bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite in the x-ray photoelectron spectra of metalloporphyrins
Authors: Muralidharan S. , Hayes R. G.
Published: February 2003

We have investigated the shake-up satellites in the 2p core level spectra of a number of Co(ii), Ni(ii), Cu(ii) and Zn(ii) porphyrins. Cu(ii) porphyrins have prominent satellites, although weaker than in many simple Cu(ii) complexes. Satellites in Co(ii) and Ni(ii) porphyrins are quite weak. The different intensities imply different final states in the two cases. For Cu(ii) chelates the major transition is 1b1g→2b1g and for Co(ii) and Ni(ii) chelates it is 4eg→5eg. The latter transition though possible for Zn(ii) chelates does not show up as a satellite in the experimental spectrum. We substantiate our assignment by a calculation on Cu (porphine) using the sudden approximation.
Hydrophobic hydration around a pair of apolar species in water
Authors: Pangali C. , Rao M. , Berne B. J.
Published: February 2003

The structure of ST2 water around a pair of spherical nonpolar (Lennard-Jones) particles, A1–A2, is studied as a function of pair separation, r, using a force-bias Monte Carlo technique with importance sampling. The change in the water structure (or equivalently the hydrophobic hydration) is correlated with the potential of mean force, WAA (r), determined in a previous study. It is found that the second minimum in WAA (r) corresponds to a water molecule lying between the two apolar particles. The water always maintains a ’’linear hydrogen bond’’ network and is more ordered in the neighborhood of the two spheres except possibly when they are separated by a distance corresponding to the position of the free energy barrier, that is the maximum in WAA (r).
A
b i
n
i
t
i
o calculation of the Raman intensity of the N2 molecule
Authors: Svendsen E. No/rby , Oddershede Jens
Published: February 2003

The dynamic polarizability tensor of N2 has been calculated as a function of the internuclear distance by the time-dependent Hartree–Fock method. From these data we obtain the Raman scattering intensity and the depolarization ratio. Good agreement is obtained with measured Raman intensities. The rotation–vibrational Raman spectrum is calculated from a numerical solution of the Schrödinger equation for the nuclear motion, which includes the centrifugal distortion potential. We have also examined the validity of expressing the measured Raman intensities in terms of derivatives of the invariants of the polarizability tensor.
A solution of the perturbed wave equation for vibration–vibration energy transfer
Authors: Shin H. K.
Published: February 2003

An approximate solution of the time dependent wave equation for the interaction of two harmonic oscillators is obtained for an arbitrary form of the perturbing force. For H2+H2 vibration–vibration energy exchange probabilities obtained from the solution are shown to be in good agreement with the exact quantum results. The applicability of the solution to the study of the temperature dependence of energy exchange processes is also discussed.
Electron attachment to N2O at pressures near one atmosphere
Authors: Shimamori Hiroshi , Fessenden Richard W.
Published: February 2003

Electron attachment to N2O in pure N2O and in several mixtures has been studied by microwave conductivity at pressures to above 1 atm. Ionization was by pulse radiolysis. The values of effective two-body rate constant exceed those predicted by the usual two-step, three-body mechanism and in several cases exceed the value of 5.5×10−13 cm3/molecule sec attributed to the first step of such a mechanism. This behavior is interpreted in terms of an additional mechanism that is only significant at higher pressures. It is suggested that this mechanism involves attachment to van der Waals complexes of N2O with the other molecules. A near zero value of activation energy supports this mechanism. Certain quantitative aspects are discussed.
Electron attachment to perfluorocarbon compounds. III. Fragmentation of aliphatic perfluorocarbons of interest to gaseous dielectrics
Authors: Sauers I. , Christophorou L. G. , Carter J. G.
Published: February 2003

Resonance nondissociative and dissociative attachment of slow electrons (0–12 eV) to the perfluorocompounds 2-C4F6, c-C4F6, 1,3-C4F6, c-C4F8, and 2-C4F8 have been studied using a time-of-flight mass spectrometer. All five compounds capture thermal energy electrons and form long-lived parent negative ions with autodetachment lifetimes, τa, equal to 6, 7, 9, 6, and 10×10−6 sec for c-C4F6−*, 1,3-C4F6−*, 2-C4F6−*, c-C4F8−*, and 2-C4F8−*, respectively. Except for 1,3-C4F6, the yield for the parent negative ions of these perfluorocarbons was more than a factor of 10 larger than that of the fragment ions. The following fragment negative ions were detected: 2-C4F6: F−, CF3−, C3F3−; c-C4F6: F−, C3F3−, C4F5−; 1,3-C4F6: F−, CF3−, C3F3−, C4F4−; c-C4F8: F−, CF3−, C2F3−, C3F5−; and 2-C4F8: F−, CF3−, C2F3−, C3F3−, C3F5−*, C4F6−*, C4F7−*, (where the asterisk indicates that these fragment ions were found to be long-lived metastables with τa values equal to 70, 17, and 7×10−6 sec, respectively). Groups of negative ion resonance peaks were found in the 0–2 eV and 4–6 eV electron impact energy range. Fragmentation patterns indicate that multiple decomposition proceeds via common negative ion states of C4Fx−* (x = 6 or 8). Fragment ions resulting from multiple bond cleavage and molecular rearrangement in the C4Fx−* systems were observed as well as ions resulting from direct cleavage. From the appearance onsets of some of the fragment ions we determined ΔHf(C3F3−) = −4.4 eV, ΔHf(2-C4F6) = −9.8 eV, E.A. (C2F3) ? 1.6 eV, E.A. (C3F5) ∼3.0 eV and other thermochemical data. The relevance of this work to the decomposition of dielectric gases is discussed.
Electron correlation and basis set effects in unimolecular reactions. A study of the model rearrangement system N2H2
Authors: Parsons Craig A. , Dykstra Clifford E.
Published: February 2003

As a model for simple 1, 2 shift rearrangements, N2H2 has been studied with ab initio wave functions at several levels of theory. Equilibrium structures for aminonitrene, trans-diimide, and cis-diimide and transition state structures for the two rearrangement reactions that interconvert the isomers were carefully determined so as to isolate basis set and electron correlation effects on the structure predictions. An examination of the changes in the calculated electron density between wave functions from different levels of treatment is presented. The self-consistent electron pairs (SCEP) method was used to handle the large correlated wave functions obtained in this study. With the largest basis set (TZ+2P) used, and with SCEP wave functions spanning a space of up to 176 000 configurations, the following energies relative to trans-diimide were found: 7.2 kcal for cis-diimide, 55.1 kcal for the trans to cis-diimide barrier, 24.5 kcal for aminonitrene, and 82.6 kcal for the trans-diimide to aminonitrene barrier. The system was found to be planar in all structures.
Quantum corrections to the equation of state of a binary mixture of hardspheres and square-well molecules
Authors: Singh N. , Sinha S. K.
Published: February 2003

The ’’modified’’ Wigner-Kirkwood method is applied to a binary mixture. The general expressions are given for the second and third virial coefficients of the equation of state. The theory is applied to evaluate the first two quantum corrections to the second and third virial coefficients of a mixture of hard spheres and square-well molecules. This work generalizes the earlier results on single-component fluids.
Quasiclassical calculations of one-dimensional potential parameters of the hydrogen migration in m
e
s
o-tetraphenylporphine from experimental tunnel rates
Authors: Limbach Hans-Heinrich , Hennig Jürgen
Published: February 2003

The migration of the two inner hydrogen atoms of meso-tetraphenylporphine (TPP) between the four nitgrogen atoms proceeds by ground state tunneling and by tunneling between the first excited degenerate NH-stretching states separated by the barrier. The experimental tunnel rates, measured previously by dynamic NMR spectroscopy, are used to compute barrier heights, Ed, and hydrogen transport distances, Δr, in quasiclassical, one-dimensional WKB approximation. Two computation methods are compared: the transmission function (TR) method and the energy splitting (ES) method. Whereas Δr is not very sensitive to the barrier type, it depends very much on the degree of cooperativity of the two-particle motion and on the computation method. There was a close agreement between the transport distances calculated from the crystallographic data of TPP and those calculated for synchronous hydrogen tunneling using the ES method. Since the TR method neglects resonance tunneling effects the transport distances calculated are too small. The calculations provide a quantitative explanation why deuterium tunneling in the two lowest ND-stretching states is too slow to be detected in the experiments. Synchronous hydrogen tunneling in TPP is then a consequence of the synchronous hydrogen motion in the potential wells.
Raman scattering from ammonia adsorbed on the amorphous silica surface
Authors: Murray Cherry Ann , Greytak Thomas J.
Published: February 2003

We have performed measurements of the perturbations of the Raman spectrum of ammonia molecules due to adsorption on the surface of porous Vycor glass. The spectrum of hydrogen bonded NH3 is studied as a function of coverage and related to changes in the substrate surface phonon spectrum. More strongly chemisorbed ammonia species are also observed. When NH3 is adsorbed on a partially deuterated surface we observe a slow chemical reaction in which the adsorbed NH3 exchanges hydrogen with a surface deuteroxyl group: we observe in addition to the changes due to NH3 interacting with OH groups the appearance of adsorbed NH2D and the near complete replacement of surface OD with OH.
Dipole–dipole interactions and Raman line shape of IR active modes of CX4 molecules in disordered phases
Authors: Yvinec M. , Pick R. M.
Published: February 2003

The influence of strong induced dipolar interactions on the Raman spectrum of the ν3 vibration of CX4 molecules is discussed in the case of dense, disordered phases. For CF4, in its plastic and its liquid phases, we show that the very peculiar two maximum spectrum can be completely reproduced by a numerical calculation which introduces only a point dipole interaction model. On the other hand, the experimental broad but featureless spectrum of CBr4 in its plastic phase cannot be explained without taking into account the high polarizability of the Br atom.
The general solution and its analyticity for growth or dissolution of a gas bubble
Authors: Tao L. N.
Published: February 2003

The isothermal diffusion of a gas bubble in an infinite liquid which is either supersaturated or undersaturated, subject to an arbitrarily prescribed initial condition and the effect of surface tension at the interface, is studied. One of the objectives of the paper is to investigate the analyticity of the solutions. For this purpose, the prescribed initial condition is considered to be a series of fractional powers of the space variable. It is found that the solution of the problem can be established in series of parabolic cylinder functions and time t. Existence and convergence of the series solutions are considered and proved. For a dissolution problem, the solution always exists. The lifetime of the bubble is determined. On the other hand, the solution of a growing bubble exists only when the initial condition at the interface is below a certain limit. A necessary and sufficient condition for the existence of solutions is established. Some numerical examples of the interfacial position are also given. On the basis of the established solutions, the analyticities of the interfacial boundary and of gas concentration are discussed. The interfacial boundary is analytic in t1/2 if, and only if, the initial condition is an analytic function of the space variable.
Dispersion forces between linear molecules
Authors: Coulon Ph. , Luyckx R. , Lekkerkerker H. N. W.
Published: February 2003

The coefficients of the R−6 and R−8 terms in the series representation of the dispersion interaction between two hydrogen molecules and between two nitrogen molecules are calculated by a simple variation method. The agreement with available calculations is encouraging.
The microwave spectrum and dipole moment of Δ6-bicyclo[3.2.0]heptene
Authors: Avirah T. K. , Cook Robert L. , Malloy Thomas B.
Published: February 2003

The rotational constants of Δ6-bicyclo[3.2.0]heptene have been derived for the ground state (in MHz: A=4419.20, B=3080.16, C=2375.33) and several excited states of the low-frequency vibrations of this molecule. The rotational constants were also derived for one monosubstituted 13C species in natural abundance. Stark effect measurements have yielded dipole moment components for the ground state of μa=0.201±0.001 D, μc=0.052±0.004 D, giving a total dipole moment of μ=0.208±0.001 D. These data are used to draw conclusions as to the conformation of this bicyclic compound.
Theory of inverse electronic relaxation
Authors: Nitzan Abraham , Jortner Joshua
Published: February 2003

In this paper we advance a theory of inverse electronic relaxation (IER) induced by high-order multiphoton excitation of collision-free molecules. The IER process involves spontaneous one-photon radiative decay of molecular eigenstates. These states originate from intramolecular scrambling of vibronic levels corresponding to the ground state electronic manifold with a discrete vibronic level (or a set of such levels) which belong to a low lying excited electronic state. For a diatomic molecule and for a small polyatomic the molecular eigenstates are excited by a coherent multiphoton excitation process, while for larger polyatomic molecules where the low electronically excited state corresponds to an intermediate level structure or to the statistical limit, incoherent multiphoton excitation of the molecular eigenstates of an ’’isolated’’ molecule prevails. Explicit expressions for the rate of IER are derived and the conditions for the observation of this novel phenomenon are established.
Re-examination of the absorption spectrum of benzene adsorbed on porous vycor glass
Authors: Aizenbud H. , Priel Z. , Scharf B.
Published: February 2003

The absorption spectra of C6H6 and C6D6 absorbed on porous Vycor glass are investigated under various conditions. Changing the surface of the adsorbent, the amount of adsorbate and the temperature at which spectra were obtained. (AIP)
Excitation of the C 3Πu state of N2 by low energy electrons
Authors: Tachibana K. , Phelps A. V.
Published: February 2003

Measurements are reported for the excitation data coefficients for N2(C3πu), using the drift tube technique. Excitation rate coefficients were obtained from measurements of the absolute intensity of 2nd position system of N2. (AIP)
The A→X system of Ni2 in argon matrices
Authors: Ahmed Fakhruddin , Nixon Eugene R.
Published: February 2003

The first observations of the vibrational frequencies of the Ni2 molecule in the grand electronic state in solid argon. (AIP)
Band structure in the C–H stretching region of the Raman spectrum of the extended polymethylene chain: Influence of Fermi resonance
Authors: Snyder R. G. , Scherer J. R.
Published: February 2003

The C–H stretching region of the Raman spectrum of the extended polymethylene chain is unexpectedly complex. This complexity is derived in large part from Fermi resonance interaction between the symmetric C–H stretching fundamental and a near continuum of overtones of the methylene &HCH scissors fundamentals. The Fermi resonance interaction equation is set up and solved for this system. Two unknown parameters are involved: the Fermi resonance interaction constant for an isolated methylene group and the frequency of the unperturbed symmetric C–H stretching fundamental. With adjusted values for these parameters and a reasonable form for the &HCH scissors dispersion curve, the observed positions and relative intensities of bands associated with the stretching fundamental can be accounted for quantitatively.
Generalized Langevin theory for gas–solid processes: Continuum elastic treatment of surface lattice dynamics
Authors: Diebold Alain C. , Adelman S. A. , Mou Chung Y.
Published: February 2003

Model studies of the systematics of elementary atom–solid energy exchange processes are presented. The studies are based on the generalized Langevin equation (GLE) classical trajectory method [S. A. Adelman and J. D. Doll, J. Chem. Phys. 64, 2375 (1976)] and on a full isotropic continuum elastic treatment of both bulk and surface solid atom velocity response functions ? (t). Within both bulk (BEM) and surface (SEM) elastic models, the solid dynamics is parameterized by two bulk properties, a Debye frequency ωD and a transverse to longitudinal sound velocity ratio Rs. The Debye model used in earlier GLE simulations is a specialization of the BEM, Rs=1.0, and thus does not include surface effects, e. g., Rayleigh waves, accounted for in the SEM. The main results of the trajectory studies are as follows: Gas–solid energy transfer efficiency within the BEM depends very sensitively on Rs (for fixed ωD). For physical Rs values ∼0.2–0.6, BEM energy transfer is often much larger than Debye energy transfer. SEM energy transfer is relatively insensitive to Rs and is, moreover, dominated by the Rayleigh mode contribution to ? (t). The SEM energy transfer is often fortuitously of comparable magnitude to Debye energy transfer.
Reorientational motions in compressed viscous fluids: Selectively deuterated glycerol
Authors: Wolfe M. , Jonas J.
Published: February 2003

The pressure and temperature dependence of the deuteron NMR spin–lattice relaxation time T1 have been measured in liquid glycerol-d4, (D2COH)2CHOH, and glycerol-d3, C3H5(OD)3, within the pressure range 1 bar to 5 kbar from −10° to 125 °C. The experimental deuteron relaxation data which reflect intramolecular reorientational motions are interpreted in terms of a Cole–Davidson distribution of correlation times. Within experimental error the distribution width β=0.44 is found to be independent of temperature and pressure. A single correlation time model and a model allowing for internal and overall reorientation fail to explain the experimental data without introducing an arbitrary adjustable parameter. The reorientational motions of the carbon backbone and of the hydroxyl groups are strongly correlated reflecting the effect of hydrogen bonds. By comparing the magnitudes of the T1 values at the minimum of the T1 vs T plots in glycerol-d4 and glycerol-d3 the deuteron quadrupole coupling constant is found to be 202 kHz for the hydroxyl deuteron. The dependence of the average correlation time ?2 upon viscosity and the ?2 variation with temperature and density is explained on the basis of a Debye type two term phenomenological equation. A discussion of the experimental data in terms of this equation suggests that the extent of the hydrogen bond network in liquid glycerol is relatively insensitive to density changes but very much reflects the temperature effects. The temperature and pressure dependence of the average correlation time ?2 suggests that the reorientation of the glycerol molecule proceeds via a large-angle jump diffusion mechanism. A detailed comparison of the present results with the conclusions of other NMR studies is presented.
Mixtures of hard spheres in the Percus–Yevick approximation. Light scattering at finite angles
Authors: Vrij A.
Published: February 2003

In a previous paper (I), a new equation for the light scattering (or small angle x-ray or neutron scattering) of a concentrated p-component mixture of spherical (colloidal) particles in a low-molecular weight solvent was derived. Use was made of Baxter’s factorization of the direct correlation matrix. It was found that the light scattering intensity can be formulated in factorized form as well. The formalism was applied to a multicomponent system of hard spheres treated in the Percus–Yevick approximation. For zero scattering angle, a rather simple, exact expression was obtained. In this paper it is proved that a closed expression can also be obtained for finite scattering angles. It contains at most 18 (averaged) functions of the scattering angle for any number of hard sphere components. This makes it possible to apply the equation to a continuous distribution of hard sphere diameters. A series expansion is given for small scattering wave numbers.
Rate constants for the reactions of metastable NO+ (a3Σ+) ions with SO2, CO2, CH4, N2, Ar, H2, D2, and O2 at relative kinetic energies 0.04–2.5 eV
Authors: Dotan I. , Fehsenfeld F. C. , Albritton D. L.
Published: February 2003

Rate constants for the reactions of NO+(a3Σ+) ions with SO2, CO2, CH4, Ar, N2, H2, D2, and O2 have been measured for relative kinetic enegeies 0.04–2.5 eV in a flow-drift tube. Most of these reactions are fast and show little kinetic energy dependence. The reaction with Ar is slightly endothermic and its rate constant increases substantially with increasing energy. For the reactions with SO2, CO2, CH4, and Ar, the reactive channel, largely charge transfer, predominates over quenching. For N2, the reactive and quenching channels are appriximately equal. Lastly, for H2, D2, and O2, quenching predominates, except at higher energies for O2, where the two channels are about equal.
The effect of phonon scattering upon resonance Raman scattering: The use of monochromatically excited resonant light scattering as a probe of ultrafast dephasing and relaxation in the condensed phase
Authors: Friedman Joel M.
Published: February 2003

The effects of excited state relaxation and dephasing upon resonance Raman scattering from a molecule in the condensed phase are considered from the perspective of a simple scattering event model, in the weak field limit. The model contains the minimum interactions necessary to produce dephasing of monochromatically excited resonant light scattering (MERLS). Emphasis is placed on how the different relaxation and dephasing processes determine the coherence properties of MERLS, from localized electronic states of a molecule perturbed by the environment. We consider how MERLS can be used to probe the line broadening mechanisms of vibronic absorption bands and associated phonon side bands. A comparison is made between the dephasing effects observed by the time dependent coherent spectroscopic techniques (e.g., photon echoes) and those detectable by spectral analysis of MERLS.
Hydrogen bonding and order–disorder phenomena in ammonium halide crystals
Authors: Garland C. W. , Lushington K. J. , Leung R. C.
Published: February 2003

The ordering of NH4+ ions in CsCl-type ammonium halide crystals is analyzed in terms of a model involving Ising pseudospin–phonon coupling. Direct interactions between NH4+ ions stablize parallel (’’ferro’’) ordering, and indirect interactions due to spin–phonon coupling stabilize antiparallel (’’antiferro’’) ordering. The strength of this coupling depends on the mass of the halide ion X, the frequency of an M-point transverse acoustic lattice mode, and the gradient ΔV′ in the potential for the hydrogen bond between NH4+ and X−. All available data for ordering in NH4Cl, NH4Br, NH4I, ND4Cl, ND4Br, NH4BrxCl1–x, (NH4)yM1–yCl, and (NH4)yM1–yBr are used to obtain empirical values of the potential parameter ΔV′. The magnitude of this quantity and the variations in its value with changes in halide ion, pressure, deuteration, and substitution of NH4+ by alkali ions are completely consistent with expectations for systems with weak N–H⋅⋅⋅X hydrogen bonding.
Shock compression data for liquids. I. Six hydrocarbon compounds
Authors: Dick R. D.
Published: February 2003

Dynamic high pressure equation-of-state data are reported for 1,3- and 1,4-cyclohexadiene, cyclohexene, cyclohexane, toluene, and n-hexane initially in the liquid state. Plane shock waves generated by high explosives produced pressures of 0.5 to 43.0 GPa and densities to twice normal density. Toluene and n-hexane exhibit transformations at 12.6 and 19.0 GPa, respectively, but cyclohexadiene, cyclohexene, and cyclohexane do not. Decomposition of the molecule is the probable cause for the transition. Results indicate that reducing the number of double bonds by adding hydrogen pairs to the benzene molecule causes the transition to disappear. The shock velocity−particle velocity (us −Up) data for toluene, toluene, cyclohexadiene, and n-hexane are best represented by one or more line segments while cyclohexene and cyclohexane are fit by a quadratic in particle velocity. An extrapolation of the Us−Up curves to zero particle velocity result in a Us value for each liquid that is approximateley 40% higher than the bulk sound speed. The specific volume at a particular pressure for these liquids is ordered such that the hydrocarbon with the larger hydrogen-to-carbon ratio has a larger specific volume. This behavior is similar to that observed for other hydrocarbons.
Theory of the Rydberg spectrum of triatomic hydrogen
Authors: King Harry F. , Morokuma Keiji
Published: February 2003

Energies and properties of the fifteen lowest Rydberg states of triatomic hydrogen are computed using Koopmans theorem with a large Gaussian basis set constructed to represent both core and Rydberg orbitals. Tests indicate that computed virtual orbital energies have converged to within a few wave numbers of the spd SCF limit. All excited electronic states are computed to have geometries and vibrational force constants close to those of H+3. Jahn–Teller effects are weak. Small quantum defects and nearly integer values of electronic angular momenta indicate atom-like character for the Rydberg states. Predicted vibronic transitions are in remarkably close agreement with rotational band spectra recently observed by Herzberg. Results using our model are in complete accord with Herzberg’s assignment of the strong emission bands observed near 5600 and 7100 Å, and offer a reasonable interpretation of the previously unassigned, weak emission bands observed near 6200 and 8500 Å.
Laser induced excitation of ammonia at 1076 cm−1 in the megawatt region
Authors: Starov Vladimir , Steel Colin , Harrison Robert G.
Published: February 2003

Absorption of high-power CO2-laser radiation by 5–244 Torr of ammonia has been studied. The incident infrared radiation energy was varied in the range 0.04–0.70 J cm−2 pulse−1 corresponding to average power levels of 0.2–3.5 MW cm−2, respectively. It is shown that experimental measurements can conveniently be summarized using an empirical absorption law, which is a modified Lambert–Beer law, written in terms of fluences or doses. A kinetic model is analyzed in relation to the data thus presented.
Physical significance of employing self-consistent orbitals (SCO) with uniform long-range behavior
Authors: Stwertka A. , Burke E. A.
Published: February 2003

The long-range behavior of Hartree–Fock wave functions has been found to result in uniform orbital behavior at large r for the first row ground state elements. Numerical techniques were developed to overcome exchange blowup at large r, and generate HF orbitals without ’’wobble.’’ Magnetic susceptibilities, nuclear shielding constants, electron scattering factors, and hyperfine structure constants were calculated to investigate the physical reality of these orbitals. The uncertainties in experimental values are too great to permit definitive conclusions. Agreement, however, between calculated values and recent experimental evaluations of 〈r2〉 was found to be very good. The present results seem to be the first indication of the necessity of considering orbitals with uniform long-range behavior for the proper description of phenomena dependent on wave function values far from the nucleus.
Laser magnetic resonance spectrum of the ν2 band of ND2
Authors: Hills G. W. , McKellar A. R. W.
Published: February 2003

The laser magnetic resonance spectrum of the ν2 band of ND2 (ν0=1108.7493 cm−1) has been observed using a CO2 laser in the 9–10 μm region. By a least-squares fit of over 300 resonances, the ν2 band origin and the rotational, centrifugal distortion, and spin–rotation parameters for both the ground (000) and excited (010) vibrational states were determined. A transition arising from the (020) → (010) hot band was also tentatively identified, and this allowed a determination of the hot band origin. A comparison of ND2 and NH2, along with some other doublet asymmetric rotor molecules for which deuterated species have been studied, showed that the spin–rotation interaction constants (εaa, εbb) scale quite accurately with rotational constants (A,B) between isotopic species.
Laser magnetic resonance spectroscopy of SO in the X 3Σ− state with a CO2 laser as a source
Authors: Kawaguchi Kentarou , Yamada Chikashi , Hirota Eizi
Published: February 2003

Vibration–rotation transitions of SO in the X 3Σ− state have been observed in the 1100 cm−1 region by laser magnetic resonance spectroscopy with a C 18O2 laser as a source. Transitions of the fundamental band observed for the normal species 32S16O were mainly of the ΔN=−1, ΔJ=0 type, and in addition magnetic-field-induced transitions with either ΔN=−1, ΔJ=3 or ΔN=−1, ΔJ=+1 and transitions with ΔN=−3 were also observed. A few weakly tunable ΔN=ΔJ=−1 transitions were observed for the v=1←0 and 2←1 bands of 32S 16O and for the v=1←0 band of 34S 16O. For 32S 18O the band origin is low enough to observe nine low-N transitions. Observed resonances were analyzed to determine rotational, spin–spin and spin–rotation coupling constants for the v=1 state, and g factors for the v=0, 1, and 2 states of 32S 16O. The band origins are 1138.0089 (4) and 1125.3085 (28) cm−1 for v=1←0 and 2←1, respectively. For 34S 16O and 32S 18O the origins of the fundamental bands were respectively determined to be 1126.9295 (30) and 1095.4265 (8) cm−1. All values in parentheses denote three standared errors. Rotational, spin–spin and spin–rotation interaction constants, and g-factors were also obtained for the v=1 state of 32S 18O. By using the four values of the band origins the harmonic frequency and the anharmonicity constant were calculated for 32 S16O: ωe =1150.710 (11) cm−1 and ωexe=6.3505 (51) cm−1.
17O pure quadrupole resonances in hydrogen peroxide
Authors: Lumpkin O. , Dixon W. T.
Published: February 2003

The first observations of the 17O pure nuclear quadrupole resonance spectrum of H2O2 are reported. (AIP)
Quenching rates and fluorescence efficiency in the A 2Σ+ state of OH
Authors: Selzer P. M. , Wang Charles C.
Published: February 2003

Using direct lifetime measurements at pressures up to 25 Torr, the quenching rates for the A 2Σ+  (v=0) state of OH due to N2, O2, H2O, and air have been determined. These values are in general agreement with other direct lifetime measurements obtained in the millitorr range and show that the quenching cross sections are pressure independent. The implications of these values on the previous ambient OH measurements are discussed.
High power electron spin echo modulation studies of silver atom solvation and desolvation in ice matrices: Geometrical models for silver cation and silver atom aqueous solvation shells
Authors: Ichikawa Tsuneki , Kevan Larry , Narayana P. A.
Published: February 2003

High power electron spin echo modulation patterns have been obtained at 4.2 K and analyzed for presolvated silver atoms produced at 4.2 K in a nonequilibrium environment by radiolysis of deuterated ice matrices containing AgF, and for solvated silver atoms produced by brief annealing at 77 K. The analysis shows that presolvated Ag0 is surrounded by eight equivalent deuterons at 3.1±0.1 Å with zero isotropic hyperfine coupling which suggests a tetrahedral model of four waters with their dipoles pointed away from Ag0 (i.e., a solvated Ag+ geometry). Solvated Ag0 has one deuteron at 1.7±0.05 Å with a 1.8 MHz isotropic hyperfine coupling and seven deuterons at 3.1±0.1 Å with zero isotropic hyperfine coupling. The solvation process appears to occur by rotation of one water around one of its OD bonds with no change in the Ag–O distance.
Mössbauer study of 57Fe in the pyrite-type dichalcogenides
Authors: Nishihara Yoshikazu , Ogawa Shinji
Published: February 2003

The isomer shift and the quadrupole splitting of 57Fe in the pyrite-type dichalcogenides, FeS2–CoS2–NiS2–NiSe2 and CoSe2, were measured at room temperature. It is concluded that the effects of atomic distance and electronegativity of ligand make comparable contributions to the isomer shift of a divalent iron in low spin state. In high spin state, the contribution of atomic distance is smaller than that of electronegativity. The lattice term of electric field gradient gives a large contribution to the quadrupole splitting. The isomer shift and the quadrupole splitting of Fe1–yCoyS2 change around y=0.5 where the concentration dependence of resistivity changes. In NiS2–xSex, the quadrupole splitting of 57Fe becomes small with increasing x at the metal–semiconductor phase boundary.
Structure of a liquid–vapor interface in the presence of a hard wall in the transition region
Authors: Rao M. , Berne B. J. , Percus J. K. , Kalos M. H.
Published: February 2003

The structure of a liquid–vapor interface, in the presence of a hard wall in the transition region, is studied using Monte Carlo simulation. Both longitudinal and transverse correlations are compared to those observed in a free interface. The density profile shows a transition from an oscillatory profile to a smooth monotonic one when the position of the hard wall is varied. It is shown that these results are consistent with a heuristic capillary wave theory of the interface.
Raman and Brillouin–Rayleigh scattering studies of the displacive phase transition in malononitrile at 294.7 K
Authors: Higashigaki Y. , Wang C. H.
Published: February 2003

A comprehensive temperature dependent inelastic light scattering study of a malononitrile single crystal using Raman and Rayleigh–Brillouin spectroscopic techniques has been carried out, with a special emphasis on the phase transition at 294.7 K, observed by Zussman and Alexander. Optical soft modes associated with the phase transition have not been observed, despite the fact that internal vibrations involving the CH2 scissoring motion and the symmetric C–N stretching vibrations are affected by the phase transition. The librational frequencies have been assigned for the first time, using the present Raman result and the low temperature heat capacity data. Among the three librational modes, the libration about the c axis, corresponding to νL(Bg, c), shows anomalies in both the frequency and the linewidth data. The temperature dependent Rayleigh–Brillouin scattering spectra have displayed the softening of the lowest frequency transverse acoustic mode at 294.7 K. A combination of the data on the librational mode, νL(Bg, c), with the Brillouin–Rayleigh results suggests the importance of coupling of the transverse acoustic mode to the νL(Bg, c) libration in malononitrile single crystal. Evidence for the coupling is also manifest in the line shape of the depolarized Rayleigh scattering spectra in various crystal orientations. The linewidth and intensity of the central Rayleigh peak as well as the linewidth of the longitudinal acoustic phonon were also found to be affected by the phase transition.
Orbit–orbit interaction
Authors: Huang Keh-Ning
Published: February 2003

A new tensor expansion of the orbit–orbit interaction is derived straightforwardly in a form which is compact and completely symmetric in the coordinates of interacting particles. The m-scheme matrix element of the orbit–orbit interaction is then obtained as a concise sum of radial integrals. The graphical form of the m-scheme matrix element is also presented, which enables one to obtain graphically many-particle matrix elements from easily constructed diagrams. Graphical analysis of different contributions to the orbit–orbit interaction in a many-particle system is demonstrated by several examples.
Torsional ground state splitting for tetrahedral molecules
Authors: Hüller Alfred , Raich John
Published: February 2003

With improved neutron scattering and nuclear magnetic resonance techniques it has been possible to observe the splitting of the torsional ground state—commonly referred to as tunnel splitting—of a number of high symmetry molecules in various crystal fields. The tunnel splitting depends nearly exponentially on the strength of the potential experienced by a molecule as it rotates in the crystal. Tunneling spectroscopy may thus be developed into a sensitive probe for measuring rotational potentials once the relation between the potentials and the tunnel splitting is known. We have used the pocket state formalism to calculate the splitting for tetrahedral molecules in tetrahedral fields. With increasing potentials the wave function becomes smaller in the overlap region making an accurate prediction of the tunnel splittings more difficult. Our calculation provides reliable results for splittings from 200 μeV down to about 1 μeV. Detailed predictions are made for the isotope effect in solid methane and for the pressure dependence of the energy levels with special reference to (NH4+)2 SnCl6−−. Tunneling experiments under pressure are well suited for providing information about the distance dependence of intermolecular forces.
Chemically induced dynamic spin polarization in two dimensional systems: Theoretical predictions
Authors: Zientara Gary P. , Freed Jack H.
Published: February 2003

Theoretical predictions for chemically induced dynamic spin polarization [CIDN(E)P] and Heisenberg spin exchange in two dimensional fluid systems are developed. An idealized model, which yields simple limiting results is first discussed in order to illustrate the importance of the geometrical aspects of this problem upon the CIDN(E)P observables. Pedersen–Freed theory, which employs numerical solutions of the stochastic-Liouville equation is then applied. This approach is appropriately modified in its use and analysis in order to fully exhibit the details of two dimensional kinetic and polarization processes. Specifically, the Laplace transformed results are calculated and related to the finite time results (rather than the t→∞ asymptotes) due to logarithmic divergences in time which characterize two dimensional processes. Approximate empirical formulas are developed to describe our exact numerical results and they illustrate the profound effects of a change of dimensionality on the CIDN(E)P observables. These results are related to experimental observables by considering the role of processes which limit the time scale for the polarization (e.g., radical scavenging and T1) and by a consideration of the role of two dimensional bimolecular encounter theory on random initial encounters. Other aspects of two dimensional effects (e.g., time-dependent diffusion coefficients and concentration effects) are briefly noted.
A semiclassical approximation to quantum dynamics
Authors: Weissman Yitzhak , Jortner Joshua
Published: February 2003

In this paper we advance a new approximation scheme for the dynamics of an N particle system, which is based on the expansion of the Heisenberg equations of motion in powers of h/ in the coherent state representation. The time evolution of the physical observables is generated classically by a Hamiltonian Hs, which is derived from the original Hamiltonian by adding 2N2 virtual particles to the system. These virtual particles are related to the dispersion of the quantum mechanical wave function, and reflect the (time dependent) sensitivity of the instantaneous positions and momenta xi, pi to the variation of the initial conditions. The approximate equations of motion preserve the commutation relations between the coordinates and the momenta and the total (quantum) energy. The present approximation may be adequate for the study of the dynamics of coupled anharmonic oscillators in the quasiperiodic regime.
Electron impact study of potassium hydroxide
Authors: Vus̆kovíc L. , Trajmar S.
Published: February 2003

An ’’elastic’’ scattering study for low impact energies (5–20 ev) is reported for electron impact excitation of KOH. The ’’elastic’’ scattering is regarded as the sum of elastic rotational and vibrational contributions to the scattering. (AIP)
Radial correlations in associated liquids
Authors: Klein M. L. , McDonald I. R. , Berne B. J. , Rao M. , Beveridge D. L. , Mehrotra P. K.
Published: February 2003

Calculations are reported for liquid ammonia and liquid H2O using Monte CCarlo Moleccular dynamics and the Ewald techniques. The results for all three models are compared with each other. (AIP)
Branching ratio determination in the O2+(b4Σg−) predissociation
Authors: Tadjeddine Mireille
Published: February 2003

An evaluation of the branching ratio in the predissociation of O2+ is presented from the wavelength spectra which have been analyzed in ref. 5. (AIP)
Comment on ’’Vibron and lattice frequency shifts in the Raman spectra of solid α-N2 and γ-N2 and librational force constants of diatomic molecular crystals’’
Authors: Chandrasekharan V. , Thiéry M. M. , Walmsley S. H.
Published: February 2003

The torsional lattic frequencies in nitrogen crystals are not formed to be affected by the variations of quadrupole movement with bond length as suggested in a previous paper by the authors. (AIP).
Transport properties of the Widom–Rowlinson hard-sphere mixture model
Authors: Karkheck John , Stell G.
Published: February 2003

The thermal conductivity, mutual diffusion coefficient, and viscosities of the hard-sphere Widom–Rowlinson Model are studied in quantitative detail within the framework of revised Enskog theory. It is found that the thermal conductivity and viscosities behave smoothly at the critical point, whereas the mutual diffusion coefficient vanishes strongly at the critical point and along the spinodal curve. (We note that the latter coefficient does not appear to vanish at the critical point, when analyzed in the framework of the less satisfactory standard Enskog theory.)
Collisional deactivation of O(2 1D2) by the atmospheric gases
Authors: Amimoto S. T. , Force A. P. , Gulotty R. G. , Wiesenfeld J. R.
Published: February 2003

The thermal rate constants for collisional deactivation of electronically excited oxygen atoms, O(2 1D2), by N2, O2, N2O, CO2, CH4, and H2O have been measured at 295 K. The optically metastable atoms were produced by pulsed photolysis of O3 at 248 nm using a KrF excimer laser and monitored by following the increase in O(2 3PJ) concentration following quenching of O(2 1D2) through the use of time-resolved atomic resonance spectroscopy. This method of analysis obviated difficulties associated with the evaluation of the curve-of-growth law which were encountered in previous attempts to measure the removal of O(2 1D2) using a similar technique. Rate constants reported here are in excellent agreement with those measured by observation of the weak O(2 1D2) →O(2 3PJ) emission at 630 nm. In addition, it was possible to determine the extent of physical quenching in the deactivation of O(2 1D2) by H2O, CO2, CH4, and N2O.
Infrared double resonance of SF6 with a tunable diode laser
Authors: Jensen C. C. , Anderson T. G. , Reiser C. , Steinfeld J. I.
Published: February 2003

Double resonance spectroscopy has been carried out on the ν3 band of SF6 using a CO2 laser pump and a tunable diode laser probe. Power broadening of the pumped transition is observed, and a value for the transition moment μ12?0.3×10−18 esu cm is obtained. Off-resonant pumping of all symmetry components in the J manifold coupled to the pump laser is observed; this is attributed to field-induced mixing of nearly degenerate fine-structure levels in the vibrational ground state of the molecule. From the decay of the double resonance signals, we measure relaxation times Pτ= (24±3) nsec Torr for 2-level signals and Pτ = (43±11) nsec Torr for 3-level signals, corresponding to an effective cross section of 170 Å2. Excited-state transitions corresponding to 2ν3←ν3 with J=32 are observed. The implications for multiple infrared photon excitation models are considered.
Nonadiabatic interactions in unimolecular decay. V. Conical and Jahn–Teller intersections
Authors: Desouter-Lecomte M. , Galloy C. , Lorquet J. C. , Pires M. Vaz
Published: February 2003

The purpose of the present paper is to discuss the properties of conical and Jahn–Teller intersections within a unified formalism. A classical trajectory description of the nuclear motion is adopted throughout. A linear transformation introduced by Nikitin defines a new diabatic basis which is specific of each particular straight line trajectory; this reduces a bidimensional surface intersection problem to an equivalent one-dimensional curve-crossing problem. For each representation (diabatic or adiabatic), it is possible and advantageous to express the transition probability in terms of a single function of a single variable (which we call the global function) instead of the four functions in terms of which the problem is originally defined (i.e., the two energies, the coupling matrix element, and the nuclear velocity). The use of such global functions provides the most general way to express the nonadiabatic transition probability in terms of quantities directly connected with ab initio calculations. Illustrative calculations are presented for the H2CO+ ion, whose dissociation mechanisms are controlled by a conical intersection.
Nitrogen isotope exchange between nitric and nitrous acids
Authors: Akhtar Mohammad Javaid , Axente Damian , Bonner Francis T.
Published: February 2003

The rate of nitrogen isotrope exchange between NO−3 and NO−2 in aqueous solution has been measured, at low acidity, as a function of pH, [NO−3], [NO2−], and temperature. Exchange does not occur in the absence of NO, and during slow exchange processes NO and NO2− remain closely similar in isotopic content. The exchange rate law is shown to be R=k[H+][HNO2][NO−3], and the measured activation parameters are EA=74.4±2.6 kJ, ΔH‡=72.0±2.6 kJ, ΔS‡=−97.4±8.5 JK−1. It is concluded that there is no direct interaction pathway for nitrate–nitrite exchange, and that this process and NO–HNO3 exchange both occur via the reversible HNO2 disproportionation reaction, involving N2O4 as intermediate.
Statistical mechanics of helical wormlike chains. X. Dipole moments, electric birefringence, and electric dichroism
Authors: Yamakawa Hiromi , Shimada Jiro , Nagasaka Kyosuke
Published: February 2003

The mean-square dipole moment, electric birefringence (Kerr constant), and electric linear dichroism of polymer molecules are evaluated on the basis of the helical wormlike chain on which dipole moments, dipole transition moments, and static and optical polarizabilities are arrayed with respect to its localized coordinate systems. Spherical dipole moment vectors are introduced along with the spherical polarizability tensors used previously in the study of the anisotropic light scattering. Evaluation is also carried out for the extreme cases of the helical wormlike chain, i.e., the rigid rod, regular helix, random coil, and wormlike chain. An analysis of experimental data is made for the mean-square dipole moments of poly(dimethylsiloxane) and poly(n-butyl isocyanate), and for the electric dichroism of the latter. In the Appendix, analytical expressions for the first and second order angular correlation functions are given.
Organic metals. van der Waals donor stacking in TTF–TCNQ (tetrathiafulvalene-tetracyanoquinodimethane)
Authors: Silverman B. D.
Published: February 2003

The slipped stacking geometry of TTF in TTF–TCNQ and in neutral TTF is shown to be consistent with the close packing of hard spheres having atomic van der Waals radii. Slipped or eclipsed stacking in TTF compounds is suggested to result from a competition between closed shell interactions and those interactions that arise from partially emptying the highest occupied π-molecular orbital. This contrasts with TCNQ stacking in TCNQ salts which has been previously argued to be a consequence of only those interactions that result from filling the π-molecular-orbital affinity level.