bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic states of Pt2
Authors: Balasubramanian K.
Published: July 2002

Complete active space MCSCF (CASSCF) followed by first-order configuration interaction (FOCI) calculations are carried out on low-lying electronic states of Pt2. The spin–orbit interaction is introduced through a relativistic configuration interaction method. Twenty-two low-lying ω–ω states with Te<15 000 cm−1 and 11 λ–s states with Te<3189 cm−1 are found. The nature of all these electronic states is discussed. The calculated Re values of all the electronic states are between 2.4 and 2.6 Å. The spin–orbit effects are found to be significant for the electronic states of Pt2. The CASSCF/FOCI dissociation energies of the strongest-bound states in the absence of spin–orbit interaction are calculated to be about 2.3 eV. The spin–orbit interaction decreases the De. The dissociation energies of the strongest-bound states in the presence of spin–orbit interaction are about 1.85–1.95 eV.
UV and CD vibronic spectra of helical polymers. I. One-phonon vibronic spectrum
Authors: Lalov I. J. , Miteva A. I.
Published: July 2002

The paper studies vibronic spectra (exciton+intramolecular vibrational quanta) of helical polymers in solutions. The theoretical model employed here makes it possible to describe the ultraviolet (UV) absorption and circular dichroism (CD) spectra in the conditions of linear and quadratic exciton–phonon interaction. On the basis of the expanded Moffitt exciton model the structure of degenerate and nondegenerate one-phonon vibronic spectra containing one-particle and two-particle (unbound) exciton–phonon states is found. The frequencies and the shape of UV and CD spectral lines are calculated for typical values of the exciton–phonon interaction constants.
Comment on Ising-type models for microemulsions and micellar solutions
Authors: Stauffer D. , Jan N.
Published: July 2002

The model suggested by Widom is investigated by Monte Carlo simulations. In this model the periodic ordering is not stable due to a lack of interface tension.
Structure, energetics, and vibrational spectrum of H2O–HCl
Authors: Latajka Zdzisl/aw , Scheiner Steve
Published: July 2002

H2O–HCl is studied using a number of basis sets including 6-31G** and variants which are augmented by a diffuse sp shell and a second set of d functions on O and Cl. Optimization of the geometry of the complex is carried out including explicitly electron correlation and counterpoise correction of the basis set superposition error (BSSE) at both the SCF and correlated levels. Correlation strengthens and shortens the H bond while BSSE correction leads to an opposite trend; these two effects are of different magnitude and hence cancel one another only partially. ΔH°(298 K) is calculated to be −4.0 kcal/mol, 1/4 of which is due to correlation. Formation of the complex causes the strong intensification and red shift of the H–Cl stretching band normally associated with H bonding, whereas the internal vibrations of H2O are very little affected, except for a doubling of the intensity of the symmetric stretch. With respect to the intermolecular modes, the bends of the proton donor are of higher frequency than those involving the acceptor. While these intermolecular bends are all of moderate intensity, comparable to the intramolecular modes, the H-bond stretch νσ is very weak indeed, consistent with a principle involving subunit dipoles. All calculated vibrational data are in excellent agreement with the spectra measured in solid inert gas matrices.
Improving the convergence of the many-body perturbation expansion through a convenient summation of exclusion principle violating diagrams
Authors: Lepetit Marie-Bernadette , Malrieu Jean-Paul
Published: July 2002

All fourth-order and some higher-order EPV (exclusion principle violating) diagrams may be summed up through a simple modification of the energy denominators in the second-order corrections. The procedure simply requires supplementary arrays of dimension N3 (N being the number of orbitals). The typical divergence of the second-order corrections for near-degeneracy cases, occuring for bond lengthenings, is slowed down; the improvement is especially clear for the Epstein–Nesbet partition of the Hamiltonian. The ground state spectroscopic constants are improved as shown on Li2, Li4, N2, and H2O; the procedure may also be used in chemical reaction studies. The above correction results in a straightforward improvement of the Davidson’s correction, which is known to overestimate the effect of quadruple excitations.
Fluorescence excitation and emission spectra of 1,8-dihydroxyanthraquinone-d and -d2 in n-octane at 10 K
Authors: Smulevich Giulietta , Foggi Paolo , Feis Alessandro , Marzocchi Mario P.
Published: July 2002

The fluorescence excitation and emission spectra in n-octane of 1,8-dihydroxyanthraquinone-d0 and -d2 at 10 K have been measured. Dual excitation and emission were observed as a consequence of excited state intramolecular proton transfer. A model, based on the Lippincott–Schroeder potential function, is proposed to predict the observed energy gaps and relative intensities of the transition. The isotopic effects are also explained. The Shpolskii matrices in n-octane show only one main site allowing a detailed vibrational analysis of the ground and the excited states. This furnished further evidence for the existence of excited state tautomers. The occurrence of an extra fluorescence was explained in terms of the ν(OH) stretching mode of the high frequency transition enhanced via vibronic coupling between the two ground states.
The microscopic theory of the Hall effect in ionic solutions. I. General formulation and the Brownian ion-continuum solvent limit
Authors: Sung Wokyung , Friedman Harold L.
Published: July 2002

The Hall effect for dilute ionic solutions is potentially a valuable measure of ion-solvent interactions. We express the intrinsic part of this effect, the ionic Hall number, exactly in terms of the perturbation made by the magnetic field on the memory function for the ionic momentum. By applying the resulting molecular theory in the Brownian ion-continuum solvent (BICS) limit we calculate the ponderomotive force contribution and find that it depends not only on the hydrodynamic boundary conditions at the surface of the ion but also on the coupling of the vorticity field to the spin field in the solvent. Comparison of the results with an earlier theoretical study shows the advantages of the statistical mechanical approach compared to the approach through the electromagnetic hydrodynamic theory. The available experimental data related to the BICS limit are not accurate enough to test the theory.
Relation between the Z−1 type expansion of the total energy of isoelectronic atoms and the many-electron theory on the electron correlation by Sinanoǧlu
Authors: Anno Tosinobu , Teruya Hirohide
Published: July 2002

By applying the economical formula for the total energies of isoelectronic atoms presented by the present authors [J. Chem. Phys. 84, 6895 (1986)] to both the nonrelativistic exact energy and the Hartree–Fock energy, an expression of the Z−1 expansion type for the correlation energy is obtained for isoelectronic series involving the first-row atoms. Based upon the expression obtained, the following conclusions are derived on the relation between the Z−1 type expansion theory and Sinanoǧlu’s many-electron theory (MET): (i) the Z2 term has nothing to do with the electron correlation; (ii) the term proportional to Z represents the internal correlation energy Eint in MET, at least when Z is large in comparison with the number of electrons N; (iii) the constant term in the Z−1 type expansion is the limiting value of the sum of the semi-internal and the all-external correlation energy (EF+Eu) when Z→∞ and its values for the ground-state atoms show a systematic trend when plotted against N; (iv) the sum of the Z−1 and the higher order terms in Z−1 represents the Z dependence of EF+Eu, although its small amount is attributable to a part of Eint when Z−N≲1.
Studies of liquid water by computer simulations. V. Equation of state of fluid water with Carravetta–Clementi potential
Authors: Kataoka Yosuke
Published: July 2002

The pressure of liquid water at normal density is obtained by molecular dynamics simulations based on four intermolecular potential functions derived from quantum chemical calculations of the water dimer; Matsuoka–Clementi–Yoshimine, Carravetta–Clementi, Clementi–Habitz, Yoon–Morokuma–Davidson. Among them, the Carravetta–Clementi potential gives the most reasonable temperature-dependence of pressure, although the absolute value is large compared with the experimental one. The fluid state is surveyed over a wide range of temperature and density with the Carravetta–Clementi potential. The equation of state of fluid water is determined by a least-square fitting of the calculated energies and pressures at 347 state points. The anomalous properties of liquid water observed experimentally are nonempirically reproduced on a semiquantitative level. The calculated equation of state of liquid water is consistent with the Speedy–Angell conjecture on the limit of stability of the liquid phase.
On the satellite bands accompanying the OH and OD stretching fundamentals of isotopically dilute HDO in ice Ih
Authors: Falk Michael
Published: July 2002

OH and OD stretching fundamentals in the infrared spectrum of isotopically isolated HDO in ice are accompanied by small satellite bands whose intensity varies linearly with HDO content. They are assigned to sum and difference bands ν(O–H)±ν(O⋅⋅⋅O) and ν(O–D) ±ν(O⋅⋅⋅O), whose occurrence is predicted by the weak-coupling model of the hydrogen bond. These results confirm an earlier observation of some of these satellite bands by Iogansen and Rozenberg.
On the approximation of diffusion memory functions by time correlation functions in inhomogeneous systems
Authors: Vertenstein Mariana , Ronis David
Published: July 2002

Approximations commonly used to relate memory functions to time correlation functions governed by Newtonian dynamics are shown to be incorrect for strongly inhomogeneous systems. An exact expression for the space dependent diffusion coefficient is given in terms of time correlation functions whose dynamics are governed by Newton’s equations. The resulting expression is evaluated using both the Bhatnagar–Gross–Krook kinetic equation and the Fokker–Planck equation to calculate the required time correlation functions for a system containing a specularly reflecting wall and for a system having a harmonic potential. For inhomogeneous systems, the memory function may not be approximated by the corresponding time correlation function. In addition, certain velocity correlations near a specularly reflecting wall are shown to contain a t−1/2 long time tail and a kinetic boundary layer whose thickness grows as t1/2; these features are absent from the memory function.
Multiphoton ionization studies of benzene in tetramethylsilane and n-pentane solutions
Authors: Faidas H. , Siomos K.
Published: July 2002

The multiphoton ionization spectra of dilute solutions (≲10−3 M) of benzene in tetramethylsilane (TMSi) and n-pentane (n-Pt) have been measured using linearly polarized light over the laser excitation wavelength (λexc) region from 360 to 560 nm. Spectra measured with circularly polarized light are also reported for 460 <λexc<540 nm. The order of the multiphoton ionization mechanisms that occur in different λexc regions has been determined, and their importance is discussed together with the observed polarization behavior. The polarization ratio and the ‘‘apparent’’ order of the ionization process were found to depend on the laser intensity. The ionization threshold of benzene in TMSi was estimated to lie between 6.6 and 5.9 eV, while in n-Pt between 7.36 and 6.8 eV.
Resonance structure in the vibrationally resolved photoelectron branching ratios and angular distributions of the 2π−1 channel of NO
Authors: Southworth S. H. , Parr A. C. , Hardis J. E. , Dehmer J. L.
Published: July 2002

We report on vibrationally resolved measurements of photoelectron angular distributions and branching ratios for NO+(2π−1)X 1Σ+ using synchrotron radiation over hν=11.5–26 eV. Normally weak vibrational levels are strongly enhanced below 18 eV, and the photoelectron asymmetry parameters and branching ratios display a vibrationally dependent, broad spectral structure over hν≂11–18 eV. These observations may reflect the presence of the expected σ shape resonance, however, various interchannel coupling mechanisms may also be involved. Resonance structure in the photoelectron asymmetry parameters is also observed in the hν≂19–22 eV region. This structure is likely associated with Rydberg excitations from the 4σ orbital.
Emission from atomic nitrogen produced by electron impact on nitrogen molecules
Authors: Rall David L. A. , Filippelli Albert R. , Sharpton Francis A. , Chung Sunggi , Lin Chun C. , Murphy R. E.
Published: July 2002

Absolute optical emission cross sections have been measured for transitions of the N atom in the wavelength range 3800–7000 Å originating from 51 terms of the N (2p2nl) configurations with n from 4 to 9 produced by electron-impact dissociation of the N2 molecule. The incident electron energy ranges from threshold to 450 eV. The excitation functions show a broad maximum at about 85 eV and a shoulder structure near 35 eV. Near the threshold energy the formation of the excited nitrogen atoms is believed to be largely due to dissociative excitation through the repulsive part of Rydberg states of N2 that converge to the N+2(D 2Πg) ion. An abrupt increase in the slope of the excitation functions at 5 eV above threshold is suggestive of the opening up of higher-energy channels of dissociative excitation. Combining the measured optical emission cross sections with theoretical transition probabilities calculated by a Hartree–Fock procedure with configuration interaction, optical cross sections have been obtained for a number of long-wave infrared emission lines of the N atom excited by electron-impact dissociation of the N2 molecule.
Radio frequency spectra of chloroacetylene in v=0 and v=1 of the C–H stretching vibration
Authors: Ebenstein W. L. , Hanning C. , Shostak Shelley L. , Muenter J. S.
Published: July 2002

Radio frequency spectroscopy has been carried out on molecular beams of chloroacetylene to yield Stark and chlorine hyperfine properties for the ground and excited C–H stretching vibrational states. For HCC35Cl v=0, μ=0.440 079(1) D, eQq=−79 733.59(4) kHz, and CCl=1.412(4) kHz. For HCC35Cl v=1, μ=0.462 792(1) D, eQq=−79 744.59(5) kHz, and CCl=1.398(3) kHz. For HCC37Cl v=0, μ=0.439 954(1) D, eQq=−62 839.68(9) kHz, and CCl=1.142(6) kHz. For HCC37Cl v=1, μ=0.462 778(1) D, eQq=−62 848.64(10) kHz, and CCl=1.127(8) kHz. The above results are for J=1 levels, while J=1 and J=2 Stark data for the ground state were combined to give an electric polarizability anisotropy, α∥–α⊥=3.87(2) Å3.
Fragmentation of CH4 in collisions with fast highly charged ions
Authors: Malhi N. B. , Ben-Itzhak I. , Gray T. J. , Legg J. C. , Needham V. , Carnes K. , McGuire J. H.
Published: July 2002

Measurements of the production cross sections for singly charged molecular ions by high energy (1 MeV/amu) Fq+ (q=4,6–9), Siq+ (q=5,6,8–12), and Cq+ (q=3–6) projectiles incident on a CH4 target are reported. Similar measurements for singly charged recoil ions are presented for H+ (E=1–11 MeV) projectiles incident on CH4. We observed good agreement between our proton results and earlier electron measurements. Theoretical calculations for the sum of the cross sections for production of all singly ionized CHn fragments from CH4 are presented using the Born and Glauber approximations, and both calculated cross sections are in reasonable agreement with the measured cross sections. Production of CH+3, CH+2, CH+, and C+ fragments is analyzed both as a function of projectile charge and projectile velocity. Deviation from quasiequilibrium theory is observed in the relatively small cross section ratios of C+ and CH+ to CH+4 as a function of projectile charge.
Polymer cyclization and ring opening kinetics. I. Theory
Authors: Russell William D. , Sceats Mark G.
Published: July 2002

A model of the initial kinetics of cyclization and ring opening of a polymer is developed using a generalized Langevin approach. The model reduces the complex problem to a simpler one of evaluating the dynamics of passage over a transition state in the one-dimensional effective potential of mean force deduced from a superposition of the end-segment binding potential and the end-segment distribution function for unreactive end segments. The model accounts not only for the short range binding, but also for the long range excluded volume and hydrodynamic interactions. It is shown how the initial rates of the theory, and the steady state of cyclization rate of Wilemski–Fixman–Doi theory combine to give the cyclization kinetics over the entire time domain. Expressions for the evolution of the yields of cyclized and linear polymers have been obtained. These include the fluorescence decay times for use in experiments which use such probes.
The vibrational spectrum of the t-HOCO free radical trapped in solid argon
Authors: Jacox Marilyn E.
Published: July 2002

When formic acid is codeposited at 14 K with a beam of excited argon atoms or of F atoms produced in a discharge, t-HOCO is produced in sufficient yield for the infrared detection of most of its vibrational fundamentals. The OH stretching, COH deformation, and torsion vibrations are considerably shifted from the positions previously reported for this species in a CO matrix, consistent with the stabilization of an OC⋅⋅⋅HOCO hydrogen-bonded complex in the earlier experiments. A detailed normal coordinate analysis for t-HOCO isolated in solid argon is reported. In the F-atom reaction studies, the HOC–O⋅⋅⋅HF hydrogen-bonded complex is also stabilized, permitting the comparison of the effects of hydrogen bonding at either end of the molecule. Although there is indirect evidence for the formation of the symmetric H–CO2 species in these experiments, it is not stabilized in concentration sufficient for the identification of its infrared spectrum.
Electronic anti-Stokes Raman scattering at Cr3+ single ions and ion pairs in optically excited states
Authors: Wannemacher R. , Heber J.
Published: July 2002

Electronic anti-Stokes Raman scattering in solids with energy shifts in the optical range is reported for the first time. It is demonstrated for transitions of Cr3+ single ions and exchange–coupled ion pairs from the excited states 2E and 2E×4A2 to the ground states 4A2 and 4A2×4A2, respectively. Whereas scattering from single ions is weak, pair transitions result in comparatively strong and markedly polarized spectra.
Translational energy distribution and asymmetry parameter of the excited hydrogen atom produced in e-C2H2 collisions: Dissociation dynamics of acetylene
Authors: Ogawa Teiichiro , Tomura Hideaki , Nakashima Keiji , Kawazumi Hirofumi
Published: July 2002

Dissociative excitation of acetylene induced in e-C2H2 collisions was investigated by measuring the Doppler profile and its angular dependence from H*(n=4) at a resolution of 0.0065 nm. The translational energy distribution and the angular difference Doppler profile were calculated. The Balmer line was unpolarized. There are three major dissociation processes for H*(n=4) from C2H2; their threshold energies and translational energy distributions are (1) 20.8, 0–2 eV, (2) ∼30, 3–5 eV, and (3) 35–40, 6–8 eV, respectively. Component 1 showed a clear anisotropy: the asymmetry parameter b is 0.5±0.1 and the anisotropy of atomic emission Jp is 0. Thus, component 1 should be produced by predissociation through Rydberg states converging to the (2σu)−1 state. The decrease of b from the theoretical maximum is due to arbitrary direction of the momentum transfer vector and a relatively long lifetime of the intermediate excited states. Components 2 and 3 are also anisotropic and b>0.
Theory of vibrational energy relaxation in liquids: Diatomic solutes in monatomic solvents
Authors: Stote Roland H. , Adelman Steven A.
Published: July 2002

A numerical study of the solute, solvent, and energy flow pathway dependence of the vibrational energy relaxation (VER) time T1 of a harmonic solute vibrational mode is presented for the prototype case of diatomic solutes in monatomic solvents. This study is based on formulas for T1 developed in the preceding paper, especially the relationship T1=β−1(ωl) where β(ω) is the frequency-dependent friction kernel of the solute normal mode and where ωl is its liquid state frequency. These formulas permit evaluation of T1 and its energy flow pathway dependence from equilibrium solute–solvent pair correlation functions. Applications are made to VER of ground electronic state molecular iodine and bromine in the fluids xenon and argon and in model Lennard-Jones solvents designed to simulate ethane and carbon tetrachloride. Satisfactory agreement between the present treatment and experimental and computer simulation results for 15 thermodynamic states is found. The VER rates (∼T−11) were found to increase with increase in the degree of resonance overlap between ωl and the solvent frequency spectrum ρℱ(ω)∼β(ω). Moreover indirect energy flow pathways, i.e., those which involve solute vibration ↔ solute translation–rotation ↔ solvent energy transfer, are found to play a qualitatively essential role for many of the systems studied here. Finally a study of the temperature and density dependence of T1 for iodine in xenon in the experimentally accessible range is presented.
Molecular dynamics of hard sphere. III. Hard spheres in an almost spherical container
Authors: Carignan Y. P. , Vladimiroff T. , Macpherson A. K.
Published: July 2002

The equation of state for hard spheres in a hard spherical container with small hemispherical imperfections in the surface was calculated. It was found that a focusing of the particles occurs at approximately one particle diameter from the center, opposite the imperfections. In this region, there is a large increase in pressure and density and a change in the equation of state at this point. The sharp focusing is due to the focused radial velocity generated by the hemisphere interacting with the bulk fluid. The effect is apparent near the center as the density is lowest there.
A Gaussian model for nematic polymers
Authors: Seitz R.
Published: July 2002

A generalized bead–spring model for lyotropic main-chain polymers is presented. Starting from a Maier–Saupe-like ansatz for the free enthalpy, the thermodynamics and dynamics for the polymer chains are derived in a Gaussian approximation. The model shows a first-order phase transition from the isotropic to the nematic phase which is studied in dependence on chain length and chain flexibility. Results are presented for the order parameter, the mean-square end-to-end distance, and the critical concentration.
Angular correlations between recoil velocity and angular momentum vectors in molecular photodissociation
Authors: Hall G. E. , Sivakumar N. , Chawla D. , Houston P. L. , Burak I.
Published: July 2002

A technique has been developed for determining the angular correlation between a photofragment’s angular momentum vector J, its recoil velocity vector v, and the transition dipole moment of the parent molecule μp . Doppler profile spectroscopy used in conjunction with laser-induced fluorescence probing by polarized light can be used to determine the correlations. The pairwise correlations between these vectors as well as their triple correlation are discussed for limiting cases using a classical approach as well as for the general case using a quantum approach based on density matrices. The current formulations differ in two ways from the recent approach of Dixon, who used a bipolar expansion of the correlated velocity and angular momentum distributions. The physical basis for the influence of the vector correlations on the Doppler profile is somewhat more transparent in the current formulations, and the direct connection between the measured correlations and the t-matrix elements occurring in the theory of Balint-Kurti and Shapiro for the photodissociation of a triatomic molecule is also demonstrated.
NMR solvent peak suppression by nonlinear excitation
Authors: Levitt Malcolm H.
Published: July 2002

Most existing NMR solvent peak suppression sequences provide a satisfactory dependence of the intensity of excited signals on frequency but poor phase characteristics. In practice this leads to spectral distortions which generally become more severe as the frequency selectivity of the sequence is increased. However, it is shown that by working well outside the linear response regime, excitation schemes which combine high frequency selectivity with good phase properties may be devised. Sequences of six rectangular radio-frequency pulses were discovered using a combination of coherent averaging theory to treat the near-resonant behavior and numerical simulation further from resonance. Extensive use of symmetry greatly simplifies both the coherent averaging calculations and the numerical simulations. The new pulse sequences have been given the acronym NERO (nonlinear excitation rejecting on-resonance). Experimental spectra of an enzyme in dilute aqueous solution are shown.
The role of dephasing in some recent theories of quantum localization
Authors: Parris Paul E. , Phillips Philip
Published: July 2002

We consider the transport of electrons or excitons through a random environment in the presence of constant site off-diagonal dephasing processes. It is shown that dephasing of this form will always defeat Anderson localization at long times. Some recent theories of quantum localization which depend upon such dephasing processes are, therefore, seen to be inconsistent.
Electron binding in clusters of polar molecules
Authors: Hernandez John P.
Published: July 2002

Model calculations have been carried out to investigate the binding of an excess electron within a hot cluster of polar molecules. The effect of the long-range electron–molecule interaction is emphasized. The energy of such negatively charged clusters relative to dissociation into molecules and electron (U−) and relative to the electron dissociated from the equilibrium neutral cluster (A) are investigated. For parameters appropriate to NH3 and H2O molecules, clusters with n=6, 14, and 38 molecules are examined with the result that U−<0, but A>0 for all the cases considered.
Nascent rovibrational distributions of OH+ and OD+ in the A 3Πi state produced from the dissociative charge transfer reactions of He+ with H2O and D2O at thermal energy
Authors: Yamaguchi Sumio , Tsuji Masaharu , Nishimura Yukio
Published: July 2002

The thermal-energy charge transfer reaction of He+ with H2O(D2O) has been investigated by observing the A 3Πi–X 3Σ− emission of OH+(OD+) at low pressures (<3 mTorr). The vibrational distributions in A 3Πi of OH+(OD+) are 0.66(0.55)v′=0, 0.20(0.26)v′=1, 0.10(0.13)v′=2, and 0.04(0.06)v′=3. The rotational distributions for v′=0–3 of OH+(OD+) are expressed by a single Boltzmann temperature of 1700±200 (1800±200) K. The fractions of the available energy deposited into rotation 〈 fr〉 and vibration 〈 fv〉 for OH+(OD+) are evaluated to be 4.9(5.5)% and 3.9(4.1)%, respectively, indicating that a large amount of the available energy is partitioned into the relative translational energy.
Calculation of the vibrational dependence of the electric field gradient in HD
Authors: Kim Hae-Won , Hameka Hendrik F. , Zeroka Daniel
Published: July 2002

We calculate the deuterium electric field gradient in the HD and D2 molecules at various internuclear separations by making use of a previously proposed variation–perturbation method. We calculate DEFG values at internuclear separations R=1.2, 1.3, 1.4, 1.5, and 1.6. We also calculate the average values for the vibrational ground state v=0 and for the vibrational states J=0, J=1, and J=2 of the HD and D2 molecules. The vibrational averaged DEFG value is very close to the equilibrium value at R=1.4 due to accidental cancellation of different contributions. The difference between our result and other theoretical values is about 2.5%.
Coexistence of precursor and direct dynamics: The sticking of O2 on a Pt(111) surface
Authors: Williams M. D. , Bethune D. S. , Luntz A. C.
Published: July 2002

The initial sticking coefficient (probability for dissociative chemisorption) has been measured for O2 on a Pt(111) surface as a function of initial energy, incident angle, and surface temperature using molecular beam techniques. The results reveal two distinct mechanisms for sticking; precursor mediated and direct dissociation, either of which can dominate depending upon the initial adsorption conditions.
S
n
←S1 and S1→S resonance CARS spectra of perylene in the S1 state
Authors: Matsunuma Satoshi , Akamatsu Naotoshi , Kamisuki Toshio , Adachi Yukio , Maeda Shiro , Hirose Chiaki
Published: July 2002

Resonance CARS spectrum of perylene in the first excited singlet (S1 ) state was observed in solution at room temperature. The observed shifts of Raman frequencies from the ground (S0 ) state values were related to the results of the PPP-SCF-CI MO calculation and the normal coordinate calculation. The experiment, intended to observe the resonance CARS signal of the S0 state, was found to give the signal predominated by the lines of the S1 state. It was also concluded that the peculiar feature originating from the simultaneous role of the pump beam depleted the molecules in the S0 state, populated the S1 state, and caused the resonance effect on CARS through the intense S1 →S0 transition.
Transport properties of a gas of rotating molecules
Authors: Curtiss C. F.
Published: July 2002

A perturbation solution of the classical Boltzmann equation of a gas of rotating molecules is presented and discussed. The use of irreducible spherical tensors then leads to equations for scalar perturbation functions. These equations lead to expressions for scalar transport coefficients in terms of elements of the inverse cross section matrix. Perturbation expressions for the cross sections developed earlier are then introduced. This leads to expressions for the effects of a magnetic field on the transport coefficients to second order in the anisotropy of the potential, with no truncation of the basis set.
Molecular dynamics simulation of direct laboratory frame cross correlations in spherical, plate-like, and rod-like molecules
Authors: Evans M. W. , Luken W. , Lie G. C. , Clementi E.
Published: July 2002

Direct laboratory frame cross correlation functions (ccfs) are reported for the spherical top sulfur hexafluoride, and the symmetric tops, methyl hexa-tri-yne, hexafluorobenzene, and benzene. The direct correlations appear between the molecular dipole moment and the molecular center-of-mass velocity. The simulation provides the time dependence of the correlation functions for all four molecules. A simple theory for the computer simulation results is given, based on linked Langevin equations.
The reaction of O(3P) atoms with ethane: An HTP kinetics study from 300 to 1270 K
Authors: Mahmud Khaled , Marshall Paul , Fontijn Arthur
Published: July 2002

Rate coefficients for the O+C2H6 reaction have been measured using the high-temperature photochemistry (HTP) technique. Strong non-Arrhenius behavior is observed. The data are well fitted by the empirical expression k(T)=1.9×10−31 T6.5 exp(−138 K/T) cm3 molecule−1 s−1. Confidence limits are discussed in the text. The results are consistent with calculations based on transition state theory and tunneling through an Eckart barrier.
Coupling interaction between the sulfate ion ν2 modes and the lithium modes in LiKSO4
Authors: Kim Seung-Bin , Frech Roger
Published: July 2002

Resonant couplings between the sulfate ion ν2 mode and the lithium ion translatory mode in E2 and E1 symmetries have been studied in single crystal 7 LiKSO4 and 6 LiKSO4 from polarized Raman spectra between 298 and 519 K and from infrared reflectivity spectra at room temperature. Coupling effects are negligible in 7 LiKSO4 whereas in 6 LiKSO4 the lithium isotope effect shifts the lithium translatory mode into resonant coupling with the sulfate ion ν2 mode. The resonant coupling mechanism between the two fundamental E2 modes is elucidated by a comparative analysis of the temperature dependence of the frequency shifts and the relative intensities. The coupling interaction in E1 symmetry can be only qualitatively described due to poor resolution of the Raman bands. It is possible to distinguish anharmonic processes which couple two modes from anharmonic processes which perturb each state individually. It was found that coupling anharmonicity decreased while perturbative anharmonicity increased with increasing temperature. Detailed consideration of various intensity ratios in E2 symmetry allows the separation of the isotope effect from the coupling contribution to the polarizability derivative tensor. In E1 symmetry TO–TO and LO–LO coupling interactions between the ν2 mode of the sulfate ion and the lithium translatory mode were deduced from the frequency and intensity data.
Direct excitation studies of the diffuse bands of alkali metal dimers
Authors: Luh Wei-Tzou , Bahns John T. , Lyyra A. Marjatta , Sando Kenneth M. , Kleiber Paul D. , Stwalley William C.
Published: July 2002

Direct dye laser excitations of the K2 yellow, Rb2 orange, and Cs2 near-infrared diffuse bands have been investigated. Experimental results are shown to be consistent with the assumed bound–free 2 3Πg–1 3∑+u excitations. It is found that for Rb2 and Cs2, spin–orbit interactions become so significant that the 2 3Πg state is strongly split into three quite independent component states.
First moments of the liquid phase far-infrared absorption cross section and the R(ω) representation of depolarized Rayleigh scattering
Authors: Rodriguez R. , McHale J. L.
Published: July 2002

A calculation of the first moment or average frequency ω̄ of the liquid phase far-infrared absorption cross section is presented. The theory also applies to the calculation of the average frequency of the R(ω) representation of depolarized Rayleigh scattering data, where R(ω)=ω[1−exp(−ℏω/kT)]I(ω). The average frequency is shown to depend on the integral of the imaginary part of the angular derivative correlation function divided by time. A semiclassical relationship between the real and imaginary parts of the correlation function is derived and shown to lead to a series representation of ω̄ in terms of fourth and higher moments of the intensity spectrum. It is demonstrated that the theory reproduces the exact semiclassical result for ω̄ of both the far-IR absorption spectrum and the R(ω) representation of the depolarized Rayleigh wing of linear free rotors. The implications of our theory concerning the comparison of peak frequencies in the far-IR absorption spectrum and the R(ω) representation of the depolarized Rayleigh scattering spectrum are discussed. The theory is able to qualitatively explain the experimentally observed dependence of peak frequency on temperature, concentration, and isotopic substitution. The ratio of the average frequencies of the absorption cross section and the R(ω) representation is shown to depend on the size of the mean square torque compared to (kT)2.
Millimeter and submillimeter wave spectroscopy of protonated and deuterated nitrous oxide
Authors: Bogey Marcel , Demuynck Claire , Destombes Jean-Luc
Published: July 2002

The a- and b-type rotational spectra of the protonated and deuterated nitrous oxide have been investigated in the millimeter and submillimeter frequency range. The molecular ions were produced in a magnetically confined glow discharge. The comparison between the accurate molecular constants deduced from the analysis of the spectra and different sets deduced from ab initio calculations gives structural information on the observed species: the experimental spectra belong to the O-protonated and -deuterated nitrous oxide.
Computer simulation methods for diffusion-controlled reactions
Authors: ben-Avraham Daniel
Published: July 2002

We discuss various computer simulation techniques for the study of nonequilibrium diffusion-controlled reactions. These include: the minimal process method which simulates a master equation describing the process; the ‘‘direct’’ method which simulates the actual motion and reactions of the particles; and a new simulation method which we term the renormalized reaction-cells method (RRC). The RRC is a variation of the minimal process method which makes use of some scaling ideas. The reaction cells of the minimal process method are renormalized as the concentration of the reactants in the system decreases. The probabilities for diffusion and for reaction, as well as the time increase associated with the processing of a cell, are renormalized in a corresponding fashion. The shortcomings and strengths of each simulation method are pointed out. Several examples of diffusion-controlled reactions are simulated by the direct method and by the RRC method. It is shown that the RRC is superior to the other simulation methods in many respects.
Alternative modes of conjugation in one-dimensional polymers
Authors: Hughbanks Timothy , Burdett Jeremy K.
Published: July 2002

Electronic delocalization may be achieved utilizing unconventional modes of conjugation between unsaturated centers. Spiroconjugation, through-bond coupling, and long-range through-space coupling have been explored as mechanisms for conjugation in one-dimensional semiconductors. Three prototypical systems are examined in order to shed light on the prospects for the actual exploitation of these modes of conjugation in electronically interesting polymers. The stabilizing or destabilizing influence of through-bond coupling and spiroconjugation is examined. A prevalent phosphorus chain system 1∞ [Px−5 ] (0<x<1) is analyzed as an example of an infinite ‘‘laticycle.’’ Through-space apex–apex interactions in this system have profound effects on the protonated derivative, 1∞ [P5H].
Nuclear spin relaxation and molecular dynamics in ordered systems: Models for molecular reorientation in thermotropic liquid crystals
Authors: Vold Regitze R. , Vold Robert L.
Published: July 2002

New models are developed to account for rotational motion in liquid crystals. A distinction is made between rotation about a molecule fixed z axis, described by Eulerian angle γ, and about a space fixed z axis, described by Eulerian angle α. Our model allows γ motion to proceed by jumps of arbitrary angular size, while motion about the space fixed axes (α,β motion) is described in terms of small step rotational diffusion in presence of a restoring pseudopotential. Calculations are presented for different forms of the restoring potential including (1−cosn β) for n=2, 4, and 10 where β is the angle between the molecule fixed and space fixed z axes, as well as angular square well potentials with finite and infinite walls. Multiexponential correction functions for α,β motion in the infinite square well (‘‘diffusion-in-a-cone’’) potential as well as the Maier–Saupe potential (cos2 β) are listed in tabular form as a function of the second rank order parameter Szz =〈 P2(cos β)〉. It is shown that spectral density functions relevant for calculation of 2H spin–lattice relaxation behavior are not very sensitive to the form of the restoring potential. J00(0), which contributes primarily to T2, appears to be more sensitive to the shape of the potential. Experimental spectral density ratios J1/J2 for numerous solutes and liquid crystalline solvent molecules can readily be explained in terms of dominant contributions from γ motion. In general, this motion seems to proceed by jumps of larger angular size as the degree of order increases.
Comment on: ‘‘Incipient triple points in films on lamellar halides’’
Authors: Larher Y. , Millot F. , Tessier C.
Published: July 2002

Niskanen’s proposal for the interpretation of our experimental results implies the existence of a strong first order transition in the adsorption isotherms measured just above the incipient triple point temperature. We show that the experimental facts contradict this proposal.
Comment on: ‘‘Laser and phosphor host La1−xMgAl11+xO19 (x=0.050): Crystal structure at 295 K’’
Authors: Kahn A. , Gaspérin M. , Saine M. C. , Lejus A. M. , Théry J. , Vivien D.
Published: July 2002

It is argued that several important papers (ref. 1,2,3,4) were not cit by the authors of the title article. The crystal growth of the title material, from nonstoichiometric congruent melting composition is also discussed.(AIP)
An improved long range potential for O(1D)+H2
Authors: Walch Stephen P. , Harding Lawrence B.
Published: July 2002

Several dynamics studies have indicated that the product isotopic distributions and vibrational energy distributions in the reaction O(1D)+H2(HD) are very sensitive to the long range interaction of the reactants. In this paper we report an improved calculation of the reactant region of the potential energy surface. In agreement with previous work we find no barrier to edge-on insertion (1A′ ground state water surface), but find a smaller (<0.2 kcal/mol) barrier to collinear addition (1Σ+ surface) than in previous work. The long range potential obtained in the present work most closely resembles the SL3 surface.
Neon matrix ESR investigation of 12C+2 and 13C+2 : Confirmation of a 4Σ−g ground electronic state
Authors: Knight Lon B. , Cobranchi S. T. , Earl E.
Published: July 2002

The 12C+2 and 13C+2 cation radicals have been isolated in neon matrices by the photoionization of C2(g) generated by the laser vaporization of thin carbon disks. A new procedure of supporting and thermally outgassing such targets for laser vaporization ESR studies in rare gas matrices is described. The ESR results confirm the 4Σ−g ground electronic state assignment for C+2 and provide a valence orbital electronic structure characterization based on the 13C hyperfine structure (hfs). The ESR lines are extremely narrow for a high-spin powder sample and an intense off-angle or ‘‘extra’’ absorption feature exibits unusual hfs. Normally forbidden (ΔMS>1) transitions were detected at low magnetic fields. The magnetic parameters for 13C+2 in a neon matrix at 4 K are: D=3668(3) MHz; g⊥ =2.0018(5); g∥ =2.0023(5); ‖A∥‖ =99.4(8) MHz; and ‖A⊥‖ =95.2(5) MHz.
Surface mediated radical recombination luminescence: O+NO+Ni
Authors: Arnold Graham S. , Coleman Dianne J.
Published: July 2002

Results of an experimental investigation of the chemiluminescence produced by the interaction of atomic oxygen and nitric oxide on a nickel foil surface are reported. Visible luminescence which depends linearly on the atomic oxygen and nitric oxide fluxes, on the substrate temperature, and on the substrate temperature history has been observed under conditions for which the three-body gas-phase reaction of O and NO is negligible. The intensity of the luminescence is greater than can be accounted for by the gas-phase two-body radiative recombination reaction of O and NO. The time, flux, and temperature dependences, along with the intensity of the emission support strongly the notion that the observed luminescence stems from excited species, most probably electronically excited NO2, formed in a surface mediated reaction.
Quantum-mechanical scattering of H2 from metal surfaces: Diffraction and dissociative adsorption
Authors: Halstead D. , Holloway S.
Published: July 2002

Some theoretical and experimental aspects of the interaction of H2 with metal surfaces are reviewed. A variety of model potential energy surfaces based on simple extensions to the Lennard-Jones model are presented. These potentials include activation barriers which vary across the surface unit cell giving rise to a variety of physically interesting and realistic topologies. The quantum-mechanical scattering of hydrogen and its isotopes from these potentials illustrate that it is possible, in a very simple way, to account for simultaneous sticking and diffraction at a single beam energy. The inclusion of tunneling in a realistic description of initial sticking coefficients is shown to be essential for these light gases. Finally, it is proposed that by inverting diffraction data, it should be possible to obtain key information regarding the form of the potential energy surface.
State-to-state rotational energy transfer in methane (13CD4) from infrared double-resonance experiments with a tunable diode laser
Authors: Foy B. , Hetzler J. , Millot G. , Steinfeld J. I.
Published: July 2002

An infrared double resonance laser spectroscopic technique is used to study state-resolved rotational and vibrational energy transfer in the isotopically substituted methane molecule,13CD4 . Molecules are prepared in a selected rovibrational state by CO2 laser pumping, with the quantum numbers v, J, and Cn completely specified. Measurements of both the total rate of depopulation by collisions, and the rates of transfer into specific final rovibrational states (v′, J′, Cn′ ) are carried out using time-resolved tunable diode laser absorption spectroscopy. The depopulation rates due to collisions between methane and the rare gases are on the order of the Lennard-Jones collision frequencies. Self-relaxation is slightly more efficient than the Lennard-Jones estimate. The rather small relaxation rates are characteristic of a short-range potential, or ‘‘strong-collision’’ regime, expected for a molecule without a dipole moment. The state-to-state energy transfer measurements reveal a dramatic selectivity of rotational energy transfer pathways with respect to the fine-structure rotational states Cn . Relaxation occurs through a surprisingly small subset of the energetically accessible pathways. Also suggested is a preference for population transfer to occur within the initial vibrational angular momentum sublevel of the ν4 (F2 ) vibrational state, which has three sublevels in consequence of Coriolis interaction. This preference can be formulated as a propensity for Δ(R−J)=0 transitions. We deduce that large changes of J(ΔJ∼5) can occur in single collisions between methane molecules, based on a simple kinetic model of the data. This is also characteristic of

short-range collisions in which it is likely that no single multipolar interaction dominates. Collisional relaxation between the ν4 and ν2 bending vibrations proceeds more slowly than rotational relaxation, but as fast as transfer among the closely grouped stretching and bend-overtone levels, measured previously in CH4 . No evidence for rotationally specific V–V transfer is found. We discuss an exhaustive spectroscopic analysis of 13CD4 that provides unambiguous spectral assignments for use in detecting vibrationally excited molecules (v4 =1) in specific rotational states.
Energy-dependent collisional deactivation of vibrationally excited azulene
Authors: Shi Jichun , Barker John R.
Published: July 2002

Collisional energy transfer parameters for highly vibrationally excited azulene have been deduced from new infrared fluorescence (IRF) emission lifetime data with an improved calibration relating IRF intensity to vibrational energy [J. Shi, D. Bernfeld, and J. R. Barker, J. Chem. Phys. 88, 6211 (1988), preceding paper]. In addition, data from previous experiments [M. J. Rossi, J. R. Pladziewicz, and J. R. Barker, J. Chem. Phys. 78, 6695 (1983)] have been reanalyzed based on the improved calibration. Inversion of the IRF decay curves produced plots of energy decay, which were analyzed to determine 〈ΔE〉, the average energy transferred per collision. Master equation simulations reproduced both the original IRF decays and the deduced energy decays. A third (simple) method of 〈ΔE〉 determination agrees well with the other two. The results show 〈ΔE〉 to be nearly directly proportional to the vibrational energy of the excited azulene from ∼8000 to 33 000 cm−1. At high energies, there are indications that the 〈ΔE〉 energy dependence may be slightly reduced.