bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of two-dimensional NMR powder patterns in rotating solids
Authors: Nakai Toshihito , Ashida Jun , Terao Takehiko
Published: July 2002

Sample-spinning NMR techniques for measuring the heteronuclear dipolar/chemical shift two-dimensional (2D) powder patterns are described. For compounds with more than one chemically distinct nucleus, the individual 2D powder patterns can be separately obtained by 3D switching-angle sample-spinning NMR. A practical application of the 3D NMR is demonstrated with the 13C 2D powder patterns of the two crystallographically inequivalent formate ions in calcium formate. The chemical shift tensors and proton positions were obtained for the individual formate ions, which agree with the results already reported by single crystal studies of 13C NMR and neutron diffraction. The 2D powder pattern of polyethylene was also obtained as an example of the CH2 system. The chemical shift principal values, the bond length, and the bond angle were determined. The chemical shift principal axes were found to be only approximately along the symmetry directions of the CH2 group, indicating a strong perturbation of the electric environment by the crystal field.
On the nature of the relationship between inhomogeneously broadened phosphorescence and ODMR spectral lines
Authors: Williamson Rodney L. , Kwiram Alvin L.
Published: July 2002

The nature of the inhomogeneous broadening of optical and ODMR spectral lines of aromatic molecules hosted in low temperature glasses is experimentally and theoretically investigated. Particular attention is paid to the relationships which exist between the various classes of inhomogeneously broadened spectral lines, and the salient features are illustrated with the results of ‘‘site selection’’ spectroscopy. A theoretical formalism based on the assumption of a uniform ‘‘solvent field’’ is presented and used to account for the major experimental features. Various ODMR line broadening mechanisms are considered and their relative importance evaluated.
Interaction of low energy reactive ions with surfaces. III. Scattering of 30–200 eV Ne+, O+, C+, and CO+ from Ni(111)
Authors: Kasi Srinandan R. , Kilburn Michael A. , Kang Heon , Rabalais J. Wayne , Tavernini Lucio , Hochmann Petr
Published: July 2002

Time-of-flight (TOF) and energy distributions of 30–200 eV Ne+, O+, C+, and CO+ scattered from Ni(111) have been investigated using pulsed ion beam techniques and classical trajectory simulations. The experiments probe the interaction potentials and the applicability of the binary collision approximation in the low energy range. The experimental scattering energies are in good agreement with the energies predicted by the classical treatment. Scattering of atomic projectiles at primary energies as low as 30 eV (scattered energies ∼15 eV) has been detected and is characterized by sharp scattering peaks. The lower limit of detectability is determined by the sensitivity of the detector to slow neutrals. The reactive ions are completely neutralized in the scattering collision while some of the Ne+ ions survive single scattering events. Scattering of molecular CO+ produces a broad scattered flux distribution due to partial dissociation and scattering of both molecular and atomic species. Trajectory simulations have been performed using a purely repulsive Biersack–Ziegler potential and a Biersack–Ziegler potential combined with a Morse potential to include an attractive component. The importance of the attractive potential in describing the trajectories of the reactive ions increases with decreasing ion energy. This attractive potential is shown to be responsible for preferential neutralization of reactive ions by altering the trajectories so that the distance of closest approach is shorter and the time spent near the surface is longer, thus enhancing electronic interaction between colliding species. Energy level diagrams are used to discuss the neutralization transitions and the differences between the reactive and noble ions.
Interactions of low energy reactive ions with surfaces. IV. Chemically bonded diamond-like films from ion-beam deposition
Authors: Kasi Srinandan R. , Kang Heon , Rabalais J. Wayne
Published: July 2002

Low energy (10–300 eV) mass-selected C+ ion beams are used to deposit thin carbon films on surfaces of Si(100), Ni(111), Ta, W, and Au in a UHV environment at room temperature. The films are characterized by Auger electron spectroscopy (AES), x-ray and UV photoelectron spectroscopy (XPS and UPS), valence level electron energy loss spectroscopy (ELS), K-shell ionization loss spectroscopy (ILS), and ellipsometry. The initial monolayer of the deposited film is in the form of a carbide layer which is chemically bonded to the substrate atoms. The film evolves gradually over the next several layers deposited, through intermediate structures, into a diamond-like structure. The diamond-like structure is confirmed by comparing the results of the above spectroscopic measurements with those of pure diamond and graphite and by referring to band structure calculations. A phase diagram, prepared as C+ ion dose vs C+ kinetic energy Ek, shows the regions of the different structures. The optimum C+ energy range for formation of the diamond-like structure is 30–175 eV. Below 10 eV the final diamond-like structure has not been attained and above 180 eV there is a sharp increase in the dose required to attain this final structure. The films are found to be free of impurities, inert to O2 chemisorption, structurally stable up to 350 °C, have a low sputtering yield, and have a sharp interface with the substrate surface. The mechanism of film deposition and growth is discussed.
Spin–orbit state selectivity in Xe*+N2, CO electronic energy transfer
Authors: Krümpelmann T. , Ottinger Ch.
Published: July 2002

During beam experiments on E–E transfer from metastable Xe(3P0) to N2, a distinct preference for the population of the product N2(B 3Πg) Ω=0 fine structure sublevel was found in the v′=11, but not v′=10 vibrational level. A collinear reaction mechanism is suggested. Similar effects were also observed in CO(d 3Δ,v′=7), formed in Xe(3P2)+CO collisions.
The internal energy of sputtered glycerol molecules, determined by photoionization mass spectrometry
Authors: Hoogerbrugge R. , Bobeldijk M. , Kistemaker P. G. , Los J.
Published: July 2002

The mass spectrum of thermally evaporated glycerol is measured as a function of temperature by photoionization mass spectrometry (PIMS) at two wavelengths, the Ar i (11.8 eV) and Kr i (10.6 eV) resonance lines. Also the PIMS of glycerol molecules sputtered from the liquid at 267 K is measured. By comparison with the vapor phase measurements, the internal temperature of the sputtered molecules is determined as 190±40 K. Then the assumed ejection by a ‘‘thermal spike’’ must be followed by an expansion which cools the sputtered molecules to an internal temperature which is even lower than the temperature of the liquid. Applying an analytical deconvolution, the breakdown curve of the glycerol molecules is calculated. Comparison between the Ar i and Kr i vapor phase data shows that only 0.3 eV of the excess energy of the argon photon is converted into internal energy.
Depolarized Rayleigh scattering in normal and para-hydrogen
Authors: Moraldi Massimo , Borysow Aleksandra , Frommhold Lothar
Published: July 2002

An expression for the shape of pressure-broadened rotational lines is obtained by perturbation techniques which account for the details of binary collisions. This expression is used for a numerical computation of the depolarized far wing of the hydrogen Q0(1) line, a Raman line at zero frequency shift, at moderate gas density (1–100 amagat). Agreement of the computed profile with an extraction of this line wing from recent measurements of the depolarized Rayleigh spectra of para- and normal hydrogen is reported in absolute intensity units. The depolarized, collision induced Rayleigh spectra, a background present in these measurements, is shown to be very nearly the same in para- and normal hydrogen.
Zero field tensor for Ni(II) in Zn (ethylenediamine)3 (NO3)2: EPR study
Authors: Sreeramachandra Prasad L. , Subramanian S.
Published: July 2002

Single crystal EPR of Ni(en)2+3 (en=ethylenediamine) doped in Zn(en)3(NO3)2 is reported. Our results beased on exact diagonalization procedure indicate that the Ni(en)2+3 units undergo distortion along the threefold axis which coincides with the crystallographic c axis. The zero field tensor is found to be axially symmetric with D being 0.831±0.006 cm−1. The utility of S=1 ions in obtaining information regarding molecular distortions is also evidenced.
Temperature dependence of resistance of solid hydrogen iodide at high pressure
Authors: van Straaten Joop , Silvera Isaac F.
Published: July 2002

Electrical resistance measurements are performed on solid HI samples below 5 GP as a function of temperature. Evidence of ionic conduction is observed and the influence of progressive growth of the impurity concentration in the sample induced by temperature, light, or pressure, is discussed. Samples are observed to transform from insulators to impurity semiconductors to metallic degenerate semiconductors.
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o RHF and CASSCF studies on Fe–O bond in high-valent iron-oxo-porphyrins
Authors: Yamamoto Shigeyoshi , Teraoka Junji , Kashiwagi Hiroshi
Published: July 2002

The electronic structure of the Fe–O bond in highly oxidized iron porphyrins was elucidated by ab initio RHF (restricted Hartree–Fock) and CASSCF (complete active space SCF) calculations on a neutral complex FeP(py)O (P=porphine, py=pyridine), which is a model of peroxidase compound II. Accounting for the correlation effects is essential for the description of the Fe–O bond. Equilibrium distance and stretching frequency of Fe–O were calculated from the potential energy curves obtained by CASSCF. Furthermore, Mössbauer spectrum parameters (quadrupole splitting, isomer shift, asymmetry parameter and direction of the principal axis of the electric field gradient tensor) and spin density were evaluated. They are in good agreement with experiments on the whole. The oxidation number of iron in peroxidase compound II was assigned to IV through an analysis of the CASSCF wave function.
Hydrodynamic interactions in a suspension of spherical particles
Authors: Ladd Anthony J. C.
Published: July 2002

A long standing problem in numerical statistical mechanics has been the incorporation of the long range, many-body hydrodynamic forces between particles in suspension. In this paper I describe a general computational method for calculating the forces and torques exerted by slowly moving spheres suspended in an incompressible fluid. In particular, the method correctly incorporates the effect of periodic boundary conditions on the hydrodynamic flow field. Results are presented for the friction and mobility matrices of small clusters of spheres as a function of the size of the periodic unit cell. An expression for the viscosity of a suspension of freely moving spheres is derived for a system with periodic boundary conditions, and numerical results are obtained for a suspension of spheres arranged in a simple-cubic lattice.
The effect of cluster scavenging on homogeneous nucleation rates
Authors: Larson Richard S.
Published: July 2002

The modification of classical homogeneous nucleation theory to account for scavenging of molecular clusters by a preexisting aerosol is considered. A mathematical model proposed by Friedlander for an aerosol in the free-molecular regime is used to derive a new criterion for the importance of scavenging in such a system. This is done by writing the governing cluster balance equations in differential form and expressing the solution as a perturbation series in terms of the aerosol surface area. It is found that scavenging has an increasingly important effect on the nucleation rate as the vapor-phase supersaturation ratio decreases or the cluster surface energy increases.
A study of the applicability of the renormalization group idea to multichain lattice systems by numerical experiments
Authors: Okamoto Hiroshi
Published: July 2002

Our numerical experiments aim to study the applicability of the renormalization group (RG) idea to multichain lattice systems. The systems are composed of multiple chains on a simple cubic lattice. The nearest-neighbor interaction is assumed between nonbonded chain elements. The RG parameter space is spanned by the inverse of the chain length 1/n, the solvent condition η, and the chain number concentration ρ. We first tentatively determine parameter flows by using two RG invariants (weak conditions). Then we examine whether the flows satisfy the RG requirements for the correlations (strong conditions). Simultaneous satisfaction will guarantee us the applicability of the RG idea. We found that the RG idea is applicable to the systems in the very good solvent region but becomes inapplicable to those in the poorer solvent regions and to the shorter spatial distances. In the range where the linearized RG defined by a fixed point in the good solvent region works successfully, we arrive at scaling forms in several fashions. One of them corresponds to Freed’s crossover form. The RG appears to work even in the nonlinear range, i.e., concentrated solutions outside the semidilute region. The RG failure in the poor solvent region is briefly discussed.
Bi- and unimolecular resonances of the collinear reaction F+DBr⇄FDBr⇄FD+Br
Authors: Bisseling R. H. , Gertitschke P. L. , Kosloff R. , Manz J.
Published: July 2002

The reaction probability function P(ν′←ν‖E) of the bimolecular collinear reaction F+DBr(ν)→FD(ν′)+Br shows sharp resonance peaks at certain collision energies Ebi. On the other hand, the unimolecular dissociation FDBr*(ν1ν3)→F+DBr(ν), FD+Br(ν) exhibits long-lived behavior for particular resonance wave functions Ψν1ν3 at energies Euni. Good numerical agreement is found in a comparison of bi- and unimolecular resonance energies and lifetimes by two complementary methods: (i) S-matrix propagation in hyperspherical coordinates for the bimolecular reaction; (ii) the diagonally corrected vibrational adiabatic hyperspherical (DIVAH) method to determine unimolecular resonances, coupled with the fast Hankel transform (FHT) method to propagate them in time. The agreement found suggests a correlation between bi- and unimolecular resonances by the reaction mechanism F+DBr(ν)⇄FDBr*(ν1ν3)⇄FD(ν′)+Br, where the unimolecular resonance states Ψν1ν3 serve as traps or doorway states, blocking or catalyzing the bimolecular reaction.
Quantum oscillations in rotationally inelastic molecule–surface scattering: Energy dependence of transition probabilities
Authors: Mowrey R. C. , Bowen H. F. , Kouri D. J. , Yinnon A. T. , Gerber R. B.
Published: July 2002

Exact quantum mechanical and quasiclassical trajectory results for rotationally inelastic N2 -corrugated surface collisions are compared over the energy range 0.01–0.04 eV. It is found that the degeneracy averaged, diffraction summed, rotationally inelastic transition probabilities display quantum oscillations.
Dynamic scattering by a flexible Brownian dumbbell in an electric field
Authors: Lipson J. E. G. , Stockmayer W. H.
Published: July 2002

We investigate the dynamic scattering function S(q,t) of a flexible Brownian dumbbell, having a net dipole moment, in an electric field. Both free-draining and preaveraged hydrodynamic conditions are considered. In both cases, the dipole–field interaction can have a significant effect on the dynamic scattering for systems having a large net end-to-end dipole moment.
Energy flow pathways and their spectral signatures in vibrationally excited acetylene
Authors: Holme T. A. , Levine R. D.
Published: July 2002

Algebraic methods and classical trajectory studies for a model Hamiltonian which includes all in-plane vibrational modes are used to elucidate the origin of spectral structure in the stimulated emission spectra of acetylene. The molecular oscillators responsible for previously established gateway states are determined as well as a plausible description of the overall IVR mechanism.
Tangled T←S spectra of benzaldehyde in methylcyclohexane at low temperature
Authors: Koyanagi M. , Futami H. , Nakashima K.
Published: July 2002

T←S phosphorescence excitation spectra of benzaldehyde and its aldehyde deuterium derivative in methylcyclohexane at 4.2 K are analyzed in terms of canonical mixture of 105 Born–Oppenheimer vibronic wave functions of the nπ* and ππ* triplet states. Two perturbation terms are employed; one accounting for vibronic interactions, and the other for direct environmental coupling interactions between T1 and T2. A good simulation of the benzaldehyde-h6 T←S spectrum is thus obtained with the zeroth order origin level of T2(ππ*) lying 675 cm−1 above the zeroth order origin of T1(nπ*). The T←S spectrum of benzaldehyde-ld1 is also approximately simulated (the zeroth order ππ* origin is located 625 cm−1 above the zeroth order nπ* origin) but with some disparities from the observed vibronic profile. For comparison, vapor phase T←S spectra are also calculated as a function of the zeroth order energy separation.
On the nonequilibrium thermodynamics of dilute suspensions
Authors: Ferrer Maria , Jou David
Published: July 2002

A nonequilibrium thermodynamic theory known as extended irreversible thermodynamics is used to obtain the frequency- and wave vector-dependent generalized viscosity for dilute suspensions. Comparison with a microhydrodynamical calculation by Bedeaux, Kapral, and Mazur allows one to obtain explicit expressions for the coefficients appearing in the macroscopic generalized viscosity.
Vibronic states of plutonium hexafluoride in the visible and near infrared spectral regions
Authors: David S. J. , Kim K. C.
Published: July 2002

The entire absorption spectrum of PuF6 in the near IR and visible regions has been obtained at 0.5 cm−1 or higher resolution. A detailed analysis of the vibronic energy levels is presented and spectroscopic assignments of all observed transitions are made. The energy levels obtained from these spectroscopic measurements of the gas phase PuF6 molecule are the most accurate values available. A comparison is shown of our assignments and results with the matrix-isolation experiment and available theoretical studies.
Photophysics of atomic magnesium isolated in solid methane and perdeuteromethane. II. Temperature dependence of steady state and time-resolved luminescence
Authors: McCaffrey John G. , Ozin Geoffrey A.
Published: July 2002

The visible emission resulting from photoexcitation of the first allowed singlet resonance transition of atomic magnesium isolated in the solid methanes is analyzed with spectral and time resolution. Two emission bands are observed in both solid methane (CH4) and solid perdeuteromethane (CD4) at 516 and 560 nm. The measured radiative lifetimes of the two bands are 12 and 19 ms, respectively, and independent of isotopic variation of the host. On the basis of their spectral position and radiative lifetimes, the emission features are assigned to the spin-forbidden 3P–1S intercombination band of atomic magnesium. Emission spectra recorded at various temperatures in the range 12–33 K were found to show reversible temperature dependence whereby the intensity of the higher energy 516 nm band decreased monotonically with a concomitant increase in that of the lower energy 560 nm band. Time-resolved measurements of the two bands in Mg/CH4 and Mg/CD4 show that the radiative lifetime of the 516 nm band decreases with increasing temperature while that of

the 560 nm band remains constant but showing a rise time component. The magnitude of this rise time is correlated with that of the decreasing lifetime of the 516 nm band. With a combination of the temperature dependence observed in the radiative lifetimes and spectral intensities of the 516 and 560 nm emission bands in the Mg/CH4 and Mg/CD4 systems, dynamical information is extracted which allows for the creation of a simple kinetic model and an identification of the mechanism giving rise to this temperature dependent phenomenon. The experimental data is found to exhibit linear behavior on an Arrhenius plot indicating an activated process of population interconversion between the emitting levels. In solid methane the barrier in this activated process is 177 and 125 cm−1 in solid perdeuteromethane. The origin of this process is discussed in terms of (a) structural phase transitions of the solid methanes and (b) the effect of strong Jahn–Teller coupling between phonon modes of the solid methane host and the spin triplet electronic state of the atomic magnesium guest yielding symmetry-distinct minima on this surface. The lengthened values of the measured radiative lifetimes in the solid methanes, indicate population equilibration amongst the total degeneracy of the triplet state J sublevels of atomic magnesium in these solids. Because of the extremely low temperatures at which the experiment is conducted, extensive orbital reduction factors are implied to achieve such equilibration conditions. This is a manifestation of very strong Jahn–Teller coupling, a necessary condition for the stabilization of symmetry-distinct minima on the triplet spin state surface and the mechanism proposed to explain the presence of the temperature dependent emission features.
Calculation of the dc Kerr and electric-field-induced second-harmonic generation susceptibilities for H2 and D2
Authors: Bishop David M. , Lam Brenda
Published: July 2002

A comprehensive theoretical investigation of the third-order susceptibilities for the nonlinear optical processes dc Kerr and dc electric-field-induced second-harmonic generation is reported for H2 and D2. Accurate wave functions of the J ames–Coolidge-type, which account for electronic correlation, are utilized and particular attention is given to the effects of vibration. Results for both the parallel and perpendicular components of the susceptibilities are given for λ=∞, 10 640, 6943, 6328, 5900, 5145, and 4880 Å. These are sufficient to enable a direct comparison with certain experimental data and, in general, the agreement is within the expected error bounds.
A theoretical study of the inclusion complexes of β-quinol
Authors: Dang Liem X. , Pettitt B. Montgomery
Published: July 2002

The thermodynamics and dynamics of clathrate inclusion complexes of β-quinol with rare gas atoms are considered and compared to previous experimental results. Many of the thermodynamic properties are found to be explainable within a harmonic approximation if one considers the flexibility of the host lattice. Dynamic simulations indicate a splitting of the low frequency motions caused by the local anisotropy of the β-quinol clathrate.
Static and dynamic hyperfine coupling of FE(II) in the FeS4 unit. Results of Mössbauer spectroscopy on a [P(C6H5)4]2[Fe(SC6H5)4] monocrystal
Authors: Winkler H. , Bill E. , Trautwein A. X. , Kostikas A. , Simopoulos A. , Terzis A.
Published: July 2002

The hyperfine coupling parameters of Fe(II) in the FeS4 unit of the complex anion [Fe(SC6H5)4]2− have been determined from an analysis of Mössbauer spectra of a monocrystal in the temperature range of 1.5 to 20 K and in magnetic fields of 0 to 6.7 T. Dynamic spin fluctuation effects have been included in the analysis by a stochastic model with spin–lattice relaxation. Anisotropy in the relaxation matrix element was of moderate significance and apparent only at low fields. The use of a monocrystal allows more precise determination of hyperfine parameters, because it avoids the averaging procedures which are inherent in studies on polycrystalline material. The set of parameters is essentially identical with that reported for reduced rubredoxin and indicates that the electronic ground state of [Fe(SC6H5)4]2−, predominantly of [3z2−r2] character, simulates very well the ground state of the protein FeS core.
The solute size effect in rotational diffusion experiments: A test of microscopic friction theories
Authors: Ben-Amotz Dor , Drake J. M.
Published: July 2002

The experimentally measured rotational diffusion times of various neutral solute molecules are compared with hydrodynamic and molecular models for microscopic friction. New viscosity and temperature dependent results for the rotational time of a large neutral solute (26 Å long) indicate nearly perfect agreement with stick hydrodynamic predictions in both alkane and alcohol solvents. For smaller solute molecules, the results of previous studies show an increasingly large deviation from hydrodynamic predictions as the solute size decreases. This solute size dependent effect is compared with the theoretical predictions of Zwanzig’s hydrodynamic ‘‘bumpy cylinder’’ model, Dote–Kivelson-Schwartz’s molecular free volume model, and a new generalized hydrodynamic model for the effects of frequency dependent viscosity on molecular rotational diffusion. Although hydrodynamic predictions agree with experiment in some respects, it is found that molecular aspects of the solvation process must be introduced in order to get quantitative agreement with the observed solute size dependence.
Doppler-free spectrum of the B 1Π–X 1Σ+ transition of NaK, and the perturbation and hyperfine splitting
Authors: Baba Masaaki , Tanaka Shinji , Katô Hajime
Published: July 2002

The Doppler-free high-resolution spectrum of the B 1 Π–X 1Σ+ transition of NaK was measured by the technique of laser polarization spectroscopy. The molecular constants of the B 1 Π state, which reproduced the observed 831 unperturbed line positions (v=0–6, J=1–94) with a standard deviation of 0.002 cm−1 , were determined. Many perturbed lines, which were attributed to the perturbation between the B 1 Π and c(2) 3 Σ+ states, were observed. By analyzing the energy shifts of the B 1 Π(v=4,J) levels around J=13, we estimated the rotational constant Bv of the c(2) 3 Σ+ state to be 0.048 cm−1, and the matrix element of the spin-orbit interaction 〈c(2) 3 Σ+ vN=JJM‖Hso‖ B 1Πv=4JM〉 to be 0.14 cm−1 . We found that the strongly perturbed lines split into four lines, and we identified them as a hyperfine splitting caused by a mixing of the c(2) 3 Σ+ state. The splitting into four lines is explained by the magnetic dipole interaction due to a nucleus of I=3/2.
The effect of a conical intersection on cross sections for collision-induced dissociation
Authors: Blais Normand C. , Truhlar Donald G. , Mead C. Alden
Published: July 2002

The cross section for H+H2(v, j)→3H, where v and j denote selected vibrational and rotational quantum numbers, is calculated by the quasiclassical trajectory method, using trajectory surface hopping to include the effect of the first excited electronic state which has a conical intersection with the ground state. The excited electronic state allows for collision-induced dissociation by the process H+H2(X 1Σ+g)→H3(1 2A′)→H3(2 2!iA′) →H +H2(b 3Σ+u) →3H, where the various transitions all occur in the course of a single collision. This new surface hopping mechanism increases the cross sections and rate constants for production of unbound states by 2%–44% for the conditions examined.
Alkali sensitization of H+ electron stimulated desorption from H adsorbed on Ni(111)
Authors: Lanzillotto A-M. , Dresser M. J. , Alvey M. D. , Yates J. T.
Published: July 2002

It is shown that alkali adatoms coadsorbed in the presence of adsorbed hydrogen on Ni(111) can cause a large increase in the cross section for H+ emission during electron stimulated desorption. This phenomenon was investigated using the digital ESDIAD (electron stimulated desorption ion angular distribution) technique as well as by temperature programmed desorption (TPD). H+ ions produced by electron impact on alkali–hydrogen complexes are ejected in sharp normally oriented ion angular distributions. The sensitization of the H(a)→e−H+ process occurs with Li, Na, and K but not as strongly with Rb and Cs. Attractive interactions exist in the adsorbed layer between the hydrogen and the alkali adatoms. A model is discussed involving the formation of ‘‘alkali–hydride-like’’ surface complexes, with Hδ− located on top of alkali atom sites.
A theoretical study of the A 1Π←X 1Σ+ system of SiH+
Authors: Matos J. Mauricio O. , Kellö Vladimir , Roos Björn O. , Sadlej Andrzej J.
Published: July 2002

Theoretical studies have been performed on the X 1Σ+ and A 1Π states of SiH+. The complete active space, self-consistent field (CASSCF) and many-body perturbation theory (MBPT) methods were employed for the X 1Σ+ and state while the A 1Π excited state potential energy curve was studied by using CASSCF, multireference contracted configuration interaction (MR CCI, (MR CEPA), and coupled pair functional (CPF) approaches. Excellent agreement was obtained with experiment for the X state spectroscopic parameters (CASSCF): re=1.505 (1.50 Å; D0=3.30 (3.22±0.03) eV; ωe=2161 (2155) cm−1; ΔG1/2=2093 (2089) cm−1, with experimental values within parentheses. The shape of the potential curve for the A state was very sensitive to the basis set and higher order electron correlation. The best results, obtained with the CPF method, were re=1.888 (1.871) Å; D0=0.15 (0.15±0.03) eV; ωe=438 (448) cm−1; ΔG1/2=318 (389) cm−1. The computed f0,0 oscillator strength for the A←X transition was 1.2×10−3 which falls between the laboratory value, (2.4±1)×10−3, and a value obtained from the solar spectrum, 0.5×10−3. The computed life time for the v′=0 state is 956 ns to be compared to the experimental value 1025±80 ns.
Classical–quantum correspondence in vibrational energy relaxation of nonlinear systems
Authors: Parson Robert
Published: July 2002

Energy relaxation in a model polyatomic is studied classically, by integrating dissipative equations of motion, and quantum mechanically, by solving a Master equation. The model consists of two Morse oscillators coupled to each other and to a dissipative bath. In both classical and quantum calculations, nonlinear resonances serve to channel the energy relaxation into intramolecular energy redistribution. Nonclassical effects are seen as well, some of which are easily understood semiclassically.
Pathways of relaxation of the N–H stretching vibration of pyrrole in liquids
Authors: Ambroseo J. R. , Hochstrasser R. M.
Published: July 2002

The v=1, N–H vibrational excitations of pyrrole flow with high selectivity into ring breathing motions. The process is intermolecular, involving a coupling of H motion in one pyrrole with the π system of another pyrrole or benzene molecule in the solution. The inter- and intramolecular contributions to vibrational relaxation are experimentally distinguished.
Fluorescence cross section of the H2O+ Ã 2A1 (0, 7, 0) produced through photoionization of H2O
Authors: Wu C. Y. Robert , Hwang M. Y.
Published: July 2002

The cross section for production of the H2O+ Ã 2A1(0,7,0)→X̃ 2B1(0,0,0) fluorescence through photoionization of H2O has been measured in the 14.5–20.5 eV region. The maximum quantum yield is 1.4×10−3 at 16.5 eV. Further, the cross sections for producing the H2O+[Ã 2A1(0,7,0)] and H2O+ Ã 2A1 have been estimated. The magnitude of the latter is about a factor of 10 smaller than that obtained by electron spectroscopy. The discrepancy can be attributed to radiationless transitions between the Ã and X̃ states of H2O+.
Grand potential densities of wall–liquid interfaces approaching complete drying
Authors: Henderson J. R. , van Swol Frank
Published: July 2002

We present molecular dynamics computer simulation data for the pressure tensor components of planar wall–liquid interfaces, along two ‘‘orthogonal’’ approaches to complete drying states. The interfacial structure varies from incipient solid-like packing, at positive adsorption, to smooth behavior, close to complete drying. We pay particular attention to the accompanying changes in the grand potential density, or to be more precise, in the transverse component of the pressure tensor of Irving and Kirkwood.
The effect of dielectric friction on the viscosity B coefficient for electrolytes. Temperature dependence
Authors: Ibuki K. , Nakahara M.
Published: July 2002

We tested the dielectric friction theory of the viscosity B coefficient for the ion in solutions which was derived using the Hubbard–Onsager electrohydrodynamic equation. The temperature dependence of the B values for some monovalent ions in water, methanol, formamide, and N-methylacetamide was examined using the literature values. The theory predicts that there is almost no temperature dependence of B. However, most of the observed B values in the nonaqueous solvents decrease with increasing temperature. The B values for medium-sized ions (such as I−) in water increase with increasing temperature. These observations cannot be explained by the theory. This result lends support to the popular idea that the sign of the temperature coefficient of B can be used as a measure of the structural effect of the ion in water. The parallelism between electrolyte viscosity and conductance is also discussed.
Rovibrational energy transfer from the (0, K′=0) and (72,K′=0) levels of S1 glyoxal in crossed beam collisions with H2
Authors: Butz Kirk W. , Du Hong , Krajnovich Douglas J. , Parmenter Charles S.
Published: July 2002

Crossed molecular beams have been used to study rotationally and vibrationally inelastic scattering from the (72, K′=0) and the (00, K′=0) levels of 1Au (S1) trans-glyoxal in collision with H2. The center-of-mass collision energy was approximately 80 meV (650 cm−1). Laser excitation was used to select each of the initial vibrational levels with rotational states limited to J′=0–10, K′=0. Dispersed fluorescence was used to monitor quantitatively the final rotational and vibrational levels populated in single collision scattering. Vibrationally inelastic scattering from each initial level has an absolute cross section large enough to allow the process to be observed easily with resolution of accompanying ΔK rotational state changes. Although many final vibrational levels are energetically accessible and in principle observable, only those reached by ±1 quantum changes in the lowest frequency mode, the OHC–CHO torsion ν7, are seen. From the initial level 72, the cross sections for Δυ7=+1 and Δυ7=−1 are nearly identical, mirroring the symmetry of UP and DOWN vibrational transitions recently observed in I*2 inelastic scattering from H2, D2, and He. The total cross section for pure rotationally inelastic scattering from 00 is about nine times larger than that for rovibrationally inelastic scattering, whereas the two cross sections are nearly equivalent for 72. With resolution of ΔK rotational state changes, it is seen that the cross sections for these processes scale approximately exponentially with the amount of energy ΔE transferred between translational motion and the internal degrees of freedom of the glyoxal molecule. For the initial level (00, K′=0), not only do these rotational and rovibrational cross sections obey the same energy scaling law, but where similar ΔE occurs, they are the same size. In contrast, the ΔK rotationally state-resolved cross sections for transitions from (72, K′=0) fall off much more rapidly in the vibrationally elastic (Δυ7=0) channel than in the vibrationally inelastic

(Δυ7=±1) channels. Consequently, some rovibrational transitions have cross sections comparable to the pure rotational transitions with the same value of ΔK. These relationships contradict the conventional rule of thumb prescribing large rotational and small vibrational cross sections.
Interstate couplings in the triplet manifold of 9-xanthone
Authors: Koyanagi M. , Terada T. , Nakashima K.
Published: July 2002

Using a heat-pulse modulation technique, phosphorescence spectra of 9-xanthone have been studied in n-pentane at 77 and 2.1 K. The three legitimate phosphorescent levels with different lifetimes are detected at 25 751, 25 766, and 25 774 cm−1 above the zero-vibrational level of the ground state. The origin of these multiple levels is explained in terms of spin–orbit interaction superimposed on environmental electrostatic coupling between T1(ππ*) and T2(nπ*). The two coupling constants obtained are: (for the spin–orbit coupling) ‖〈1ξ‖Hso‖2η〉‖ =15.70 cm−1 (ξ=x, η=y or vice versa); (for environmental direct coupling) 〈1ζ‖Henv‖2ζ〉 =3.14 cm−1 (ζ=x, y, or z). For comparison, the T←S phosphorescence excitation spectrum, measured in the same matrix, are in good agreement with the calculated ones.
Effect of interchain interactions on 13C nuclear magnetic resonance chemical shifts and electronic structures of polyacetylene in the solid state as studied by tight-binding molecular orbital theory
Authors: Ishii Takahiro , Kurosu Hiromichi , Yamanobe Takeshi , Ando Isao
Published: July 2002

The 13C NMR chemical shifts of undoped cis and trans polyacetylenes in the solid state were calculated using the tight-binding sum-over-state theory within the CNDO/2 framework. In order to investigate the effect of the interchain interactions on the 13C NMR chemical shifts and electronic structures of the polymers, the calculation was carried out using the multichains models. The calculation for the seven-chains model explains reasonably the experimental data. From this, it was found that the interchain interactions greatly influence the electronic structures of polyacetylene chains.
Angular correlation between photofragment velocity and angular momentum measured by resonance enhanced multiphoton ionization detection
Authors: Mons Michel , Dimicoli Iliana
Published: July 2002

REMPI detection of photofragments is discussed as a probe technique to measure the angular distribution of the velocity as well as the angular correlation between velocity and angular momentum existing in fragments formed during a polarized photolysis. The symmetry properties of the REMPI probe process induced by polarized light are expressed in terms of sensitivity to the moments of the rotational angular momentum distribution and the angular state of the photofragment is described in the formalism of bipolar moments. Original explicit expressions of the ion velocity profiles are given with probe geometry characteristics as parameters for two kinds of fragment detection (time-of-flight mass spectrometry and angular measurements of the ion yield) and the consequences of the v–J correlation on the observed profiles are discussed. Some experimental geometries are proposed in order to either determine the angular correlation or to avoid its effects.
Resonance Raman studies of oriented chromophores: Metmyoglobin single crystals
Authors: Sage J. Timothy , Morikis Dimitrios , Champion P. M.
Published: July 2002

We report Soret enhanced resonance Raman studies of single crystals of metmyoglobin. Differing scattering intensities of the 345 cm−1 mode in solution and crystalline forms of the protein indicate a structural perturbation of the heme upon crystallization, possibly involving a propionate substituent of the heme. The immobilization of the heme in the crystal also allows observation of low-quantum-yield photoreduction of the heme that appears to be driven by Soret band absorption. We present experimental investigations of the orientational dependence of the intensity and polarization of several strong heme Raman modes along with calculations that explore the effects of vibrational mode symmetry and of differential coupling to x-, y-, and z-polarized electronic transitions. Orientation studies provide evidence that the vinyl C=C stretching band at 1622 cm−1 is a superposition of two independent modes that couple selectively to the x- and y-polarized Soret transitions. We also demonstrate how modes of nominal B1g and B2g symmetry can be distinguished by crystal studies. Modes that couple preferentially to charge transfer transitions polarized perpendicular to the heme plane are shown to be easily distinguishable from the majority of heme modes, which couple to the in-plane polarized Soret transition; we observe no modes of the former type in metmyoglobin. Finally, we present calculations showing that single-crystal polarization studies of resonance Raman scattering as a function of excitation frequency should be sensitive to the splitting of the nearly xy-degenerate Soret band as well as to the orientation of the x- and y-polarized transitions.
The thermodynamics of a coherent interface
Authors: Voorhees P. W. , Johnson William C.
Published: July 2002

A Gibbsian thermodynamic description of a simple coherent interface in a nonhydrostatically stressed, N component, crystalline solid is developed. Interfacial excess properties are defined in a manner consistent with the thermodynamics of nonhydrostatically stressed crystalline solids. This formalism is then used to describe the relationship between the independent thermodynamic variables and the interfacial energy. A result of the crystalline nature of the solid is that the interfacial energy and the interfacial stress are distinct quantities. This difference, along with the presence of a nonhydrostatic stress, results in fundamentally different forms for the standard interfacial thermodynamic relationships. In particular, we show that the Gibbs adsorption isotherm for a coherent spherical misfitting particle in a matrix contains terms which are related to both interfacial and bulk stresses and that these terms can be dominant in certain cases.
Comment on: ‘‘Adiabatic processes in monatomic gases’’
Authors: Lin Shu-Kun
Published: July 2002

The adiabatic processes at zero rate are reversible processes, while at a constant finite rate are irreversible. The formulation employing state variables to describe the irreversible process of nonequilibrium system and the illustration of the finite-rate model with a Carnot cycle are not valid. The intermediate nonequilibrium processes should be described through a state-variable-free approach.
The potential energy surface of triplet H+3 : A representation in hyperspherical coordinates
Authors: Wormer P. E. S. , de Groot F.
Published: July 2002

A large number of full CI calculations has been performed in order to obtain an accurate representation of the potential energy surface of the molecular ion H+3 in its lowest triplet state. It is found that the surface is very flat, so that the molecule is very floppy and has a great likelihood of tunneling between the three symmetry-related minima. The potential is expanded in terms of elements of Wigner D matrices depending on hyperspherical angles. An extensive discussion of the Smith–Whitten hyperspherical coordinates, used in this work, is given.
Microscopic expression for frequency and wave vector dependent dielectric constant of a dipolar liquid
Authors: Chandra Amalendu , Bagchi Biman
Published: July 2002

A microscopic expression for the frequency and wave vector dependent dielectric constant of a dense dipolar liquid is derived starting from the linear response theory. The new expression properly takes into account the effects of the translational modes in the polarization relaxation. The longitudinal and the transverse components of the dielectric constant show vastly different behavior at the intermediate values of the wave vector k. We find that the microscopic structure of the dense liquid plays an important role at intermediate wave vectors. The continuum model description of the dielectric constant, although appropriate at very small values of wave vector, breaks down completely at the intermediate values of k. Numerical results for the longitudinal and the transverse dielectric constants are obtained by using the direct correlation function from the mean-spherical approximation for dipolar hard spheres. We show that our results are consistent with all the limiting expressions known for the dielectric function of matter.
The pressure dependence of ion–molecule association rate coefficients
Authors: Smith Sean C. , McEwan Murray J. , Gilbert Robert G.
Published: July 2002

Two new techniques are presented for calculating the pressure dependence of ion/molecule association rates: (i) a semiclassical method of incorporating the effect of the hindered dipole rotation into an RRKM calculation of the microscopic rate coefficients k(E,J), and (ii) a solution for the master equation for unimolecular dissociation and recombination reactions, which incorporates angular momentum (J) conservation and is applicable when the moments of inertia of reactant and activated complex differ by a large amount. These techniques provide the optimal currently available means for calculating the pressure dependence of rate coefficients for ion–molecule reactions, which are highly sensitive to J-conservation effects. The method may be used for reliable estimates and fitting of experimental fall-off data. The new technique shows that Troe’s solution of the low-pressure J-conserving master equation is accurate for the nonequilibrium population distribution but overestimates (by up to a factor of 2) the rate coefficient; extensions to Troe’s method to provide more accurate analytical approximations are derived. Application is presented to the association of CH3+ with HCN. The experimental pressure dependence, which cannot be fitted without proper accounting for J conservation, is fitted using the new treatment with values of ∼125 cm−1 for the average downward energy transfer for both rotational and internal energies. The new J-conservation method is also applicable to reactions of neutrals where the moment of inertia of the activated complex is more than six times that of the stable reactant.
Photoelectron spectroscopy of BH−3
Authors: Wickham-Jones C. Tom , Moran Sean , Ellison G. Barney
Published: July 2002

We have studied the photoelectron spectra of BH−3 and BD−3 and have measured the electron affinities of borane; we find EA(BH3)=0.038±0.015 eV and EA(BD3)=0.027±0.014 eV. The peak splittings and intensities demonstrate that the BH−3 ion and the BH3 neutral have very similar geometries; our spectra are consistent with a planar structure for both species. Variational calculations of a coupled oscillator basis over an ab initio potential give an excellent fit to the experimental frequencies and photodetachment Franck–Condon factors. This ab initio model leads to equilibrium geometries with both BH3 and BH−3 as planar molecules with re(BH−3) =1.207 Å and re(BH3)=1.188 Å. We find ΔH○f0(BH−3) =23.1±3.8 kcal mol−1.
Photodissociation dynamics of C2H2 at 193 nm: Vibrational distributions of the CCH radical and the rotational state distribution of the Ã(010) state by time-resolved Fourier transform infrared emission
Authors: Fletcher T. Rick , Leone Stephen R.
Published: July 2002

Time-resolved Fourier transform infrared (FTIR) emission is used to study the formation of CCH in the photodissociation of C2H2 at 193 nm. Excitation of C2H2 at 193 nm is known to populate the 10ν3 level of the trans–bent electronically excited state of acetylene, which undergoes decomposition. State-resolved infrared emission is obtained from the CCH radicals that are produced. Only vibronic levels which originate or borrow oscillator strength from the low-lying electronically excited state of CCH, Ã 2Π, are observed in this study. The relative intensities of these bands are measured and the rotational state distribution for the Ã(010) state is obtained. The observed average rotational energy of CCH is ∼156 cm−1, which is less than the average rotational energy of the acetylene precursor. A kinematic model which can account for a rotational cooling effect in the Ã(010) state is described. The model incorporates the angular momentum generated by the impulsive kick due to the release of the H atom and the cooling due to the orbital angular momentum carried away by the tangential velocity of the H atom, which is imparted by the initial C2H2 rotation.