bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-mode tapered waveguide laser in Er-doped glass with multimode-diode pumping
Authors: Madasamy Pratheepan , Honkanen S. , Geraghty D. F. , Peyghambarian N.
Published: February 2003

We report on a demonstration of a planar waveguide laser configuration for single-mode operation around 1550 nm using cost-effective multimode diode pumping. The laser was fabricated by Ag film ion exchange in a hybrid phosphate glass which has active and passive regions monolithically integrated in a single glass chip. Power of 54 mW at 1538 nm was measured from the single-mode output waveguide.
Self-limiting size control of hemispherical grains of microcrystalline Si self-assembled on an amorphous Si film surface
Authors: Akazawa Housei
Published: February 2003

When a hydrogen-free amorphous silicon film deposited by rf plasma sputtering is annealed at temperatures above 540 °C, hemispherical grains of microcrystalline Si nucleate on its surface. The film surface is maintained macroscopically flat without any protrusions around the grains, indicating that only Si atoms at the outermost surface aggregate into grains. The size distribution of the grains was very narrow; the deviation from the mean was less than 8%. Even when the annealing temperature was varied between 600 and 850 °C, the mean base radii and the mean heights of the grains stayed within the ranges of 45 to 48.5 and 35 to 42 nm, respectively. Also, 3 h of annealing produced a saturation of the self-assembling process. This observation suggests that the grain size can be controlled in a self-limiting manner in terms of the temperature and period of annealing.
Surface plasmon transmission across narrow grooves in thin silver films
Authors: Seidel J. , Grafström S. , Eng L. , Bischoff L.
Published: February 2003

We report on the direct measurement of surface plasmon transmissivity of narrow grooves in thin silver films using near-field optical microscopy in an attenuated-total-reflection setup. For different groove widths, we observe characteristic changes in transmissivity that are attributed to resonant gap modes. The results are in good agreement with existing theoretical predictions.
Comments on the quantum Monte Carlo method and the density matrix theory
Authors: dos Santos Politi José Roberto , Custodio Rogério
Published: February 2003

Density matrix theory is implemented in a variational quantum Monte Carlo computation of electronic properties of atoms and molecules. Differences between electronic densities from conventional and density matrix methods are detected. However, calculated properties present similar behavior and partial antisymmetry can be ignored in the cases studied.
Compressive stress relaxation through buckling of a low-k polymer-thin cap layer system
Authors: Iacopi F. , Brongersma S. H. , Maex K.
Published: February 2003

The thermomechanical stability of a system composed of a metallic cap layer on top of a low-k thermosetting polymer film is investigated. It is observed that, when metal layers with high compressive stresses are used, a stress relaxation takes place during thermal anneal at temperatures above 300 °C through buckling of the two-layer system (wrinkling on rigid base). When designing low-k films for interconnects, this should be considered through a careful analysis of structural stability. The onset of this instability is allowed by the high compliance of the polymeric film, due to its transition from elastic to viscoelastic behavior through creep phenomena. This mechanism is more pronounced when a polymer film with 20% subtractive porosity is used.
Trajectory studies of model H–C–C→H+C=C dissociation. I. Random vibrational excitation
Authors: Wolf Ralph J. , Hase William L.
Published: February 2003

Classical trajectories were used to study H–C–C→H+C=C dissociation on ten different empirical potential energy surfaces. The surfaces were modified so that the effect of various surface properties on the unimolecular dynamics could be investigated. Surfaces with early dissociation barriers were found to give intrinsically non-RRKM lifetime distributions, but RRKM translational energy distributions at the exit-channel barrier. The final product translational energy distributions for these surfaces are strongly nonstatistical. This arises from exit-channel coupling, which involves HC-stretch–CC-stretch interactions and not HC-stretch–HCC-bend interactions. Surfaces with late barriers yield intrinsically RRKM lifetime distributions and statistical product translational energy distributions.
The inhomogeneous Airy functions, Gi(z) and Hi(z)
Authors: Lee Soo-Y.
Published: February 2003

Accurate and efficient algorithms are derived for evaluating the inhomogeneous Airy functions that arise in Raman scattering, predissociation, construction of wave functions for nonlocal potentials and wave forms in a dispersive medium. By a proper choice of the integral representation for the inhomogeneous Airy functions the problem of poles in the approximate sum that Gordon encounters does not arise.
Rotational relaxation, anharmonic shifts, and excited state absorption in CH3CHF2
Authors: Kung R. T. V. , Friedman H. W.
Published: February 2003

An intense nsec CO2 laser pulse was used to deplete a fraction of the rotational population of CH3CHF2. Rotational redistribution was monitored with a cw probe laser. The measured rotational self-relaxation rate constant is ∼1.7×10−9 cm3/sec. The rate constants for relaxation collisions with H2 and N2 are 2.9×10−10 and 1.1×10−10 cm3/sec respectively. Measurements of the instantaneous absorption of excited vibrational levels which are directly populated by the short pulse laser, yield anharmonic shifts (2ω3χe) of ∼7.5 cm−1 for the 942 cm−1 C–F stretch mode of this molecule.
Depolarized Rayleigh scattering near the critical point of the nitroethane–isooctane mixture
Authors: Zalczer G. , Beysens D.
Published: February 2003

Intensity and linewidth measurements of the depolarized Rayleigh line in the critical mixture of nitroethane and isooctane in the temperature range T−Tc=2 m°K−60°K are reported. The linewidth presents no anomaly and behaves like the regular part of the viscosity. The intensity however exhibits a linear anomaly which levels off for T−Tc≳35°K.
Theory of phase transitions in crystals of long-chain molecules and the application to n-paraffins
Authors: Ishinabe Takao
Published: February 2003

A statistical theory of crystals of long-chain molecules is developed in terms of the mean-field approximation. Simultaneous-transcendental equations describing states of the system, which has a somewhat complicated interchain potential, are derived; they are solved in a few simple cases. The rotational transition and melting of n-paraffins along with a correlation between them are explained using the results.
Comparative study of the gradient expansion of the atomic kinetic energy functional-neutral atoms
Authors: Murphy Danny R. , Wang Wen-Ping
Published: February 2003

In a previous work, it has been shown that for the noble gas atoms, the ground state kinetic energy functional T[ρ], where ρ is the electronic density, can be computed to surprising accuracy from the truncated gradient expansion: T[ρ]=T0[ρ]+T2[ρ]+T4[ρ], with T0[ρ] =3/10(3π2) ℱρ5/3dτ, T2[ρ]=1/72ℱ (∇ρ)2/ρdτ, and T4[ρ] given by the formula of Hodges. In this work, we report systematic calculations for improved near-Hartree–Fock atomic densities up to Z=54. We find that the truncated gradient expansion of T[ρ] can also lead to very good kinetic energies for open-shell and unpaired-electron atoms. The value given by T[ρHF] generally gets better, as compared with the Hartree–Fock result, as Z increases. For the Xe atom, T0+T2+T4 is within 0.08% of the exact Hartree–Fock kinetic energy with T2/T0=0.048, T4/T2=0.16. It is interesting to note that some minima appear in the deviation curves for T0, T0+T2, and T0+T2+T4, as compared with Hartree–Fock results. For the near-degenerate ground and lower excited states of some atoms, the truncated kinetic energy expansion can reproduce the relative kinetic energies qualitatively. On the other hand, because the cusp condition at the atomic nucleus and the exponentially vanishing density are valid for every Hartree–Fock density, it may not be possible to reproduce the Hartree–Fock or exact results with the gradient expansion in a systematic way.
A new general methodology for deriving effective Hamiltonians for atoms and molecules. Application to the transferability of atomic potentials in the hydrocarbon series
Authors: Nicolas G. , Durand Ph.
Published: February 2003

A new general methodology for deriving, from first principles, effective Hamiltonians by Fourier techniques is presented. The Fock operator is shown to be a particular one-electron effective Hamiltonian. Other one-electron effective Hamiltonians are suggested. The methodology is applied to a first study of the transferability of atomic potentials in the hydrocarbon series.
Absolute rate constant for the chemiluminescent reaction of atomic oxygen with nitric oxide
Authors: Sutoh Masako , Morioka Yumio , Nakamura Masatoshi
Published: February 2003

The absolute rate constant for light emission from the NO–O reaction has been determined, as a function of wavelength, by using a standard brightness source, which has a surface of uniform brightness. The spectral distribution measured between 0.4 and 1.4 μm is in good agreement with those of the previous studies except for a little difference in the near infrared region. The influence from NO–O3 chemiluminescence is demonstrated for atomic oxygen production from O2 discharges.
An experimental survey of the reactions of NHn+ ions (n = 0 to 4) with several diatomic and polyatomic molecules at 300 K
Authors: Adams Nigel G. , Smith David , Paulson John F.
Published: February 2003

A study has been made of the binary reactions at 300 K in a SIFT apparatus of the ions N+, NH+, NH2+, NH3+, and NH4+ with CH3NH2, NO, NH3, H2S, CH3OH, H2CO, COS, O2, H2O, CH4, CO2, CO,H2, and N2. The N+, NH+, and NH2+ reactions are generally fast, their rate coefficients being close to the collisional limit, and multiple product channels result, especially for reactions with the polyatomic molecules. Several reaction mechanisms are apparent, including charge transfer, proton transfer, and H-atom abstraction, although it is argued that many of the reactions proceed via a short-lived, ion–molecule complex which separates along the observed reaction channels. The NH3+ ions are seen to be generally less reactive than the lesser hydrogenated ions, the product of most of the reactions being HN4+ ions which do not undergo binary reactions with any of the molecules (except CH3NH2) but rather undergo ternary association reactions with a few of them. A few measurements were made using the deuterated analogs ND+, ND2+, ND3+, and ND4+ in order to shed further light on some of the reaction mechanisms.
A semiclassical series solution of the generalized phase shift atom–diatom scattering equations
Authors: Squire Kevin R. , Curtiss C. F.
Published: February 2003

A semiclassical series solution of the previously developed operator form of the generalized phase shift equations describing atom–diatom scattering is presented. This development is based on earlier work which led to a double series in powers of Planck’s constant and a scaling parameter of the anisotropic portion of the intermolecular potential. The present solution is similar in that it is a double power series in Planck’s constant and in the difference between the spherical radial momentum and a first order approximation. The present series solution avoids difficulties of the previous series associated with the classical turning point.
The photoconduction threshold in anthracene single crystals
Authors: Kato Keishi , Braun C. L.
Published: February 2003

We report the excitation spectrum for intrinsic photoconductivity measured with unpolarized light incident on the 001 face of an anthracene single crystal. Over the photon energy range 3.75 to 4.4 eV, the room temperature (near 295 K) quantum yield of free carriers rises by a factor of 103. The activation energy for free carrier production rises steeply between 3.87 and 4.06 eV and then levels off. These results are compared with recent work by Lyons and Milne and some discrepancies are noted.
Dynamics of van der Waals molecules: A scaling theoretical analysis of I2*He
Authors: Ramaswamy Ramakrishna , DePristo Andrew E.
Published: February 2003

A variational method is used to analyze the vibrational predissociation of I2*He. (AIP)
ESR study of the phenylselenonyl radical trapped in a single crystal
Authors: Geoffroy M. , Leray N.
Published: February 2003

Diphenylselenone crystals were exposed at 77 °K to the radiation of a 60Co source. The ESR spectra of resulting species of radicals are reported. (AIP)
Comments on ‘‘A classical/semiclassical theory for the interaction of infrared radiation with molecular systems’’
Authors: Milonni P. W.
Published: February 2003

Miller’s conclusion regarding spontaneous emission in ref. (1) is disputed upon. The question of whether the induced and spontaneous emission processes are essentially classical phenomena is discussed in this note. (AIP)
Flow birefringence and hydrodynamic boundary conditions
Authors: Calef Daniel F. , Wolynes Peter G.
Published: February 2003

The correct choice of boundary conditions for applying hydrodynamics to molecular transport properties has been widely discussed. In this paper, we explore the possibility that flow birefringence data can be used to distinguish between the stick and slip boundary conditions. We present results for the flow birefringence from ellipsoidal particles. We discuss the related phenomena of the Rytov dip in depolarized light scattering. We report calculations for this dip for both boundary conditions. The use of mixed boundary conditions is also discussed.
Stochastic modeling of generalized Fokker–Planck equations. I.
Authors: Stillman Arthur E. , Freed Jack H.
Published: February 2003

A relatively simple method is developed whereby the many-body features of a typical generalized Fokker–Planck equation (GFPE) for a diffusing molecule are first replaced by stochastic bath variables that are assumed to be Markovian. Then the combined molecular and bath variables are characterized as a multidimensional Markov process obeying a stochastic–Liouville equation, which is, in general, incomplete, because it ignores the back reaction of the molecule on the bath variables. In the final step, the equation is completed by subjecting it to the appropriate constraints required for detailed balance. In this form the augmented Fokker–Planck equation (AFPE) properly describes relaxation to thermal equilibrium, and, for the appropriate limiting conditions, it reduces to the classical Fokker–Planck equation. This procedure for stochastic modeling of GFPE is both an improvement on and a generalization of a method previously outlined by Hwang, Mason, Hwang, and Freed (HMHF). Detailed illustrations of AFPE’s are presented for the simple case of a planar rotator subjected to fluctuating torques, and these models are extended to the case of three-dimensional rotational diffusion. Examples include fluctuating torque models related to that used by HMHF. It is shown that only if the fluctuating torque is independent of the orientation of the molecule (more precisely of any fluctuating equilibrium orientation of the molecule), does the model become equivalent to the usual generalized Langevin equation. Otherwise, more general nonlinear models are obtained, which, however, are easily handled by the present methods. Models related to the slowly relaxing local structure (SRLS) model of Polnaszek and Freed are also developed. They are shown to be a consequence of requiring relaxation to the instantaneous value of the fluctuating potential associated with the torque, whereas the fluctuating torque models are a consequence of requiring relaxation to a uniform orientational distribution. They differ further in that the SRLS models are ’’nonfrictional’’. For these reasons we characterize the fluctuating torques as being ’’collision-induced’’ and the SRLS as being ’’structure-induced’’.
ESR studies of radical pairs of galvinoxyl radical in corresponding phenol matrix
Authors: Mukai Kazuo , Sogabe Akemi
Published: February 2003

ESR studies have been carried out on powder samples of galvinoxyl radical doped in its diamagnetic corresponding phenol matrix, which has the same crystal structure with that of galvinoxyl. The existence of a radical pair of the galvinoxyl has been confirmed by the observation of the ESR zero-field splitting and half-field resonance of its powder sample containing 0.3%–6.0% galvinoxyl in the phenol matrix. The zero-field splitting parameters ‖D‖ and ‖E‖ have been determined to be 81.4±0.3 and 16.0±0.3 G, respectively, being independent on radical concentration. The D and E parameters were calculated for the four kinds of radical pairs existing in the crystal, based on the molecular structure and packing in crystalline galvinoxyl investigated by D. E. Williams. The calculations were performed, using (i) point-charge, (ii) half-charge, and (iii) point-spin approximations, and the obtained results were compared to each other. Consequently, the observed radical pair of galvinoxyl was attributed to a nearest-neighbor radical pair.
Three dimensional quantum mechanical studies of D+H2→HD+H reactive scattering. III. On the a
b i
n
i
t
i
o potential energy surface
Authors: Yung Y. Y. , Choi B. H. , Tang K. T.
Published: February 2003

Three dimensional quantum mechanical calculations are carried out for the reactive scattering of D+H2→DH+H on the ab initio potential energy surface calculated by Liu and Siegbahn and fitted by Truhlar and Horowitz. The differential and total cross sections as well as the S matrix elements are obtained from the adiabatic distorted wave method. Threshold energy, cross sections and product distributions over final states are all in good agreement with experimental measurements. Results are also compared with the corresponding ones obtained on the Porter–Karplus and the Yates–Lester semi-empirical surfaces.
The magnetic properties of several quasi two-dimensional Heisenberg layer compounds: A new class of ferromagnetic insulators involving halocuprates
Authors: Estes William E. , Losee D. Bruce , Hatfield William E.
Published: February 2003

Magnetic susceptibility measurements on powdered samples of bis(benzylammonium) tetrachlorocuprate (II), bis(phenethylammonium) tetrachlorocuprate(II), bis(3-phenyl-1-propylammonium) tetrachlorocuprate(II), and bis(benzylammonium) tetrabromocuprate(II) have shown that these four substances order ferromagnetically with Curie temperatures of 8.0±0.5, 9.0±0.2, 7.0±0.5, and 12.3±1.0 K, respectively. Fits of a series expansion for a two-dimensional lattice to the magnetic susceptibility data obtained from powdered samples in the paramagnetic region yielded exchange constants J for the chloride compounds in the range 16.7–18.8 K, and a value of 25.3 K for the bromide compound. For these fits the <g≳ value of 2.14±0.01 determined from EPR measurements was used. Magnetic susceptibility measurements made at 10 Oe on a single crystal of bis(phenethylammonium) CuCl4 at temperatures just below Tc revealed ratios of susceptibilities of 30:7:1 along the c, a, and b axes, respectively, where the b axis is perpendicular to the thin tabular plates. Magnetization measurements on a single crystal sample of this compound showed that the easy axis, the c axis, and the next-preferred axis, the a axis, were saturated above 60 and 200 Oe, respectively, while magnetic fields greater than 1800 Oe were required for saturation along the b axis. Magnetization measurements on a single crystal of bis(benzylammonium) tetrabromocuprate(II) did not reveal any anisotropy within the plane of the plate, where the saturation field was 50 Oe at 4.2 K, while a field of 1800 Oe was required for saturation along the direction perpendicular to the plate. Anisotropy fields derived from the magnetic susceptibility and magnetization data obtained from measurements on single crystals of bis(benzylammonium) tetrachlorocuprate(II) and bis(phenethylammonium) tetrachlorocuptrate(II) cannot be explained by the calculated exchange and dipolar fields, and it is suggested that an additional mechanism contributes to the anisotropy.
The symmetry groups of nonrigid molecules as generalized wreath products and their representations
Authors: Balasubramanian K.
Published: February 2003

The symmetry groups of nonrigid molecules first defined by Longuet–Higgins, in the most general cases are generalized wreath product groups. We first outline the representation theory of wreath product groups. Then the representation theory of generalized wreath product groups is developed. Several illustrative examples of NMR groups are offered. The character tables of several nonrigid molecular groups are presented. An example of a nonrigid triphenyl molecule is given to illustrate the use of the generalized wreath product in deriving optical selection rules.
Normal mode calculations of trigonal selenium
Authors: Hansen Flemming Y. , McMurry H. L.
Published: February 2003

The phonon dispersion relations for trigonal selenium have been calculated on the basis of a short range potential field model. Electrostatic long range forces have not been included. The force field is defined in terms of symmetrized coordinates which reflect partly the symmetry of the space group. With such coordinates a potential energy, calculated with only a diagonal force matrix, is equivalent to one calculated with both off diagonal and diagonal elements when conventional coordinates are used. Another advantage is that often some force constants may be determined directly from frequencies at points of high symmetry. The intrachain force field is projected from a valence type field including a bond stretch, angle bend, and dihedral torsion. With these coordinates we obtain the strong dispersion of the upper optic modes as observed by neutron scattering, where other models have failed and give flat bands. The interchain force field is projected from relative rotations and translations of groups of atoms in adjacent chains. This type of coordinate is very well adopted to describing interactions between groups of nonbonded atoms as found in molecular crystals, and they also seem to apply very well for this crystal. In this way we have eliminated the ambiguity in the choice of valence coordinates, which has been a problem in previous models which used valence type interactions. Calculated sound velocities and elastic moduli are also given.
The ground state of rhombohedral crystals in an external magnetic field
Authors: Theophilou A. K. , Thanos S.
Published: February 2003

This paper deals with the ground state of spin systems in an external magnetic field interacting with dipole–dipole and exchange interactions. The Luttinger and Tisza approach is adopted. By using group theoretic techniques a simplified form of the equation and constraints results. It is shown that the ground state problem can be solved by using only two out of the eight constraints. Application has been made in the case of cerium magnesium nitrate (CMN). It is found that in general the magnetic moment increases with the magnetic field but it is not parallel to it. Above a critical field hc the crystal goes into the metamagnetic state. Comparison is made with the experimental results.
Vibrational relaxation cross sections and rates of equilibration in electronically excited benzene (2537 Å excitation)
Authors: Logan L. M. , Buduls I. , Knight A. E. W. , Ross I. G.
Published: February 2003

The fluorescence spectrum of benzene vapor, excited to a vibrational level 6211 of the 1B2u state by Hg 2537 Å, has been studied in the presence of up to 600 Torr of 16 different added gases. Benzene-d6 has been similarly studied in the presence of N2 and CO2. Low pressure data yield cross sections (which are of the order of hard sphere) for the process 6211→ other vibrational states which conform with the expectation of H. M. Lin, M. Seaver, K. Y. Tang, A. E. W. Knight, and C. S. Parmenter, [J. Chem. Phys. 70, 5442(1979)] that such cross sections should be determined by the intermolecular well depths. High pressure data yield efficiencies in respect of bringing about vibrational equilibration. Estimated average energies lost per hard sphere collision are broadly determined by the number of degrees of vibrational freedom possessed by the colliding molecules. Quantum yields decline to a limiting value as the 6111 state is depopulated.
Partial photoionization cross section and photoelectron angular distribution for the X 2Σg+ state of N2+ in the static-exchange approximation
Authors: Raseev G. , Le Rouzo H. , Lefebvre-Brion H.
Published: February 2003

The partial photoionization cross section of N2 leading to the production of N2+ in its X 2Σg+ ground state is calculated in the single-center frozen core static-exchange approximation. The initial and final states are antisymmetrized products using SCF molecular orbitals of either N2 or N2+ ground states. All these calculations reproduce well the σu shape resonance in the partial cross section. The photoelectron angular distribution is also calculated and the average over the vibrational motion is performed. The R-averaged results are in agreement with recent measurements using synchrotron radiation. The branching ratio of the cross sections leading N2+ in its two lowest vibrational states compares rather well with the experimental values obtained recently by West et al.
Electron propagator theory of molecular anions
Authors: Ortiz B. J. V. , Öhrn Yngve
Published: February 2003

Recent developments of self-energy approximations, using renormalization techniques, are applied to the problem of calculating molecular electron affinites as poles of the electron propagator. Particular emphasis is put on the size of orbital bases used. The CN and the Cl2 molecules are studied and the results show promising agreement with recent experiments.
Multiple stationary points in open chemically reacting systems. Minimal requirements
Authors: Karmann Klaus-Peter , Hinze Juergen
Published: February 2003

We examine homogeneous open chemical reaction systems under constant temperature and pressure with two species, and show that, if the concentration of one species is held constant in time by coupling the system to an infinite reservoir, there is exactly one stationary point, independent of the reaction mechanism. Hence for an open system to have more than one stationary point, the reaction mechanism must involve at least three species, two of which may be held constant. This result contradicts some recent papers on the behavior of certain model reaction systems.
Molecular dynamics simulation of the plastic phase of solid methane
Authors: Bounds David G. , Klein Michael L. , Patey G. N.
Published: February 2003

A molecular dynamics (MD) calculation has been carried out for a model of solid methane at a state condition close to the triple point. We have used systems of 32 and 108 molecules interacting via atom–atom potentials. Equilibrium properties such as the configurational energy, pressure, and specific heat have been evaluated and compared where possible with experimental data. The simulated static structure factor has been analyzed assuming that rotational and translational motion can be decoupled and that the rotational structure factor can be developed as a power series in Kubic harmonics. This description is shown to yield a reasonably faithful representation of the structure in the plastic phase. The dynamical structure factor S(Q,ω) has been calculated for selected values of the momentum transfer h/Q. These results have been used to estimate the velocity of sound and hence the elastic constants. The overall agreement of the dynamical properties with experiment is not particularly good, indicating the need for a more refined intermolecular potential.
Measurement of the rate coefficients for the bimolecular and termolecular ion–molecule reactions of Ne2+ with selected atomic and molecular species
Authors: Collins C. B. , Lee F. W.
Published: February 2003

This work reports the measurement of second and third order ion–molecule reactions of diatomic neon ions with eight reactants selected because of their widely varying values of polarizability and dipole moment. In this study Ne2+ destruction frequencies have been experimentally determined from measurements of the selectively excited fluorescence of N2+ in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of neon pressure over the range from 500 to 1500 Torr and as functions of the partial pressure of reactant from 100 to 900 mTorr. From this data pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from second order, bimolecular, and third order, termolecular, components. The bimolecular components have been found to agree with tabulated values appearing in the literature. The sensitivity of the method has been sufficient to detect termolecular components as small as 2×10−30 cm6 sec−1 and values were found to range from 3.5×10−30 cm6 sec−1 for Ar to 10−28 cm6 sec−1 for HBr. A classical approximation to the three-body capture rate has been evaluated which explains these values in terms of the rates at which third body encounters change glancing collisions into inwardly spiraling orbits. The data reported here are in agreement with this model and indicate that the reaction probabilities in this channel are generally high. The sizes of these termolecular rates suggest their general importance in charge transfer reactions in plasmas at atmospheric pressures.
Isotope, electric field, and vibrational state dependence of single rotational level lifetimes of S1 formaldehyde
Authors: Weisshaar James C. , Moore C. Bradley
Published: February 2003

Additional single rovibronic level lifetimes of S1 H2CO and D2CO have been measured under collisionless conditions. The H2CO 41 lifetimes vary at least a factor of 150, from 20 nsec to 3.10 μsec. The observed D2CO 41 lifetimes fluctuate about ±20% around a mean value of 6.2 μsec, which is probably close to the pure radiative lifetime. In contrast, the observed D2CO 43 lifetimes vary from 1.09 to 2.46 μsec and the 2143 lifetimes vary from 212 nsec to 1.61 μsec. The onset of rotational state lifetime fluctuations in D2CO thus coincides with the high pressure D2+CO photochemical threshold. All of these results are explained in terms of a collisionless sequential decay mechanism, S1→S0→H2(D2)+CO. The last step probably involves tunneling through a barrier for the lower energies studied. For several H2CO 41 rotational levels application of a uniform external electric field of 0–4.6 kV/cm can change the fluorescence lifetime by at least a factor of 4. This result is understood in terms of small (≲0.05 cm−1) shifts in S1−S0 energy spacings. Quantitative estimates of S1−S0 intramolecular couplings, S0 widths due to dissociation, and S0 level spacings are derived in favorable cases.
Electron thermalization in gases. II. Neon, argon, krypton, and xenon
Authors: Mozumder A.
Published: February 2003

Following the theoretical procedure outlined in an earlier paper [J. Chem. Phys. 72, 1657 (1980)], hereinafter referred as I, the present work in an extension to the other rare gases. The following quantities are computed and evaluated: thermalization time and the position distribution at thermalization, time-dependent relaxation rates and evolutions of the directed velocity, width of the positional distribution, and the diffusion coefficient. A Newtonian cooling law has been demonstrated when the effective electron temperature 〈T〉 is close to the gas temperature with an equation for the relaxation time of the excess electron temperature. Weighted moments of the form Mn=〈vnσm(v)〉T have been calculated for n=1 to 10, where σm is the momentum transfer cross section and the symbol 〈−−−〉T denotes averaging with respect to the equilibrium electron velocity distribution at T. The fifth and the seventh moments are related, respectively, to the energy loss rate when 〈T〉 is ≫T and to the Newtonian cooling rate then 〈T〉?T. As in I the thermalization parameters are largely independent of initial velocity if the initial electron kinetic energy is much greater than that for the Ramsauer minimum (Ar, Kr, and Xe). Otherwise the thermalization time is considerably reduced. A somewhat analogous situation in neon is attributed to the ’’incipient’’ Ramsauer effect. Thermalization time at gas temperature ∼300 K increases, according to the present work, in the sequence He, Xe, Kr, Ne, Ar which is contributed jointly by the mass ratio and the behavior of momentum transfer cross section at low energies including the presence or absence of the Ramsauer effect. Comparison with experiments have been made where possible.
Observation of halos in rotationally inelastic scattering of Na2 from Ar
Authors: Serri John A. , Morales Alejandro , Moskowitz Warren , Pritchard David E. , Becker Christopher H. , Kinsey James L.
Published: February 2003

We have measured level to level differential cross sections for rotational level changing collisions in ground state Na2 with Ar: Na2 (v\=0, ji=7)+Ar→Na2 (v\=0, jf)+Ar. Measurements range in Δj(jf−ji) from −4 to 80 and in Θ to π. A seeded supersonic beam source produces rotationally cold Na2 with a narrow velocity distribution; the levels are isolated and the differential cross sections are measured with cw dye lasers, using a new technique, angular distributions using the Doppler shift. The differential cross sections display a sharp rise and slow decline, reaching a maximum at an angle which is roughly proportional to Δj. We term these features ’’halos’’. (AIP)
Energy transfer as a function of collision energy. III. State-to-state cross sections for rotational-to-translational energy transfer in HF+Ar
Authors: Barnes J. A. , Keil M. , Kutina R. E. , Polanyi J. C.
Published: February 2003

Infrared laser pumping of a supersonic beam followed by infrared fluorescence was employed to measure the energy dependence of the R↔T energy transfer. (AIP)
Structure and properties of the argon⋅acetylene van der Waals molecule
Authors: DeLeon Robert L. , Muenter J. S.
Published: February 2003

Radio frequency spectroscopy and Stark effect measurements have been carried out on Ar⋅HCCH and Ar⋅DCCD produced in acetylene seeded argon beams. Because of the very small electric dipole moment, μ=0.02697(3) D, only the 110–111 transition and low frequency pure Stark transitions were observed. Observations are only compartible with a T-shaped equilibrium structure with an Ar to acetylene distance of 3.25(1)Å. Deuterium hyperfine data provide a 204.4(10) KHz value for eqQ of acetylene and arcos (√<cos2ϑ≳)=72(1)° for the complex.
Emission of Mg–Xe discharge and the MgXe excimer band
Authors: Schumann L. , Wildman D. , Gallagher A.
Published: February 2003

The emission intensities and excited-state densities of a Mg-doped high-pressure Xe discharge are reported. The normalized emission of the MgXe excimer band associated with the Mg 3 1P1–31S0 resonance transition is obtained from the data, as well as a 320–380 nm band attributed to XeMg+. The Mg2 A–X band is not seen in emission under any discharge conditions in Mg doped Xe or Ne. This Mg–Xe mixture does not appear to be a reasonable candidate for a discharge-excited excimer laser due to the large excitation energies associated with the Mg and Mg+ resonance transitions.
A random network model calculation of the free energy of liquid water
Authors: Sceats Mark G. , Rice Stuart A.
Published: February 2003

The random network model (RNM) of liquid water previously proposed by the authors is extended by imposition of a self-consistency condition designed to minimize the consequences of approximations used in representing the physical content of the model. The self-consistency condition imposed is the requirement that the computed values of T (∂S/∂T)p and (∂H/∂T)p be identical; this is achieved by modifying the quasiharmonic hindered translational and librational frequencies of the RNM. The temperature dependences of the frequencies so found are in good agreement with experiment. It is shown that the Gibbs free energy of the RNM is a minimum with respect to variation of the width of the hydrogen bond angle distribution when the new frequencies are used. As a test of the adequacy of the self-consistency condition for reduction of the error of prediction of thermodynamic properties, the isotope effect on the vapor pressure of ice I and liquid water is calculated; the RNM predictions are in good agreement with the observed values of ln(pH/pD).
Photodissociation of vibrationally excited ozone
Authors: Zittel P. F. , Little D. D.
Published: February 2003

A two laser photodissociation technique has been used to measure the effect of ozone vibrational excitation on the cross section for photodissociative production of O(1D) at several UV wavelengths in the Hartley band. Below the 310 nm energy threshold for the process, O3+hν ⟶λ⩽310 nm O2(1Δg)+O(1D), vibrational excitation of O3 was found to increase the cross section for production of O(1D) by nearly two orders of magnitude. Substantial increases in both the O3 photoabsorption cross section and the O(1D) quantum yield were observed. Between the 310 nm threshold and the 255 nm absorption peak of the Hartley band, the effect of vibrational excitation was observed to decrease with increasing UV photon energy. The quantum yield of O(1D) for photodissociation of unexcited, room temperature (300 °K) ozone was also measured to be Φ0=0.15±0.07 at λ=314.5 nm.
Primitive model electrolytes. I. Grand canonical Monte Carlo computations
Authors: Valleau John P. , Cohen L. Kenneth
Published: February 2003

Monte Carlo calculations in the grand canonical ensemble are described for coulombic systems, and carried out for 1:1, 2:2, 2:1, and 3:1 aqueous electrolytes in the primitive model with equal ion sizes. Energies and activity coefficients are obtained, and the scope and reliability of the method is discussed.
Remarks on the dynamic perturbation effects upon the circular dichroism intensity for chromophore aggregates in the Frenkel exciton model
Authors: Kamiya Mamoru
Published: February 2003

The dynamic perturbation effects of polarizable chromophoric perturbers upon the circular dichroism intensity arising from absorption transitions of an arbitrary chromophore aggregate in the Frenkel exciton model were formulated on the basis of an extended linear response model which is adaptable for treating the dynamic perturbation as an internal electric field perturbation arising from interchromophoric multipolar interactions. The interchromophoric retardation phase factors were eliminated by a first-order Taylor expansion which is compatible with the use of the retarded helix selection rules under the long-wavelength approximation. In the limit of the weak dynamic perturbation a space-averaged closed-form expression of the nonconservative circular dichroism intensity which is perturbed by intensity sharing with the perturber transitions was derived by means of the projection operator method to partition the full resolvent operator.
Extracting the two-photon polarization ratio of the n→3s transition in acetaldehyde from MPI measurements
Authors: Heath Barbara A. , Fisanick G. J. , Robin M. B. , Eichelberger T. S.
Published: February 2003

The ratio of signals for circularly and linearly polarized light obtained by multiphoton ionization of acetaldehyde at 3633.8 Å has been measured under a wide variety of experimental conditions. Laser flux was found to strongly affect the ratio, with measured values ranging from 0.02 to 0.77. Pressures up to 50 atm of added second gas at low acetaldehyde pressure and low flux increased the ratio by a factor of two. At absorber pressures of several hundred Torr, there is a dramatic increase in the polarization ratio compared to that at <1 Torr, possibly due to resonance energy transfer in the Rydberg state. A theoretical treatment based on a population rate equation model of MPI indicates that useful two-photon absorption polarization ratios may be obtained only at very high added gas pressure and low laser flux.
The temperature dependence of the diamagnetism of liquids
Authors: Kunze R. K. , Day E. P.
Published: February 2003

We have measured the temperature dependence of the mass magnetic susceptibility of a representative group of liquids using a superconducting susceptometer. This study was undertaken to test the hypothesis that the known temperature dependence of the mass susceptibility of water [(13.35±0.03)×10−5 K−1] is due to thermally induced changes in its hydrogen bonding structure. The liquids we have measured in increasing order of their temperature dependent susceptibility (given in parentheses in units of 10−5 K−1) are: carbon tetrachloride (1.37±0.30); chloroform (2.90±0.35); carbon disulfide (3.65±0.39); acetone (3.93±0.39); methanol (4.02±0.34); and acetic acid (4.02±0.35). These results indicate there is no simple quantitative correlation between hydrogen bonding and the temperature dependence of the diamagnetism of a liquid. Our results can be expressed in the form of a virial expansion: χ(T) =χ0+χ1ρA(T), with the virial coefficients χ0 and χ1 being independent of temperature. Thus the observed temperature dependence in liquids other than water may be due entirely to changes in molar volume brought about by changes in density with temperature. This hypothesis could be tested by measurements at various fixed temperatures of the pressure dependence of the mass susceptibility of these liquids.
Photoelectron spectroscopy of AgCl, AgBr, and AgI vapors
Authors: Berkowitz J. , Batson C. H. , Goodman G. L.
Published: February 2003

He I photoelectron spectra of AgCl, AgBr and AgI vapors have been obtained which differ significantly from earlier work. In each instance, the characteristic features of the diatomic molecule are prominent. The spectral features separate into a valence region, predominantly halogen p-like, and a deeper region, predominantly of Ag 4d character. The latter is split by spin–orbit and ligand field interactions, which are parametrized from the experimental data. Relativistic calculations of the Xα–DVM–SCC type have been performed for these species. At the transition state level, they agree very well with the experimental peak positions. Nonrelativistic calculations of this type have been performed for CuCl and cyclic Cu3Cl3. Unlike the AgX species, the CuCl and Cu3Cl3 exhibit strong mixing of metal d and halogen p orbitals for the uppermost occupied orbital, and other Cu 3d-like orbitals above the Cl 3p-like orbitals. It is suggested that the occurrence of Cu 3d orbitals in the valence region may play a role in the anomalous diagmagnetic signal and large conductivity changes of CuCl condensed from the vapor.
The chemical dynamics of the reactions of O(3P) with saturated hydrocarbons. II. Theoretical model
Authors: Luntz A. C. , Andresen P.
Published: February 2003

Quasiclassical trajectory calculations on model potential surfaces are used to explain the experimental results of the previous paper on the O(3P) abstraction reactions with saturated hydrocarbons. OH rotational and vibrational state distributions and excitation functions are calculated assuming a triatomic R–H–O model for the reactions. A simple empirical LEPS potential surface is constructed to fit the experimental data for only reaction with a secondary hydrocarbon. The potential surfaces for other hydrocarbons are identical except for known variations in the C–H bond strength. The excellent agreement of these calculations with the experimental results for all hydrocarbons justifies the triatomic model, and demonstrates the predictive nature of the O(3P)+ hydrocarbon model surfaces.
Stability of Hartree–Fock solutions and symmetry breaking in the independent particle model: A
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o case study of the LCAO–MO–SCF solutions for finite chains of hydrogen atoms
Authors: Bénard M. , Paldus J.
Published: February 2003

The stability of restricted Hartree–Fock solutions and the implied spin and/or space broken symmetry Hartree–Fock solutions are studied using ab initio models of finite chains of hydrogen atoms with Born–Kármán boundary conditions and nondegenerate ground state. We also examined the basis set effects, the role of the nuclear framework distortion as related to the bond-length alternation problem in cyclic polyenes and the higher order instabilities for a large range of internuclear separations. The possible physical implications of the symmetry breaking in the independent particle model are discussed and studied in a considerable detail for the smallest cycle considered, containing six hydrogen atoms. An excellent agreement with the existing infinite chain results is also pointed out. Finally, the relationship with the stability problem and broken symmetry solutions for cyclic polyene models and the sources of these instabilities are examined and discussed as well as their implications for the character and reliability of the self-consistent field potential energy surfaces.
Photodissociation of nitric acid and water in the vacuum ultraviolet; vibrational and rotational distributions of OH 2Σ+
Authors: Okabe H.
Published: February 2003

The absorption cross sections of nitric acid have been measured in the 1100–1900 Å region. The process HONO2 → OH(2Σ)+NO2 occurs below 1475 Å, much shorter than the thermochemical threshold at 2040 Å. The OH(2Σ) fluorescence yield is less than 2%. The vibrational and rotational distributions of OH(2Σ) from HONO2 photolysis at 1236 Å have been measured and compared with those from H2O and H2O2 photolysis. The excess energy beyond that required to dissociate the molecule and to excite ground state OH to OH(2Σ) is converted to rotation and much less to vibration of OH(2Σ) in contrast with linear cyanogen molecules where the excess energy appears as vibration and much less as rotation of a CN product. The results of internal energy partitioning have been compared with calculations based on a simple quasidiatomic impulsive model. The deviation from the model is attributed to either a process involving a large change in bond angle or in bond length. The rotational distributions of OH(2Σ) at v′=0 show a narrow peak at N′=20 for H2O photolysis and a broad peak at N′=10 for HONO2 photolysis both at 1236 Å. The extent of rotational excitation is expressed in terms of an impact parameter. The large impact parameter is found for H2O and H2O2 photolysis while for HONO2 photolysis the impact parameter is small. The rotational distributions of OH(2Σ) from H2O and H2O2 photolysis at 1236 Å deviate completely from Boltzmann behavior while that from HONO2 approaches the Boltzmann distribution. The process to yield the electronically excited NO2 from HONO2 photolysis at 1236 Å is less than 0.5%.
Theory of thermal and photoassisted electron tunneling
Authors: Redi M. , Hopfield J. J.
Published: February 2003

A simple quantum mechanical theory of electron tunneling appropriate for biological electron transfers is developed. The theory predicts discrepancies between optical and thermal tunneling data and clarifies how fast charge separation is produced in photosynthesis. Barrier heights and intermolecular separations are determined for a variety of biomolecular electron transfer experiments.