of cm3 s−1 molecule−1, are approximately equal in the two phases. The implications of this result with respect to the cell and statistical models of vibrational relaxation in liquids is discussed.
Vibrational phase relaxation in ethane at moderate densities, including the critical region
Authors: Wood Kurt A. , Strauss Herbert L.
Published: February 2003

The bandwidth of the isotropic component and the frequency of the ν3 (C–C stretch) Raman band of ethane have been measured for a range of densities at constants temperature, and for a range of temperatures at the critical density. No critical anomaly is observed. The rotation-vibration coupling contribution to the bandwidth is calculated. The remaining contribution to the bandwidth increases with increasing density in a manner consistent with current theories that take into account both the repulsive and attractive intermolecular forces. However, the attractive force contribution cannot be related in a simple fashion to the macroscopic compressibility. Data taken over a wider range of density and temperature will be required to quantitatively determine the separate repulsive and attractive contributions to the width.
A microwave double resonance study of collision-induced transitions between the M components of a rotational transition of OCS
Authors: Bomsdorf H. , Mäder H.
Published: February 2003

Four-level MW–MW double resonance experiments on the rotational Stark levels M=0 and M±1 of the OCS j=1→2 transition have been performed to investigate collision-induced population transfer due to OCS self-collisions. A MW bridge has been used as a filter in order to discriminate between the pump and signal radiation and the relative change of signal line intensity η has been determined for both M components by means of a double modulation technique. A two-level Bloch-type description of the signal transition is given to estimate additional effects of the off-resonant pump radiation in the absence of collisions.
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3Kr nuclear quadrupole coupling, microwave spectrum, and structure of KrHCN
Authors: Campbell E. J. , Buxton L. W. , Legon A. C.
Published: February 2003

Rotational spectra have been observed for ten isotopic species of KrHCN using the pulsed Fabry–Perot Fourier transform technique. The 83Kr nuclear quadrupole coupling constant has been measured in 83KrHC 14N, 83KrHC 15N, and 83KrDC 14N. Values of the rotational constants B̄0, centrifugal distortion constants DJ and H, 14N and 83Kr nuclear quadrupole coupling constants are These constants are consistent with a linear or near-linear configuration, with a Kr–HCN center-of-mass separation of 4.54 Å, and the Kr atom located 27° off the HCN figure axis on average, where the vertex of this angle is placed on the HCN center-of-mass. KrHCN exhibits unusually large centrifugal distortion in comparison to previously studied Kr–hydrogen halide systems. We find that the measured 83Kr nuclear quadrupole coupling constants in 83KrHC 14N and 83KrDC 14N are consistent with a long range polarization model previously used to explain values of χKr in KrH(D)Cl and KrH(D)F.
The rotational spectrum and molecular structure of the benzene–hydrogen chloride complex
Authors: Read W. G. , Campbell E. J. , Henderson Giles
Published: February 2003

The microwave spectrum of the weakly bound complex benzene–HCl was studied in the gas phase using Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity with a pulsed supersonic nozzle as the molecular source. Several R-branch a-dipole transitions have been observed for benzene–H 35Cl, benzene–D 35Cl, benzene–H 37Cl, and benzene(d6)–H 35Cl. The spectrum was characteristic of a symmetric top, indicating that the time averaged displacement of the H and Cl atoms from the benzene C6 axis is zero. Deuterium substitution of HCl demonstrated that the acidic proton lies between the Cl atom and the benzene ring. The chlorine nuclear quadrupole coupling constant χClaa, was measured for all four isotopic species and is interpreted in terms of a projection of the chlorine quadrupole coupling constant in free HCl, averaged over two degenerate vibrational ground state bending modes involving the angles between the benzene C6 axis and the HCl bond axis. The spectroscopic constants for benzene–HCl are: aNumbers in parentheses represent one standard deviation in the fit.
The rotational and hyperfine spectrum and structure of H2CO–HF2
Authors: Baiocchi F. A. , Klemperer W.
Published: February 2003

The rotational spectrum of the hydrogen bonded complex formed between hydrogen fluoride and formaldehyde has been obtained from 3 to 55 000 MHz using molecular beam electric resonance spectroscopy. The molecule is found to be a prolate slightly asymmetric rotor with κ=−0.98 and an inertial defect of Δ=0.62 amu Å2. The rotational constants determine that the average geometry of the three heavy atoms is bent with an O–F distance of 2.66 Å and a C–O–F angle of 109.5°. The large value of μa shows that HF is hydrogen bonded to the oxygen. The average orientation of the HF axis with respect to the inertial axes is obtained from the two components (Sa and Sb) of the direct nuclear spin–spin hyperfine coupling tensor. Both the hyperfine data and the value of μb indicate a nonlinear hydrogen bond in this species. Finally, the observation of hyperfine splittings in the spectrum attributable to the presence of the triplet spin state of formaldehyde provides experimental information regarding the tunneling of the formaldehyde protons. The spectra is consistent with a rigid planar structure. Some of the spectroscopic and average structural constants are summarized: A−ΔK=50 543.205(23) MHz; B=4832.232(33) MHz; C=4386.621(33) MHz; μa=3.7535(2) D; μb=1.399(1) D; SHFa=93.6(8) kHz; SHFb=−31.7(11) kHz; rO–H=1.794 Å; rO–F=2.659 Å; ∠C=O⋅⋅⋅F=109.5°; ∠C=O⋅⋅⋅H=115°.
The structure and molecular properties of the acetylene–HCN complex as determined from the rotational spectra
Authors: Aldrich P. D. , Kukolich S. G. , Campbell E. J.
Published: February 2003

The microwave spectra for four isotopic species of a complex formed between acetylene and HCN have been obtained using the pulsed, Fourier-transform method with gas pulsed into an evacuated Fabry–Perot cavity. The spectra indicate the complex to be a T-shaped near-prolate asymmetric rotor (κ=−0.993) in its ground vibrational state in which HCN lies on the C2 symmetry axis with the hydrogen atom of HCN pointing to the middle of the triple bond of acetylene. The carbon atom of HCN is situated 3.656 Å from the acetylene center of mass. Nuclear quadrupole coupling constants for N are obtained for all four isotopes and deuterium quadrupole coupling constants are obtained for two isotopes. Various contributions to the electric field gradients at quadrupolar nuclei are discussed.
Microwave spectral study of bicyclo[2.2.2]octene and bicyclo[2.2.2]octadiene
Authors: Nandi R. N. , Harmony Marlin D. , Howard Allison E. , Staley Stuart W.
Published: February 2003

Microwave spectral studies of bicyclo[2.2.2]octene (C8H12) and bicyclo[2.2.2]octadiene (C8H10) have led to the following rotational constants in MHz: for C8H12, A=2576.721±0.002, B=2508.998±0.002, C=2462.272±0.009; and for C8H10, A=2730.116±0.002, B=2650.520±0.002, C=2631.710±0.002. The dipole moments of the C2v molecules have also been obtained, the values along the symmetry axis being μc=0.253±0.001 D for C8H12 and μc=0.432±0.002 D for C8H10.
Microwave spectrum, dipole moment, barrier to internal rotation of 1,1-dimethyldiborane
Authors: Chiu C. W. , Burg A. B. , Beaudet R. A.
Published: February 2003

The microwave spectra of four isotopic species of 1,1-dimethyldiborane have been investigated in the region between 18.0 and 40.0 GHz. The observed rotational constants (MHz) for the normal species are A=7070.68(7), B=6606.57(3), C=3660.33(1); for 10B1 species, A=7069.87(15), B=6605.79(5), C=3659.88(3); and for 10B2 species, A=7070.63(27), B=6889.89(10), C=3745.92(6). The B–B distance determined by the Kraitchman method is 1.76(2) Å. The carbon–boron structure could be fitted to the moments of inertia by assuming reasonable values for the other structural parameters: r(B1−C)=1.59 Å and <CBC=121.2°. From the Stark effect measurements, the dipole moment is measured to be 0.87(3) D. Assuming no coupling between the rotors, the barrier height to internal rotation is 1.39(16) kcal/mol.
Spin–spin and spin-lattice contributions to the rotating frame relaxation of 13C in L-alanine
Authors: Akasaka K. , Ganapathy S. , McDowell C. A. , Naito A.
Published: February 2003

The spin-lattice relaxation times in both the Zeeman (TC1) and rotating (TC1ρ) frames were determined for three chemically distinct carbon atoms (13C) in polycrystalline L-alanine by combining crosspolarization and magic angle spinning techniques together with proton decoupling. The spin-lattice and spin–spin contributions to the experimentally measured TC*1ρ could be separated by an experiment in which the 13C spin-locking field was varied. The spin-lattice contributions (TC1ρ), which contain motional information, were determined to be 21.7, 23.4, and 138 ms for the Cα, CH3, and COO− carbons, respectively. The spin–spin contribution (TDCH) was found to be exponential, namely, (TDCH)−1 ∝exp(−2πνeCτD) in the low 13C spin-locking field. Therefore, the assumption of a Lorentzian correlation function for the proton dipolar fluctuations is adequate for L-alanine. Furthermore, the proton dipolar correlation times τD were found to be the same (31±1 μs) for all three carbons in L-alanine. The spin-lattice relaxation times in the Zeeman frame TC1 were determined to be 4.0 s, 38 ms, and 13 s for the Cα, CH3, and COO− carbons, respectively. The experimental values of TC1ρ and TC1 can be explained quantitatively by considering the internal rotations of the methyl and amino groups.
A semiclassical inversion procedure for the dipole-moment function for diatomic molecules
Authors: Stine J. R. , Noid D. W.
Published: February 2003

A simple formalism is presented to deduce the dipole moment as a function of internuclear distance from experimental vibrational intensity data. This method, like the RKR method for obtaining the potential-energy function, is based on the semiclassical WKB formalism and no particular functional form need be assumed for the dipole moment. The method is applied to the experimental data of Sileo and Cool for HF.
Raman spectra, ab initio molecular orbital calculations, vibrational analysis, and thermodynamic functions for NH3:AlX3 (X=F, Cl, Br)a)
Authors: Papatheodorou G. N. , Curtiss L. A. , Maroni V. A.
Published: February 2003

Raman spectra of gaseous NH3:AlCl3 and NH3:AlBr3 were recorded at 400 °C. The observed Raman frequencies in combination with reported infrared frequencies for NH3:AlCl3 and ab initio molecular orbital calculations on NH3:AlCl3 and NH3:AlF3 were used to derive force constants for all three NH3:AlX3 complexes (X=F, Cl, Br) based on an adjusted valence force field (AVFF) concept. The resulting force constant calculations produced complete sets of A1 and E mode frequencies for each complex. Statistical mechanical analyses were then performed using the A1 and E mode frequencies together with estimated values for the torsional mode of each complex and published enthalpy data. From these analyses, the relative thermodynamic stability of each complex was determined. At 700 and 1000 K, NH3:AlCl3 was found to be more stable than NH3:AlBr3. It was further predicted that the reaction of gaseous NH3 with solid AlF3 to form NH3:AlF3 is not favored in this temperature range, which provides an explanation for the lack of success in prior efforts to produce NH3:AlF3.
Systematic blobbing procedure for the calculation of universal polymer properties
Authors: Al-Noaimi G. F. , Martínez-Mekler G. C. , Velasco R. M. B.
Published: February 2003

A systematic renormalization group transformation along the chemical sequence of a polymer chain, systematic blobbing procedure (SBP), is introduced for the calculation of universal configurational properties. The method, which does not rely on the field theoretic analogy, gives to first order in ε (ε=4−d, d=space dimension) a firm basis to the decimation procedure suggested by de Gennes and put into practice by Gabay and Garel (GG). The renormalization transformation acts on a ‘‘Hamiltonian’’ of the system and produces Wilson-type approximate recursion relations for the coupling parameters. The SBP is used to calculate the exponent ν for a polymer chain in the good solvent region to first order in ε. The method can in principle be extended to higher orders in ε. By means of the SBP it is shown that the static universal properties of a polymer chain are not modified by the presence of a Gaussian random potential. The validity of the GG method is further strengthened by showing the equivalence, in the determination of ν, of their method and a Fixman perturbation matching procedure. The exponent ν is consequently obtained to second order in ε. All the results agree with the ‘‘corresponding’’ field theoretic calculations.
The mode of attack of oxygen atoms on the basal plane of graphite
Authors: Wong Chor , Yang Ralph T. , Halpern Bret L.
Published: February 2003

Gold decoration of the basal lattice plane of graphite etched by atomic oxygen has been made possible by first desorbing the surface oxide layer on the basal plane. The formation of monolayer pits, as revealed by gold decoration, shows that anisotropy does exist, i.e., carbon atoms are preferentially attacked by atomic oxygen in the direction of a axes, rather than the direction of c axis. The monolayer pits are initiated from lattice vacancies which are continually formed by atomic oxygen. The monolayer pits created by atomic oxygen are, unlike the pits by O2 which are circular, hexagonal in shape, the sides of which are composed of 〈101̄l〉 lattice planes.
Observation of the asymmetric O–U–O stretch in the vibronic absorption spectrum of uranyl formate monohydrate
Authors: West W. P. , Muller Clifford H. , Porter John T. , Malley Michael M.
Published: February 2003

Fluorescence excitation spectra of uranyl formate monohydrate UO2 (HCOO)2⋅H2O at 4.2 K show the UO+22 asymmetric mode to be active in the vibronic absorption. This assignment is based on the measure uranium isotope shift. It is also observed that the asymmetric mode occurs with a lower frequency than the symmetric in this compound, contrary to the order reported in other uranyl compounds.
Broken symmetry far from equilibrium in molecules within HF formalism
Authors: Ficker T.
Published: February 2003

Symmetry restricted and unrestricted HF calculations have been performed on the ground, core hole, and inner valence hole states of N2 at various internuclear distances. It has been shown that the are regions of N–N distances at which the localized HF solutions exist both for the core hole and the inner valence hole states.
Benzaldehyde photochemistry studied with laser ionization mass and photoelectron spectroscopy
Authors: Long S. Randolph , Meek Jon T. , Harrington Patrick J. , Reilly James P.
Published: February 2003

Laser ionization of gas phase benzaldehyde is induced with a narrow-band frequency doubleddye laser, and the resulting mass and photoelectron spectra are recorded by time of flight. The mechanism of ion formation is interpreted by comparison with similar data for molecular benzene.
Mechanism of electrical conduction in rare-earth ferrocyanides
Authors: Tennakone K.
Published: February 2003

A simple theory is presented to explain the observed electronic conduction in rare-earth ferrocyanides. (AIP)
Further comments concerning large amplitude motion in an anharmonic chain with nearest neighbor interactions
Authors: Bradlow Steven , Collins Michael A. , Rice Stuart A.
Published: February 2003

Collins and Rice’s1 calculations are extended to the fifth excited state, and the effect of anharmonicity in the potential on mode shape and energy is examined. (AIP)
Translational energy distribution and production mechanism of H* and D* produced by controlled electron impact on water and heavy water
Authors: Kurawaki Junichi , Ueki Kenji , Higo Morihide , Ogawa Teiichiro
Published: February 2003

The high resolution spectra of the Balmer lines of H* (n=3,4) and D* (n=3,4) have been measured with the use of a Fabry–Perot interferometer. Translational energy distributions of H* and D* calculated from their Doppler profiles have four components; their peaks lie at about 0.5, 4, 2, and 6–8 eV. There are four thresholds for the formation of H* (n=4) and D* (n=4) at about 18.7, 25.5, 31.3, and 38.9 eV. The production mechanisms of these components have been assigned to dissociation through Rydberg states converging to some ionic states of water such as the B̃ 2B2, 2B1, 2A1, and doubly ionized states, respectively.
Tests of the quasiclassical trajectory cross-correlation moment method against accurate quantum dynamics for V–V energy transfer in HF–HF collisions
Authors: Schwenke David W. , Thirumalai Devarajan , Truhlar Donald G. , Coltrin M. E.
Published: February 2003

V–V energy transfer probabilities for breathing–sphere HF–HF collisions are calculated both by a quasiclassical trajectory moment analysis and by converged quantal close coupling calculations. The two methods agree within factors of 1.1–1.5 for transition probabilities greater than or equal to 0.17 and within factors of 1.9–9.5 for transition probabilities in the range 0.04–0.065, but only within factors of 5.1–82 for those in the range 0.0008–0.004 and within factors of 20–150 for those in the range 0.0002–0.0004.
Theoretical study of the properties of methyl radical
Authors: Chipman Daniel M.
Published: February 2003

A detailed ab initio study of the structure and properties of methyl radical in its ground electronic state is presented. The primary focus is on the spin density distribution and its dependence on basis set, wave function model, and molecular geometry. By using a natural orbital analysis that provides an unambiguous decomposition into core and valence contributions, interesting theoretical and computational results are found that clarify the relationships among CI, UHF, and PUHF models. In particular, it appears that the better agreement with experiment for the PUHF model as compared to UHF is simply fortuitous. A large and negative core contribution found in the 13C isotropic hyperfine coupling constant explains why minimal basis set calculations always greatly overestimate this property, regardless of what wave function model is used. All the models studied give good results for anisotropic hfc and for the vibrational corrections to isotropic hfc, although not for the isotropic hfc themselves. Through comparison to the ab initio results, some conditions are revealed where semiempirical methods such as INDO should fail. The dependence of potential energy and various charge density properties on molecular geometry is also studied.
Fitting the Coulomb potential variationally in Xα molecular calculations
Authors: Dunlap B. I.
Published: February 2003

The method of Mintmire and Dunlap which variationally fits the Coulomb potential rather than the charge density is extended to linear combination of Gaussian-type orbitals Xα calculations on molecules. This approach is more efficient than fitting the charge density since the same integrals are used to treat the Coulomb and exchange potentials. Furthermore, the required Fock matrix elements are simple overlap rather than Coulomb integrals. However, the method is somewhat less accurate than fitting the charge density in a test on H2.
Inelastic neutron scattering studies of some intramolecular hydrogen bonded complexes: A new correlation of γ(OHO) vs R (OO)
Authors: Howard J. , Tomkinson J. , Eckert J. , Goldstone J. A. , Taylor A. D.
Published: February 2003

Inelastic neutron scattering spectra of several complexes {potassium hydrogen maleate, nickel dimethylglyoxime, and tripotassium cis-dichloro (hydrogen disulfito) and tripotassium cis-dichloro (hydrogen disulfito) platinate (II)} with strong intramolecular hydrogen bonds have been obtained and the out-of-plane bending modes γ(OHO) of the hydrogen bond assigned. Using previously published data, primarily for intermolecularly hydrogen bonded complexes, it is shown that as the oxygen–oxgyen distance {R(OO)} decreases γ(OHO) increases. Our new data do not follow this correlation since γ(OHO) is also observed to decrease as R(OO) decreases. It is suggested that this observation is due not to a fundamental difference in the behavior of inter- and intramolecular hydrogen bonds but rather to the different range of values of R(OO) found for each type. For the intermolecular systems R(OO) is greater than ∼ 2.44 Å, while for the intramolecular complexes (including potassium monochloromaleate) R(OO) is less than this value. It appears that hydrogen bonds undergo a change in dynamic properties at R(OO) 2.44 Å and some geometric properties of ring systems are discussed which support this idea.
Convergence acceleration in Monte Carlo computer simulation on water and aqueous solutions
Authors: Mehrotra Prem K. , Mezei Mihaly , Beveridge David L.
Published: February 2003

The convergence characteristics of standard Metropolis Monte Carlo calculations on liquid water and aqueous solutions are described, and documentation of the need for convergence acceleration procedures is presented. The acceleration procedures are additional importance sampling schemes added to the Metropolis method. The recently proposed ‘‘forced bias’’ and ‘‘preferential sampling’’ procedures are specifically considered. Comparative studies on liquid water at T=25 °C using the force bias method show that convergence is improved by a factor of 2–3 over standard Metropolis results. For aqueous solutions, force bias and preferential sampling procedures used separately and together were studied on a prototype aqueous solution problem based on the liquid water simulation. Neither method alone was found to be adequate for describing structural characteristics of solutions in realizations of the length presently used for simulations on pure liquids. A combination of the force bias and preferential sampling methods was found to be quite successful, and makes aqueous solutions accessible to simulation studies at levels of rigor commensurate with that obtained for pure liquids. Preliminary convergence acceleration results on [CH4]aq using the combined force bias-preferential sampling acceleration methods are also presented.
Equilibrium properties of a nonadditive hard-sphere mixture in the semiclassical limit
Authors: Singh U. N. , Sinha S. K.
Published: February 2003

The problem of calculating the quantum corrections to the thermodynamic properties of a binary mixture of nonadditive hardspheres is studied. Numerical results are given for the first order quantum correction to the excess pressure and to the excess free energy. It is found that the ‘‘excess’’ quantum effect increases with the increasing density and increasing Δ the nonadditive parameter. A significant feature is that the excess quantum effect becomes negative with decrease of Δ and increase of density, when Δ<O.
On the properties of inhomogeneous charged systems
Authors: Blum Lesser , Gruber Christian , Henderson Douglas , Lebowitz Joel L. , Martin Philippe A.
Published: February 2003

We give a proof and an extension of equations previously derived by Wertheim and Lovett, Mou and Buff, relating the gradient of the density to an integral of the external force over the pair correlation function; when the system has boundaries it also involves a surface contribution. These equations are derived and used for systems which may contain free charges, dipoles, and a rigid background (jellium). In particular, we derive an equation for the density profile near a plane electrode and we show that the correlation function has to decay no faster than ‖x‖−N(N=space dimension) parallel to the electode.
Applications of sum rules and the contact value theorem to dipolar fluids
Authors: Blum Lesser , Rasaiah J. C. , Vericat F.
Published: February 2003

Applications of the contact value theorem and two sum rules to a dipolar fluid adjacent to a charged wall are considered. Statistical mechanical formulas for electrostriction, changes with the field of the singlet density at contact with the wall and changes in the distribution functions at contact with the wall are derived.
Dielectric absorption of the surfactant n-octylammonium formate and some related molecules in various media
Authors: Desando M. A. , Walker S. , Calderwood J. H.
Published: February 2003

Relaxations around the C–C and/or C–N+ bonds account for the dielectric absorption in the 10–105 Hz region of n-octylammonium formate in polystyrene and frozen toluene matrices, and as a pure compressed solid. Small segment relaxations involving the intramolecular hydrogen bonded +NH3−O2CH unit would explain the 120–180 K relaxations (ΔHE∼15–20 kJ mol−1), and the relaxations of larger segments with possible contributions from the molecular process would account for the 240–320 K absorption. Conversion of n-octylammonium formate into its amide does not alter the nature of the low temperature relaxations. Comparisons of the relaxation data with simple molecules have been made (a) containing the C–C–X–C–C (X=+NH2, O, and S) structure and (b) two of the simplest amides.
Dissociative excitation of TlI and TlCl by rare-gas metastable atoms and N2 A 3Σ+u
Authors: Baltayan P. , Pebay-Peyroula J. C. , Sadeghi N.
Published: February 2003

The reactions of TlCl and TlI with rare gas He(3S), Ar(3P2), Kr(3P2), Xe(3P2), and N2(A 3Σ+u) metastable species were studied in a flowing afterglow apparatus. In all cases, emission from the excited states of Tl was observed, and with helium we also observed the 190.8 nm line issued from the 3P1 level of Tl+. We have verified that these excited levels are populated following a first-order process. The rate constants for the different exit channels of dissociative excitation have been determined and the influence of radiative cascade effects is discussed. The largest rate constants, on the order of 10−10 cm3 mol−1 s−1, were obtained for the reactions of TlCl and TlI with xenon, and TlCl with krypton, for which an ionic exit channel is not possible because of energy conservation criteria. The rate constants for the reactions with argon are much smaller, about 10−13 cm3 mol−1 s−1. A large rate constant, 1.3×10−9 cm3 mol−1 s−1 was obtained for the excitation of Tl+(3P1) level by helium metastable atoms.
Improved parametrization of diatomics-in-molecules potential energy surface for Na(3p 2P)+H2 → Na(3s 2S)+H2
Authors: Blais Normand C. , Truhlar Donald G. , Garrett Bruce C.
Published: February 2003

We report a new set of diatomics-in-molecules potential energy surfaces and electronically adiabatic couplings for the process Na(3p 2P) +H2 → Na(3s 2S)+H2. The surfaces of our previous paper [D. G. Truhlar, J. W. Duff, N. C. Blais, J. C. Tully, and B. C. Garrett, J. Chem. Phys. 77, 764 (1982)] are improved by employing a new parametrization for the 3Σ+ diabatic potential energy curves of NaH. The 3Σ+ diabatic Hamiltonian matrix Hn is based on small-basis-set valence-bond calculations for Hn12, and the diagonal elements are adjusted to yield accurate 3Σ+ adiabatic potential curves. The new surfaces are compared to the recent ab initio results obtained by the coupled-electron-pairs approximation [P. Botschwina, W. Meyer, I. V. Hertel, and W. Reiland, J. Chem. Phys. 75, 5438 (1981)], and the comparison indicates good agreement between the semiempirical and ab initio surfaces.
Elastic scattering of electrons by N2, O2, and CO in the energy range 0.1–3 keV
Authors: Tayal S. S. , Jain Ashok , Tripathi A. N. , Srivastava M. K.
Published: February 2003

Elastic differential cross sections for the scattering of electrons from N2, CO, and O2 are calculated at intermediate and high energies using the second order eikonal approximation and the multiple scattering approach due to Glauber in the independent atom model. The polarization potential describing the long range and nonlocal dynamic effects has been included. The second order eikonal approximation results show an improvement over those obtained in the first order eikonal approximation at scattering angles Θ≤30° and compare favorably with the available absolute experimental measurements. The interference of single and double scattering terms is investigated.
A natural potential surface dissection technique for molecular scattering
Authors: Korpela Seppo , Askar Attila , Rabitz H.
Published: February 2003

This paper is concerned with the dissection of general potential scattering surfaces in a way that takes into account their natural contour structure. In this fashion, the scattering problem can be broken into a set of pieces based on the slowly varying nature of the potential surface along its natural contours. The boundary integral method is used to represent the solution in each subregion in terms of its value and normal derivative along the subregion boundaries. A simple illustrative example was considered based on direct numerical solutions of the resulting algebraic equations. For efficient treatment of realistic problems, we also show how previously developed R-matrix theory ideas may be readily applied in the present circumstances.
Supersonic copper clusters
Authors: Powers D. E. , Hansen S. G. , Geusic M. E. , Michalopoulos D. L. , Smalley R. E.
Published: February 2003

Copper clusters ranging in size from 1 to 29 atoms have been prepared in a supersonic beam by laser vaporization of a rotating copper target rod within the throat of a pulsed supersonic nozzle using helium for the carrier gas. The clusters were cooled extensively in the supersonic expansion [T(translational) 1 to 4 K, T(rotational)=4 K, T(vibrational)=20 to 70 K]. These clusters were detected in the supersonic beam by laser photoionization with time-of-flight mass analysis. Using a number of fixed frequency outputs of an exciplex laser, the threshold behavior of the photoionization cross section was monitored as a function of cluster size. The 7.9 eV photon energy of the F2 excimer laser was found to be above the ionization potential of all clusters, and the photoion mass spectrum thus produced showed the copper cluster concentration in the beam to follow a monotonically decreasing function of cluster size. The 6.4 eV ArF exciplex laser photon energy was found to be above the photoionization threshold of clusters with three or more atoms in the case of odd-numbered clusters, but only for clusters with eight or more atoms for even-numbered clusters. Extending out to clusters as large as 29 atoms, laser photoionization at 6.4 eV produced a time-of-flight mass distribution with a pronounced even/odd alternation in cluster photoion intensity. This alternation in ionization threshold behavior was attributed to an even/odd alternation in the electronic structure of the copper clusters with the highest occupied molecular orbital (HOMO) of the even clusters being considerably more strongly bonding than it is in the clusters with an odd number of copper atoms. The 4.98 eV photon energy of the KrF exciplex laser was found to lie below the ionization threshold of all clusters in the 1 to 29 atom range. An extensive survey of the ultraviolet absorption spectrum of the copper dimer was also performed with this supersonic beam source. Resonance two-photon ionization (R2PI) with mass selective detection allowed the detection of five new electronic band systems in the region between 2690 and 3200 Å, for each of the three naturally occurring isotopic forms of Cu2. In the process of scanning the R2PI spectrum of these new electronic states, the ionization potential of the copper dimer was determined to be 7.894±0.015 eV.
Analysis of the Rouse model in extensional flow. II. Stresses generated in sink flow by flexible macromolecules and by finitely extended macromolecules
Authors: King D. H. , James D. F.
Published: February 2003

Stresses generated by a solution of Rouse macromolecules in planar and axisymmetric sink flow were analyzed by solving the momentum equation together with the constitutive relation corresponding to the Rouse model (i.e., the generalized convected Maxwell equation). The results show that the additional normal stress in the radial direction is of order [η]c when compared with the corresponding Newtonian viscous stress. However, in the high Reynolds number range where sink flow conditions are valid, the additional stress must be compared with inertial stresses, and in that case the results show that the ratio of non-Newtonian to Newtonian hydrodynamic stresses is of order [η]c/Re, where Re is the Reynolds number. Since experimental data exceed this small ratio by two orders of magnitude, a new molecular model was developed to accommodate limited molecular extension. The model presumes that, in a converging flow, a molecule initially deforms as a Rouse molecule and then its configuration is frozen after a certain amount of extension. This ‘‘frozen-necklace’’ model consequently provides an estimate of hydrodynamic effects caused by finite extension, as might be created by intramolecular entanglements. Non-Newtonian stresses predicted by the model are compared with available data for strictly dilute solutions and agree to the same order of magnitude.