bluuebunny/crossref_metadata_2025 huggingface dataset:
Bethe surface and Compton profile of NH3 obtained by 35 keV electron impact
Authors: Lahmam-Bennani A. , Duguet A. , Wellenstein H. F. , Rouault M.
Published: February 2003

Complete inelastic electron impact spectra have been obtained for NH3 for a momentum transfer range from 0.4 to 12.5 a.u. using 35 keV electrons. These spectra were converted to relative generalized oscillator strengths (GOS), were placed onto an absolute scale by the Bethe sum rule, and higher order sum rules were used to test the accuracy of the GOS. The Compton profile (CP) of NH3 was determined from the GOS by means of the impulse approximation (IA) and it was found that the CP’s were asymmetric and shifted in respect to the free electron theoretical CP. This Compton defect was analyzed in detail and was shown to be due to the failure of the IA. The area under the CP is discussed in terms of the x-ray incoherent scattering factor and experimental results for the valence, inner shell, and total CP’s are compared to several theoretical profiles.
Intermolecule vibrational energy transfer dynamics in IR laser pumped SO2/18O2 mixtures
Authors: Lester Marsha Isack , Flynn George W.
Published: February 2003

Intermolecule vibrational energy sharing in SO2/18O2 mixtures has been observed by monitoring fluorescence emission from the SO2 ν3 state following pulsed CO2 laser excitation of the ν1 mode. The rate constant for the vibrational energy crossover step from the SO2 ν3 state to the v=1 level of 18O2 has been determined to be 5.74 (±0.91) msec−1 (Torr 18O2)−1 or approximately 1400 gas kinetic collisions. The present results are compared with an earlier ultrasound investigation of vibrational relaxation in the SO2/16O2 system. Theoretical probabilities of intermolecule energy transfer due to short-range repulsive forces and long-range dipole–quadrupole forces have been calculated for the SO2/18O2 and SO2/16O2 systems. Comparison of experimental and theoretical results suggests that both short-range and long-range forces contribute to the intermolecule vibrational energy process in SO2/18O2 mixtures while only short-range forces appear to be important in the SO2/16O2 exchange. A general technique has been developed for determining the error in kinetic rate constants from the experimental uncertainty of the measured fluorescence eigenvalues.
Rotationally inelastic collisions of LiH with He. I. A
b i
n
i
t
i
o potential energy surface
Authors: Silver David M.
Published: February 2003

The diagrammatic many-body perturbation theory is applied through third order in the correlation energy to the interaction potential between He and a rigid LiH molecule. The ab initio calculations are used to derive an analytic representation of the potential surface in terms of orthogonal polynomials. Several different basis sets are employed to demonstrate the sensitivity of the energies to the computational techniques. The resulting potential surfaces are highly anisotropic with respect to the LiH center-of-mass and allow for a weak binding (∼7 meV) of the He to the Li end of the LiH axis.
Rotationally inelastic collisions of LiH with He. III. Experimental determination of state-to-state cross sections
Authors: Dagdigian Paul J. , Wilcomb Bruce E.
Published: February 2003

State-to-state rotationally inelastic cross sections for the scattering of 7LiH with helium have been determined by the use of electric quadrupole rotational state selection and dye laser fluorescence detection. Results for the incident j=1 state and final states j′=0, 2–15 at an average collision energy of 0.32 eV are reported. As a result of the finite angular acceptance of the laser detection zone and the observed dependence of the cross sections on the scattering path length l, the present values are lower limits to the absolute integral σj=1→j′ values. Because of the theoretical simplicity of the LiH–He system, comparison with accurate quantum calculations for the cross sections (see Papers I and II of this series) has been possible. Calculations using the coupled states dynamical approximation with an ab initio potential surface reproduce well the qualitative behavior of the experimental cross sections. Comparison with results from simpler theoretical models suggests that the accuracy of the potential energy surface employed is crucial for an adequate theoretical description of the dynamics.
Photoionization of atomic silver between 17 and 41 eV
Authors: Krause M. O.
Published: February 2003

Photoelectron spectra of free silver atoms were measured at six energies of the He and Ne discharge lamps. Spectra were obtained at 90 ° and 54.7 ° in relation to the photon beam. The four D term levels were resolved and their branching ratio was found to be nearly statistical and to vary slowly with energy. Spectra indicate the presence of an autoionization resonance near 16.8 eV. The partial photoionization cross section of the 5s level is about 5% of that of the 4d level. The atomic 4d cross section rises slowly above threshold in qualitative agreement with the trend of the atomic potential, and it displays an energy dependence similar to that reported for metallic silver.
Laser induced fluorescence of Se2 and Te2 in rare gas matrices
Authors: Bondybey V. E. , English J. H.
Published: February 2003

The laser induced fluorescence excitation and resolved emission spectra of Se2 and Te2 suggest that these species are only insignificantly perturbed by the solid medium. The spectroscopy of both molecules in the matrix is governed by efficient nonradiative transitions among numerous low lying electronic states and fast vibrational relaxation. Several new electronic states of these species are observed and characterized.
Experimental and theoretical study of rotationally inelastic polar molecule collisions: 7LiH–HCN
Authors: Dagdigian Paul J. , Alexander Millard H.
Published: February 2003

This article describes the study of rotational energy transfer in the strongly polar LiH–HCN system. A supersonic beam of LiH, rotationally state selected in ja=1 by an electric quadrupole field, is scattered by HCN gas at room temperature. Laser fluorescence detection is used to determine integral cross sections for ja=1→j′a LiH transitions. The measured cross sections (in Å2) are 245±30 (2σ), 519±88, 222±47, 125±26, 64±17, and 41±12 for j′=0,2,3,4,5, and 6, respectively. The large magnitudes of the cross sections reflect the strong, long-range dipolar coupling. A comparison is made with the predictions of various theoretical models, based on the approximate solution of the time-dependent classical-path equations of motion for rectilinear trajectories. The usual Born approximation significantly overestimates the cross sections for the dipole allowed (ja→ja±1) transitions, even when statistical microreversibility is imposed. Worse, extension of the Born approximation to second order appears to introduce even larger errors. Better agreement with experiment is obtained within the sudden approximation, although the predicted ja=1→j′a=0,2 cross sections are still too large, due to the breakdown of this approximation at large impact parameter for this long-range system. This can be remedied in the adiabatically corrected sudden (ACS) approximation, which we have recently developed, by the introduction of an effective dephasing frequency into the sudden action integral. In a confirmation of our earlier study of the LiH–HCl, DCl systems, we find that the ACS cross sections are in good agreement with the experimental values, especially for the strongest transitions.
Picosecond study of electron ejection in aqueous phenol and phenolate solutions
Authors: Mialocq Jean-Claude , Sutton Jack , Goujon Paul
Published: February 2003

The photoionization of aqueous phenol and phenolate solutions was investigated using picosecond absorption spectroscopy. Phenol and phenolate were excited in the first singlet excited state using a single picosecond pulse of 27 ps duration, at 265 nm (4th harmonic of a Nd–YAG laser). Hydrated electron formation was ascertained by following the kinetics of formation and disappearance at 630 nm with a picosecond pulse obtained by stimulated Raman scattering (SRS). Similarly to the ferrocyanide ion, the excited phenolate ion undergoes a very fast electron ejection process. The lifetime of this process is shorter than the time resolution of our experimental device. In the excited phenol molecule, hydrated electron formation is retarded, the delay between the half-rise times of the exciting pulse and the electron absorption signal being (12±1) ps. This delay is not reduced at low pH. These observations and the high yield of ̄eaq formation are best explained by a consecutive two photon process, the second photon being absorbed by the excited singlet state S1 and the deprotonation occuring after ejection of the electron. The kinetics of hydrated electron disappearance with NO3− as scavenger, are in excellent agreement with literature values. Using H3O+ and Cd++ to scavenge the hydrated electron, its initial formation yield remains constant, showing that Cd++ does not react with any hydrated electron precursor. This difference between our results and those obtained in picosecond pulse radiolysis shows that the precursor of the hydrated electron is not the same in the two techniques. The precursor obtained in pulse radiolysis appears to be more reactive with scavengers. A possible explanation is that after phenolate or phenol excitation, the resultant internal state of the aromatic molecule is capable of undergoing electron transfer to the adjacent solvent molecules, thus producing at least partially hydrated electrons directly.
Surface enhanced Raman spectra: A critical review of the image dipole description
Authors: Hilton Peter R. , Oxtoby David W.
Published: February 2003

Recent experiments have demonstrated enhancements of several orders of magnitude for Raman scattering of pyridine and other molecules adsorbed on a silver surface. One explanation which has been proposed is an image dipole model, in which a point dipole is mirrored in the metal, with the mirror image inducing an additional dipole in the adsorbed species and thus changing its effective polarizability αeff. In this paper we suggest that the large enhancements obtained from such a point dipole description result from the use of an symptotic theory at unphysically short distances. We demonstrate this through a model calculation of αeff of a hydrogen atom near a mirror surface. A point dipole approximation gives a divergent αeff near a critical distance Rc from the surface, while a more exact self-consistent Hartree calculation (including the finite extent of the hydrogen charge cloud) gives only a slight enhancement or even a de-enhancement near Rc.
The electronic structure of the lithium trimer anion and cation
Authors: Gole J. L. , Childs R. H. , Dixon D. A. , Eades R. A.
Published: February 2003

SCF and SCF–CI calculations have been performed on Li3, its anion and cation. We predict a value of 1.1 eV for the adiabatic electron affinity. The Li−3 bond energy is found to be 0.9 eV versus the 0.4 eV energy required to dissociate Li3 to dimer and atom. Thus, the bond strength of the anion considerably exceeds that of the neutral parent. The difference in the nature of electron binding to Li2 and Li3 can be understood through modification of simple MO concepts. The energy required to dissociate Li3+ to Li2++Li is found to be 1.28 eV. Hence, the bond strength of the cation also greatly exceeds that of the neutral. The Li3+ bond energy is comparable to the Li2+ dissociation energy (1.24 eV). The adiabatic ionization potential is found to be 3.95 eV. The combination of the present study and those of previous researchers indicates that the Li3 surface is weakly varying with bond angle and may be characterized by multiple minima. The current results for Li3 and Li3+ are discussed in the light of recent mass spectrometric studies of the trimer.
Distribution function of the end-to-end vector for short polymer chains
Authors: Freire Juan J. , Rodrigo M. M.
Published: February 2003

A method is presented for the evaluation of the end-to-end vector distribution function for short polymer chains. The method is based on the expansion of this quantity in terms of a spherical harmonic series and is related with a very efficient algorithm recently proposed by Fixman et al. for the calculation of high moments. Numerical results are reported for a rotational isomeric representation of short polymethylene chains. The results are compared to those obtained earlier by other authors with an alternative procedure and the advantages of the new scheme are stressed.
Selectively excited, wavelength resolved emission spectra of gaseous organic ions
Authors: Sears Trevor , Miller Terry A. , Bondybey V. E.
Published: February 2003

Previously reported laser excitation spectra of a number of gaseous organic ions have characterized the vibrational structure of the excited electronic states, but have given only slight information about that structure in the ground electronic state. We now report wavelength resolved emission spectra induced by laser excitation of specific excited state vibrational levels for C6H3F3+ and C6H3Cl3+. These spectra directly characterize the ground state vibrational structure. Excitation of the vibrationless level confirms that previously reported ground state vibrational frequencies obtained for the ions in Ne matrices are characteristic of the isolated molecules. Similar spectra obtained by pumping excited, nontotally symmetric, vibrational levels show directly, for the first time, the split components of the most active Jahn–Teller modes in the ground electronic state. The splittings show that several previous analyses of Jahn–Teller effects in these ions were either incorrect or incomplete, and provide the necessary additional information to perform a complete analysis.
Theoretical determination of the magnetic properties of HCl, H2S, PH3, and SiH4 molecules
Authors: Lazzeretti Paolo , Zanasi Riccardo
Published: February 2003

Coupled Hartree–Fock perturbation theory has been applied to evaluate second-order magnetic properties of HCl, H2S, PH3, and SiH4 molecules. An efficient procedure for processing only symmetry distinct two-electron integrals in the coupled HF algorithm is outlined, which permits the use of very large basis sets of expansion with limited computer efforts. Several near Hartree–Fock wave functions are examined, particular attention being devoted to the role of polarization functions for the second-row atoms. Comparison between computed and available experimental results is gratifying and demonstrates the practicability of perturbed HF calculations based on the group-theoretical procedure sketched in this paper. An analysis of the gauge dependence affecting the calculated values is performed, which yields a severe test on the reliability of the present calculations.
Substitution effect on formaldehyde photochemistry. Potential surface characteristics of HFCO
Authors: Morokuma Keiji , Kato Shigeki , Hirao Kimihiko
Published: February 2003

The potential energy surface for the lowest singlet states for fluoroformaldehyde HFCO is calculated. The geometries of the reactant HFCO, the elimination products HF+CO and the isomerization product FC̈OH as well as the transition states have been determined with the ab initio SCF method. At these optimized geometries, CI calculations have been performed using the 6-31G basis sets. (AIP)
The role of convective transport in the dissolution or growth of a gas bubble
Authors: Subramanian R. Shankar , Weinberg Michael C.
Published: February 2003

The significance of convective transport in the dissolution/growth of a stationary bubble is illustrated. The approximation made by ignoring such transport in the fluid but including boundary movement is shown to be worse than the quasi-stationary approximation which ignores all motion.
Comment on ‘‘Detection of spurious avoided crossings’’
Authors: Mead C. Alden
Published: February 2003

It is argued that spurious avoided crossings do not occur and that even if they did, their presence could never be detected by methods given in Ref. 3. The contention of Carrington regarding the detection of spurious avoided crossings is disputed. (AIP)
Uniform JWKB amplitudes and phases for turning-point problems
Authors: Bieniek Ronald J.
Published: February 2003

Semiclassical wave functions written in the form A (E,R)  sin[Φ (E,R)] can be used in conjunction with the method of stationary phase to obtain analytic expressions for T-matrix elements. Such expressions are functions of the amplitudes, phases, and their derivatives at the points of stationary phase. Generally, simple JWKB formulas for amplitude [As(E,R) =k (R)−1/2] and phase [Φs(E,R) =ℱRRtk (r) dr+1/4π] have been used. Unfortunately these become invalid for stationary-phase points that are near a classical turning point. This occurs at a crucial time, since T-matrix elements are often unusually large under these circumstances. To preserve the advantages of semiclassical stationary-phase methods, expressions for modified amplitudes, phases, and their derivatives are presented that remain uniformly valid both near to and far from the turning points in the three most commonly encountered problems: the single turning-point of a simple free state, the double set of a bound state, and the triple set associated with a centrigual barrier. These expressions are analytic functions of the simple JWKB amplitude [As(E,R)]. Explicit numerical criteria are given that one can employ to determine when the simple amplitude and phase are no longer sufficiently accurate, but instead should be used to calculate the uniform values.
Spin-echoes for diffusion in bounded, heterogeneous media: A numerical study
Authors: Zientara Gary P. , Freed Jack H.
Published: February 2003

The diffusive behavior of spin-bearing species in a bounded heterogeneous medium is analyzed in a manner appropriate for spin echo experiments in the presence of field gradients. A numerical method based upon the stochastic Liouville equation (SLE) is discussed that includes the discontinuities in transport and solubility properties due to the different spatial regions. The double step computational algorithm, which takes advantage of the different time scales of diffusive and spin-quantum phenomena, is then introduced as a general approximate solution of the time dependent SLE. This method is applied to the calculation of the decay of spin echo amplitudes, and it suggests a new approach for analyzing such experiments in terms of the microscopic details and chemical properties of heterogeneous systems.
ESR studies of barriers to ring inversion in cyclic monocarboxylic acid radicals
Authors: Suryanarayana D. , Sevilla M. D.
Published: February 2003

Activation energies for ring inversion have been estimated for a number of cyclic monocarboxylic acid radicals, of structure (CH2)n≳ĊCOOH (I) with n=3,4, and 5, using electron spin resonance (ESR) methods. These radicals were produced from the corresponding cyclic monocarboxylic acids, by γ irradiation (at 195 K) and subsequent annealing. The ESR spectra of these radicals vary with temperature. The variations are attributed to ring inversion of the cyclic group in these radicals. Computer simulations of the temperature dependent ESR spectra were employed using the solutions of modified Bloch equations for a two-jump process. From these simulations the rate of ring inversion (τ) as well as the ESR parameters were estimated as a function of temperature (T). Arrhenius parameters found for the ring inversion in cyclohexane carboxylic acid radical (i.e., I with n=5) are Ea=4.0±0.3 kcal/mol and ln(1/τ0) =29.0±0.7 (τ0 in sec). The radical species with five-membered ring (n=4) was studied in a number of matrices: (i) sodium cyclopentane carboxylate, (ii) 12M LiCl(D2O), (iii) 8M NaOD, (iv) cycloleucine and (v) cyclopentane carboxylic acid. In the last two matrices, the five-membered ring was found to have twisted configuration yielding four nonequivalent β-proton splittings. In the other matrices a symmetrical configuration was found revealing two pairs of equivalent splittings. The barrier (Ea) to ring inversion for this radical (n=4) varies only slightly (from 1 to 1.5 Kcal/mole) in different matrices.
Pressure broadening of the HCO+ J=0–1 transition by hydrogen
Authors: Anderson Thomas G. , Gudeman Christopher S. , Dixon Thomas A. , Woods R. Claude
Published: February 2003

Measurements have been made of the broadening of the HCO+ J=0–1 microwave absorption line by hydrogen. The linewidths (Δν, half-width at half-intensity) were obtained from a nonlinear least squares analysis of the individual spectra, taken over the pressure range of 4–40 mTorr. The pressure dependence of the linewidth, dΔν/dP was determined to be 29.6±3 MHz/Torr for the HCO+ transition broadened by H2 near 100 °K. This corresponds to a collisional cross section of 182±20 Å2 for HCO+–H2. Also, a new and more reliable measurement is reported for broadening of the J=7–8 transition of 18OCS, which gives dΔν/dP=7.11±0.15 MHz/Torr for self-broadening at 296 °K.
Application of virial theorem for the total binding energy of neutral atomic systems
Authors: Shih Chia C.
Published: February 2003

Hartree–Fock–Roothaan–Clementi (HFRC) densities are used to calculate approximately the total exchange energies of neutral atoms (Z=2 to 36) according to the gradient expansion. Through the use of the virial theorem, total binding energies can be estimated. Second order corrections to the total exchange energies lead to approximated values of the total binding energies in excellent agreement with the tabulated HFRC values.
Tunneling frequencies for internal rotation computed using V3 and V6 terms in the potential function
Authors: Smith David
Published: February 2003

The intersap rotation of the methyl group is studied using the potential junction V (φ) =V3/(2) (1−cos 3φ) +V6/(2) (1−cos6φ). The tunnelling frequencies have been compulsed using both V3 and V6 terms for barriers to rotation higher than G00 cal/mole.(AIP)
Piezo- and elasto-optic properties of deuterium oxide under high pressure
Authors: Chen C. C. , Vedam K.
Published: February 2003

The variation of the refractive index of D20 with pressure has been determined using g the high precision optical interferometric method.(AIP)
Photochemical ionogenesis in solutions of zinc octaethyl porphyrin
Authors: Ballard S. G. , Mauzerall D. C.
Published: February 2003

Absolute ion yields and the kinetic parameters of ion formation and decay have been determined by transient conductimetry for two photochemical ionogenic reactions of zinc octaethyl porphyrin in a variety of inert organic solvents. One reaction (T–P) involves electron transfer in the encounter complex of the porphyrin triplet state (T) and ground state (P); it is relatively slow (kTP∼108M−1s−1, and solvent insensitive). The second (T–T reaction) involves reactive collision between two triplets; it occurs at the encounter limit (kTT∼1010M−1s−1). Neither rate constant depends on solvent dielectric constant. Reaction yields are very dielectric-dependent, however, and provide unusually straightforward experimental access to the problem of geminate ion-pair decorrelation. A two-parameter model is presented in which the initial photochemically-formed ion pair is created by electron tunneling in a specific spin state at nontrivial separation. The electron transfer radii for the two reactions are determined by completely independent analysis of the kinetic and yield data to be ∼21 Å, some 7 Å greater than twice the radius of the porphyrin π-electron system. Following e− transfer, the solvent-separated components of the geminate pair diffuse in their Coulomb field, undergoing both coherent and incoherent changes in their combined spin state as they do so. They either escape beyond the Coulomb radius to give uncorrelated and conductimetrically active doublet ions, or approach to the critical radius for reverse electron transfer to the ground state (2P) and, subject to a spin selection rule, are annihilated. The dominant mechanism of spin interconversion appears to be spin–orbit coupling to the molecular rotations rather than nuclear hyperfine interactions. The coupled diffusion and spin relaxation equations are solved numerically by the method of finite differences; theoretical yields of free ions show good fit to the data over five orders of magnitude. Recombination of the escaped and randomized radicals occurs at the electrostatically accelerated encounter limit and conforms well to the Debye–Smoluchowski equation. Rate constants in excess of 2×1011 M−1s−1 are observed. A third ionogenic mechanism, direct 2-photon ionization of the porphyrin, is briefly reported. We also briefly characterize the weakly ionogenic quenching reaction of the prophyrin triplet state with molecular oxygen.
Radiation effects in x-irradiated hydroxy compounds
Authors: Budzinski Edwin E. , Potter William R. , Box Harold C.
Published: February 2003

Radiation effects are compared in single crystals of xylitol, sorbitol, and dulcitol x-irradiated at 4.2 °K. In xylitol and dulcitol, but not in sorbitol, a primary oxidation product is identified as an alkoxy radical. ENDOR measurements detected three proton hyperfine couplings associated with the alkoxy ESR absorption, one of which is attributed to a proton three bond lengths removed from the seat of unpaired spin density. Intermolecular trapping of electrons is observed in all three crystals. ENDOR measurements were made of the hyperfine couplings between the trapped electron and the hydroxy protons forming the trap.
Iodine chemical shifts in alkali metal metaperiodates and iodates
Authors: Segel S. L. , Vyas H. M.
Published: February 2003

Iodine chemical shift tensors have been measured using nuclear magnetic resonance in a variety of alkali metaperiodates, which include ammonium, potassium, silver, and sodium. The values for the isotropic component of the shift tensor range form +0.54% for silver to −0.54% for sodium. In saturated solutions of metaperiodates the iodine shifts are equal with a value of +0.39%. These shift values have been compared with the experimentally determined value for the perpindicular shift in the iodates of lithium, cesium, and rubidium. The shift values for the iodates are of the order +0.50%. The reference material for these shift measurements is taken to be sodium iodide (solid) where γ=8.5202 MHz/10 kOe.
Orthonormal series expansion solution of the Percus–Yevick equation
Authors: Mier y Terán Luis , del Río Fernando
Published: February 2003

The PY equation is converted into an algebraic set of equations by expanding the correlation functions in an orthonormal basis. Using a Hermite basis, the PY equation is solved for the Gaussian model, the Lennard-Jones 12:6 and the repulsive LJ potentials. The method provides a direct representation of the correlation functions, the structure factor, and the thermodynamic properties. The algebraic set shows solutions to be quite independent of the initial trial values.
Direct observation of intramolecular anthracene excimer in 1,3-dianthrylpropane
Authors: Itoh Michiya , Fuke Kiyokazu , Kobayashi Sachiko
Published: February 2003

The observation of intramolecular anthracene excimer in 1,3,-dianthrylpropane by coincidental line constant of the excimer rise with fluorescence decay of anthryl moiety is reported. (AIP)
Extension of Glauber theory to account for intratarget diffraction in multicenter scattering
Authors: Miller B. R. , Bartell L. S.
Published: February 2003

A 1975 treatment of single-double multiple scattering of electrons by randomly oriented vapor-phase molecules is put on a firmer footing and extended to higher order. It is shown how to include effects of intramolecular Fresnel diffraction, as an electron scattered by one atom propagates to the next, without ever explicitly evaluating the scattered wave function in the target. Theoretically derived estimates are made of the limitations of the approach at various levels of approximation. Numerical calculations are compared as a function of energy and scattering angle with newly available high quality calculations by Kohl and Arvedson (KA). In the expected range of applicability — roughly, 10 keV and higher − the present approach yields results that are satisfactory and (unlike those of KA) inexpensive enough for use in routine electron diffraction analyses.
ESR–ENDOR studies of x-irradiated glucose-1-phosphate dipotassium salt
Authors: Locher Sarah E. , Box Harold C.
Published: February 2003

Single crystals of the dipotassium salt of gluocose-1-phosphate were grown out of water or deuterium oxide and x-irradiated at 4.2 °K. The products of irradiation were identified by means of ESR and ENDOR spectroscopy. In crystals grown out of water, three different alkoxy radicals were observed as oxidation products. In partially deuterated crystals only one of the aforementioned alkoxy radicals was produced. A hydroxyalkyl radical, RHĊOH was also produced by loss of hydrogen from the C6′ position. Electrons trapped at intermolecular sites were identified. The distances between the electron and the protons of the polar hydroxy groups forming the trap were deduced from ENDOR measurements and found to be relatively large, namely 1.732 and 1.738 Å.
Viscosity of the ice surface layer
Authors: Mantovani S. , Valeri S. , Loria A. , del Pennino U.
Published: February 2003

The thermal contraction of ice single crystals between 0 and −50 °C has been measured by the use of silicon strain gauges frozen on the crystal basal surface. The experimental results cannot be explained without assuming the existence of a Newtonian viscous layer at the ice-strain-gauge interface; this layer has a thickness which changes in temperature as predicted by Fletcher, and a viscosity intermediate between that of ice and that of supercooled water. The activation energy of the viscosity, (0.36±0.04) eV, seems to indicate that it is controlled by a vacancy mechanism in which only the vacancy migration is effective.
The WINIMAX approximation and its application to the thermal properties of a Debye lattice
Authors: Lee Myung W. , Bigeleisen Jacob
Published: February 2003

The WINIMAX method is used to expand the thermodynamic functions of a Debye oscillator in a finite series as a function of (ϑD/T)2j. The series is valid for all values of ϑD/T. Comparisons are made with the MINIMAX expansion, the Sack, Maradudin, and Weiss method and exact calculations. The WINIMAX method gives the exact value of each of the thermodynamic functions for any order polynomial.
The properties of clusters in the gas phase. IV. Complexes of H2O and HNOx clustering on NOx−
Authors: Lee Naisin , Keesee Robert G. , Castleman A. W.
Published: February 2003

Thermodynamic quantities for the gas-phase clustering equilibria of NO2− and NO3− were determined with high-pressure mass spectrometry. Comparison of ΔG°n,n+1 values derived from our data shows good agreement with formerly reported values at 296 °K. New data for larger NO2− and NO3− hydrates as well as NO2−(HNO2) were obtained in this study. To aid in understanding the bonding and stability of the hydrates of nitrite and nitrate ions, CNDO/2 calculations were performed, and the results are discussed herein. A correlation between the aqueous phase total hydration enthalpy of a single ion and its gas-phase hydration enthalpy was obtained. Atmoshperic implications of the data are also briefly discussed.
The photodissociation of van der Waals molecules: Complexes of iodine, neon, and helium
Authors: Kenny Jonathan E. , Johnson Kenneth E. , Sharfin Wayne , Levy Donald H.
Published: February 2003

A supersonic free jet expansion was used to prepare van der Waals complexes of the type I2NeaHeb. Complexes containing as many as seven rare gas atoms were identified as satellites in the fluorescence excitation spectrum of the I2 B (v′=13 to 26) ←X (v″=0) band system by their relative dependence on the concentrations of neon and helium. For a+b?6, the frequencies of the van der Waals satellites follow a simple band shift rule: ν (I2NeaHeb) =ν (I2)+Aa+Bb, where A and B are weak functions of the I2 vibrational state. This observation, along with the failure of the rule for I2Ne7, provide some information concerning the geometry and binding in these molecules. Progressions (w′=0,1, and 2) in van der Waals modes of I2Ne and I2NeHe were also identified. The problem of intramolecular energy transfer was studied by observation of the dispersed emission spectra of the I2* fragments produced upon laser-induced photodissociation of these complexes. The product vibrational state distributions could be determined by using the known Franck–Condon factors and the observed intensities of the iodine transitions. All complexes required at least one I2 stretching quantum per rare gas atom for complete dissociation. Larger species favored dissociation channels involving more than one vibrational quantum per rare gas atom.
MCSCF wave functions for excited states of polar molecules: Application to BeO
Authors: Bauschlicher Charles W. , Yarkony David R.
Published: February 2003

A previously reported multiconfiguration self-consistent field (MCSCF) algorithm based on the generalized Brillouin’s theorem is extended in order to treat excited states of polar molecules. In particular, the algorithm takes into account the proper treatment of nonorthogonality in the space of single excitations and invokes, when necessary, a constrained optimization procedure to prevent variational collapse of exited states. In addition, a configuration selection scheme (suitable for use in conjunction with extended configuration interaction methods) is proposed for the MCSCF procedure. The algorithm is used to study the low-lying singlet states of BeO, a system which has not previously been studied using an MCSCF procedure. MCSCF wave functions are obtained for three 1Σ+ and two 1Π states. The 1Σ+ results are juxtaposed with comparable results for MgO in order to assess the generality of description presented here.
Structure of a simple fluid near a wall. II. Comparison with Monte Carlo
Authors: Sullivan D. E. , Levesque D. , Weis J. J.
Published: February 2003

Monte Carlo methods are used to calculate density profiles of a dense simple fluid, interacting through a pair potential containing a hard-sphere core and truncated Lennard-Jones attractive tail, near a hard repulsive wall. The results are compared with integral–equation calculations based on the wall-particle Ornstein–Zernike equation, with closure approximations such as EXP. The integral equations fail to show several features of the Monte Carlo results, namely dependence on the distance at which the Lennard-Jones attraction is truncated, and the accumulation of conjugate vapor phase near the wall, which tends to suppress oscillations in the profiles.
Vibrational study of and conduction mechanism in β alumina. I. Stoichiometric β alumina
Authors: Colomban Ph. , Lucazeau G.
Published: February 2003

Single crystals of the stoichiometric β alumina containing H3O+, Na+, K+, Ag+, Tl+ ions have been studied by Raman spectroscopy between 2 and 4000 cm−1 in the 10–1400 K temperature range. Single crystals of isomorphous gallates have also been studied. Far infrared measurements have been performed between 10 and 250 cm−1. The Raman bands assigned to the spinel block vibrational modes of the stoichiometric compound are very narrow, Δν1/2?2 cm−1 as expected for an ordered crystal, while those of the nonstoichiometric compound are much broader Δν1/2?10 cm−1, this confirms the mechanism of the Al3+ Frenkel defects. The in plane cation vibrations have been identified below 100 cm−1 in infrared and in Raman. The most prominent Raman feature corresponds to the in plane E2g species and its halfwidth was measured as a function of temperature. The results indicate that there is a transition from an ordered state at low temperature to a state where the conducting cations are dynamically disordered. The stoichiometric β alumina can thus be considered as a superionic conductor above a characteristic temperature (Tc?350 K for Ag+, Tc?100 K for Na+) which is consistent with the x-ray study. The conductivity mechanism and activation energy are also discussed.
Primary radiation products of d
l-tartaric acid: ESR and ENDOR at 4.2 K
Authors: Moulton Grace C. , McDearmon Graham
Published: February 2003

Several primary radiation products are trapped in dl-tartaric acid at 4.2 K. A primary reduction product and a primary oxidation product are identified by ESR–ENDOR spectroscopy in partially deuterated dl-tartaric acid. Hyperfine tensors were obtained for the β-hydrogen and 13C in the reduction product and for the α-hydrogen in the oxidation product. The oxidation product trapped at 4.2 K appears to be the decarboxylation radical before reorientation into the planar π orbital configuration.
Classical transition state theory: A lower bound to the reaction probability
Authors: Pollak Eli , Child Mark S. , Pechukas Philip
Published: February 2003

We derive a rigorous lower bound to the microcanonical reaction probability in classical collinear atom–diatom collisions. This lower bound complements the upper bound provided by transition state theory, and the information needed to calculate the bound is acquired automatically in the search for the periodic orbit dividing surfaces that are possible transition states for the reaction. Numerical calculations for F+H2 and H+Cl2 over a wide energy range show that the lower bound provides the best available estimate of the reaction probability, short of a full dynamical calculation.
Infrared spectra of liquid and solid HT and HD in mixtures with T2
Authors: Souers P. C. , Fuentes J. , Fearon E. M. , Roberts P. E. , Tsugawa R. T. , Hunt J. L. , Poll J. D.
Published: February 2003

The collision-induced fundamental vibration–rotation spectra of liquid and solid HT and T2 in a mixture of 50% H and 50% T have been recorded. The spectra of liquid and solid HD in a 90% HD plus 10% T2 mixture have also been observed. The frequencies of the numerous single and double transitions have been compared with those calculated from the known molecular constants. Deep holes have been observed in the Q (O) phonon band of solid HD, HT, and DT. The position and extent of these holes have been related to a theoretical treatment which attributes the holes to a coupling of the rotational and translational motion of the molecules through the anisotropic part of the intermolecular interaction. The effect of J=1 impurity molecules on the intensity of the sharp Q1(O) line of liquid HD is discussed and the effect of the radioactive decay heat on the temperature of the liquid and solid samples is evaluated.
Internal heavy atom effect on the triplet spin sublevels of the lowest triplet state of naphthalene. II. Intersystem crossing processes from the singlet excited state to the individual spin sublevels of the lowest triplet state
Authors: Saigusa Hiroyuki , Azumi Tohru , Sumitani Minoru , Yoshihara Keitaro
Published: February 2003

The rate constants of the intersystem crossing from the singlet excited state to the individual triplet sublevels are determined for a series of halonaphthalenes. The heavy atom enchancement is most significant for the rates to the in-plane sublevels and is less significant for the rate to the out of-plane sublevel. The experimental results are interpreted satisfactorily within the framework of current theories of radiationless transitions.
A consistent semiempirical theory for the calculation of ground and excited state properties
Authors: Dinur U. , Honig B.
Published: February 2003

It is shown that all valence semiempirical theories are incapable of treating screening effects in a consistent fashion. This is due to their development in terms of the zero differential overlap assumption which leads to an imbalance of interactions in off-diagonal matrix elements. A new formulation of semiempirical theories is presented which is based on an expansion of the Fock operator in terms of averaged potentials centered either on atoms or in bonds. STO-3G calculations are carreid out to demonstrate that our averaging procedure is a reasonable one. The form of current semiempirical theories is easily recovered although many of the integrals are ascribed a somewhat different meaning. Screening now arises naturally as does a valence index and obvious corrections that should be made upon changes in hybridization. The resonance integral is given a somewhat modified interpretation and on this basis, a unified treatment of both ground and excited state properties is developed. A new method of calculation is proposed which makes use of CNDO/S matrix elements and wave functions and hence, yields reliable ionization potentials and transition energies. Ground state properties are calculated with a modified, theoretically consistent expression for the total energy and new parameters are introduced for this purpose.
An analytical approximation for vibrational relaxation. A study of the p-H2+4He system
Authors: Grosjean Alain , Jolicard Georges
Published: February 2003

We present an analytical approach to the energy exchanges between rotation and vibration in diatom–atom collisions. Our formulation tries to accurately describe the resonance effect and the adiabatic evolution of the rotator. These two phenomena appear to be essential for the system p-H2+He4 and our calculations are in good agreement with the corresponding close-Coupling and effective potential results.
Intermolecular Raman intensity transfer in the ν (CO) vibrations of Mn(CO)5Br and Re(CO)5Br
Authors: Arif M. , Kettle S. F. A.
Published: February 2003

The change in Raman intensities as (≳85%) 13CO enriched Mn(CO)5Br is isomorphically mixed with Re(CO)5Br demonstrates that a molecular E mode factor group component steals intensity from a B1-derived component by an intermolecular process. A mechanism is proposed for this intensity transfer.
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o studies of the geometry, electronic spectrum, and vertical ionization potentials of oxygen difluoride (F2O)
Authors: Valenta K. E. , Vasudevan K. , Grein F.
Published: February 2003

Self-consistent field (SCF) and large-scale configuration interaction (CI) studies with double zeta (DZ) and extended basis sets were performed on F2O for its geometry, vertical electronic excitation energies, and vertical ionization potentials (VIP). A DZ plus polarization basis gives the SCF bond distance too short by 0.05 Å, and CI methods are required for the experimental distance (1.41 Å). A large number of low-lying excited electronic states are predicted, the lowest ones being 3A2 at 4.1 (2b1→3py), 3B1 at 4.2 (2b1→7a1) and 1B1 at 5.6 eV (2b1→7a1), where 7a1 is essentially a valence orbital. Comparison with the H2O spectrum is made. For the VIP’s, CI results obtained for various states of F20+ suggest some reassignments of experimental values, although unresolved questions remain.
Diagrammatic perturbation theory: An application to the nitrogen, carbon monoxide, and boron fluoride molecules using a universal even-tempered basis set
Authors: Wilson Stephen , Silver David M.
Published: February 2003

Diagrammatic many-body perturbation theory is applied to the nitrogen, carbon monoxide, and boron fluoride molecules. The same universal even-tempered basis set of Slater functions is used to parameterize the single particle state functions in each of the molecules. Calculations are performed at nuclear separations of 1.75, 2.00, 2.25, and 2.50 bohr. Approximately 83.7%, 82.7%, and 77.1% of the correlation energy is recovered in N2, CO, and BF at their respective equilibrium internuclear distances.
Specific heats of the pyrochlore compounds Eu2Ir2O7 and Lu2Ir2O7
Authors: Blacklock K. , White H. W.
Published: February 2003

The specific heats of the pyrochlore compounds Eu2Ir2O7 and Lu2Ir2O7 were measured below 20 K. The data was found to be described by the expression C=γT+αT3 below 6 K for both compounds. The Debye temperatures were calculated from the T3-term coefficients. The values for γ were found to be 13.0 mJ/mole K2 for Eu2Ir2O7 and 12.5 mJ/mole K2 for Lu2Ir2O7. The ΘD values were 304 and 352 K, respectively.
On the analytical evaluation of magnetic multipole moment integrals for Slater-type orbitals
Authors: Guseinov I. I.
Published: February 2003

A simple and general formula for the magnetic multipole moment integrals with orbital and spin magnetic multipole moment operators is presented. (AIP)
Electron paramagnetic resonance of Cr3+ in (NH4)xTl1−xAl(SO4)2⋅12H2O
Authors: Jain Vimal Kumar
Published: February 2003

The electron paramagnetic resonance EPR of Cr3+ has been studied in ammonium aluminium alum and thallium aluminium alum. The zero-field splitting has been studied with variations of composition. (AIP).
Microscopic theory of condensed phase chemical reactions. II. Configuration space equations
Authors: Cukier Robert I. , Kapral Raymond , Mehaffey J. R. , Shin K. J.
Published: February 2003

Configuration space equations for the description of reactive pair dynamics are obtained from the pair phase space kinetic equations derived in the preceding paper. These configuration space equations are generalizations of the conventional ’’sink’’ Smoluchowski equations. In addition to displaying the modifications in Smoluchowski equation descriptions due to velocity relaxation effects, computationally tractable expressions for the diffusion and friction tensors are obtained. The structure of the rate kernel which follows from the phase space kinetic equation is also examined.
Photophysical and photochemical molecular hole burning theory
Authors: de Vries Harmen , Wiersma Douwe A.
Published: February 2003

In this paper theories are given, describing photophysical and photochemical hole burning experiments on molecular mixed crystals at low temperature. Population saturation hole burning is treated for a two-level system where the lower level is the ground state. Hole burning due to a triplet state acting as a population bottle neck is also described by a steady-state density matrix theory. Connection is made with optical free induction decay. To obtain T2 (the decay time of the off-diagonal elements of the density matrix), which is the main goal of these hole burning experiments, a linear extrapolation method is discussed. For photochemical hole burning a time-dependent density matrix treatment is given. Using this theory numerical simulations were performed of the experimental results obtained by Völker and co-workers for porphin in n-octane at low temperature. Good agreement with experiment is obtained. For this case extrapolation methods are discussed in order to obtain reliable T2 values. A time-dependent kinetic theory is used to simulate the photochemical hole burning experiments on dimethyl-s-tetrazine in durene and s-tetrazine in benzene. This theory accounts for the recently revealed two-photon character of these photodissociations. It is shown that despite this complication the hole full width at half-maximum may still equal twice the homogeneous width of the So-S1 transition.
The molecular constants and potential energy curves of the Ca2 A 1Σ+u–X 1Σ+g system from laser induced fluorescence
Authors: Vidal C. R.
Published: February 2003

From laser induced fluorescence of the Ca2 A–X system improved molecular constants and potential energy curves are given. A new technique for determining the standard error of molecular potentials is presented. The dissociation energies are De=1095±0.5 cm−1 for the X state and 3980±0.5 cm−1 for the A state which dissociates into the 1S and 1D states of the separated atoms due to an avoided curve crossing. Discrete and continuous Franck–Condon factors have been measured.