bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution infrared absorption spectra of BCl3 and BCl2F dissolved in solid argon and solid krypton
Authors: Maier William B. , Holland Redus F.
Published: February 2003

High-resolution (≈0.035 cm−1) infrared absorption spectra of BCl3 and BCl2F dissolved in solid argon and krypton have been obtained. The solids were grown from liquid solutions, were 1.4 cm thick, and were reasonably clear optically. The ν2, ν3, ν1+ν4, ν3+ν4, ν1 +ν3, and 2ν3 bands of BCl3 were found, and the positions of the ν1 and ν4 bands of BCl2F were inferred. An observed perturbation of the ν2 band of 10BCl3 is explained by invoking a lattice-induced distortion of BCl3 from planarity. The observed spectral lines are very narrow, so the absorption bands of different boron and chlorine isotopomers are well resolved. The observed full spectral width of the absorption lines at half maximum absorbance is <0.04 cm−1 for the ν2 lines of BCl3 and ∼0.08 cm−1 for the other fundamentals. The wave number ṽ of a given line depends on solid solvent and on temperature T; dṽ/dT is within the range 0.014⩽dṽ /dT⩽0.09 cm−1/°C for all bands. Anharmonicities and harmonic frequencies have been obtained from the data, and the anharmonicity constants lie between −1.8 and 0.8 cm−1. Energies have been estimated for the first excited states of the ν1 and ν4 modes of BCl3 and also for the A′1 and A′2 levels of the v3=v4=1 state of BCl3. The usual theory of harmonic oscillators having D3h symmetry does not adequately describe the ν3 and ν4 band positions and isotopic splittings.
Symmetries, propensity rules, and alternation intensity in the rotational spectrum of N2 (C 3Πu) excited by metastables Ar(3P0,2)
Authors: Derouard J. , Nguyen T. D. , Sadeghi N.
Published: February 2003

We have obtained high resolution spectra N2(C 3Πu→B 3Πg) afterglow fluorescence resulting from excitation transfer from state selected Ar metastable 3P0 or 3P2. This was achieved by selective depopulation of one metastable by optical pumping using a tunable c.w. dye laser. Relative probabilities of excitation of well defined rotational, spin, and parity molecular Λ doublet substates were obtained for reaction of 14N2 and isotopic 15N2 with Ar*(3P2) and Ar*(3P0). A semiclassical model is proposed and found in fairly good agreement with the observed relative yields. The physical bases of the model are justified and imply that (a) spin–orbit interactions are effective during the collision, (b) the plane of rotation of the excited N2 molecule is a plane of symmetry, (c) Λ doublet c states are preferentially populated in the excitation transfer process.
Electron acceptor surface states due to oxygen adsorption on metal phthalocyanine films
Authors: Dahlberg S. C. , Musser M. E.
Published: February 2003

The dependence of the surface photovoltage of NiPc and CuPc films on oxygen ambient has been measured, and the observed effects can be quantitatively accounted for with a theoretical model which involves the transfer of charge from the Pc ring to the adsorbed O2 and the formation of a Pcδ+–Oδ−2 species at the surface of the Pc film. Symmetry arguments based on a simple bonding model are used to explain the nature of these O2 electron acceptor surface states. Charge transfer complexes such as this are important both to the doping of these organic semiconductors, and to a fundamental understanding of the oxidations photocatalyzed by these porphyrinlike materials which are closely related to some of the processes which occur during photosynthesis.
The effect of pressure on the molecular structure of Hg(CN)2 and the anomalous pressure dependence of the phonon frequencies
Authors: Wong P. T. T.
Published: February 2003

Anomalous pressure-induced phonon frequency shifts of certain lattice modes and of the ν7 internal bending mode and the nonlinear pressure dependence of the phonon frequencies have been observed in the pressure range 0–16.5 kbar for the Raman spectrum of crystalline Hg(CN)2. The mechanism of these pressure effects is discussed in terms of the strong intermolecular interaction and the molecular configurational distortion in the crystal. The effect of pressure on the molecular structure of Hg(CN)2 is discussed in relation to the pressure dependence of the internal stretching frequencies.
State-to-state dynamics using dual molecular beam excitation difference spectroscopy
Authors: Torres-Filho Afranio , Pruett J. Gary
Published: February 2003

The vibrationally resolved state-to-state kinetics of the molecular beam reaction Ba+HF→BaF+H has been investigated using a unique dual reaction differencing technique which is sensitive to 0.04 cm−1 Doppler shifts and allows detection of the full distribution of products from low fractionally excited reagents. Contrary to earlier results, BaF at low vibrational levels is found to dominate the product distribution in reaction proceeding from HF (v=1). The difference spectrum also reveals that the total reaction rate increases by a factor of three by vibrationally exciting the reagents.
Some relations connecting volume and enthalpy relaxation in the order parameter model of liquids and glasses
Authors: Lesikar Arnold V. , Moynihan Cornelius T.
Published: February 2003

A general inequality connecting linear enthalpy and volume relaxation is derived in the context of the order parameter model of liquids and glasses. This inequality is shown to yield a wide variety of relationships among the quantities characterizing these relaxations.
On band shapes of electronic transitions in the multimode weak coupling limit
Authors: Champion P. M. , Albrecht A. C.
Published: February 2003

The influence of multidimensional Franck–Condon (FC) active vibrational subspace on the band shapes of electronic transitions is explored in the linear weak coupling limit. Given a constant (weak) coupling coefficient, computer calculated band shapes are seen to fall into three classes depending on the number of active vibrational modes, N. For large N, the electronic band of a polyatomic molecule will have a relatively weak zero–zero absorption compared to the ’’side-band’’ absorption, which arises from a rapidly increasing density of states (DOS). For small N, a normal, weak FC progression is seen in which the peak absorption is in the zero–zero transition. The implications of the DOS/FC model are further discussed in relation to previous work. Calculations are presented to emphasize the effect of the multidimensional subspace on the relationship between the absorption band shape and the resonance Raman excitation profile.
Perturbation solutions of a two state–two mode vibronic coupling model
Authors: Özkan İlker , Goodman Lionel
Published: February 2003

The Born–Oppenheimer and crude adiabatic perturbation methods are discussed quantitatively. A modified Born–Oppenheimer procedure is presented. The model problem consists of two electronic states (of different symmetry) interacting through a nontotally symmetric mode responsible for direct coupling; and a totally symmetric Franck–Condon mode representing geometry differences between the two states. Comparisons of approximate and exact solutions are made for several cases.
Infrared, Raman, and visible spectroscopic studies of Zn and Cd matrix reactions with ozone. Spectra of metal ozonides and oxides in solid argon and nitrogen
Authors: Prochaska Eleanor S. , Andrews Lester
Published: February 2003

Reactions of zinc and cadmium atoms with ozone during condensation with excess nitrogen or argon produced B+O3− ion-pairs having infrared, Raman, and optical spectra similar to the analogous alkali and alkaline earth metal species. Additional infrared and Raman evidence was found for a different B+O3− ion-pair geometry. Mercury arc photolysis reduced ozonide absorptions and produced new 810 cm−1 zinc isotopic triplets which showed the appropriate 18O shifts for ZnO, and a new 719 cm−1 band which showed the proper 18O displacement for CdO. This nitrogen matrix work provides good measures of the yet-to-be-observed gas-phase fundamentals of these high temperature oxides.
Absolute rate parameters for the reaction of O(3P) with H2CO over the temperature range 250 to 750 K
Authors: Klemm R. Bruce , Skolnik Edward G. , Michael Joe V.
Published: February 2003

Absolute rate constants for the reaction of ground state oxygen atoms with formaldehyde were determined over the temperature range 298 to 748 K using the discharge flow-resonance fluorescence technique. The results were combined with rate data from a flash photolysis-resonance fluorescence study (250 to 498 K) of this reaction to obtain an Arrhenius expression that is linear from 250 to 748 K: k1(T) = (2.94±0.26) ×10−11 exp  (−3065±67/RT) cm3 molecule−1 s−1. This result is compared with those of previous studies and possible kinetic complications are discussed in terms of a detailed mechanism. The significance of an extrapolation of this determination of k1 to higher and lower temperatures is also discussed.
Quantum intramolecular dynamics: Criteria for stochastic and nonstochastic flow
Authors: Heller Eric J.
Published: February 2003

This paper proposes new criteria by which to gauge the extent of quantum intramolecular randomization in isolated molecules. Several hallmarks of stochastic and nonstochastic behavior are identified, some of which are readily available from spectral data. We find that it is very important to tailor the criteria to the specific experimental situation, with the consequence that a given molecule can be labeled both stochastic and nonstochastic, even in the same general energy regime, depending on the experiment. This unsettling feature arises as a quantum analog of the necessity, in classical mechanics, of specifying the a priori known integrals of the motion before ergodic or stochastic behavior can be defined. In quantum mechanics, it is not possible to have flow or measure local properties (analog of trajectories and phase space measure) without some uncertainty in the integrals of the motion (most often the energy). This paper addresses the problems this creates for the definition of stochastic flow. Several systems are discussed which show significant differences in their quantum vs classical stochastic properties.
Dynamical calculation of satellite intensities
Authors: Cederbaum L. S. , Domcke W. , Schirmer J. , Köppel H.
Published: February 2003

A formalism to calculate molecular electronic spectra is developed which takes account of electronic configuration interaction as well as of vibronic coupling between the electronic states. The formalism allows the dynamical calculation of electronic spectra, i.e., the inclusion of the effects of the nuclear kinetic energy operator on the electronic motion. When neglecting the dynamical effects, the usual statical adiabatic and Franck-Condon approximations are obtained as special cases. The formalism is applied to cyanogen the photoelectron spectrum of which exhibits an unexplained peculiar satellite structure. Ab initio calculations are performed which show that vibronic interaction between close lying 2Σg and 2Πu states takes place through the bending vibration. The vibronic coupling effects are enhanced by the simultaneous excitation of the totally symmetric C–N stretching vibration. Guided by these results a dynamical calculation is performed which reproduces nicely the experimental spectrum. The adiabatic and Franck-Condon approximations turn out to be inapplicable. As a consequence of the strong vibronic interaction with the 2Σg state, the 2πu state has a strongly bent equilibrium geometry.
The collision-induced polarized and depolarized Raman spectra of helium and the diatom polarizability
Authors: Proffitt Michael H. , Frommhold Lothar
Published: February 2003

The spectral distributions and absolute intensities of collision-induced Raman spectra of helium are obtained at 30 amagat, with incident beam polarizations parallel and perpendicular to the observation. These spectra can readily be separated into the polarized and the depolarized Raman continuum of the helium diatom. For comparison, spectra are also computed from wave mechanics, on the basis of Placzeck’s polarizability theory. Accurate, semiempirical interaction potentials are used as input, together with ab initio computations of the helium diatom polarizability tensor components. The computed spectra of selected trace and anisotropy functions agree with the observed polarized and depolarized continua. Anisotropy functions consistent with the depolarized spectrum differ by less than 5% from the classical dipole-induced dipole (DID) values at 2.685 Å separation.
Photoacoustic photocalorimetry of a solid state reaction
Authors: Chance R. R. , Shand M. L.
Published: February 2003

We have developed a new photocalorimetric technique for the study of photoinduced chain reactions. This technique is based on photoacoustic detection and is applied to the solid-state photopolymerization of diacetylenes. At early stages of the polymerization process, the thermal energy evolved is as much as four times greater than the total light energy deposited in the sample. This result is shown to require that an average of approximately eight polymerized diacetylene units is produced per absorbed photon. This experiment is the first definitive demonstration of the exothermic, chain-reaction nature of the photopolymerization process in these materials. A kinetic model for photoinduced reactions in highly absorbing materials is presented and shown to be in good agreement with experimental results.
Relaxation in an A2 coupled spin system dissolved in a perdeuterated liquid crystal: The intermolecular dipolar random field cross relaxation term
Authors: Courtieu J. , Jullien J. , Lai Nguyen Thoi , Guillois A. , Gonord P. , Kan S. K. , Mayne Charles L.
Published: February 2003

A perdeuterated nematic liquid crystal N- (p-ethoxybenzylidene) -p-n-butylaniline (EBBA-d23, 98% deuterium) was synthesized to study relaxation of small molecules dissolved in anisotropic solvents. Proton spin–lattice relaxation in the coupled A2 spin system of methylene chloride (CH2Cl2) was studied using both perhydro and perdeutero EBBA as the solvent. The relaxation was modeled as intramolecular dipole–dipole interactions plus other mechanisms that were treated collectively as fluctuating external random magnetic fields. Comparison of relaxation in EBBA and EBBA-d23 allowed the first experimental measurement of the correlation coefficient between external random fields at the two protons due to dipolar interactions of the methylene protons with the protons or deuterons of the solvent (78% correlated). The selective nuclear Overhauser effect was also studied.
Brownian motion of particles near a free surface: Desorption from a monolayer
Authors: Bilkadi Zayn , Parsons J. D. , Mann J. Adin , Neuman Ronald D.
Published: February 2003

A simple model for desorption from a monolayer is presented based on the Smoluchowski equation for the Brownian motion of a particle in a potential well located in the liquid–vapor interfacial region. For a simple square-well potential of depth Q we find an analytic expression for the probability p (t) that the particle will remain at the surface after time t. The relaxation time for desorption is shown to be proportional to exp(2Q). At short time p (o) -p (t) ∝t1/2 whereas for very long times p (t) ∝t−1/2. Interactions between molecules in the monolayer are taken into account by using a mean field approximation to the pair interaction. In its simplest form the theory reduces to solving the Smoluchowski equation for a time-dependent square well. Comparison is made to published experimental data, and additional experiments are suggested which will adequately test the theory.
Dissociation of metal carbonyls by metastable rare gases: Fe and Ni emission analysis
Authors: Hartman Dennis C. , Hollingsworth William E. , Winn John S.
Published: February 2003

Chemiluminescence from Ni(CO)4 and Fe(CO)5 collisions with metastable He, Ne, and Ar atoms is described. The emission spectra are due to atomic Ni and Fe. An analysis of these spectra indicate a dissociative energy transfer process which is not spin–differentiated among the metal atom states. Because of this, certain low-lying quintet states are seen here in emission for the first time. Steady state population analysis of all features permits a determination of the radiative lifetimes of these new states. For both carbonyls, a restricted statistical rate theory, in which the CO fragments are allowed to translate in one dimension only (the radial reaction coordinate) and are prohibited from rotating, gives good agreement with all the data. The nature of metastable electronic energy transfer is compared to photolytic energization, and a comparison of the likely excited electronic states involved in each indicates the source of the differences in product distributions observed by each method.
Is spin-aligned hydrogen a Bose gas?
Authors: Freed Jack H.
Published: February 2003

The Born−Oppenheimer approximation is used to discuss Bose statistics of spin aligned H atoms under conditions of low temperature, high magnetic field and high density. (AIP)
Time-dependent multiconfigurational Hartree–Fock theory
Authors: Dalgaard Esper
Published: February 2003

A time dependent version of multiconfigurational Hartree–Fock theory is formulated as an extension of the time-dependent Hartree–Fock approximation. The time variation of the reference state is calculated using a form of Frenkel’s variation principle, which was suggested by Langhoff, Epstein, and Karplus. A linearized form of the equations provides linear response functions, which transform correctly under contact transformations generated by one particle operators. A consequence of this feature is that the various formally equivalent expressions for the oscillator strengths of electronic transitions will give the same result, apart from truncation errors when a finite orbital basis is used. Example calculations are carried out for some π electron systems within the Pariser–Parr–Pople model using a correlated reference state suggested by Clementi and Veillard.
On electronic energy transfer in disordered systems
Authors: Klafter J. , Silbey R.
Published: February 2003

A generalized master equation (GME) describing the incoherent motion of an excitation in a disordered system is developed. The connection of the GME to the semi-Markovian theory of Scher and Lax, the generalized continuous random walk, and the self-energy approaches to the temporal properties of the transport is discussed. The theory is used in a model calculation to compute the mean square displacement and the probability of the excitation to remain at the origin as one dimensional systems, in which only nearest neighbor interactions are included.
The construction of modified virtual orbitals (MVO’s) which are suited for configuration interaction calculations
Authors: Bauschlicher Charles W.
Published: February 2003

A simple method, requiring the work of a single SCF iteration, is presented for the construction of modified virtual orbitals (MVO’s). Test calculations on H2O, Ar, and two states of CH2 show that for the truncation of orbitals at the CI level, the MVO’s are far more efficient than canonical SCF virtual orbitals or such related SCF virtuals as improved virtual orbitals (IVO’s) and for some cases approach the efficiency of natural orbitals. MVO’s are shown to be suitable for configuration selection based on energy contributions. The CI wave function is observed to be more compact with MVO’s, allowing better interpretation of the results.
Diffusion of a test particle in a hard sphere liquid
Authors: Selme M. O.
Published: February 2003

Using the quasihydrodynamic approximation of Resibois, the diffusion coefficient of a dilute impurity in a hard sphere liquid is calculated as a function of the liquid density, size, and mass of the diffusing species. The comparison with the computer simulation results shows that the obtained mass and density effects are qualitatively described by the Resibois theory whereas size effects are overestimated.
Charge distributions and chemical effects. XXII. On the partitioning of molecular energies and the relationships between energy components
Authors: Fliszár Sándor , Béraldin Marie-Thérèse
Published: February 2003

The exact quantum mechanical formulation of atomic and molecular energies and the postulate that ’’chemical bonds’’ exist combine to show that the nuclear–electronic and nuclear–nuclear potential energy V (k,mol) involving the kth atom in a molecule is for its largest part determined by ’’local effects’’ related to the number and type of bonds formed by k. These local effects are measured by the derivatives ∂εkj/∂Zk of the bond energies εkj involving k, with respect to its nuclear charge Zk. To a good approximation, neglecting the small nonbonded contributions, V (k,mol) =Vne (free atom k)−Zkj𝒥∂εkj/∂Zk. Applications to saturated hydrocarbons at the level of experimental accuracy indicate that the Emol/(Vne+2Vnn) ratios derived in this manner are close to their ab initio counterparts. These ratios are averages KmolAv=𝒥KmolkV (k,mol)/𝒥V (k,mol) of the ratios Kmolk=Ek(mol)/V (k,mol) defining the individual total energies Ek(mol) of atoms being part of a molecule, whereby Emol=𝒥Ek(mol). The Kmolk’s, in turn, are shown to be constants in saturated hydrocarbons, i.e., 1/2.3329 for C and 1/2 for H, and are instrumental in accurate calculations of molecular energies, Emol=𝒥Kmolk V (k,mol), and for deriving energy differences, Ek(free atom)−Ek(mol) =ΔEk =kmolkZk𝒥∂εkj/∂Zk +(Katomk−Kmolk) Vne(free atom k), between free and bonded atoms. Positive ΔEk values indicate that both the carbon and the hydrogen atoms are more stable in their bonded states than the free atoms, which is now understood in terms of dominating local binding properties, rather than in terms of local electron populations which play only a minor, though chemically significant, part on the scale of molecular energies.
Mechanisms of particle ejection from Cu(001) induced by the relative orientation of the bombarding primary ion
Authors: Foley Karin E. , Garrison Barbara J.
Published: February 2003

The effect of the angle of incidence of 600 eV Ar+ ions on the yields and mechanisms of particle ejection from a clean Cu(001) and a c (2×2) overlayer of oxygen on Cu(001) has been examined. The total yield of particles ejected as a function of polar angle is in qualitative agreement with experiment. The azimuthal dependence of the yields for both the clean Cu(001) and Cu(001) with a c (2×2) overlayer has been predicted. Mechanisms of particle ejection which are specific to a particular angle of incidence have been identified. Of particular interest is a shearing mechanism which contributes to the ejection process at an angle of ϑ=45° in the <100≳ directions. This shearing is responsible for the ejection of a large number of dimers which were originally next nearest neighbors on the surface. By energy selecting the dimers which eject, one can preferentially select the original sites of the two components. The angular distribution of the ejected particles, both substrate and adsorbate, due to normal incidence ion bombardment has previously been found to reflect the original surface site symmetry. The angular patterns of the ejected atoms are still dominated by the site sensitive effects, but the intensity is shifted due to the primary ion’s off-normal angle of incidence.
Transition from fluid to registered solid of the krypton monolayer adsorbed on the basal face of graphite
Authors: Larher Y. , Terlain A.
Published: February 2003

Precise measurements of adsorption isotherms of Kr on graphite in the coverage range corresponding to the transition between the fluid and the registered monolayer have been made. This transition is shown to remain first order up to a temperature of 115 K, contrarily to earlier studies which suggested 98 K. A critical analysis is made of theories recently proposed for this transition.
Electron thermalization in gases. I. Helium
Authors: Mozumder A.
Published: February 2003

A theory is presented for the thermalization of subexcitation electrons in a monoatomic gas and calculations performed for helium. Evolutions of both the velocity and the position distribution functions are considered in an approximate manner. Of particular interest are the time scale for thermalization and width of the spatial distribution at thermalization. Satisfactory agreement has been obtained with experiments and earlier calculations, where comparison is possible. Additionally, time-dependent relaxation rates, diffusion coefficient and distributional widths have been introduced and evaluated. At a given gas temperature thermalization parameters are not sensitive to initial energy within the subexcitation range. Variation of gas temperature, on the other hand, produces significant changes in these quantities. Momentum transfer cross sections for lower energies have been taken from swarm drift data and, for higher energies, constructed from phase shifts measured by Andrick and Bitsch. Calculated thermal electron mobilities agree well with experiment at different temperatures.
Semiclassical statistical mechanics of fluids. II. An improved mean field effective pair potential
Authors: Stratt Richard M.
Published: February 2003

An improved model is developed for an effective two body potential which incorporates quantum effects into classical equilibrium statistical mechanics. Just as in a previously derived model, a mean field approximation to a first quantum correction is employed in order to obtain nonperturbative expressions which include corrections to all orders. However, unlike the previous model, the resulting thermodynamic functions are exact to first order in h/2.
Raman studies of the orientational motions of small diatomics dissolved in argon
Authors: Hanson F. E. , McTague J. P.
Published: February 2003

We report a study of the orientational motions of oxygen and nitrogen dissolved in argon, using Raman spectroscopy. First, second, and fourth moments are reported for the rotation and vibration–rotation bands of these molecules at various concentrations along the liquid–vapor coexistence curve. It was found that less mean square torque is exerted on an oxygen molecule in argon solution than in the pure liquid at similar temperatures. The nitrogen data are probably in accord with this, although the experimental uncertainty is greater. Experimental values of the second moments are significantly in excess of the predicted classical values, even including important quantum corrections. This is probably due to ’’collision-induced’’ effects which were not accounted for in the moment analysis. Molecular dynamics simulations of rigid rotor ’’nitrogen’’ were made and the first order DID contributions to the collision-induced vibration–rotation spectrum were calculated. Even leaving out any high frequency overlap mechanism, the effect on the second moment was suprisingly large.
Equilibrium configurations and binding energies for small ionic ArN−1K+ clusters
Authors: Pan Ru-Pin , Etters R. D.
Published: February 2003

The potential energy surfaces for ionic clusters ArN−1K+ have been explored by numerical optimization techniques. Stable configurations and binding energies are found for all clusters ranging from 3 to 15 particles. Isomers are found for N?5. The binding energy per particle is found to decrease with N when N≳5, and the structure for N=4 acts as a basic unit in the construction of larger clusters.
Nuclear magnetic relaxation and low temperature molecular mobility in organic glasses
Authors: Müller-Warmuth W. , Otte W.
Published: February 2003

Proton spin–lattice relaxation times T1 at 15 and 30 MHz, and relaxation times in the rotating frame T1ρ, have been measured over the temperature range 20–230 K for cyclohexane, cyclohexene, 1,3-cyclohexadiene, benzene, and substituted benzenes in glasses made of simple organic molecules. Results for different glass-forming systems with guest molecules of various concentrations and for molecules in the cavities of a zeolite, have been compared. Asymmetric logT1−1 vs 1/T curves with a relaxation rate that decays more slowly at the low temperature side have been observed for all samples. This indicates high molecular mobility in the mixed glasses. An explanation is offered in terms of intramolecular dipolar interaction and exponential correlation functions which are distributed by the Cole–Davidson distribution. Various parameters have been derived, and models for this behavior have been discussed.
Steady state velocity distribution in hot atom reaction
Authors: Koura Katsuhisa
Published: February 2003

Analytical hot atom velocity distributions in the hot atom reaction are obtained using the BGK elastic collision model in the Boltzmann equation for the high-temperature steady state in the strong nonequilibrium limit and for the low-temperature steady state in the weak nonequilibrium case in correspondence to Kelzer’s steady state theory. The steady state velocity distributions are in qualitative agreement with the nonequilibrium steady state distributions by the Monte Carlo simulation.
Spectroscopy of the CH3O A 2A1–X 2E system by laser-excited fluorescence method
Authors: Inoue Gen , Akimoto Hajime , Okuda Michio
Published: February 2003

Laser-excitation spectra and single vibronic level fluorescence spectra of CH3O and CD3O A 2A1–X 2E transitions are reported. The spectral origin of the excitation spectrum is at 31 540 cm−1 (317.06 nm); extensive progressions in the stretching mode ν3′ (678 cm−1 for CH3O and 655 cm−1 for CD3O) dominate the spectra. Fluorescence bands appear that are assigned as the transition to the C–O stretching mode and CH3 deformation modes, giving ν3″=1015 cm−1 for CH3O and 1010 cm−1 for CD3O. Measured vibronic band intensities agree well with the Franck–Condon calculation. The band shape is well reconstructed on the assumption of SCF calculated geometry. No predissociation occurs below 35 900 cm−1.
On a time dependent Hartree theory of anharmonically coupled oscillators
Authors: Harris Robert A.
Published: February 2003

We point out that, as in the case of other interacting systems, a time dependent Hartree theory provides a very simple way of examining the interaction between modes of coupled anharmonic oscillators. We determine the susceptibilities which are manifestations of both ordinary absorption spectroscopy and Raman scattering.
Positive orbital energies and the instabilities of orbital-optimized wave functions
Authors: England Walter B.
Published: February 2003

A simple relation between positive orbital energies and the instability of many-particle wave functions is established for many-particle systems. Positive orbital energies in Hartree–Fock wave functions imply many-particle wave function instability. Positive orbital energies in multiconfiguration self-consistent-field wave functions do not necessarily imply total wave function instability. The determining factor is the occupation number of the orbital having the positive energy. Based on this, an approximate stability condition is stated for general multideterminantal wave functions.
Photochemistry of the chlorine monofluoride, ClF. Thermal and photochemical reactions with sulfur tetrafluoride SF4
Authors: Naulin Christian , Bougon Roland
Published: February 2003

The thermal and photochemical reactions of chlorine monofluoride have been studied with xenon, perfluoroethane O2F6, and sulfur tetrafluoride, SF4, which had been considered as possible scavengers for the excited or unstable species. No reaction has been observed with Xe and O2F6 either under thermal or photochemical activation. Photochemical reaction of ClF with SF4 has been studied at several wavelengths with a cw laser. From these studies, two reaction paths have been emphasized: (1) the molecular addition of ClF* to SF4 to give sulfur chloropentafluoride SF5Cl and (2) a typical laser induced radical process yielding disulfur decafluoride S2F10 and chlorine Cl2. This former effect has been shown to be hidden at low mean power irradiation by the thermal reaction which seems to be dramatically enhanced at low pressure by wall-catalyzed processes.
Electronic absorption spectra of molecular cations
Authors: Bondybey V. E. , Miller Terry A. , English J. H.
Published: February 2003

The absorption spectra of the radical cations of C6F6, m-C6H4F2 and p-C6H4F2 in solid Ne are obtained using a novel waveguide technique to increase the effective pathlength. Sharp, structured spectra are obtained for all three ions despite the face that the quantum yields for emission from the upper state are respectively 1:10−3: <10−4. Broad, relatively unstructured absorptions are attributed to C6H5F+ and C6H6+.
Dynamics of CO2+–D2 collisions. II
Authors: Hansen Steven G. , Mahan Bruce H.
Published: February 2003

The reactions CO2+(H2,H) HCO2+ and CO+(D2,OD)DCO+ have been studied using a new ion-molecular beam apparatus designed to operate at low ion energies. The threshold energy for HCO+ formation is determined from the study of the reactions. (AIP)
A new isotope effect in the radiationless transitions of nitrogen–heterocyclic compounds
Authors: Lai Ting-ing , Lim E. C.
Published: February 2003

A new isotope effect in radiationless transitions of n-heterocyclic compounds is reported. The nonradiative decay rate increases upon deuteration in sharp contrast to the normal isotope effects on radiationless transitions. (AIP)
Absolute CO coverage: Direct comparison between the (111) and (110) faces of Ni, Pd, and Pt at 300 K
Authors: Erley W. , Wagner H.
Published: February 2003

The Co uptake for the (111) and (110) surfaces of Pt, Pd and Ni is compared by recording flash desorption traces with a mass spectrometer. From these measurements, the absolute CO coverage is deduced. (AIP)
Divalent europium in tetragonal sites of RbCl single crystals
Authors: Rubio O. J. , Cory W. K. , Hernandez A. J.
Published: February 2003

A new EPR spectrum of EU2+ ions in RbCL single crystals is reported. The spin-Hamiltonian parameters describing the new site of EU2+ ion in RbCL are obtained. (AIP)
On the relation between collinear and three dimensional rate constants associated with vibrational energy transfer in diatom–diatom collisions
Authors: Wassam W. A.
Published: February 2003

An information-theoretic approach to the transformation of collinear energy transfer rates for diatom–diatom collisions to 3-D results is given. The present work is an extension of the Wassam–Levine 1-D to 3-D conversion scheme for atom–diatom collisions. An expression for the 3-D detailed rate constants, at a well-defined rotational-translational temperature, is obtained. This expression is employed in a numerical analysis of the temperature dependence of vibrational relaxation in O2  (v=1)  :H2, HCL  (v=1)  :H2, O2  (v=1)  :O2, and CO  (v=1)  :CO. 3-D rate constants are characterized in terms of V-T and V-V-T sum rules and suprisal plots. We find that the minimum in the suprisal does not occur in the region of resonance vibrational energy exchange.
The notion of an algebraic invariant and the related basis concepts in the investigation of certain physical properties
Authors: Meinköhn Dirk
Published: February 2003

Introducing the notion of relative and absolute invariants and the related basis concepts (module basis and integrity basis), it is demonstrated that these algebraic concepts can be of advantage in the investigation of physical properties which are represented by analytic functions of an equivalent algebraic structure. In particular, the discussion centers on the case of a module basis containing only a single element and on analytic absolute invariants depending only on the differences of the independent variables, for which the related integrity basis turns out to be redundant.
Quenching of Hg (3P1) atoms by halogen bearing molecules
Authors: Shay T. , Hemmati H. , Stermitz T. , Collins G. J.
Published: February 2003

We report the first measurements of the total quenching of Hg (3P1) atoms by CHFCl2, CF2Cl2, CF3Cl, CF3Br, CHBr3, and CBr4. Total quenching of Hg (3P1) atoms in collisions with halogen bearing molecules (RX) has been investigated in a binary reaction of the form, Hg (3P1)+RX→ products, where X represents a Cl or Br atom and R is a free radical such as CF2Cl or CBr3. No determination of the predominant output channel has been made, however, we have determined an upper limit on the individual cross sections for the B 2Σ+ output channel, Hg (3P1)+RX→HgX(B 2Σ+)+ R, where RX is one of the compounds mentioned above. The measured total quenching cross sections are all greater than 60 Å2. However, no HgX(B 2Σ+) formation was observed for any of these compounds and an upper limit on these single channel cross sections is 1 Å2. Hence we conclude that CHFCl2, CF2Cl2, CCl4, CF3Cl, CF3Br, CHBr3, and CBr4 are unsuitable halogen donors for efficient production of HgX(B 2Σ+) molecules.
Generalizations of the direct CI method based on the graphical unitary group approach. II. Single and double replacements from any set of reference configurations
Authors: Siegbahn Per E. M.
Published: February 2003

The direct CI method is generalized to the case of all single and double replacements from an arbitrary set of reference configurations. This is a continuation of the work and ideas presented in an earlier paper on first order wave functions. The analysis is done using the unitary group formulation of the correlation problem, and the resulting method is a combination of the direct CI method and the unitary group approach as formulated particularly by Paldus and Shavitt. The main idea in the present work is the factorization of the coupling coefficients appearing in the direct CI formalism, into a complicated internal part and a simple external part. The general philosophy is like in all direct CI methods to allow long CI expansions by avoiding the storage and retrieval of a large formula tape. The longest CI expansion treated in this paper is an application on the system CH2(3B1)+H2→CH3+H with five reference states, resulting in 16 096 configurations. The barrier height for the reaction is calculated to be 11.3 kcal/mol and predicted to be slightly below 10 kcal/mol.
Analytic solution of relaxation in a system with exponential transition probabilities. II. The initial transients
Authors: Forst Wendell , Penner Alvin P.
Published: February 2003

Using an exponential transition probability model normalized in the (0,∞) energy domain, we have obtained an analytical solution for the time-dependent population density below threshold, c (x,t), in the form of the eigenfunction expansion where x is internal energy, t is time, A0 and Aj are constants that depend on initial conditions, S and Rj are solutions of a determinant of a matrix of coefficients and k0−1 and τj are the relaxation times, the lowest of which (subscript 0) represents the reciprocal of the steady-state rate constant. From c (x,t) we then obtain all other time-dependent properties such as the non-steady-state rate constant and average energy, as well as incubation times and dead times for both number density and vibrational energy. Calculations relative to shock tube decomposition of N2O, CO2, and O2 in inert gas are compared with experiment, with generally good results. For the triatomics, average energy transferred per collision, as calculated from the experimental relaxation time, compares well with that calculated from the Schwartz–Slawsky–Herzfeld theory. The calculated diatomic rate constants (but not the relaxation and incubation times) are too low. Calculations relative to shock tube decomposition of cyclopropane are compared with numerical calculations of Malins and Tardy using a stepladder model. It is concluded that non-steady-state effects are unlikely in the cyclopropane shock tube work, and that diatomic rate constants are sensitive to rotational energy transfer.
The photochemistry of nitrosyl halides: The X+NOX→X2+NO(v) reaction (X=Cl, Br)
Authors: Grimley A. J. , Houston P. L.
Published: February 2003

The primary and secondary photochemistry of NOBr and NOCl has been monitored by detecting infrared fluorescence from vibrationally excited NO following pulsed photolysis of the parent compound with a tunable laser. For wavelengths greater than 480 nm the primary photolysis of NOX to NO+X produces little if any vibrational excitation in the NO product. However, secondary photochemistry produces excited NO through the reaction X+NOX→X2+NO(v). From the dependence of the rise time of NO fluorescence on the pressure of NOBr or NOCl at a constant pressure of added argon, it is found that the rate constants for the Br+NOBr and Cl+NOCl reactions are (5.16±0.28) ×10−12 and (5.40±0.47) ×10−12 cm3 molecule−1 sec−1, respectively. The reaction of Br with NOBr produces more NO in v=3 and/or v=2 than in v=1. At 355 nm roughly half of the NO vibrational fluorescence is due to the primary dissociation NOX→X+NO(v).
Einstein A coefficients, oscillator strengths and lifetimes for some selected triplet–triplet transitions of N2: A comparison between theory and experiment
Authors: Francke R. E. , Gallas J. A. C. , Grieneisen H. P. , Schifino J. , Chakraborty B. P.
Published: February 2003

Einstein A coefficients, oscillator strengths and lifetimes have been calculated by an asymptotic expansion method, introduced by Chang and Karplus, for the N2, B 3Πg→A 3Σ+u (first positive), C 3Πu→B 3Πg (second positive), W 3Δu⇄B 3Πg (Wu–Benesch) and B′ 3Σ−u→B 3Πg (infrared afterglow) band systems, using theoretical electronic transition moments, Re (r), of Yeager and McKoy. Whenever possible, comparison has been made with those calculated from the electric dipole moment functions, Re (r̄), which are functions of r̄ centroids, obtained from band intensity or lifetime measurements. Excellent agreement has been obtained in the case of the second positive band system of molecular nitrogen. However, for all other cases, conventional Re (r̄) functions are found to be superior to the theoretical Re (r) functions of Yeager and McKoy.
Brownian dynamics simulation of alkane chain reorientation: A comparison of models
Authors: Evans Glenn T. , Knauss Donald C.
Published: February 2003

Orientational time correlation functions and correlation times are determined using a Brownian dynamics and rigid body formalism and are compared with the results obtained from our previous Mori approach. It is found that the Mori method equipped with a minimum set of primary variables approximately represents the freely rotating chain. The correlation functions obtained from Brownian dynamics were found to display a rapid initial decrease, followed by a slow nearly exponential fall-off. First and second rank correlation times for pentane, hexane, nonane, and undecane are reported.
Temperature dependence of vibrational energy transfer in NH3 and H2 18O
Authors: Hovis Floyd E. , Moore C. Bradley
Published: February 2003

The V→T, R relaxation rate for NH3  (ν2) has been studied from 198 to 398 °K by the method of laser-excited vibrational fluorescence. The self-deactivation rate constant decreases from 4.9×10−11 cm3 molecule−1 sec−1 at 198 °K to 2.7×10−11 cm3 molecule−1 sec−1 at 398 °K. The rate constants for deactivation by He, Ar, N2, and O2 are much smaller and show a weak temperature dependence in the opposite direction. For H2 18O the vibrational relaxation rates of the coupled ν1, ν3 stretching level manifold and of the 2ν2 bending level have been studied from 250 to 400 °K. The ν1, ν3 self-deactivation rate goes from 3.5×10−11 cm3 molecule−1 sec−1 at 250 °K to 2.0×10−11 cm3 molecule−1 sec−1 at 400 °K. For 2ν2 it goes from 1.2×10−10 to 7.8×10−11 cm3 molecule−1 sec−1. The temperature depencence of the deactivation of both levels by He and Ar is much weaker and the rates are several hundred times slower. CO2 deactivates ν1, ν3 about 50 times faster than He or Ar at 293 °K.
Self-diffusion in binary liquid solutions of n-paraffins and hexafluorobenzene
Authors: von Meerwall E. , Ferguson R. D.
Published: February 2003

Steady and pulsed gradient spin echo measurements of the self-diffusion of both components (1H and 19F NMR) at 80 °C were performed in solutions of C6F6 and each of six n-paraffins between n-octane and n-hexatriacontane across the full concentration ranges; activation energies were also measured. The results are interpreted in terms of hydrodynamic and free-volume models of binary self-diffusion.
Electric field dependence of collisionless, single rotational level lifetimes of S1 H2CO
Authors: Weisshaar James C. , Moore C. Bradley
Published: February 2003

A glass fluorescence cell with two stainless steel stark electrode disks was used to measure the time decay of the fluorescence intensity of formaldehyde. (AIP)
Electron spin echo modulation study of the geometry of solvated electrons in ethanol glass: An example of a molecular dipole oriented solvation shell
Authors: Narayana M. , Kevan Larry
Published: February 2003

The analysis of the electron spin echo modulation patterns of solvated electrons in variously deuterated ethanol glasses shows that four ethanol molecules constitute the first solvation shell of the solvated electron with average distances of 2.2 Å to the OH protons, 3.3 Å to the CH2 protons, and 3.8 Å to the CH3 protons. These distances show that the OH bond of ethanol cannot be oriented towards the solvated electron. Instead the electron must be located along a line which approximately bisects the COH bond angle. This is the same direction as the molecular dipole orientation in ethanol and demonstrates that the solvated electron in ethanol has a molecular dipole oriented solvation shell in contrast to the OH bond oriented solvaton shell for the solvated electron in aqueous systems.
Molecular beam study of the hydrogen/hydrogen halide system: New results on the exchange reaction
Authors: Beck W. H. , Götting R. , Toennies J. P. , Winkelmann K.
Published: February 2003

A refined and extensive experimental study of the system H+H’X is reported (X is a halogen cl and I and H’ an isotopic variant namely D. (AIP)
The time-scale of intraspur muonium formation
Authors: Percival P. W.
Published: February 2003

The gate of muons in water is discussed in terms of the spur model. The model supposes that the muon comes to rest in the immediate neighbourhood of a presolvated electron and OH. If the muon and electron combine, muonium is formed, otherwise the muon will hydrate. (AIP).
Collisional ionization induced by the presence of intense optical fields
Authors: Weiner John
Published: February 2003

Collisional ionization in the presence of a laser field is discussed in terms of a two-step optical/collisional perturbation sequence. This point of view is used to develop a cross section formula for laser-induced Penning ionization applicable to the design of laboratory experiments. Characteristic magnitude of the laser-induced effect as well as functional dependence on laser intensity and frequency predicted by the perturbation approach may be directly compared to experimental observation.