bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of one-electron properties of LiH from Xα multiple-scattering wave functions
Authors: Cook Michael , Karplus Martin
Published: February 2003

One-electron properties of LiH are calculated from Xα wave functions for a number of parameter sets by use of the charge-partitioning method. To test the method, the results are compared with the Xα numerical quadrature values of Woodruff and Wolfsberg, with Hartree–Fock and CI results, and with experiment. The charge-partitioning procedure is found to introduce errors on the order of those in the Xα wave function itself and to improve in accuracy with parameter variations that improve the Xα wave function. The variations of one-electron properties as functions of the Xα parameters are studied; it is found that these variations can be interpreted in terms of a simple electronegativity picture. Implications of these results for calculations of one-electron properties of polyatomics are discussed.
Production and properties of O(1S) in liquid argon (88 °K) and nitrogen (77 °K)
Authors: Black G. , Sharpless R. L. , Lorents D. C.
Published: February 2003

O(1S) is produced by photodissociation of N2O in liquid argon and liquid nitrogen with an efficiency similar to that previously measured in the gas phase (for 144–148 nm). Spectra of the resulting emissions have been recorded. In both liquids, the emissions have a radiative lifetime of (13±1) μsec. Studies of the quenching of O(1S) by N2O in these liquids and in the gas phase over the temperature range 298–120 °K suggest that an impurity in the N2O becomes the dominant quencher at low temperatures. It is suggested that the gas phase quenching of O(1S) by N2O is best represented by 7.0×10−11 exp(−1250/RT) cm3 molecule−1 sec−1 with an estimated uncertainty of ±10% over the temperature range 370 to 200 °K.
Collisional quenching kinetics for the HgCl* and HgBr* (B1/2) state
Authors: Mandl A. , Parks J. H. , Roxlo C.
Published: February 2003

Measurements of the rates of collisional quenching of HgCl* (B 2Σ+1/2) by He, Ne, Ar, Kr, Xe, and N2 at pressures up to 3000 Torr, and HgBr* (B 2Σ+1/2) by He, Ar, Xe, N2, Br2, HBr, CF3Br, and CCl3Br at pressures up to 1000 Torr, are reported in this paper. Steady state measurements are made of HgCl* and HgBr* fluorescence produced by photolyzing HgCl2 and HgBr2, respectively, using Xe2* radiation. A modified Stern–Volmer analysis is used in determining the rates. This analysis accounts for absorption of Xe2* radiation measured for the quenching species Cl2, HCl, CCl4, Br2, HBr, CF3Br, and CCl3Br. The measured vacuum UV cross sections for these species are included.
ESR and ENDOR studies of x-irradiated l-proline monohydrate and l-thioproline single crystals
Authors: Nelson William H. , Taylor Donald R.
Published: February 2003

Radicals with extended lifetimes at room temperature, and formed by x irradiation of the parent compounds, were studied by ESR and ENDOR spectroscopy. The radicals’ characteristics in each case are similar and include significant couplings to one α proton (Aiso = −54.8 MHz for proline and −51.0 MHz for thioproline), and one β proton (Aiso = 64.0 MHz for proline and 53.8 MHz for thioproline). Further analysis of the results indicates the radicals to result from a reaction similar to deamination, evidently originating with electron capture by the respective parents.
Vibrational dephasing in organic solids: Temperature dependence of a Raman active localized internal mode of naphthalene
Authors: Hess Larry A. , Prasad Paras N.
Published: February 2003

For a localized vibrational transition which is subject to both inhomogeneous and homogeneous broadenings, study of temperature dependence of its linewidth can still be used to identify the mechanism of vibrational dephasing. In the Raman spectra of naphthalene, temperature dependence of the line shape, the linewidth, and the vibrational frequency is investigated for the 764 cm−1 internal mode which is localized even in the neat crystal. At 2 °K the line is found to be a Gaussian and, thus, inhomogeneously broadened. At higher temperatures the line shapes are between a Lorentzian and a Gaussian. A computer simulation method is used to separate the homogeneous and the inhomogeneous components of the linewidth. The temperature dependence of the homogeneous linewidth is explained by a mechanism of dephasing which involves a T2′ process due to an off-diagonal mixed mode quartic anharmonic interaction with 140 cm−1 phonons. This process produces a modulation broadening but no T1 relaxation. The observed temperature dependence of the vibrational frequency is explained by a larger contribution from thermal expansion and a smaller contribution of opposite sign from a diagonal quartic anharmonic interaction with the 140 cm−1 phonon.
Dynamics of spheroid-cylindrical molecules in dilute solution
Authors: Yoshizaki Takenao , Yamakawa Hiromi
Published: February 2003

The dilute solution dynamics of spheroid–cylindrical molecules, i.e., straight cylinders with oblate, spherical, or prolate hemispheroid caps at the ends, is studied in detail. The translational and rotatory diffusion coefficients and the dynamic intrinsic viscosity are evaluated numerically for short cylinders by determining the frictional force by an orthodox method of classical hydrodynamics. For long cylinders, the Oseen–Burgers procedure is shown to be valid, and the results previously obtained by it are still useful. Thus, empirical interpolation formulas for the transport coefficients above are also constructed to be applied to spheroid–cylinders of arbitrary size. The end effects on the translational and rotatory diffusion coefficients are rather small, while the effect on the zero-frequency intrinsic viscosity is remarkable, depending appreciably on the shape of the ends, though for relatively short cylinders. In general, for a rigid body of revolution having a plane of symmetry perpendicular to its axis, it is shown that the dynamic intrinsic viscosity may be expressed in terms of the zero-frequency intrinsic viscosity, the rotatory diffusion coefficient about a principal axis in the symmetry plane, and a newly defined factor, which is also associated with the rotational motion about this axis.
Critical test of equation-of-motion–Green’s function methods. I. Theory of higher order terms
Authors: Herman Michael F. , Freed Karl F. , Yeager Danny L.
Published: February 2003

The equation-of-motion–Green’s function method for calculating ionization potentials is analyzed within the framework of a linear matrix eigenvalue representation, and an extended form of the theory is developed. The utility of the modifications presented in this paper is strongly suggested by recent numerical studies which successfully employ a generalized definition of the primary operator space in analogy with configuration selection procedures that have proven useful in configuration interaction calculations. The basic theoretical questions are associated with the choice of the basis operators for the primary space and the approximations to be employed in the evaluation of the individual matrix elements. This extended form of the theory incorporates the lowest order effects of ground state correlation on matrix elements between the shakeup basis operators in the primary operator space. A first approximation to the contributions of basis operators involving ionization and double excitation or ionization and double de-excitation is incorporated. These terms can contribute in second order to the generalized EOM primary matrix. The possible importance of yet higher order contributions are analyzed in light of the modified primary space. The effect of these generalizations of the theory are studied numerically in the following paper and comparison is made with accurate configuration interaction results on the same systems using identical basis sets.
Reaction path Hamiltonian for polyatomic molecules
Authors: Miller William H. , Handy Nicholas C. , Adams John E.
Published: February 2003

The reaction path on the potential energy surface of a polyatomic molecule is the steepest descent path (if mass-weighted Cartesian coordinates are used) connecting saddle points and minima. For an N-atom system in 3d space it is shown how the 3N-6 internal coordinates can be chosen to be the reaction coordinate s, the arc length along the reaction path, plus (3N-7) normal coordinates that describe vibrations orthogonal to the reaction path. The classical (and quantum) Hamiltonian is derived in terms of these coordinates and their conjugate momenta for the general case of an N atom system with a given nonzero value of the total angular momentum. One of the important facts that makes this analysis feasible (and therefore interesting) is that all the quantities necessary to construct this Hamiltonian, and thus permit dynamical studies, are obtainable from a relatively modest number of ab initio quantum chemistry calculations of the potential energy surface. As a simple example, it is shown how the effects of reaction path curvature can be incorporated in the vibrationally adiabatic approximation, and application to the collinear and 3 dH+H2→H2+H reaction shows that the tunneling probabilities given within this approximation are considerably improved when these curvature effects are included.
Kinetics of conformational transitions in chain molecules
Authors: Skolnick Jeffrey , Helfand Eugene
Published: February 2003

A theory is developed for the rate of conformational transitions (trans→gauche) of bonds in chain molecules, such as alkanes and polymers. This is a multidimensional extension of Kramers’ reaction rate theory. Central to the understanding of how changes in the chain’s geometry affect transition rate is the determination and examination of the reaction coordinate. The reaction coordinate is a localized mode; i.e., the rotational motion of the transforming bond is accompanied by motion in neighboring bonds, but this motion diminishes with distance. Comparison is made between the calculated rates and those determined by Brownian molecular dynamics simulations.
Detailed features in the local mode overtone bands of ethane, neopentane, tetramethylbutane, and hexamethylbenzene
Authors: Henry Bryan R. , Greenlay Wayne R. A.
Published: February 2003

The overtone spectra of ethane in the gas phase at room temperature and neopentane in the liquid phase at 0 °C are measured and analyzed in the region of the pure local mode overtones corresponding to ΔvCH=3, 4, and 5. Overtone spectra are also measured and analyzed for 2, 2, 3, 3-tetramethylbutane in hexachlorobutadiene solution and for hexamethylbenzene in carbon tetrachloride solution, both at room temperature in the region of ΔvCH=3 and 4. For ethane, neopentane, and tetramethylbutane, the dominant contribution to the overtone band corresponds to a pure CH3 local mode overtone. Combination peaks between different CH3 local oscillators are characterized. Combination peaks are also identified involving a CH3 local oscillator and a low frequency normal mode, with the transitions originating from both the ground vibrational state and a state containing one quantum of the low frequency mode. A computer decomposition of the overtone bands is carried out and a satisfactory fit is achieved in terms of Lorentzian peaks, independently of the degree of vibrational excitation or phase. Narrow bandwidths are observed for the pure local mode overtones of neopentane and the narrow linewidths are attributed to weak intermolecular interactions. Doublet structure in the pure local mode overtones of hexamethylbenzene is attributed to two types of configurationally inequivalent hydrogens.
Multiphoton ionization spectroscopy of acetaldehyde in its lowest Rydberg state
Authors: Heath Barbara A. , Robin M. B. , Kuebler N. A. , Fisanick G. J. , Eichelberger T. S.
Published: February 2003

The multiphoton ionization spectrum of acetaldehyde vapor, two photon resonant at the n→3s Rydberg transition, has been studied at 1 cm−1 resolution. Vibrational analysis shows that the molecule remains planar in the resonant state, and that the methyl group torsional barrier has a value of 755±10 cm−1 in that state, compared to 413 cm−1 in the ground state. GTO calculations in the ground state and in the lowest ionic state are only partly successful in explaining the barrier. The Rydberg nature of the resonant state has been verified by the extreme broadening of its two photon absorption when pressurized by ?80 atm of argon. Due to the near resonance of the first absorbed photon with the (n,π*) state, the multiphoton transition is extraordinarily intense; the origin band is at 55 039 cm−1, and displays a circular-to-linear polarization ratio varying from 0.08 to 0.8 depending upon the laser power and sample pressure.
Deuterium separation at high pressure by nanosecond CO2 laser multiple-photon dissociation
Authors: Marling Jack B. , Herman Irving P. , Thomas Scott J.
Published: February 2003

Photochemical deuterium separation is evaluated at pressures up to 1 atm using 2 ns duration CO2 laser pulses to achieve multiple-photon dissociation (MPD) as the isotopic separation step. Photochemical performance is compared for Freon 123 (2,2-dichloro-1,1,1-trifluoroethane), difluoromethane, and trifluoromethane based on deuterium optical selectivity in absorption, photoproduct yield, and single-step deuterium enrichment factor. The absorption coefficient versus energy fluence is measured from 0.01 to 3 J/cm2 fluence for CF3CDCl2, CDF3, and CHDF2; added buffer gas results in an order-of-magnitude increase in the CDF3 absorption coefficient. The deuterium optical selectivity in absorption at 0.5 J/cm2 fluence with added buffer is 80 for CF3CDCl2 at 10.65 μ, 800 for CHDF2 at 10.48 μ, and 2500 for CDF3 at 10.21 μ. The absorption coefficients and hence optical isotopic selectivities are dependent on fluence, and the optical selectivity attains a maximum value of 8000 for CDF3 below 0.01 J/cm2 fluence. The deuterium-bearing MPD photoproducts at high pressure are trifluoroethylene for Freon 123, hydrogen fluoride for trifluoromethane, and both hydrogen fluoride and monofluoroacetylene for difluoromethane. Yield data determined by gas chromatography are analyzed using a model describing MPD due to a focused Gaussian beam in an absorbing medium to remove compositional and geometrical effects; this analysis results in a saturation fluence (at which the dissociation probability approaches 100%) of 12±2 J/cm2 for CF3CDCl2, 20±2 J/cm2 for CDF3 buffered by 1 atm argon, 30±2 J/cm2 for CDF3 buffered by 60–400 Torr CHF3, and 22±3 J/cm2 for CHDF2 buffered by 100–400 Torr CH2F2. Near unity dissociation probabilities are obtained for samples unbuffered by argon with operating pressures up to 40 Torr for Freon 123, and up to 400 Torr for both difluoromethane and trifluoromethane; the methane derivatives are much more resistant to high pressure collisional quenching than Freon 123. The single-step deuterium enrichment factor is 1200±300 for natural isotopic abundance Freon 123 at 30–100 Torr (10.65 μ) determined by mass spectrometry of the main trifluoroethylene photoproduct. The single-step deuterium enrichment factor determined indirectly from gas chromatographic analysis is 2500±500 for natural difluoromethane at 200 Torr (10.54 μ), and 11, 000+4000−2000 for natural trifluoromethane at 100 Torr (10.21 μ). It is concluded that both difluoromethane and trifluoromethane are photochemically satisfactory for viable large-scale laser production of heavy water.
Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane
Authors: Eilerman Donna , Rudman Reuben
Published: February 2003

Between 5 °K and its m.p. (446.0 °K), tris, H2NC(CH2OH)3, exhibits one phase transition, at 407.3 °K, to form the orientationally disordered (plastic) phase I. The ordered form, phase II, is orthorhombic, Pn21a, a=8.844(1) Å, b=7.794(1) Å, c=8.795 (1) Å, Z=4, Dx=1.327 g/cm3, and Dm=1.320 g/cm3. The crystal structure can be described in terms of layers of molecules approximately normal to the c axis, with strong intralayer hydrogen bonding and weak interlayer hydrogen bonding. The crystal structure of phase II was studied using x-ray diffraction at 144, 295, 297, 348, 382, and 395 °K. Full-matrix least-squares refinement of single-crystal diffractometer data resulted in R values between 2–4% for all but the highest-temperature data sets. Although the integrity of the structure is maintained throughout this temperature range, subtle effects are noted that indicate the increased thermal motion as phase I is approached. Phase I is body-centered-cubic, Im3m, with a=6.876(6) Å at 423 °K, Z=2, and Dx=1.237 g/cm3. A comparison of the two structures and the experimental investigation of a single sample in both phases indicate that the mechanism of the phase transition involves a realignment of the molecules within the the layers and a lessening of the interlayer distance. The formation of a bcc lattice in phase I, rather than a fcc lattice as was found in the other members of this series, has been tentatively interpreted in terms of the ellipsoidal shape of the tris molecule.
Accurate solutions to integral equations describing weakly screened ionic systems
Authors: Rossky Peter J. , Friedman Harold L.
Published: February 2003

A procedure recently developed by Talman for the rapid numerical evaluation of Fourier transforms of slowly decaying functions is applied to the evaluation of convolution integrals appearing in integral equations describing pair correlations in ionic systems. The correlation functions are tabulated at uniformly spaced intervals in a variable ρ=lnr, where r is the interparticle distance. In the regime of weak screening, this procedure permits simultaneous efficient sampling of both the rapidly varying part of the functions near particle contact and the long range slowly decaying portion. The effectiveness of the procedure is demonstrated by evaluating accurate solutions to the hypernetted chain equation for a model of a 2–2 aqueous electrolyte at 25 °C over the range of salt concentrations from 10−7 to 10−2 M. Comparison of these results to those obtained from other approximate integral equations shows that significant differences persist to exceedingly small concentrations.
O2* (a 1Δg) in the reaction of H+O3
Authors: Washida N. , Akimoto H. , Okuda M.
Published: February 2003

The reaction of atomic hydrogen with ozone is studied in order to clarify whether O2(aΔg) is formed in the reaction. A photoionization mass spectrometer compiled to a fast flow reaction was used.(AIP).
Penning ionization of metastable helium in the metastable helium–metastable neon system
Authors: Neynaber R. H. , Tang S. Y.
Published: February 2003

Chemi-ionization in the He*–NE* system is studied. The reaction studied is He*+Ne*→He+Ne+e. Merging beam apparatus was used. Penning ionization cross sections are obtained.(AIP)
Analytic formula for chemically induced magnetic polarization by S–T±1 mixing in a strong magnetic field
Authors: Adrian F. J. , Monchick L.
Published: February 2003

An analytical formula is derived for the chemically induced polarization by S−T+1 mixing of a diffusing radical pair in a strong magnetic field.(AIP)
Perturbation theory for the free energy of two-center-Lennard-Jones liquids
Authors: Fischer Johann
Published: February 2003

Recently a perturbation theory for molecular liquids using hard dumbbells as reference system was suggested by Kohler et al. Here, with a somewhat modified approach, it is shown that this type of perturbation theory yields a nearly accurate equation of state even for the most anisotropic two-center-Lennard-Jones molecules, for which simulation results have been reported. In addition to that, an investigation of the different approximations in this approach is given.
Logarithmic terms in the softness expansion of dilute gas transport properties
Authors: Kayser R. F.
Published: February 2003

We consider the dilute gas coefficients of viscosity and thermal conductivity for the inverse power potential, φ(x,r)=φ0(σ/r)x−1, and prove that as x→+0 they have the form a0+a1x+a2x2lnx+a3x2+a4x3ln2x +0(x3lnx). We determine the coefficients a0–a4 in closed form and the analysis may be easily adapted to other properties such as the self-diffusion coefficient. We also show that the logarithmic terms are due to binary collisions for which the distance of closest approach of the particles is greater than the diameter σ and discuss the implications of this for developing a general perturbation theory for transport properties.
Collisional deactivation of selectively excited N+2
Authors: Katayama D. H. , Miller Terry A. , Bondybey V. E.
Published: February 2003

Individual vibrational levels of the A 2Πu state of the N+2 molecular ion are excited by a tunable dye laser. Detection of an optical–optical double resonance fluorescence signal produced by a second laser demonstrates that the ions originally pumped into the A 2Πu state are rapidly deactivated by collisions with He into high vibrational levels of the ground X 2Σ+g state. Time and wavelength resolved studies show clearly that the population of a given high vibrational level of the X 2Σ+g state returns into lower A 2Πu state levels giving rise, effectively, to vibrational relaxation within the A state. Rate constants and cross sections are derived for these collisional, internal-conversion processes. In homonuclear N+2, where symmetry considerations prohibit X and A state perturbations, these processes proceed as rapidly as in heteronuclear species where perturbations are known to be present in the free molecule.
Theoretical investigations of rotationally inelastic collisions in the CO2+He system using a
b i
n
i
t
i
o, electron-gas, and ‘‘experimental’’ potential-energy surfaces
Authors: Stroud C. L. , Raff L. M.
Published: February 2003

The inelastic collision dynamics of the rigid rotor (CO2,He) system have been examined on three different potential-energy surfaces, an ab initio SCF surface, an electron-gas surface, and a potential obtained by deconvolution of molecular-beam scattering data. Thermally averaged cross sections, state-to-state integral cross sections, and differential cross sections have been computed on each surface as a function of collision energy and initial CO2 rotation state from the results of about 28 500 quasiclassical trajectories. At energies less than the depth of the van der Waals well, the SCF surface is found to be inadequate in that it underestimates the state-to-state cross sections by as much as a factor of 5. However, at collision energies in excess of the well depth, all surfaces are found to yield results whose maximum difference is about 20%. Of the surfaces investigated, the electron-gas model predicts the largest degree of rotational inelasticity. Previously reported computations by Preston and Pack indicate this inelasticity to be too large. The present calculations suggest that this is not directly connected to the magnitude or location of the attractive well but rather to the steepness of the repulsive potential which is largest for the electron-gas surface. Nearly linear surprisal plots are obtained for the SCF and electron-gas surfaces. The surprisal for the ’’experimental’’ surface is significantly more sigmoid in shape. The shapes of the state-to-state differential cross sections are very similar, and they may be correlated with the magnitude of the integral state-to-state cross sections. In general, it is concluded that except at very low collision energies on the SCF surface, each of the potentials permits reasonably accurate calculations of the properties associated with thermal scattering.
Extensions of the LSD approximation in density functional calculations
Authors: Gunnarsson O. , Jones R. O.
Published: February 2003

Multiplet splittings of first row and iron series atoms and ions have been calculated using two modifications of the local spin density (LSD) functional approach. (a) The energies of individual states are related to linear combinations of energies calculated from single determinants. (b) The spin dependent part of the functional is constructed to reflect the symmetry between electrons and holes. Agreement with experiment is improved significantly and trends are described remarkably well. There is a general tendency for the LSD approximation to overestimate the relative stability of states with greater p- and d-character and singlet–triplet splittings for sd-configurations.
The electronic spectrum of TiN
Authors: Douglas A. E. , Veillette P. M.
Published: February 2003

The electronic spectrum of TiN has been observed in absorption for the first time and has been photographed at high dispersion. From the rotational analysis of a number of bands, new constants have been determined for the X 2Σ, A 2Π and B 2Σ states. The vibrational frequency of the ground state determined from the new measurements disagrees with a previously published value.
Electron correlation, isoelectronic, isonuclear, spin, and excitation aspects of Politzer–Parr partitioning
Authors: Boyd Russell J. , Markus George E.
Published: February 2003

The effect of electron correlation on the Politzer–Parr procedure for partitioning the electron density of an atom into core and valence regions is investigated by use of configuration interaction (CI) wave functions. Although the effect is generally small, substantial qualitative differences are observed between the 3, 4, and 6 electron cases. Analytical Hartree–Fock (HF) wave functions are used to reveal the trends in isoelectronic and isonuclear sequences. Correlated wave functions, which explicitly include the interelectronic distance, are used to study the effect of spin and electronic excitation on the populations and dimensions of the core and valence regions in the 1sns excited states of He.
Mössbauer effect investigations on frozen solutions of 129I2 in p
a
r
a- and o
r
t
h
o-xylene
Authors: Wynter C. I. , Chow Y. W. , Mukerji Ambuj
Published: February 2003

The Mössbauer effect in 129I due to the 27.75 keV gamma The Mössbauer effect in 129I due to the 27.75 eV gamma transition was used to investigate the frozen solutions of I2 in para- and ortho-xylene at 20 K temperature. In p-xylene the electric quadrupole constant and isomer shift were found to be e2qQ/h=−2360±20 MHz and δ=0.922±0.002 mm/s, respectively. A nonzero value of the asymmetry parameter η=0.18 was also obtained. In ortho-xylene–I2 complex two sets of octet of Mössbauer lines were observed. The values of e2qQ, δ, and η for the two sites of iodine were found to be quite different. The electronic structure of the I2-organic solvent complexes has been discussed in the light of the charge transfer theory.
Wavelength and vibrational-state dependence of photoelectron angular distributions. Resonance effects in 5 σ photoionization of CO
Authors: Cole B. E. , Ederer D. L. , Stockbauer Roger , Codling Keith , Parr Albert C. , West J. B. , Poliakoff E. D. , Dehmer J. L.
Published: February 2003

Photoelectron angular distribution were studied for the photoionization of CO for v=0−3 in the range 16–26 eV. (AIP)
The electronic structure of ferrous heme with imidazole as the fifth ligand. II. Explanation of MCD spectra from the near IR region to the Soret region
Authors: Seno Yasunobu , Kameda Noboru , Otsuka Jinya
Published: February 2003

On the basis of the ASMO–CI calculation, the MCD associated with x- and y-polarized electronic transitions in the ferrous heme of the high-spin type is studied by computational and analytical methods. The ground state 5Eη is split into five substates by the mixing of the other low-lying quintets, 5Eξ and 5B2, through the spin–orbit interaction. The temperature dependent factor in ellipticity is proportional to the z component of orbital angular momentum averaged over the five substates. For excited states, 28 configurations of one-electron excitations from the three low-lying quintets are considered; 12 π→π (3a2u, 1a1u→4eg), 14 d→π (u,v→4eg; d̄π→2̄b̄1u, 3̄b̄2u), and 2 d→d (d̄π→ū,v̄) configurations. In the configuration interaction among them, the spin–orbit interactions of the 3d electrons are also taken into account. With the use of the energy eigenvalues and eigenfunctions, MCD curves are computed in the range of wavelength 400–1000 nm. Observed MCD spectra of deoxymyoglobin are well reproduced especially at low temperature. The theoretical consideration is also developed for the essential mechanism underlying the complex shapes of the MCD spectra with the use of the perturbation analysis and the group theory. Basically, the present theory is also applicable to ferric compounds of the low-spin type.
Jahn–Teller distortions in C6H3F3+ and C6H3Cl3+
Authors: Sears Trevor , Miller Terry A. , Bondybey V. E.
Published: February 2003

The simple, linear theory of Jahn–Teller coupling is reviewed. The effects of quadratic terms and mode mixing are incorporated into the theory. It is then applied to the previously determined vibronic structure of the organic radical cations, C6H3F3+ and C6H3Cl3+. Quadratic effects are shown to be small but not neglible for these ions, and mode mixing effects are quite significant. Jahn–Teller distortion parameters are determined for three modes including the benzene ring in-plane stretching and bending modes. These parameters are used to obtain the distorted geometry of the ions at the minima of their potential energy surfaces and the energy lowering due to the Jahn–Teller effect.
A strong asymmetric N–H–N hydrogen bond: Neutron diffraction and IR spectroscopic studies of 4-aminopyridine hemiperchlorate
Authors: Rozière J. , Williams Jack M. , Grech E. , Malarski Z. , Sobcyzk L.
Published: February 2003

The structure of 4-aminopyridine hemiperchlorate, C5H6N2⋅1/2HClO4, has been determined from three-dimensional neutron diffraction data. The crystals are monoclinic, space group P21/n, with cell dimensions a=11.224 (7) Å, b=9.325 (6) Å, c=16.631 (9) Å, β=102.72 (3) ° and Z=4. The structure was refined to an R(F02) =0.102 for 862 reflections with F02≳σF02. The structure consists of perchlorate anions and asymmetrically H-bridged (NH2Py⋅H⋅⋅PyNH2)+ cations. The cations contain a short, asymmetric, nearly linear (N⋅H⋅⋅⋅N)+ hydrogen bond (N⋅⋅⋅N=2.698 (8) Å, N–H=1.17 (2) Å). The dihedral angle between the planes of the N–H⋅⋅N bridged pyridine rings is 85°. The IR spectra are consistent with those predicted for this type of bridge system. Strong temperature effects were found to occur both in the stretching frequency region νNH2 and in the low-frequency broad absorption band below 800 cm−1. The νNH+band shift towards lower frequencies indicating that the bridge becomes shortened which, in turn, results in an increase of the low-frequency absorption intensity interpreted as a ’’tunneling’’ transition.
Bispectral analysis as a probe of quasielastic light scattering intensity fluctuations
Authors: Phillies George D. J.
Published: February 2003

The bispectrum 〈I(0)I(t)I(τ)〉 of the intensity I of light scattered quasielastically from a fluid system is shown to be a potentially useful tool for studying complex fluids. Bispectra and time cumulants are calculated, in the time domain, for systems with 1, 2, or many diffusing components, treating separately the consequences of homodyne and heterodyne detection at times 0, t, and τ. The experimentally accessible cumulants of the all-homodyne bispectrum distinguish between systems with exactly two relaxation times and systems with more than two relaxation times. The signal-to-noise ratio in a bispectral measurement is shown to be proportional to T1/2, T being the integration time. Clipped scaling of the heterodyne intensity I(t) allows study of the odd powers 〈‖ak(0)a*k(t)ak(τ)‖〉 of the density correlations.
Nuclear magnetic relaxation study of solid sulfolan
Authors: Kydon D. W. , Sharp A. R. , Hale M. E. , Watton A.
Published: February 2003

Sulfolan has been studied by pulsed NMR measurements of laboratory frame spin–lattice relaxation T1 and rotating frame spin–lattice relaxation times T1ρ in the temperature range from 186 to 339 K. The previously reported phase transition at 288 K has been observed, but the data also show the presence of two additional, as yet unreported, phase transitions. The two crystalline phases are characterized by twofold rotations of the sulfolan molecules while the two plastic phases are both characterized by isotropic rotation and translational diffusion. It is suggested that the lower temperature plastic phase involves monovacancy diffusion while the higher temperature one involves relaxed vacancy diffusion. The relaxation times at most temperatures in the solid phases are dependent on the previous thermal history of the sample, with the transitions being sluggish and displaying hysteresis effects.
Properties of vibrational energy levels in the quasi periodic and stochastic regimes
Authors: Noid D. W. , Koszykowski M. L. , Tabor M. , Marcus R. A.
Published: February 2003

Several aspects of the quantal energy spectrum are explored for the Henon–Heiles Hamiltonian system: a striking and initially unexpected continuation of sequences of eigenvalues from the quasiperiodic to the stochastic regime, the origin of large second differences Δ2Ei of eigenvalues arising from variation of a parameter, the comparison of classical and quantal spectra, and a comparison of the ’’classical’’ and quantal number of states. In the study of the second differences we find both ’’crossings’’ and ’’avoided crossings’’ of the eigenvalues. We discuss the importance of overlapping avoided crossings as a basis for a possible theory of ’’quantum stochasticity’’.
Experimental studies of acoustically induced birefringence
Authors: Lipeles R. , Kivelson D.
Published: February 2003

The theory of acoustically induced birefringence in liquids indicates that the birefringence should be proportional to the shear viscosity (η), the acoustic frequency (Ω/2π), and the square root of the acoustic intensity. Furthermore, the birefringence should be proportional to the square root of a dimensionless rotational translational coupling parameter (R0), a coupling parameter which also enters the theories of flow birefringence and of VH and HH depolarized light scattering. We have studied the acoustically induced birefringence of triphenylphosphite and have found the predicted dependence upon Ω,ℐ1/2 and η; in addition we find that R0 is independent of η and T, and that R0 has a value close to that obtained from flow birefringence and depolarized light scattering experiments. We have also studied the acoustically induced birefringence of solutions of large colloidal particles (gold sol); the existing theories predict that the birefringence should be linear in ℐ, and independent of Ω and η. Both previous work and ours indicate a strong Ω dependence; where previous work indicated linearly in ℐ, we find a dominant ℐ1/2 dependence together with a small term linear in ℐ; the dependence on η is still rather unclear. Our results on the gold sols are somewhat qualitative, in part because of insufficient characterization of the sols.
Laser-induced fluorescence study of reactions of Ba with HCl and HBr at different collision energies
Authors: Siegel Augustin , Schultz Arnulf
Published: February 2003

Barium halide molecules produced under single collision conditions by the reactions (1) Ba+HCl→BaCl+H and (2) Ba+HBr→BaBr+H were studied by the method of laser induced fluorescence (LIF). The collision energy was varied in the range 0.08–0.34 eV and 0.10–0.51 eV for reactions (1) and (2), respectively. The vibrational population distribution, Nv, of the product molecules was found to be only slightly influenced by a change of the collision energy; moreover the mean vibrational energy remains unchanged within the accuracy of our experiment. The insensitivity of Nv against changes in the collision energy justifies, in turn, the use of nonvelocity selected beams in the determination of vibrational population distributions in reactions of this type. Because of the narrow spacing of the rotational lines of alkaline earth monohalides only mean rotational energies were determined here, which were found to increase gradually as the collision energy is raised. This allows a determination of the maximal impact parameter, bmax, which depends on the potential surface of the reactants. The total reaction cross section decreases with the collision energy as is qualitatively expected fro exothermic reactions. Because of the special mass combination (H+HL) of the two reactions the rotational distributions are expected to be essentially determined by the kinematics of these reactions, and the rotational distributions will therefore primarily reflect the spread of the collision energy.
Dielectric relaxation spectrum of undiluted poly(4-chlorostyrene), T≳T
g
Authors: Yoshihara M. , Work R. N.
Published: February 2003

Dielectric relaxation characteristics of undiluted, atactic poly(4-chlorostyrene), P4CS, have been determined at temperatures 406 K⩽T⩽446 K from measurements made at frequencies 0.2 Hz⩽f⩽0.2 MHz. After effects of electrical conductivity are subtracted, it is found that the normalized complex dielectric constant K*=K′−i K″ can be represented quantitatively by the Havriliak–Negami (H–N) equation K*=[1+(iωτ0)1-α]−β, 0⩽α, β⩽1, except for a small, high frequency tail that appears in measurements made near the glass transition temperature, Tg. The parameter β is nearly constant, and α depends linearly on log τ0, where τ0 is a characteristic relaxation time. The parameters α and β extrapolate through values obtained from published data from P4CS solutions, and extrapolation to α=0 yields a value of τ0 which compares favorably with a published value for crankshaft motions of an equivalent isolated chain segment. These observations suggest that β may characterize effects of chain connectivity and α may describe effects of interactions of the surroundings with the chain. Experimental results are compared with alternative empirical and model-based representations of dielectric relaxation in polymers.
The temperature dependence of hydrogen abstraction reactions: F+HCl, F+HBr, F+DBr, and F+HI
Authors: Würzberg E. , Houston P. L.
Published: February 2003

A laser photolysis/infrared fluorescence technique has been used to study the temperature dependence of the F+HCℓ, F+HBr, F+DBr, and F+HI absolute rate constants in the range from 195 to 373 °K. Multiphoton dissociation of SF6 with a TEA CO2 laser was used to provide a transient concentration of fluorine atoms. Their subsequent reaction with hydrogen donors was monitored by observing the appearance rate of HF(v?1) through its infrared fluorescence. The observed rate constants show a marked nonlinear Arrhenius behavior which is consistent with a model in which reaction takes place both vai direct attack by the fluorine atom at the hydrogen end of HX and via formation of a collision complex FXH which rearranges to FHX and then dissociates to HF and X products.
Tunnel splittings in solid CD4 estimated from heat capacity data
Authors: White M. A. , Morrison J. A.
Published: February 2003

Heat capacity measurements have been made on CD4, isotopically purified by gas chromatography, in the temperature region 0.15–4.0 K. For T<0.5 K, the heat capacity is found to increase with decreasing temperature by much more than can be accounted for by contributions from impurities such as CHD3. An analysis shows that the results can be reproduced by an array of low-lying tunneling states with maximum splitting of 0.042±0.010 K. States in this region have been predicted by theory and found recently by measurements of inelastic neutron scattering. Enhanced thermal relaxation is observed in the calorimetric measurements in the region T<0.25 K. The onset of conversion between nuclear spin symmetry species is a possible cause.
Collisional ionization of atomic cesium and potassium by CH3CN
Authors: Warmack R. J. , Stockdale J. A. D. , Schweinler H. C.
Published: February 2003

Collisional ionization of ground state Cs and K atoms by CH3CN has been investigated in a crossed-beam experiment for laboratory alkali kinetic energies from 26.5 to 90.7 eV (Cs) and 13.1 to 37.6 eV (K). The kinetic energies and angular distributions of product postive (Cs+ and KK+) and negative (CN−) ions were measured. From these, estimates of the internal energy of the molecular fragments were made. No evidence for production of a stable CN3CN− ion through alkali collisions was obtained.
A threshold photoelectron–photoion coincidence study of the N2O+ dissociation between 15 and 20.5 eV
Authors: Nenner Irene , Guyon Paul-Marie , Baer Tomas , Govers Thomas R.
Published: February 2003

Branching ratios and the kinetic energy released in the various fragmentation channels of energy selected N2O+ (15–20.5 eV) were investigated by the technique of threshold photoelectron–photoion coincidence. Pulsed synchrotron radiation from ACO, Orsay’s storage ring, dispersed by a monochromator, was used as a photon source. Threshold electrons were energy selected on the basis of angular and temporal discrimination against energetic electrons. The energy region below 16.388 eV and the ? state were investigated in detail. Below the ? state the most abundant fragment ion is O+, while above the ? state NO+ dominates. Results for the ? and ? states are also reported.
Direct absorption measurement of the spin–orbit splitting and 2P1/2 radiative lifetime in atomic fluorine (2p5)
Authors: Stanton Alan C. , Kolb Charles E.
Published: February 2003

We report the first direct measurement of the fluorine atom ground state fine structure transition. The transition was measured by diode laser absorption spectroscopy. The position of the (J=3/2, F=2)→(J=1/2, F=1) absorption line was measured with high precision relative to a pure rotational transition in H2O, establishing the fine structure energy splitting as 404.082 cm−1 ±0.025. The measured transition probability for the hyperfine component is 1.26×10−3 s−1 (±25%), yielding a radiative lifetime of 660 s for the 2P1/2 fine structure level.
A method to reduce the number of two electron integral transformations in a second order multiconfigurational Hartree–Fock procedure
Authors: Jo/rgensen Poul , Albertsen Preben , Yeager Danny L.
Published: February 2003

In standard multiconfigurational Hartree–Fock (MCSCF) theory, a two electron integral transformation is performed before application of the equation defining the MCSCF approach in each iterative cycle. It is shown how the two electron integral transformation may be replaced by an approximate orbital transformation introduced directly into the equation that defines the second order MCSCF approach. In this way, the number of two electron integral transformations required to obtain a set of MCSCF orbitals is reduced considerably. Numerical examples for the 3Σ−g, 1Δg, and 1Σ+g states of O2 indicate that an accuracy of 10−6 a.u. in the total energy may be obtained by carrying out 2–3 two electron integral transformations, which is about half the number of transformations required to obtain the same accuracy in the second order MCSCF approach. An accuracy of 10−10 a.u. is obtained after one further iteration is carried out with a second order MCSCF scheme.
Exchange formalism applied to one-dimensional triplet excitons: Observation of restricted and temperature-dependent k to k′ scattering in the zero-field optically detected magnetic resonance spectrum of 1,2,4,5-tetrachlorobenzene
Authors: Breiland W. G. , Saylor M. C.
Published: February 2003

Zero-field optically detected magnetic resonance (ODMR) spectra of the D–‖E‖ transition in 1,2,4,5-tetrachlorobenzene excitons have been obtained for a variety of temperatures (1.2–4.2 °K), microwave powers (0.1–5000 mW), and modulation frequencies (25–1000 Hz). These data have been fit to a theoretical model for band-to-band transitions of one-dimensional triplet excitons that explicitly incorporates the effects of k to k′ scattering, microwave power, and interaction of the band with a thermal bath. It is shown that a proper interpretation of the data can be made only if one considers the actual observables used in monitoring the zero-field spectrum. Analysis of the data indicates that low-temperature k to k′ scattering is restricted to k′ states that lie within roughly one third of the total bandwidth from k. This restricted or nonuniform range is temperature independent below 2.2 °K, but increases above this temperature. At temperatures below 1.35 °K, the ODMR line shape depends on the microwave modulation frequency used. Explicit consideration of the actual distribution of one-dimensional chain lengths and potentially chain-length dependent effects that occur in a real crystal are also discussed, and questions concerning the validity of an exciton ’’lifetime’’ are raised.
Infrared photodissociation of polyatomic ions
Authors: Coggiola M. J. , Cosby P. C. , Peterson J. R.
Published: February 2003

Dissociation of CF3I+, CF3Br+, and CF3Cl+ ions resulting from the absorption of a single 10 μ IR photon by highly vibrationally excited parent ions under collision-free conditions is reported. In each case, the only observed products are CF3++X. Dissociation yields as a function of photon wavelength for CF3I+ and CF3Br+ peak sharply at ∼950 cm−1 corresponding to a strong absorption frequency in the molecular ion. Product ion translational energy distributions are measured for CF3I+ and CF3Br+ photodissociation, and indicate that the energy release is ≪hν. The observed dissociation can be interpreted as resulting from the unimolecular decomposition of ions, initially formed with a total energy within 900–1000 cm−1 of the disociation limit, that absorb a single infrared photon. Thus, this process corresponds directly to the final step in IR multiphoton dissociation of polyatomic ions.
Reaction of magnetically state selected NO with O3: Effect of f
s states and rotational states on reactivity
Authors: Anderson Scott L. , Brooks Philip R. , Fite James D. , Van Nguyen On
Published: February 2003

The visible chemiluminescent channel of the NO+O3→NO2+O2 reaction is studied to determine the effect of the NO fs states (2Π1/2 and 2Π3/2) on reactivity. Chemiluminescence is observed from an ozone-filled scattering cell through which a NO beam passes. Molecules in both the upper and lower fs states are present in the beam, and the intensity of molecules in the upper state can be enhanced by magnetic focusing. Although the beam intensity is observed to increase upon focusing, the increase in chemiluminescence is much smaller showing that the upper state is not solely responsible for chemiluminescence. However, the magnetically selected molecules are rotationally cooler than the unselected molecules, and a reasonable interpretation of the small increase in chemiluminescence is that for the chemiluminescent channel both fs states are equally reactive, but that the reactive cross section increases rapidly with rotational state.
Molecular dynamics simulation of submonolayer krypton films on graphite
Authors: Hanson Frank , McTague John P.
Published: February 2003

Molecular dynamics simulations of submonolayer krypton films on graphite show a first order transition from a low temperature √3×√3 registered phase to a disordered one which is fluid and not localized in the graphite wells (not lattice–gas-like). This contrasts with simulations in the absence of a substrate ordering potential. There the transition is continuous.