bluuebunny/crossref_metadata_2025 huggingface dataset:
Diatomic interhalogen laser molecules: Fluorescence spectroscopy and reaction kinetics
Authors: Diegelmann M. , Hohla K. , Rebentrost F. , Kompa K. L.
Published: February 2003

Mixtures of halogen-containing molecules and rare gases have been excited by a short pulse of high energy electrons. The D′→A′ transitions occurring between an ionically bound upper level and a weakly bound covalent lower level in the diatomic halogens F2, Cl2, and interhalogen compounds ClF, ICl, IF, IBr, BrCl, and BrF formed under these conditions have been studied systematically. Emission wavelengths calculated from a simple model are in good agreement with the experimental data. The processes responsible for the population of the upper level have also been studied. The exchange reaction of an electronically excited atom with a halogen donor molecule appears to be the key step in the kinetic excitation sequence. A rate equation model satisfactorily describes the time development of the observed halogen fluorescence. Based on these results, successful laser experiments have been conducted on several of the interhalogen systems.
Modulation of proton NMR free induction decay by spin diffusion
Authors: Cheung T. T. P.
Published: February 2003

The effects of spin diffusion on the free induction decay (FID) of protons associated with the noncrystalline domains of two polymers, polyethylene and blended Nylon 66 (ZYTEL-408), have been examined using Goldman–Shen NMR pulse sequence [(1/2)πx−t0−(1/2)πx̄−τ−(1/2)πx−t]. At τ≲100 μs, the FID is drastically distorted from the exponential form while at longer τ(τ≳500 μs) an exponential FID is observed; but its transverse spin relaxation rate is smaller than that of the FID obtained after a single (1/2)πx pulse and approaches this value at the limit of large τ. These findings are interpreted in terms of the theory of rapid spin diffusion. The spatial variation in the spin relaxation rate within the noncrystalline domain is inferred.
Fine structure in the dependence of final conditions on initial conditions in classical collinear H2+H dynamics
Authors: Agmon Noam
Published: February 2003

The dependence of final vibrational energy, final phase, and trajectory time on the initial phase of the H2 reagent is examined on a novel potential energy surface for the collinear H3 system. For the first time, the fine structure in the borders of the reactivity bands is reported in some detail. A complex, exponentially crowding structure is found in contrast to the common impression of ’’chaotic’’ behavior in these regions. The close relation of this structure to the concepts of periodic and exponentiating trajectories is discussed. A suggestion for the implications to Feshbach resonances in semiclassical theory is made.
Rotational effects in multiphoton excitation of hot molecules
Authors: Ruhman Sanford , Haas Yehuda
Published: February 2003

The visible chemiluminescence resulting from infrared multiphoton excitation (MPE) of CrO2Cl2 is used to study the effect of inert gas addition on the yield and branching ratio of MPE induced reactions. In some cases, addition of foreign gases increases the chemiluminescence yield, and also leads to a blue shift in the emission spectrum. This result may indicate bottleneck formation in the quasicontinuum region. This bottlenecking is discussed using a model that calls for a gradual broadening of single rotational lines as energy is accumulated in the molecule. Under appropriate conditions, fast rotational relaxation can lead to higher average vibrational energy, as well as to a significant population increase in the high energy tail of the vibrational distribution. A stochastic method is used to solve the rate equations. This computationally simple technique is particularly useful in the limiting case of fast rotational relaxation.
A quantum mechanical model of vibrational-electronic energy exchange during collisions
Authors: Schmalz T. G.
Published: February 2003

A model for the interchange of energy between an electronic and a vibrational mode during a collinear atom–molecule collision is proposed. Although crude, the model is simple enough to be solved exactly using the R-matrix propagator method for treating quantum close-coupling problems. These exact results can be compared to semiclassical and approximate treatments of the same problem. Several interesting features of the model system are discussed in terms of elementary energy transfer concepts.
A criterion for the applicability of the method of diatomics-in-molecules to potential surface calculations. I. Selection of the DIM basis
Authors: Schreiber J. L. , Kuntz P. J.
Published: February 2003

A self-consistency criterion is applied to the method of diatomics-in-molecules in order to determine, in a resasonable manner, the minimum DIM polyatomic basis set needed to describe a given state of a polyatomic system. The method requires only the calculation of overlap integrals of the DIM basis functions with ab initio wave functions for the diatomic fragment states. The procedure is applied to the reaction Be+HF→BeF+H (1A′ ground state), for which extensive DIM model calculations are available.
A rapidly convergent expansion technique for local quantum mechanical operators
Authors: Augustin Stuart D. , BelBruno Joseph J. , Rabitz Herschel , Gelfand Jack
Published: February 2003

A general technique is described for efficiently expanding quantum mechanical operators. The basis is a particular set of wave functions and the expansion coefficients are physically meaningful matrix elements of the operator. Two applications to molecular properties, the transition dipole operator and the anharmonic force field, are discussed. We demonstrate that the entire force field can be expressed exactly in terms of anharmonic perturbations of the ground state, and that a great deal of information can be easily obtained from the spectroscopic frequencies. Similarly, the dipole moment matrix elements in any vibrational band are shown to be given in terms of a sum of only the R(1) matrix elements for various vibrational levels. Numerical results are presented for HCl rotational line strengths. These applications are only two examples of the potential experimental and theoretical uses of this method.
Generalized localized atomic orbitals
Authors: Aufderheide Keith H.
Published: February 2003

Recent publications concerning localized atomic orbitals (LAOs) for atoms in closed shell molecules showed a number of LAO properties to be highly transferable insofar as the atom experienced equivalent bonding environments in a series of molecules. Assuming that transferability of LAO properties (such as interorbital angles and Mulliken populations) portends a concurrent transferability of LAO structure, we here deduce a set of average hybrids, or generalized LAOs (GLAOs). The GLAOs may, in principle, serve the same purpose as the familiar spn (n = 1, 2, 3,) orbitals; however, the former evidence a number of desireable trends not represented in the latter. For instance, GLAOs allow hybridization to vary in response to alterations in both degree of unsaturation (e.g., –C– vs    C = vs = C = vs. –C≡) and atomic number (e.g., –C– vs.   N– vs –O– vs F–   ). This is in accord with experimental data such as bond angles, which tend to vary in conjunction with the same sorts of phenomena. It is important to note that, once the connections between hybridization and atomic number and bonding environment are deduced, one is empowered to both understand the driving forces behind previous LAO results and to predict the compositions of GLAOs on atoms hybridized in fashions not treated as yet via LAOs. This feature is illustrated by a consideration of B in BH3 and N in N2H2. Finally, it is shown that GLAOs preserve trends in interorbital angles found so useful in past encounters, and a quantitative relationship is uncovered between interorbital angles and interorbital repulsions.
Theory of magnetic susceptibilities and NMR chemical shifts in terms of localized quantities. II. Application to some simple molecules
Authors: Schindler Michael , Kutzelnigg Werner
Published: February 2003

A coupled Hartree–Fock method with individual gauge for localized orbitals (IGLO) proposed previously is reformulated and applied to the calculation of the magnetic susceptibility χ and the chemical NMR-shifts σ of various small molecules. The agreement with experiment is usually very good. Unlike in traditional methods, the results are not very sensitive to the size of the basis, and the application to large molecules does not pose serious problems. The results are analyzed in terms of orbital contributions, and it is shown that local diamagnetic terms are transferable, while local paramagnetic as well as nonlocal contributions are not. Pictorial explanations of the large antishielding effects in F2 and H2CO are given. In CH+3, a large dependence of χ and σ on changes of the geometry (pyramidalization) is found.
Multidimensional many-body theory: Diagrammatic implementation of a canonical van Vleck formalism
Authors: Redmon Lynn T. , Bartlett Rodney J.
Published: February 2003

A size-extensive multidimensional many-body theory is developed from an order-expanded van Vleck transformation. This provides an effective Hamiltonian in a model space consisting of a set of determinants whose zeroth-order energies may be nondegenerate. Expressions for the effective Hamiltonian in terms of the perturbation and a set of resolvents generalized from the Rayleigh–Schrödinger form are given. Perturbative evaluation of the resultant formulas via diagrammatic expansion is illustrated and discussed. The diagrams required through second order for a model space consisting of a Hartree–Fock solution plus selected singly and doubly excited determinants are presented, and their relation to those employed in the method of Hose and Kaldor is discussed.
Efficient and accurate expansion methods for molecules in local density models
Authors: Delley B. , Ellis D. E.
Published: February 2003

The effects of truncation of the effective Hamiltonian of local density theory through shape approximations to the molecular charge density are examined. A self-consistent multicenter-multipolar (SCM) representation of the density is introduced, which allows calculation of the Coulomb and exchange-correlation potentials to any desired level of precision. The related question of quality of wave function expansion bases required to reproduce spectra and densities with chemical accuracy is explored. The efficiency and accuracy of the SCM approach are verified by applications to O2 and CO; results are given for the metal cluster compound Ru3(CO)12.
The field-induced instability in the planar texture of cholesteric liquid crystals
Authors: Vertogen G. , van Groesen E. W. C.
Published: February 2003

A more accurate calculation is given of both the striped perturbation pattern and the square grid perturbation pattern that are formed in the planar cholesteric layer as soon as the applied field reaches a threshold value. Notably, it is shown that the distance between the boundaries must exceed a critical value in order to allow such a distortion. The values of the critical field and the wavelength of the distortion are compared with existing calculations.
On the phase transition in benzil
Authors: Yoshihara A. , Wilber W. D. , Bernstein E. R. , Raich J. C.
Published: February 2003

The phase transition in crystalline benzil [(C6H5CO)2] at 84 K is investigated through Brillouin scattering. The major experimental findings are two transverse acoustic phonon modes exhibiting softening near the phase transition, a longitudinal acoustic mode that is temperature sensitive, and the ratio of the Rayleigh peak intensity to the soft mode intensity behaves anomalously. These results are discussed using a theory developed for an elastic phase transition in sym-triazine (C3N3H3). It is found that bilinear-coupling terms involving strains and the order parameter can explain transverse mode behavior but not that of the longitudinal acoustic mode.
Decay of an excited molecule near a small metal sphere
Authors: Ruppin R.
Published: February 2003

The decay of an excited molecule near a small metal sphere is considered from the viewpoint of electromagnetic theory. The total decay rate of the emitting dipole is obtained by considering the two mechanisms through which energy is dissipated. One is the radiative loss, which is calculated from the Poynting vector, and the other is the nonradiative decay which is calculated from the Ohmic losses inside the sphere. Numerical computations are performed for the case of a molecule near a small silver sphere, and the results are compared with those for a molecule near the planar boundary of a silver half-space.
Dynamics for CH3F and CD3F isolated in rare gas solids
Authors: Jones Llewellyn H. , Swanson Basil I.
Published: February 2003

High resolution infrared spectra have been obtained for CH3F and CD3F in argon and krypton matrices from 3 to 39 K. Low-temperature spectra show structure indicative of two stable monomer sites. As temperature is raised, the structure collapses to give symmetric peaks for each mode. The line shapes and their broadening with temperature show large dependence on the modes, isotope, and host matrix. On the basis of the absence of rovibrational structure and the very different line shapes for the various modes, we conclude that free or hindered rotation does not contribute to the absorption lines of methyl fluoride in argon or krypton matrices below 40 K. The mode dependent line broadening with increasing temperatures has been attributed to vibrational dephasing involving low energy site local phonon modes. Implications with regard to vibrational energy relaxation, which is currently thought to be dominated by a vibration to rotation energy transfer, are discussed.
A matrix method for the calculation of rate constants for complex bimolecular exchange reactions
Authors: Davis Jon P.
Published: February 2003

A method is proposed for calculating, classically, the rates, selectivities, and product distributions of complex bimolecular exchange reactions. The method replaces the full numerical integration of the classical trajectories by the numerical integration of ’’single vibrations’’ of the collision complex plus the formation of sequences of these single vibrations (by matrix combination or table search rather than by further numerical integration) to yield multiple vibrations. The method is tested on three collinear atom–diatom systems and found to give satisfactory results. The reasons for and problems of extension of the method to three dimensions and larger systems are discussed.
Plasmon mediated, long range, oscillating van der Waals forces between molecules adsorbed on metals
Authors: Metiu Horia
Published: February 2003

We use qualitataive arguments to propose a propensity rule stating that the van der Waals forces between adsorbed molecules may be strongly influenced by the surface plasmon. As a result, if the molecule has a narrow level resonant with a weakly damped surface plasmon, the van der Waals forces oscillate as a function of their separation and have an unusually long range.
Temperature dependence of the activation energy: D+H2
Authors: Blais Normand C. , Truhlar Donald G. , Garrett Bruce C.
Published: February 2003

Rate constants and activation energies are calculated for D+H2→DH+H over the temperature range 444–2400 K by trajectory calculations and over the temperature range 300–2400 K by improved canonical variatonal theory with small-curvature-approximation semiclassical adiabatic ground-state transmission coefficients. Both calculations use the most accurate available potential energy surface. The results are compared to each other results for this system and for H+H2μH2+H.
Improvement of the effective nuclear charge model for diatomic molecules. VI
Authors: Ohwada Ken
Published: February 2003

The effective nuclear charge model previously proposed for predicting the valence force constants of polyatomic molecules is further developed to make the exact description of molecular vibrations. The effective intramolecular potential function assumed in such a model is somewhat improved for diatomic molecules, i.e., the correction term due to the delocalized valence electrons is expanded near equilibrium in the analytic form of an inverse power series of the internuclear distance. It is shown that the resulting potential is useful in estimating the anharmonic force constants as well as in describing the excited electronic states of diatomic molecules.
Study of cohesion and thermodynamical properties of fluorite-type AB2 crystals
Authors: Singh R. K. , Sanyal Sankar P. , Pandey N. K.
Published: February 2003

A study of the cohesion and thermodynamic properties of fluorite-type AB2 crystals has been carried out by means of an interionic potential, which consists of the long-range Coulomb interactions and short-range overlap repulsion and van der Waals (vdW) dipole–dipole and dipole–quadrupole interactions. The vdW coefficients have been evaluated from the Slater–Kirkwood variational method. The effect of second-neighbor overlap repulsion is incorporated via the Hafemeister and Flygare approach. The calculations of cohesive energy, Debye temperature, Grüneisen constant, thermal expansion coefficients, molecular force constant, reststrahl frequency, compressibility, and its pressure and temperature derivatives have been performed for ten solids. The agreement between theoretical and experimental results is generally good.
The steady-state shear viscosities of some bromopentanes
Authors: Wilson William L. , Mellon Paul F. , Berberian ]John G.
Published: February 2003

The steady-state shear viscosities of 3-methylpentane, 3-bromomethylpentane, 3-bromopentane, and 3-bromo-3-methylpentane are presented as a function of temperature. The temperature range of the measurements is from 138 down to 76 K; the range of viscosities measured is from 3.07×101 up to 1.80×1011 Pa s.
Second order ferro-paraelastic phase transition in the layer crystal (n-C3H7NH3)2 ZnCl4 at 310 K
Authors: Zuñiga F. J. , Tello M. J. , Mato J. M. Perez , Jubindo M. A. Perez , Chapuis G.
Published: February 2003

Bis-propylammonium tetrachloro-zincate (II) shows a second order ferro-paraelastic phase transition with a Pnma-P21/n symmetry change at 310.20±0.02 K. Experimental studies involving the description of both structures from x-ray measurements as well as thermal and optical measurements allow us to characterize this phase transition. It is equitranslational and is described by means of an order parameter which transforms according to the irreducible representation B3g of space group Pnma. The critical behavior of the spontaneous monoclinic shear u4, the spontaneous birefringence and the specific heat suggest that this compound may belong to the group of ’’proper ferroelastics’’ for which the Landau theory is strictly valid. A soft mode discussion that accounts for the displacive part of this phase transition and a phenomenological approach following Landau’s theory are carried out. Finally, a possible order–disorder contribution is also discussed.
Photocurrent generation in zinc phthalocyanine films
Authors: Twarowski Allen J.
Published: February 2003

Photovoltaic activity has been frequently reported for various phthalocyanine dyes incorporated into Schottky barrier devices. An important step in the conversion of visible light to electrical work with these devices is the process of photocarrier generation. This process is examined here for thin films of zinc phthalocyanine by studying the electric field dependence and the temperature dependence of photoconductivity. Results of these investigations are interpreted using the Onsager mechanism of charge pair separation in an external field. An Onsager distance ro of 9 Å is found in zinc phthalocyanine. The consequences of such a small charge ejection distance are discussed.
Atomization energies of gaseous molecules of Li with Bi and Pb
Authors: Neubert A. , Ihle H. R. , Gingerich K. A.
Published: February 2003

In continuation of an analysis of the saturated vapor over condensed phases of Li–Bi and Li–Bi–Pb alloys by mass spectrometry, the atomization energies of recently detected polyatomic molecules were determined. The following results were obtained:             These experimental values were compared with those calculated according to Pauling’s rule.
Electric field induced fluorescence quenching and photocarrier generation in x-metal-free phthalocyanine
Authors: Popovic Zoran D.
Published: February 2003

The electric field induced fluorescence quenching and transient photoconductive response of x-H2Pc particles dispersed in an inert polymer matrix have been measured for different applied electric fields and temperatures between 22 and 70 °C. The results of the measurements show that fluorescence quenching and carrier generation are the different aspects of the same process, namely, the depopulation of the first excited singlet state by exciton dissociaton into electron hole pairs. The linear correlation between fluorescence quenching and relative photoresponse enables the determination of absolute quantum efficiency by performing only relative measurements. The temperature dependent studies showed consistency between carrier generation and fluorescence quenching, and established an activation energy for the generation of charge carriers.
Photochromic switching in semiconducting films of triphenylformazan
Authors: Dahlberg S. C. , Reinganum C. B.
Published: February 2003

A photochromic transition between the red (R) and yellow (Y) forms of triphenylformazan has been followed experimentally by measuring the photovoltage of this semiconducting film. To the authors’ knowledge, this is the first time such switching behavior has been observed electronically in an organic solid. The wavelength for maximum photovoltage signal is 408 nm, which corresponds to the maximum optical absorption of the yellow form. This is consistent with the following photo-induced reaction:           The dynamics of this photochromic switching were probed with a pulsed tunable dye laser and (k1)−1 and (k2)−1 are both faster than ∼10 ns. (k−1)−1 is faster than ∼0.1 s, and (k−2)−1 is 0.218 s.
UV-laser photochemistry of diborane at 193.3 nm: The exchange reaction with deuterium
Authors: Irion M. P. , Kompa K. L.
Published: February 2003

Excitation of diborane by an ArF exciplex laser induces a chain reaction with deuterium. A mechanism is proposed and computer modeling is applied to simulate experimental results. Rate constants are obtained for the reactions                   The problem of the primary photochemical step is discussed thoroughly and BH3, not B2H5⋅ , is found to be most probably the reactive intermediate.
Cross-correlation trajectory study of vibrational relaxation of DF(v = 1 to 7) by DF(v = 0) and of HF by HF
Authors: Coltrin M. E. , Marcus R. A.
Published: February 2003

Three-dimensional quasiclassical trajectories and a cross-correlation method of analysis are used to study the vibrational relaxation of DF(v1 = 1 to 7) by DF(v2 = 0). Rate constants are calculated for V–V and V–R, T energy transfer. As was seen in earlier studies on HF–HF, the V–R, T mechanism becomes increasingly important at higher initial v1, as the V–V transfer moves further off resonance and also becomes increasingly endothermic. Both factors contribute to the decrease of V–V transfer rates with increasing v1 for the higher values of v1. Comparisons are made with results of a classical path study of vibrational relaxation in DF–DF and with experiment where possible. New results on the HF–HF V–V transfer rates are presented.
Ion–molecule reactions of Cl2 with Cl− and F−
Authors: Babcock Lucia M. , Streit Gerald E.
Published: February 2003

Using the flowing afterglow technique, we have examined the process Cl2+Cl−→Cl3− in helium buffer gas. The system was studied over a range of helium pressures and the dependence of the apparent two-body rate upon the buffer gas concentration gives a three-body rate constant for the process: k = 0.9×10−29 cm6 molecule−2 s−1. In addition, we looked at the analogous process involving a fluoride ion. There is no evidence for formation of the trihalide Cl2F− under our experimental conditions. A charge exchange process between Cl2 and F− to produce Cl− and neutral ClF does occur, however. This rate is independent of the pressure of the helium buffer gas: k = 8.8×10−10 cm3 molecule−1 s−1.
The dynamics of the reaction H+3+D2→HD+2+H2, and the effects of reactant vibrational excitation on the product energy and angle distributions
Authors: Douglass Charles H. , Ringer Geoffrey , Gentry W. Ronald
Published: February 2003

The dependence of the absolute total cross section and the product ion kinetic energy distribution on the reactant kinetic energy have been measured for the reaction H+3+D2→HD+2+H2 over the energy range from 0.002 to 11 eV, by means of the merged molecular beam technique. At low collision energies, the reaction occurs with high probability per close collision, and at all collision energies the product ion is scattered preferentially in the direction of the D2 reactant in center-of-mass coordinates. Because the reactants in these experiments are vibrationally excited, comparison of the present results with the crossed-beam data of M. L. Vestal, C. R. Blakly, P. W. Ryan, and J. H. Futrell [J. Chem. Phys. 64, 2094 (1976)] reveals the influence of reactant vibration on the reaction dynamics.
Relationship between configuration interaction and coupled cluster approaches
Authors: Paldus J. , Wormer P. E. S. , Visser F. , van der Avoird A.
Published: February 2003

A variational principle for the linear coupled pair many-electron theory (L-CPMET) is given and its implications for the relationship between certain configuration interaction (CI) and coupled cluster approaches (CCA), and for the computational aspects of solving the algebraic systems occurring in CCA, are discussed. An exact relationship between the correlated energies and wave functions as obtained with the L-CPMET and with the CI limited to at most doubly excited configurations (D-CI) is derived and used to provide a new viewpoint on the origins of Davidson’s correction for unlinked cluster contributions in the D-CI energy. The results are illustrated on the CO molecule.
Covalency effects on O–O interactions in NiO
Authors: Sabelli N. H.
Published: February 2003

The effect of covalency in NiO was investigated as a function of the O–O internuclear separation. A spin-dependent effective-core potential for Ni++ and a charge compensated array of point charges representing the ions in NiO have been used to stabilize O= and obtain the electronic potential energy curve. Ab initio SCF calculations were performed on the 1Σ+g state of both the purely ionic [O4−2] system and the covalent system [Ni1004−2]. Covalency effects have strong influence on the pair potential obtained; parameters for both models are compared with estimates used in the modeling of oxides.
Dynamic dipole polarizability of HeH+
Authors: Bishop David M. , Cheung Lap M.
Published: February 2003

The recently introduced ’’vibronic’’ method of calculating dynamic dipole polarizabilities has been applied to HeH+. Because this molecule has a vibrational component to its polarizability, it is shown that special care has to be taken when the method is applied. The method has been modified and the calculations carried out more rigorously than before in order to avoid certain problems which were previously undetected. New and more accurate results are reported and these are compared with those that can be obtained by using the traditional clamped nucleus method.
Theoretical study of cyclopropane and cyclopropyl radical: Structure and vibrational analysis
Authors: Dupuis M. , Pacansky J.
Published: February 2003

A b initio Hartree–Fock calculations of the structure and vibrational frequencies of cyclopropane and cyclopropyl radical are presented. It is found that the αCH bond in the radical is bent 39.3° out of the CCC plane, the inversion barrier is 3.0 kcal/mol and the pyramidal bending mode has a frequency of 713 cm−1. Compared to cyclopropane, the αCC bonds are stronger, and the βCC bond is weaker in the radical. The shortening of the αCH bond, and the hyperconjugative interaction of the unpaired electron onto the βCH bonds previously observed in alkyl radicals, are found to be much less pronounced in the cycloproply radical.
A simple theoretical model for the van der Waals potential at intermediate distances. IV. The bond distance dependence of the potential hypersurfaces for He–H2 and Ne–H2 also for the repulsive region
Authors: Tang K. T. , Toennies J. Peter
Published: February 2003

A simple theory for the van der Waals potential in the region of the well minimum, which previously has been successfully applied to the prediction of the isotropic atom–atom [J. Chem. Phys. 66, 1496 (1977)] and the anisotropic atom–diatom potentials [J. Chem. Phys. 68, 5501 (1978); 74, 1148 (1981)], has been extended to calculate the full potential hypersurface including the H2 bond distance dependence for He–H2 and Ne–H2. By taking advantage of the known potential parameters in the united atom limits He–He and Ne–He, respectively, the potential hypersurface is predicted over a wide range of bond distances. The model is modified to also provide a good estimate of the true potential in the repulsive region (V≃1 eV). The results for He–H2 are compared with a recently calculated CI type hypersurface [Meyer, Hariharan, and Kutzelnigg, J. Chem. Phys. 73, 1880 (1980)] and found to be in good agreement in the region of intermediate distances of the center of masses (R≈3.0 Å), and for H2 bond distances r in the range (0.50–1.00 Å). The R dependence of the vibrational coupling matrix elements are presented for both systems and the implications for the vibrational relaxation rates of both systems are discussed.
Formation of perbromate radical anions by attachment of O− to bromate in a solid matrix
Authors: Byberg J. R.
Published: February 2003

Migration of O− in x-irradiated KClO3 crystals is exploited to study the reaction between O− and BrO−3 occupying anion sites in KClO3. ESR spectra show that O− becomes attached to BrO−3, forming a tetrahedral adduct BrO2−4, which is virtually identical to the species arising from electron-capture on BrO−4, in accordance with the structural equivalence between [XO−3+O−] and [XO−4+e−] established earlier for X = iodine in aqueous solution.
Interpretation of the nitrogen K
V
V Auger line shape from alkali metal nitrates
Authors: Hutson F. L. , Ramaker D. E. , Dunlap B. I. , Ganjei J. D. , Murday J. S.
Published: February 2003

Experimental N KVV Auger line shapes from sodium nitrate, produced by both x-ray (XEA) and electron (EEA) excitation, are compared to theoretically derived line shapes based on populations derived from a GTO-LCAO-Xα model. The one-electron orbital energies and valence line widths are determined from x-ray emission and photoelectron data; the Auger matrix elements are determined from experimental gas phase atomic Auger data. The theoretical Auger energies include hole–hole repulsion and relaxation. Theoretical lines shapes using the local and the Mulliken Xα populations are generated, and a set of empirical populations are also determined. This work emphasizes the importance of shake-off arising from creation of the initial core hole and its effect on the Auger line shape. A theoretical shake/Auger satellite line shape is generated and found to contribute up to 35% of the total intensity. The XEA and EEA line shapes (after correction for the sample and spectrometer transmission response) each show five features, but some differences are noted. These are attributed primarily to beam damage and charging effects on the EEA line shape. The theoretical line shapes reproduce the five principal features of the experimental spectra; specific features in the line shape are shown to reflect the relative size of the Auger matrix elements, the symmetry of the NO−3 ion, and satellite contributions. Arguments for the validity of a one-electron orbital model to describe the Auger line shape are presented.
Brillouin scattering in oligobutene
Authors: Kono Ryusuke , Yoshizaki Haruyo , Yamaoka Toshihiko
Published: February 2003

Ultrasonic and hypersonic relaxation data are reported for a polymeric liquid oligobutene at frequencies between 51 kHz and 8 GHz in the temperature range from -60 to 100 °C. It is found that the superposition principle holds up to 0.76 GHz for shear data, while for the bulk process spectral narrowing takes place around 3 GHz. This difference can be interpreted in terms of a local theory presented by one of the authors.
The characterization of supersonic sodium vapor expansions including laser induced atomic fluorescence from trimeric sodium
Authors: Gole James L. , Green Gary J. , Pace S. A. , Preuss D. R.
Published: February 2003

A supersonic expansion of pure sodium metal has been used to form small sodium clusters Mn, n⩾2. Discussion focuses on the characterization of variously produced sodium supersonic expansions and the analysis of laser induced atomic fluorescence (LIAF) resulting from the photodissociation of triatomic sodium clusters. We consider: (1) the nature of observed ’’fluctuation’’ bands corresponding to the pumping of bound-free transitions which yield P2 (Na D-line) sodium atoms and ground state Σg+1, Na2 and the distinctly different spectral characteristics associated with these bound-free transitions as they are observed in either high purity of highly disrupted supersonic expansion; (2) the possibility of controlled ’’hot band’’ formation through disruption of the free jet expansion, allowing the mapping of vibronic structure in the ground electronic and low-lying electronic states of the weakly bound sodium trimer molecule; (3) the determination of an upper bound Do⩽4250 cm−1 for the Na–Na2 bond energy from the analysis of the sodium trimer LIAF spectrum obtained in high purity expansion; and (4) the observation of very efficient energy transfer between sodium dimer and polyatomic sodium. The current studies are discussed in the light of recent experimental and theoretical characterization of bound–bound transitions in Na3, and the possible application of LIAF to the study of bound-free transitions in other small metal clusters is considered.
Optically detected magnetic resonance studies of photoexcited 17O-benzophenone. Orbital rotation in the lowest triplet state
Authors: Wäckerle G. , Bär M. , Zimmermann H. , Dinse K.-P. , Yamauchi S. , Kashmar R. J. , Pratt D. W.
Published: February 2003

The magnetically active isotope of oxygen 17O has been used to probe the changes in the electron charge and spin density distributions in oxygen valence orbitals which occur when benzophenone is excited to its lowest triplet state. The data obtained include the optically detected magnetic resonance (ODMR) and electron-nuclear double resonance spectra at both zero and high magnetic fields. New methods of analysis of zero-field ODMR spectra, appropriate when the second-order hyperfine splitting exceeds the quadrupole coupling, are described. This analysis yields the principal values of the electron fine-structure (D), oxygen hyperfine (A), and oxygen quadrupole (Q) tensors, and the orientation of their principal axes with respect to the molecular frame. It is found, consistent with expectations for an nπ* state, that the direction of the largest component of Q is different from that of the ground state. It is also found, by two independent methods, that the principal transverse axes of A and Q do not conform to the local C2v symmetry axes of the carbonyl group. This result is interpreted to mean that the axis of the n-type oxygen 2p orbital is rotated out of the carbonyl plane, a rotation which appears to be direct consequence of nπ*/ππ* configurational mixing. In agreement with this, the principal values of D, A, and Q are different from those expected for a ’’pure’’ nπ* state. Other consequences of nπ*/ππ* mixing, not only in benzophenone but also in the lowest triplet states of other aromatic carbonyls, are discussed briefly.
New semiempirical method of modeling potential energy surfaces for generalized TST and application to the kinetic isotope effects in the Cl–H–H system
Authors: Garrett Bruce C. , Truhlar Donald G. , Magnuson Alan W.
Published: February 2003

We present a test of bond-energy-bond-order (BEBO)-type potential energy surfaces for the Cl–H–H reaction system. We consider two methods, the rotated–Morse BEBO (RMBEBO) method and the Agmon–Levine-plus-anti-Morse bend (AL/AB) method. Each method is treated as a one-parameter semiempirical method. The parameter is adjusted to the energy of activation for Cl+H2 and the test of the method is the comparison of predicted kinetic isotope effects (KIE’s) to experiment. Dynamical calculations are carried out by the improved canonical variational transition state theory with Marcus–Coltrin-path semiclassical adiabatic ground-state transmission coefficients as well as with simpler methods. The RMBEBO surfaces are not successful, but the AL/AB method is as successful as previously employed two-parameter methods. The anti-Morse-bend approximation is a general procedure, and it is tested successfully against ab initio calculations.
Donor and acceptor state selectivity in resonant energy transfer
Authors: Yersin Hartmut , Stock Manfred
Published: February 2003

Sm2 [Pt(CN)4]3⋅18H2O compounds exhibit a radiationless energy transfer from linear [Pt(CN)4]2− stacks (donors) to Sm3+ cations (acceptors). A Sm3+ emission is found, resulting from the lowest excited Sm3+ state (4G5/2–4F5/2). The energy transfer is a selective process, which has been investigated by polarized emission measurements on single crystals under high pressure. As donor state we identify the lowest excited state of the stacks (mainly emitting E⊥c polarized light) while the relevant acceptor state is the Sm3+ 4F3/2 state being the second excited state.
Third and fourth virial coefficients of hard hyperspheres of arbitrary dimensionality
Authors: Luban Marshall , Baram Asher
Published: February 2003

We derive exact expressions for the third virial coefficient B3 and two of the three terms B4(⧠) and B4(⧅) contributing to the fourth virial coefficient B4 for an assembly of hard hyperspheres of arbitrary dimensionality d. A semiempirical formula, accurate for all d, is proposed for the remaining term B4(⊠). This formula is suggested by the large-d asymptotic behavior of B3 and B4(⧠). We find that B4 is positive for dd4, with d4 estimated to be d4≈7.8, whereas B4(⧠)+B4(⧅) changes sign for d = 9.073
Solutions of the HNC equations for lattice gas models of point defects in doped silver chloride
Authors: Allnatt A. R. , Allnatt E. Loftus
Published: February 2003

Solutions of the hypernetted chain equations have been obtained for temperatures from 50 to 450 °C for models of the Coulombic lattice gas of cation vacancies and impurity ions in AgCl doped with 0.5% to 5% of CdCl2. The method, based on coupled Newton–Raphson and Picard iterations, is outlined. Activity coefficients calculated from the results show substantial deviations from the Debye–Hückel values. At 350 °C, increasing with decreasing temperature, there is a concentration dependent enhancement of the like-charge correlation function h++(r) to positive values at the second to fourth neighbor separations. This probably reflects the formation of defect clusters of more than two defects, but the effect may be exaggerated by deficiencies in the HNC approximation. The possibilities for similar HNC calculations on other lattice defect systems are discussed.
Electron thermalization in gases. IV. Relaxation time in molecular hydrogen
Authors: Mozumder A.
Published: February 2003

Theory of electron thermalization derived earlier by the author for rare gases [J. Chem. Phys. 72, 1657, 6289 (1980)] is extended to molecular gases, taking into account inelastic processes. Both direct and inverse collisions are considered, with due regard to microscopic reversibility and detailed balancing. After developing the general equations, specific application is made to molecular hydrogen in the long-time limit. Thus, relaxation times for electron thermalization are reported in H2 at different temperatures over the interval 20–1000 K. Analysis of relative contributions of elastic scattering, rotational, and vibrational processes to the relaxation time shows that these are temperature dependent. As such, sequences of collision processes in decreasing order of importance to the thermalization phenomenon are presented at several temperatures. Comparison with an experiment shows reasonable agreement.
I
n s
i
t
u tunneling spectroscopy: Carbon monoxide on alumina supported cobalt particles
Authors: Kroeker R. M. , Pacansky J.
Published: February 2003

Tunneling spectroscopy is a rapidly developing method for obtaining vibrational spectra of monolayers of materials incorporated in tunneling junctions. To date, tunneling spectroscopy has been restricted to observing spectra of junctions that have been warmed to room temperature and exposed to the atmosphere prior to immersion in liquid helium. Here, we report on a method for the in situ preparation of tunneling juncions at low temperatures. This technique avoids questions about atmospheric contamination, and allows the observations of systems too volatile to be otherwise observed. Most of all, due to the low temperature at which the junction is prepared, important mechanisms regarding the change from physiadsorption to chemiadsorption of monolayers on catalytic surfaces may be observed as a function of temperature. In the work discussed here, differential tunneling spectra are shown for the first time on junctions prepared in situ. This has permitted the observation of physioadsorbed CO on aluminum supported cobalt particles with tunneling spectroscopy.
The interaction of ethane, propane, isobutane, and neopentane with the (110) surface of iridium
Authors: Wittrig T. S. , Szuromi P. D. , Weinberg W. H.
Published: February 2003

The adsorption and reaction of ethane, propane, isobutane, and neopentane with the reconstructed Ir (110)–(1×2) surface have been studied with the thermal description mass spectrometry. As the surface is heated, these hydrocarbons decompose to yield gaseous hydrogen and adsorbed carbon. No hydrocarbons other than the hydrocarbon initially adsorbed was observed to desorb under any of the conditions described in this investigation. The reactivity of the surface for the dissociation of the saturated hydrocarbons is linearly related to the availability of vacant β2 hydrogen adsites on the surface. Three thermal desorption states of hydrogen, identified as the α, β′2, and γ thermal desorption states, were observed following the dissociation of propane, isobutane, and neopentane. The α and γ thermal desorption states are hydrogen molecules desorbing from the surface following the dehydrogenation of hydrocarbon fragments on the surface, and the β′2 thermal desorption state represents hydrogen atoms that are bound to the metal surface in sites that are similar to the β2 adsites of hydrogen on the clean surface. The thermal desorption of hydrogen following exposure of the surface to ethane exhibits only a β′2 thermal desorption peak.
Kinetics of diffusion-controlled processes in dense polymer systems. I. Nonentangled regimes
Authors: de Gennes P. G.
Published: February 2003

We investigate diffusion-controlled processes, where the reacting groups (A and B) are attached to long, flexible, macromolecules in melts or in concentrated solutions. We first give a general discussion of the rate constants, and are led to distinguish two fundamental types of behavior, depending on the rms displacement x(t) of one reacting group during a time t. (1) If t−1 x3(t) is an increasing function of time, the space volumes [∼ x3(t)] explored by A and B may overlap significantly without any reaction taking place: we call this regime noncompact exploration. It is obtained in the classical case where A and B belong to small molecules and where simple diffusion prevails [x(t)∼t1/2]. This regime leads to a second-order rate constant k in the chemical kinetics which is well-defined (independent of the time). (2) If x3(t)/t is a decreasing function of time, we have compact exploration: as soon as the space volumes explored by A and B overlap, the reaction takes place. Then the rate constant k is proportional to x3(t)/t and is thus time dependent. We analyze here the case of dense chains which are not long enough to be entangled (degree of polymerization N smaller than a certain threshold Ne). (a) At reaction times t smaller than the Rouse time TR of the chains we show that this is a case of compact exploration, with x(t)∼t1/4 and k(t)∼t−1/4. (b) For t≳TR we recover a noncompact exploration, and k∼DRR0, where DR is the Rouse diffusivity of the chains, and R0 their rms end-to-end size. Thus, we predict k∼N−1/2.
Infrared absorption spectrum of C2H radical with color center laser
Authors: Carrick P. G. , Pfeiffer J. , Curl R. F. , Koester E. , Tittel F. K. , Kasper J. V. V.
Published: February 2003

P. Q. and R branches are studied for C2H free radicals. (AIP)
Long range interaction mechanism for the collision-induced electronic relaxation of single rotational levels of SO2 (Ã 1A2)
Authors: Holtermann Dennis L. , Lee Edward K. C. , Nanes Roger
Published: February 2003

Cross sections for collision induced electronic relaxation of single rotational levels of SO2 (Ã 1A2) have been measured for a variety of collision partners. Large cross sections (∼10 times the gas kinetic value of ∼80 Å2) have been observed. A strong correlation with results from microwave line broadening and rotational relaxation suggest that a long range dipole-type mechanism is responsible for the efficient electronic quenching. (AIP)
On Raman evidence for conformational order in liquid n-alkanes
Authors: Snyder Robert G.
Published: February 2003

The Raman spectra of neat n-hexadecane and of n-hexadecane in dilute solutions in CCl4 and n-C16D34 are reported. From these measurements, chain order in the liquid alkanes is inferred. (AIP)
Intermolecular interactions and Fermi resonance in methylene groups
Authors: Merajver Sofia D. , Lapidus Claudia , Wunder Stephanie L.
Published: February 2003

Raman spectra of propane-d6 and propane d6 in CCl4 solutions are reported. The spectra exhibit Fermi resonance. Raman spectra of dibromethane and dichloromethane are also reported, these present no Fermi resonance. The intermolecular interactions and conformational dynamics are discussed. (AIP)
Light scattering study of the phase transition in s
y
m- triazine
Authors: Yoshihara A. , Pan C. L. , Bernstein E. R. , Raich J. C.
Published: February 2003

The ferroelastic phase transition in sym-triazine C3N3H3 has been investigated by means of Brillouin scattering and correlation spectroscopy. Soft TA modes are observed by Brillouin scattering but a well-defined central peak could not be found. Near the transition in the high temperature phase a 50% increase in Rayleigh intensity is found. No correlation function was observed in the time domain between 1 and 10−6 s. These results are discussed by a Landau mean field theory and dynamical rotation–translation coupling theory.
The electronic structure of alkali trimer anions and cations
Authors: Eades R. A. , Hendewerk M. L. , Frey R. , Dixon D. A. , Gole J. L.
Published: February 2003

Vibrational frequencies for the alkali trimer cations have been calculated. The frequencies of the trimer cations provide good estimates for the frequencies of the neutral trimers in the absence of affects due to the conical intersection characteristic of the trimer potentials. The frequencies decrease with increasing atomic number, this variation resulting from both mass effects and a decrease in the force constant. The electron affinities for the alkali trimers have been estimated from Koopman’s theorem based upon comparisons with SCF–CI calculations. The trimer electron affinities decrease with increasing atomic number. They are found to be much larger than the known dimer electron affinities exhibiting a trend opposite to that of the dimer and trimer ionization potentials.