bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the spring constant of an optical trap by external sinusoidal excitation and lock-in detection
Authors: Ding Zhihua , Lai Guanming , Sakakibara Teruhiko , Shinohara Shigenobu
Published: July 2002

We report a method for determining the spring constant of an optical trap by external sinusoidal excitation and lock-in detection. A polystyrene latex particle trapped in a focused Nd:YAG laser beam is forced to oscillate by another intensity-modulated laser-diode beam. Lock-in detection for measuring particle oscillations is also implemented to obtain the phase delay and amplitude of the harmonic oscillation that correspond to the excitation frequency. Experimental results of trials to determine the spring constant are given to demonstrate the improved precision and reproducibility of our method.
Room temperature polarized photoreflectance characterization of GaAlAs/InGaAs/GaAs high electron mobility transistor structures including the influence of strain relaxation
Authors: Chen T. H. , Huang Y. S. , Lin D. Y. , Pollak Fred H. , Goorsky M. S. , Streit D. C. , Wojtowicz M.
Published: July 2002

Using room temperature photoreflectance (PR) we have characterized the properties of three GaAlAs/InGaAs/GaAs high electron mobility transistor structures with two different well widths fabricated by molecular beam epitaxy on (001) GaAs substrates. The samples were denoted as #1, #2, and #3 with well widths of 140, 160, and 160 Å, respectively. Samples #2 and #3 were grown on substrates with different threading dislocation densities. For the latter two samples the well width exceeds the pseudomorphic limit so that there are some strain relaxation and related misfit dislocations as determined from the x-ray measurements. In order to detect the anisotropic strain of the misfit dislocations related to strain relaxation, the PR measurements were performed for incident light polarized along [110] and [11̄0] directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polarized PR signal in the InGaAs channel layer. Signals have been observed from every region of the sample, making it possible to evaluate the In and Al compositions, channel width and two-dimensional electron gas density, as well as the properties of the GaAs/GaAlAs multiple quantum well buffer layer.
Deep level transient spectroscopy and pseudopotential superlattice calculation for an InAs monolayer embedded in GaAs
Authors: Pickenhain Rainer , Schmidt Heidemarie , Gottschalch Volker
Published: July 2002

We present deep level transient spectroscopy measurements and pseudopotential supercell calculations for InAs monolayers embedded in GaAs. The insertion of InAs MLs into GaAs generates two states in the fundamental gap of the GaAs host material, namely, MV above the valence band edge and MC below the conduction band edge. The density distribution shows that these states MV and MC are localized at the InAs layer. We determine the distance between MV and the valence band edge as well as that between MC and the conduction band edge. In addition, the thermal activation energies EMV and EMC and the photo cross section σno of the state MC are measured. The value of the optical threshold derived from σno agrees well with the calculated onset of a continuum of conduction band states. Our calculations are based on transferable pseudopotentials for InAs and GaAs. The lattice relaxation of the InAs layer is included consistently, and the influence of the strain and the exchange of atomic pseudopotentials is discussed.
Optimization processes of giant magnetoresistance characteristic for mixed magnetic multilayers
Authors: Schepper W. , Hütten A. , Reiss G.
Published: July 2002

Up to now, giant magnetoresistance (GMR) multilayers usually consist of only one type of double layer (e.g., permalloy/copper). In this work, we report on results obtained on mixed systems, i.e., multilayers containing simultaneously the first and second maximum of the antiferromagnetic coupling. Both a phenomenological numerical approach as well as experimental results demonstrate, that such systems can be used for tailoring new shapes of GMR curves.
Transmission electron microscopy structure and platinum-like temperature coefficient of resistance in a ruthenate-based thick film resistor with copper oxide
Authors: Jiang J. C. , Crosbie Gary M. , Tian W. , Cameron K. K. , Pan X. Q.
Published: July 2002

As an alternative to thin-film platinum temperature sensor elements, thick film resistor ones are of interest for circuits which can withstand a near-engine environment. From a pyrochlore paste (DuPont 5091D), a close match is obtained (after firing) to the positive temperature coefficient of resistance (TCR) of Pt. Within the glassy matrix during 850 °C firing, needle-like RuO2 grains grow by a mechanism consistent with periodic bond chain theory. The acicular growth habit is attributed to a Cu2O additive, which is assumed to oxidize upon firing. The needles provide direct paths for metallic conduction and a characteristic positive TCR to the thick film in spite of having a low RuO2 volume fraction.
On the classical path method using Delves coordinates: Asymptotic solution for time-dependent amplitudes
Authors: Gilbert R. D. , Muckerman J. T.
Published: July 2002

An analytic perturbation series procedure is developed for evaluating transition amplitudes in an adiabatic basis throughout the asymptotic region of a molecular collision process described in Delves coordinates. This procedure is used in conjunction with the classical path method in a treatment of collinear atom-harmonic oscillator collisions. The importance of the new procedure in the application of the classical path method to reactive scattering is discussed.
Direct vs redistributed fluorescence of supercooled molecules: The onset of intramolecular vibrational redistribution
Authors: Mukamel Shaul
Published: July 2002

The observability and relative yield of distinct ‘‘direct’’ and ‘‘redistributed’’ components in the fluorescence of supercooled molecules is analyzed. The static and dynamic effects of anharmonicities underlying the redistributed component and their implication for experiments which are both time and frequency resolved, are specified. Analysis of the recent picosecond beam studies of Felker and Zewail in Anthracene shows evidence for a selective anharmonic coupling scheme in which the doorway state is coupled to a few harmonic states which are sequentially coupled to the other harmonic states.
Local and hyperspherical mode approximations to resonances in collinear atom–diatom reactions
Authors: Kulander K. C. , Manz J. , Schor H. H. R.
Published: July 2002

A collinear, symmetric reactive scattering system which exhibits a highly oscillatory reaction probability as a function of collision energy has been studied. The A+BA model consists of two coupled Morse oscillators. The peaks in the reaction probability are due to resonances which have been analyzed using local and hyperspherical mode bound state expansions. In a small range of collision energy, resonances are found some of which are local and some hyperspherical in character. Resonance energies calculated using bound state techniques are compared to those from exact quantum mechanical scattering calculations.
Molecular jet study of van der Waals complexes of flexible molecules: n-Propyl benzene solvated by small alkanesa)
Authors: Law K. S. , Bernstein E. R.
Published: July 2002

A combination of atom–atom potential calculations and experimental molecular jet spectroscopic studies is used to elucidate the geometry and binding energy of n-propyl benzene/methane, ethane, and propane clusters. Two color time-of-flight mass spectroscopy data and calculations are presented for both trans and gauche configurations of n-propyl benzene with up to three hydrocarbon molecules of solvation. Cluster shifts and geometry are treated in detail for the observed and calculated systems. Solvation, as observed in the clusters, seems to have little effect on the geometry of the solute in this instance. Alkyl chain motion is also discussed for the n-propyl benzene isolated molecule.
Effect of bending potential on calculated product-state distributions for the reaction H+D2 → HD+D
Authors: Blais Normand C. , Truhlar Donald G. , Garrett Bruce C.
Published: July 2002

We have calculated trajectories for H+D2 → HD+D using two potential energy surfaces that are identical for collinear geometries but differ for bent geometries. Weakening the bend potential has a negligible effect on the shape of the opacity function and product vibrational distribution but shifts the final rotational distribution upwards.
The direct experimental determination of a dipole–dipole cross-correlation spectral density
Authors: Brondeau J. , Canet D. , Millot C. , Nery H. , Werbelow L.
Published: July 2002

A novel method for ascertaining certain dipolar cross-correlation spectral densities is described in detail. This method is based upon the inherent simplicity associated with the perturbation-initial-response characteristics of various multiplet or multispin magnetizations. Furthermore, it is demonstrated that suitable multipulse sampling sequences can be devised which effectively sequester conventional nuclear magnetization and, hence, facilitate the study of multispin magnetization. The outlined methodology is applied to determine a three-spin cross-correlation spectral density for an adamantyl methylene spin grouping.
Ab initio self-consistent-field studies of ClNOx (x=1–3)
Authors: Bhatia Subhash C. , Hall John H.
Published: July 2002

Ab initio self-consistent-field (SCF) studies of the electronic charge distributions of isomers of ClNOx (x=1–3) are reported. Three basis sets are employed. The first is a 4-31G basis. The second, only in the ClNOx (x=1, 2) calculations, employed a near Hartree–Fock basis with d orbitals on all centers and is designated PDZ*. The third basis set is a near Hartree–Fock basis, with d orbitals only on the chlorine atom, and is designated PDZ. The geometry of each isomer was optimized at the 4-31G level. Ionization potentials are calculated from Koopmann’s theorem and from the ΔSCF between the neutral molecule and the positive ion. Dipole moments are also reported. The resulting calculations indicate that the ClNO2 isomers are of comparable electronic stabilities. The calculations for ClNO3 indicate that ClONO2 is 16.0 kcal/mol more stable, electronically than ClOONO. The planar structure for ClONO2 is favored over the nonplanar structure by 80 kcal/mol.
Density profiles and surface tension of spherical interfaces. Numerical results for nitrogen drops and bubbles
Authors: Guermeur Robert , Biquard Francis , Jacolin Christian
Published: July 2002

The effect of droplet size on surface tension is discussed. The inhomogeneous fluid in the interface is described with the help of a stress tensor in the frame of gradient theory. Numerical results are given for nitrogen drops and bubbles. For bubbles, the surface tension γ is always lower than for a plane interface and decreases as the sphere radius decreases. The behavior of drops is more complicated. Their surface tension γ is not a monotonic function of the radius. As the curvature increases γ, increases and reaches a maximum for R≃35 Å, then it decreases rapidly. Minimum energies of drops and bubbles formation are also given.
Effect of pressure on the Raman and electronic absorption spectra of naphthalene- and perylenetetracarboxylic dianhydrides
Authors: Jayaraman A. , Kaplan M. L. , Schmidt P. H.
Published: July 2002

The effect of pressure on the optical absorption and Raman spectra of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and on the optical absorption edge in 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was investigated, using a diamond anvil cell. In NTCDA the absorption edge shifts red by about 8000 cm−1 in the range 0–180 kbar and in PTCDA by about 3000 cm−1 in the range 0–60 kbar pressure. At the upper limit of pressure the materials turn black, but on release of pressure the shifts were perfectly reversible. In the case of NTCDA, where both absorption and Raman data (up to 70 kbar) were obtained, the shift in the electronic absorption has been related to a parameter proportional to the intermolecular force constant. The latter was obtained from the pressure shift of an external mode Raman frequency, which showed the largest pressure dependence. The shift, which is nonlinear with pressure, becomes linear when plotted against the square of this frequency, normalized to its ambient pressure value [ν(p)/ν(0)]2. To our knowledge, this is the first time a combined absorption and Raman study has been performed on an organic system to establish such a direct relationship between electronic absorption and intermolecular interaction. No pressure-induced phase transition was encountered in NTCDA up to 180 kbar and in PTCDA up to 60 kbar, the limits of pressure in the present study. Earlier explanations for the pressure-induced red shifts in aromatic systems are briefly discussed.
Vibrational spectra of epoxypropane
Authors: Polavarapu P. L. , Hess B. A. , Schaad L. J.
Published: July 2002

Vibrational band assignments for epoxypropane were derived from experimental vibrational spectral data and ab initio calculations with a 6-31G basis. Using the ab initio normal coordinates and bond moment theory, vibrational circular dichroism (VCD) parameters for (S)-epoxypropane were calculated and compared to experimental VCD observations.
Exponent optimization by uniform scaling technique
Authors: Koga Toshikatsu , Kobayashi Hisayoshi
Published: July 2002

A simple optimization method for orbital exponents embedded in a molecular wave function is proposed by combining the uniform scaling technique and the energy gradient method with respect to nuclear positions. No additional gradient calculations are needed. In this method, all the exponents are optimized through a single common scale factor and the resulting wave function satisfies the virial theorem. Illustrative examples are given for several simple molecules.
State-resolved rotationally inelastic cross sections of CaCl (X 2Σ+) with polar molecule targets
Authors: Dagdigian P. J. , Bullman S. J.
Published: July 2002

State-to-state rotationally inelastic integral cross sections for the scattering of Ca35Cl(X 2Σ+) by the polar molecules HCl, HCN, and SO2 have been determined. CaCl in the incident N=2 e level is prepared by electric quadrupole state selection of a supersonic beam, and final states are detected by single-mode cw dye laser fluorescence excitation in the B 2Σ+–X 2Σ+ band system. The cross sections clearly display a propensity for conservation of fine-structure level, i.e., e → e, in collisional rotational transitions, predicted by Alexander [J. Chem. Phys. 76, 3637 (1982)] from examination of the fully quantum description of the dynamics. The magnitudes of the cross sections are also found to be large, as expected from the long range of the electrostatic dipole–dipole interaction. However, in spite of the relatively high collision energy, the sudden approximation considerably overestimates the cross sections and does not explain their nonmonotonic ordering with target dipole moment. The adiabatically corrected sudden (ACS) theory, on the other hand, satisfactorily explains the absolute magnitudes of the cross sections and, more importantly, provides an explanation for the dependence on target molecule properties. The peculiar dependence of the cross sections on target molecule dipole moment was found to be a result of differences in the adiabatic damping of the sudden cross sections due to the energy level spacings, and hence rotational constants, in the target molecule.
Exact solution of a deterministic model for isomerization kinetics. Effect of activation energy
Authors: Elskens Y. , Nicolis G.
Published: July 2002

Isomerization kinetics is studied on a one-dimensional gas model with deterministic transitions involving an activation threshold. The one-particle functions are found to decay nearly exponentially and their decay is compared to that of phenomenological theories. In the long-time regime, higher correlations present long tails indicating a strongly non-Markovian behavior. The effect of the activation energy in the general behavior is discussed.
Rotational resolution of the NeBr2 B–X 10–0 transition
Authors: Thommen Fritz , Evard Dwight D. , Janda Kenneth C.
Published: July 2002

The fluorescence spectrum of NeBr2 was recorded using a dye laser as the excitation source. The rhodamine 6G dye was pumped with an Ar2 laser to obtain a bandwidth of 0.001 cm−1 tunable over 1 cm−1 segments. The 1 cm−1 segment was divided into 1024 data points and was recorded in 9 min sequences. The spectra are shown in Fig. 1. (AIP).
General theory of dynamic light scattering from cylindrically symmetric particles with translational-rotational coupling
Authors: Aragón S. Sergio R. , Pecora Robert
Published: July 2002

The general solution to the scattered electric field time autocorrelation function for a dilute system of cylindrically symmetric, optically anisotropic particles undergoing coupled translational-rotational diffusion is presented. The solution is exact within the Rayleigh–Gans–Debye approximation. The scattered time autocorrelation function is an infinite series of decaying exponentials with time constants τ−1Ms =q2D+[s(s+1)+wMs(γ)−γ/3]Θ⊥, (M=0,1,2; s=0,1,2, ⋅ ⋅ ), containing both translational and rotational diffusion coefficients and spheroidal harmonic eigenvalues. The latter depend on the coupling parameter γ=q2 (ΔD)/(Θ⊥), where ΔD is the anisotropy in the translational diffusion coefficient. The dynamical terms are weighted by structure factors that depend on scattering geometry, the particle geometry, and the coupling parameter. These structure factors are given for arbitrary geometries and polarization of the radiation. In general, the weights for two to six exponentials will be significant depending on the scattering geometry and particle size. The domain of applicability of the theory is also discussed.
Conformational properties, torsional potential, and vibrational force field for methacryloyl fluoride: An a
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o investigation
Authors: Laskowski Bernard C. , Jaffe R. L. , Komornicki Andrew
Published: July 2002

We have examined the structure, torsional potentials, vibrational spectra, and harmonic force fields for the s-cis and s-trans isomers of methacryloyl fluoride with the aim of understanding some of the conformational properties of these molecules and their relationship to macroscopic polymer properties. The calculations have been performed at the SCF level with a split valence basis set. We find the structure to be in reasonably good agreement with experiment and as expected find the structural variations between the two isomers to be slight. However, we do suggest a reexamination of the carbonyl geometry in light of our studies. Our calculations show the energy difference between the s-cis and the s-trans isomers to be less than 1 kcal/mol at both the split valence and the split valence polarized levels, favoring the s-trans form. An examination of the torsional potential reveals that a rigid rotor approximation provides an adequate description of the motion of either the methyl group, or of the COF moiety. For the methyl group we find a barrier of 1.5 kcal/mol, with the preferred conformation having the hydrogen atom eclipsed with respect to the carbon–carbon double bond. Our best calculations show that the torsional barrier to interconvert the s-trans to the s-cis form is 7.0 kcal/mol, somewhat higher than the recent experimental values of 6.5 and 5.1 kcal/mol. This study also points out the need to include the difference in zero point energies between reactants and the transition state when evaluating torsional potentials. Our calculated vibrational spectra show the similarities and differences between these two isomers, and suggest areas where the assignments should be further examined. In particular, we suggest that some of the low frequency torsional modes deserve further scrutiny. A fit of our data to a three term Fourier series shows that we are able to reproduce the experimentally derived barrier, even though a direct determination shows that the predicted barrier lies higher.
Continuous wave optically pumped iodine monofluoride B 3Π(0+) → X 1Σ+ laser
Authors: Davis Steven J. , Hanko Leonard , Wolf Paul J.
Published: July 2002

A continuous wave optically pumped iodine monofluoride laser operating on the B 3Π(0+) → X 1Σ+ system is described. The laser operated on a series of rovibronic lines originating from v′=2–5. By tuning the dye laser pump source over a single rovibronic line, spectral structure was produced on the IF laser output that was analyzed and found to be consistent with hyperfine structure in IF. Hyperfine coupling constants were determined in this analysis. Implications for a chemically pumped IF laser are also presented.
The linearly driven parametric oscillator: Its collisional time-correlation function
Authors: Gazdy Bela , Micha David A.
Published: July 2002

A time-correlation function is explicitly constructed for the linearly driven parametric oscillator. The model is applied to atom–diatomic collinear collisions with a Boltzmann distribution of the initial states of the diatomic molecules. Illustrative numerical calculations have been performed for He–H2 scattering in a semiclassical approximation. The Fourier coefficients of the time-correlation functions can be readily calculated, and provide transition probabilities. A pronounced difference is found between results for the harmonic oscillator and the parametric oscillator models of He+H2.
Dipole (electric field) and quadrupole (field gradient) polarizabilities of hydrogen, nitrogen, and acetylene from the application of derivative Hartree–Fock theory
Authors: Dykstra Clifford E.
Published: July 2002

The electrical polarizabilities of a molecule are of potential importance in the molecule’s response to an applied field or in the interaction with other proximate molecules. Derivative Hartree–Fock (DHF) theory, which is an open-ended, uniform procedure for calculating properties corresponding to derivatives of the electronic energy, has been applied in obtaining electrical polarizabilities of hydrogen, nitrogen, and acetylene. In order to provide a more complete description than previously available, this has been carried through the third level of differentiation with respect to electric field and field gradient components, thereby yielding dipole and quadrupole hyperpolarizabilities. Extensive basis set tests performed on hydrogen reinforce the established need for extended sets with diffuse functions, and for balance in the flexibility of the s, p, d,...type functions on each center. DHF is well suited to the use of such large basis sets and in the case of acetylene, a basis of 100 functions was used to calculate its electrical properties.
Method for the determination of parametric potential energy surfaces by the direct inversion of inelastic scattering data
Authors: Clary D. C.
Published: July 2002

A direct method is described for inverting inelastic scattering data to obtain parameters in potential energy surfaces. A scattering perturbation technique is adapted to obtain a set of equations for the parameters. These equations are solved iteratively by a repeated solution of the close-coupled equations. The technique is used to determine C6 coefficients in pair potentials for He+CH3F by inverting experimental vibrational relaxation rate constant data. The azimuthal and vibrational close-coupling, rotational infinite-order sudden method is used in these computations.
Theoretical study of the bonding in CuH and Cu2
Authors: Raghavachari Krishnan , Sunil K. K. , Jordan K. D.
Published: July 2002

The configuration interaction, Möller–Plesset perturbation theory, and coupled-cluster procedures are utilized to determine the dissociation energies, vibrational frequencies, and bond lengths of CuH and Cu2. Good agreement is found between the theoretical and experimental values for these properties. Triple and quadruple excitations and the inclusion of diffuse f functions in the basis set are found to be important for quantitative predictions. A CCD+ST(CCD) approximation, in which the contributions of single and triple excitations are evaluated using the coupled-cluster doubles (CCD) wave function, is found to give a value of De(Cu2) within 0.1 eV of the experimental value when a correction for a relativistic effects is included.
Multiply enhanced site selective CARS spectroscopy
Authors: Steehler J. K. , Wright J. C.
Published: July 2002

Three tunable lasers are used to perform site selective coherent anti-Stokes Raman (CARS) spectroscopy in pentacene:p-terphenyl crystals at 2 K. The vibrational and vibronic levels of pentacene in the individual substitutional sites of p-terphenyl can be selectively examined by matching the resonances of a particular site. The signals from a site and the selectivity between sites are much higher than CARS performed with two tunable lasers. The spectra are dominated by lines from processes where the vibrational and vibronic states involved in the four-wave mixing are associated with the same molecular mode. There are also important lines from processes where different vibrational and vibronic modes are involved in the nonlinear mixing. The intensities of lines from the resonant site are strongly dependent on the laser energy because of saturation of the electronic transition.
Evaluation of microcanonical rate constants for bimolecular reactions by path integral techniques
Authors: Thirumalai D. , Garrett B. C. , Berne B. J.
Published: July 2002

An expression for the microcanonical rate constant that can be conveniently evaluated by path integral techniques is proposed. The efficacy of the method is illustrated by obtaining accurate transmission probabilities as a function of energy for a particle tunneling through an Eckart barrier. The application of the method to systems involving many degrees of freedom is discussed.
Emission spectra of SiH(A 2Δ→X 2Π) and SiCl2(Ã 1B1→X̃ 1A1) in the VUV photolyses of silane and chlorinated silanes
Authors: Washida N. , Matsumi Y. , Hayashi T. , Ibuki T. , Hiraya A. , Shobatake K.
Published: July 2002

Vacuum UV photolyses of silane and chlorinated silanes were investigated by using rare gas resonance lamps. Strong emissions, from the A 2Δ→X 2Π transition of SiH and the 1P0→1D2 transition of Si were observed in the photolysis of SiH4 by Ar and Kr resonance lamps. It was suggested that the threshold energies for the appearance of both emissions were lower than the values obtained by the electron impact of SiH4 reported by Perrin et al. A new broad unstructured emission band in the region 300–400 nm was observed in the photolysis of SiH2Cl2 and SiHCl3 by Ar, Kr, and Xe lamps. The band was attributed to the Ã 1B1→X̃ 1A1 transition of SiCl2 radicals from the measurement of the appearance energy of the emission by using synchrotron orbital radiation.
Electron T1 measurements in short-lived free radicals by dynamic polarization recovery
Authors: Bartels D. M. , Lawler R. G. , Trifunac A. D.
Published: July 2002

A dynamic polarization recovery method for measurement of electron spin T1 relaxation times in free radicals in liquids is described, which is valid even in the presence of chemically induced dynamic electron polarization (CIDEP) and fast chemical decay of the radicals. The method is based on pulsed microwave perturbation and detection of transient magnetization following radical creation in a short pulse. Analysis of the experimental approach and a theoretical description of the method is presented together with a detailed discussion of the advantages and the limitations of the technique. Electron T1 measurements are presented for 14 short-lived free radicals generated in aqueous solution. The magnitudes of the observed relaxation times, which range from 0.1 to 4 μs, are discussed within the framework of current theories of relaxation for small radicals in liquids. It is tentatively concluded that the spin rotation mechanism is responsible for the very short T1’s in this series of radicals.
Neutron diffraction structural study of pyroelectric Sr(NO2)2⋅H2O at 294, 100, and 20 K
Authors: Lundgren J.-O. , Kvick Å , Liminga R. , Abrahams S. C.
Published: July 2002

Strontium nitrite monohydrate [Sr(NO2)2⋅H2O] has been studied at 294, 100, and 20 K by neutron diffraction. Integrated intensities of 2958 (294 K), 4239 (100 K), and 2154 (20 K) reflections were measured at the Brookhaven National Laboratory high flux beam reactor, resulting in 2068 (294 K), 2030 (100 K), and 1934 (20 K) independent structure factors. Structural refinement in monoclinic space group P21 led to R(F)=0.029 (294 K), 0.019 (100 K), and 0.034 (20 K). Lattice constants at 295 K are a=12.5831(4), b=8.94941(15), c=4.4860(2) Å, β=99.111(4)°; at 100 K, a=12.539(2), b=8.909(1), c=4.475(1) Å, β=99.086(20)°; and at 20 K, a=12.542(2), b=8.901(1), c=4.472(1) Å, β=99.030(20)°.

The expansivity of all four lattice parameters is nonlinear, with α1=32.8×10−6 K−1, β1=76×10−9 K−2; α2=31.6×10−6 K−1, β2=44×10−9 K−2; α3=15.6×10−6 K−1, β3=15×10−9 K−2; α4=−2.8×10−6 K−1, β4=−21×10−9 K−2 for αTi =α295i [1+αiΔT+βi(ΔT)2], ΔT=T−295 K. The mean-square amplitude of Sr varies linearly with temperature between 20 and 294 K, and extrapolates to a zero-point value of 0.0010(2) Å2. A survey shows that atoms with masses greater than about 80 have similar zero-point amplitudes which increase toward the maximum exhibited by H, with its zero-point amplitude of about 0.023 Å2, as the atomic mass decreases. The coordination (9 and 10) of the two independent Sr2+ ions remains unchanged with temperature: the coordination shell radius decreases on average by 0.012 Å from 294 to 20 K. Comparison with previous x-ray structural results on Sr(NO2)2⋅H2O shows the latter are influenced by scattering from the nitrogen atom lone-electron pair. Small but significant differences in N–O distances among the four independent NO−2 ions are detected at 294 K (0.020 Å) and at 20 K (0.017 Å). The mean N–O distance at 20 K for all four ions is identical at 1.253–1.254 Å. The maximum atomic displacement between 294 and 20 K is that by a nitrite ion oxygen, of 0.045 Å.
Dynamics of inelastic H+D2 collisions: Product quantum state distributions at 1.1 and 1.3 eV collision energy
Authors: Gerrity Daniel P. , Valentini James J.
Published: July 2002

We have measured the quantum state distributions of rotationally and vibrationally excited D2 formed in inelastic H+D2 collisions at 1.1 and 1.3 eV, under effectively single-collision conditions. The distributions are derived from highly time-resolved CARS spectra of D2. The hydrogen atoms are generated by laser photolysis of HI in an HI/D2 gas mixture. The D2 produced in these inelastic collisions is less rotationally and vibrationally excited than the HD produced in reactive H+D2 collisions at the same energies. The results also show that at 1.3 eV the H+D2 cross section for producing vibrationally excited D2 is about one-half the cross section for producing vibrationally excited HD. The measured D2 quantum state distributions are in excellent agreement with distributions derived from quasiclassical trajectory calculations on an ab initio H3 potential surface. However, the quasiclassical trajectory calculated ratio of the vibrationally inelastic nonreactive cross section to the vibrationally nonadiabatic reactive cross section is about 1.5.
A variation-perturbation method for atomic and molecular interactions. II. The interaction potential and van der Waals molecule for Ne–HF
Authors: Gallup G. A. , Gerratt J.
Published: July 2002

A recently developed variation-perturbation theory for calculating intermolecular forces has been applied to the Ne–HF system for fixed H–F distances. The maximum well depth is 0.49 kJ/mol (41 cm−1) for a linear configuration with the H between the Ne and F and the Ne–H distance approximately 5.5 bohr. A secondary minimum of depth 0.24 kJ/mol (20 cm−1) was found for the other linear configuration at a Ne–F distance of about 7.0 bohr. A saddle point, about 0.20 kJ/mol (17 cm−1) deep, for the T-shaped configuration is present also at about 7.0 bohr. The potential has been used to calculate some of the bound state internal energies of the Ne–HF van der Waals molecule. The dissociation energy is 15 cm−1 from the lowest state.
CO+(A–X) chemiluminescence in reactions of C+ ions with CO2, NO2, and N2O at thermal energy
Authors: Tsuji M. , Susuki T. , Mizukami K. , Nishimura Y.
Published: July 2002

Ultraviolet and visible chemiluminescence have been observed from the reactions of C+ with CO2, NO2, and N2O in a flowing afterglow. The CO+(A–X) chemiluminescence from v′=0–2 was identified in the C++CO2 reaction, while chemiluminescence from levels up to v′=11 was found in the C++NO2 and N2O reactions. The relative vibrational populations of CO+(A) have been determined and are compared with statistical prior distributions. The experimental data show that only about 10% of the total available energy is deposited in the CO+(A) vibration for all cases. The relative rate constants for formation of CO+(A) in the C++CO2, O2, NO2, and N2O reactions are estimated to be 1.0:9.8:18:60, respectively. In the C++N2O reaction, CN(A–X,B–X) chemiluminescence was also observed: the CN(B–X) system is produced exclusively as a result of rotational perturbations between the B and A states. Adiabatic correlation diagrams have been used to explain the specific formation of the emitting excited species.
Three-dimensional quantum calculation of the vibrational energy levels of ozone
Authors: Atabek O. , Miret-Artes S. , Jacon M.
Published: July 2002

The Fox–Goodwin propagator associated with an iterative matching procedure is used for the exact quantum mechanical calculation of the vibrational-rotational energy levels of a triatomic molecule. The method starts with the specification of a potential energy surface monitoring the relative motion of the atoms and utilizes the well-known close coupled equations technique of molecular scattering theory formulated in a body-fixed reference frame. The number of equations is optimized by the choice of some judicious local basis. Accurate values for the lowest energy eigenvalues obtained for ozone molecule in its fundamental electronic state and corresponding to zero total angular momentum are presented and compared with results arising from variational and spectral methods. The method seems to be an accurate tool not only for bound states calculations but also for resonances occuring in photodissociation processes.
Semiclassical wave packet studies of elastic and inelastic atom–surface scattering from a 3D model surface
Authors: Smith Charles B. , Raff Lionel M. , Agrawal P. M.
Published: July 2002

The semiclassical wave packet method for the investigation of elastic and inelastic gas–surface scattering is extended to the calculation of diffraction patterns and Debye–Waller factors for scattering from a three-dimensional surface. Application of the method to a model 3D surface yields energy transfer coefficients in good accord with our previous 2D semiclassical results and with the experimental molecular beam data. The calculated final-state momentum and energy distributions are highly structured and show that inelastic effects dominate the scattering process at high surface temperatures. At Ts=300 K, the scattering is found to be more nearly elastic. The structural features of the distributions are shown to be correlated with the power spectrum for the lattice motion. Diffractive scattering is evident even at Ts=1500 K. At Ts=300 K, the diffraction is much more pronounced due to the increased elasticity of the collision and a larger Debye–Waller factor. The positions of the calculated diffraction peaks are found to be in excellent accord with that expected from the known surface grating and distribution of incident wavelengths. The dependence of the computed Debye–Waller factors upon Ts, the surface Debye temperature and the gas-surface potential well depth is found to be accurately described by the simplified expressions developed by Beeby and by Comsa et al. In general, the method is shown to be well suited to the study of elastic and inelastic gas–surface processes.
Collisional relaxation of vibrationally excited NO+(v) ions
Authors: Federer W. , Dobler W. , Howorka F. , Lindinger W. , Durup-Ferguson M. , Ferguson E. E.
Published: July 2002

Vibrational quenching rate constants have been measured for NO+(v) ions in collision with 17 neutral molecules. The dependence of the quenching rate constants on collision energy have been determined from near thermal energy up to ∼ 1 eV in some of these cases. The experimental results can be satisfactorily interpreted using a model of complex formation followed by vibrational predissociation with a rate constant of the order of 109–1010 s−1.
Angle resolved photoelectron study of resonances near the Si 2p edge of the Si(CH3)4 molecule
Authors: de Souza G. G. B. , Morin P. , Nenner I.
Published: July 2002

Photoelectron spectra of tetramethylsilane, were measured at selected photon energies in the vicinity of the Si 2p edge, using synchrotron radiation. In addition to known valence and core Si 2p bands, three LVV Auger lines (69, 76, and 80 eV electron energy) were observed for the first time. Partial and differential cross sections for the Si 2p band and two of the Auger lines have been measured at several photon energies from the Si 2p onset up to 135 eV. An intense resonance is evident in the Si 2p continuum as well as in the LVV Auger decay channels. Its position, right above threshold, accounts for only a part of the absorption feature. Another maximum, already seen in absorption around 124 eV, may be a shape resonance associated with the Si 2p continuum.
Quantum mechanical reactive scattering via exchange kernels: Infinite order exchange on a grid
Authors: Dardi Peter S. , Shi Shenghua , Miller William H.
Published: July 2002

A general methodology is described for carrying out quantum mechanical reactive scattering calculations. The approach is based on Miller’s [J. Chem. Phys. 50, 407 (1969)] formulation of quantum reactive scattering in which rearrangement processes (i.e., chemical reactions) are characterized by nonlocal exchange interactions that couple different arrangements. The specific approach described here requires that nonreactive coupled channel calculations first be carried out separately in the various arrangements—this is a relatively standard inelastic scattering problem—and the non-local exchange interactions are then discretized on a grid in (translational) coordinate space; straightforward linear algebra calculations then lead to the scattering matrix. (Discretizing the exchange kernels on a grid is suggested because exchange is very short range.) The attractiveness of the overall method is its straightforwardness, generality, and special suitability for the vector-processing character of modern supercomputers. Application to a standard test problem (the collinear H+H2 reaction) shows that it is numerically stable over a wide range of collision energies.
Path integral approach to multiparticle systems: The sudden representation
Authors: Chan C. K. , Kouri D. J.
Published: July 2002

The recently developed (energy) sudden representation of the Schrödinger propagator is examined in conjunction with the path integral method. The perturbation expansion of the propagator in this representation (with the sudden approximation as the zeroth order term) is easily understood using Feynman diagrams. The zeroth order term is a form involving only sudden paths (i.e., paths resulting from the sudden approximation). Each higher order term is a series of sudden paths which are connected to one another due to the nonsudden effects of the dynamics. The sudden representation, and in particular its perturbation expansion, is also used to study the bath effects in many body systems which are expressed in the form of influence functionals in the path integral formalism. In our treatment, the bath coordinates are assumed to be the slow coordinates. The zeroth order (sudden approximation) influence functionals are expressed in a very simple form; they involve only an ordinary integral over the bath coordinates. Finally, to illustrate the approach, a harmonic oscillator coupled linearly to an unspecified primary system is used as a simple model bath. The reduction of the exact influence functional to the sudden approximation form is also considered.
Coupled dynamics between DNA double helix and hydrated water by low frequency Raman spectroscopy
Authors: Tominaga Yasunori , Shida Megumi , Kubota Kenji , Urabe Hisako , Nishimura Yoshifumi , Tsuboi Masamichi
Published: July 2002

Low frequency Raman spectra (±50 cm−1) of DNA gels from 0 to −140 °C have been obtained. A drastic spectral change near −20 °C has been observed, and this is well explained by the model of coupled dynamics between the collective vibrational mode of the DNA and the relaxational mode of the secondary hydration shell. The obtained relaxation time of the secondary hydration shell at 0 °C is τ≈4×10−12 s which is the same order as that of bulk water.
Energy and charge transfer in O+2 on O2 collisions: Effects of a ‘‘vibrational rainbow’’
Authors: McAfee K. B. , Hozack R. S.
Published: July 2002

The efficient conversion of up to eight vibrational quanta into translational energy is found to occur during O+2 –O2 collisions. The high efficiency and low deflection angle which are observed in the experiment reported are explained by the occurrence of multiple crossings of the O+2 –O2 system interaction potentials, specifically the attractive and repulsive symmetry potentials. The energy and charge transfer model evolved from the experimental data proposes that energy transfer in symmetric molecule–ion collisions takes place at very large intermolecular separations. It differs in an important way from previous concepts which suggest that impulsive momentum transfer at relatively short distances is necessary to the exchange of vibrational energy. To explain the data, a distortion of the electron cloud surrounding the colliding systems is conceived to produce charge-transfer oscillations whose frequencies at the crossing points are multiples of molecular vibration frequencies. Such resonances are similar to the more familiar rainbows often observed in molecular collisions. The ease with which energy has been found to be transferred between modes of motion in charged systems affects the thermal, optical, and other properties of plasmas.
Discrete sudden perturbation theory for inelastic scattering. I. Quantum and semiclassical treatment
Authors: Cross R. J.
Published: July 2002

A double perturbation theory is constructed to treat rotationally and vibrationally inelastic scattering. It uses both the elastic scattering from the spherically averaged potential and the infinite-order sudden (IOS) approximation as the unperturbed solutions. First, a standard perturbation expansion is done to express the radial wave functions in terms of the elastic wave functions. The resulting coupled equations are transformed to the discrete-variable representation where the IOS equations are diagonal. Then, the IOS solutions are removed from the equations which are solved by an exponential perturbation approximation. The results for Ar+N2 are very much more accurate than the IOS and somewhat more accurate than a straight first-order exponential perturbation theory. The theory is then converted into a semiclassical, time-dependent form by using the WKB approximation. The result is an integral of the potential times a slowly oscillating factor over the classical trajectory. A method of interpolating the result is given so that the calculation is done at the average velocity for a given transition. With this procedure, the semiclassical version of the theory is more accurate than the quantum version and very much faster. Calculations on Ar+N2 show the theory to be much more accurate than the infinite-order sudden (IOS) approximation and the exponential time-dependent perturbation theory.
Infrared–infrared double resonance in a supersonic molecular beam: Accurate determination of the cross section of collision induced rotational transitions in state selected NH3
Authors: Honguh Yoshinori , Matsushima Fusakazu , Katayama Ryuichi , Shimizu Tadao
Published: July 2002

A method of infrared–infrared double resonance in a nozzle beam is developed for the study of elementary processes of molecular collisions. A spectroscopic method to characterize the molecular states in the beam is also described. The NH3 molecules are prepared in a kinematically and also spectroscopically ‘‘pure’’ state and then are subjected to collisions with various species of target molecules such as NH3, CH3F, CH3Cl, and N2O. A simplified calculation of the cross sections based on Anderson–Tsao–Curnutte theory can give a fairly good reproduction of the measured values. The elimination of a systematic error in the total cross section measurements is discussed.
A microscopic model for the heteromolecular theory of nucleation
Authors: Kobraei Hamid R. , Duncan G. Comer
Published: July 2002

We have extended the microscopic model of homogeneous nucleation to the heteromolecular case. This model, interacting clusters and heteroclusters (ICH), consists of a distribution of heteroclusters and clusters. The interaction between monomers, cluster–monomer, heterocluster–monomer, and heterocluster–heterocluster are taken into account. The method of correlation functions is extended so that configuration integral of the ICH model can be calculated. The concentration of heteroclusters is derived in terms of microscopic quantities. In the limit of no interaction between clusters and heteroclusters, the heterocluster concentration is expressed in terms of monomer concentration, the chemical potential of monomers, and the internal free energy of a heterocluster. In this limit the heterocluster concentration may also be expressed in terms of the total number of ions and the internal free energy of heteroclusters. The formation energy of a heterocluster is calculated.
The effect of intermolecular potential model on the structure and conformational equilibrium of liquid n-butane
Authors: Bañón A. , Adán F. Serrano , Santamaría J.
Published: July 2002

Several Monte Carlo simulations with a sample of 125 molecules of n-butane with four Lennard-Jones centers and internal rotation, have been carried out by varying the values of ε and σ parameters of the intermolecular potential. In this way the effect of such changes on the thermodynamic, structural, and conformational properties have been studied. Although the structure remains practically unaffected by moderate variations in the Lennard-Jones parameters, nevertheless the conformational equilibrium is very sensitive to them. Also specific properties of chain molecules in the n-butane, such as the effect of the relative position of centers (external vs internal ones) and the possibility of orientational correlation have been explored. The difference between the effects of the external centers vs the internal ones can be quantified and it turns out to be significant; on the other hand the orientational correlation is very weak at room temperature and normal liquid density.
Dynamics of eigenstate transitions induced by external fields: A new approach
Authors: Milfeld Kent F. , Castillo Jose , Wyatt Robert E.
Published: July 2002

We present a new general method to obtain the dynamics of molecular eigenstates perturbed by an external field. The method uses the Davidson algorithm and the recursive residue generation method (RRGM) to obtain molecular states and dynamic information, respectively. For sparse matrices, as many as 106 basis states can be used to represent the molecule’s Hamiltonian and its perturbation.