bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum study of vibrational excitation in the three-dimensional collisions of CO2 with rare gas atoms
Authors: Clary D. C.
Published: February 2003

A combined vibrational close-coupling and rotational infinite order sudden technique is described for calculating vibrational excitation cross sections σvv′ for the three-dimensional collisions of atoms with linear triatomic molecules. The method treats anharmonic, Coriolis, and vibrational angular momentum terms in the molecular Hamiltonian accurately, and is applicable to any realistic potential energy surface expressed in numerical or functional form. Application of the method to X–CO2(v1v2λv3) collisions, where X = He, Ne, or Ar, is described. An accurate anharmonic CO2 potential, expressed in terms of bond and angle displacements, is employed. The X–CO2 interaction potentials are more approximate and are expanded in terms of atom–atom pair potentials. Calculations of σvv′, over a grid of energies sufficient to give rate coefficients kvv′ for transitions between the low-lying states of CO2 for temperatures up to 300 K, have been performed. Propensities for particular collisional excitations involving the symmetric stretch, bending, and asymmetric stretch vibrational modes of CO2 are examined. It is found that the magnitudes of the σvv′ are largely determined by the energy differences between the v and v′ levels. For example, excitation of the ground (00 00) state to the first excited bending state (0110) is found to be favored. σvv′ for near resonant transitions such as (02 00)→(02 20) are found to increase with increasing mass of X. Deactivation of the (00 01) state to the (11 10) state is favored over other transitions. The ratios of the deactivation cross section for the level (00 01) to the deactivation cross sections for lower levels such as (01 10) are small, although these ratios do increase with increasing mass of X, in agreement with experimental findings. Comparison of calculated kvv′, for deactivation of the (01 10) level, with those obtained in recent photoacoustic experiments is quite encouraging, considering the approximate nature of the X–CO2 interaction potentials used. For X = He and Ne these calculated kvv′ are within a factor of 5 of the experimental results and have the correct temperature dependence, while for X = Ar the calculations are much larger than the experimental results, and the temperature dependence is too shallow. The computer program used in the calculations is automatic and general, and should be applicable to many other atom–linear triatomic molecule collisions.
A nonempirical effective Hamiltonian technique for polymers: Application to polyacetylene and polydiacetylene
Authors: Brédas J. L. , Chance R. R. , Silbey R. , Nicolas G. , Durand Ph.
Published: February 2003

The recently proposed ab initio effective Hamiltonian technique is extended to polymer calculations and applied to various conformations of polyacetylene (all-trans, cis-transoid, and trans-cisoid) and polydiacetylene (acetylenic and butatrienic backbones). Band structures, density of states (DOS), and XPS theoretical spectra are presented. Comparison of the band structures and DOS with those obtained by ab initio SCF (self-consistent-field) Hartree–Fock calculations of double zeta quality is excellent. The XPS theoretical spectrum for all-trans polyacetylene is in good agreement with experiment. In polyacetylene, it is found that the π bands are quite similar for all three backbone conformations, though the σ bands differ significantly. For polydiacetylene, low ionization potentials are predicted—a few tenths of an eV larger than polyacetylene for the acetylenic backbone and a few tenths of an eV smaller than polyacetylene for the butatrienic backbone.
Laser wavelength dependence of the REMPI mass spectrum of 2,4-hexadiyne: Direct evidence for dissociation through ionic states
Authors: Carney Thomas , Baer Tomas
Published: February 2003

Results on the REMPI mass spectrum of 2,4-hexadiyne, a benzene isomer, are presented.(AIP)
Reaction cross sections of helium, neon, and argon excited diatomic molecules
Authors: Doba Takahisa , Arai Shigeyoshi
Published: February 2003

Quenching cross sections of He2, Ne2, and Ar2 have been determined by detecting their transient near-infrared absorptions. (AIP)
Rotational tunneling in NH4ClO4: Reanalysis of neutron spectra
Authors: Prager M. , Press W.
Published: February 2003

A rotational tunneling in NH4Cl4 is studied by a reanalysis of neutron spectra.(AIP)
Products of the reaction between Cl and HOCl
Authors: Cook Jac-E L. , Ennis Christine A. , Leck Thomas J. , Birks John W.
Published: February 2003

There are two possible channels for the reaction between Cl and HOCl leading to the products HCl+ClO and Cl2+OH. The product of the rate constant for the reaction OH+Cl2→products and the equilibrium constant for the reaction Cl+HOCl?Cl2+OH is (1.8±0.5)×10−12 cm3 molecules−1 s−1, in excellent agreement with our recently measured rate constant for the reaction of Cl with HOCl of (1.9±0.3)×10−2 cm3 molecules−1 s−1. This suggests that the products of the reaction of Cl with HOCl are predominantly Cl2+OH rather than HCl+ClO. The reaction Cl+HOCl→Cl2+OH is equivalent to HOCl photolysis in the stratosphere and need not be included in models of ozone depletion due to ClX. (AIP)
Comment on ‘‘An isothermal–isobaric computer simulation of the supercooled-liquid/glass transition region: Is the short-range order in the amorphous solid fcc?’’
Authors: Abraham Farid F.
Published: February 2003

It is demonstrated that one can easily distinguish between a supercooled liquid that becomes a glass and a supercooled liquid that nucleates to a defect crystal during a quench using the isothermal–isobaric Monte Carlo method.(AIP)
Two photon resonant multiphoton ionization spectroscopy in the ultraviolet: A new Rydberg system in Br2
Authors: Morrison Richard J. S. , Grant Edward R.
Published: February 2003

Analysis of the laser included multiphoton ionization spectrum of Br2 in the ultraviolet from 295 to 275 nm has revealed three new Rydberg states of g symmetry. Our preliminary assignment yields the following parameters: Te′ = 68 835 cm−1, we′ = 365 cm−1; Te′ = 70 576 cm−1, we′ = 371 cm−1; and Te′ = 72 118 cm−1, we′ = 334 cm−1. Using visible light we observe an additional state in the same region as a three photon resonance. This state, with parameters Te′ = 68 620 cm−1 and we′ = 338 cm−1, appears to correspond to the g Σu− previously assigned from absorption data.
Measurement of the vibrational band strength of 11BF using a tunable diode laser
Authors: Zahniser Mark S. , Gersh Michael E.
Published: February 2003

The infrared band strength for the fundamental vibrational mode of 11BF is measured by line absorption of the P(11) transition at 1343.5 cm−1 using a tunable diode laser and multipass absorption cell coupled to a discharge flow apparatus. The BF number density is simultaneously determined by ultraviolet absorption at the bandhead of the A 1Π←X 1Σ transition at 196 nm. The resulting value for the band strength is 650±200 cm−2 (STP atm)−1, which is in good agreement with existing theoretical calculations.
Measurement of the LiD (A–X) transition moment from laser-excited fluorescence and test of the R-centroid approximation
Authors: Ennen G. , Fiedler B. , Ottinger Ch.
Published: February 2003

Improved Dunham coefficients of the X 1Σ+ and A 1Σ+ states of LiD were derived, based on the observation of vibrational levels up to v″ = 26, corresponding to 96% of the ground state dissociation energy. From accurate intensity measurements over long fluorescence progressions, the electronic transition moment M was obtained as a function of the internuclear distance R. The dependence M(R) has an unusual S shape. The R-centroid method was found to be valid even in this case.
Angle-resolved photoelectron spectroscopy of CO2 with synchrotron radiation
Authors: Grimm Frederick A. , Allen John D. , Carlson Thomas A. , Krause Manfred O. , Mehaffy David , Keller Paul R. , Taylor James W.
Published: February 2003

The angular asymmetry parameter β has been determined for the first four bands in the photoelectron spectrum of CO2 as a function of photon energy: X 2Πg(15–50 eV), A 2Πu(19–28 eV), B 2Σu+(19–28 eV), and C 2Σg+(21–67 eV). Use is made of a monochromatized beam of photons from the Wisconsin Synchrotron Radiation Center. The experimental results are compared with theoretical calculations employing the multiple scattering method and the overall agreement is good. In addition, the theoretical predictions for the effect on β of shape resonances have been verified except that the experimental widths are broader. This broadening has been partially accounted for in recent calculations of Swanson et al. by including the effects of vibrational motion. Finally, sharp changes in β as a function of vibrational level have been noted for the second and fourth electronic bands. Such behavior has been found for a variety of photon energies, and the results are examined against prevailing theory.
Electron orbital energies of H2S and H2O chemisorbed on the Si(111) 7×7 surface
Authors: Fujiwara Kenzo
Published: February 2003

Electron orbital energies of H2S and H2O chemisorbed on the Si(111) 7×7 surface were investigated by means of ultraviolet photoemission spectroscopy. It is experimentally shown that these molecules are nondissociatively adsorbed on the surface at room temperature. Photoemission spectra of these molecular chemisorption states revealed adsorbate-induced features at E−EVAC = −9.4 and −12.4 eV for H2S and −10.0, −12.3, and −14.8 eV for H2O, respectively, in the surface electronic density of states. These are related to the molecular 1b1, 2a1, and 1b2 orbitals of the corresponding free molecule. Comparison of the gaseous ionization potentials of the molecules with the features for the adsorbed phases indicates that the chemisorption bonds are formed in these cases via the sulfur or oxygen end of the molecule through hybridization between the 1b1 and 2a1 molecular orbitals and the Si:sp3 dangling bond orbital, assuming uniform polarization and relaxation shifts. It is also shown that at higher temperatures (≳800 °K) these molecular chemisorption states substantially change into the different ones, and the photoemission spectra revealed essentially new features at E−EVAC = −8.3, −9.7, and −12.0 eV for H2S and −8.3, −11.5, and −15.0 eV for H2O, respectively. These energy levels are associated with the atomic sulfur and oxygen chemisorption states, respectively, that are formed as a result of the decomposition of the molecules and the hydrogen desorption. From comparsion between these observed extrinsic surface electronic structures and the theoretical local density of states of the chemisorbed oxygen atom by Chen et al., the experimental results are interpreted in terms of the Si–O covalent bond formation. That is, the energy levels at −11.5 and −15.0 eV are attributed to π-bonded O (px, py) and σ-bonded O (pz) orbitals, respectively, whereas a structure at −8.3 eV to Si bulk p-like states. By chemical analogy, corresponding orbital energy structures for the atomic sulfur chemisorption state are also assigned.
Behavior of polymer end-to-end distance in two dimensions at the theta point
Authors: Marqusee J. A. , Deutch J. M.
Published: February 2003

The end-to-end distance of a flexible polymer in a theta solvent in two dimensions is investigated. A mean field theory is presented which predicts significant deviations from ideal behavior at the theta point. A real space renormalization group approach is employed to investigate further the behavior of the polymer’s end-to-end distance at the theta point and to elucidate the analogy with thermodynamic tricritical behavior. Our results suggest that the correct result may be numerically closer to the mean prediction than to the values obtained from second order ε = (3−d) expansions of field theory models of critical phenomena.
New approximate quantum cross sections for the H+H2 reaction
Authors: Bowman Joel M. , Ju Guan-Zhi , Lee Ki Tung
Published: February 2003

The H+H2 cross section is calculated using a transition state theory is used based on collinear exact quantum reaction probabilities. (AIP)
Interaction-induced resonance enhancement of Raman scattering as derived from perturbation theory
Authors: Tobias Irwin
Published: February 2003

The cross section for Raman scattering is calculated for a system consisting of a nonabsorbing molecule with some characteristic Raman spectrum weakly interacting with a species which absorbs at the frequency of the incident light. With the interaction treated as a perturbation, it is found that after the first-order correction to the wave function is introduced, a resonance term appears in the cross-section. This term serves to increase the intensity of the Raman bands associated with the isolated molecule. Enhancements as large as 106 can result when the interaction is sufficiently weak to change the unperturbed wave function by as little as 10%. The model also accounts for different enhancements for the various Raman bands.
Electronic factors leading to Peierls and spin-Peierls distortions: Effects of pairing-distortion on the electronic properties of the metallic and the insulating states of a half-filled band
Authors: Whangbo Myung-Hwan
Published: February 2003

A common theoretical link between Peierls and spin-Peierls distortions was explored in the present work by studying the effects of pairing-distortion on the electronic properties of the metallic and insulating states of a half-filled band. It is possible to discuss the cause for a spin-Peierls distortion in terms of the electronic energy as in the case of a Peierls distortion if the ground electronic state of a Heisenberg antiferromagnetic chain is approximated by the Slater antiferromagnetic state of a very narrow band. The present work suggests that a spin-Peierls distortion can be regarded to originate from a bond density wave developed on top of an antiferromagnetic state, just as a Peierls distortion can be considered to result from a bond density wave created on top of a metallic state. Formation of a bond density wave in a regular chain is found to be independent of the on-site repulsion but enhanced by the intersite repulsion. The potentials exerting on the two sides of each lattice site of a regular chain become inequivalent upon introducing a bond density wave, so that the leading term of the energy variation with the lattice distortion becomes linear in the lattice displacement.
Direct measurement of mobility for cluster ions K+(H2O) in N2 at room temperature
Authors: Takebe M. , Satoh Y. , Iinuma K. , Seto K.
Published: February 2003

The mobility of the clustered ion K+(H2O) has been measured in nitrogen at 305 K over the E/N range 5–45 Td, by two methods using a drift tube without mass spectrometer. Nitrogen and water vapor pressures used were 3 to 28 Torr and 2 to 20 mTorr, respectively. It is found that the mobility is constant over the E/N range measured and the zero-field reduced mobility is 2.17±0.03 cm2/V s. This value is 10.0% lower than the Langevin value. One of the methods provides a new experimental technique for obtaining an isolated arrival time spectrum for clustered ions from a composite one.
Mobilities of negative halogen ions in various gases
Authors: Fujii T. , Meisels G. G.
Published: February 2003

The mobilities of SF−6 in He and of F−, Cl−, Br−, and I− in Ar, Xe, H2, N2, CO, and CH4, have been investigated over the field-strength (E/P) range of 5 to 25 V/cm Torr using time-resolved high pressure mass spectrometry and an ion source with coaxial electron entrance and ion drift fields. The reduced mobilities obtained by this method are in good agreement with those obtained in drift tubes when comparison is possible. Results are compared with ’’Langevin’’ polarization limits and with the drift properties of isoelectronic positive alkali ions measured previously.
Change of free energy in heteromolecular nucleation: Electrostatic energy contribution
Authors: Suck Sung Ho
Published: February 2003

The presence of foreign particles in vapor is known to promote the formation of clusters and phase transition at lower supersaturation. Our primary object here is to assess the contribution of the electrostatic energy to the total free energy change owing to the presence of a charged or uncharged foreign particle (atom or molecule) during the formation of heteromolecular clusters. Unlike the Thomson’s ’’electrothermodynamic’’ theory, we introduce the contribution of the higher electric moment (dipole) and polarization of the foreign particle, in addition to its monopole charge contribution. The present theory predicts: (1) there is no strong charge sign preference in the promotion of nucleation, (2) the size (’’radius’’) differences of ions or neutral foreign particles largely determine differences in the free energy change and thus in the promotion of nucleation, and (3) the differences in the dipole moments and polarizabilities of the charged or uncharged foreign particles are also important for such distinctions, particularly in the case of the foreign particles of nearly the same size. In the limiting case of zero polarizability and zero dipole moment associated with an ion, our present theory recovers exactly the same functional dependency on the charge, ionic radius, and the cluster size as in the electrothermodynamic theory of Thomson. .
Emission of light from Ag metal gratings coated with dye monolayer assemblies
Authors: Knoll Wolfgang , Philpott Michael R. , Swalen J. D. , Girlando Alberto
Published: February 2003

The emission of light from silver gratings coated with dye monolayer assemblies is reported for the first time. The monolayer assembly was laid down by the Langmuir–Blodgett dipping technique. When the grating is illuminated with s- or p-polarized light, weak fluorescence from the dye monolayer is detected. In addition there is emission of light from all plasmon surface polariton modes with energy lower than that of the exciting light. This latter emission is identified by a characteristic polarization and dependence of wavelength on angle of emission in the plane perpendicular to the grooves of the grating. At energies within the absorption bands of the dye monolayer, this emission is shown to be enhanced.
A unified approach to the determination of infrared and Raman vibrational optical activity intensities using localized molecular orbitals
Authors: Nafie Laurence A. , Freedman Teresa B.
Published: February 2003

The localized molecular orbital (LMO) model of infrared vibrational circular dichroism (VCD) is extended to vibrational Raman optical activity (ROA). Using the equations arising from the finite perturbation approach to ordinary infrared and Raman intensities we show that VCD and ROA intensities can be determined in the same manner provided that localized molecular orbitals are used to describe the motion and response of electronic charge density in the molecule. In this approach a small perturbing electric field is used to obtain the first and second derivatives of the potential energy gradient of the molecule with respect to the electric field and these derivatives are in turn related to infrared and Raman intensities, respectively. Since only a few SCF calculations are required by this method to obtain both VCD and ROA intensities for all the vibrational modes of a molecule, the way is now open for the efficient and complete calculation of vibrational optical activity intensities using molecular orbital methods.
Nascent product vibrational state distributions of ion–molecule reactions: The proton transfer reactions F−+HX→HF(v)+X−, X = Cl, Br, and I
Authors: Weisshaar James C. , Zwier Timothy S. , Leone Stephen R.
Published: February 2003

Nascent vibrational state distributions are obtained for the HF products of the proton transfer reactions F−+HX→HF(v)+X−, X = Cl, Br, and I. The reactions are carried out in a flowing afterglow apparatus in which the reagents are fully thermalized (300 K). The product states are measured by low resolution infrared chemiluminescence spectra obtained with a Ge:Cu infrared detector and a circular variable filter. The nascent HF(v) distributions are as follows: for F−+HCl, N1:N2:N3 = 0.46:0.33:0.21; for F−+HBr, N1:N2:N3:N4 = 0.28:0.27:0.24:0.21; for F−+HI, N1:N2:N3:N4:N5 = 0.20:0.23:0.22:0.20:0.15. All three reactions channel the available exothermicity quite efficiently into product vibration. Product rotational state information cannot be obtained due to collisions with the He carrier gas. In spite of the deep attractive wells of the F−+HX potential energy surfaces, in all three cases the degree of vibrational excitation in the ion–molecule reaction is remarkably similar to, although distinctly smaller than, that of the corresponding neutral F+HX reactions. The results strongly suggest that these ion–molecule reactive collisions are direct encounters and that the kinematic effect of the mass combination (transfer of a light particle between two heavy particles) dominates over the influence of the shape of the potential energy surface in determining the product vibrational state distributions.
Relative vibrational quenching of N2+(B 2Σ) by N2 and He
Authors: Neff S. H.
Published: February 2003

The relative quenching of vibrational states in N+2(B 2Σ) has been studied in gas mixtures of He and N2 excited by He resonance radiation (50.4 nm). The quenching rate coefficient for the v = 1 state by N2 is estimated to be 2×10−9 cm3/s, which is approximately twice the reported value for quenching of the v = 0 state. Relative quenching of N+2(B 2Σ) by He was found to be unmeasurably small.
Rotational relaxation rates in HF and Ar–HF from the direct inversion of pressure broadened linewidths
Authors: BelBruno Joseph J. , Gelfand Jack , Rabitz Herschel
Published: February 2003

Self- and argon-broadened HF linewidths have been inverted to obtain state-to-state rate constants using the energy corrected sudden (ECS) scaling theory inversion procedure. Both rotation–translation and rotation–rotation rates are presented as a function of vibrational level. We find that rotation–rotation processes are dominant for relaxation in pure HF and that these processes decrease with increasing vibrational excitation of one of the collision partners. We also find that the contribution of rotation–translation mechanisms increases with increasing vibrational excitation.
Transient spontaneous Raman observation of the reaction dynamics of triplet quinoxaline in aqueous solution
Authors: Beck S. M. , Brus L. E.
Published: February 2003

A sensitive apparatus for transient spontaneous Raman studies of reactions in solution is described. The apparatus involves two Nd:YAG lasers coupled with multichannel, low noise spectral detection. The technique is applied to the chemistry of aqueous triplet quinoxaline (1,4-diazanaphthalene). The transient Raman spectra exhibit a sequence of previously unobserved protonation reactions, showing the chemistry to be more complex than appeared in earlier transient absorption studies. The spectra are sensitive to acidic deuterium substitution in the protonated triplet T1H+, and (apparently) the diprotonated triplet T1H2++.
Analytical solution of the linearized Poisson–Boltzmann equation in cylindrical coordinates
Authors: Rice Richard E. , Horne Frederick H.
Published: February 2003

By separating the electrical potential into an applied part and an internally induced part, we can write the linearized Poisson–Boltzmann equation as two equations, each of which can be transformed into a modified Bessel equation. The reciprocal of the Debye length is written as the product of a constant and an axial-dependent function that describes the ionic strength distribution. It is possible to solve for the applied part of the potential only when the function is know explicitly, but the solution of the internally induced part remains completely general. The complete solution provides a means for testing assumptions of various ionic strength distributions within the accuracy of the linearized Poisson–Boltzmann equation. (AIP)
Localization of excess electrons in a compressible nonpolar fluid
Authors: Ichikawa Tsuneki , Yoshida Hiroshi
Published: February 2003

A cavity model for the localization of excess electrons in a compressible nonpolar fluid is proposed. The model is based on a semicontinuum potential framework in which the electrostriction of the fluid around the localized electrons is taken into consideration. The total energy of electron localization is taken as the sum of the electronic binding energy and the energy of cavity formation. The former is estimated through the use of an approximate polarization potential and the minimum energy V0 for quasifree electrons. The latter is composed of a surface work, pressure–volume work, and compression work. The model shows that the ground states of the excess electrons in dense liquid ethene are localized, whereas in the fluid at <13 mol/dm3 they are quasifree. With decreasing fluid density the total energy of electron localization increases, passes through a maximum near the density at minimal V0, decreases, passes through a minimum near the critical density, and increases again. It is indicated that in the high density fluid the excess electron is localized in a vacuum cavity mainly due to a repulsive interaction with surrounding molecules, whereas in the low density fluid the electron can be localized in cluster with a cavity at the center. The density dependence of the electron mobility has been discussed on the basis of the present model.
Dynamical thresholds and quantum undulations in the energy dependence of rotationally inelastic integral cross sections
Authors: Schinke Reinhard
Published: February 2003

We report the observation of distinct structures in the energy dependence of rotationally inelastic integral cross sections for the systems He–Na2 and Ne–Na2. The calculations are performed within the infinite-order-sudden and the coupled states approximation using accurate ab initio potential energy surfaces. The integral cross section for a 0→j′ transition typically rises steeply at low energies, reaches a maximum, and declines slowly to the high energy region showing more or less pronounced quantum undulations. The onset of the cross section is determined by dynamical constraints rather than energy conservation. All structures in the integral cross sections are explained in terms of the energy dependence of rotational rainbow features in the corresponding differential cross sections. In particular, the undulations at higher energies stem from the supernumerary rotational rainbows. In this sense they are interpreted as analogous to the glory maxima in the elastic integral cross section for scattering from isotropic potentials. The observed structures are sensitive to the anisotropy of the repulsive branch of the potential energy surface.
Investigations of static properties of two-dimensional bulk polymer systems
Authors: Bishop Marvin , Ceperley David , Frisch H. L. , Kalos M. H.
Published: February 2003

The static properties of two dimensional excluded volume continuum multichain systems are investigated by a ’’reptation’’ Monte Carlo algorithm. All beads interact via a repulsive (shifted) Lennard-Jones potential. In addition, nearest neighbors along chains are linked by a quasiharmonic potential which permits limited pair extensions. Chain lengths of 5, 10, 20, 32, 50, and 70 beads have been studied. Studies at densities of 0.1, 0.3, and 0.5 demonstrate that chain dimensions are compressed as the concentration is increased. Both the mean square end-to-end distance <R≳, and the mean square radius of gyration <S2≳ have a power law dependence upon l-1, the number of bonds, with exponent approximately 1.44 for ρ = 0.1, 1.33 for ρ = 0.3, and 1.20 for ρ = 0.5. The asphericity ratios indicate the extent of compression as the density is increased. In addition, nonexcluded volume chains are studied via straightforward Monte Carlo integration. <R2≳ and <S2≳ have a power law dependence upon l-1 with exponent 1.00.
The ground state and zero-field splitting of the GdO molecule
Authors: Van Zee R. J. , Ferrante R. F. , Zeringue K. J. , Weltner W.
Published: February 2003

The X-band ESR spectrum of GdO was obtained in an argon matrix at 4 °K as a series of 16 fine-structure lines between 0 and 12 000 G. Analysis proved that most of these lines were due to off-principal-axis transitions and established the ground state as 9Σ. An accurate fit to the data required the inclusion of a small b40 term (quartic in Sz) besides the usual b20 = D term in the spin Hamiltonian. The derived parameters in an argon matrix are g∥ = 1.990(9), g⊥ = 1.986(5), ‖ b20 ‖ = ‖ D ‖ = 0.2078(3) cm−1, and ‖ b40 ‖ = 0.000 40(5) cm−1. The two strongest lines were also observed in a neon matrix.
Study of OCS by electron energy loss spectroscopy
Authors: Leclerc B. , Poulin A. , Roy D. , Hubin-Franskin M.-J. , Delwiche J.
Published: February 2003

A high resolution study of the OCS molecule is presented using low-energy electron energy loss spectroscopy. Measurements have been carried out at various incident electron energies and scattering angles, covering the whole range from 5 to about 17 eV. The high energy resolution (∼30 meV) has allowed the detailed analysis of the vibrational progressions and Rydberg series, and some identifications are supported by the plots of their differential cross sections. For the first time, the two overlapping progressions of the (10σ) 1Π state, around 7.4 eV, are resolved by electron impact. A new triplet state is observed at 7.59 eV, assigned to the (11σ) 3Π known state, whose 1Π term would correspond to a known progression lying under the strong 1Σ+ band. Above the first ionization limit, the spectrum presents a striking similarity with the photoionization efficiency curves, with the strong autoionizing features which form Rydberg series converging to the ? 2Σ+ state of OCS+. Even the weak series VIII is present, appearing as a small dip. Further measurements carried out at low residual electron energy (?5 eV) reveal that such features then become peaks of strength comparable with the other features. Typical triplet behavior are pointed out for some of them. Two new series (X and XI) are thus proposed, while another feature is assigned to the n = 3 term of series VII converging to the ? 2Σ+ state. For all of the series observed in this region, the quantum defects are determined and orbital assignments are proposed.
Kinetic isotope effects: Theoretical prediction of the thermal rate coefficient for the reaction D+O2→OD+O
Authors: Miller James A.
Published: February 2003

Quasiclassical trajectory (QCT) and quasiclassical trajectory quantum mechanical threshold (QCT–QMT) calculations are reported for the reaction D+O2→OD+O. The thermal rate coefficient from the QCT–QMT analysis was determined to be k2 = 8.12×1015T−0.659 exp(−15 041/RT) cm3/mol s, for 250<T<2500 K, in excellent agreement with the experimental results available. Comparing with the QCT–QMT result [J. Chem. Phys. 74, 5120 (1981)] for (R1) H+O2→OH+O, the ratio k2/k1 is found to vary from 7.5 at 250 K to 0.8 at 2500 K. The primary isotope effects controlling this difference are the difference in zero-point vibrational energies of the product diatoms at low temperature and the difference in reactant collision frequencies at high temperature. In addition the calculations show slightly less negative Arrhenius curvature (n2 = −0.659, n1 = −0.816) for R2 than for R1, an effect anticipated from the previous analysis. However, the magnitude of the difference between n1 and n2 is approximately the same as estimates of the maximum uncertainty in the calculations themselves. It is concluded that a factor of 2 in the mass of the attacking atom is not sufficient to distinguish accurately differences in Arrhenius curvature arising from the L+HH mass combination of the reactants, either theoretically or experimentally.
The long time behavior of the rate of recombination
Authors: Pedersen J. Boiden , Sibani Paolo
Published: February 2003

Simple closed form expressions for the geminate and homogeneous recombination rates are given. These relations are valid for three-dimensional, spherically symmetric systems with arbitrary potential interaction, space dependent diffusion coefficient, and reactivity; they contain the previously derived expressions as special cases. For extremely long times the familiar t−3/2 (respectively, t−1/2) behavior is obtained, but the relations are valid also for shorter times where deviations from the simple behavior are important. Also included are closed form expressions for the partially diffusion controlled recombination probability. All expressions are derived from one fundamental quantity: the diffusion controlled recombination probability, which is given as an asymptotic series.
Electronegativities of the elements from a nonempirical electrostatic model
Authors: Boyd Russell J. , Markus George E.
Published: February 2003

An electrostatic model, according to which the electronegativity of an atom is identified with the electrostatic force between the effective nuclear charge and an electron at a distance equal to the relative radius of the atom, is used to calculate a nonempirical electronegativity scale for the first 54 elements. The relative radius is calculated from the free-atom wave function by use of the density contour approach, while intergration of the radial density from the nucleus to the relative radius yields the effective nuclear charge. In contrast to the empirical methods, the nonempirical electrostatic method is not only applicable to all elements, but treats all elements equally. In addition to correlating well with empirical scales, the proposed model is consistent with the major conclusions of the density functional approach of Parr and his co-workers. In particular, the model is easily extended to yield valence state electronegativities.
Diode laser study of the ν2 band of the methyl radical
Authors: Yamada Chikashi , Hirota Eizi , Kawaguchi Kentarou
Published: February 2003

The v2 = 1←0, 2←1, and 3←2 bands of the methyl radical were observed in the gas phase by infrared tunable diode laser spectroscopy at 606.4531, 681.6369, and 731.0757 cm−1. The observed vibration–rotation spectra were analyzed to derive precise values for the rotational constants, centrifugal distortion constants, and spin–rotation interaction constants. The absence of N = odd, K = 0 levels in the v2 = even states and of N = even, K = 0 levels in the v2 = odd states was confirmed, indicating that each vibrational state is nondegenerate. The observed band origins, when analyzed, led to a potential function for the out-of-plane bending vibration that has no potential hump at the planar configuration. The large negative anharmonicity of this potential was ascribed to a vibronic interaction with excited electronic states. The methyl radical was generated by a 60 Hz discharge in di-tert-butyl peroxide and was found to have a lifetime of about 1.4 msec; its concentration in the absorption cell was estimated to be about 1013 molecules/cm3, provided that a recombination reaction is the only route for eliminating methyl radicals.
Relaxation parameters for power-broadened microwave line shapes. II. Sudden approximation
Authors: Peterson Keith L.
Published: February 2003

A sudden approximation, utilizing linear trajectories and a dipole–dipole potential as developed by Cross [J. Chem. Phys. 55, 510 (1971)], is extended to enable calculation of collisional relaxation parameters of arbitrary tensor order. Expressions are given for linear rotors and symmetric tops. The relaxation parameters factorize into a dynamical part and an angular momentum part and are expressible as linear combinations of collisional transition probabilities out of the j = 0 rotational level. This is in agreement with previous discussions of the infinite order sudden approximation to the coupled states equations. An experiment is proposed which would enable the determination of all polarization relaxation times of a given transition. The results of such an experiment would help to define the validity of the sudden approximation in calculating relaxation cross sections. Finally, application of the sudden approximation to four-level double resonance experiments is discussed.
Superparamagnetic effects in the ferromagnetic resonance of silica supported nickel particles
Authors: Sharma V. K. , Baiker A.
Published: February 2003

A silica supported Ni catalyst has been investigated by electron magnetic resonance between 293 and 4.2 K. A relatively narrow absorption signal with linewidth ΔHpp?400 Oe is observed at temperatures ?150 K as a result of motional averaging of the magnetocrystalline anistropy field Ha of the Ni particles resulting from superparamagnetism. Broadening of the resonance occurs at lower temperatures because of a reduction of the influence of thermal fluctuations. A line shape analysis of the observed resonance signals is carried out employing the theory of ferromagnetic resonance in polycrystalline material. The calculated anisotropy field is reduced in the particles as compared to bulk Ni. The Landau–Lifshitz relaxation frequency obtained from the calculated ’’single crystal’’ linewidths are found to be larger than those of bulk Ni single crystals. Concurrently with line broadening, the resonance shifts to lower magnetic fields. The resonance shifts are approximately Ha/2. The appearance of magnetoelastic effects in the resonance below 120 K indicates the presence of small but significant strain in the particles resulting from particle-support interaction.
Resonance enhanced dynamic Rayleigh scattering
Authors: Stanton Susan G. , Pecora R. , Hudson Bruce S.
Published: February 2003

A semiclassical theory relating the molecular resonance Rayleigh scattering intensity to the extinction coefficient of an electronic transition is presented. For isotropic molecules, the theory is shown to be equivalent to classical fluctuation theory. The semiclassical theory is then extended to include anisotropic polarizabilities. Depolarized scattering intensities and depolarization ratios are calculated for a model system, and the general features of previous experimental data are explained. Inclusion of inhomogeneous broadening in the theory predicts increased scattering intensities and decreased vibrational resolution of the scattering profile. Depolarized Rayleigh linewidths and intensity profiles are presented for a series of diphenylpolyenes, several coumarin laser dyes, and 3,4-dinitrophenol in its neutral and ionic forms. The ideal molecular properties and experimental conditions for the use of resonance enhanced dynamic Rayleigh scattering are deduced.
Intersystem crossing in cold isolated molecules of naphthalene
Authors: Behlen Fred M. , Rice S. A.
Published: February 2003

We report the results of an extensive study of the rate of radiationless decay in very cold, isolated, naphthalene molecules. The experimental method employed, namely, pulsed narrow band laser excitation of a pulsed seeded supersonic free jet, avoids the complications imposed by the sequence congestion generated by the thermal excitation characteristic of ordinary vapor samples. Our analysis of the fluorescence decay includes a method for transforming room temperature quantum yield data to quantum yields characteristic of the molecules in the supersonic free jet. It is concluded that (a) the out of plane vibration 2(b2g) is very likely a promoting mode for intersystem crossing; (b) there is no need to invoke near resonant coupling of levels in the prepared singlet and final triplet manifolds to explain features of the radiationless decay; and (c) in general, the broad features of radiationless decay in naphthalene are very much like those of the corresponding decay in benzene, and can be similarly explained.
Picosecond kinetics of p-dimethylaminobenzonitrile
Authors: Huppert D. , Rand S. D. , Rentzepis P. M. , Barbara P. F. , Struve W. S. , Grabowski Z. R.
Published: February 2003

The nanosecond and picosecond resolved dual fluorescences of p-dimethylaminobenzonitrile (DAB), in various solvents and glasses excited by 266 nm 20 ps FWHM laser pulses, have been investigated. Pulse-limited rise times are exhibited by the b*-state emission whose decay in turn feeds directly the risetime of a*-state emission at 440–600 nm in most solvents studied. The a*-state emission was monitored at 520–600 nm in order to eliminate contribution from the b*-state. Within the experimental resolution, the b*-state fluorescence decay times vary approximately linearly with solvent viscosity. The a*-state fluorescence decay times vary with both solvent and temperature, and may reflect either thermally assisted intersystem crossing from the solvated singlet a*-state (presumably of twisted internal charge transfer character) to a corresponding solvated triplet of slightly higher energy, or a thermally activated internal conversion of the 1TICT to the ground state.
Experimental appraisal of the maximal-entropy theory of multiphoton ionization-fragmentation: The alternative ionization pathway test
Authors: Lichtin D. A. , Bernstein R. B. , Newton K. R.
Published: February 2003

An experimental test of the Silberstein–Levine (SL) maximal-entropy theory of multiphoton ionization-fragmentation has been devised and applied to a diverse group of polyatomic molecules. The MPI fragmentation pattern of a given compound is strongly dependent upon the laser wavelength (which governs the ’’pathway’’ to the continuum) and the laser power density (and pulse energy). Nevertheless, it is found possible to obtain similar fragmentation patterns at several wavelengths (i.e., via different pathways) by adjusting the laser power so as to excite the molecule/ion system to the same average value of internal energy 〈E〉. Data are presented for benzene, toluene, t-butylbenzene, triethylenediamine, quinuclidine, and iodomethane, all of which tend to confirm the major premise of the SL theory that the branching fraction pattern is governed by the single parameter 〈E〉.
Statistical fragmentation patterns in multiphoton ionization: A comparison with experiment
Authors: Silberstein J. , Levine R. D.
Published: February 2003

Breakdown curves computed in the statistical limit are presented for benzene, toluene, t-butylbenzene, triethylenediamine, and iodomethane. The statistical limit is that of the fragmentation pattern of maximal entrophy (subject only to conserved quantities). In this limit the fragmentation pattern is governed by the mean energy 〈E〉 absorbed per molecule. By varying 〈E〉 it is found possible to span the range from low to extensive fragmentation. For the five molecules tested, the statistical limit reproduces the experimental multiphoton ionization-fragmentation patterns reported by Lichtin, Bernstein, and Newton as is expected on the basis of their experimental, ’’alternative doorway’’ appraisal. Another prediction, not yet tested by experiment, is that in the statistical limit it should prove possible to obtain similar fragmentation patterns for different isomers (e.g., naphthalene and azulene). Internal state distributions offer a third way in which the statistical limit can be compared with experiment.
Wave functions in momentum space. I. Iterative computation for the helium atom in Hartree–Fock approximation
Authors: Monkhorst Hendrik J. , Szalewicz Krzysztof
Published: February 2003

The possibilities of obtaining wave functions for atoms and molecules by iteration of equations in momentum space have been examined. Using a first-iterate orbital some approximations to the Hartree–Fock ground state energy have been calculated. The accuracy of these results is strongly dependent on a variation of the parameters that characterize the orbital. The second-iterate orbital contains logarithmic and arctangent functions and there appear unfamiliar special functions in the third- and higher-iterate orbitals.
Kinetic study of the conversion of presolvated to solvated silver atoms in polycrystalline ice: Activation energy of water molecule rotation with D-defect annihilation
Authors: Li A. S. W. , Kevan Larry
Published: February 2003

The kinetics of the conversion of presolvated silver atoms formed in polycrystalline ice at 4 K to the solvated state has been studied in the temperature range of 38 to 49 K. The kinetics are approximately first order and give an activation energy of 0.09±0.01 eV. This is lower than the 0.24 eV activation energy for diffusion of orientational defects by water molecule rotation in ice and is identified with water molecule rotation together with D-defect annihilation in the silver atom solvation shell. (AIP)
Diffusion theory of reaction rates for multiple potential barriers
Authors: Mangel Marc
Published: February 2003

The diffusion theory of reactions, due to H. Kramers, is studied in the case where the reaction coordinate moves in a potential that has n barriers separating reactant and product states. Exact and asymptotic (for large barriers) values of the rate constant are derived and the dependence of the rate constant on viscosity and on temperature is studied. Particular attention is paid to the interpretations of the results, since there are a number of experiments of present interest that are thought to involve systems with multiple barriers. (AIP)
A light scattering study of orientation of liquid-crystalline rodlike textures of poly(γ-benzyl-L-glutamate) in an electric field by saturation electric birefringence method
Authors: Matsuo Masaru , Kakei Kumiko , Nagaoka Yoshie , Ozaki Fumihiko , Murai Masato , Ogita Tetsuya
Published: February 2003

The orientation behavior of liquid crystalline solutions of poly (-γ-benzyl-L-glutamate) (PBLG) in chloroform under an electric field was investigated with respect to characteristic electro-optical properties of macromolecules using small angle light scattering and birefringence techniques. The Hv light scattering pattern showed a circular type in the absence of an applied field. This indicates large orientation disorder of optical axes with respect to the molecular cluster axis. When an electric field was applied, the scattering pattern became X type, characterizing the scattering from rodlike textures being a sort of molecular cluster and the scattering lobes were extended to the horizontal direction. This means the preferential orientation of the molecular cluster in the direction of an electric field. In order to analyze the variation of the scattering pattern with increasing electric field, we have carried out theoretical calculations of the basis of a model. In this model system, the orientation distribution function of rods was assumed to be the steady-state orientation distribution function of macromolecules under an electric field which was proposed to investigate electric properties of a dilute solution of rigid macromolecules by O’Konski et al. By using this method, the electric parameters and the optical anisotropy factor of PBLG molecules were separately determined by fitting the experimental birefringence saturation results to the theoretical curve proposed by O’Konski et al. Thus, the steady-state distribution function was determined, and consequently the light scattering patterns were calculated as a function of an electric field strength. The calculated results were found to be rather close to observed ones with a proper choice of parameter associated with the magnitude of the disorder of the optical axes.
Collisionless intramolecular vibrational energy transfer in methyl formate
Authors: Stewart G. M. , McDonald J. D.
Published: February 2003

Direct observation by state resolved infrared fluorescence of the fate CH stretching vibrational energy deposited in an intermediate sized molecule methyl formate, by a single infrared photon is reported. (AIP)
Vibrational overtone spectroscopy of benzene and pyridine on Ag(111)
Authors: Avouris Ph. , Demuth J. E.
Published: February 2003

Electron energy loss spectroscopy is used to study vibrational overtones for monolayer converages of pyridine and benzene adsorbed under UHV conditions.(AIP)