bluuebunny/crossref_metadata_2025 huggingface dataset:
Second harmonic generation in collagen
Authors: Roth Shmuel , Freund Isaac
Published: February 2003

Ordered collagen in native, intact rat tail tendon has been studied by means of optical second harmonic generation (SHG). The two independent hyperpolarizability tensor elements of the collagen molecule, β3 and β1, have been found to be of opposite sign and roughly equal in absolute magnitude. Evidence is presented for a systematic variation in the ratio β3/β1 with age which may reflect the effects of progressive cross linking. Our experimental findings are in reasonably good agreement with a simple theory constructed on the basis of current models of the tendon structure, and thereby confirm this structure in the native, intact tissue. The many advantages of SHG for the structural study of intact partially ordered biological tissues are outlined.
A statistical model for rotationally and vibrationally inelastic collisions
Authors: Eastes Walter , Toennies J. Peter
Published: February 2003

A statistical model is described which is able to treat the collisional excitation of internal degrees of freedom in collisions of large molecules in a simple way. In contrast to most previous statistical theories, this theory is able to treat direct collisions as well as collisions involving a long lived complex. A wide variety of collisional interaction strengths can be handled by the model. This is accomplished by the use of a coupling strength parameter, which limits the energy in any internal degree of freedom. This energy limit is the only adjustable parameter in the model and, when held small, allows a good description of glancing collisions and threshold effects, which are not normally considered to be amenable to statistical treatment. The results of this model are compared both with an exact theoretical treatment of the direct collinear atom–diatom collision and also with experimental ion beam data on average energy transfer in direct collisions with polyatomic molecules. In both cases good agreement is found. A simple semiempirical formula is obtained which can be used to predict the energy and angular dependence of the average relative energy transfer under conditions encountered in hot atom and in radiation chemistry and plasmas.
Time of flight measurements of the vibrational excitation of CH4 by collision with 3−6 eV Li+ ions
Authors: Eastes Walter , Ross Ulrich , Toennies J. Peter
Published: February 2003

Angular distributions and time of flight spectra for the scattering of Li+ ions from ground state CH4 have been measured over a range of center of mass scattering angles (7° to 19°) and energies (2.7 to 6.5 eV). The spectra reveal transitions to groups of CH4 vibrational states which could be clearly resolved. As in previous studies of CO2 and N2O, very little rotational excitation is observed. The vibrational transition probabilities show an extremely strong dependence on the scattering angle, not seen in similar experiments using simpler target molecules. Certain state to state differential cross sections as well as the average energy transfer and the second and third central moments of the energy transfer are compared for Li+ + CH4, CO2, and CO. The different behavior of the average energy trnasfer for these targets is well explained by a statistical model recently developed by two of the authors.
Rate constant for the reaction HO2+NO→OH+NO2
Authors: Leu Ming-Taun
Published: February 2003

The rate constant for the reaction HO2+NO→OH+NO2 has been determined over the temperature range 270 to 425 K in a discharge flow/mass spectrometer/resonance fluorescence apparatus. Results, expressed in the Arrhenius form k1= (5.7+5.6−4.0) ×10−12 exp[(130±270)/T] cm3 sec−1, are compared with previous measurements.
ESR of phosphite radicals trapped in x-irradiated single crystals of o-phosphorylethanolamine
Authors: Fouse George W. , Bernhard William A.
Published: February 2003

Two different species of phosphite radicals are trapped at 300 K in x-irradiated single crystals of o-phosphorylethanolamine, H3N+CH2CH2OPO3H−. One radical, resulting from cleavage of the P–OH bond, is characterized by eigenvalues of 2173±16 MHz, 1733±19 MHz, and 1713±19 MHz, and 2.0065±0.0004, 2.0045±0.0004, and 2.0038±0.0004, for the hyperfine coupling tensor and g tensor, respectively. The other radical, produced by cleavage of the P–OCH2CH2NH+3 bond, has corresponding eigenvalues of 2131±15 MHz, 1710±15 MHz, and 1689±13 MHz, and 2.0054±0.0004, 2.0052±0.0004, and 2.0044±0.0004. Both radical species are present in approximately equal concentrations in the crystal, suggesting that both the P–OH and P–OCH2CH2NH+3 bonds are equally susceptable to electron dissociative capture, the assumed mechanism for radical formation.
Extended London theory of diamagnetism. I. General theory and saturated hydrocarbons
Authors: Pesquer M. , Hoarau J. , Caralp L. , Ducasse L.
Published: February 2003

In this paper a method is proposed to calculate diamagnetic susceptibilities of organic compounds. This method uses the extended Hückel formalism generalized to include the perturbation due to a magnetic field ℋ. Parameters are varied to obtain agreement with experimental results. The diamagnetic properties of the alkanes are examined and all the terms contributing to the susceptibility are analyzed. The importance of a coupling term between matrix elements of first order in ℋ and London terms is shown. Some results are discussed, particular to methane and the cycloalkanes.
SCF treatment of charge polarization effects in intermediate-energy electron scattering calculations with applications to N2
Authors: Onda Kunizo , Truhlar Donald G.
Published: February 2003

We report converged rotational close coupling calculations of the differential, integral, and momentum-transfer cross sections for seven model potentials for electron–N2 scattering at an impact energy of 30 eV. The model potentials involve a static potential calculated by the INDO/1s or INDOXI/1s method, an exchange potential calculated by the semiclassical exchange approximation from the INDO/1s or INDOXI/1s unperturbed electronic density, and a polarization potential. The polarization potentials used include the Buckley–Burke semiempirical one and various modifications of the INDOXI and INDO self-consistent-field adiabatic polarization potentials. We are able, without adjusting parameters, to obtain good agreement with the angle dependence of the experimentally measured sum of the elastic and rotational excitation differential cross sections although the absolute value of our calculated cross sections is about 20%–30% larger than the measured values in the best case, perhaps indicating that the model potentials are too strong or should have a nonzero imaginary part. We discuss the sensitivity of the computed results to details of both the static and polarization parts of the model potentials, and we present some predictions of the rotationally resolved state-to-state cross sections.
Simulation of chain molecules in solutions at finite concentrations under several solvent conditions
Authors: Okamoto Hiroshi
Published: February 2003

Computer experiments simulating chain molecule solutions on a tetrahedral lattice have been performed at various concentrations and under several solvent conditions. In good and athermal solvents, mean squares of end to end distance 〈R2〉/b2 and of radius of gyration 〈S2〉/b2 decrease monotonically with the increase in the concentration of chain molecules. In poorer solvents, the monotonic decrease was sometimes not found and in the solutions under very poor solvent conditions, they seemed to have a slight positive dependence on the concentration. The principal moments of inertia of chain molecules were also computed in this connection. The element density distributions around the mass center of a chain were also evaluated and discussed. The numbers of chain element to chain element and chain element to solvent contact pairs, which are closely related to the heat of mixing, were evaluated and compared with the prediction of the quasichemical theory. The agreement was good in good or athermal solvent solutions at moderate concentrations. The disagreement, however, was found in dilute solutions and in poorer solvent solutions.
Measurements of the branching ratios for the reaction of O(1D2) with N2O
Authors: Davidson J. A. , Howard Carleton J. , Schiff H. I. , Fehsenfeld F. C.
Published: February 2003

The relative rate constants for the reaction channels were determined using chemical-ionization mass spectrometry to measure the products of Reaction (1). O(1D2) atoms were produced by the photodissociation of N2O at wavelengths greater than 1950 Å. The measurements were carried out in mixtures of N2O with helium added to remove the excess kinetic energy carried by the O(1D2). We find the ratio k1a/k1b is sensitive to the presence of helium increasing from a value of 0.68 in pure N2O to a value of 0.80 with [He]/[N2O]?10. In addition, at 300 K we find that (1a) and (1b) consititute the only significant channels for the reaction with (k1c+k1d+k1e)/(k1a+k1b ) ?0.038. The ratio k1a/k1b is found to decrease slowly with increasing temperature over the range 170–434 K. These data can be fitted by the expression k1a/k1b= (0.72±0.11) +(21.6±7.0)/T.
Temperature dependence of HF(v1=1)+HF(v2=0) vibrational relaxation
Authors: Wilkins R. L. , Kwok M. A.
Published: February 2003

A kinetics model of infrared laser-induced fluorescence experiments has been used to simulate the experimental quenching rate coefficients reported between 300 and 4000 K for the vibrational relaxation of HF(v1=1) by HF. This rotational nonequilibrium model is based on the predicted energy-transfer mechanisms in hydrogen fluoride systems reported in a trajectory study by Wilkins. This model includes v→R, R→v, R→ (R′, T′), and (R′, T′) →R energy-transfer processes. A key process is vibrational-to-rotational intramolecular energy transfer in which HF(v1=1,J1) terminates on high J′ 1 states ofv′1=0. The calculated temperature- dependent quenching rate coefficient for self relaxation of HF(v1=1) at temperatures between 300 and 2000 K is dependent on v→R andR→v energy-transfer processes, and beyond 2000 K only on v→R processes. The temperature dependence observed for HF(v1=1) vibrational relaxation by HF(v2=0) is explained by this model. For the high roational states in the v′ 1=0 manifold, this model predicts incomplete rotational therma lization at high temperatures. No mechanisms involving dimerization appear to be necessary in understanding the inverse temperature dependence of the re ported quenching rate coefficients.
Theoretical studies of atmospheric triatomic molecules. New a
b i
n
i
t
i
o results for the 1Πg–1Δu vertical state ordering in CO2a)
Authors: Englandb) Walter B. , Ermlerc) Walter C.
Published: February 2003

Vertical energy levels are computed with MC–CI wave functions for the 1Δu valence state and the 1Πg mixed character state of CO2, and for the 2Πg state of CO+2. Using the computed MC–CI results and results from previous work, vertical energy levels for the low-lying valence states, mixed character states, and Rydberg states of CO2 are determined. An adiabatic correlation diagram for these states is constructed for the process CO2→CO+O. Qualitative features in the potential energy surfaces which arise from the ordering are discussed. Comparisons with theory and experiment are given.
Picosecond kinetics of copper and silver protoporphyrins
Authors: Kobayashi T. , Huppert D. , Straub K. D. , Rentzepis P. M.
Published: February 2003

By the use of the dual beam picosecond absorption spectroscopy technique, the initial events in the energy relaxation process of Cu(II) and Ag(II) protoporphyrin IX dimethyl esters were studied. The energy decay channels were found to be as follows. Cu(II) (Z=29) complex: After picosecond excitation, a Franck–Condon state of 2S1 is populated which decays into 2T1 within 8 psec. This state relaxes with a time constant of 450–460 psec to 2T1 and 4T1 equilibrium state from which phosphorescence is emitted. Ag(II) (Z=47) porphyrin: Picosecond excitation to the 2S1 state results in energy relaxation to 2T1 state within 8 psec which is followed by equilibration between 2T1 and 4T1 with a time constant of 11–12 psec. Subsequently the relaxation proceeds via nonradiative channels to 2Td and 4Td or 2(d,π*) states.
Mass-reduced quantum numbers: Application to the isotopic lithium hydrides (X 1Σ+)
Authors: Li Kwong C. , Stwalley William C.
Published: February 2003

The mass-reduced quantum number (MRQN) method of combining isotopic data is applied to the lithium hydride X1Σ+ ground state. The ΔG (η) =μ1/2 ΔG (v), B (η) =μB (v), and D (η) =μ2D (v) isotopically combined functions are obtained. An isotopically combined Rydberg–Klein–Rees (ICRKR) potential is constructed using the G (η) and B (η) functions. Evidence for breakdown of the Born–Oppenheimer approximation is presented and examined. The Dunham, Simons–Parr–Finlan, and Thakkar methods of potential expansion are also applied to lithium hydride and compared to the RKR potential.
Surface excitons in mixed molecular crystals
Authors: Ueba Hiromu , Ichimura Shoji
Published: February 2003

A theory of surface excitons in mixed molecular crystals is presented by extending the coherent potential approximation developed in the study of an infinite bulk crystal to a suitable one for a semi-infinite crystal. The effect of the semi-infinite nature of the crystal is taken into account by a localized perturbation method. The surface coherent potential is introduced to calculate the concent ration dependence of the energy of the surface excitons. The results give a qualitative explanation of the recent observation of surface excitons in the mixed crystal system antheracene–perdeuteroanthracene.
Thermal rate constants, energy dependence, and isotope effect for halogen–hydrogen halide reactions
Authors: Mei Chang-Chi , Moore C. Bradley
Published: February 2003

Thermal rate constants have been determined for the reaction C1+DI and Br+HI in the temperature range 220–400 K. For C1+DI, the effective reaction cross section reaches a maximum of 18.8 Å2 near 345 K. The isotope effect increases in favor of HI from 1.5 to 2.7 as the temperature decreases from 400 to 223 K. For Br+HI, the effective reaction cross section decreases slightly with increasing temperature. The cross section at enhanced collisional energy, with various rotational energies, is determined for the reaction C1+HI (DI). It is found that a factor of 3.9 increase in translational velocity over room temperature actually decreases the cross section for C1+HI and DI by factors of 9 and 6.6, respectively. At 11.4 kcal/mole relative translational energy, the cross section for the reaction C1+HI increases by 1.2 as the rotational temperature increases from 223 to 295 K. The results are discussed in terms of a reaction model in which the attacking halogen atom is attracted to the halogen end of the hydrogen halide and then rotation of the hydrogen completes the reaction. A semiquantitative analysis shows that tunneling makes an important contribution to the isotope effect.
Non-Franck–Condon transitions in resonant autoionization of N2O
Authors: Baer Tomas , Guyon Paul-Marie , Nenner Irene , Tabché-Fouhaillé Abdallah , Botter René , Ferreira Luis F. A. , Govers Thomas R.
Published: February 2003

Autoionization of N2O between 12.89 and 16.4 eV was investigated by photoionization using the pulsed synchrotron radiation from ACO, Orsay’s storage ring. Measurements were performed of threshold photoelectron spectra, photoionization spectra, and of photoelectron energy spectra. The latter were obtained from photoelectron time of flight distributions at selected wavelengths. The results suggest that autoionization in the Franck–Condon gap between the ? 2Π and the ? 2Σ+ states of N2O+ proceeds via two distinct mechanisms. The major autoionization process (?90%) produces the ? 2Π state in its low vibrational levels, while a resonant autoionization path (?10%) produces vibrationally excited ? 2Π ions. The latter process is associated with the production of low energy electrons with a distribution peaking sharply at zero energy. This resonant autoionization process appears to be a general phenomena for polyatomic molecules.
Classical theory of light scattering by an adsorbed molecule. I. Theory
Authors: Efrima Shlomo , Metiu Horia
Published: February 2003

We develop a classical theory for the intensity and the depolarization ratio of the light scattered (Raman or Rayleigh) by an absorbed molecule. It is assumed that the optical properties of the system can be described by the polarizability of the molecule and the dielectric constant of the two media. The presence of the surface modifies the field incident upon the molecule as well as the field emitted by the induced dipole. We compute these effects, exactly, by using a dyadic Green’s function method, and approximately, by using a perfect mirror model. The theory provides the angular distribution of the scattered radiation, and its polarization as a function of the polarization, the frequency and the direction of incidence of the incoming radiation, as well as of the dielectric properties of the metal and the position of the molecule with respect to the surface. We use these equations to analyze the possible sources for the experimentally observed enhancement of the scattering caused by the presence of the metallic surface.
First excited state of the O−2 ion
Authors: Rolfe John
Published: February 2003

Zero-phonon lines in the absorption and excitation spectra of O−2 in molecules in NaCl crystals at 2 °K have been measured. The calculated spectroscopic constants for the first excited state 2Πu of O−2 were used to construct potential energy curves, which are compared with recent theoretical calculations.
The coupled channel R-matrix propagation method
Authors: Schneider Barry I. , Walker Robert B.
Published: February 2003

Using a Green’s function approach, we present an alternate derivation of the R-matrix propagation equations. We also present an extension of the method which employs a basis set expansion for both translational and target motions within each R-matrix sector. This new approach is then investigated in comparison to the original close-coupling approach, studying a model collinear vibrational excitation problem. The new approach allows much larger R-matrix boxes to be used in regions of configuration space where the potential is changing rapidly with the scattering coordinate.
Multiphonon theory of scattering of atoms from solid surfaces: Tetradic scattering approach
Authors: Mukamel Shaul
Published: February 2003

The tetradic scattering formalism is used to develop a theory for inelastic scattering of atoms from solid surfaces. The theory accounts for the correlated dynamics of the colliding atom and the solid surface, and an analytical expression is derived for the multiphonon energy transfer probability in a collinear collision. The present formulation does not rely on a separation of time scales and is thus valid for any value of the lattice correlation time τc relative to the gas–surface interaction strength d. In the high temperature and strong coupling limits, dτc≫1 and the inelastic cross section contains a Gaussian broadening term. In the extreme Markov limit, dτc≫1 and the cross section contains a Lorentzian broadening term. In both extremes, the lattice dynamics is weakly correlated with the collision. We discuss and analyze the behavior of the inelastic cross section under various physical limits.
Electron paramagentic resonance and phase transitions in Mn2+ doped Cd(ClO4)2⋅6H2O
Authors: Dayal R. , Rao D. Ramachandra , Venkateswarlu Putcha
Published: February 2003

An electron paramagnetic resonance study of Mn2+ doped in Cd(ClO4)2⋅6H2O has been made from 328 K to liquid nitrogen temperature. The site symmetry of Cd2+ is trigonal with a water octahedron distorted parallel to the crystallographic c axis. Mn2+ substitutes for Cd2+ and exhibits a characteristic 30-line hyperfine spectrum at room temperature (298 K) for the magnetic field H along the c axis. The D parameter is small and therefore there is considerable overlapping of lines in the spectrum. The spectrum is axially symmetric. On lowering the temperature, phase transitions are found to occur at 272±1 and 115.5±1 K.
Collision induced intramolecular vibrational energy transfer in 1B2 aniline
Authors: Chernoff Donald A. , Rice Stuart A.
Published: February 2003

The technique of SVL fluorescence spectroscopy was used to observe collision-induced intramolecular energy transfer in a large polyatomic molecule in the gas phase. Vibrational energy transfer was traced from eight vibronic levels in 1B2 aniline with argon as a collision partner. Overall rates for depletion of the initial level range from 0.1 to 0.5 of the equivalent hard sphere collision rate. The vibrational levels below 800 cm−1 are found to fall into groups: energy transfer is much more efficient between levels in the same group than between levels in different groups. This pattern of energy disposal indicates that specific dynamic characteristics of the vibrational modes are as important as the energy gap and vibrational overlap integrals. Another interesting feature of the results is the importance of endoergic processes, even when exoergic pathways for vibrational energy exchange are available. Rotational relaxation was also examined, but only with low resolution, and not in a systematic study. The rate of rotational equilibration found approximates the collision rate.
Polarized fluorescence measurements of orientational order in a uniaxial liquid crystal
Authors: Chapoy L. Lawrence , DuPré Donald B.
Published: February 2003

The second and fourth orientational order parameters 〈P2〉 and 〈P4〉, have been measured throughout the liquid crystalline phase of p-methoxybenzylidene-p′-n-butylaniline (MBBA) using small quantities of a fluorescent probe. Complications of rotational Brownian motion and the intramolecular transfer of excitation energy were considered in the analysis. The results are in agreement with previous Raman measurements on the doped liquid crystal.
The variation of V/T and Politzer’s k due to change of molecular geometry: The water molecule
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2003

It is contended that Politzer’s k takes different values for different molecular geometries represented by the ratio V/T (ratio of total potential to total kinetic energy). The water molecule is discussed. (AIP)
Photon enhanced field ionization on semiconductor surfaces
Authors: Viswanathan B. , Drachsel W. , Block J. H. , Tsong T. T.
Published: February 2003

The results of experiments reported in Ref. 1 are questioned. It is claimed that the results do not show a photon enhancement of field ionization of metal surfaces. (AIP)
Notes on photon assisted field ionization
Authors: Niu Bill H. C. , Bryant Paul J.
Published: February 2003

A response to comments by Viswanathan et al (2) on a previous publication(1) by the authors is given. It is contended that the original hypothesis of photon assisted field ionization at metal surfaces correctly explains the results reported in Ref. 1. (AIP)
Search for vibrational activation in the chemisorption of methane
Authors: Yates J. T. , Zinck J. J. , Sheard S. , Weinberg W. H.
Published: February 2003

Direct laser excitation of the excited ν3 and 2ν4 vibrational modes of CH4 has been used to determine whether either state is active for inducing CH4 dissociative chemisorption on the (111) surface of Rh. The upper limit of the efficiency of chemisorption from either of these states was measured to be approximately 5×10−5. This experimental finding suggests that thermally activated dissociation of CH4 on metal surfaces may proceed via hydrogen atom tunneling from higher excited states or via H⋅⋅⋅H vibrational extensions which are greater than those experienced in the excited ν3 or 2ν4 vibrational states.
High temperature vapor pressure of pure plutonium
Authors: Bradbury M. H. , Ohse R. W.
Published: February 2003

High temperature vapor pressure measurements have been made on pure plutonium metal by the Knudsen effusion technique. The reported experimental results extend into the transition region between molecular and viscous or hydrodynamic flow. Under the conditions used, linearity was observed up to temperatures in excess of 2200 K where pressures approaching 100 Pa were measured. The results over the temperature range 1724–2219 K yield log10PPu(Pa) = (9.735±0.105) −17066±208/T and the enthalpy and entropy of vaporization and the standard deviations therein are ΔH0v(Pu,1975 K) =326.78±3.97 kJ mol−1, ΔS0v(Pu,1975 K) =90.54±2.01 J K−1 mol−1. Based on the most recently available free energy functions for plutonium liquid and gas, the values of the standard enthalpy of vaporization calculated via second- and third-law methods are ΔH0v(II, Pu,298 K) =344.14±3.97 kJ mol−1, ΔH0v(III, Pu,298 K) =341.67±1.26 kJ mol−1. Single crystal tungsten containers were used to hold the charge of plutonium and proved to be very satisfactory in alleviating problems of liquid metal creep and liquid/cell interactions normally encountered with actinides held at high temperatures for long periods.
A quasiclassical trajectory study of the four-center reactions: HBr+Cl2 and HBr+BrCl
Authors: Brown James Corgan , Bass H. E. , Thompson Donald L.
Published: February 2003

A quasiclassical trajectory study has been made of the dynamics of two four-center reactions: HBr+Cl2→HCl+BrCl, HBr+BrCl→HCl+Br2. Semiempirical, valence-bond potential-energy surfaces were employed, with potential parameters obtained from related atom–diatomic molecule systems. Reaction probabilities and cross sections were computed as functions of reactant vibration, rotation, and translation. Extrapolated cross section curves were used to make estimates of thermal rate coefficients. The dependence of the reaction probability on other dynamics variables such as impact parameter and orientation angles was also investigated. These results indicate that under attainable laboratory conditions (including IR excitation) the reaction proceeds at a rate too slow to be observed by usual methods.
Quenching of the lowest-lying metastable excimer of argon by N2 and effects of ’’three-body’’ Ar(1s) quenching on the yield of Ar2(3Σ+u)
Authors: Chen Mon-Chao , Firestone R. F.
Published: February 2003

Fast absorption spectrophotometry has been used to monitor the growth and decay of the Ar2(3Σ+u) excimer species at 992 nm in argon–nitrogen mixtures following passage of single pulses of a high current, high energy electron beam. The rate constant for electronic energy transfer to N2 is equal to 2.24 (±0.08)10−12 cm3 molecule−1 s−1 at 294 K. The yield of Ar2(3Σ+u) is found to be markedly enhanced relative to predictions based on the total quenching efficiencies of N2 for the Ar(1s) atoms. This enhancement is attributed to ’’three-body’’ quenching by N2, i.e., vibrational and rotational relaxation of dissociative excimer molecules formed by two-body Ar(1s)+Ar(1S0) combinations.
Torsion angle dynamics in three bond chainsa)
Authors: Evans Glenn T.
Published: February 2003

The correlation times for torsion angle fluctuations of three bond molecules in a liquid are investigated as a function of the barrier hindering internal rotation. The algorithm for the correlation time is general and can be applied for any torsional potential and bond angle. Correlation times obtained from this analysis are in basic accord with the Kramers theory.
Electron correlation in molecular many-electron systems by diagrammatic many-body perturbation theory: Correlation energies and dipole polarizabilities of the hydrogen molecule
Authors: Itagaki T. , Saika A.
Published: February 2003

Diagrammatic many-body perturbation theory is used to calculate the electronic energy and the static electric dipole polarizability of the hydrogen molecule in its ground state. An amply extended discrete basis set of Gaussian orbitals is employed to minimize basis set errors and single-electron states are generated by the Hartree–Fock VN potential. The correlation energy is evaluated through third order and with some higher-order corrections included by denominator shifts to recover about 95% of the total correlation energy. Dipole polarizabilities are calculated through second order in electron correlation with an accuracy of ∼2%. Also the energy-denominator decoupling theorem is explicitly proved by invoking combinatorial analysis to implement extensive denominator shifts. Considering the values obtained, some comments are given on the application of partial summation techniques to molecular problems.
Hydrodynamic solution of the time-dependent Ising model
Authors: Huang H. W.
Published: February 2003

It is shown that although Glauber’s time-dependent Ising model with a magnetic field cannot be solved in general, it can be solved in a hydrodynamic limit. This solution is useful for describing the relaxation kinetics of polymers, whose equilibrium properties are equivalent to a one-dimensional Ising model. The general properties of the hydrodynamic approach are discussed.
Lifetimes and predissociation in (AlH(AlD) A1Π
Authors: Baltayan P. , Nedelec O.
Published: February 2003

Radiative lifetimes of AlH(AlD) A1Π have been measured in a hollow cathode discharge by dye laser excitation, in ns: Predissociated rotational levels lifetimes are given and used to precise the shape of the hill of the A1Π potential energy curve crossed by tunnel effect. The AlH dissociation energies are found: for A1Π, De(eV) =0.24±0.01 and for X1Σ+, De(eV) =3.17±0.01. The normal levels lifetimes variation with v′ is attributed to a configuration mixing in A1Π.
Photoionization of ethylene clusters
Authors: Ceyer S. T. , Tiedemann P. W. , Ng C. Y. , Mahan B. H. , Lee Y. T.
Published: February 2003

The energetics of the ethylene ion–molecule reactions has been investigated in more detail than previously possible in two body collision experiments by photoionization of the neutral van der Waals ethylene dimer. The stability of the ion–molecule collision complex (18.2±0.5 kcal) as well as the highest potential barrier along the reaction coordinate for decomposition have been determined for this exothermic reaction. In a similar manner, the energetics of the solvated ethylene ion has been investigated by photoionization of the ethylene trimer.
Forbidden Raman scattering processes. I. General considerations and E1–M1 scattering
Authors: Harney R. C.
Published: February 2003

The generalized theory of forbidden Raman scattering processes is developed in terms of the multipole expansion of the electromagnetic interaction Hamiltonian. Using the general expressions, the theory of electric dipole–magnetic dipole (E1–M1) Raman scattering is derived in detail. The 1S0→3P1 E1–M1 Raman scattering cross section in atomic magnesium is calculated for two applicable laser wavelengths using published f-value data. Since resonantly enhanced cross sections larger than 10−29 cm2/sr are predicted it should be possible to experimentally observe this scattering phenomenon. In addition, by measuring the frequency dependence of the cross section near resonance, it may be possible to directly determine the relative magnitudes of the A⋅p and A⋅A contributions to the scattering cross section. Finally, possible applications of the effect in atomic and molecular physics are discussed.
Spectral line parameters of the ν4 s
R
R (8,3) transition of NH3 using a CO laser
Authors: Farrow L. A. , Richton R. E.
Published: February 2003

The close coincidence between the 13–12 P (8) CO laser line and sRR (8,3) transition in the ν4 band of NH3 is used to find the spectral parameters of the absorbing line by fitting the Doppler and Voigt shapes to the appropriate regions of the transmittance curves. The self-broadening parameter (linewidth) is found to be (8.11±0.43) ×10−4 Torr−1 cm−1. The foreign gas broadening coefficient with respect to N2 is measured to be 5.28±.90. The frequency offset between the laser and the center of the transition is determined to be approximately half the full Doppler width. From the line strength measurement, δμ/δQ is found to be 6.3±1.8 esu, approximately 20% smaller than that derived in an earlier determination based on total band strength, rather than that of a single line as is done here. The difference may be due in part to the unavoidable inclusion in the earlier work of the overlapping 2ν2 band.
Estimation of the dissociation energy of weakly-bound molecules from spectroscopic data
Authors: Goble James H. , Winn John S.
Published: February 2003

Expressions for the dissociation energy of the Morse potential and the Lennard-Jones (2n,n) potential are derived in terms of low-order mechanical constants of diatomic molecules. These expressions are related to a more general series expansion of the potential, and a new expression for the dissociation energy of a weakly bound diatomic is derived. This expression contains Be’αe’ and the power of R−1 which leads a long-range expansion of the potential. The expression is accurate to a few percent when compared to reliable experimental values and should be of value when only a limited number of spectral constants can be obtained from experiment.
ν3 mode absorption behavior of CO2 laser excited SF6
Authors: Deutsch T. F. , Brueck S. R. J.
Published: February 2003

Infrared–infrared double resonance measurements of the SF6 ν3 mode spectral region for excitation levels of up to 1.2 J/cm2 are reported. Immediately following the pump laser excitation, the induced absorption spectrum of the ν3 mode shows a pronounced red shift. The spectrum then shifts to shorter wavelengths on a time scale of several microseconds, showing a cooling of the ν3 mode. At an excitation level of 3 photons/molecule the measured spectra approach the thermal spectrum expected for complete vibrational energy thermalization among all of the vibrational degrees of freedom on a time scale of 3±2 μsec. At higher excitation levels (∼10 photons/molecule) the induced spectrum still shifts on a comparable time scale but is broader than a thermal spectrum. At the lower fluence levels (∼3 photons/molecule), a ν3 mode temperature can be assigned to the spectra. The time evolution of this temperature exhibits only a weak pressure dependence. A much broader induced absorption band, approximately a factor of 100 weaker than this ’’hot’’ ν3 mode absorption, has been observed extending more than 100 cm−1 to the high frequency side of the ν3 mode absorption band. The spectral dependence of this absorption band is in qualitative agreement with the multiphoton excitation spectrum found in two-frequency dissociation experiments.
A study of 3d→4s transitions by modulation spectroscopy
Authors: Shatwell Robert A. , McClure Donald S.
Published: February 2003

In order to gain further information on the 3d→4s transitions of transition metal ions (V++, Mn++, and Co++) in host crystals both the magnetic circular dichroism (in KMgF3) and the linear dichroism (in MgF2) were studied. A quantitative interpretation of the results shows the following: the transitions are promoted by tiu-type modes and the intensity comes from the nearby 3d→4p transitions; the zeroth moment of linear dichroism is heavily dependent upon the modification by the crystal of the vibronic matrix elements connecting the 4p and 4s states. The orthorhombic perturbation parameters of the 3dn−14s states in MgF2 host are not the same as those of the 3dn states. The symmetry assignments of the 3dn−14s states are confirmed.
Evidence for a very slow transformation in ice VI at low temperatures
Authors: Johari G. P. , Whalley E.
Published: February 2003

The high-frequency permittivity of ice VI decreases steadily at 123.1 K and increases again when warmed to 127.8 K. There is therefore a new transformation occurring slowly in this region. The transformation of samples of H2O, D2O, and 1% D2O in H2O was followed for 252 days, and it was not yet completed. The experimental conditions were within the region of stability of ice VI, so the transformation is not to a known phase of ice. It was too slow to be an ordering transformation determined by the dielectric relaxation time, and it is likely that a wholly new phase was being produced.
Electron impact spectra of methane, ethane, and neopentane
Authors: Johnson Kenneth E. , Kim Kangjin , Johnston David B. , Lipsky Sanford
Published: February 2003

Electron impact spectra of methane, ethane, and neopentane have been obtained at scattering angles of 0° and 90° and at impact energies from ?30 to 250 eV. The data are consistent with the lowest excitation in all of these systems to involve promotion of an electron to a 3s Rydberg-like orbital. Differences between 0° and 90° onsets are attributed to large-angle intensity enhancements of transitions to the 3s Rydberg triplets. At 90° all of the spectra exhibit very similar intensity redistributions with strong enhancement of transitions in the 12 and 15 eV region as compared to lower-lying transitions. Assignments of the spectra and possible origins of the angular dependence are discussed.
Magnetic circular dichroism spectra of decacyclene and hexabenzocoronene
Authors: Higashi M. , Yamaguchi H.
Published: February 2003

The magnetic circular dichroism (MCD) spectra of decacyclene (I) and hexabenzocoronene (II) have been measured. The absorption spectra of I and II located in the lowest wavenumber region (22–30×103 cm−1) were assigned by using the MCD spectra and the results of the SCF screened potential π-MO CI calculations. The 1E′ and 1Elu excited states of I and II are located at 26.5 and 26.1×103 cm−1, respectively. The calculated Faraday A/D values for these excited states agreed well with the experimental values both in signs and in magnitudes. The calculated Faraday B values for these excited states tended to be larger than the experimental values.
A statistical theory of three-body ion–molecule reactions
Authors: Herbst Eric
Published: February 2003

A theory of three-body ion–molecule reactions at low pressures which incorporates the principle of detailed balancing is presented. Agreement between theory and recent experiments on a variety of polyatomic reactive systems is assessed and found to be satisfactory.
Resonances in photodetachment of sodium halide negative ions
Authors: Novick Stewart E. , Jones Patrick L. , Mulloney Thomas J. , Lineberger W. C.
Published: February 2003

The cross sections for photodetachment of the alkali halide negative ions NaCl−, NaBr−, and NaI− have been measured in the photon energy range 2.0–2.3 eV. In this energy range, well above the photodetachment threshold at approximately 0.6 eV, the only processes energetically accessible are photodetachment to produce the ground electronic state neutral alkali halide, and photodissociation. For each of the sodium halides, we observe a single isolated resonance in the cross section, occurring approximately 160 cm−1 to the high energy side of the neutral sodium atom 3s–3p energy difference. This resonance is interpreted as autodetachment of a 2Π state of the negative ion imbedded in the photodetachment continuum. The X 2Σ–A 2Π energy difference in NaX− is almost completely halide independent, providing strong support for the qualitative picture of the negative ion as being composed of a neutral sodium atom adjacent to a closed shell halide ion. Qualitative fits of the experimental data utilizing the Fano formalism indicate that the lifetime of the autodetaching state is on the order of 10 −12 sec and that the shape of the potential well for the 2Π state is virtually identical to that of the negative ion ground state.
Calculation of nonlinear susceptibilities of nitrogen-containing heterocycles and of nitriles
Authors: McIntyre Eugene F. , Hameka Hendrik F.
Published: February 2003

We calculated the nonlinear third-order electric susceptibilities of a group of nitrogen-containing heterocyclic molecules and of a group of nitrile molecules. We obtain unusally large susceptibility values for three molecules, namely, 2,2,6,6,-tetracyanonaphthoquino dimethane (XL), 1,1,5,5-tetracyanonaphthoquino dimethane (XLI), and TCNQ (XXXV). The values are approximately -40, 000 ×10−36 esu, −12, 000×10−36 esu, and −4, 000×10−36 esu, respectively. We express our hope that these theoretical predictions will be verified experimentally.
On ’’Theory of collisions between an atom and a diatomic molecule in the body-fixed coordinate system’’
Authors: Choi B. H. , Poe R. T. , Tang K. T.
Published: February 2003

The nonparity asymptotic boundary conditions for the S matrix in the body−fixed close-coupling approximation are discussed.
Theoretical studies of the translational diffusion coefficient of charged macromolecules applied to bovine serum albumin
Authors: Schora) R. , Serrallach E. N.
Published: February 2003

Our results suggest that there is an ’’intimate relationship’’ between the Doherty–Benedek–Stephen and Phillies theory for the diffusion coefficient of charged macromolecules. By introducing the hard sphere approximation for the radial distribution function between the macromolecules into the Phillies theory, we obtain a good approximation to the Doherty–Benedek–Stephen result. In order to take into account correlations in the positions of the proteins, we have also introduced the more realistic dilute gas approximation for the radial density function into the Phillies theory. Significantly better agreement with the experimental data has been obtained.
A modulated molecular beam study of the mechanism of the H2–D2 exchange reaction on Pt(111) and Pt(332) crystal surfaces
Authors: Salmeróna) M. , Gale R. J. , Somorjai G. A.
Published: February 2003

The interaction of hydrogen with platinum has been studied by the exchange reaction H2+D2=2HD on two crystal surfaces, a flat (111) and a stepped (332) (in step notation, (S)−[6(111) × (111)]). The adsorption of hydrogen appears to be an activated process on the Pt(111) surface, with a barrier height of ∼0.5–1.5 kcal/mole. On the Pt(332) surface, the adsorption of hydrogen requires no activation energy. The recombination of H and D atoms to form HD follows, on both surfaces, a parallel mechanism with one of the branches operative in the entire temperature range studied, 25–800° C. This branch has an activation energy and pseudo-first-order preexponential of E1=13.0±0.4 kcal/mole and A1= (8±3) ×104sec−1 for the Pt(332) surface and E1=15.6±0.5 kcal/mole and A1= (2.7±1) ×105sec−1 for the Pt(111) surface. For temperatures above ∼300° C, the second branch is observed, but the values of the preexponential factors and activation energies could not be uniquely determined for either of the two crystals. Below ∼300° C, a third process appears in series with the first branch. The scatter in the data at low temperatures due to the small signal amplitude prevents accurate determination of the rate constants for this reaction step.
Rotational energy transfer in hydrogen halide molecules at supersonic beam velocities
Authors: Turfa Alexander F. , Marcus R. A.
Published: February 2003

Rotational energy transfer cross sections are calculated for HCl–HCl and HCl–HF collisions using classical trajectories. The exponential model for the rotational results is compared with transitions j→j′ in collisions of a supersonic HCl molecular beam with a thermal beam. Reasonable agreement with the functional form of that model is obtained. The trajectory results indicate that some modification is needed in the exponential formula, to account for microscopic reversibility in rotor–rotor collisions. Using a simple intermolecular potential without adjustable parameters, in which the only anisotropic terms are of the dipolar and dispersion type (i.e., long range), reasonable agreement is obtained with the experimental constant for HCl–HCl in the exponential. Calculations are also described for HCl–HI and HCl–HBr collisions. Microscopic reversibility for the averaged cross sections is discussed in connection with the exponential model.
Reacting hard sphere dynamics: Liouville equation for condensed media
Authors: Bose S. , Ortoleva P.
Published: February 2003

A rigorous formalism is presented for analyzing a model of chemical reactions that may occur upon classical hard sphere impact. Between hard sphere encounters, the particles interact via a continuous potential. Reaction of the type A+X→B+Y are allowed to occur if threshold energy or steric criteria are satisfied. Third body effects such as catalysis or solvent mediation are accounted for via the dependence of the latter criteria. Using methods of hard sphere kinetic theory, we formulate a (pseudo-)Liouville equation, valid for all densities. This equation allows for the use of a variety of analytical procedures to generate kinetic and correlation function equations. A projection operator technique is used to derive exact chemical kinetic results valid for slow reactions and the reciprocal limit of diffusion limited reaction, both valid at all densities. We find that Enskog-like reaction rates are valid for all densities in a special case of the slow reaction limit. For this case, the overall rate in a mustistep process can be written as a sum of terms, each associated with an elemental reaction process but having concentration dependent rate coefficients.
Intramolecular hydrophobic interaction in light and heavy water
Authors: Wilf J. , Ben-Naim A.
Published: February 2003

The solubilities and standard free energies of solution of 1,2-dialkylbenzene, 1,4-dialkylbenzene, 2,3-dialkoxynaphthalene, and 2,7-dialkoxynaphthalene, were determined in H2O and in D2O. From these data the intramolecular hydrophobic interaction has been determined. It was found that the strength of the hydrophobic interaction in H2O is larger than in D2O.
The influence of the phase shift on the vibration energy transfer for a collision between an atom and a highly asymmetric diatomic molecule
Authors: Jolicard Georges
Published: February 2003

We study the influence of the oscillator phase shift on some basic transition probabilities (P0→1, P1→2, P0→2) during a collision between an atom and a highly asymmetric diatomic molecule (D+H–Br). Both molecular compression and translation distortion contribute to this phase shift which is approximated by (Δψ)j=Δψo+(2j+1) Δψ1 for the lowest vibrational levels j. This phenomenon disturbs the initial and the final levels in the transition 0→1 and 1→2 and also the intermediate level in the sequential transition 0→1→2. This considerably reduces these transition probabilities over a large energy range and is able to cut off certain transition channels at precise energy values.
On the application of the variational principle to a type of nonlinear ’’Schrödinger equation’’
Authors: Sanhueza J. E. , Tapia O. , Laidlaw W. G. , Trsic M.
Published: February 2003

’’Schrödinger equations’’ in which the potential of the ’’Hamiltonian’’ H (φ) =H0+V (φ) depends on the first order density σσ− have received some attention in recent literature. The direct variation of the functional <φ‖H (φ) ‖φ≳/<φ‖φ≳ does not lead to the eigenequation H (φ) φ=εφ. A variational functional J (φ) is proposed which has the form J (φ) =H (φ) −(q/q+1) V(q)(φ), q being the degree in φφ*. The functional j (φ) leads to solutions of the eigenequation H (φ) φ=εφ and, provided the potential Vq(φ) fulfil <φ‖V(q)(φ) ‖φ≳? (q+1) < (q+1) <φ‖V‖φ≳, its expectation value is bounded by the lowest exact eigenvalue E0, i.e., <σ‖J (φ) ‖φ≳?E0.
Structure of dense liquids at solid interfaces
Authors: Snook Ian , van Megen William
Published: February 2003

Detailed calculations of dense fluids of hard spheres, soft repulsive spheres and Lennard-Jones molecules between hard, soft repulsive and attractive solid walls reveals a pronounced stratification of the fluid’s density profile. The calculations have been performed using the NVT Monte Carlo method with about 200 fluid molecules. The results indicate that a very significant role is played by the attractive component in the intermolecular potentials, which suggests that the usual hard-sphere perturbation theories are not applicable in their present form.