bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective electronic relaxation in the supersonic expansion: Rotationally resolved intersystem crossing in 1A
u glyoxal
Authors: Jouvet C. , Soep B.
Published: February 2003

Radiation from a N2-pumped dye laser is used in the determination of the cross section for collision-induced intersystem crossing in glyoxal.(AIP)
The inelasticity correction for heavy water
Authors: Rovere M. , Blum L. , Narten A. H.
Published: February 2003

The inelasticity or Placzek correction developed in an earlier paper is applied to D2O, using a quantum mechanical model in which the dynamical part of the time dependent rotational correction function is that of a sphere. The corrected data show the required asymptotic behavior for large q. No adjustable parameters are used.
Pattern formation in a ferroin-bromate system
Authors: Showalter Kenneth
Published: February 2003

Stationary mosaic patterns may spontaneously develop in a thin film of solution containing H2SO4, NaBrO3, KBr, ferroin, and 4-cyclohexene-1,2-dicarboxylic acid. The pattern formation is affected by initial reactant concentrations and depends on the generation of elemental bromine. Depending on initial reactant concentrations, a vivid nonsynchronous oxidation transition may also occur. Results of experiments designed to distinguish between physical and chemical mechanisms are presented.
Stable oscillating properties of interacting three-state cyclic enzyme systems
Authors: Tsuchiya Takashi
Published: February 2003

Interacting one-way, three-state cyclic enzyme systems introduced by Hill and Stein are investigated further by introducing time evolution equations. Stable oscillating solutions for particular sets of parameters are found by numerical calculation.
Elastic electron scattering from molecular potentials
Authors: Kohl D. A. , Arvedson M. M.
Published: February 2003

Fink and co-workers have reported a molecular electron density function for the nitrogen molecule which was derived from an experimental differential electron scattering cross section. The transformation of the data was accomplished by assuming that the first Born approximation could be used to describe the scattering process. This procedure is analyzed by considering a higher order treatment of the elastic scattering from two-center potentials. When the experiment is simulated by considering a model potential and 40 keV electrons, the errors in the Born treatment are found to be comparable to typical experimental uncertainties. However, corrections to the Born cross section would be significant at lower incident energies or if experimental accuracy were improved.
Laser fluorescence study of ytterbium plus halomethane reactions
Authors: Dirscherl R. , Lee Henry U.
Published: February 2003

The reactions of ytterbium (Yb) with a series of halomethanes (RX) have been studied in a beam plus gas arrangement. The unrelaxed YbX products are detected by cw tunable dye laser excitation. Prominent sequences belonging to the YbX (A 2∏1/2−X 2Σ+) band systems are readily identified in the region 5350–6450 Å. The vibrational state distributions exhibited by the YbX products are characteristically bell-shaped, suggesting a direct reaction mechanism. Moreover, the fraction of energy released into YbX product vibration is found to increase with the reaction exoergicity and with the degree of halogenation in RX. These systematic trends in the energy partitioning are correlated with recent results from the well-studied alkali and alkaline-earth analogs.
A p
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i
o
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i electronic structure calculations on highly conducting polymers. I. Hartree–Fock studies on c
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s- and t
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a
n
s-polyacetylenes (polyenes)
Authors: Suhai S.
Published: February 2003

Results of a priori Hartree–Fock electronic structure calculations on five different polyacetylene models are reported. All significant matrix elements of the one- and two-electron interactions (including the correct and nonlocal exchange) were exactly calculated for a region of ∼120 CH units until every relevant physical property of the polyacetylenes properly converged. The alternating structures are found to be energetically favorable for both the trans- and cis-isomer in this work, the most stable model being the cis-transoid one. Various one- and many-electron properties as well as the possibilities to obtain reasonably localized Wannier functions for polyacetylenes are discussed.
The electronic states of Ne2+, Ar2+, Kr2+, and Xe2+. II. Absorption cross sections for the 1(1/2)u→1(3/2)g, 1(1/2)g, 2(1/2)g transitions
Authors: Wadt Willard R.
Published: February 2003

The lowest three dipole-allowed absorption bands in Ne2+, Ar2+, Kr2+, and Xe2+ are investigated using ab initio configuration interaction wave functions. Potential curves (reported in paper I) and transition moments (reported here) are obtained for Ar2+, Kr2+, and Xe2+ using the POL CI method. By shifting the Re of the 1(1/2)u state, the theoretical absorption profiles are normalized to the absolute cross sections of Lee and Smith and also Vanderhoff for the 1(1/2)u→2(1/2)g transition at (350.7 and 356.9) nm and 413.1 nm. The resulting absorption profiles are not only in good agreement with the remaining data of Lee and Smith, Vanderhoff, and Hunter for 1(1/2)u→2(1/2)g, but are also in good agreement with the experimental data of Lee et al. on the 1(1/2)u→1(1/2)g transition. The absorption profiles for Ne2+ are based on the ab initio potential curves and transition moments of Cohen and Schneider. The agreement with the few available cross sections of Lee and Smith is excellent. Comparison with the other theoretical calculations of the transition moments reveals the important effects of configuration interaction not included by Stevens et al. and the inaccuracies of the R/2 approximation employed by Michels. Finally, comparison with temperature dependent studies of Lee and Smith indicates much faster equilibration between the translational and vibrational degrees of freedom in Ne2+ than Ar2+.
Transition state and Brownian motion theories of solitons
Authors: Skinner James L. , Wolynes Peter G.
Published: February 2003

We investigate some aspects of the nonequilibrium statistical mechanics of the φ4 and sine-Gordon models. In particular we focus on the single site process of hopping between stable states. As a first approximation we calculate the rate constant for this process using a generalization of classical transition state theory, finding that the transition state is a soliton, and the hopping process results from the free streaming translational motion of these solitons. We then consider the possibility that the solitons can interact with their surroundings such that their translational motion becomes Brownian. With this model we calculate the hopping correlation function, finding that in the limit of no friction it decays exponentially with the time constant predicted by transition state theory, and in the high friction limit it is exp (−αt1/2) corresponding to soliton diffusion.
A simulation of preferential solvation in ternary Lennard-Jones liquid mixtures by the molecular dynamics method
Authors: Narusawa Hiroshi , Nakanishi Koichiro
Published: February 2003

Molecular dynamics calculations have been carried out for ternary Lennard-Jones liquid mixtures where one test particle (solute) is dissolved in binary equimolar solutions. Three different models have been adopted for the purpose of obtaining information about fundamental characteristics of preferential solvation of the solvents to the solute. Both static and dynamic properties such as radial distribution functions, the local composition around the solute, self-diffusion coefficient, and decay of nearest-neighbor structure to the solute have been calculated. It was revealed that the degree of preferential solvation depends not only on the difference in the attractive interaction of the two solvents to the solute but also on the thermodynamic properties of the binary solutions.
On the entropy of mixing of liquid transition metal based alloys
Authors: Khanna S. N. , Cyrot-Lackmann F. , Hicter P.
Published: February 2003

Experimental results on the entropy of mixing of liquid transition metal based alloys FeSi, CoSi, and NiSi show that there is an exceptional negative entropy of mixing. In this work, we have shown that this effect is due to the filling of the d band of the transition metal as it is alloyed with Si. We propose a simple model which successfully accounts for the various features of the experimental results.
Defect structure and oxygen diffusion in undoped and La-doped polycrystalline barium titanate
Authors: Shirasaki S. , Yamamura H. , Haneda H. , Kakegawa K. , Moori J.
Published: February 2003

Oxygen diffusion coefficients in undoped and La-doped polycrystalline barium titanate were measured at an ambient oxygen pressure of about 40 Torr over the temperature range 770–1430 °C by a solid–gas exchange technique of O18. The undoped material was characterized only by an extrinsic region with a high diffusivity, whereas two types of La-doped materials displayed an intrinsic region with E?100 kcal/mol in addition to a common extrinsic region of a very low level of diffusivity. New ideas concerning defect equilibria for the doped materials are proposed for the extrinsic and intrinsic region. In addition, the origin of semiconducting behavior characteristic of the doped specimens is interpreted on a basis of new idea.
A one-to-one mapping between one-particle densities and some n-particle ensembles
Authors: Valone Steven M.
Published: February 2003

A one-to-one mapping between the one-particle densities and a particular set of n-particle ensembles is constructed. The construction entails simultaneous minimization of the energy and minimization of the L2-norm over the set of ensembles which yield a given density. Differences between the present approach to density functional theory and other approaches, such as Kohn–Sham theory (Ref. 12) and Thomas–Fermi–Dirac–Weizsacker theory (Ref.13) are emphasized. The Levy density functional may be decomposed into kinetic and electron–electron interaction components.
The grand canonical ensemble Monte Carlo method applied to the electrical double layer
Authors: van Megen William , Snook Ian
Published: February 2003

The grand canonical ensemble Monte Carlo method is applied to the electrical double layer, using a discrete surface charge distribution and the restricted primitive model for the electrolyte. A systematic examination of the effects of the dimensions of the basic Monte Carlo cell shows that the usual minimum image technique, for determining the potential energy of the system, must be supplemented by long range corrections. Alternatively, very large dimensions or numbers of ions must be employed. The calculated ion distribution functions are compared with the Gouy–Chapman theory for bulk electrolyte concentrations up to 0.2 C/m2. The Gouy–Chapman theory compares very well with the Monte Carlo results for electrolyte concentrations up to 0.1 mole/dm3, but quantitatvive differences appear at 1 mole/dm3. These differences are more pronounced at 2 mole/dm3 for which the Monte Carlo results indicate an inversion of the positive and negative charge distribution functions.
The three body partition function for hard core square well clusters
Authors: Zurek W. H. , Schieve W. C.
Published: February 2003

Physical cluster partition functions introduced by Hill can be simplified for hard core square well gas, when either proximity or negative energy definitions of a chemical bond are adopted. For trimers this leads to estimates for mole fractions and topology abundances, which compare favorably with the outcome of Molecular Dynamics computer experiments. In agreement with previous studies of dimers proximity partition function and negative energy partition function provide, respectively, upper and lower bond on the actual number of trimers observed in a computer experiment.
A simple method for determining the mean passage time for diffusion controlled processes
Authors: Deutch J. M.
Published: February 2003

The author presents a more direct method for obtaining the mean passage time than the operator method presented by Szabo, Schulten, and Schulten for diffusion controlled reactions. (AIP)
Hartree–Fock–Slater transition state calculations of KLL Auger energies in Na and Mg
Authors: Sen K. D.
Published: February 2003

The Hartree–Fock–Slater transition state method is used to calculate the energies for the K-L,L, KL,L2,3 and K-L2,3 L2,3 Auger transitions in Na and Mg atoms. (AIP)
Theoretical molecular structures and electric dipole moments of CCCNH, HCCNC, HCCCNH+, NCNC, and NCCNH+
Authors: Haese Nathan N. , Woods R. Claude
Published: February 2003

Molecular structures and energies have been computed at the double zeta SCF level for several linear triple bonded molecules that are either isomers or protonated forms of the familiar molecules cyanoacetylene and cyanogen. These structures have been used to predict rotational constants that can be used as a guide for locating or assigning laboratory or astrophysical microwave spectra. For the same molecules the dipole moments have been computed at the double zeta plus polarization configuration interaction level. Similar structure and dipole moment calculations have also been done on several related known molecules to assess the accuracy of the numerical results. All of the computed dipole moments fit into a pattern that can be roughly explained by simple polarization arguments.
Potential energy hypersurface for the 1 2Π(1 2B1,1 2A′′) Rydberg state of the HeH2+ system
Authors: Hopper Darrel G.
Published: February 2003

The 1 2Π(1 2B1,1 2A″) state of the helium dihydride ion HeH2+ has been examined with ab initio electronic structure calculations. In particular, the potential energy hypersurface for this Rydberg state has been surveyed with an MCSCF/CI wavefunction involving orbital expansions in a double-zeta plus double polarization plus diffuse one-electron basis. The surface is essentially a trough falling monotonically from the atom–diatomic asymptote He(X 1S) +H2+(C 2Πu), through the triatomic region, to the asymptote HeH(1 2Π)+H+. At some triatomic geometries the 1 2Π state is one of the lowest excited electronic states of this molecular ion system. The results obtained here are the first reported explicit treatment of HeH2+ Rydberg states, and will contribute towards the elucidation of the manifolds of the lowest two Rydberg series arising from the (HeH,H)+ excited asymptotes.
Evidence of viscoelastic effects in highly concentrated aqueous solutions of the bile salt sodium deoxycholate by ultrasonic measurements
Authors: D’Arrigo G. , Sesta B. , La Mesa C.
Published: February 2003

Absorption (5–300 MHz and velocity (5–65 MHz) of ultrasound, density, and viscosity have been measured in highly concentrated aqueous solutions of sodium deoxycholate at 20 °C. Ultrasonic results show that classical viscous losses represent a large fraction of the experimental ones and that a small velocity dispersion is present. These experimental findings are interpreted on the grounds of a viscoelastic behavior of these solutions. Accordingly, the contributions from both volume and shear viscosity relaxation processes have been evaluated. For the former process a previously suggeted model of associated reactions is considered while the dynamic shear viscosity is related to the flexibility of the large micellar super aggregates.
Interpretation of the optical absorption spectrum and of the paramagnetic susceptibility of NdAlO3
Authors: Antic-Fidancev E. , Lemaitre-Blaise M. , Beaury L. , de Sagey G. Teste , Caro P.
Published: February 2003

The absorption spectrum of pure rhombohedral NdAlO3 was determined at 4.2 K from 10 000 to 34 000 cm−1. Adding the levels determined for the 4I multiplet by other authors, a total of 117 Stark levels was obtained. They were fitted to a mean square deviation of 13 cm−1 with a Hamiltonian involving 12 free atom parameters and six D3 crystal field parameters applied on the 364 kets basis in the 4f3 configuration. The values are B02=−481 cm−1, B04 =481 cm−1, B34=−390 cm−1, B06=−1700 cm−1, B36=−950 cm−1, B66=−1080 cm−1. Free atom parameters are very close to those of Nd3+ in LaCl3. The powder paramagnetic susceptibility was measured from 4 to 1000 K. The 1/χ versus T curve shows a pronounced curvature, even below 300 K, which is fairly well reproduced by a crystal-field-only calculation involving the complete wave vectors of the 18 lowest Kramers doublets.
On the systematics of vibrational relaxation in polyatomic molecules
Authors: DePristo Andrew E.
Published: February 2003

The systematic variation of vibrational relaxation rates with initial excitation, i.e., the quantum number scaling, is investigated for collisions involving polyatomic molecules. We consider the contrasting behavior of diatomic and polyatomic relaxation and the impact of the more varied behavior in polyatomics on experimental measurements. Particular emphasis is placed on the effect of collision-induced intramolecular vibrational transitions on the rate scaling. The theory utilized to accomplish such an analysis involves an extension of the energy corrected (ECS) scaling relationship to polyatomic vibrational transitions. This development is presented for vibrationally inelastic processes in a single electronic level. We apply the theory to the inversion of total rates for bending mode relaxation in CF2. The resulting state-to-state rates display peculiarities which reflect both the energy spectrum of the CF2 molecule and the nature of the collision partner.
Spectroscopy of the NaH, NaD, KH, and KD X 1Σ+ ground state by laser excited fluorescence in a high frequency discharge
Authors: Giroud Marc , Nedelec Odette
Published: February 2003

By laser excited fluorescence of the hydrides obtained in a discharge, the ground state vibrational levels of NaH, NaD, KH, and KD have been observed up to v″=15, 20, 14, and 16, respectively, instead of v″=8, 2, 4, and 4 by conventional spectroscopy. Experimental values of Gv″, Bv″, and Dv″ are obtained. Spectroscopic parameters and RKR potential curves are calculated. In NaH and NaD, a comparison can be made with ab initio calculations.
The use of resonant Raman intensities in refining molecular force fields for Wilson G–F calculations and obtaining excited state molecular geometries
Authors: Peticolas Warner L. , Strommen Dennis P. , Lakshminarayanan Vasudevan
Published: February 2003

In this paper equations are developed for the quantitative refinement of molecular force fields for Wilson G–F calculations through the use of molecular orbital (MO) calculations of the bond order change between the resonant excited electronic state and the ground state together with the observed intensity of the resonant Raman spectrum (RRS). The method should permit an unambiguous choice between two or more force fields which give equally good fit of the observed frequencies but which give different potential energy distributions among the internal coordinates. We have used this method to study methyl uracil, a planar ring molecule of low symmetry, where partitioning of the matrices is not possible. A least-squares calculation of the difference between the MO bond order changes and the bond order changes calculated from the force field together with the measured intensities in the RRS allows a choice of the correct sign for the excited state changes in the normal coordinates of modes which are active in the RRS. This least-squares calculation allows us to improve a previous choice of signs taken for uracil and obtain calculated excited state geometry in better agreement with bond order changes obtained from MO calculations. From our force field we have not only calculated all the in-plane vibrational frequencies but also the relative intensities for the RRS in both the 260 nm and 200 nm excited states. The theory correctly predicts that only 8 of the 21 in-plane molecules will be observed in the RRS.
Comparison of ion pair formation in the systems Ar*+I2 and K+I2
Authors: Hickman A. P. , Gillen Keith T.
Published: February 2003

A simple model that has been used extensively by Los and co-workers to treat ion pair formation in collisions of alkali atoms with diatomic molecules is extended to include continuum coupling via a competing Penning ionization channel. This extended model is then used to calculate the differential cross sections for ion pair formation for the system Ar*+I2 over the energy range 28–154 eV and to compare with a previous treatment of K+I2. In the absence of significant competition from continuum processes, Ar* is expected to behave in a manner similar to K, since the active electron is an unpaired 4s electron in both cases. We perform model calculations for Ar*+I2 to investigate the effects of varying the potential curves and charge exchange matrix elements and of including a continuum coupling function Γ (R). Comparison with previous calculations for K+I2 suggests increased repulsion on the Ar*–I2 surfaces relative to those of K–I2. The competing mechanisms of excitation transfer and Penning ionization may have a small effect upon the ion pair angular distributions.
Temperature dependence of the laser-induced fluorescence of UF6 in the A–X̃ band
Authors: Rice W. W. , Oldenborg R. C. , Wantuck P. J. , Tiee J. J. , Wampler F. B.
Published: February 2003

The temperature dependence of the time-resolved laser-induced fluorescence (LIF) of gaseous UF6 has been investigated in 10 °C increments from −30 to 80 °C over the 0.005–85 Torr pressure range. The UF6 was excited to the A state with a pulsed dye laser at 392.1 nm and the fluorescence emission peaked at 421 nm and was monitored to determine the LIF lifetime. The pressure/lifetime data at each temperature have been fit by computer with our LIF kinetic expression reported previously in this journal [J. Chem. Phys. 69, 2181 (1978)]. The six quenching rate constants of our kinetic model have been evaluated in terms of their temperature dependences. Each rate constant has been represented with an Arrhenius type expression; pre-exponential A factors and activation energies are presented.
The dissociative ionization of CO2 by fast heavy ions
Authors: Wood R. M. , Edwards A. K. , Steuer M. F. , Monce M. N. , Shah A. V.
Published: February 2003

The time–energy spectroscopy (TES) technique has been used to study the dissociative ionization of CO2 induced by bombardment with 1 MeV H+, He+, and O+ ions. Fragments observed in the dissociation process include C+, O+, CO+, C2+, and O2+. The technique used permits separation and identification of the different fragment species, and measurement of a kinetic energy spectrum for each species. The kinetic energy spectra and relative intensities of the different fragments are reported. The O+ ions constitute more than half of the total charged fragment yield. The C+ and CO+ yields are nearly equal and the yield of doubly charged ions is small. The energy spectra and yields are compared to electron impact and neutral helium impact dissociation studies. The O+ and CO+ data suggest that the channel (CO2)2+→CO++O++6.0 eV is a major contributor to the observed spectra.
Molecular dipole model for the internal optic modes of surface adsorbed molecules: Classical image theory
Authors: Nichols Henry , Hexter Robert M.
Published: February 2003

A molecular dipole model is developed to describe dipolar coupling in surface adsorbed molecules using classical image theory. Only the internal optic modes of the adsorbed molecules are considered. Expanding the dipoles associated with both real and image molecules in terms of the same molecular normal coordinate results in a frequency shift twice that previously expected for dipolar coupling in adsorbed molecules. Application of the model to carbon monoxide adsorbed on platinum indicates that the observed frequency versus coverage behavior can be attributed to dipolar coupling. The irreducible corepresentations of Shubnikov type II, or grey, groups are used to describe the symmetry and spectroscopic activity of the molecule-plus-image system. Infrared activity is associated only with molecular vibrations having nonzero dipole moment derivative components perpendicular to the surface. Raman activity is associated only with those molecular vibrations having nonzero Raman scattering tensor elements αxx, αyy, αzz, or αxy, where z is perpendicular to the surface.
Angularly resolved temperature programmed decomposition—nitrogen emission from the decomposition of hydrazine on Ir(111)
Authors: Sawin H. H. , Merrill R. P.
Published: February 2003

Strong angular dependence has been found in the emission of N2 from the temperature programmed decomposition of hydrazine on oridium (111). (AIP)
Inhomogeneous kinetics in the quenching of prompt radioluminescence: Analysis of alpha particle and proton induced fluorescence decay curves
Authors: Miller John H. , West Martin L.
Published: February 2003

Fluorescence decay curves for dilute solutions of benzene in cyclohexane excited by pulsed proton and alpha particle irradiation are analyzed in terms of a spur diffusion model. This model predicts a reduction in the quenching of fluorescence induced by alpha particles relative to that observed with proton irradiation of the same stopping power due to the more diffuse radial distribution of energy deposited by the higher velocity ion. However, to explain the observed reduction in quenching with alpha particle irradiation on the basis of this model requires a mean spur energy significantly smaller than that used to explain related phenomena in the radiation chemistry of aqueous media.
Spin-1 antiferromagnetic Ising model. I. Bulk phase diagram for a binary alloy
Authors: Saito Y.
Published: February 2003

A spin-1 antiferromagnetic Ising model is introduced to simulate a binary alloy which undergoes crystallization as well as an order–disorder phase transition. The phase diagram is calculated in the mean-field approximation, and three phases are found: the gas(=low density) phase and the two solid (=high density) phases which are ordered and disordered. For some regions of model parameters the disordered-solid phase coexists with the gas phase, and for other regions with the ordered solid. In addition, for certain regions of parameters there is a gas–ordered solid coexistence, which is important in the growth of ordered crystals.
Energy transfer kinetics of the VUV emissions for Kr–Xe mixtures
Authors: Salamero Y. , Birot A. , Brunet H. , Dijols H. , Galy J. , Millet P. , Montagne J. P.
Published: February 2003

Spectroscopic study of KrXe mixtures shows large excitation energy transfers from krypton to xenon. When small quantitities of xenon are added to krypton, these processes can be seen through the fast disappearance of the continuous krypton emissions coupled with an increase in the atomic and molecular emissions of the minority gas. The excitation transfers are very efficient since the spectra of mixtures with only a few percent Xe are very similar in shape and intensity to those of pure xenon. Kinetic analysis of all the VUV emissions enabled a complete kinetic schema of the transfer phenomena to be drawn up. They are due to binary collisions from the molecular states, Kr*2(3Σu+), which are responsible for the second krypton continuum (k2=2.107 Torr−1 s−1) and from the atomic precursor states of molecular krypton (k1=7.106 Torr−1 s−1). Both processes have large cross sections. The two paths compete in the creation of resonant Xe(3P1) states, either through direct molecule–atom transfer or by atom–atom transfer followed by infrared cascade emissions. In the mixture, the molecular Xe2* states responsible for the 173 nm continuum have a different origin to that found in the pure gas. They are created by three-body collisions Xe*(3P1)+Xe+Kr; the reaction constant is k=40±10 Torr−2 s−1.
Photoisomerization of polyenes; reaction coordinate and trajectory in triplet mechanism
Authors: Ohmine Iwao , Morokuma Keiji
Published: February 2003

Dynamical aspects of the triplet mechanism for cis–trans photoisomerization processes of polyenes have been investigated. Reaction coordinates for isomerization are determined for the ground and triplet states of several polyenes in order to understand how various vibrational modes mutually interact during the course of reaction. We have carried out trajectory calculations on the triplet state potential surface of butadiene and found a trajectory that exhibits a dynamical simultaneous isomerization around two double bonds.
Electronic structure of the negative ion of HCl
Authors: Krauss M. , Stevens W. J.
Published: February 2003

The negative ion states of HCl− that go asymptotically to the Cl−+H and H−+Cl asymptotes have been studied as a function of the internuclear distance using first-order configuration interaction wave functions. The 1 2Σ+, 2 2Σ+, and 1 2Π states all cross the neutral HCl energy curve. To the right of the crossing all three curves are bound relative to their asymptotes and exhibit energy minima. The crossings occur on the left hand limbs of the negative ion curves. To the left of the crossing the lowest negative ion curve mimics the neutral and the attached electron is in an orbital which is as diffuse as the basis set permits. Several roots of the FOCI were examined in the unstable region. A root that has a large component of the ’’tight’’ wave function appears in a number of the calculations and possibly can be attributed to a broad resonance. Transition and dipole moments of the bound energy curves exhibit the behavior expected of charge transfer interaction and polarization among these states.
Implications of the virial theorem on the description of weak bonds
Authors: Winn John S.
Published: February 2003

The origins of and variations in bonding among weakly bound diatomics are discussed in terms of the virial theorem as applied to Born–Oppenheimer total energy curves. These curves are represented by accurate and flexible analytic functions. Expressions are given for the relations among the parameters of these functions and the electron average kinetic energy 〈T(R)〉 and the total molecular potential energy 〈V(R)〉. The relatively brief distance through which weak bonding occurs (as opposed to the relative distances for chemical bonding) is discussed, as is the origin of bond saturation through a homologous series of weakly bound diatomics.
Auger electron spectra of the cycloalkanes C3 through C6
Authors: Houston J. E. , Rye R. R.
Published: February 2003

Gas phase Auger electron spectra are presented for the cycloalkane series C3 through C6. In a comparison with similar data taken on ethylene and the normal alkanes it is shown that the lineshapes grade smoothly from being ethylenelike (prototypical of sp2 hybridization), for cyclopropane to normal alkanelike for cyclohexane (normal sp3 hybridization). Cyclobutane shows observable remnants of olefinic character while cyclopentane differs only slightly from its corresponding normal alkane analog. These spectral changes closely mirror the relative chemical reactivity found for the cycloalkanes, which is often discussed in terms of the degree of double bond character present in small ring systems. As was the case for the normal alkanes, the overall position and widths of the Auger features remain essentially constant in energy over the entire series with an average hole–hole repulsion energy near 8 eV. The two-hole final state appears, therefore, to be probing properties localized to the original core-hole site.
Charged-particle production in low-energy H+H2 and H+He collisions
Authors: Van Zyl B. , Le T. Q. , Amme R. C.
Published: February 2003

Absolute cross sections for producing H+, H−, H+2, He+, and e− have been measured for fast hydrogen atom impact on H2 and He targets. The hydrogen atom energy ranged between 50 eV and 3.0 keV. For the H+H2 reaction, the dominant ion-formation process for hydrogen atom energies below 250 eV was found to be H−+H+2 production. For He targets, production of H+ dominated over the entire hydrogen atom energy range. The results are compared, where possible, with the data of other investigators and are discussed in terms of possible reaction mechanisms.
Velocity distributions as a function of the internal state of reactively scattered species from Fourier transform Doppler spectroscopy
Authors: Murphy Edmond J. , Brophy John H. , Kinsey James L.
Published: February 2003

The OH(OD) product of the reaction H(D)+NO2 has been studied in crossed molecular beams by laser-induced fluorescence. A new experimental technique of Fourier transform Doppler spectroscopy has been used to extract the velocity information within the Doppler profiles of several features in the excitation spectra. In this way, the speed and angular distributions of the reactively scattered products have been obtained as a function of the molecules’ internal states. The observed distributions do not vary strongly from state to state. The angular distributions peak in the forward direction along the initial H(D) atom direction in the center of mass coordinates system but show a large amount of backward scattering. Approximately 25% of the reaction exoergicity is manifested in product translation.
Photofragment spectroscopy of O3+
Authors: Moseley J. T. , Ozenne J.-B. , Cosby P. C.
Published: February 2003

Photofragment kinetic energy distributions have been measured for O+ fragments from the photodissociation of O3+ over the wavelength range from 4579 to 7525 Å, using a fast ion beam photofragment spectrometer. Three vibrational levels of the ground state of O3+ are observed, and vibrational spacings determined. The partition of energy into rotation and translation of the product O2 molecule is measured for transitions from each of these three vibrational levels. Partition of energy into vibration of the O2 photofragement is also observed. The polarization of the transition leading to dissociation is determined to be more nearly parallel than perpendicular. The results are interpreted in terms of the structure of O3+ and the dissociation process, and are compared with results from the photoionization of O3, and with theoretical calculations.
Charge transfer cross sections for Hg+, Xe+, and Cs+ in collision with various metals and carbon
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2003

Cross sections for charge transfer between Hg+, Xe+, and Cs+ and the atomic species Fe, Mo, Al, Ti, Ta, and C have been measured in the ion energy range from 1 to 5000 eV. In general, the cross sections for charge transfer were found to be less than 2×10−15 cm2 for most processes over the total energy range. The one exception is Hg+ in collision with Ti. The reactants are all open shell atomic species and in most cases where the charge transfer process is exothermic, several resonant pathways exist leading to the products. Some discussion of possible reaction paths is given. The techniques used to form neutral beams of the various species studied is included.
Structural study of sulfamic acid at 4.2 K by ENDOR-detected NMR
Authors: Reuveni Amikam , Marcellus Daniel , Parker Robert S. , Kwiram Alvin L.
Published: February 2003

The electron–nuclear double resonance method (ENDOR) is used to obtain greatly enhanced NMR signals from the distant deuterium nuclei of perdeuterated sulfamic acid (ND3SO3) in single crystals at 4.2 K. The structural information is obtained by measuring the quadrupole coupling tensors of the deuterium atoms and their direction cosines. There is very good agreement between the N–D bond angles derived from these ENDOR-detected NMR (EDNMR) results and bond angles from neutron diffraction data at 78 K. Relationships between the deuterium quadrupole constants and N–D and D⋅⋅⋅O bond lengths are derived and discussed.
The photodissociation of van der Waals molecules: Complexes of iodine, argon, and helium
Authors: Johnson Kenneth E. , Sharfin Wayne , Levy Donald H.
Published: February 2003

We have observed the fluorescence excitation and dispersed fluorescence spectra of van der Waals molecules produced in a supersonic expansion of mixtures of iodine, helium, and argon. The spectral position of a given van der Waals molecule was found to follow a band shift rule which states that the displacement of the feature of the molecule I2AraHeb from the feature of uncomplexed I2 is given by Aa + Bb, where A and B are constants. The band shift produced by an argon atom was found to be ∼13.5 cm−1. Complexes containing more than three argon atoms were not observed, and this was attributed to rapid electronic predissociation in the larger complexes. Spectral features attributed to progressions in excited state van der Waals vibrational modes were identified. The vibrational product state distributions of the fragment I2* produced by dissociation of various complexes were measured. Larger van der Waals complexes tended to require more vibrational quanta per rare gas atom to dissociate. Excitation of a given complex to higher initial vibrational state also tended to favor channels requiring more vibrational quanta per atom. In the dissociation of the molecule I2ArHe, a single vibrational quantum appeared to be shared between the helium and argon atoms. Information on the rotational product state distribution of the fragment I2* was obtained by measurement of the fluorescence band contours.
Spectroscopy of the benzil–bibenzyl mixed crystal system: High resolution optical studies
Authors: Kohler Bryan E. , Loda Richard T.
Published: February 2003

The S0→S1 excitation and T1→S0 emission spectra of a benzil doped bibenzyl mixed crystal at temperatures ranging from 300 to 2 K have been measured. Two kinds of spectra have been found and assigned to the benzil molecule trapped in two different molecular configurations. One of the observed sets of spectra is nearly identical to those of the benzil single crystal. The other, red shifted with respect to those of the benzil single crystal, is similar to the spectra of systems known to contain a trans-planar 1,2-dicarbonyl fragment. Such a geometry change is consistent with the manner in which the benzil molecule would most probably substitute into the bibenzyl lattice. The red shifted spectra are broad, beyond the extremely sharp 0–0, and this broadness is attributed to the strong excitation–phonon coupling expected for molecules that undergo large geometrical changes upon photoexcitation.
EPR and ENDOR of triplet state diphenyl-h10 in diphenyl-d10 single crystals. Molecule conformation and spin distribution
Authors: Hutchison Clyde A. , Kemple Marvin D.
Published: February 2003

The results of EPR and ENDOR spectroscopic measurements for the lowest energy triplet state of diphenyl-h10 molecules dilutely substituted for host molecules in diphenyl-d10 single crystals at 1.9 °K are reported. These measurements show clearly that the triplet state molecules do not have the center of symmetry possessed by the host molecules, with their two parallel ring planes, in the crystal at room temperature. However, the host molecules have lost their center of symmetry at low temperature by a twisting of the two rings about the central inter-ring bond, whereas the triplet state molecules at 1.9 °K are found to have parallel ring planes and have not lost the center as a result of such a twisting. The reported results also show that although the nuclear coordinates are very close (relative to the precision of the ENDOR measurements) to those required by an ideal molecular D2h symmetry, nevertheless the principal axes of the fine structure interaction are rotated in the plane of the molecule by the relatively large angle, 0.046π(8.3°), from the directions of the approximate molecular symmetry axes. This last fact removed the previously reported discrepancy between the value of the angle between the long molecular axes of the two translationally inequivalent molecules per unit cell determined by x-ray diffraction and that determined by EPR under the assumption that the fine structure principal axes and the molecular symmetry axes were coincident. This lack of coincidence arises from the large deviations of the spin distribution, from that demanded by D2h symmetry, produced by the very small deviations of the nuclear coordinates from the ideal symmetry. The spin distribution has been measured in these experiments and the spin densities reported here are shown to be in agreement with the preceding statements.
Matrix isolation spectra of metal atoms and ions: Ti, Zr, and Mo in Ar and Kr
Authors: Steinbrüchel Christoph , Gruen Dieter M.
Published: February 2003

UV-absorption spectra are reported of neutral atoms and ions of Ti, Zr, and Mo in Ar and Kr matrices. The matrix-isolated species are produced by ion bombardment of a bulk metal target. Thermal and photoannealing experiments indicate that sputtered neutral atoms may occupy one or two distinct matrix sites, depending on the system. Sputtered ions, after being neutralized in the matrix, either go preferentially into the higher energy site, i.e., the site whose absorption bands are shifted farther to the blue, when atoms already populate two sites, or they create a new site at higher energy when there is only one site for atoms. Deconvolution of matrix isolation spectra into contributions from individual sites shows that spectra due to atoms in a particular site correspond much better to gas phase spectra than do total matrix isolation spectra. Matrix shifts of atomic absorption bands for both sites can be rationalized using a model by McCarty and Robinson if allowance is made for matrix distortion around solute atoms. The blue, or close-packed, site is found to correspond to a solute atom replacing a single matrix atom without inducing appreciable matrix distortion, whereas the red, or expanded, site requires the cage around a solute atom to be enlarged by a few percent.
Quenching, electronic energy transfer, and rotational relaxation of S1 formaldehyde
Authors: Weisshaar James C. , Bamford Douglas J. , Specht Eliot , Moore C. Bradley
Published: February 2003

Three types of fluorescence decay measurement are reported in order to clarify the collisional decay mechanisms of S1 formaldehyde. From the fluorescence decay of an H2CO/D2CO mixture after selective excitation of 40 H2CO, the rate constant for electronic energy transfer from S1 H2CO to S0 D2CO is derived to be less than 2% of the gas kinetic collision rate. The fluorescence decay after excitation of single rotational levels of pure H2CO in the 41 band was measured in the pressure range 10−3–5 Torr. A simple model shows that rotational and vibrational relaxation to S1 levels of different lifetime from that of the initially prepared state makes a major contribution to the observed curvature of Stern–Volmer plots. Intrinsic curvature of the electronic relaxation rate definitely occurs for pure D2CO and may occur for pure H2CO. Quenching of 40/41 H2CO and D2CO by up to 700 Torr of Ar, CO2, CH3F, O2, and NO was studied. The Stern–Volmer plots for Ar, CO2, and CH3F curve gradually, again due to intrinsic curvature of the electronic relaxation rate. Quenching by O2 and NO is more linear and more efficient. Surprisingly, Ar, CO2, and CH3F quench D2CO more efficiently than H2CO, while the opposite is true for O2 and NO. The results are discussed in terms of mixed state theories of electronic relaxation. Inferences concerning the collisional photochemical decay of S1 formaldehyde are suggested.
Crystal spectra and vibrational assignments in α-resorcinol
Authors: Tripathi G. N. R.
Published: February 2003

The infrared and Raman spectra of α-resorcinol crystals are investigated at low temperatures. Fine structure in the vibrational exciton states are resolved. Symmetry assignments of the crystal and molecular transitions are proposed based on the polarization properties of the bands. Most of the earlier assignments are revised.
Suppression of multiple scattering effects in quasielastic light scattering by homodyne cross-correlation techniques
Authors: Phillies George D. J.
Published: February 2003

By studying cross correlations in the intensity of light scattered by a fluid sample in different directions at different times, it is possible to measure the dynamic scattering function S(k,t) for the fluid. The multiple scattering contribution to the time-dependent cross correlations is very substantially less than the multiple scattering contribution to S(k,t) as obtained by a conventional single-detector quasielastic light scattering system.
A quadratically convergent MCSCF method for the simultaneous optimization of several states
Authors: Werner Hans-Joachim , Meyer Wilfried
Published: February 2003

A quadratically convergent MCSCF method is described which allows one to optimize an energy average of several states with arbitrary weight factors. An analysis of the problems connected with the variational determination of excited states is given and it is concluded that the averaging method is a natural solution to these problems. In the energy expansion minimized in each iteration, certain cubic and higher order terms can be included. It is demonstrated that this greatly facilitates convergence in cases where the Hessian matrix of second energy derivatives has many negative eigenvalues. Several approximations to the exact quadratically convergent scheme, which are useful when calculating potential surfaces, are discussed.
Autoionization of highly excited Rydberg states of diatomic molecules
Authors: Takagi Hidekazu , Nakamura Hiroki
Published: February 2003

Autoionization due to the vibrational and/or rotational de-excitation of highly excited Rydberg states of diatomic molecules is investigated by using the multichannel quantum defect theory. In the two-channel approximation, an analytical expression for the decay width is obtained which is expressed in terms of the adiabatic quantum defects. A formula in the crude Born–Oppenheimer approximation can be derived as a simplification limit of the present formula. The crude Born–Oppenheimer approximation is shown to work in the case that the linearity holds well for the dependence of the adiabatic quantum defect on the internuclear distance, and that the vibrational quantum number of the initial Rydberg states is not large. The autoionization of H2 is investigated with use of the present formula and a comparison with the experimental data is made.
A method for obtaining absolute potentials of mean force at infinite dilution for nonelectrolyte solutes from Monte Carlo simulations
Authors: Goldman Saul
Published: February 2003

A method is presented for converting a potential of mean force curve for nonelectrolytes at infinite dilution from a relative to an absolute scale. It is based on the extrapolation of a series of absolute values of the first minimum in the potential of mean force curve from finite concentrations to infinite dilution. The method, which utilizes the conventional Metropolis algorithm (i.e., Boltzmann sampling), is illustrated by an application to a Lennard-Jones solute dissolved in a generalized Stockmayer solvent. The principle should be applicable to any nonelectrolyte solute in any solvent, provided the screening due to the presence of other solute particles is sufficient to disrupt long-lived solute clusters.
Dielectric relaxation in undiluted poly (4-chlorostyrene). II. Characteristics of the high frequency tail
Authors: Yoshihara M. , Work R. N.
Published: February 2003

The shape of the principal dielectric relaxation process that occurs just above the glass transition temperature Tg in well annealed, atactic, undiluted poly (4-chlorostyrene) exhibits a small tail at the high frequency end of the spectrum of relaxation times. This high frequency tail (HFT) has been characterized at temperatures varying from 351 to 413 K by using the Havriliak–Negami equation. The glass transition temperature Tg of P4CS is about 400 K. It is suggested that the HFT is distinct from the β relaxation process which occurs in polystyrene at temperatures just below Tg; and that the HFT is experimental evidence of the existence of localized, fast conformational changes. This fast process is presumed to be slowed and broadened by interactions with the surroundings.
Infrared, Raman, and Brillouin spectra of CsH2PO4
Authors: Marchon B. , Pasquier B. , Le Calve N. , Novak A. , Čopič M. , Zgonik M. , Fox D-L. , Lavrenčič B. B.
Published: February 2003

Parelectric–Ferroelectric phase transitions are studied in single crystals of CsH2PO4 and CsD2PO4.(AIP)