bluuebunny/crossref_metadata_2025 huggingface dataset:
Comment on the off-diagonal Hellmann–Feynman formula
Authors: Castro Eduardo A. , Fernández Francisco M.
Published: February 2003

A new sufficient condition is given for variational wave functions and energies to satisfy off-diagonal Hellman–Feynman formulas, which exact wave functions and energies satisfy. (AIP)
Piezoelectric KCo[Au(CN)2]3: Room temperature crystal structure of a cobalt-hardened gold electrodeposition process component
Authors: Abrahams S. C. , Bernstein J. L. , Liminga R. , Eisenmann E. T.
Published: February 2003

Potassium cobaltous cyanoaurate(I), KCo[Au(CN)2]3, a new piezoelectric material that is also a component in the electrodeposition process for cobalt-hardened gold, crystallizes in the trigonal system with space group P312 and one formula in the unit cell. The lattice constants at 298 K are a =6.82802±0.00005, c=7.80807±0.00009 Å (λCuKα1=1.540598 Å). The integrated intensities of most reflections within an extant of reciprocal space having radius (sin ϑ)/λ?1.15 Å−1 were measured diffractometrically, resulting in 1130 independent nonzero structure factors. The crystal structure was solved by use of Patterson and Fourier series and refined by the method of least squares, with final agreement factor R=0.0578. The Au(CN)2− ion is close to linear, with Au–C distance of 1.994±0.011 Å, C–N=1.147±0.014 Å, and C–Au–C angle of 178.2±1.7°. The Co2+ ion occupies an octahedral environment, with six equal Co–N distances of 2.124±0.010 Å. The K+ ion is 12-coordinated with six N atoms at 2.950±0.022 Å and six C atoms at 3.215±0.020 Å. A site with similar environment, but slightly shorter contacts, remains vacant. The piezoelectric d22 coefficient is about 5.8×10−12 CN−1. Possible roles for KCo[Au(CN)2]3 in the hard-gold electrodeposition process are considered.
Model studies of mode specificity in unimolecular reaction dynamics
Authors: Waite Boyd A. , Miller William H.
Published: February 2003

Essentially exact quantum mechanical calculations are carreid out to determine the energies and lifetimes of the quasibound states for a system of two (nonlinearly) coupled oscillators (one of which is harmonic, the other being able to dissociate). For weak coupling the system displays mode specificity, i.e., the unimolecular rate constants are not a monotonic function of the total energy, but increased coupling and frequency degeneracy tends to destroy mode specificity. A somewhat surprising result is that for a given coupling the degree of mode specificity is roughly independent of the energy, in marked contrast to the fact that there is an energetic threshold for the onset of ’’stochastic trajectories’’ of the corresponding classical system: i.e., there seems to be no relation between statistical/mode-specific behavior of the unimolecular rate constants and stochastic/regular classical trajectories. In order to be able to treat more physically relevant models—i.e., those with more than two degrees of freedom—a semiclassical model is constructed and seen to be able to reproduce the accurate quantum mechanical rates reasonably well.
Orbiting trajectories in noncentral fields
Authors: Pechukas Philip
Published: February 2003

It is shown that orbiting trajectories exist in noncentral as well as central fields and serve the same purpose of separating ’’soft’’ from ’’hard’’ collisions. (AIP)
Predissociation probes of vibrational energy localization
Authors: Hopkins J. B. , Powers D. E. , Smalley R. E.
Published: February 2003

Ring-bound van der Waals complexes of the alkylbenzenes are studied.(AIP)
Analytical potentials from a
b i
n
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t
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o computations for the interaction between biomolecules. VII. Polar amino acids and conclusions
Authors: Clementi Enrico , Corongiu Giorgina , Ranghino Graziella
Published: February 2003

Analytical atom–atom pair potentials are obtained from ab initio interaction energies between a sodium ion and glutamate, aspartate and alanine, complementing the water–amino acid potentials previously reported. A detailed discussion on optimal generation of pair potentials and related problems is presented. The view is advanced that complex chemical systems of several hundreds of atoms can realistically be analyzed by using interaction potentials rather than by direct but drastically approximated quantum-mechanical simulations.
Fragmentation and molecular dynamics in the laser photodissociation of iron pentacarbonyl
Authors: Yardley James T. , Gitlin Barbara , Nathanson Gilbert , Rosan Alan M.
Published: February 2003

We report measurements of the primary photochemical fragmentation of iron pentacarbonyl into the species Fe(CO)5-n(1⩽n⩽4) resulting from one-photon absorption at 352, 248, and 193 nm. We have observed a high degree of fragmentation, with increasing fragmentation at shorter wavelengths. We believe that the fragmentation results from sequential loss of carbon monoxide with a high degree of retention of internal excitation in the resulting Fe(CO)5-n fragments. A surprisal analysis shows that the fragmentation pattern is highly nonstatistical. The variation in fragmentation with input energy is consistent with a statistical model in which the vibrational space is restricted to a single vibrational degree of freedom. Alternatively, dissociation may proceed through a sequence of electronically excited fragments. Both pictures are consistent with a plausible molecular orbital argument.
Thermal electron attachment to oxygen and van der Waals molecules containing oxygen
Authors: Shimamori Hiroshi , Fessenden Richard W.
Published: February 2003

Thermal electron attachment to O2 has been studied for pure O2 (16O2 and 18O2), O2–N2, O2–CO, and O2–n-C4H10 (16O2 and 18O2) systems at temperatures from ∼330 down to 78° K using pulse radiolysis and microwave conductivity. For pure O2, O2–N2, and O2–CO mixtures, the electron attachment rates showed three-body pressure dependences at all temperatures over the pressure range studied (PO2<10Torr, PN2<60 Torr, PCO<40 Torr). The three-body rate constant of 16O2 decreases from ∼2.4×10−30 cm6 molecule−2 sec−1 at 330 °K to about 0.9×10−30 cm6  molecule−2 sec−1 at ∼ 140 °K but unexpectedly increases again to about 1.7×10−30 cm6 molecule−2  sec−1 at 79 °K. Similarly, the three-body rate constant of 18O2 decreases from 5.1×10−30 cm6  molecule−2 sec−1 at 300 °K to 1.8×10−30 cm6 molecule−2 sec−1 at ∼110 °K but increases to 2.3×10−30 cm6 molecule−2 sec−1 at 80 °K. The three-body rate constant of N2 shows a more dramatic monotonic increase from 0.9×10−31 cm6 molecule−2 sec−1 at 300 °K to 9.4×10−31 cm6 molecule−2 sec−1 at 78 °K. In the case of CO, the three-body rate constant appears to have a very shallow minimum around 170 °K and again increases with further decrease of temperature. Since theory predicts a simple decrease in rate constant with reduced temperature, an extra contribution to the rate constant which increases with lowered temperature is evident. Electron attachment to the van der Waals molecules (O2)2, (O2⋅N2), and (O2⋅CO) is proposed to account for this behavior. It has been found that the dependence of the excess rate on temperature follows rather closely the predicted concentration of van der Waals molecules. Qualitatively, this observation suggests that the rate constant for electron attachment to the van der Waals molecules is only weakly dependent on temperature. The estimated rate constants for this attachment are nearly two orders of magnitude larger than for O2 itself. A discussion of possible reasons for this large increase is given. Analysis of the data for O2–n-C4H10 mixtures suggests that van der Waals molecules contribute significantly only at higher pressures in this system.
Low lying electronic states of CeO
Authors: Linton C. , Dulick M. , Field R. W. , Carette P. , Barrow R. F.
Published: February 2003

A summary is given of the results of laser induced fluorescence experiments on the CeO molecule, which result in the determination of the relative energies of seven low lying electronic states. Both argon ion and cw dye lasers were used to excite several transitions from the X1(Ω=2), X2(Ω=3), and X3(Ω=4) states and the resulting fluorescence spectra showed that (i) the X2(3) state is 80.4±0.7 cm−1 above X1(2), (ii) X4(3) is 100.6±1.5 cm−1 above X3(4), and (iii) there are three states labeled u(2), w(3), v(2), which are 834, 2537, and 2688 (±3) cm−1 respectively above X2(3). It was also shown that the vibrational frequencies ΔG1/2, of the seven low lying states are all between 820 and 825 cm−1.
Laser photofragment spectroscopy of the NO2 dissociation at 337 nm. A nonstatistical decay process
Authors: Zacharias H. , Geilhaupt M. , Meier K. , Welge K. H.
Published: February 2003

The dynamics of the photodissociation of the NO2 molecule into NO(X 2Π1/2,3/2; v, J)+O(3P0,1,2) at the N2 laser wavelength 337 nm (=29 965 cm−1) has been investigated by laser photofragment spectroscopy at room temperature in bulk. The internal energy distribution of the NO(X 2Π) fragment has been analyzed state selectively with respect to the electronic energy (Ω=1/2, 3/2) and rotation–vibration energy (v, J) using laser induced fluorescence excitation for the NO observation by the A–X transition in the ultraviolet. The rotational and vibrational populations strongly deviate from equilibrium distribution indicating a nonstatistical decay mechanism. The partitioning of the maximum available excess energy of 4842 cm−1 is about 70% into internal and 30% into recoil fragment energy. The distribution of the internal energy is about 51% into vibration and 16% into rotation of NO, with an inversion in the vibrational population of the accessible levels v=0,1,2.
MCSCF study of the avoided curve crossing of the two lowest 1Σ+ states of LiF
Authors: Werner Hans-Joachim , Meyer Wilfried
Published: February 2003

Potential energy, dipole moment, and transition moment functions have been calculated for the two lowest 1Σ+ states of LiF using MCSCF wave functions. By optimizing both states simultaneously with a particular choice of configurations it is possible to account for the major part of the correlation energy difference of the neutral and ionic states and to obtain the correct separation of the states at infinite internuclear distance. A simple method to obtain a diabatic description of the two states is proposed. In the crossing region nonadiabatic coupling elements have been calculated.
Thermodynamic properties of 1,4-benzoquinone (BQ), 1,4-hydroquinone (HQ), 1,4-naphthoquinone (NQ), 1,4-naphthohydroquinone (NHQ), and the complexes BQ–HQ 1:1, NQ–HQ 1:1, NQ–NHQ 2:1, and NQ–NHQ 1:1
Authors: de Kruif C. G. , Smit E. J. , Govers H. A. J.
Published: February 2003

Simultaneous torsion and mass loss effusion techniques are applied to measure vapor pressure as a function of temperature. The enthalpy of sublimation is derived from the temperature dependence of vapor pressure. Overall mean values for both techniques are as follows: 1,4-benzoquinone, ΔH°s(261.50 K) = (68.0±0.5) kJ mol−1; 1,4-hydroquinone, ΔH°s(342.37 K) = (103.9±1) kJ mol−1; 1,4-naphthoquinone, ΔH°s(313.21 K) = (90.7±2) kJ mol−1; 1,4-naphthohydroquinone, ΔH°s(381.09 K) = (119.0±1) kJ mol−1. The complexes evaporate incongruently. The enthalphies of sublimation of the first mentioned constituent when evaporated are found as follows: BQ–HQ 1:1, ΔH°s(312.97 K) = (88.6±1) kJ mole−1; NQ–HQ 1:1, ΔH°s(324.03 K) = (98.7±1) kJ mole−1; NQ–NHQ 2:1, ΔH°s(328.49 K) = (88.7±3) kJ mol−1; NQ–NHQ 1:1, ΔH°s(342.36 K) = (102.3±2) kJ mol−1. The temperatures given are midrange values at which the saturation vapor pressure of each substance is 0.4 Pa. From the measured vapor pressures and the enthalphies the sublimation of Gibbs energies and enthalpies of complexation are calculated: BQ–HQ 1:1, 295 K, ΔG°compl = (−13.8±1) kJ mol−1, ΔH°compl = (−20.6±1) kJ mol−1; NQ–HQ 1:1, 320 K, ΔG°compl = (−3.2±2) kJ mol−1, ΔH°compl = (−8.0±2) kJ mol−1; NQ–NHQ 2:1, 320 K, ΔG°compl = (−12.9±1) kJ mol−1, ΔH°compl = (−9.6±4) kJ mol−1; NQ–NHQ 1:1, 330 K, ΔG°compl = (−8.6±1) kJ mol−1, ΔH°compl = (−11.6±2) kJ mol−1.
2H nuclear magnetic relaxation study of the rotation of adamantane in n-alkanes
Authors: Ancian Bernard , Tiffon Bernard , Dubois Jacques-Emile
Published: February 2003

Deuteron spin–lattice relaxation time has been measured for adamantane-d1 in several n-alkane solutions at variable temperature. It is found that solvent viscosity plays only a minor role in adamantane reorientation. This latter involves an activated Arrhenius process with a solvent-independent activation energy (1.3 kcal/mole in the 183–423 °K temperature range). It follows that adamantane rotation is mainly governed by microscopic collisional motions rather than by collective hydrodynamic effects and can be pictured by the concept of transient solvent cavities in which the solvent molecule reorients.
Microwave spectrum of borinic acid BH2OH
Authors: Kawashima Yoshiyuki , Takeo Harutoshi , Matsumura Chi
Published: February 2003

The microwave spectrum of BH2OH, a transient intermediate in the reaction between diborane and water, has been detected and analyzed. This molecule has also been found in the reaction between diborane and oxygen. The lifetime of BH2OH in a copper waveguide cell is a few seconds, which is much shorter than that of BH(OH)2. The rotational and centrifugal distortion constants have been determined for the 11BH2OH, 10BH2OH, 11BD2OD, and 11BH2 18OH species. From the rotational constants the molecular structure has been determined as r(B–O) = 1.352(4) Å, r(O–H) = 0.967(14) Å, &BOH = 112.0(17)°, &HcBO = 121.8(8)°, and &HtBO = 117.2(8)°, the r(B–H) = 1.200 Å being assumed. For the normal species, the dipole moments have been determined as μa = 0.497(7)D, μb = 1.423(15)D, and μtotal = 1.506 D. The quadrupole coupling constants have also been determined.
Dielectric and NMR study of conformational dynamics in t
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s-1,2-dichlorocyclohexane
Authors: Ehrhardt William C. , Vaughan Worth E.
Published: February 2003

The complex dielectric permittivity of trans-1,2-dichlorocyclohexane (DCCH) in supercooled o-terphenyl at audio frequencies is reported. These data are interpreted in terms of a dynamical model involving internal site exchange coupled to a cooperative solvent controlled molecular reorientation process. Fourier transform 13C lines shapes are reported for DCCH in mixed carbon tetrachloride–deuterochloroform solvent over a range of temperatures encompassing the coalescence region. Details of the site dynamics are extracted from these data via numerical line shape analysis. Reasonable agreement between the parameters common to both models is found.
Laser fluorescence spectroscopy of sputtered zirconium atoms
Authors: Pellin M. J. , Wright R. B. , Gruen D. M.
Published: February 2003

Doppler shift laser induced fluorescence spectroscopy was used to determine the relative sputtering yields and number density velocity distribution of sputtered neutral ground state zirconium atoms. Neither change in primary ion energy over the range 1–3 keV nor change in primary ion mass (Ar+, Kr+) affected the velocity distribution despite large changes in the sputtering yield. The measured number density velocity distributions n(v) are well explained by standard linear collision cascade theory and follow the expression n(v)dv α [v2/(v2+v2b)3]dv, where vb is the velocity corresponding to a surface binding energy, Eb = 1/2mZrv2b, with Eb = 6.305 eV, the bulk zirconium sublimation energy. Surprisingly, the number density velocity distributions of zirconium atoms sputtered in two excited states (a 3F3,4) are indistinquishable from that measured for ground state zirconium atoms. Further, the sputtering yield dependence on primary ion energy for the 3F3,4 was also, within experimental error, the same as for the 3F2 ground state zirconium. The sputtering yield for the two excited states represents almot 40% of the total yield of zirconium. Evaluation of the results incorporates for the first time the effects of power broadening, transit time broadening, and velocity dependent fluorescent detection efficiencies.
IF (A→X, B→X) chemiluminescence from the F+I2F reaction
Authors: Trickl T. , Wanner J.
Published: February 2003

Weak IF (A→X, B→X) chemiluminescence was found to be emitted from the F+I2 reaction system under the conditions of a crossed molecular beam experiment. In addition, laser induced fluorescence product state analysis of IF formed in the electronic χ 1Σ+ state in the reaction F+I2→IF+I was carried out. This measurement resulted in a bimodal vibrational product state distribution indicating a partly direct and a partly complex mechanism. We conclude that long lived trihalogen radicals I2F are formed during the reaction F+I2. Secondary encounters of F atoms lead to the luminescent step F+I2F→IF±+IF. The exoergicity of this step is comparable with the experimentally observed B 3π(0+) state excitation. It is likely that the observed meachanism also plays a role in the iodine fluorine flame.(AIP)
High resolution radiofrequency spectroscopy of Ar⋅⋅⋅HCl
Authors: Hutson Jeremy M. , Howard Brian J.
Published: February 2003

Experimental results obtained with the Belousov–Zhabotinskii reaction in a continuous stirred reactor are analyzed in order to distinguish between periodic and chaotic behavior. Power spectra and stereoscopic three dimensional state space trajectories are presented for both periodic oscillations and for chaos. A next amplitude map is constructed for the chaotic case and from it a Liapunov characteristic exponent of +0.62 is calculated. The rate of divergence of trajectories is illustrated by following the behavior as predicted from the next amplitude map of 10 points initially very close together.
Cascade production of Ar(3p54p) following electron bombardment
Authors: Keto J. W. , Kuo Chien-Yu
Published: February 2003

We observe the time dependence of the fluorescence of Ar(3p54p) following electron excitation of argon at pressures from 2–3000 Torr. The population of these levels at the lowest pressures observed is dominated by radiative cascade from Ar(3p53d) and Ar(3p55s). For argon states 4p′[1/2]0, 4p′[3/2]2, and 4p[1/2]0 we find the cascade transitions can be identified and we assign radiative lifetimes of 61±10, 69±12, and 61±6 nsec to 3d′[3/2]1, 3d′[5/2]3, and 3d[3/2]1, respectively. For cascade lifetimes to other levels, unique assignments cannot be made until values for forbidden electron impact cross sections to 3p53d and 3p55s can be obtained. The collisional quenching rates for the cascading levels are measured and found to explain the pressure dependence of the decay of Ar(3p54p) over the full range of pressure except for Ar(3p54p′[1/2]1) which has a unique and interesting behavior at high pressures.
Circular and elliptical dichroism of partially oriented helical polymers
Authors: Rabenold David A.
Published: February 2003

A linear response theory for the circular and elliptical dichroism of partially oriented helical polymers is presented. Circular and elliptical dichroism arise for light propagating parallel and perpendicular, respectively, to the direction of orientation. Expressions are presented for the difference of the oriented and unoriented circular dichroism. Specializing to polypeptide systems we provide a firm theoretical foundation for resolution of oriented circular dichroism spectra into component bands.
Single-particle motions in liquid water. II. The hydrodynamic model
Authors: Sposito Garrison
Published: February 2003

A compilation is made of available data on the self-diffusion coefficient, the dielectric relaxation time, and the NMR orientational time constant for liquid water under 1 atm pressure at temperatures between 273 and 333 K. The data then are examined in a self-consistent manner for their adherence to a simple hydrodynamic model of single-particle motions. In this model, a water molecule is treated as a rigid sphere with the van der Waals radius which carries out diffusive translations and rotations while surrounded by a viscous continuum. Arbitrary boundary conditions on the velocity field in the surrounding liquid are permitted at the sphere–liquid interface. It is found that the measured coefficient of self-diffusion in liquid water is in quantitative agreement with the predictions of the hydrodynamic model under near-slip boundary conditions, whereas the experimental values of the two orientational time constants are described well by the model under stick boundary conditions. Physical arguments are presented to show why the hydrodynamic model should account accurately for single-particle motions in liquid water at low pressures and temperatures.
The antiferromagnetic Mn2 molecule
Authors: Van Zee R. J. , Baumann C. A. , Weltner W.
Published: February 2003

ESR measurements are reported for Mn2 in kypton and xenon matrices at 4 °K.(AIP)
Viscous force and torque constants for a cylinder
Authors: Broersma S.
Published: February 2003

The effect of the forces, added at the end of a cylinder, upon the velocity of the wall of the cylinder was not taken into account in a previous calculation [J. Chem. Phys. 32, 1626 (1960)]. We correct for this. The purely theoretical result is contained in Table I.
A simple interpretation of Raman excitation spectra of metalloporphyrins
Authors: Shelnutt J. A.
Published: February 2003

A simple treatment of vibronic coupling in metalloporphyrins is described. Electronic degeneracy in the excited states is treated to arrive at simple expressions for the Raman excitation spectra and the absorption spectrum. The expressions are simple analogs of the usual A and B term expressions for the scattering tensor and are easily programmed for a small computer. They are only applicable in the weak vibronic coupling limit, but are nevertheless suitable for interpretation of the spectra of most biologically relevant porphyrin systems, at least as a starting point. They allow a simple discussion of a number of interference phenomena that influence the Raman intensity distribution in the excitation profiles of metalloporphyrins and other molecular systems. Some of these phenomena are consequences of electronic degeneracy in the resonant excited state. Nonadiabatic coupling contributions are also included in the expressions. Experimental Raman excitation spectra are discussed in light of this simple model.
Desorption from solid surfaces via generalized Slater theory
Authors: Adams John E. , Doll Jimmie D.
Published: February 2003

The recently reported generalization of Slater’s theory of unimolecular reactions has been applied to the problem of atomic desorption from a crystalline solid (specifically, helium from solid xenon). Using this formalism we are able to calculate the temperature and surface coverage dependence of the desorption rate constant as well as to observe the extent to which the rate is sensitive to the structure of the crystal substrate. In addition, our results suggest that a cooperative desorption mechanism may become important at low surface temperatures for some systems.
The structure of electrolytes at charged surfaces: The primitive model
Authors: Carnie Steven L. , Chan Derek Y. C. , Mitchell D. John , Ninham Barry W.
Published: February 2003

The effects of ion size on the structure of a primitive model electrical double layer at a charged surface is considered using the integral equation method based on a combined hypernetted chain and mean spherical approximation (HNC/MSA). The HNC/MSA is shown to be a nonlinear weak field approximation. The contact values of the surface ion distribution functions are shown to have the correct quadratic dependence on the surface charge density, An analytical comparison between the HNC/MSA and earlier work based on the modified Poisson–Boltzmann equation is given.
Electron affinities of B, Al, Bi, and Pb
Authors: Feigerle C. S. , Corderman R. R. , Lineberger W. C.
Published: February 2003

A sputter ion source has been used to obtain beams of B−, Al−, Bi−, and Pb− ions. A mass analyzed beam of each of these ions was crossed with a fixed frequency argon ion laser operating at 488 nm, and a photoelectron spectrum obtained at a resolution of 60 meV. From an analysis of these data the following electron affinities were obtained: B, 0.278±0.010 eV; Al, 0.442±0.010 eV; Bi, 0.947±0.010 eV; Pb, 0.365±0.008 eV. In addition, a1D excited state of Al− was observed 0.332±0.010 eV above the ground state of the negative ion.
Relativistic effects on bonding
Authors: Ziegler T. , Snijders J. G. , Baerends E. J.
Published: February 2003

A recently proposed perturbational approach to relativistic calculations on molecules has been applied to a number of compounds containing heavy elements. Comparison of calculated spectroscopic constants with experiment and results from other theoretical models shows that the method is a viable alternative to more involved treatments. Relativistic corrections are essential for compounds containing heavy elements and result in a contraction of bond distances and a substantial change in bond energies. The perturbational approach lends itself readily to a straightforward interpretation of both effects. It appears that the bond contraction is not due to the relativistic contraction of valence atomic orbitals. It is a direct relativistic effect, the repulsion due to the rise in kinetic energy when bonds are shortened being diminished by the mass–velocity correction.
Tracer diffusion in polyatomic liquids
Authors: Evans D. F. , Tominaga T. , Davis H. T.
Published: February 2003

New tracer diffusion data are reported. These plus other recently published work provide a wide range of solute (monatomic and polyatomic species) size and solvent molecular type. A hard sphere model, making use of diffusion data from computer simulations on hard sphere fluid, predicts fairly well the diffusivities for the solutes in nonpolar solvents of compact molecules. The model fails for solvents of normal alcohols (except methanol) and of noncompact molecules. Stokes’ law is re-examined and found to be invalid except for solute molecules large compared to solvent molecules. The oft-quoted validity of Stokes’ law for self-diffusion is shown to be an accident of conditions under which the law is usually applied. Further verified is a recently published correlation formula relating tracer diffusivity, solvent viscosity, and particle size.
A metastable complex model for vibrational relaxation
Authors: Gordon Robert J.
Published: February 2003

The probability of vibrational relaxation of a number of molecules is known to increase at lower temperatures. The role of intermediate complexes in such processes is discussed. A model similar to one previously introduced by Tully and co-workers is used to describe complex formation and decay. An orbiting capture cross section is assumed, and unimolecular theory is used to estimate the rate of vibrational predissociation. Fair agreement with a large body of experimental data is obtained.
The indole H-adduct radical in single crystals of tryptamine⋅HCL: An ESR–ENDOR study
Authors: Theisen Håkon , Sagstuen Einar
Published: February 2003

Single crystals of tryptamine hydrochloride have been irradiated with 4.0 MeV electrons at 295 K and studied by ESR and ENDOR techniques. The main species trapped at 295 K was identified to be a radical formed by hydrogen addition to the C7 position of the indole moiety. The ENDOR analysis of five proton interactions in the strong coupling region (ν≳17 MHz) yielded the supporting evidence for this interpretation. Two of the couplings are due to the methylene β protons, with principal values (corrected for second-order contributions) of 100.9, 96.4, and 94.2 MHz, and 125.6, 121.3, and 119.2 MHz. The other three are are due to α protons, two of them of the ordinary type with principal values of −43.9, −27.5, and −13.0 MHz, and −57.4, −34.8, and −18.2 MHz. The third α-proton interaction is due to the central proton in an allyl fragment, exhibiting a coupling tensor with principal values of 11.72, 7.74, and 3.86 MHz. The g value is nearly isotropic at 2.0022. Spectral simulations show that these five interactions are the only ones resolved by ESR at any orientation of the crystal in the applied magnetic field.
A molecular theory of Stokes–Einstein behavior. I. Translational Brownian motion
Authors: Masters A. J. , Madden P. A.
Published: February 2003

By using the Mori generalized Langevin equation an expression for the velocity autocorrelation function of a Brownian particle is obtained. By an appropriate choice of the potential of interaction between the particle and the fluid molecules the frequency dependent friction coefficient reduces to the value found when the slip boundary condition is applied in a hydrodynamic calculation; a different choice gives almost exactly the stick value. The reasons why the previous ’’mode-coupling’’ calculations give an incorrect form for the friction coefficient are discussed.
A spectroscopic study of intermediates in the condensation of refractory smokes: Matrix isolation experiments of SiO
Authors: Khanna R. K. , Stranz D. D. , Donn B.
Published: February 2003

The infrared and Raman spectra of N2 matrix-isolated silicon oxides were investigated. The vibrational frequencies of SiO, Si2O2, and Si3O3 were identified and assigned on the basis of normal coordinate analyses. Heating the solid to ∼50 K (evaporating the matrix) leaves a residue whose infrared spectrum is identical to that of a smoke condensed at ambient temperatures. Further heating of the sample to ∼500 K leads to significant changes in the band shapes. Investigations of the infrared spectra at several stages of the diffusion process enable us to propose a mechanism for the transition from molecular properties to those of the residue (bulk) material, which has been characterized as Si2O3.
Condensation theory for finite, closed systems
Authors: Donoghue Edward , Gibbs Julian H.
Published: February 2003

The applicability of Mayer’s cluster integral formulation of statistical mechanics in the canonical ensemble has been restricted to the gas phase by two difficulties: the enormous labor required for the calculation of cluster integrals from realistic intermolecular potentials and the divergence of the cluster integral expansions of thermodynamic observables and n-particle correlation functions prior to condensation. In this paper the divergence of the cluster expansions is shown to be due to the way in which the limit of a system of infinite size is taken, implicitly, when the partition function, written as a sum over all the cluster size distributions attainable by the closed system, is approximated by its maximum term alone. The use in condensation theory of this ’’maximum term approximation,’’ and of the particular infinite limit it entails, are obviated herein by demonstration that the full theory with use of all the terms in the partition function, can be solved conveniently and exactly by recurrence relation (or formal power series) methods. The cluster size distributions thus found, since they describe finite systems, can have no associated divergences. Because no realistic set of volume dependent cluster integrals is known, we demonstrate the new formalism and the use of the recurrence relations in the case of cluster integrals obtained in the infinite volume limit from the virial expansion determined by the van der Waals equation of state. At low densities these are seen to predict correctly the ideal, imperfect, and metastable states of the homogeneous gas phase. Beyond the spinodal density, they predict bimodal cluster size distributions distinctive of coexisting vapor and liquid; the corresponding pressure isotherms are found to be constant, rather than diverging or displaying a van der Waals loop. Because the sole approximation made is the replacement of the volume dependent cluster integrals by their infinite volume limits, this evidently is the cause of the occurrence of condensation first at the spinodal density rather than at the coexistence density.
Thermodynamics of the lanthanide trifluorides. IV. The heat capacities of gadolinium trifluoride GdF3, lutetium trifluoride LuF3, and yttrium trifluoride YF3 from 5 to 350 °K
Authors: Flotow Howard E. , O’Hare P. A. G.
Published: February 2003

The heat capacities of three isostructural trifluorides GdF3, LuF3, and YF3 were determined from 5 to 350 °K by adiabatic calorimetry. Below 15 °K GdF3 contained an excess heat capacity contribution over the usual lattice heat capacity; LuF3 and YF3 showed no unusual heat capacities over the entire temperature range. Results in tabular form which list the heat capacity C°p, the entropy S°, the enthalpy [H°(T)−H°(0)], and the Planck function −[G°(T)−H°(T)]/T are given for the three trifluorides. Also presented are recommended thermochemical functions at 298.15 °K and tables of recommended high-temperature thermodynamic functions from 400 °K to the melting temperatures. The excess entropy associated with GdF3 is discussed and values of the lattice heat capacity of GdF3 below 15 °K are estimated.
Chemical kinetic functional sensitivity analysis: Elementary sensitivities
Authors: Demiralp Metin , Rabitz Herschel
Published: February 2003

Sensitivity analysis is considered for kinetics problems defined in the space–time domain. This extends an earlier temporal Green’s function method to handle calculations of elementary functional sensitivities dui/daj where ui is the ith species concentration and aj is the jth system parameter. The system parameters include rate constants, diffusion coefficients, initial conditions, boundary conditions, or any other well-defined variables in the kinetic equations. These parameters are generally considered to be functions of position and/or time. Derivation of the governing equations for the sensitivities and the Green’s funciton are presented. The physical interpretation of the Green’s function and sensitivities is given along with a discussion of the relation of this work to earlier research.
Dielectric friction and dielectric dispersion in electrolyte solutions with spin
Authors: Hubbard J. B. , Kayser R. F.
Published: February 2003

A self-consistent continuum model of dielectric friction on a moving ion is developed in which the only adjustable parameters are the hydrodynamic boundary conditions and a ’’rotational viscosity’’ hR. Ion mobility and the solution dielectric properties are calculated as a function of ion size, ion charge, low and high frequency dielectric constants of the solvent, dielectric relaxation time of the solvent, rotational viscosity, and solvent shear viscosity. The consequences of varying hR are investigated: For hR→∞ the continuum theory analyzed by Hubbard and Onsager (HO) is recovered; for small hR, however, the polarization and ’’spin’’ fields in the solvent near the ion differ significantly from the HO model. While this has remarkably little effect on calculated ionic mobilities, the solution dielectric properties are noticeably altered. In particular, the kinetic dielectric decrement diverges as ln hR as hR vanishes.
Pseudopotential and all-electron atomic core size scales
Authors: Zunger Alex
Published: February 2003

It has been previously shown by Politzer, Parr, and Boyd that the radius rm at which atomic radial charge densities 4rr2P(r) have their outer minimum constitutes a chemically meaningful quantum mechanical core radius. It is shown here that {rm} correlates linearly with the position r(0)nd of the outer node in the l = 0 valence orbital and also with the l = 0 classical crossing point rl = 0 of the recently developed a priori density-functional atomic pseudopotential. The universality of these definitions of the quantum core size is indicated in view of these surprising correlations. (AIP)
Force field, dipole moment derivatives, and vibronic constants of benzene from a combination of experimental and a
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Authors: Pulay Péter , Fogarasi Géza , Boggs James E.
Published: February 2003

The quadratic and the most important cubic force constants of benzene have been determined from ab initio Hartree–Fock calculations with a double-zeta basis set. Some constants have also been recalculated using other basis sets, including a polarized one. A few empirical scale factors, applied to the ab initio force field, allow the reproduction of a large number of observed vibrational frequencies, isotope shifts, and Coriolis constants within the uncertainties of experiment and the harmonic model. It is shown that the simultaneous utilization of ab initio and spectroscopical information is sufficient for the conclusive resolution of the uncertainties and alternatives in previous empirical force fields. The resulting scale factors can be used directly to obtain force fields for other aromatic hydrocarbons from ab initio calculations. Reproduction of the observed infrared intensities is only moderately successful, even with the polarized basis set. The calculated vibronic coupling constants show qualitative agreement but important deviations from previous simpler calculations. The predicted vibrational patterns confirm Lindholm’s assignment of the photoelectron spectrum of benzene.
Internal rotation barrier and transition state for glyoxal
Authors: Osamura Yoshihiro , Schaefer Henry F.
Published: February 2003

Complete structural optimizations have been carried out for the electronic ground states of cis- and trans-glyoxal and for the transition state connecting them. Self-consistent-field (SCF) theory was used in conjunction with gradient techniques and a double zeta plus polarization basis set of contracted Gaussian functions. Configuration interaction studies confirm the view that correlation effects are relatively unimportant in the treatment of this rotational barrier. The trans conformation is predicted to lie 5.86 kcal below the cis isomer. From the cis side, the barrier to rotation is only 0.94 kcal. These results and the predicted ionization potentials are discussed in light of recent experiments. Finally, some mechanistic comments on the photodissociation of glyoxal are presented.
Interpretations of XeI and XeBr bound–free emission spectra and reactive quenching of Xe(3P2) atoms by bromine and iodine containing molecules
Authors: Tamagake K. , Setser D. W. , Kolts J. H.
Published: February 2003

The XeBr and XeI emissions spectra have been recorded in a flowing afterglow apparatus from the reaction of Xe(3P2) atoms with 16 bromine and iodine containing reagents. In all cases both the B and C states of XeI and XeBr are observed; the inital B/C ratio is ∼1.5. The ratio increase with pressure because of collisional transfer from C to B. Comparison of the total XeBr and XeI emission intensities with the XeC1 emission intensity from Xe(3P2)+C12 is used to obtain rate constants for XeBr and XeI formation. The branching fractions for XeI and XeBr formation are large, probably unity, for Br2, I2, IC1, and IBr and relatively small for the polyatomic molecules except for CF3I and possible CBr4. From the short wavelength limit of the B–X spectra, upper limits to D0(R–Br) and D0(R–I) are assigned. The theoretical potential curves calculated by Dunning and Hay for the A, B, C, and X states of XeI and XeBr were slightly adjusted so that good agreement was obtained between the simulated and experimental spectra from low vibrational levels of the B and C states. These adjusted potential curves were used to simulate the spectra from high levels of XeBr and XeI, and initial XeBr and XeI vibrational distributions were assigned from matching the low pressure spectra. A systematic decrease in <fV(XeX)≳ is observed in the C12, Br2, I2 series and interpreted as evidence for X(2P1/2) formation. The XeBr and XeI vibrational energy disposal is compared to that from reactions of metal atoms with halogen donors and with reactions of Xe(3P2) with chlorine and fluorine donors.
Rotational and angular distributions from photodissociations. III. Effects of dynamic axis switching in linear triatomic molecules
Authors: Morse Michael D. , Freed Karl F.
Published: February 2003

An analysis is presented of the effects of dynamic axis switching on the three-dimensional quantum mechanical theory of photodissociations of linear triatomic molecules. The dynamic axis switching phenomenon arises from the fact that there are small deviations of the orientation of the diatomic fragment axis from that of the equilibrium triatomic molecule axis in the initially bound state of the molecule. While these deviations vanish on the average, the dynamic axis switching is shown under certain circumstances to alter significantly the calculated rotational, orbital angular momentum and angular distributions from the results of the previous work in which these small deviations are ignored. The dynamic axis switching is demonstrated to be important for determining the proper partitioning of the triatomic initial state rotational angular momentum (J) into nascent diatomic rotational angular momentum and orbital angular momentum of the atom about the diatom. Thus, the dynamic axis switching effect vanishes for J = 0. The effects of this dynamical axis switching transformation are shown to be particularly important for dissociations involving heavy atomic fragments, with lighter atomic fragments giving a smaller effect. The correspondence is established between these quantum mechanical results and those obtained classically. Illustrative calculations are provided of the rotation–bending factor contribution to rotational energy and state resolved angular distributions in HCN and ICN photodissociation. Bending vibrations influence the angular distributions such that a state averaged distribution produces a preferred off-axis recoil direction which can be related to the mean square bending amplitude in the initial bound state.
Dynamics of reactions involving diffusive barrier crossing
Authors: Schulten Klaus , Schulten Zan , Szabo Attila
Published: February 2003

We develop a first passage time description for the kinetics of reactions involving diffusive barrier crossing in a bistable (and also in a more general) potential, a situation realized, for example, in some photoisomerization processes. In case the reactant is in thermal equilibrium, the first passage times account well for the reaction dynamics as shown by comparison with exact numerical calculations. A simple integral expression for the rate constants is presented. For a case involving a reactant initially far off equilibrium, a two relaxation time description for the particle number N(t) is derived and compared with the results of an ’’exact’’ calculation. This description results from a knowledge of N(t = 0), Ṅ(t = 0), ℱ∞0dt N(t), i.e., the first passage time, and ℱ∞0dt t N(t).
Electron beam excited mixtures of O2 in argon. II. Electron distributions and excitation rates
Authors: Keto J. W.
Published: February 2003

We calculate the effect on the electron energy distribution of small partial fractions of oxygen in electron beam excited argon discharges. We find the calculated dissociation rates of O2 by electrons do not explain experimentally observed dissociation rates if we include only the 8.4 eV energy loss peak as dissociation.
On the calculation of mean first passage times for simple random walks
Authors: Gillespie Daniel T.
Published: February 2003

The equivalence of two recently proposed methods for calculating mean first passage times in unit-step, one-dimensional random walks is established. An intermediate result of the demonstration is a new analytic expression for the mean accumulated residence time in any particular state. This expression is used to obtain some simple approximate results concerning (i) extreme fluctuations in unimodal systems and (ii) transitions between steady states in bimodal systems.
Molecular dynamics and spectra. I. Diatomic rotation and vibration
Authors: Berens Peter H. , Wilson Kent R.
Published: February 2003

The pure rotational and vibrational–rotational absorption bands for a diatomic are calculated directly from classical molecular dynamics, classical linear response theory, and classical statistical mechanical ensemble averaging, with the use of simple quantum corrections. The experimental spectral band intensities and contours are well reproduced for CO from dilute gas phase through solution in compressed Ar to solution in liquid Ar by these ’’Newtonian’’ classical spectral calculations. The typical evolution seen in vibrational spectra from multiple-peaked gas phase bands to single-peaked solution bands is observed. The Newtonian gas phase calculations also match quantum and correspondence principle classical spectral calculations. This molecular dynamic approach may be applied to compute the spectra of complex molecules or of liquids for which a normal model analysis may be impractical, and may also be extended to nonequilibrium systems, for example, to compute transient vibrational spectra during chemical reactions.
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Authors: Laskowski Bernard , Stallcop James R.
Published: February 2003

The structure of the X 1Σ+ and A 1Σ+ states of the CsH molecule has been calculated by a modified effective core potential (ECP) method. An extensive Gaussian basis set was required to accurately describe the diffuse electron charge distribution. The computed potential energies agree well with experimental results for internuclear separations larger than 6a0, where the ECP method is valid. The electric dipole and transition moments have also been calculated; they are presented here and compared with experiment by Yang et al., to be published in a subsequent paper.
A polarizability theory of the resonance Raman effect
Authors: Schulman Jerome M. , Lee Wellington S.
Published: February 2003

The theory of Rayleigh and Raman resonance vibrational transition amplitudes for the case of intermediate continuum vibronic states is considered. An extended polarizability theory similar to that of Placzek for the nonresonance case is given. Detailed calculations on the transition amplitudes for H+2 using an exact Kramers–Heisenberg–Dirac expression and the extended polarizability expression show good agreement between the two methods.
Total internal reflection Raman spectroscopy
Authors: Iwamoto Reikichi , Miya Masaru , Ohta Koji , Mima Seiichi
Published: February 2003

Feasibility of total internal reflection (TIR) Raman spectroscopy as a new tool for characterizing thin surface layers has been investigated, starting with selection of the material for the internal reflection element (IRE). Sapphire was found to be the most suitable for the IRE among TiO2, SrTiO3, several kinds of flint glasses, and sapphire itself. The potential of TIR Raman method was proved by measurements on the two-layered samples consisting of a thin surface layer of polystryene and a base layer of polyethylene. The thickness of the surface layer that could be measured by the present technique was then extensively investigated for the two-layered samples which had the surface layer of polystryrene varying in thickness (0.006–0.93 μm) and the base layer of a constant thickness of polycarbonate (12 μm). We could measure vibrational spectra of the surface layers as thin as 0.006–0.2 μm sufficiently separately from those of the base layer. Thickness of the measurable surface layer could be varied to a great extent by changing the incident angle. The observed results were in good agreement with what was deduced from the nature of the evanescent wave.