bluuebunny/crossref_metadata_2025 huggingface dataset:
A molecular dynamics study of the structure of a model Langmuir monolayer of amphiphile molecules
Authors: Harris Jonathan , Rice Stuart A.
Published: July 2002

We study the thermodynamics and structure of a model monomolecular film of pentadecanoic acid on water. In this model the water is treated as a uniform polarizable continuum and the pentadecanoic acid molecules as chains of 15 pseudoatom with internal bond constraints, angle bending and torsional intramolecular interactions, and Lennard-Jones atom–atom intermolecular interactions. The only low pressure phases exhibited by this model at temperatures between 300 and 400 K are the very low density vapor phase and a well ordered condensed phase with a reciprocal density ≤23 Å2 per molecule. This is in sharp contrast with experimental studies which show the existence of a stable liquid-expanded phase with a density of about 35 Å2 per molecule at pressures <15 dyn cm−1.
Size distribution for aggregates of associating polymers. II. Linear packing
Authors: Wang Zhen-Gang , Safran S. A.
Published: July 2002

We study the micellization of associating polymers (hydrocarbon chains with dipolar head groups in hydrophobic solvents) for the case where the polar heads form a linear array. The head interaction is assumed to be short ranged and the chain conformation (free) energy is assumed to follow spherical scaling in the small aggregation number limit and to have cylindrical scaling in the large aggregation number limit. In the small aggregation number limit, the aggregation number is only weakly dependent on the chain length. Numerical solutions as well as analytical studies show that the size distribution displays features of both the spherical and cylindrical aggregates: namely the absence of a sharp CMC transition and a rather sharp distribution function with a width that increases slowly with the mean aggregation number. In the large aggregation limit, the aggregation number can be a strong function of the chain molecular weight. We discuss the importance of the ‘‘end cap’’ effect in determining the mean size as a function of the chain lengths.
Calculated vibrational intensities for photoionization of a mixed Rydberg–valence 3Σ state of O2
Authors: Wang J. , Blake A. J. , Torop L.
Published: July 2002

Vibrational intensities for the photoionization of oxygen molecules from the v′=0 level of the mixed Rydberg–valence E 3Σ−u state to the v+=0–4 levels of the X 2Πg state of the ion have been calculated using the solutions of coupled Schrödinger equations to represent the nuclear motion. The results are compared with the photoelectron spectrum for this transition obtained recently by Miller et al.
Velocity modulation infrared laser spectroscopy of negative ions: The (011)–(001) band of azide (N−3)
Authors: Polak Mark , Gruebele Martin , Peng Grace S. , Saykally Richard J.
Published: July 2002

We have measured 43 transitions centered at 1972 cm−1 in the (011)–(001) bending hot band of the azide ion (N−3) using diode laser velocity modulation spectroscopy of an NH3/N2O discharge. The data, ranging from P(32) to R(40), were fit to a standard l-type doubling Hamiltonian through quartic terms. The l splittings in the spectrum were unusually large compared with similar molecules. Intensity measurements indicate that the vibrational and rotational degrees of freedom are equilibrated, unlike the case for isoelectronic NCO−. Additional lines of the ν3 fundamental have also been measured, which further refine the values of the ground state parameters.
Rovibrational Raman scattering of CH3I vapor: Resonance with a perpendicularly polarized electronic transition
Authors: Wang P. G. , Ziegler L. D.
Published: July 2002

The Raman scattering due to resonance with a perpendicularly polarized electronic transition of a symmetric top molecule in the gas phase is described in a sum-over-all-states approach. The derived intensity and depolarization ratio expressions in an irreducible two-photon tensor basis are applied to the analysis of the ν2 (a1 ) and ν6 (e) bands of CH3 I derived from resonance with the predissociated X→B absorption system. A lifetime of 0.5±0.1 ps is determined for the electronic origin and several K-specific rovibronic levels of the v′6 =1 band of the resonant excited state. These results are contrasted with recent dynamical interpretations of the corresponding jet-cooled CH3 I absorption spectra.
Static and dynamic light scattering studies of water-in-oil microemulsions in the critical region. Evidence of a crossover effect
Authors: Rouch J. , Safouane A. , Tartaglia P. , Chen S. H.
Published: July 2002

Extensive light scattering measurements, including the intensity, turbidity, and linewidth, on a three-component microemulsion system consisting of mixtures of water, decane, and a surfactant sodium di-2 ethylhexylsulfosuccinate (AOT) (WDA), have been made. The critical and several off-critical mixtures have been studied along constant microemulsion droplet volume fraction lines in the one-phase region over a very large temperature range. In the vicinity of the lower phase separation temperature Tp the intensity data are very well accounted for by the standard theory of critical binary fluids using a single value for the short range correlation length ξ0=(13.5±1.5) Å. By combining a mode-coupling theory including the background effects and a linear model equation of state applicable in the critical region, we have been able to fit the dynamic light scattering data using a Debye cutoff length q−1D which is equal to the constant average diameter of microemulsion droplets. Furthermore, we find clear evidence for a crossover from critical to single particle behavior in both static and dynamic light scattering data. A crossover temperature Tx has been identified at which qDξ(Tx)=1. Analyses of the dynamic light scattering data show that qD, which can only be measured far away from Tp, in fact plays a decisive role in controlling the critical dynamics in the whole temperature range.
Multireference coupled-cluster method: Ionization potentials and excitation energies for ketene and diazomethane
Authors: Rittby Magnus , Pal Sourav , Bartlett Rodney J.
Published: July 2002

A linked, size-extensive multireference coupled-cluster method (MRCC) is presented, and has been used to calculate the ionization potentials and excitation energies of the interesting molecules ketene and diazomethane. Comparisons are made with experimental numbers and theoretical results from configuration-interaction (CI) studies. Good agreement is found between the MRCC results, CI calculations, and experiment.
Single crystal electron paramagnetic resonance spectra of triplet excitons in [(Cp*Ru)2(η6,η6-[22](1,4)cyclophane)2+][(TCNQ)2−4 ]
Authors: Morton John R. , Preston Keith F. , Ward Michael D. , Fagan Paul J.
Published: July 2002

Single crystals of [(Cp*Ru)2(η6,η6-[22](1,4)cyclophane)2+][(TCNQ)2−4] (Cp*=η5-C5Me5, TCNQ=tetracyanoquinodimethane) have been examined by EPR spectroscopy at temperatures down to 4 K. The anisotropic spectrum measured in the 77–150 K range is characteristic of an excitonic triplet species (I). This behavior is attributed to interactions between electrons located in one of the TCNQ acceptor stacks present in the title compound. The direction of maximum electronic interaction coincides with the stacking axis of the crystals (the crystallographic a axis). Intensity measurements establish that I is a thermally excited triplet with a J=560±30 cm−1, exhibiting zero field splittings of ‖D‖=187 MHz (66G) and ‖E‖=32 MHz (10 G). A second although weaker feature in the spectrum is tentatively assigned to a second triplet (species II) having very much smaller values of ‖D‖ and J than those of I. Species II is attributed to an impurity present in very low concentrations.
Infrared and microwave spectra of OCO–HF and SCO–HF
Authors: Fraser G. T. , Pine A. S. , Suenram R. D. , Dayton D. C. , Miller R. E.
Published: July 2002

The H–F stretching bands of the OCO–HF and SCO–HF complexes have been studied by optothermal (bolometer-detected) molecular-beam spectroscopy. Both species exhibit spectra of a quasilinear molecule red shifted from free HF by 52.1 and 57.5 cm−1, respectively. The principal band in both molecules is accompanied by a slightly red-shifted doublet-type subsidiary band that can be interpreted as a hot band of a low frequency bending vibration or a K=1 subband of a bent molecule. Accurate doublet splittings in the ground H–F vibrational state have been measured by pulsed-nozzle Fourier-transform microwave spectroscopy.
Dynamics for CH3F trapped in rare gas crystals and spectroscopic consequences
Authors: Lakhlifi A. , Girardet C.
Published: July 2002

The dynamics of CH3F molecule trapped in a rare gas crystal is determined in order to explain the infrared spectra and vibrational relaxation data which had led to controversial qualitative interpretations. It is shown that the orientational motions of the molecular axis are strongly coupled to the translational dynamics of the molecule and, in a smaller extent, to the lattice vibrations. As a first consequence, the molecular axis remains nearly anticollinear to the axis joining the molecular center of mass and the site center, and the molecule behaves as a slightly hindered rotor implying both the molecular axis and its center of mass; the spinning motion appears to be a tunneling motion which considerably narrows the splitting between the k=0 and k=1 levels. As a second consequence, the orientational signals are strongly broadened by the translational dynamics of the molecule and of the crystal. So, the only observed sharp signal with a large foot is interpreted as the superimposition of a pure vibrational Q(1) branch and of broadened rotational structures connected to R( j0) and R( j1) ( j=0,1,2) signals. Moreover, there is not a dominant channel for the vibrational relaxation mechanism of CH3F trapped in argon matrix, since the transfers to the orientational modes, to the local or to the bulk phonon modes are shown to be equally efficient, with times (∼10 μs) in agreement with experimental data. In xenon matrix, the direct transfer to the lattice vibrations seems to be the most efficient mechanism of relaxation.
Silaketene: A product of the reaction between silylene and carbon monoxide?
Authors: Hamilton Tracy P. , Schaefer Henry F.
Published: July 2002

Molecular structures and vibrational frequencies for silaketene, H2SiCO, are predicted using ab initio techniques. A weakly bound nonplanar structure is found to be the equilibrium geometry, whereas the ketene-like planar structure is the transition state for inversion between the two equivalent nonplanar conformations. The barrier to inversion about the silicon atom is 18 kcal/mol. The ab initio heat of reaction of SiH2 and CO to form H2SiCO is 16 kcal/mol. The results are discussed in light of recent matrix isolation experiments attempting to make and detect dimethylsilaketene.
Anomalous behavior of the refractive index of a critical microemulsion near the critical end point
Authors: Rebbouh N. , Lalanne J. R.
Published: July 2002

We have performed investigations of the thermal variations of the refractive indexes of four microemulsions in a system which exhibits a line of critical points, ending at a critical end point (CEP). Both refractometric and interferometric measurements lead us to the conclusion that this system exhibits anomalous behavior in the vicinity of the CEP. Such an anomaly cannot be explained by any of the existing theories generally used in the case of classical critical binary mixtures and is probably due to morphological modifications of the microemulsions, associated with aggregation and partial merging of micelles. Both a qualitative and quantitative description of the observed anomaly are proposed.
A classical trajectory study of intramolecular vibrational relaxation and unimolecular decomposition in methyl hydroperoxide
Authors: Gai Huadong , Thompson Donald L. , Fisk George A.
Published: July 2002

This paper presents a quasiclassical trajectory study of the energy flow that occurs consequent to high-overtone excitations of either a CH or an OH local mode in methyl hydroperoxide, CH3 OOH. The potential energy surface employed is an empirical one based on available spectroscopic, thermodynamic, and theoretical data. Energy initially localized in a CH stretch transfers irreversibly on the time scale of the calculations into the methyl bending modes within 0.2 ps. Transfer of energy out of the methyl group to the rest of the molecule occurs more slowly. An initially excited OH bond retains energy longer than does a CH bond and, unlike the energy transfer for an excited CH stretch, partial recurrences in the energy content of the OH mode occur for some excitations. Vibrational resonances are important in determining the rates and pathways of energy flow in the molecule. At total energies near 104 kcal/mol the rate of the O–O bond scission is twice as fast for OH excitation as it is for CH excitation.
Effects of a quantum-mechanical lattice on the electronic structure and d–d spectrum of the (MnF6)4− cluster in Mn2+ :KZnF3
Authors: Luaña V. , Bermejo M. , Flórez M. , Recio J. M. , Pueyo L.
Published: July 2002

The electronic structure of the Mn2+ :KZnF3 impurity system has been computed by means of a Hartree–Fock–Roothaan cluster model. First, the Mn2+ center has been simulated by the (MnF6 )4− unit in vacuo. Then, the effects of the KZnF3 lattice have been included in the cluster calculation using three different lattice models. The well-known point–charge approximation has been compared with two rigorous quantum–lattice models derived from the ideas of the theory of electronic separability. In these two models the lattice ions are represented by an effective lattice potential and a lattice projection operator that enforces the cluster–lattice orthogonality. In the Coulomb or Hartree model the cluster–lattice exchange interactions are neglected. The ab initio model potential (MP) lattice model makes use of model potentials for representing the lattice ions and includes an accurate nonlocal exchange operator. According to the present results, the point–charge lattice model destroys the acceptable picture of the electronic ground state of the (MnF6 )4− unit obtained at the cluster-in vacuo stage, giving a continuously repulsive nuclear potential. The quantum–lattice models restore the bound ground state and give an equilibrium geometry qualitatively correct and quantitatively reasonable. The seven d–d electronic transitions observed in this system are computed within a quarter of eV after correcting the Hartree–Fock description with a configuration interaction limited to the octahedral configurations of the d5 problem and a semiempirical correlation-energy correction. Lattice effects on vertical transition energies turn out to be small. However, important indirect lattice effects are encountered in the theoretical spectrum as a consequence of the lattice-induced modification of the equilibrium geometry of the ground state.
Multichannel Rydberg spectra of the rare gas dimers
Authors: Du Ning Yi , Greene Chris H.
Published: July 2002

Rydberg levels of several heteronuclear rare gas dimers are treated theoretically by combining multichannel quantum defect methods with a nonperturbative Fermi-type analysis. Calculations confirm many major spectral features observed in experiments by Dehmer and Pratt, and permit the first detailed interpretation and classification of some of the observed spectra. The dimer spectra closely resemble atomic spectra in many cases, while others show dramatic molecular effects.
Jump transition due to a time-dependent bifurcation parameter in the bistable ioadate–arsenous acid reaction
Authors: Erneux T. , Laplante J. P.
Published: July 2002

Bifurcation or limit point problems with slowly varying parameters are of interest in many research areas. Typically, the time dependency of the bifurcation parameter introduces a delay in the transition from one type of solution to the other. In this article, we study both theoretically and experimentally the bistable iodate–arsenous acid reaction when subjected to a time-dependent bifurcation parameter. This problem is tractable analytically and allows us to derive an expression for the transition delay with respect to the static bifurcation point as a function of the dimensionless ramping rate ε. For small and moderate values of ε, we predict that the delay is proportional to εp where the exponent p=2/3≈0.67. For the experimental conditions considered in this paper, our experimental data yield p=0.63±0.10.
Photochemistry of BrNCO and INCO
Authors: Liu X. , Gilbert J. V. , Coombe R. D.
Published: July 2002

The absorption spectra of BrNCO and INCO in the region 160–400 nm are continuous in nature, and photolysis of these molecules with pulsed excimer lasers leads to dissociation. Photolysis of BrNCO and INCO at 308 and 351 nm, respectively, produces vibrationally cold ground state NCO radicals. Weak NCO A 2Σ+→X 2Π emission results from two-photon absorption processes at these wavelengths. Photolysis of BrNCO and INCO at 193 and 222 nm, respectively, produces intense NCO A 2Σ+→X 2Π emission. The NCO(A) is a direct one-photon photofragment in each case, and has considerable vibrational excitation. The yield of NCO(A) from BrNCO photolysis at 193 nm is approximately 16%; the yield of NCO(A) from INCO photolysis at 222 nm is near 13%. From the production of NCO(A) at these wavelengths and the short wavelength limit of the NCO A 2Σ+→X 2Π emission, limits on the heats of formation of these molecules are found to be ΔHf(BrNCO)≥−1.7 kcal mol−1 and ΔHf(INCO)≥10.9 kcal mol−1. These results demonstrate the preference of the halogen isocyanates for dissociation to doublet fragments by scission of the nitrogen–halogen bond, in contrast to the analogous halogen azides which photodissociate to singlet or triplet fragments.
Mean field approach to molecule–surface scattering at finite temperature: Multiphonon theory
Authors: Jackson Bret
Published: July 2002

A theory is presented for the phonon inelastic scattering of molecules from surfaces. Both the molecule and the surface and bulk vibrations of the solid are treated in a fully quantum mechanical fashion. The model includes multiphonon interactions and is thus applicable to both heavy and light gas species at both high and low beam energies. The method is a mean field approach in that both the molecule and the bath are evolved simultaneously and self-consistently. The result is that the molecular wave function obeys a Schrödinger-like equation, but propagates on a gas–surface interaction potential which is both time and temperature dependent. The theory is easily applied to standard zero temperature time dependent scattering techniques, with only a small increase in computer requirements. The model is extended to the specific case of atom–metal scattering. Results are presented for Ne scattered from a Cu(100) surface.
The dissociative chemisorption dynamics of N2 on catalytic metal surfaces: A quantum-mechanical tunneling mechanism
Authors: Haase G. , Asscher M. , Kosloff R.
Published: July 2002

A tunneling mechanism is suggested for explaining the dissociative chemisorption of nitrogen molecules on metal surfaces. The time-dependent Schrödinger equation was numerically solved for the transition dynamics from the N2–metal to the N–metal potential-energy surfaces for two degrees of freedom. The dynamics was found to be sensitive to the topology at the crossing region between the two nonadiabatic potential-energy surfaces (PES). The resulting rapid increase of the dissociation probability (S0) with incident kinetic energy, its saturation at high energies and vibrational enhancement are in good agreement with recent experiments. A substantial isotope effect is predicted by the calculations. Recombinative desorption experiments of 14N2 and 15N2 from Re(0001) are in excellent agreement with the tunneling model.
Picosecond fluorescence depletion spectroscopy. I. Theory and apparatus
Authors: Côté M. J. , Kauffman J. F. , Smith P. G. , McDonald J. D.
Published: July 2002

This paper describes the experimental implementation and theory of a new technique for the time resolved study of intramolecular vibrational redistribution: time resolved fluorescence depletion (TRFD). Picosecond time resolution is obtained by using two pulses of identical wavelength and duration to create and then stimulate emission from a vibrational state in S1. Spontaneous emission intensity is measured as a function of delay between pulses. By monitoring the efficiency with which the second pulse stimulates emission, the evolution of the initial optically prepared state can be followed. A description of the apparatus built for these experiments is also presented.
The torsional Raman spectra of C2H6 and C2D6
Authors: Fernández-Sánchez J. M. , Valdenebro A. G. , Montero S.
Published: July 2002

The torsional Raman spectra of C2H6 and C2D6 have been experimentally investigated with an improved conventional Raman spectrometer. Wave numbers and absolute cross sections of all observed bands have been satisfactorily interpreted within the experimental accuracy by means of a simple, pure-torsional Hamiltonian and a model for the torsional dependence of the molecular polarizability. The effective threefold potential barrier parameters for C2H6 have been taken from the recent literature, whilst for C2D6 the values V3eff (C2D6)=990±2 cm−1 and V6eff (C2D6)=7.9±1 cm−1 were obtained.
Observation of internal rotation in the NH+4(NH3)4 ionic cluster
Authors: Price J. M. , Crofton M. W. , Lee Y. T.
Published: July 2002

The infrared vibrational predissociation spectrum for the title ionic cluster is presented. The interesting feature observed in the spectrum is the presence of rotation−vibration transitions due to the nearly free internal rotation of the solvent ammonia molecules attached to the ammonium ion core. Internal rotation within an ionic cluster has never been observed before.(AIP)
Molecular orientational correlation in liquid halogens
Authors: Misawa Masakatsu
Published: July 2002

The characteristic features of structure factor Sm(Q) of liquid halogens F2, Cl2, Br2, and I2 have been discussed in terms of preferred orientational correlations introduced between the nearest neighbors. The orientational correlations estimated directly from the experimental Sm(Q)’s of these liquids are rather similar to each other and are related to a ‘‘staggered parallel’’ orientation proposed previously for liquid Br2. The characteristic features of these Sm(Q)’s are interpreted quite well by two structurally simple quantities, i.e., the ratio of intramolecular bond length to intermolecular center–center separation of correlated molecules l/Rc and that of intramolecular bond length to effective diameter of uncorrelated molecule l/σ. The characteristic features of the experimental radial distribution functions are also reproduced quite well.
Rotationally resolved photoelectron angular distributions in resonance enhanced multiphoton ionization of NO
Authors: Rudolph H. , McKoy V.
Published: July 2002

We report calculated ionic rotational branching ratios and associated photoelectron angular distributions for (1+1′) resonance enhanced multiphoton ionization (REMPI) via the R21(20.5), P21+Q11(25.5), and P11(22.5) branches of the A 2 Σ+(3sσ) state of NO. The branching ratios are dominated by even angular momentum transfer peaks, in agreement with the ΔN+l=odd (ΔN≡N+−Ni ) selection rule. Whereas the calculated photoelectron angular distributions are very branch dependent alignment, the ionic branching ratios are found to be less so. The present calculated results agree well with the experimental results of Allendorf et al.
Chemical branching in two chromophore systems: Application to the photodissociation of C2F4IBr
Authors: Das Sanjukta , Tannor David J.
Published: July 2002

Time dependent quantum mechanical calculations of the photodissociation of C2F4IBr are reported. The calculations successfully model the experimental absorption spectra [W. H. Pence, S. L. Baughcum, and S. R. Leone, J. Phys. Chem. 85, 3844 (1981)] as well as the branching ratio of final products due to photodissociation [D. Krajnovich, L. J. Butler, and Y. T. Lee, J. Chem. Phys. 81, 3031 (1984)]. The model used consists of two degrees of freedom, an iodine and a bromine coordinate, and two diabatic potential energy surfaces which are repulsive in the iodine and bromine cordinates, respectively. The study gives a consistent picture of the experimental I:Br branching ratio at 266, 248, and 193 nm in terms of a crossing of diabatic potential energy surfaces. However, the same model requires an anomalously small surface coupling when applied to the related CH2IBr system to agree with experiment. The time dependent formulation of absorption spectroscopy and photodissociation is extended to systems with chemical branching, and a simple new technique for calculating frequency dependent chemical branching ratios from short time dynamics is presented.
Fluorescence from photoexcitation of BCl3 at 45–106 nm
Authors: Lee L. C. , Han J. C. , Suto Masako
Published: July 2002

The photoabsorption, fluorescence cross sections, and the fluorescence yield of BCl3 are measured in the 45–106 nm region. Fluorescence spectra are dispersed to identify the emitting species. The emission observed at excitation wavelengths longer than 96 nm is attributed to the excited BCl*2. The BCl (A–X) emission appears at excitation wavelengths shorter than 97.5 nm. Emissions observed at the thresholds of 88 and 81 nm are attributed to the excited BCl+*3 (C̄ 2A″2 and D̄ 2E′) states, respectively. Emissions from excited B* atoms appear in the 48–64 nm region. In the 88–96 nm region the maxima and minima of the fluorescence cross section are complimentary with those of the BC1+3 ionization yield, indicating where superexcited state(s) exist that decay through competitive channels of fluorescence and autoionization.
Kinetics of optically pumped ZnHg
Authors: Fournier G. R.
Published: July 2002

We have studied the various rates of formation and decay of ZnHg using a frequency doubled dye laser at 307.6 nm as a pump source for the zinc 3 P1 state. More specifically we have measured the rate of decay of the atomic 3 P1 state, the rate of three-body formation of excited ZnHg, the spontaneous emission coefficient of excited ZnHg, the rate of quenching of ZnHg by Hg atoms and the rate of biexcimer quenching. We have also carried out new measurements of the spectrum of excited ZnHg and of the intrinsic stimulated emission cross section.
Molecular dissociation dynamics of H2S at 193.3 nm studied via emission spectroscopy
Authors: Person M. D. , Lao K. Q. , Eckholm B. J. , Butler L. J.
Published: July 2002

We present a study of the fragmentation dynamics of H2S excited at 193.3 nm using the technique of emission spectroscopy of dissociating molecules. The emission spectrum measured extends from near 50 000 cm−1 to 35 000 cm−1, corresponding to emission to vibrational levels in the ground electronic state with seven quanta of S–H stretching vibration. We assigned the emission to previously unobserved vibrational levels of H2S using the calculated energies of Halonen and Carrington [J. Chem. Phys. 88, 4171 (1988)]. The early part of the spectrum contains progressions in both symmetric stretching and in symmetric/antisymmetric combination bands, as well as stretching progressions in combination with one quantum in the bend. In the latter part of the spectrum, which reflects the latter part of the dissociation dynamics, emission occurs selectively to vibrational levels characterized best in a local mode basis as having the vibrational energy localized in one of the two S–H bonds. We interpret emission to these local mode vibrations as evidencing the evolution of the dynamics into dissociative motion of one of the S–H bonds with little HSH bending or vibrational excitation of the other S–H bond, which correlates to the SH fragment. The emission spectrum thus reveals the progression of the dynamics, providing a crucial link between the absorption spectrum and the final observed SH product quantum state distributions.
The generalized log-derivative method for evaluation of second-order transition amplitudes
Authors: Mrugal/a Felicja
Published: July 2002

The log-derivative method of Johnson is generalized to calculate matrix elements of multichannel Green’s functions—second-order transition amplitudes—which arise from description of a variety of physical processes involving weak interactions of initial and final (bound) states with a set of strongly coupled continuum and/or bound intermediate states. A purely approximate-solution algorithm and two hybrid approximate-solution approximate-potential versions, based on the use of piecewise constant reference potentials, are presented and tested on problems concerning investigations of nonadiabatic effects in the spectroscopy of H2. A comparison with the renormalized Numerov method, extended to calculation of considered transition amplitudes, is made and superior efficiency of the hybrid log-derivative algorithms is demonstrated. It is shown both practically and theoretically that discretization errors of the hybrid algorithms grow linearly with increasing energy in calculations, whereas cubic growth of errors with energy is characteristic for the purely approximate-solution log-derivative and Numerov algorithms.
Group theoretical approach to semiclassical dynamics: Multimode case
Authors: Gilmore Robert , Yuan Jian-Min
Published: July 2002

A recently proposed procedure for computing the S matrix for collinear molecular collisions is extended from the single-mode case to the multimode case. In this procedure the semiclassical Hamiltonian describing the molecular collision is integrated in a finite-dimensional, faithful nonunitary representation of the dynamical group. When the integration is completed, the resulting group operation is mapped into the infinite-dimensional unitary representation to describe the S matrix which acts on the molecular Hilbert space and describes collisional excitation of the internal vibrational modes. This procedure is implemented to study the two-mode collision process N2+O2 and the two three-mode collision processes N2+CO2 and NO+CO2. The results compare favorably with other treatments of these collinear collision processes.
One-electron diatomics in momentum space. VI. Nonvariational approach to excited states
Authors: Koga Toshikatsu , Ougihara Tsutomu
Published: July 2002

Based on the Fock transformation of momentum variable, we can reduce the momentum-space Schrödinger equation for one-electron diatomics to a homogeneous Fredholm-type integral equation with a degenerate kernel. A nonvariational LCAO solution to this integral equation is applied to various nontrivial excited states of the hydrogen molecular ion for the first time. The results show an excellent convergence and the exact electronic energy given in the literature is reproduced almost completely.
Electrostatic interactions in host–guest complexes. I
Authors: Bruning H. , Feil D.
Published: July 2002

In the first article of this series a study of the K+ ⋅⋅⋅H2 O interaction is presented. The calculations are done with the local density approximation using the Xα-LCAO-DVM approach. The polarization of the water molecule in the complex are compared with the polarization of water in several electrostatic fields (homogeneous field, point charge, field of K+ cation). The effect of exchange repulsion on the polarization is analyzed. A decomposition of the interaction energy as computed in the Xα approach is carried out. This shows that the various effects of the interaction are well reproduced by this approach.
A new crossed beam approach to vibrationally inelastic scattering in neutral collision systems. State-to-state cross sections for He+I*2 (υ′=15, 25, 35) at Ec.m.=89 meV
Authors: Krajnovich Douglas J. , Butz Kirk W. , Du Hong , Parmenter Charles S.
Published: July 2002

Details are given of a new type of crossed beam experiment that is designed to study state-resolved vibrationally inelastic scattering of neutral atoms from neutral diatomics or polyatomics. The molecule is initially excited to a selected vibrational level in an excited electronic state by laser pumping. Dispersed fluorescence from molecules that have undergone inelastic scattering is used to observe the final vibrational state distributions. The technique is used here to characterize the vibrationally inelastic scattering of He from each of three initial levels υ′=15, 25 and 35 within the B0+u state of I2 . The center-of-mass collision energy is 89 meV (720 cm−1). Thirty cross sections (relative, not absolute) for vibrationally inelastic scattering are obtained. The cross sections characterize processes with vibrational quantum changes extending to Δυ=±3 for the initial level υ′=15, to Δυ=±5 for υ′=25, and to Δυ=±7 for υ′=35. Relative cross sections for pure rotationally inelastic scattering within the initially pumped υ′ levels are also reported. The data analysis incorporates much new information about I2 predissociation, spectroscopy, and Franck–Condon factors that has become available within the last ten years. An error analysis of the cross sections has been performed so that they are suitable benchmarks for theoretical calculation. Procedures are given for estimating fluorescence signal intensities in experiments of this type. The signal expectations are consistent with the I2 observations and suggest that extension to certain polyatomics is quite feasible.
A molecular dynamics study of the influence of elongation and quadrupole moment upon some thermodynamic and transport properties of linear heteronuclear triatomic fluids
Authors: Chialvo Ariel A. , Heath David L. , Debenedetti Pablo G.
Published: July 2002

The influence of elongation, quadrupole strength, temperature, and number density upon the pressure, energy, translational diffusion, rotational relaxation, and shear viscosity of linear, rigid, three-site, heteronuclear, shifted-force Lennard-Jonesiums (RTSLJ) was studied via (N,V,T) molecular dynamics. For quadrupolar systems, molecular elongation was systematically perturbed about a base case, with quadrupole strengths scaling as the square of the elongation. The same elongation perturbations were applied to otherwise identical, nonquadrupolar systems. At constant density, the configurational energy increases in magnitude with elongation for the quadrupolar systems, and decreases in the nonquadrupolar case. The pressure exhibits a maximum at intermediate elongation in the presence of quadrupolar interactions, and increases monotonically with elongation at constant density for nonquadrupolar systems. Center-of-mass mobility decreases due to the presence of quadrupolar interactions, which also tend to slow down rotational relaxation rates.
Proton chemical shifts in some hydrogen bonded solids and a correlation with bond lengths
Authors: Kaliaperumal R. , Sears R. E. J. , Ni Q. W. , Furst J. E.
Published: July 2002

Using multipulse techniques, principal values of the proton nuclear magnetic resonance (NMR) chemical shift tensors were measured at room temperature for the monoclinic form of oxalic acid, potassium hydrogen oxalate, and potassium hydroxide. The isotropic and perpendicular shifts of the first two compounds, which are of medium hydrogen bond strength, were found to fit the linear correlation with O⋅⋅⋅O distance, RO⋅O, established by Rohlfing, Allen, and Ditchfield for medium and strongly O–H⋅⋅⋅O hydrogen bonded solids. Although KOH is very weakly hydrogen bonded, the shifts were also found to conform to the correlation, at least as well as does the other data, thus extending this to weakly hydrogen bonded solids. An empirical correlation of the isotropic and perpendicular shifts with exp(−RO⋅O/ρ), where RO⋅O is in Å and ρ is 0.94 Å, is given here which has better agreement with the data and has an interpretation in terms of a simple ionic model of an O–H⋅⋅⋅O bond.
A study of some Rydberg states of CO2 by (3+1) multiphoton ionization spectroscopy
Authors: Wu Ming , Johnson Philip M.
Published: July 2002

The MPI spectra of CO2 were recorded in the range 275 to 338 nm in both a conventional MPI cell and a molecular beam apparatus. The polarization ratio of each MPI peak was measured in order to assign the symmetry of excited states. The 3pσu 1Πu and 3pσu 1Πu110 Rydberg states were observed, while the 3pπu 1Σ+u Rydberg state was missing, and a new Rydberg state, 3pπu 1Δu was observed at 333.03 and 333.70 nm. In the nf (n=4,5) Rydberg series, evidence was found of interaction with other nearby Rydberg states. A mass selected pure CO+2 ion signal was measured for the 3pπu 1Δu state, but both CO+ and CO+2 ion signals were detected for the other Rydberg states. Predissociation and fragmentation in MPI processes are discussed. Lower limit lifetimes for the observed Rydberg states of CO2 are given.
The enthalpy of sublimation and thermodynamic functions of fermium
Authors: Haire Richard G. , Gibson John K.
Published: July 2002

The enthalpy of sublimation of fermium (Fm), element 100, has now been determined directly by measuring the partial pressure of Fm over alloys, for the temperature range of 642 to 905 K. The partial pressures were determined using Knudsen effusion and target collection techniques. Dilute (10−5–10−7 atom %) solid alloys of Fm and mixtures of Fm and Es in both Sm and Yb solvents were studied. The presence of Es in two of the alloys allowed a direct comparison of the behavior of Fm and Es, where the latter could be used as a reference. It was possible to calculate enthalpies of sublimation and a hypothetical vapor pressure/temperature relationship for pure Fm metal by selecting Yb as the solvent most likely to form a nearly ideal alloy with Fm. From the experimental vapor pressure data, we derived average Second Law values of 33.8±3 kcal/mol and 23.5±3 cal/mol deg for the enthalpy and entropy of sublimation of Fm at 298 K. Third Law enthalpy values were also calculated using the experimental partial pressure data and entropies estimated from derived free energy functions and heat capacities for the solid and gaseous forms of Fm. The average Third Law values (34.8 kcal/mol and 25.1 cal/mol deg, respectively, at 298 K) are in agreement with those obtained via the Second Law. These results establish that Fm, like Es (element 99), is a divalent metal. The finding that Fm metal is the second divalent actinide element experimentally establishes the trend towards metallic divalency expected in the second half of the actinide series.
Low frequency polarized and depolarized light scattering in H-bonded liquids: CH3(CH2)n−1OH (n=1,...,5)
Authors: Benassi P. , Mazzacurati V. , Nardone M. , Ruocco G. , Signorelli G.
Published: July 2002

Polarized and depolarized room temperature light scattering spectra of normal alcohols from methanol to pentanol have been measured up to 80 cm−1 frequency shift. At low frequency shifts (smaller than 4 cm−1), resolutions as high as 0.04 cm−1 have been used. The possibility of using the same spectrometer for measuring both low frequency Brillouin structures and high frequency depolarized tails allows for the first time a precise determination of both lineshapes and relative integrated intensities between the various spectral components. The experimental results are presented and briefly discussed on the basis of the existing theories for depolarized scattering from molecular liquids.
Mechanisms of photodissociative ionization of HCOOH: The heat of formation of COOH+
Authors: Ruscic B. , Schwarz M. , Berkowitz J.
Published: July 2002

The dissociative ionization of HCOOH to form COOH+ +H+e has been reinvestigated. Experiments with DCOOH and HCOOD demonstrate that rearrangement competes with direct bond cleavage in this dissociation, even near threshold. Extrapolation of the photoion yield curve of COOH+ to the background level is ambiguous. A photoelectron–photoion coincidence experiment was thereupon performed, to obtain a breakdown diagram. From the 0 K cross over energy of 12.30±0.02 eV, we infer ΔHf00 (COOH+)=143.2±0.5 kcal/mol, and proton affinity (PA) (CO2)=129.2±0.5 kcal/mol. Some possible mechanisms for the rearrangement process are explored, but the calculated barriers are too high to explain the observation.
Computer simulation of reptation theories. I. Doi–Edwards and Curtiss–Bird models
Authors: Öttinger Hans Christian
Published: July 2002

An algorithm for simulating the Doi–Edwards and Curtiss–Bird models for concentrated polymer solutions and melts in homogeneous flow situations is developed. For steady shear flow, it is demonstrated that this simulation algorithm is capable of supplying high-precision results for the viscometric functions. The proposed simulation algorithm is not only useful for studying arbitrary time-dependent flows and various generalizations of the original Doi–Edwards and Curtiss–Bird models, but it also further illuminates the mathematical and physical content of the basic equation describing the polymer dynamics in these reptation theories.
A numerically exact full wave packet approach to molecule–surface scattering
Authors: Mowrey R. C. , Sun Y. , Kouri D. J.
Published: July 2002

A numerically exact spectral method for solving the time-dependent Schrödinger equation in spherical coordinates is described. The angular dependence of the wave function is represented on a two-dimensional grid of evenly spaced points. The fast Fourier transform algorithm is used to transform between the angle space representation of the wave function and its conjugate representation in momentum space. The time propagation of the wave function is evaluated using an expansion of the time evolution operator as a series of Chebyshev polynomials. Calculations performed for a model system representing H2 scattering from a rectangular corrugated surface yield transition probabilities that are in excellent agreement with those obtained using the close-coupling wave packet (CCWP) method. However, the new method is found to require substantially more computation time than the CCWP method because of the large number of grid points needed to represent the angular dependence of the wave function and the variation in the number of terms required in the Chebyshev representation of the time evolution operator.
Time dependence of hole spectrum due to dispersive burning kinetics in dye-doped polymers
Authors: Kanematsu Y. , Shiraishi R. , Imaoka A. , Saikan S. , Kushida T.
Published: July 2002

Time evolution of a persistent hole spectrum has been investigated for dyes doped in polyvinyl alcohol films at 2 K. The zero-phonon hole profile measured for resorufin using a single-mode dye laser has been found to be nearly Lorentzian even in the case of relatively deep holes. The observed fluence-dependent depth and width of the zero-phonon hole are reproduced well by the numerical simulation based on a dispersive burning-kinetics model. It is pointed out that a large distribution of the burning rate is responsible for the fluence-dependent hole broadening. Time evolution of the phonon-sideband hole simulated using the same model is also compared with the experimental data. It is shown that the low-energy sideband hole is enhanced when the burning kinetics is dispersive.
Observation of an excimer emission band of the ArOD van der Waals molecule
Authors: Lemaire J. L. , Tchang-Brillet W.-Ü. L. , Shafizadeh N. , Rostas F. , Rostas J.
Published: July 2002

An excimer emission band attributed to a transition from the first excited state to the ground state of the van der Waals Ar(OD) molecule has been observed in experiments where D2O was dissociated in presence of rare gases by two photons of a quadrupled YAG laser (266 nm). KrOD has also been observed in the same experiments. The ArOD excimer band comprises three main peaks at 313.9, 315.1, and 316.0 nm as well as several minor ones nearer to the main OH (A2 Σ+ ,v=0–X2 Π,v=0) emission band. The emission profile is realistically simulated by a one dimension model using recently published potentials for the excited state and modeling the ground state by that of the ArF X 2 Σ+ state. This result tends to demonstrate that the ground state geometry of Ar(OD) involved in the transition is probably L shaped although the high intensity of the observed excimer band is not satisfactorily explained.
Improved phase diagram of nitrogen up to 85 kbar
Authors: Vos W. L , Schouten J. A.
Published: July 2002

A quasi-isochoric scanning method has been used to study the phase diagram of nitrogen from 150 to 550 K and up to 85 kbar in a diamond anvil cell in order to make a comparison with previous measurements of the binary phase diagram He–N2. It has been confirmed that there is only one solid-solid-fluid triple point in N2 up to 85 kbar. However, both the δ–β transition line and the melting line have shifted appreciably towards lower pressures. The present experiment shows that, as a result of this, the triple point is located at 555±5 K and 80±2 kbar, which is 20% lower in pressure than previous data.
Theory of the electrical double layer: Ion size effects in a molecular solvent
Authors: Torrie G. M. , Kusalik P. G. , Patey G. N.
Published: July 2002

Recent application of the reference hypernetted-chain theory to the calculation of the structure of electrical double layers in wholly molecular models of aqueous electrolytes [J. Chem. Phys. 90, 4513 (1989)] is extended to NaCl solutions. The strong interaction of the small Na+ ion with the solvent molecules leads to a number of novel features, notably a very high adsorption of Na+ into a region about 4 Å from the surface next to the first solvent layer. This is sufficient to produce a positive potential of zero charge of about 29 mV and to cause the effective surface charge experienced by the diffuse layer to be positive even when the surface carries a substantial negative charge. In most cases, however, the surface potential is found to be remarkably insensitive to the details of the structure of the double layer for a given surface charge.
Electron thermalization distances and free ion yields in dense gases and liquids: Effect of molecular dipole moment
Authors: Gee Norman , Freeman Gordon R.
Published: July 2002

The effect of a molecular dipole moment on electron thermalization in X-irradiated fluids was examined by determining the effect of density on the density-normalized electron thermalization distance bGPd in dimethyl ether. Free ion yields were measured as a function of electric field strength at 0.06≤d/dc<2.7 (critical fluid density dc =271 kg m−3), and bGP values were obtained using an extended Onsager model. The permanent dipole increases the thermalizing ability of the fluid at all densities. However, the effect is smaller in the dense fluids and the transition from low-density gas behavior occurs at d/dc≊0.2.
Microscopic model of amphiphilic assembly
Authors: Gunn John R. , Dawson K. A.
Published: July 2002

A microscopic model of lyotropic systems is presented. Amphiphile and water molecules are described by simple intermolecular potentials which correctly include important excluded volume effects and the relative energy scales in the system. The present model represents an attempt to bridge the gap between more primitive lattice models and highly complex all-atom descriptions of amphiphilic systems. A constant-temperature molecular dynamics study in which the divergence of the pressure tensor is constrained to zero is discussed. Preliminary calculations on the phase diagram, order parameters, and dynamical observables of the model are reported. Some comments on improvements to the model and the theoretical techniques used to study it are made in the final section of the paper.