bluuebunny/crossref_metadata_2025 huggingface dataset:
The A 1Σ+–X 1Σ+ system of the isotopic lithium hydrides: The molecular constants, potential energy curves, and their adiabatic corrections
Authors: Vidal C. R. , Stwalley W. C.
Published: February 2003

The molecular constants and their adiabatic corrections have been determined for the A 1Σ+–X 1Σ+ system of the isotopic lithium hydrides: 6LiH, 7LiH, 6LiD, and 7LiD. Using a fully quantum mechanical variational method, the potential energy curves (IPA potentials) are determined. Extending the variational method, we have obtained for the first time adiabatic corrections of potential energy curves from isotopic spectroscopic data. A significant difference between the potential energy curves of the lithium hydrides and the lithium deuterides has been observed. When 6Li was replaced by 7Li, a significant difference was only observed for the A 1Σ+ state, but not for the X 1Σ+ state.
CNDO/2-FPP atom-in-molecule polarizabilities
Authors: Rhee C. H. , Metzger R. M. , Wiygul F. M.
Published: February 2003

The finite perturbation (FP) method of obtaining molecular and atom-in-molecule polarizabilities from the semiempirical CNDO/2 algorithm has been extended by the addition of parametrized polarization orbitals (PO) (2p for H, 3d for C, N, O, F, P, S, Cl, and 4d for Se and Br). The new parameters in CNDO/2-FPP are a screening constant for the off-diagonal core Hamiltonian terms, the PO orbital exponent, and, for the heavier elements, the PO electrongativities and the resonance integral. The parametrization preserves the charge distribution and the occupied molecular orbitals, and is designed to fit 13 model molecules; it obtains extra polarizability from the new hybrid contributions to the dipole moment and from reshuffling the virtual molecular orbitals. Excellent molecular and atom-in-molecule polarizabilities are obtained, for 47 other molecules, in agreement with available experimental data, and in competition with the best ab initio calculations.
2H NMR line shapes and molecular motion in solid charge-transfer complexes
Authors: Ripmeester J. A.
Published: February 2003

2H MNR lineshapes are discussed and the molecular motion in charge transfer complexes of various electron donors molecules with exectron acceptors such as tetracyanobenzene is discussed. (AIP)
Slow decay of ion correlations parallel to an electrolyte solution surface
Authors: Nichols Albert L. , Pratt Lawrence R.
Published: February 2003

Our recent theoretical calculation of ion correlations near an an eltrolyte solution surface is used to examine the conjecture of Blum, et al, that corrlelations parallel to the surface exhibit slow power laaw decay. We confirm that these correlations have dipolar range in our theory, and we predict their dependence on dielectric constant mismatch across the surface. We suggest a physical explanation of these long range correlations. (AIP)
Electrostriction and dielectric saturation in a polar fluid
Authors: Carnie Steven L. , Stell G.
Published: February 2003

We extend our earlier study of magnetic systems to give a unifying statistical–mechanical treatment of nonlinear effects in dielectrics in the presence of an external electric field. In so doing, we make contact with—and broaden the scope of−the Ho/ye–Stell mean-field theory of such effects. In particular, we find that when the applied field is fully eliminated in favor of the macroscopic field, our P1HNC approximation (a hypernetted chain approximation truncated after the first spherical harmonic) yields the Ho/ye–Stell expression for dielectric susceptibility χ as a function of macroscopic field. We also show the equivalence of our formalism and an open-system version of the nonlinear formalism of Nienhuis and Deutch as well as the correspondences between our results and the nonlinear results of Ramshaw. Similarly, we note the direct connection between our approach and the wall-particle approach used by Rasaiah, Isbister, and Stell and by Martina and Stell. The latter approach permits the extension of our P1HNC approximation for the one-particle correlation function of the dielectric medium into the immediate vicinity of a surface of that medium defined by a spherical macrocavity through which an applied field E0 is passing (although we do not focus on that extension here). The wall-particle approach yields expressions initially in terms of applied field E0 rather than macroscopic field E. We compare our microscopic method of eliminating E0 with the use of the most complete macroscopic relation between E and E0 currently available and conclude that microscopic elimination of E0 is decidedly advantageous, at least in the regime we study here, which is far from the wall on a microscopic scale. We also make some comparisons with the computer simulation results of Adams and Adams. Other specific results we obtain include a new microscopic derivation of the electrostriction effect exact through O(E2) as well as the P1HNC result for the dielectric-saturation coefficient. It predicts for an open system a crossover from ’’normal’’ saturation (i.e., negative ∂χ/∂E) to ’’anomalous’’ saturation (positive ∂χ/∂E) as a dielectric liquid approaches its critical point. We note that, although not exact, the P1HNC theory yields a dielectric susceptibility that is exact in the low-density limit (where it reduces to the celebrated Debye–Langevin result for noninteracting particles). In contrast to the oversimple Debye–Langevin result, which gives anomalous saturation for all states of an open system, the P1HNC result yields normal saturation in the liquid-state region.
Predictions for partial and monolayer coverages of O2 on graphite
Authors: Pan R. P. , Etters R. D. , Kobashi K. , Chandrasekharan V.
Published: February 2003

Monolayer properties of O2 on graphite are calculated using a pattern recognition, optimization scheme. Equilibrium monolayers are predicted at two different densities with properties in agreement with recent x-ray diffraction, specific heat, and neutron scattering data. Properties of the extremely low density regime are calculated using a model based upon a distribution of two-dimensional O2 clusters. The results are consistent with experimental evidence.
The accuracy of the small s approximations to the probability of recombination in a Coulomb field
Authors: Pedersen J. Boiden , Larsen Jan Emil
Published: February 2003

Numerical calcualtions are reported for the recombination probability of an islated pair in a three-dimensional isotropic medium with a samll concentration fo scavenger. The accuracy of these expressions is discussed in detail. (AIP)
Comment on ‘‘Intrinsic convergence in close-shell SCF calculations. A general criterion’’
Authors: Facelli J. C. , Contreras R. H.
Published: February 2003

The general criterion proposed by Stanton1, on the intrinsic convergence in close-shell, SCF calculations is discussed. Molecular SCF wave functions are found to exhibit instabilities. These instabilities are further discussed. (AIP)
An improved analysis of the OH stretching region of the vibrational spectrum of ice Ih
Authors: Bergren Michael S. , Rice Stuart A.
Published: February 2003

We report the results of an analysis of the OH stretching region of the vibrational spectrum of ice Ih. The model of ice Ih discussed in an earlier paper [J. Chem. Phys. 69, 3483 (1978)] is considerably improved in that a larger section of the proton disordered lattice is included in the dynamical description, the shift in the OH stretching force constant on hydrogen bonding is calculated from molecular properties, the interaction force constants are re-evaluated using newer and more extensive data, and Fermi resonance and internal field effects on the lattice dynamics are accounted for. We show the following: (i) Strong coupling between OH oscillators on different molecules is responsible for the major features of the vibrational spectrum, namely, its breadth and gross distribution of intensity. (ii) Internal field effects, which lead to wave vector dependent polar mode mixing in a proton ordered model of ice I, do not influence the distribution of intensity in the Raman spectrum of proton disordered ice Ih, despite the fact that the internal field does play an important role in altering the states of the system. Our calculations provide no support for the suggestion that structure in the Raman spectrum of ice Ih can be assigned using the Lyddane–Sachs–Teller relation, i.e., that structure in the Raman spectrum can be related to system modes arising under the influence of the longitudinal field. (iii) Fermi resonance between the OH stretching mode and the overtone of the bending mode has more influence on the vibrational spectrum of D2O ice Ih than on that of H2O ice Ih. The inclusion of Fermi resonance in the description of the OD stretching dynamics materially improves the agreement between the predicted and observed vibrational spectra. However, the redistribution of spectral intensity attributable to Fermi resonance is a second order effect relative to the distribution of intensity determined by the interaction between OH oscillators on different molecules. (iv) The change in OH stretching frequency when a water molecule is incorporated in ice Ih can be accounted for self-consistently using only the known free molecule anharmonic potential energy coefficients and a parametric description of the dependence of the harmonic force constants on the strength of hydrogen bonding. This finding validates and provides an interpretation of the quasiharmonic representation of OH stretching motions used in our earlier work.
Population and rotational kinetics of the rhodamine B monomer and dimer: Picosecond transient spectrometry
Authors: Smirl Arthur L. , Clark James B. , Van Stryland E. W. , Russell B. R.
Published: February 2003

We use picosecond excite-and-probe techniques at 532 nm, a subnanosecond fluorescence spectrometer, and a transient-transmission spectrometer with picosecond temporal resolution to measure the population kinetics and rotational diffusion of aqueous rhodamine B monomer and dimer. The excited-state lifetimes of the monomer and dimer are determined to be 1.6 ns and 100 ps, respectively, and the rotational randomization time of the monomer is measured to be 250 ps. The dimer rotational diffusion time is determined to be longer than that of the monomer, indicating that there is a large molecular species in equilibrium with the monomer.
Long and short range effects in surface enhanced Raman scattering
Authors: Tsang J. C. , Kirtley J. R. , Theis T. N.
Published: February 2003

Surface plasmon polariton enhanced Raman scattering, from molecular monolayers adsorbed onto continuous Ag surfaces at 300 K and low temperatures, has been studied. The observed spectra, at the multilayer level, are similar to the Raman spectra of the condensed bulk. The first layer scattering shows changes in both the scattering intensity and the spectral features similar to those seen in surface enhanced Raman experiments using substrates prepared in other ways.
A comparison of measured nucleation rates with the predictions of several theories of homogeneous nucleation
Authors: Sharaf Mostafa A. , Dobbins Richard A.
Published: February 2003

An expansion cloud chamber with extensive instrumentation is used to test the success of several prominent nucleation theories in describing the nucleation rate of water vapor in the presence of argon. The instrumentation of the cloud chamber permits the time-resolved measurement of pressure, temperature, supersaturation ratio and, during the later stages of condensation, the droplet size and number concentration. These observations are used directly to examine the variation of the maximum supersaturation ratio and the droplet number concentration as the initial temperature and the expansion rate are varied. When used with an algebraic form appropriate to any specific nucleation theory, these observations additionally allow the experimental determination of the pre-exponential and exponential rate constants that may be compared with the respective theoretical values. In this way, a comparison of theoretical and experimental nucleation rates is possible. The classical and Reiss nucleation theories give essentially identical results and they show the closer agreement with the measured nucleation rates.
HF rotational lasers: Enhancement of V→R multiquantum energy transfer by CO and CO2
Authors: Sirkin Eric R. , Pimentel George C.
Published: February 2003

The effects of CO, CO2, H2, D2, and HC1 on rotational laser emission from HF have been examined in the HF photoelimination lasers initiated by flash photolysis of vinyl fluoride and 1,1 difluoroethene. Whereas only 1.4 Torr of H2, D2, or HCl act to quench or reduce the gain of those transitions observed in the presence of 50 Torr Ar, a few Torr of either CO or CO2 enhance both the number of transitions observed and their gain. With added CO (to both ethenes), a total of 58 transitions emit in the v = 0 to 5 vibrational manifolds, extending from J = 8→7 to 31→30. For CO2, the total number of transitions reaches 52. The patterns of laser enhancement identify energy transfer pathways that are active, of which VHF→RHF is most easily discerned. Multiquantum transfers involving ΔvHF = 3, ΔJ = 20 and ΔE<kT entering into translation are observed. Some specific emissions that are quenched or reduced in gain by CO2 suggest that RHF→VHFVM is also active. Undoubtedly partcipating, but less easily recognized are VHF→RHFVM transfers involving Δv = 1 or 2 for M = CO. The contrasting quenching behavior of H2, D2, and HC1 is attributed to removal of rotational energy from HF by RHF→RM processes that are most efficient for HF when the collision partner is also a diatomic hydride. The implications for our understanding of vibrational and rotational relaxation and the behavior of HF rotational lasers are discussed.
Classical and quantum mechanical studies of HF in an intense laser field
Authors: Dardi Peter S. , Gray Stephen K.
Published: February 2003

The behavior of an HF molecule in an intense laser field is investigated with both classical trajectories and quantum dynamics. Vibration-rotation transition probabilities and energy absorption as a function of laser pulse time are calculated for the diatomic initially in its ground state. For comparison, results are also reported for a model nonrotating HF molecule. It is found that classical mechanics does not predict the correct time behavior of the system, nor does it predict the correct rotational state distributions. Classical mechanics does, however, predict pulse time averaged quantities to be the correct order of magnitude. There is also a correct general trend of increased multiphoton excitation for laser frequencies red-shifted from the one-photon resonance, although multiphoton resonance peaks are not observed in the classical results and far too little multiphoton excitation is predicted. The effect of laser phase has also been investigated and shown to be relatively unimportant in both the classical and quantum dynamics.
Electronic energy transfer in near-resonant electron capture collisions of H+2 with metal atoms: Radiative and nonradiative transitions
Authors: Gellene Gregory I. , Cleary David A. , Porter Richard F. , Burkhardt Charles E. , Leventhal Jacob J.
Published: February 2003

Modes of energy disposal in electron capture of H+2 with metal atoms (Cs, K, Mg, and Zn) for ion velocities in the range 3–7×107 cm/s are examined using combined optical and beam scattering techniques. Radiative and nonradiative transitions are observed for processes occurring under near resonant conditions. The following branching sequences are identified: Branching ratios are dependent on the vibrational state and the nuclear separation (Franck–Condon factors) of the H+2 ion at the time of electron capture. The branching ratio decreases for the (triplet)/(singlet) formation for H2 produced from reactions of vibrationally relaxed H+2 ion with K or Cs. Under conditions of H+2 ion relaxation, the kinetic energy of scattered atomic hydrogen following radiative decay from 3Σ+g state of H2 increases, implying a shift in the 3Σ+g→3Σ+u continuum toward longer wavelengths. The results also show that, at these velocities, the reations occur under near-resonant conditions with vertical transitions.
Integral equation predictions of liquid state structure for waterlike intermolecular potentials
Authors: Pettitt B. Montgomery , Rossky Peter J.
Published: February 2003

An application of our recently developed extended RISM equation formulation to several three-site models of water is presented. The site–site correlation functions are obtained and compared to available computer simulation results. Further, the variation of liquid state structure with the model site charge is examined. The analysis of these results has demonstrated that the integral equation approach provides a correct qualitative description of the liquid structure, although the amplitudes of most structural features are somewhat less accurate that their positions. Comparison to our earlier results for simpler models suggests that the nature of the quantitative deficiencies of the approach is predictable. The charging study has shown that the development of waterlike structure with increasing site charge follows a qualitatively different pattern for oxygen–oxygen pairs, compared to those involving hydrogen. This is attributed to interference between the amplitudes characteristic of liquid water and of simple liquids. These results suggest that this is the origin of a relatively flat 0–0 correlation function for several models studied in the past, and, further, that such results should not be properly characterized as ’’unstructured.’’
Energy level bending at molecular crystal surfaces
Authors: Twarowski Allen J.
Published: February 2003

Energy levels of ionized states in molecular crystals bend at the crystal surface—a result of different polarization conditions near the interface. The effects of a vacuum–crystal or a metal–crystal interface on the polarization energy of a charge near the interface can be estimated using the macroscopic dielectric constant to describe the polarization of the molecular crystal, and image forces to describe the surface polarization. These calculations predict a decrease in the hole-electron energy level splitting Eg of 0.3–0.5 eV, 5 Å from the metal surface if the dielectric constant of the molecular crystal is in the range of 3–4.5. In crystals where the singlet exciton energy exceeds the energy splitting Eg by less than 0.5 eV, selective exciton ionization at the surface is possible.
Importance of using Eulerian representation of strain in high pressure studies on liquids
Authors: Vedam K. , Chen C. C.
Published: February 2003

It is shown that all the published data on the static dielectric constant of liquids at high pressures can be expressed in simple linear relationship between √ε0 and ε, the Eulerian strain, just like earlier reported relation between √ε∞ and ε. The reason for the necessity of using the Eulerian representation in such high pressure studies is presented.
Satellite EPR resonances of the N4− radical in ultraviolet irradiated potassium azide
Authors: Willis James S. , Pella Peter
Published: February 2003

When EPR spectra of irradiated KN3 are recorded at low temperatures for the magnetic field in the [100] crystal direction, a nine-line spectrum is found which is attributable to the presence of N4− ion–molecules in the material. Between each pair of the lines of the N4− pattern is found a satellite line of less intensity. The literature has conflicting explanations for these lines, either ascribing them to an exchange interaction between closely neighboring N4− ion molecules or to the presence of N32− ion molecules. This paper compares predictions of the two proposals to measurements of EPR spectra for angles near the [100] direction and finds that only the exchange model is compatible with experimental results.
Measurement of atomic densities using radiation trapping
Authors: Garver W. P. , Pierce M. R. , Leventhal J. J.
Published: February 2003

The apparent lifetimes of the 2P1/2 and 2P3/2 states of Na have been measured as functions of n, the atomic density, and the results compared to theory. It is shown that these measurements made under equilibrium, steady-state conditions may be used to determine n under nonequilibrium, nonsteady-state conditions. This technique of measuring n has advantages over the surface ionization technique, especially for values of n greater than about 1010 cm−3. Extension of the technique to other atoms and molecules is discussed.
Effects of inhomogeneous broadening on the resonance Raman excitation profile of lycopene
Authors: Cotting J. E. , Hoskins L. C. , Levan M. E.
Published: February 2003

The resonance Raman excitation profiles for the ν1, ν2, and ν3 vibrations of lycopene in ethyl alcohol, toluene, and carbon disulfide solvents have been measured. The results are interpreted in terms of a three-mode vibrational theory which includes both homogeneous and inhomogeneous broadening effects. Excellent agreement between calculated and observed excitation profiles and visible spectra was found, thus emphasizing the need to interpret resonance Raman data using a multimode vibrational model. The results indicate that the major broadening mechanism is homogeneous broadening, with about a 25% contribution from inhomogeneous broadening. The excitation profiles in carbon disulfide gave the largest inhomogeneous broadening.
T
1 and T1ρ study of proton motion in hydrazine nitrate N2H5NO3
Authors: Harrell J. W.
Published: February 2003

Proton T1 and T1ρ measurements have been made in hydrazine nitrate N2H5NO3 from 140 to 362 K. Two previously reported solid phases have been distinguished. In form I the relaxation times have been analyzed in terms of reorientations of the –NH+3 and –NH2 groups, and correlation times for these motions have been obtained. A detailed calculation of T1ρ due to –NH2 reorientations has made based on the geometry of the hydrazinium ion in N2H5HC2O4. The relaxation is due to both H–N dipole–dipole interactions within the –NH2 group and to H–H dipole–dipole interactions between the –NH2 and –NH+3 groups which are modulated by 180° flips of the –NH+2 group about the H–N–H bisectrix. In form II the correlation times for –NH3 reorientation are shorter and the correlation times for –NH2 reorientation are longer than in form I. The relaxation and free induction decay measurements show a high-mobility component in form II.
Infrared gas phase intensity measurements, polar tensors, and effective charges of vinylidene fluoride and its deuterated modifications
Authors: Kagel R. O. , Powell D. L. , Overend John , Ramos Mozart N. , Bassi A. B. M. S. , Bruns Roy E.
Published: February 2003

All gas phase fundamental vibrational intensities for vinylidene fluoride and its deuterated modifications have been measured. Isotopic invariance, G sum rule, and quantum chemical information have been used in selecting preferred experimental values for the dipole moment derivatives and polar tensor elements of these molecules. The values of these intensity parameters are compared with those found for other molecules. The experimental values are interpreted in terms of electronic charge distortions occurring in these molecules for the various vibrations.
Raman scattering study of the D182h→D152h structural phase transition in (C2H5NH3)2CdCl4
Authors: Mokhlisse R. , Couzi M. , Wang C. H.
Published: February 2003

Temperature dependent studies of the low frequency (10–350 cm−1) Raman spectra of (C2H5NH3)2CdCl4 in the orthorhombic D182h and D152h phases have been carried out. Polarization information obtained in various scattering geometric configurations is used to provide tentative assignments for the observed Raman bands. The anomalous features associated with the temperature dependent Rayleigh wing observed in the αxx, αyy, and αxy spectra are also explained.
The dynamics of the infrared multiphoton pumping of optically excited NO2 molecules
Authors: Tsao Jeffrey Y. , Simpson Thomas B. , Bloembergen N. , Burak Itamar
Published: February 2003

The infrared multiphoton (IRMP) pumping of optically excited NO2 molecules is investigated. From changes in the fluorescence emission spectrum due to the IRMP pumping, both the fraction of the NO2 molecules that has dissociated, as well as the fraction that remains within one IR photon in energy below the dissociation limit, are deduced. This has made possible the first direct measurements of the final, dissociative step in the IRMP pumping of molecules, and of IRMP stimulated emission. The dynamics of the IRMP pumping is studied by systematically varying the optical excitation energy. The results are compared with numerical solutions to the well-known rate equation model for the IRMP pumping of polyatomic molecules. From this comparison the best fit transition cross sections connecting various energy regions in highly vibrationally excited NO2 molecules were deduced. Except for the final, dissociative transition, they depend significantly on both laser intensity and pulse width for intensities as large as 10 GW/cm2 and pulse widths as short as 500 ps. These dependences are probably due to the sparse density of vibrational states in such a small molecule as NO2. In addition, the rotational energy present in room temperature NO2 can enhance considerably the IRMP dissociation probability of optically excited NO2.
Observation of the v = 3←0 band of SO(X 3Σ−) with a difference frequency laser
Authors: Wong M. , Amano T. , Bernath P.
Published: February 2003

The second overton band (v = 3→0) of SO(X 3Σ−) near 3 μm has been observed by using a tunable difference frequency laser spectrometer and a 2 m multiple-reflection discharge cell. An analysis of the overtone data yields the band origin and molecular constants of the v = 3 state. (AIP)
Intense quadrupole transitions in the spectra of molecules near metal surfaces
Authors: Moskovits M. , DiLella D. P.
Published: February 2003

The fluorescence, Raman, and fluorescence excitation spectra of diphenyloctatetraene and diphenylhexatriene condensed on rough silver are reported. The fluorescence excitation spectra reveal that on silver the normally dipole-forbidden 1Ag←X 1Ag absorption takes place in addition to the allowed 1Bu←X 1Ag process. This is attributed to the large electric field gradient which is present near an illuminated metal surface causing the intensity of quadrupole absorptions to become unusually great. The possible contribution of this field gradient to two-photon processes in centrosymmetric molecules and to the intensity of bands in infrared and EELS spectra is also noted. In addition, the relative fluorescence intensities of these molecules adsorbed on rough and smooth silver are discussed in terms of the effectiveness of nonradiative decay into metal channels.
The line of contact of three fluid phases
Authors: Kerins John , Widom B.
Published: February 2003

We study the variation of density or chemical composition in the neighborhood of the line in which three phases meet and we determine the associated line tension. Three models are considered: a phenomenological model based on a primitive approximation to the excess free-energy density that arises from the inhomogeneities at the two-phase interfaces and at the three-phase line; a generalized van der Waals approximation, in which the excess free-energy density is the sum of an analytic function of the densities and a quadratic form in the density gradients; and a microscopic model of a three-component, three-phase fluid, for which the properties of the interfaces and of the three-phase line are determined in mean-field approximation as solutions of nonlocal functional equations. Both positive and negative line tensions are found. In the third model, when the nonlocal functional equations for the composition profiles of the two-phase interfaces are approximated by gradient expansions truncated in second order (van der Waals approximation), the resulting profiles are fairly accurate but the surface tensions are not.
Monte Carlo study of two-dimensional vesicles shapes
Authors: Ostrowsky Nicole , Peyraud Jean
Published: February 2003

The method of functional integration, in conjunction with a Monte Carlo technique, is used to study ’’two-dimensional vesicles,’’ represented by closed loops analogous to ring polymers. The generation of arbitrary shape functions obeying a number of topological constraints is described. The probability distribution functions of several parameters, such as radius of curvature, internal surface, closest and largest distances between edges, and symmetry factors, are presented.
The entropies of the hard sphere alkali halide crystals
Authors: Cox John W. , Beyerlein Adolph L.
Published: February 2003

An asymptotic expansion for the entropy of hard-sphere alkali halide crystals with N small and large particle pairs is obtained: SN/NkB ≃τ→13 ln(σls2e)/(λlλs) +3 ln(τ1/3−1)+3 ln ε−C−Dε−Eε2+⋅⋅⋅, where kB is the Boltzman constant, e is the natural number, τ is the ratio of the system volume to its high compression limiting volume, λl and λs are the mean thermal de Broglie wavelengths [λ=(h2/2πmkBT)1/2, m being the mass] of the large and small particles, respectively, σls is the hard-sphere collision diameter of nearest neighbor large and small particles; C, D, E, etc. are well-defined parameters dependent on the small to large particle radius ratio and the lattice structure, and ε=[(τ1/3−1) +(1−σls/σls′)], where σls′ is the average distance between nearest neighbor large and small particles in the high compression limit. If the small to large particle radius ratio is less than √2−1 for the ’’NaCl’’ lattice and less than √3−1 for the ’’CsCl’’ lattice σls<σls′. For greater small to large particle radius ratios σls=σls′. The result differs from the asymptotic expansion for a crystal of N uniform spheres obtained by Salsburg, Stillinger, and co-workers [J. Chem. Phys. 49, 4857 (1968)] in that it contains the additional logarithmic term 3 ln ε and a smallness parameter ε that differs from τ1/3−1, used by the earlier workers. Estimates of the leading parameter C were made using the modified cell cluster expansion. The predicted entropies of the alkali metal fluoride salts approach the experimental values at temperatures approaching the melting point which is consistent with the contention that the hard sphere contribution to the entropy dominates other contributions at high temperatures. The predicted difference between the entropies of the two alkali halide lattices is also consistent with the experimental data at higher temperatures.
Raman and x-ray investigations of ice VII to 36.0 GPa
Authors: Walrafen G. E. , Abebe M. , Mauer F. A. , Block S. , Piermarini G. J. , Munro R.
Published: February 2003

Raman data for ice VII to 30 GPa and x-ray lattice parameters to 36 GPa, all at room temperature, are presented and discussed. Both the Raman OH-stretching peak frequency (Δv̄) and the edge distance of the body-centered cubic unit cell (a) decrease at a decreasing rate with pressure rise. The OH peak frequency is found to be virtually linear in the nearest-neighbor O–O distance (rOO) between about 2.5 and 2.9 Å. However, the data can also be fitted with a slight cubic dependence, which when extrapolated, gives rise to a minimum in Δv̄ at rOO=2.35±0.06 Å. This is close to the value of 2.4 Å found for the symmetric O–H–O units in other materials. This minimum suggests, but does not prove, that a symmetric hydrogen bond structure O–H–O, and thus a new ice, may result at pressures of about 75±20 GPa. Treatment of the O–H⋅⋅⋅O units according to couplet oscillators using experimentally confirmed assumptions indicates that Δv̄≊A/rOH2 which when combined with present and previously published data yields, approximately, A≊2943 cm−1 Å2. Thus, the decrease observed in Δv̄ is thought to occur because the OH bond length (rOH) increases with increasing pressure as the O–O distance rOO in the corresponding hydrogen-bonded O–H⋅⋅⋅O unit decreases.
On the isotope effect of the electronic-to-vibrational energy transfer from Hg(6 3P) to CO and NO
Authors: Horiguchi Hiroyuki , Tsuchiya Soji
Published: February 2003

The electronic−to−vibrational energy transfer from Hg(6 3P) to 13CO and 15NO is reported for collisions of excited mercury atoms with CO and NO. (AIP)
Multiphoton photofragmentation of SO2 at 248 nm
Authors: Wilson M. W. , Rothschild M. , Muller D. F. , Rhodes C. K.
Published: February 2003

Sequential two-photon photoexcitation of SO2 at 248 nm is found to lead to a number of primary fragments including S(3P) and SO(X 3Σ−). Further excitation of some of these photoproducts was also observed, occurring by both linear and two-quantum mechanisms. The resulting molecular X←B (v\,2) ultraviolet fluorescence from SO and the atomic 3P←3S vacuum ultraviolet emission from S atoms were detected and an analysis of the energy flow patterns was made.
Rare gas–halogen atom interaction potentials from crossed molecular beams experiments: I(2P3/2)+Kr, Xe(1S)
Authors: Casavecchia Piergiorgio , He Guozhong , Sparks Randal K. , Lee Y. T.
Published: February 2003

Angular distributions of I(2P3/2) scattered off Kr and Xe(1S0) in the thermal energy range have been measured in crossed molecular beams experiments. The interaction potentials for two relevant states (X 1/2 and I 3/2) for each of the systems are obtained by using an approximate elastic scattering analysis, which neglects nonadiabatic coupling, as previously done for other rare gas–halogen systems. The I–Xe  (X 1/2) potential (ε = 0.69 kcal/mol, rm = 4.30 Å) and, to some extent, I–Kr (X 1/2) potential (ε = 0.55 kcal/mol, rm = 4.05 Å) shows a slightly more attractive interaction than the interaction potentials of Xe–Xe and Xe–Kr, but the I–Xe (I 3/2) potential (ε = 0.48 kcal/mol, rm = 4.60 Å)) and the I–Kr (I 3/2) potential (ε = 0.36 kcal/mol, rm = 4.32 Å) present shallower ε’s, a larger rm, and stronger repulsive walls than the corresponding rare gas pair potentials. The results obtained from this and previous investigations are reviewed.
A physical interpretation of the collinear reactive scattering resonances in the F+HD, H2, and D2 systems
Authors: Babamov Vasil K. , Kuppermann Aron
Published: February 2003

A simple model is presented that explains the main characteristics of the low energy resonances found in accurate quantum mechanical scattering calculations of collinear reactive collisions of the type F+XY→FX+Y, where X and Y are H or D atoms. The wave function of the resonance complex can be approximately described by a product of a function of the F–XY distance and a vibrationally adiabatic function of the X–Y distance. The corresponding vibrational eigenvalues of the XY diatom as a function of the F–XY distance form an attractive, effective one-dimensional potential for the F–XY motion that supports a quasibound state. The resulting resonance is broadened by its interaction with the reagent and product scattering states. The resonance energies given by the model are in good agreement with those obtained by exact scattering calculations for the F+HD, H2, and D2 systems.
The solitonic mechanism for proton transport in a hydrogen bonded chain
Authors: Kashimori Yoshiki , Kikuchi Takeshi , Nishimoto Kichisuke
Published: February 2003

We find that the proton transfer in a hydrogen bonded chain subjected to the appropriate electrostatic field behaves as a soliton. The energy of soliton and the rate constant for this proton transfer process are calculated by transition state theory. We obtain the results that the energy of soliton is considerably small compared with the band gap of the polypeptide chain and the rate constant is quite large which is enough to reveal the biological function. With these results, a few biological significances are discussed.
Electron correlation effects on magnetic properties of molecules
Authors: Iwai Masahiro , Saika A.
Published: February 2003

The nuclear magnetic shielding and magnetizability tensors for the H2, HF, and F2 molecules are calculated within the many-body perturbation theoretic and coupled Hartree–Fock (CHF) schemes. By separating out the non-CHF diagrams or true correlation effects, it is found that they make a fairly small contribution. Thus, the CHF approach appears to be a feasible method yielding good approximations to the magnetic field properties. Among the CHF diagrams, particle-hole ladder-type diagrams make an overwhelming contribution, ring-type diagrams being exactly canceled for pure imaginary perturbations.
Force in SCF theories. Second derivative of potential energy
Authors: Nakatsuji Hiroshi , Kanda Katsuya , Yonezawa Teijiro
Published: February 2003

The analytic second derivative of a potential energy hypersurface is studied with the use of the Hellmann–Feynman theorem at the stage of the first derivative. As shown previously, the use of the {r, r′} basis in the SCF calculation guarantees that the Hellmann–Feynman theorem is essentially satisfied. (r′ is a derivative of the AO r = χr, r′ = ∂χr/∂xr.) In comparison with the straightforward second derivative of the SCF energy, the number of terms and the labors in calculations are much reduced in the present method. Furthermore, the added {r′} basis improves the quality of the calculated force constant, and an intuitive physical picture is associated with the calculated second derivative, as the intuitive Hellmann–Feynman force picture is associated with the first derivative. The applications are given for the force constants of the molecules N2, CO, and H2O. Some interesting features of the electron density reorganizations during vibrations are reported.
Experimental study of nucleation in binary mixtures: The methanol–ethanol, methanol-n-propanol, and ethanol-n-propanol systems
Authors: Garnier J. P. , Mirabel P.
Published: February 2003

The upward diffusion cloud chamber was used to study the binary homogeneous nucleation in helium of the MeOH–EtOH, MeOH-n-PrOH, and EtOH-n-PrOH mixtures at 280 K. The experimental results given in terms of activities of both components needed to achieve a rate of nucleation of 1 droplet cm−3 s−1 compare favorably with the theoretical predictions deduced from the classical theory.
Intracavity laser excitation of NCO fluorescence in an atmospheric pressure flame
Authors: Anderson William R. , Vanderhoff John A. , Kotlar Anthony J. , Dewilde Mark A. , Beyer Richard A.
Published: February 2003

Laser excited fluorescence of the NCO radical has been obtained using discrete prism selected lines of an argon ion laser pump source. To our knowledge this is the first time NCO fluorescence has been obtained in a flame environment. NCO was formed in a slightly rich atmospheric pressure CH4/N2O flame. This flame was placed inside the extended cavity of the argon laser to take advantage of the much higher light intensity levels. All of the available laser lines pump vibrational hot bands of the NCO A 2Σ+ ← X 2Π system. The 4658 Å line appears to be the most useful for probing NCO densities. This line pumps in the A 2Σ+(0,00,0) ← X 2Π (1,01,0) vibrational band. NCO is pumped to N′ = 31 by this line, probably via the Q231 transition although the R230 and P232 transitions could not be ruled out in the present analysis. The 4658 Å line was used to determine a relative NCO density profile through the reaction zone of a CH4/N2O flame. Profiles of C2, CN, and temperature were also obtained in this flame and are compared with the NCO profile. A lower limit of approximately 3×1014 cm−3 was placed on the peak NCO density in the flame. Attempts to find NCO or CN fluorescence in a CH4/air flame failed indicating probable differences in nitrogen chemistry for the two flames.
An experimental and theoretical study of the 3p3/2 level of atomic cesium: Beyond the one-electron picture
Authors: Slaughter A. R. , Mathews R. D. , Key R. J. , Banna M. S. , Beck D. R.
Published: February 2003

A 3p3/2 binding energy of 1005.0±0.3 eV has been measured in atomic cesium by x-ray photoelectron spectroscopy using Al Kα radiation. The same binding energy has been calculated as the difference between the total energies of the 3p3/2 hole state and the ground state using the Dirac–Fock program of Desclaux, minus the difference between the correlation energies of the two states. The correlation energy for the final 3p3/2 hole state has been found to be 2.17 eV greater than the correlation energy for the ground state using configuration interaction with the form of the correlated wave function dictated by first order perturbation theory. The resulting theoretical binding energy of 1005.70 eV is in good agreement with experiment.
Angle resolved photoelectron spectroscopy of CS2 and COS measured as a function of photon energy from 21 to 70 eV
Authors: Carlson Thomas A. , Krause Manfred O. , Grimm Frederick A.
Published: February 2003

Data have been taken on both the partial cross sections and angular distribution parameters for the first five bands in CS2 with a photon energy from 21 to 70 eV and for the first four bands of COS from 21 to 40 eV. The results are compared with calculations based on the multiple scattering method. In the case of photoionization of the 2πg orbital of CS2 and the 3π orbital of COS, the experimental results and calculations have been successfully explained in terms of the Cooper minimum. The behavior of the fifth band of CS2 is accounted for by assigning it to a satellite peak arising from photoionization of the 2πu orbital by way of configuration interaction. Comparison between the experimental results and calculations showed some problem areas, particularly with regard to the prediction of shape resonances, and suggestions are made for future improvement of the calculations.
Optical emission spectra and crystal field analysis of Eu3+ in the cubic Cs2NaYCl6 host
Authors: Morley J. P. , Faulkner T. R. , Richardson F. S.
Published: February 2003

Unpolarized and magnetic-field-induced circularly polarized luminescence spectra are reported for Eu3+ doped into the cubic Cs2NaYCl6 host. These spectra were obtained at high resolution under variable temperature conditions, and they span the 5DJ(J = 0–3)→7FJ(J = 0–5) transition regions of Eu3+. A detailed analysis of the spectra leads to a nearly complete location and assignment of the crystal field levels split out of the 7FJ(J = 0–5) and 5DJ(J = 0–3) term levels of Eu3+. Essential to the spectral analysis are crystal field energy level calculations and intensity calculations for both the magnetic dipole origin transitions and the electric dipole (one-phonon) vibronic transitions. The dominant contributions to the vibronic structure in the spectra are assigned to vibronically induced electric dipole transitions which involve coupling between the 4f electrons and the three ungerade vibrational modes localized within the EuCl3−6 chromophoric moiety. Lesser contributions are made by vibronic transitions involving vibrational modes not localized within the EuCl3−6 cluster (e.g., low-frequency lattice modes). Excellent agreement between theory and experiment is achieved for the luminescence intensities and the magnetic-field-induced circularly polarized luminescence spectra associated with the magnetic dipole allowed origin transitions. Very good agreement is also achieved between the calculated and observed vibronic intensity spectra. The latter were calculated using a theoretical model for vibronically induced electric dipole transition intensities which includes contributions from both the static-coupling and dynamic-coupling Eu3+-ligand interaction mechanisms.
Role of phonon coupling in the broadening of rotational lines of diatomics trapped in rare gas matrices. A model calculation for HCl in Ar
Authors: Allavena M. , Chakroun H. , White David
Published: February 2003

The near infrared spectra of HCl trapped in pure and N2-doped Ar matrices at low temperature are reported. In pure Ar, a hindered rotational spectrum is obtained and the R(0) line exhibits a strong temperature dependence. The ’’Q’’ feature observed in the N2-doped experiment is rather insensitive to temperature. The temperature dependence of the rotational line is interpreted on the basis of a rotational-phonon coupling model. The absorption coefficient is calculated within the framework of the linear response theory applied to the case of a diatomic molecule embedded in a linear chain of matrix atoms. The calculated full-width at half-maximum is in good agreement with the observed trend.
Raman spectra at low temperatures and depolarization ratios for styrene and polystyrene
Authors: Sears W. M. , Hunt J. L. , Stevens J. R.
Published: February 2003

The Raman spectra of styrene and atactic polystyrene have been recorded at 85 and 225 K. As the temperature is lowered, all 42 vibrational modes of the styrene molecule were resolved including those normally of very low intensity in Raman scattering. A general increase in the intensity of all lines and in the number of overtones and combination bands was observed. The frequency of out-of-plane vibrational modes was increased due to increased steric hindrance, whereas the frequency of in-plane modes remained relatively stable. Of particular interest are 11 low frequency modes, most of which are believed to track low frequency benzene-vinyl torsional oscillations from gaseous styrene and are enhanced by the crystal field. Depolarization ratios were measured for styrene at 300 K and polystyrene at 300 and 85 K. We have confirmed that there is some correlation between very symmetric vibrational modes in styrene and atactic polystyrene and strong polarization (ρV<0.2), and between very asymmetric vibrational modes and strong depolarization (ρV⩾0.5). Because of the polycrystalline nature of solid styrene it was not possible to measure depolarization ratios in this case. There is no significant change in the spectra of atactic polystyrene on lowering its temperature.
Nonlocal density functional theories of the liquid–gas interface
Authors: Robert M.
Published: February 2003

It is shown that the nonlocal free-energy density functional of the penetrable sphere model yields, in a mean-field approximation, a density profile of finite thickness in which the pair correlation function decays slowly in the transverse directions. This result shows that simultaneous occurrence of a finite interfacial thickness and a slow decay of the transverse correlations is not linked to a local free-energy density functional of the van der Waals type.
Theoretical studies of the chemisorption of hydrogen on copper
Authors: Madhavan P. , Whitten J. L.
Published: February 2003

The chemisorption of H2 on Cu(100) is treated using a many-electron embedding theory in which the copper lattice is modeled as a 38-atom cluster. Ab initio valence (4s) CI calculations carried out on a local electronic subspace permit an accurate description of bonding at the surface. Dissociated hydrogen is found to bind exotherimically to the (100) surface at several stable adsorption sites in fourfold, bridge, and atop atom H positions. Calculated H2 binding energies are in the range 13–22 kcal/mol. However, high energy barriers to dissociation of 35–40 kcal/mol exist due to the repulsion of molecular H2 by the surface and the difficulty of stretching H2 significantly above the surface. A characteristic of stretched or dissociated H2 is the occurrence of H levels well up into the Cu 4s band from 5.5 to 7.8 eV below EF.
Semiclassical prediction of resonance energies in three-dimensional reactive collisions
Authors: Pollak Eli , Wyatt Robert E.
Published: February 2003

The lowest energy resonances are calculated for the H + H2 and F + H2 chemical reactions.(AIP)
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Planar or not planar? A charge transfer complex or a van der Waals molecule?
Authors: Kochanski E.
Published: February 2003

The structure and other characteristics of the chlorine dimer (Cl2)2 are discussed. (AIP)
Addendum to ‘‘A simple equilibrium statistical mechanical theory of dense hard-sphere fluid mixtures’’
Authors: Andrews Frank C. , Ellerby H. Michael
Published: February 2003

The comments of R. J. speedy2 on a previous publication by the authors,1 regarding the equilibrium statistical mechanical theory for a hard core fluid, are answered. (AIP)