bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute elastic differential electron scattering cross sections in the intermediate energy region. IV. CO
Authors: Tanaka H. , Srivastava S. K. , Chutjian A.
Published: February 2003

Using a crossed electron beam–molecular beam scattering geometry and a relative-flow technique, ratios of elastic differential cross sections of CO to those of He have been measured at electron impact energies of 3, 5, 7.5, 9.9, 15, 20, 30, 50, 75, and 100 eV. At each energy, an angular range of 15° to 130° has been covered. These ratios have been multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for CO. Since pure rotational excitations were not resolved, the elastic differential cross sections are a sum of elastic and pure rotational excitations at room temperature. From a knowledge of differential cross sections (DCS), integral and momentum transfer cross sections have been calculated. Both the DCS and integral cross sections are compared at 50, 75, and 100 eV to a recent two-potential theory of e–molecule scattering. Present results show that the isoelectronic molecules CO and N2 have very similar magnitudes and shapes of their differential cross sections.
Vibrational relaxation in HCl–CO2 and HCl–N2O mixtures studied by the laser-induced fluorescence method
Authors: Doyennette Lucien , Al Adel Fida , Chakroun Annie , Margottin-Maclou Monique , Henry Lucien
Published: February 2003

Rate constants kM–HCl and kHCl–M for the energy transfer between the vibrational levels 0001 of M=CO2 or N2O and v=1 of HCl have been measured from 300 to about 900 K using the laser induced-fluorescence method. The V–RT de-excitation rates kHClM of M(0001) by HCl, and kMHC1 of HCl(v=1) by M have also been determined from measurements of the relaxation constants versus the molar fraction of M in the mixture. These rates are found to be on the same order of magnitude as the V–V transfer rates kM–HCl and kHCl–M, respectively. The V–V transfer and V–RT de-excitation rates are evaluated from a method, developed by Shin, on the basis of a transfer of vibrational energy into rotational energy of HCl, and the calculated values are compared to the experimental results.
A model for the surface of molten salt. II. Electroneutrality and parameter changes
Authors: Goodisman Jerry
Published: February 2003

The Fowler model for an interface, which assumes two-particle distribution functions to be those of bulk liquid whenever both particles are on the liquid side of a geometric dividing surface and zero otherwise, gives ridiculous results for a molten salt. A correction to ensure local electroneutrality, demanded by the Coulombic forces, re-establishes qualitative agreement with reality. Equations for the electroneutrality correction (previously made only approximately) are given and solved by a variational technique. A simplified route to the bulk liquid distribution functions is developed; this permits experimentation with changes in parameters in the reduced primitive model used for the molten salt. The effect of such changes on calculated surface properties is investigated, and further improvements in the model discussed.
Interspecies vibrational energy flow in CO2 or N2O mixtures with the series of deuterated methanes
Authors: Mehl Rosemary , McNeil Scott A. , Napolitano Louis , Portal Luisa M. , Drozdoski Walter S. , Bates Richard D.
Published: February 2003

Time-resolved laser-induced infrared fluorescence was used to study the rates of deactivation of vibrationally excited CO2 and N2O by the series of deuterated methanes CHnD4−n, where n=0–4. Rates varied from 4.7 msec−1 torr−1 for CO2–CH4 to 199 msec−1 torr−1 for N2O–CD4. Within experimental error, the deactivation probabilities for CO2 or N2O by the same collision partner are identical. The rates observed were determined to increase linearly with the number of deuterons per substituted methane, and thus with the number of C–D stretches nearly resonant with the 001 state of CO2 or N2O. The results are interpreted by examining the role that rotational state changes of the collision partners can play in reducing the vibrational energy defect, thus minimizing the amount of energy that must go into translations.
Steady states in hot atom chemistry
Authors: Shizgal B.
Published: February 2003

A detailed comparison is made with the predictions of the hydrodynamic steady state theory of hot atom reactions developed by Keizer [J. Chem. Phys. 58, 4524 (1973)] and those obtained from a more precise moment method solution of the Boltzmann equation. Agreement is found to occur only if there is a good separation in the time scale for reactive collisions and the time scale for energy redistribution in elastic collisions. This requires that the system parameters, which includes mass ratios and cross sections, be such that the reaction proceeds slowly relative to the rate of elastic collisions. The steady state theory was intended to be a qualitative theory of hot atom reactions and fulfills that expectation for systems that possess the neccesary separation in relaxation times.
Resonance Raman spectra of copper tetraphenylporphyrin: Effects of strong vibronic coupling on excitation profiles and the absorption spectrum
Authors: Shelnutt J. A. , O’Shea D. C.
Published: February 2003

Raman excitation profiles of copper tetraphenylporphyrin have been obtained and interpreted in terms of strong vibronic coupling. The Duschinsky mixing of normal modes in the excited Q electronic state has a dominant effect on the excitation profiles and the absorption spectrum. A general theoretical technique for calculating the vibronic states of molecules is described and applied to metalloporphyrins. The analytical expressions obtained from a new perturbation treatment of the vibronic problem permit a detailed physical understanding of strong coupling influences and interference effects observed in copper tetraphenylporphyrin excitation spectra. A modified interpretation of the Q band absorption is indicated.
Asymptotic behavior of the mean-square lengths of self-avoiding walks terminally attached to a surface
Authors: Guttmann A. J. , Middlemiss K. M. , Torrie G. M. , Whittington S. G.
Published: February 2003

We present some exact enumeration data on the mean-square lengths of self-avoiding walks on a lattice confined to a half-space (or half-plane) with the walk originating on the dividing plane (or line). We argue that the exponent characterising the asymptotic behavior is unchanged by this spatial constraint.
An atom monopole–dipole interaction model with charge transfer for the treatment of polarizabilities of π-bonded molecules.
Authors: Olson Mark L. , Sundberg Kenneth R.
Published: February 2003

A classical model of the polarizability of π-bonded molecules is developed. The model is an extension of the atom dipole model which allows charge transfer within the molecule to reproduce the effect of delocalized π electrons. The model is applied to several test systems and is found to provide better agreement with experimental polarizabilities than the atom dipole model.
X-ray photoelectron spectroscopy of titanium tetrahalide vapors
Authors: Wallbank B. , Perera J. S. H. Q. , Frost D. C. , McDowell C. A.
Published: February 2003

X-ray photoelectron spectra of the Ti 2p and 3p and halogen core levels from titanium tetrahalide vapors have been obtained. Satellites are observed at higher binding energies than the halogen core levels as well as the titanium levels. The origin of these satellites is discussed by comparison with published data on octahedral Ti(IV) compounds. It was also observed that the separation of the Ti 2p spin–orbit doublet in TiF4 was lower than the separations observed in the other three molecules (5.2 eV in TiF4 as compared to 6.1 eV).
The generator coordinate method for molecular wavefunctions: A moment method and a simple intrinsic function
Authors: Laskowski Bernard , Diamond James , Waleh Ahmad , Hudson Bruce
Published: February 2003

An extension of the generator coordinate method to the description of the electronic structure of molecules is presented. An exact formal solution to the Hill–Wheeler equation is obtained for a certain class of intrinsic functions, namely, those whose Hamiltonian and overlap kernels are of degenerate form. Since the exact kernels are used in the Hill–Wheeler equation, the variational principle is retained. The formal solution is represented by the set of moments of the generator coordinate with respect to the weighting function. The features of the method are illustrated by application to the hydrogen molecule. A simple trial intrinsic function and a PPP Hamiltonian are used to describe the π-electron structure of three linear conjugated polyenes (1,3-butadiene; 1,3,5-hexatriene; and 1,3,5,7-octatetraene). A significant part of the apparent ground state correlation energy is recovered for each molecule and π-electron excited state energies are also calculated. These results are compared with PPP CI calculations and the limitations of this simple trial intrinsic function are discussed.
On the contribution of the exciton–photon interaction to the exciton absorption line shape in the spatially inhomogeneous wave model: Application to the a-singlet exciton of naphthalene
Authors: Robinette S. L. , Stevenson S. H. , Small G. J.
Published: February 2003

The problem of determining the contribution of the exciton–photon coupling to the absorption line shape or width of an exciton is addressed. In this regard, both the spatially homogeneous (polariton) and inhomogeneous wave models are considered. For the latter model, the theory is complex although a line shape expression is derived for the case of high exciton velocity and low oscillator strength. The related problem of determining the conditions under which the strong exciton–photon coupling limit is attained is also discussed. It is in this limit that light attenuation is independent of the oscillator strength. The theory plus new experimental data on the a exciton of naphthalene argue for the inadequacy of the polariton model. On the other hand, reasonable agreement between the data and the spatially inhomogeneous wave theory developed here is obtained. Thus, it is possible to estimate that the exciton–photon coupling contribution to the a-exciton linewidth is 0.26 cm−1. This is the major portion of the 2 K linewidth of 0.3 cm−1.
Ultraviolet dispersion of the donor–acceptor charge transfer contribution to the second order hyperpolarizability
Authors: Levine B. F. , Bethea C. G.
Published: February 2003

We have measured for the first time electric field induced optical mixing (ω+2ω=3ω) in the liquid state. Two molecules DANS (trans-4-dimethylamino-4′-nitrostilbene) and p-NA (p-nitroaniline) possessing large intramolecular charge transfer interactions were used and the second order mixing hyperpolariabilities β (3ω) were determined to be β (3ω) = (−7.2±2.6i) ×10−28 and β (3ω) = (+9.6±38i) ×10−30 esu for DANS and p-NA, respectively, with 3ω=3.50 eV. Combining these measurements with the simple two level quantum mechanical model yields the theoretical prediction of β (2ω) = (+38+15i) ×10−28 and β (2ω) = (+48+5.3i) ×10−30 esu for the second harmonic hyperpolarizability of DANS and p-NA, respectively. These predictions are not in good agreement with the experimental values ‖β (2ω) ‖ =2.1×10−28 esu (obtained using the measurements of Oudar and Chemla) and β (2ω) =+22×10−30 esu.
Reactive dynamics for diffusive barrier crossing
Authors: Northrup Scott H. , Hynes James T.
Published: February 2003

A theory is presented for intramolecular reactions A?B regarded as potential barrier crossing between two stable states A and B in the large friction limit. This limit, in which dynamics are governed by spatial diffusion in the potential, is an important example of extreme deviation from transition state theory predictions. Our theory expresses the full reaction rate constants in terms of simpler contributions: (a) the barrier rate constants and (b) the internal rate constants. The former depend solely on dynamics near the barrier top and govern the rate when stable state internal equilibrium is maintained. The latter depend solely on internal equilibration dynamics in the stable states A and B (defined away from the barrier top). The internal rate constants correct the barrier rate constants for stable state internal nonequilibrium effects. These two contributions are discussed in dynamical terms in some detail. Our theoretical rate constants are evaluated and compared with the rate constants observed by monitoring population decays obtained by direct numerical integration of the Smoluchowski equation. A simple minimum principle predicts the reaction rate constants with high accuracy at any value of the barrier height. For high barriers, our predictions approach (but are more accurate than) those of the classic approximate analysis of Kramers. For very low barriers (e.g., 1.6kBT), internal nonequilibrium effects neglected by Kramers are found by our theory to account for approximately 33% of the rate constant.
Initial condition effects for diffusive barrier crossing
Authors: Northrup Scott H. , Hynes James T.
Published: February 2003

A formulation and analysis of transient initial condition effects on reaction is given for the diffusive limit of barrier crossing between two stable chemical states. We focus on the case where the system is initially prepared in the high energy intermediate barrier region located between the stable states. It is shown how branching fluxes into and branching probabilities for stable states can be both calculated for and determined from analysis of stable state population dynamics.
Representation of a
b i
n
i
t
i
o energy surfaces by analytic functions
Authors: Vance R. L. , Gallup G. A.
Published: February 2003

A method for the analytical representation of ab initio energy surface results is described. For a three-atom surface, the potential function is written as a sum of atomic, two-body, and three-body terms. This allows an easy fitting of the whole surface, including the dissociated and united atom limits. The theory is applied to an H3 surface of limited accuracy calculated for these purposes. Comparisons are made, where possible, with more accurate calculations. Extensions to surfaces involving four or more atoms are also discussed.
Nuclear magnetic resonance of 11B in sodium borohydrides, NaBH4 and NaBD4, in the structural transition region
Authors: Trokiner A. , Theveneau H. , Papon P.
Published: February 2003

11B spin-lattice relaxation time, T1, has been measured in NaBH4 and NaBD4, in the near vicinity of the structural phase transition. The experimental results have confirmed the first order nature of the phase transtion, showing up a thermal hysteresis, phases coexistence and a discontinuity of the spin-lattice relaxation time. We have explained the discontinuity, experimentally found for T1 at the phase transition, by a theory which only takes into account the order–disorder nature of the phase transition.
Snowballing effect for electron solvation in dilute solutions of polar molecules in nonpolar solvents
Authors: Tachiya M.
Published: February 2003

Electron solvation in dilute solutions of polar molecules in nonpolar solvents involves a formation of a localized state by electron attachment to a pre-existing cluster, followed by subsequent attachment of polar molecules to that charged cluster. We studied the effect of subsequent attachment of polar molecules on the transition energy of the solvated electron by use of the continuum model, and found that subsequent attachment has a negligible effect on the transition energy. An implification of this finding is that the snowballing effect cannot probably be observed by means of optical methods. The relative importance of short-range and long-range interactions in electron solvation is also discussed.
Vibrational and electronic energy transfers from a single vibronic level of H2CO (?, 1A2), the 41 level
Authors: Shibuya Kazuhiko , Lee Edward K. C.
Published: February 2003

The vibrational deactivation rates from the 41 level to the 40 level of H2CO (?, 1A2) and the electronic quenching rates of H2CO (?,41;40) have been measured for various foreign gases; acetaldehyde, acetone, n-butane, CH2F2, NO, CO, N2, O2, and Ar including H2CO itself. Single vibronic level emission spectroscopy of laser induced fluorescence from H2CO indicates that the collisional vibrational energy removal of 125 cm−1 is quite efficient for all of the collision partners, but O2 is abnormally less efficient. The collisional electronic quenching has been measured by the pressure dependence of the overall fluorescence emission yield, and it is shown to be inefficient in general. Hard sphere collision efficiency of the self-quenching by H2CO(?), ∼0.05, is higher than the collisional efficiencies of the π-bonded foreign gases, ∼0.02 for NO and ∼0.005 for O2, CH3CHO and (CH3)2CO. Probable explanations for the measured rates are given, especially to account for the observed anomalies.
Low temperature heat capacity, dielectric constant, and thermodynamic properties of solid germane
Authors: Mountfield K. R. , Weir R. D.
Published: February 2003

The heat capacity of solid germane, GeH4, has been measured over the range 2.8 K<T<111 K with an estimated precision of ±1%, except below 5 K where it becomes ±2%. Substantial differences between our data and those of Clusius and Faber [Z. Phys. Chem. Abt. B 51, 352(1942)] occur in the region of overlap. Analysis of our data shows the presence of a residual entropy of R ln1.6 and the presence of a nonvibrational contribution to Cp at T<5 K. Present is an AT−2 term in the Cp beginning around 4 K which is consistent with the Schottky-type anomaly, suggesting the possibility of conversion of the spin species. Our analysis also shows the translational and librational branches of the frequency spectrum are separated with the latter modes becomes fully excited at 60 K. The dielectric constant ε of GeH4 has been measured over the range 4.2 K<T<141 K with an estimated precision of ±1%. Density of solid GeH4 has been measured at temperatures of liquid nitrogen and of liquid air.
Temperature dependence of microtubule structure
Authors: Marchi Ezio , Benegas Julio , Ripoll Daniel
Published: February 2003

In this paper we present a theoretical model for the temperature dependence of microtubule structures. We use the Ising model to describe the interaction among dimers constituting the microtubules. Some denaturation curves are presented which show the general type of change of number of dimers in the microtubule.
Electronic structure and spectra of small rings. VI. Multiphoton ionization spectra of the saturated three-membered rings
Authors: Robin M. B. , Kuebler N. A.
Published: February 2003

The multiphoton ionization spectra of cyclopropane-h6, cyclopropane-d6, and ethylenimine have been recorded, and the resonances observed at the two-photon levels compared with the corresponding single-photon transitions. In the cyclopropanes, a complex band system is observed in the two-photon 51 000–56 000 cm−1 region which is shown to be electronically allowed [origins at 51 059 cm−1 (−h6) and 51 109 cm−1 (−d6)] for both one-photon and two-photon absorption, and to be due to the 3e′→3s Rydberg transition. The 1E′ state is strongly Jahn–Teller distorted, with conspicuous display of e′ ring deformation in the Franck–Condon envelope. In ethylenimine, the 8a′→3s band is structured in the two-photon spectrum, but not in one. A second band is also found near 55 000 cm−1 which does not coincide in detail with the one-photon n→3p band in the same region, and is thought to be a second component of the (n,3p) manifold.
High pressure luminescence studies of indole and 5-methoxyindole in polymethylmethacrylate
Authors: Hook J. W. , Drickamer H. G.
Published: February 2003

High pressure luminescence measurements have been made on indole and 5-methoxyindole in PMMA. At both 300 and 110 K the fluorescence peaks shifted to lower energy and the quantum yield decreased with increasing pressure. The peak shift at 110 K was identical with that at 300 K, and the quantum yield increased by a pressure independent factor over the temperature range studied (2.3 for indole and 1.8 for 5-methoxyindole). At 110 K pressure shifted the phosphorescence peaks to lower energy but less rapidly than it shifted the fluorescence peak. The observed phosphorescence lifetime dropped with increased pressure. The loss of fluorescence quantum yield is explained as due to an increase in the intersystem crossing rate. This intersystem crossing scaled quite well with the S1–T1 energy difference. Differences in behavior between indole and 5-methoxyindole may be related to differences in the energies of the triplet states involved.
Excited-state proton transfer in the crystals of 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile
Authors: Itoh Michiya , Tanimoto Yoshifumi , Iitaka Yoichi
Published: February 2003

The crystal and molecular structures of 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (HBMN) were determined at room temperature. The molecule is almost planar and packed along the b axis with a spacing of approximately 3.7 Å in a monoclinic unit cell. The molecules include a weak hydrogen bonding between the 4-hydroxy proton and one of the two nitrogen atoms of the malononitrile group along the a axis within the a–c plane. Polycrystalline HBMN exhibits very strong green fluorescence in the 490-nm region at low temperature, while the crystal shows a weak fluorescence at 450–460 nm at room temperature. The large temperature dependence of the fluorescence spectra is discussed in terms of an excited-state proton transfer in the weak hydrogen bonded system in the crystals.
The far-infrared vapor phase spectra of some halosubstituted anilines
Authors: Kydd R. A. , Krueger P. J.
Published: February 2003

Vapor phase far-infrared spectra from 35 to 675 cm−1 of the nine ortho-, meta-, and para-substituted fluoro-, chloro-, and bromoanilines obtained with an interferometer are reported. The vi=1, 2, and 3 levels of the amino group inversion vibration are established from the observed transitions, and the barriers to inversion are derived from these, using a simple double minimum harmonic well potential with a Gaussian barrier. Calculated barrier heights range between 385.9 cm−1 (2-bromoaniline) and 599.9 cm−1 (4-fluoroaniline). The following out-of-plane vibrations are also assigned: amino group wag, substituent wag, and ring deformation. The ντ±νi combinations lead to deduced frequencies for the torsional vibration ντ in a number of cases.
Laser-initiated chemical reactions: Cl+H2S→HCl+HS: Rate constant, product energy distribution, and direct detection of a chain mechanism
Authors: Braithwaite Martin , Leone Stephen R.
Published: February 2003

Laser-initiated, time-resolved infrared chemiluminescence techniques are used to study the detailed kinetics of chlorine/hydrogen sulfide systems. Measurements on the Cl+H2S→HCl+HS reaction are carried out by pulsed laser photolysis of S2Cl2→S2Cl+Cl in a flowing mixture with H2S, while detecting vibrational chemiluminescence from the HCl product. The measured rate constant for the Cl+H2S reaction is 6.0 ±1.2×10−11 cm3 molecule−1 sec−1 at 296°K. The vibrational product distribution is predominately excitation of HCl to v=1 and v=2, with the ratio (v=1):(v=2) =15. The dynamical interpretation of the Cl+H2S reaction data is discussed. Photolysis of Cl2→2Cl in the presence of H2S produces a rapid chain reaction, Cl+H2S→HCl+HS, HS+Cl2→HSCl+Cl. The chain mechanism and its real time development are observed directly from the product chemiluminescence signal.
Comparison of the coherent anti-Stokes and coherent Stokes Raman line shapes of the ν1 line of β-carotene near a one photon resonance
Authors: Carreira L. A. , Goss L. P. , Malloy Thomas B.
Published: February 2003

Experiments to detemine the signs of the imaginary damping factors in the resonance denominators of the expressions for the third order susceptibilities governing coherent anti-Stokes and coherent Stokes Raman spectroscopy (CARS and CSRS) have been carried out using the ν1 line of β-carotene. The experimental results are compared to the two different theoretical results predicted by the fully quantum mechanical and the semiclassical calculations for the third order susceptibilities for CARS and CSRS.
Vibrational energy flow in CD3H and CD3H–polyatomic mixtures
Authors: Drozdoski Walter S. , Bates Richard D. , Siebert Donald R.
Published: February 2003

Laser-induced fluorescence studies showed that the higher CD3H vibrational fundamentals (ν2 at 2142 cm−1 and ν4 at 2263 cm−1) are populated more rapidly than the intermediate fundamental (ν5 at 1291 cm−1) when ν6 at 1037 cm−1 is excited by a Q-switched CO2 laser. The experimentally observed rate for the (ν2,ν4) fluorescence at 4.5 μ is 300±50 msec−1 torr−1. Possible activation pathways are identified using the results of thermal lensing experiments and studies of fluoresence intensity as a function of laser power. Interspecies energy transfer rates from CD3H to SF6, SiF4, and CF4 were determined to be 154±7, 146±9, and 33±1 msec−1 torr−1, respectively.
Experimental and calculated energy levels of Sm2+:BaClF
Authors: Gâcon J. C. , Grenet G. , Souillat J. C. , Kibler M.
Published: February 2003

New investigations on the optical properties of divalent samarium in barium chlorofluoride single crystals have been performed. As a result, an energy level diagram including 42 Stark components of the 7FJ and 5DJ multiplets of the 4f6 configuration has been deduced from the excitation and fluorescence spectra. Parameter optimizations involving combined spin–orbit and crystal-field interactions have been achieved from the experimental Stark levels of the 7F ground term. An interpretation of the fitted crystal-field parameters has been developed in the framework of an additive ligand-field model. The irreducible tensor method applied to the chain O3⊆C∞v⊆C4v⊆C2v is used throughout this paper.
Potential function for the low frequency bending mode of silylisocyanate
Authors: Durig J. R. , Kalasinsky K. S. , Kalasinsky V. F.
Published: February 2003

The infrared spectral (3500–200 cm−1) for H3SiNCO and D3SiNCO in the vapor and solid states and the Raman spectra (3000–50 cm−1) for all three physical states have been recorded. The Raman spectra of the gas-phase samples exhibit a number of Q branches between 90 and 150 cm−1 which have been assigned to the double quantum transitions associated with the skeletal bending mode of a quasilinear molecule. An anharmonic potential of the form V=Aq4+Bq2 has been used to adequately explain the observed spectra, and the values for the potential constants are A=0.858 and B=−12.5 for the ’’light’’ species and A=0.780 and B=−11.9 for the ’’heavy’’ isotope. These potential surfaces indicate a barrier of 45 cm−1 at the linear skeletal configuration with only two vibrational levels below the barrier. The potential function and barrier are discussed in the context of previous studies.
An accurate criterion for the retention of two-electron integrals, the EBIR method
Authors: Jensen J. Robert , Fenske Richard F.
Published: February 2003

A method for performing electronic structure calculations on large systems is described wherein only a fraction of the integrals used by an ab initio calculation need be retained. The criterion for integral retention in the method is based on upper bounds to two-electron integrals. This procedure, the energy based integral retention (EBIR) method, is applied to the nitrobenzene molecule and a linear arrangement of three nickel atoms, and the results are found to be in very good agreement with ab initio calculations. The accuracy of the method and its control are discussed and compared to the accuracy of an overlap criterion for integral retention as well as an alternative energy bound.
Effects of high pressure on molecular electronic spectra
Authors: Tompkins Robert C.
Published: February 2003

The experimental tests by Okamoto and Drickamer of the Drickamer model of high-pressure effects on electronic spectra are re-examined. It is here shown that the method of data processing that they used with this model leads to contradictions. However, a generalization based on a theory of Lin appears compatible with the data.
Low lying 1A2u(σ,π*) and 1E2g(π,π*) states of benzene as suggested by Raman intensities
Authors: Ito Mitsuo , Abe Haruo , Murakami Junichi
Published: February 2003

The Raman spectra of benzene, substituted benzenes, and charge transfer complexes between benzene and halogens were observed. The great preresonance intensity enhancement of the out-of-plane ν10(e1g) Raman line of benzene and its intensification upon the complex formation strongly suggest the existence of the low lying 1A2u(σ,π*) state of benzene. On the other hand, the preresonance Raman effect of the overtone of the ν14(b2u) vibration of benzene and the strong appearance of Raman and infrared inactive fundamentals ν16(e2u) and ν17(e2u) of benzene upon the complex formation can be explained by assuming the low lying 1E2g(π,π*) states. It is qualitatively concluded that the perturbation imposed on benzene in the direction perpendicular to the molecular plane induces the intensity enhancements of the out-of-plane vibrations, while the perturbation parallel to the molecular plane contributes greatly to the Raman intensities of the in-plane modes.
Band strength factors with asymptotic expansion for Morse–Pekeris oscillators
Authors: Gallas J. A. C. , Grieneisen H. P. , Chakraborty B. P.
Published: February 2003

Band strength factors have been calculated by asymptotic expansion technique for N+2 (B 2 Σ+u–X 2 Σ+g) and N2(C 3πu–B 3πg) and the rotational dependences have been studied for J up to 100. A comparison between the band strengths has been made using experimentally derived electronic transition moment function for the N2(C 3πu–B 3πg) system. The present method of calculation does not use the usual r-centroid approximation.
Effect of centrifugal distortion and anharmonic vibration on the chemical shielding of 31P in PH3 and PD3
Authors: Jameson Cynthia J. , Jameson A. Keith
Published: February 2003

The observed temperature dependence of 31P NMR chemical shift and the sign of the 31P isotope shift in the PH3–PD3 system are found to be inconsistent with the thermal average of Δα which can be calculated using approximate cubic force constants for PH3 and PD3 [K. Kuchitsu, J. Mol. Spectrosc. 7, 399 (1961)]. By using a reasonable estimate for k222 and k244, and keeping all other cubic force constants the same as Kuchitsu’s, the observed temperature dependence of the 31P NMR signal is reproduced within experimental error.
Selective excitation transfer and separated relaxation measurements of degenerate transitions in NMR spectroscopy
Authors: Henrichs P. M. , Schwartz L. J.
Published: February 2003

A method is described by which phase coherence induced by selective excitation of a single line in a spin–spin multiplet is transferred to one or more nonirradiated transitions. Under the appropriate conditions, excitation may be transferred to individual members of groups of degenerate lines or to forbidden transitions. Detailed calculations and experimental results are given for heteronuclear AX, AX2, and AX3 systems. Selective excitation of individual transitions in degenerate groups of lines allows their transverse relaxation to be studied. Differing linewidths of various degenerate resonances in 13C-methanol doped with chromium acetylacetonate were measured by the excitation-transfer procedure.
Polymer chain moments and related problems
Authors: Freire Juan , Fixman Marshall
Published: February 2003

Earlier work on the calculation of the characteristic function, moments, and distribution function of polymer chains is generalized and numerical calculations are reported for polymethylene.
Raman spectroscopy and local order in aqueous solutions of strong II–I electrolytes
Authors: Fontana M. P. , Maisano G. , Migliardo P. , Wanderlingh F.
Published: February 2003

We report polarized Raman spectra for aqueous solutions of NiCl2, CdCl2, ZnCl2, CuCl2, Cu(NO3)2, and SrCl2. Our analysis of the Raman data provides an interpretation for the diffuse low frequency Raman scattering in transition metal halide–water solutions in terms of a vibrational density of states. Such a density corresponds to collective vibrational modes in a solute-connected middle range lattice. The results are also discussed on the basis of recent measurements of viscosity, thermodynamic quantities, and EXAFS.
Correlations for interacting Brownian particles. II
Authors: Ackerson Bruce J.
Published: February 2003

The generalized Smoluchowski equation is used in a projection operator formalism to find an equation for the intermediate scattering function. Several different approximations are made to investigate the behavior of the intermediate scattering function for intermediate and long times. The generalized Stokes–Einstein relation is not given exactly by the formalism in the hydrodynamic regime. The hydrodynamic interaction is needed to produce a separation between the intermediate and long time scales in the small k limit.
Monochromatic excitation of the A1Π–X1Σ+ (13,0) band of 13C16O and 12C18O
Authors: Vikis A. C.
Published: February 2003

The narrow unreversed 123.58 nm resonance radiation of Kr was shown to excite exclusively the 13C16O A–X (13,0) Q (13) transition. A broader reversed 123.58 nm Kr resonance radiation was shown to excite the 13C16O A–X (13,0) P (11), Q (13), and R (15) transitions and the 12C18O A–X (13,0) P (10), Q (11), and R (14) transitions. Excitation of the above transitions was verified by high resolution absorption measurements of the A–X (13,0) band in the vacuum ultraviolet and resonance fluorescence measurements of the 13C16O and 12C18O A–X (13,v″) resonance progression in the 200–300 nm wavelength region. The 12C16O did not show any detectable fluorescence with either of the above excitation lines. This fortuitous isotopic selectivity favors photochemical enrichment of carbon-13 and oxygen-18, provided that the excited 13C16O and 12C18O can be effectively scavenged.
Energy transfer in monochromatically excited 13C16O and 12C18O (A1Π v′=13) molecules
Authors: Vikis A. C.
Published: February 2003

The 123.58 nm resonance radiation of Kr excited 13C16O and 12C18O to resonant rotational energy levels of the A1Π v′=13 state. The steady state fluorescence of the 13C16O (A1Π–X1Σ+) (13,v″) resonance progression was quenched by 13C16O, 12C18O, 12C16O, CO2, O2, N2, H2, D2, He, Ar, and Xe. The respective electronic quenching cross sections of these molecules, in Å2, in the order given above, were: 198, 38.0, 57.1, 119, 43, 78.5, 19.0, 29.3,<0.4, 3.23, and 114. The rotational relaxation cross sections of the 13C16O A1Π v′=13 Q (13) state by He, 13C16O, and 12C18O were 13, 16 and ∼16 Å2, respectively. The 12C18O (A1Π) v′=13 state was quenched by 12C18O and 12C16O with cross sections of 257 and 28.0 Å2, respectively.
Polarized fluorescent emission in uniaxial liquid crystals. The effect of intramolecular energy transfer and rotational Brownian motion on measurements of the orientational distribution function
Authors: Chapoy L. Lawrence , DuPré Donald B.
Published: February 2003

An expression is derived for the anisotropic fluorescent emission in uniaxial liquid crystals where fluorescent sites governed by an initial nonrandom distribution of orientations are subject to rotational Brownian motion. The possibility of nonparallelism of absorption and emission oscillators is also considered.
The second Born approximation for electron scattering. I. The high energy limit for small angle elastic scattering from atoms
Authors: Bonham R. A. , Konaka S.
Published: February 2003

The second Born approximation, including coupling to all channels, is considered for elastic electron scattering by atoms. A model within the framework of the LS coupling approximation is adopted for the interaction potential. The analytic results of this model are expanded in increasing positive powers of the momentum transferred to the scattered electron. The leading coefficients of the terms in this expansion are identified with matrix elements of known operators. The sum of the matrix elements over all channels is carried out with the final results expressed in terms of certain optical sums.
Kinetic theories of evaporation
Authors: Algie S. H.
Published: February 2003

Theories of evaporation and condensation which apply to a wide range of disequilibrium conditions must be based on assumptions regarding the form of the velocity distribution function of vapor molecules at the surface. However, the distribution function describing vapor molecules at the surface and moving away from it is not the same as that which applies to the emission of molecules from the condensed phase. A number of previous treatments of the half-space evaporation problem are shown to be incorrect and an improved solution, taking into account the evaporation coefficient, is presented.
Infrared spectra of matrix-isolated plutonium nitrides
Authors: Green David W. , Reedy Gerald T.
Published: February 2003

The infrared stretching frequencies of Pu14N and Pu15N in solid Ar at 20 K have been measured as 855.73 and 828.62±0.05 cm−1, respectively. The calculated harmonic frequency ωe is 861.9±1.6 cm−1 and the first anharmonic correction ωexe is 3.1±0.8 cm−1. The frequencies of the ν3 stretching modes of Pu14N2, Pu14N15N, and Pu15N2 were measured (±0.05 cm−1) as 1029.74, 1017.73, and 998.87, respectively. The plutonium dinitride molecule is linear.
Matrix reactions of ozone and oxygen atoms with hydrogen iodide. HOI formation
Authors: Walker N. , Tevault D. E. , Smardzewski R. R.
Published: February 2003

Oxygen atoms and ozone react with hydrogen iodide in dilute nitrogen and argon matrices at 8°K to produce new infrared absorptions at 3597, 1103, and 575 cm−1 which are attributed to the HOI intermediate species hypoiodous acid. The observed oxygen-18 and deuterium isotopic frequencies and associated band assignments identified isolated H–O and O–I stretching modes which defined the H–O–I structural arrangement. Partially enriched oxygen-18 and deuterium isotopic experiments confirmed the fact that the product contains one oxygen and one hydrogen atom per molecule. The vibrational spectrum of HOI is analogous to those of the other hypohalous acids.
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o SCF MO calculations of the potential surfaces of thiocarbonyls. I. ? 1A1 and ? 3A2 electronic and ? 3A2(b1) vibrational states of F2CS
Authors: Kapur A. , Steer R. P. , Mezey P. G.
Published: February 2003

A b initio SCF MO calculations using an STO-3G basis set have been carried out to obtain the potential energy surfaces of the ground ? 1A1 and lowest triplet ? 3A2 states of F2CS. The calculated equilibrium geometry of the ground state is in good agreement with the experimental geometry. Using a suitable analytic approximation to the triplet state potential surface, energies of the stack of triplet state inversion vibrational levels associated with a double minimum potential curve along the out-of-plane bending coordinate have been calculated. Good agreement with experiment is obtained.
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o effective core potentials including relativistic effects. II. Potential energy curves for Xe2, Xe+2, and Xe*2
Authors: Ermler Walter C. , Lee Yoon S. , Pitzer Kenneth S. , Winter Nicholas W.
Published: February 2003

Potential energy curves for the ground 1Σ+g state of Xe2, the first four states of the Xe+2 ions, and the eight Xe*2 excimer states corresponding to the addition of a 6sσg Rydberg electron to these ion cores have been computed using averaged relativistic effective core potentials (AREP) and the self-consistent field approximation for the valence electrons. The calculations were carried out using the LS-coupling scheme with the effects of spin–orbit coupling included in the resulting potential energy curves using an empirical procedure. A comparison of nonrelativistic and averaged relativistic EP’s and subsequent molecular calculations indicates that relativistic effects arising from the mass–velocity and Darwin terms are not important for these properties of Xe2 molecules. Spectroscopic constants for Xe+2 are in good agreement with all electron CI calculations suggesting that the computed values for Xe*2 excimers should be reliable. The lifetime for the Ou+ state of the Xe2* is computed to be 5.6 nsec which is in the range of the experimentally determined values.
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o studies of AuH, AuCl, HgH and HgCl2 using relativistic effective core potentials
Authors: Hay P. Jeffrey , Wadt Willard R. , Kahn Luis R. , Bobrowicz Franck W.
Published: February 2003

Relativistic effective core potentials (ECP) are derived for Au and Hg atoms, where the ECP incorporates the Coulomb and exchange contributions of the core orbitals, the core-orthogonality terms for the valence orthogonality terms for the valence orbitals, and the effect of the ’’mass–velocity’’ and ’’Darwin’’ relativistic effects on the valence orbitals. The results of atomic valence-electron (VE) calculations with the ECP’s compare favorably with relativistic Hartree–Fock and Dirac–Hartree–Fock calculations and with experiment, when the effects of spin–orbit coupling are included in the VE calculations. Nonrelativistic calculations, by contrast, lead to erroneous predictions and to differences in excitation energies of 1.5–3.5 eV. The large relativistic effects in the atoms carry over into the AuH, AuCl, and HgCl2 molecules, as they are important in determining correct bond lengths and bond energies and in influencing the charge distributions. Similarly large relativistic effects are encountered in ionization potentials calculated for HgCl2 from orbital energies and from SCF calculations. Spin–orbit coupling is introduced to compare with the experimental photoelectron spectrum. An extensive study of the lowest electronic states of HgH is presented, where the effects of spin–orbit coupling are critical in describing the potential energy curves of the excited 2Π1/2 and 22Σ+1/2 states.
Collisionless multiple photon excitation of SF6: A comparison of anharmonic oscillators with and without octahedral splitting in the presence of rotational effects
Authors: Ackerhalt J. R. , Galbraith H. W.
Published: February 2003

We reinvestigate the importance of octahedral splitting in multiple photon absorption by SF6 gas in view of the recent measurement and analysis of the 3ν3 spectrum by Kildal. A simple anharmonic oscillator model which includes rotational effects to first order is an excellent approximation to the more complicated octahedral splitting model. Indeed it is the rotational splittings which are essential to the physics of multiple photon absorption modeling.
Rayleigh scattering from methane
Authors: Ackerson Bruce J. , Straty Gerald C.
Published: February 2003

The decay rate of spontaneous thermal fluctuations in methane has been determined from Rayleigh scattering experiments. Measurements have been made in a broad region about the critical point, along the coexistence curve, the critical isochore, and an isotherm 0.8 K above the critical temperature. Values of thermal diffusivity obtained from the data are compared with other available data. In the immediate critical region the measured thermal diffusivity is compared with calculated thermal diffusivity values based on a recent prediction of the anomalous thermal conductivity of methane. The comparison involves assumptions concerning the scattered wave vector dependence of the decay rate in the critical region but involves no adjustable parameters. In addition, the critical isochore data are also fitted by other theoretically predicted forms for the decay rate to estimate parameters in these theories. Good agreement between measurement and prediction is found.
Temperature dependence of the deactivation of O(1D) by CO from 113–333 K
Authors: Davidson J. A. , Schiff H. I. , Brown Terry J. , Howard Carleton J.
Published: February 2003

Absolute rate constants for the deactivation of O(1D) by CO have been measured at temperatures between 113 and 333 K. A very small temperature dependence is observed and is described by the Arrhenius expression (4.7±0.9) ×10−11 exp{ (126±33)/RT} cm3/molecule⋅s, where E is in cal/mol.
Transition states, trapped trajectories, and classical bound states embedded in the continuum
Authors: Pollak Eli , Pechukas Philip
Published: February 2003

We show that the best choice of transition state, for the atom exchange reaction in a classical collinear collision of an atom with a diatomic, is a classical bound state embedded in the continuum: a periodic vibration of the triatomic system across the interaction region of the potential surface. These unstable bound states also serve as limit sets of the trapped trajectories that form the boundary of reactivity bands in molecular collisions, and we comment on the implications of this result for calculation of product state distributions. Numerical calculations of transition states are presented for the collinear H+H2 and F+H2 reactions.
Comparison of distorted wave and close-coupling results for scattering of HD by He at thermal energies
Authors: Sharma R. D. , Hart R. R.
Published: February 2003

Results of first and second order distorted wave calculations are compared with the close-coupling results of Itikawa–Takayanagi and Itikawa for scattering of HD by He at relative energies of 0.02 and 0.04 eV. The distorted wave Born calculation converges for this system. The (0→0) elastic and (0→1) inelastic DW and CC differential cross sections are in good agreement. The total DW inelastic cross section for the l=0 partial wave is much higher than the CC result. For other partial waves, which make much larger contribution to the total cross section, the DW results differ by about 15% from the CC results. The desirability of computing DW phase shifts modulo 2Π is also pointed out.
Semiclassical phase shifts for potentials containing a hard core
Authors: Korsch H. Jürgen
Published: February 2003

An improved wkb approximation is derived for hard core potentials. Phase shifts are calculated.(AIP)
Determination of the spectrum of recoil energies for chlorine atoms generated by the 37Cl(n,γ) 38Cl nuclear process
Authors: Ferro L. J. , Spicer L. D.
Published: February 2003

The distribution of recoil energies for chlorine-38 produced in the 37Cl(nγ) 38Cl nuclear reaction is calculated using the prompt gamma ray spectrum for the process. The average recoil energy is found to be 294 eV and the most probable value for the recoil distribution below the maximum recoil energy of 528 eV is 298 eV. Failure to bond rupture from organochlorine source molecules is estimated to contribute less than 0.2% of the total recoil events.
Comments on the use of time resolved N2+ (B→X) emission as a probe of charge-transfer processes in Ne–N2 and He–N2 mixtures
Authors: Govers T. R.
Published: February 2003

The experiments of Chen et al1,2 on time resolved emission spectroscopy for the study of charge transfer reactions between N2+ and He and N2+ and Ne are discussed and commented upon.(AIP)
Kinetic instabilities in first order phase transitions
Authors: Lovett Ronald , Ortoleva Peter , Ross John
Published: February 2003

Linear stability analysis is used to show that an homogeneous system in the early ’’aging’’ stage of a first order phase transition is unstable to heterogeneous development. A detailed analysis appropriate to precipitation out of a solution is presented although only the most general features of a first order phase transition are actually necessary. A linear dispersion relation is constructed which can also be applied to an initially heterogeneous system and which predicts heterogeneous development in general agreement with observed Liesegang ring formation.