bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical mechanics of linear molecules. VII. Application of ``blip function'' theory to dense fluids
Authors: Steele William A. , Sandler Stanley I.
Published: February 2004

The ``blip function'' theory proposed by Andersen, Weeks, and Chandler for the calculation of radial distribution functions and thermodynamic properties of dense fluids is written in a form which yields explicit expressions for both the angular and the radial correlations of a dense fluid of linear molecules. This approximation is compared with a variety of correlation functions obtained by numerically solving the extended Percus-Yevick equation for nonspherical molecules. It is found that agreement is generally good at high densities, but worsens at lower densities because of the omission of the effects of attractive interactions in the blip function theory. It is noted that the H.T.A. approximation has certain implications concerning an extension of the theorem of corresponding states which should be applicable to nonspherical as well as spherical molecules. Tests of the extended theorem indicate that it will be necessary to include attractive interactions if this approach is to be useful in a quantitative way.
13C chemical shielding tensors in polyalkylbenzenes
Authors: Pausak S. , Tegenfeldt J. , Waugh J. S.
Published: February 2004

High-resolution double resonance methods have been employed to study the anisotropic 13C chemical shifts in single crystals of hexamethylbenzene, hexaethylbenzene, and pentamethylbenzene. Methyl and methylene shifts have small anisotropies. Shielding of the ring carbons is a maximum when the magnetic field is normal to the ring and a minimum when it lies along the bond to the substituent. The hexaethylbenzene molecule is shown to have D3d symmetry. The orientations of the two molecules in the unit cell of pentamethylbenzene are determined.
Variational perturbation theory investigations on two-electron atomic systems. IV. Nonrelativistic results for the state 1s3s 3S
Authors: Aashamar Kjell , Midtdal John , Lyslo Gudmund
Published: February 2004

We have applied the variational perturbation (HSK) procedure to the 1s3s 3S state of the helium isoelectronic sequence. The nonrelativistic energies and corresponding total wavefunctions have been determined with estimated errors less than 5 parts in 1010 and one part in 104, respectively, for all Z≥2. For He in particular we report the value E = −4.13737 81348 Rh, and correspondingly for Li+, E = −9.50415 29115 Rh. The values quoted are the best converged results for these states reported so far. We present the numerical results in tables and illustrative figures.
Interpretation of dissociative-electron attachment processes for silicon tetrachloride
Authors: Wang J. Ling-Fai , Margrave J. L. , Franklin J. L.
Published: February 2004

Appearance potentials and translational energies of the products resulting from several dissociative-electron capture processes have been measured. Hypothetical potential surfaces for SiCl4− compound states and the possible dissociated products have been shown. The heat of formation of SiCl3(g) has been determined.
Multistep initial ionization behind strong shock waves in argon
Authors: Wojciechowski Paul H. , Weymann Helmut D.
Published: February 2004

A spectroscopic investigation of the initial ionization behind strong shock waves in argon was made to determine the role of atomic levels in addition to the first excited state. For a numerical modeling of the ionization process a six-level argon atom was assumed. A comparison of analytical and numerical results shows that in the initial ionization process, two-step ionization and multistep (``ladder-climbing'') ionization as originally suggested by de Boer, compete with each other. For an initial pressure of 5 torr and a Mach number of 9 the contributions of two-step ionization and multi-step ionization are roughly equal, with increasing pressure and temperature favoring the latter. The appropriate atom-atom excitation and ionization cross sections have been determined.
van der Waals forces between parallel chains of two kinds of molecules in alternation
Authors: Yorke Ellen D.
Published: February 2004

The effect of van der Waals forces in distinguishing between aligned and unaligned chains of two types of molecules is investigated. For both additive forces and a Drude model of nonadditive forces the effect is found to be small. The implications of this for meiotic pairing are discussed.
Deconvolution methods in elastic total cross section measurements
Authors: Sheen S. H. , Skofronick J. G.
Published: February 2004

Deconvolution methods and their applicability to removal of distortion in elastic total cross section measurements will be discussed. The usefulness and the ``end effect'' problems of the iterative method of Van Cittert will be presented, along with an analytic method to remove the end effect problem. Application to 4He+4He total cross section measurements will be made.
Dielectric constants and molar polarizabilities of saturated and compressed fluid nitrogen
Authors: Ely James F. , Straty G. C.
Published: February 2004

In this paper we present accurate, wide range measurements of the dielectric constant of saturated and compressed fluid nitrogen. Measurements were made from 65 to 125 K along the saturated liquid boundary and along selected liquid and gaseous isotherms ranging from 92 to 300 K at pressures to 34.5 MPa. Densities ranged from the dilute gas to nearly three times the critical density. Molar polarizabilities, thought to be accurate to better than 0.10%, were calculated by combining the dielectric constant measurements with densities obtained from least-squares analyses of experimental pVT data. A correlation function based on selected experimental data is given for the saturated liquid densities. Dielectric virial coefficients, derived from the calculated molar polarizabilities, are also presented.
Microscopic reversibility and complex-valued trajectories in a semiclassical theory of molecular collisions
Authors: Lin Ying-Wei , George Thomas F.
Published: February 2004

The role of microscopic reversibility and time reversal in a semiclassical theory of molecular collisions is discussed. The boundary conditions for time-reversed classical trajectories are written in terms of those for forward trajectories in a manner consistent with microscopic reversibility. Special care must be taken in calculating time-reversed complex-valued trajectories when branch points exist in the complex time plane. Such points can arise from an explicit branch point structure of the potential energy function, such as in a semiclassical treatment of electronic transitions, and/or from the branch point structure of the numerically computed equations of motion. If a forward trajectory crosses a branch cut in the upper (lower) half time plane, the time-reversed trajectory must cross the corresponding branch cut in the lower (upper) half time-plane.
Some theoretical aspects of chemically induced dynamic nuclear polarization
Authors: Pedersen J. Boiden , Freed Jack H.
Published: February 2004

An analysis of aspects of the theory of chemically induced dynamic nuclear polarization (CIDNP) is given in terms of rigorous numerical solutions to the stochastic Liouville equation, in accordance with the methods previously developed for CIDEP. This analysis includes not only a model in which the exchange interaction is of finite extent in the spin Hamiltonian (EFA model) but models in which the exchange interaction explicitly affects the reactive trajectories (EFP model) by their inclusion in a spin-dependent diffusion equation and in which charge interactions between reacting ionic radicals and their surroundings are accounted for in the Debye-Hückel fashion. Several useful and simple relationships are found for the CIDNP phenomenon, and their dependence upon the model is discussed. It is found that the CIDNP polarizations are readily described in terms of two fundamental parameters-Λ, the spin-independent probability of reaction of singlets per collision, which includes all re-encounters, and F*, which measures the conversion from triplets to singlets for the whole collision. Exact relations for the CIDNP polarizations are given in terms of these two parameters and are found to be nearly independent of model. The parameter Λ is shown to be simply related to k(r), the singlet reaction rate when the radicals are in contact, and to τ1, the effective lifetime of the reacting pair. Simple expressions for τ1 are given for all the models, and these results are compared with those for the usual discussions of diffusion rates on chemical kinetics. It is found that for normal diffusion rates, F* obeys the relation (1/2)Qτd, very similar to that first proposed by Adrian, where Q is half the difference in resonant frequencies of the radicals, and τd =d2/D with D the relative diffusion coefficient and d the distance of closest approach. This relation is not appropriate for viscous systems, and the correct results are given for such cases. The effects of the finite range of the exchange interaction and the longer range Coulombic interactions between radicals upon F* for the different models are also obtained. In particular, for EFA the finite range of exchange yields an ``excluded volume'' effect wherein singlet-triplet mixing (or Q mixing) is ineffective. The model dependent effects upon F* are closely related to the recurrence probabilities, and further results are obtained implying a simple expression for the first encounter probabilities of separated radicals under the effects of the different interactions. The polarizations are related to the time-dependent CIDNP intensities that one may observe for a typical scheme of radical production, reaction, and relaxation.
Further studies on the solid-state chemistry of irradiated choline chloride
Authors: Nath Amar , Agarwal Ramesh , Lemmon Richard M.
Published: February 2004

The remarkable radiation sensitivity of crystalline choline chloride has been investigated by studies of infrared and ESR spectra, photochemical transformation of radicals, microwave electrodeless conductivity, and exposure to hydrogen atoms, vacuum ultraviolet, and thermal electrons. These studies lend support to the involvement of both ethanol radicals and electrons in the chain decomposition. They also show that hydrogen atoms can induce the decomposition. These observations indicate that during subsequent thermal treatment of γ-irradiated choline chloride, the detrapped electrons interact with ethanol radicals to form hydrogen atoms, which propagate the chain decomposition.
Electronic-energy exchange cross sections for Ar* (3P) and N2(X 1Σg+)
Authors: Winicur D. H. , Fraites J. L.
Published: February 2004

Differential cross sections for Ar* (3P) scattered by N2(X 1Σg+), obtained at 0.051 eV using crossed molecular beams, are reported from 4° to 174° c.m. A rainbow maximum is observed at 6.3° c.m. The small-angle elastic scattering is analyzed to obtain parameters for a double-Lennard-Jones potential. At large angles the cross sections are depleted by exchange scattering. The exchange probabilities are obtained by subtracting the experimental cross sections from elastic scattering cross sections calculated from the double-Lennard-Jones parameters. The resulting total exchange cross section and threshold energy are σex = 11.8±3.5 Å, E0=0.0081±0.001 eV. Comparison with cross sections deduced from published rate constants indicates that σex increases with initial relative kinetic energy from threshold to 0.051 eV.
Correlation functions and structure factors for a lattice in a viscous medium
Authors: Imry Y. , Gavish B.
Published: February 2004

The displacement-displacement space time correlation functions are calculated for a cubic harmonic lattice embedded in a viscous fluid. For the one-dimensional case we find a |t| type of behavior of the correlation functions at long times. This may lead to observable effects in the dynamic structure factors. A strong dependence of the static and dynamic structure factors both on the angle of scattering and on the orientation of the lattice, is found.
Ionic collision processes in simple gas mixtures containing hydrogen
Authors: Ryan K. R.
Published: February 2004

Bimolecular reactions that occur in weakly ionized mixtures of [H2+N2], [H2+CO], [H2+N2O], and [H2+CO2] have been studied while the ions are contained in the space charge trap generated by the passage of a low-energy electron beam through the ion source of a mass spectrometer. The results obtained for [H2+N2] are generally in agreement with those from earlier studies with the qualification that a charge transfer reaction of low probability has now been observed for collisions between N2+ and H2. For the other three mixtures disagreement exists between these and earlier measurements. The rate coefficient for the transfer of a proton from H3+ to N2, CO, N2O, or CO2 has been found to depend strongly upon the ratio of H2 to the other molecular constituent of the mixture. This observation is consistent with the view that the reaction rate coefficient for H3+ is determined by the internal energy of this ion.
Infrared and Raman spectra and the vibrational assignment of hexamethylenetetramine-h12 and -d12
Authors: Bertie John E. , Solinas Marco
Published: February 2004

The infrared spectra of polycrystalline hexamethylenetetramine-h12 and -d12 (HMT-h12 and HMT-d12) at 300 and 100°K, and the Raman spectra of polycrystals, single crystals, and saturated aqueous solutions of HMT-h12 and HMT-d12 at 300°K, have been recorded. The infrared spectra and the Raman spectra of the single crystals yielded an unambiguous assignment of most of the zero wave vector fundamental vibrations in the solid. Product rule and normal coordinate calculations verified the mutual compatibility of the assignments for the two isotopic molecules, and gave a detailed description of the vibrational modes. The spectra of HMT-h12 and their assignment differ slightly from those of previous authors, while the spectra of HMT-d12 have not been reported previously. The only F1 mode whose frequency is well established is ν16, at 378 cm−1 in HMT-h12 and 315 cm−1 in HMT-d12. The longitudinal and transverse components of several of the infrared-active F2 modes have been unambiguously assigned in the Raman spectra.
Influence of large amplitude vibrational motion on the rate of intersystem crossing: A study of single vibronic level fluorescence from aniline-h7, aniline N, N-d2, aniline-d5, and aniline-d7
Authors: Scheps Richard , Florida Donald , Rice Stuart A.
Published: February 2004

Results of single vibronic level fluorescence measurements in aniline-h7, aniline-N, N-d2, aniline-d5, and aniline-d7 are reported. For each excited level the radiative and nonradiative lifetimes and fluorescence yields have been obtained. The dependence of the nonradiative lifetime of the excited level on the excess energy in aniline-h7 is seen to behave similarly to that in benzene for states independent of inversion mode excitation. Levels involving inversion amplitude must be treated separately; we interpret their lifetimes by postulating that a nonplanar triplet state is involved in the intersystem crossing. Deuteration in the ring and amino positions affects the nonradiative lifetimes to different degrees and leads to the rejection of crossing to the 3B2 state as the rate determining step. A detailed study of the dependence of the nonradiative process on excitation of the inversion mode was carried out using the methods of Heller, Freed, and Gelbart. The numerical calculations were based on Franck-Condon overlap factors appropriate for transitions from a near planar initial state to a significantly bent final state. The experimental trends observed with excitation of inversion mode were qualitatively reproduced for all the molecules studied except aniline N, N-d2.
Electron impact excitation of fluorescence in benzene, toluene, and aniline
Authors: Smyth Kermit C. , Schiavone James A. , Freund Robert S.
Published: February 2004

Electron impact excitation functions for fluorescence from benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Each excitation function exhibits a number of features, including several sharp peaks at electron energies below 20 eV. Possible identifications of these features are discussed, with the result that for each molecule at least one of the low-energy peaks is assigned as a new resonance which decays to produce the lowest excited singlet state S1.
Virial expansion of the second layer in physical adsorption. An ab initio calculation for helium on argon crystal
Authors: Oh Byung K. , Kim Shoon K.
Published: February 2004

A theory of localized and nonlocalized adsorption is given by applying the virial expansion theorem to the second layer. An ab initio calculation of the thermodynamic functions is carried out for the system of helium on an argon crystal. The gas-solid interaction potential is calculated using lattice summation. The periodic potential along the directions parallel to the solid surface is described by a polynomial φn (x/d)/V0 = 1−[1−(2x/d)2]n within a site spacing d, where V0 is the height of potential barrier and n is an integer to be determined from the minimum potential surface. The values of n used for the first and second layers in the present work are 7 and 4, respectively. The second virial coefficient under the external potential is very well approximated by that of the two dimensional gas in free space. The Boyle temperature is 16.3°K for the system which is close to the experimental temperatures (10–20°K) of Ross and Steele. The deviation from the ideality due to the second virial coefficient is small in the experimental temperature ranges; in the isosteric heat, the contribution coming from the second virial coefficient is less than 10% of the total heat. The theory is in excellent agreement with experiment of Ross and Steele.
Measurements of the average electric dipole polarizabilities of the alkali dimers
Authors: Molof Robert W. , Miller Thomas M. , Schwartz Henry L. , Bederson Benjamin , Park John T.
Published: February 2004

The average electric dipole polarizabilities of the homonuclear alkali dimers have been measured in an electric deflection experiment. The molecular results are normalized to the corresponding atomic polarizabilities by comparing deflections of atomic and molecular alkali beams passing through an inhomogenous electrostatic field. The average polarizabilities in units of 10−24 cm3 are: Li2(990°K), 34±3; Na2(736°K), 30±3; K2(569°K), 61±5; Rb2(534°K), 68±7; Cs2(515°K), 91±7.
Chemiluminescent emission spectra and possible upper-state potentials of KCl and KBr
Authors: Kaufmann Kenneth J. , Kinsey James L. , Palmer Howard B. , Tewarson Archibald
Published: February 2004

Chemiluminescent optical spectra of potassium chloride and potassium bromide have been observed in dilute flames. In the KCl spectra 56 ``fluctuation bands'' could be resolved. A table of 66 such bands were measured for KBr, extending the observed spectral range by about 1000 Å to the red for this molecule. Possible upper-state potential curves accounting for the observations are proposed.
Motion of the proton in an asymmetric double minimum potential
Authors: Flanigan Marie C. , de la Vega Jose R.
Published: February 2004

A method different from the semiclassical WKB method was developed for calculating the energy levels of a proton and its penetration through a barrier under an asymmetric double minimum potential. The potential was written as the sum of a parabolic term with minimum at X = 0 and a Gaussian with maximum at X0. The stationary states were found by the variational method using the eigenfunctions of the harmonic oscillator for the parabolic potential. The time dependence of the system was found by expanding the eigenstate of the proton at t = 0 in terms of the stationary states. A Gaussian centered at the minimum of the left well and with an exponent consistent with the ground state of the proton in this well represented the proton at t = 0. The proton is found to oscillate anharmonically between the two wells. The penetration through the barrier is conveniently described in terms of the average frequency of oscillation and in terms of the extreme of the expectation value of the proton's position in the second well. Both the average frequency of oscillation and the extent of penetration decrease as the height of the barrier increases from 3.0 to 5.0 kcal/mole. At 6.2 kcal/mole no penetration was observed.
General rotational relaxation matrix: Its properties, M dependence, and relation to experiment
Authors: Pickett Herbert M.
Published: February 2004

A general rotational relaxation matrix, R, is introduced which governs relaxation among density matrix elements. A definition of R in terms of the scattering S matrix is made which has the properties of conservation of mass and detailed balance at equilibrium. The relation between R and S shows that the only nonzero elements of R are those which connect density matrix elements with approximately the same time dependence. Using only spatial invariance of the S matrix, the dependence of R on M, the space projection quantum number for rotational angular momentum, is found to lead to important information about the qualitative physical nature of collisions. Linewidth experiments, saturation experiments, and double resonance experiments are discussed in terms of what parts of R they measure and how they might yield information about the M dependence of R.
Influence of smectic order on the static dielectric permittivity of liquid crystals
Authors: de Jeu W. H. , Goossens W. J. A. , Bordewijk P.
Published: February 2004

In some p, p′-di-n-alkyl-azoxybenzenes, an anomalous decrease of ε‖ and increase of ε⊥ is observed when the nematic phase is cooled to below the nematic/smectic-A transition temperature. This is attributed to dipole-dipole interaction, which becomes especially important for neighboring molecules in the same smectic layer. The Kirkwood-Fröhlich theory for the dielectric properties of anisotropic polar liquids is used in order to account for these interactions.
Excimer formation in vinyl polymers. III. Fluid and rigid solutions of poly(4-vinylbiphenyl)
Authors: Frank Curtis W.
Published: February 2004

Excimer formation has been examined in fluid and rigid solutions of poly(4-vinylbiphenyl) (PVBP) over the temperature range 373–77°K. The concentration of suitable excimer-forming sites is fixed by the temperature at which the film is cast. A statistical model for the excimer-forming site fraction was previously developed for poly(2-vinylnaphthalene) (P2VN) and is now shown to satisfactorily fit the PVBP data, using the excimer site conformation energy of 800 cal. Furthermore, as was previously demonstrated for P2VN and polystyrene (PS), excimer sampling in the rigid solution is shown to arise from an activated exciton migration to preformed excimer sites. The proposed mechanism for this process involves a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. An effective vibrational frequency for this process has been determined to be 150±30 cm−1 for PVBP. Finally, excimer sampling mechanisms for fluid and rigid solutions are compared in terms of qualitative potential energy concepts.
Equations of state for the Lennard-Jones potential calculated from a parametric integral equation
Authors: Carley David D.
Published: February 2004

A parametric integral equation is tested by obtaining radial distribution functions along an isotherm (T* = 2.74) for a system of particles interacting via the Lennard-Jones potential. The parameter is fixed to give good agreement between the pressure as obtained from Monte Carlo simulation and the integral equation at high density. The agreement between Monte Carlo simulation and integral equation pressures and energies over the fluid portion of the isotherm is good. The integral equation solutions are used to obtain Padé approximant equations for the energy and pressure as a function of density for the T* = 2.74 isotherm.
Numerical solution of the Rowlinson equation for liquid argon and liquid lead
Authors: Muller E. R.
Published: February 2004

The Rowlinson equation, which reduces to the Percus-Yevick equation and to the hypernetted chain equation for two different parameter values, has been investigated numerically. The work is based on the values of the radial distribution and direct correlation functions for liquid argon reported by Mikolaj and Pings and the structure factor data for liquid lead measured by North, Enderby, and Egelstaff. For each set of data, real solutions of the Rowlinson equation-that is, the effective interatomic potentials-exist for a restricted range of parameter values. Over this range of parameter values the pressure has been calculated from the equation of state obtained from the virial theorem. In the majority of cases no value of the parameter has been found for which both a real solution exists and the calculated pressure is consistent with experiment.
Electron energy dependence of the kinetic energy and angular distributions of O+ from dissociative ionization of O2
Authors: Van Brunt R. J. , Lawrence G. M. , Kieffer L. J. , Slater J. M.
Published: February 2004

The electron energy dependence of the kinetic energy and angular distributions of O+ have been measured for the process of dissociative ionization of O2. The kinetic energy distributions for energies above 0.5 eV are compared with other dissociative ionization measurements as well as results of dissociative photoionization and dissociative excitation by electrons leading to production of Rydberg excited neutral fragments. Angular distributions are interpreted in terms of symmetries of possible molecular ion states contributing to dissociation, and the results near threshold are compared with recent measurements of O− from dissociative ion pair formation in O2. Information about the states of excitation of the dissociation fragments as a function of ion energy is obtained from appearance potential measurements. The results indicate that predissociation may be important and that dissociative ionization of O2 is in general a complicated process involving many O2+ states.
Auger electron spectroscopic investigations of chemical shifts in some vanadium compounds
Authors: Szalkowski F. J. , Somorjai G. A.
Published: February 2004

The Auger spectra of vanadium metal and of the compounds V2O4, V2O3, VO, VN, VC, V2S3, and VSi2 have been observed. Shifts in energy of the vanadium L3M2,3M2,3 inner-shell Auger transition peak as the result of chemical bonding effects have been measured. These shifts have been found to be related to the chemical bond ionicity as determined by the Philips-Van Vechten ionicity scale. The ratio of the anion to cation Auger peak intensities observed for the compounds can also be utilized in the determination of the surface composition.
Magnetic exchange in transition metal complexes. X. Parallel spin coupling in di-μ-chloro-octachlorodimolybdenum(V)
Authors: Lines M. E. , Ginsberg A. P. , Salvo F. J. Di
Published: February 2004

A measurement and analysis has been made of the temperature dependence of the magnetic susceptibility of dimeric Mo2Cl10. Ferromagnetic exchange is found within the dimer, a result which is anomalous by comparison with the antiferromagnetic coupling found in other d1 dimers. A crystal field analysis is given of Mo5+ in the local C2ν environment of the dimeric configuration, and an explanation of the ferromagnetic coupling proposed. The resultant interdimer interaction is also found to be ferromagnetic, though small, and suggests that a ferromagnetic or ferrimagnetic ordering of the essentially fully aligned (spin triplet) dimers occurs at low temperatures.
Quadrupole fine structure in MODR spectroscopy and the determination of the absolute signs of the ZF parameters of excited triplet states. MODR spectrum of the 3A′ state of 1-bromonaphthalene in durene
Authors: Kothandaraman G. , Yue H. J. , Pratt D. W.
Published: February 2004

We report measurements of the complete orientational dependence of the 3 cm microwave-optical double resonance (MODR) spectrum of the lowest 3(π,π*) state of 1-bromonaphthalene (1BN) in a durene host crystal at liquid helium temperatures. An analysis of the high-field spin Hamiltonian of triplet states containing quadrupolar nuclei shows that both the absolute signs and magnitudes of each of the zero-field (ZF) parameters as well as the principal values of the g, quadrupole, and hyperfine tensors can be determined using MODR techniques. For 3A′ 1BN, we find X/hc = +0.0434 cm−1, Y/hc = +0.0229 cm−1, Z/hc = −0.0663 cm−1, gxx = 2.003, gyy = 2.002, and gzz = 1.994. A comparison of these values with those obtained for 3B2u naphthalene suggests that the ZF scheme of the lowest triplet state of 1BN is modified by spin-orbit coupling with higher excited states, principally in the triplet manifold.
Photoionization and ion cyclotron resonance studies of the reaction of vibrationally excited C2H2+ ions with H2
Authors: Buttrill S. E. , Kim J. K. , Huntress W. T. , LeBreton P. , Williamson A.
Published: February 2004

The reaction C2H2++ H2 → C2H3+ + H has been studied using ion cyclotron resonance and photoionization mass spectrometric techniques. At thermal kinetic energies, the cross section for the reaction is near zero for ground state reactants but increases rapidly with increasing vibrational energy in the C2H2+ ions. The ratio of the cross sections for ions in the ν2 = 1 and ν2 = 2 states is approximately 1:2, respectively. Some reaction is observed at photoionization energies below the theshold for formation of ν2 = 1 ions owing to reaction of thermally excited ions and neutrals. For the distribution of vibrational energies in C2H2+ ions formed by electron impact at 15 eV, the rate constant for the reaction is 6.3±1.8×10−11 cm3/sec. Exchange of hydrogen atoms in nonreactive collisions between C2H2+ ions and D2 molecules has also been observed. An upper limit of Δ Hf(C2H3+)=267 kcal/mole is obtained.
Solution of a model for the solvent-electrolyte interactions in the mean spherical approximation
Authors: Blum L.
Published: February 2004

An electrolytic solution is simulated by a mixture of charged hard spheres and hard dipoles, all of the same size. This model can be solved exactly in the mean spherical approximation (MSA), yielding a set of three coupled high order algebraic equations for three unknowns, which are essentially the excess internal energies due to the charges alone, the dipoles alone, and the charge-dipole cross interaction. A rapidly converging series solution of these equations is proposed for the dilute solution regime. The first term in this series is the hard-core Debye-Hückel theory term, with electrostrictive corrections. We also obtain the leading term in the expansion for the infinite dilution limit of the ion-solvent excess chemical potential. Other relevant information could be obtained using standard formulas.
Laser heterodyne study of water droplet growth
Authors: Gollub J. P. , Chabay Ilan , Flygare W. H.
Published: February 2004

Droplet growth by condensation under simulated atmospheric conditions has been studied quantitatively in a diffusion cloud chamber. Droplet size distributions were obtained from heterodyne spectra of scattered laser light. The distributions were typically quite narrow, and the time dependence of the mean radius agrees well with theoretical predictions for supersaturations of 1.02–1.05 in the size range 3–7 μm. Our data indicate no need to postulate very small condensation and thermal accommodation coefficients in contrast to previously published work at higher supersaturations. However, the growth rates are anomalously low at supersaturations less than about 1.015.
Crossed molecular beam study of reactive scattering: O + CS2 →SO + CS
Authors: Geddes J. , Clough P. N. , Moore P. L.
Published: February 2004

The angular distribution and velocity of SO reactively scattered from crossed molecular beams of oxygen atoms and CS2 have been measured. In c.m. coordinates, the SO is strongly forward scattered with an in plane angular distribution represented by exp(−θ/50°), indicating a direct reaction mechanism. The mean recoil velocity of SO is independent of the c.m. angle, showing that the average fraction of reaction exoergicity appearing as translational energy of product separation is <10%. Combined with other evidence on vibrational excitation of products, this suggests that the main channel for released energy is into rotation and that the reaction proceeds via highly bent intermediate configurations. The total reaction cross section is estimated to be 1.1 Å2.
Interpretation of phenomenological rate constants in the Bodenstein approximation
Authors: Donoghue Edward
Published: February 2004

A new formula is derived for the phenomenological rate constants in terms of the rate constants of a more detailed reaction mechanism that involves intermediate chemical species. The formula is derived in the Bodenstein, or steady-state, approximation and applies to the particular case of a purely first order system of chemical reactions. The new formula suggests a physical interpretation for the phenomenological rate constants. The phenomenological rate constant kij for the observed chemical reaction (for the reverse reaction, kji) xi⇄xj between chemical species xi and xj is seen to be the number of molecules of species xi per unit time per unit concentration that are transformed into species xj either in one reaction or in a sequence of two or more reactions in which the molecule is first transformed to one intermediate chemical species after another, finally being transformed into chemical species xj. The new formula displays very explicitly the precise functional dependence of the phenomenological rate constants on the rate constants of the reaction mechanism. This particular dependence leads to a notion of the dependence and independence of phenomenological rate constants. It is shown that this dependence of phenomenological rate constants could be exploited in kinetics studies to infer the presence of intermediate chemical species present only in extremely small concentrations.
Integral equation approach to collinear reactive scattering: A + BC → AB + C
Authors: Adams John T. , Smith Richard L. , Hayes Edward F.
Published: February 2004

An integral equation approach to collinear reactive scattering has been developed. The technique has been implemented on a computer for calculation of scattering matrices for the following reactions: H+H2→H2+H; D+H2→HD+H; and F+H2→HF+H. The results of these calculations are found to be in good agreement with those obtained by earlier workers. The attractive features of this method are discussed.
Flash photolysis-resonance fluorescence kinetics study: Temperature dependence of the reactions OH + CO → CO2 + H and OH + CH4 → H2O + CH3
Authors: Davis D. D. , Fischer S. , Schiff R.
Published: February 2004

Two reactions involving the transient chemical species OH(ν″ = 0) and the reactants CO and CH4 have been investigated over a temperature range of nearly 140°C. Of particular importance were the measurements made below 300°C where data has heretofore been lacking. The rate constant expressions in Arrhenius form are kCO = (2.15±0.19)×10−13 exp[−(160±80 cal mol−1)/R T] and kCH4 = (2.36±0.21)×10−12 exp[−(3400±175 cal mol−1)/R T]. Units are cm3 mol−1 · sec−1. Wide variations in the total pressure, H2O concentration, initial OH concentration, and the nature of the diluent gas showed no indication of complex secondary reactions. The activation energies reported in this work for both processes, virtually zero for Reaction (1) and 3400 cal mol−1 for Reaction (2), are incompatible with those same quantities previously reported at elevated temperatures and indicate either nonlinear Arrhenius behavior for these OH reactions or possibly errors in experimental measurements.
Standardization of convention for zero field splitting parameters
Authors: Poole Charles P. , Farach Horacio A. , Jackson William K.
Published: February 2004

Transformation formulas have been derived for conversions between the various conventional systems for reporting zero field splitting data using the Hamiltonian H = D [Sz2 − (1/3)S(S + 1)] + E(Sx2−Sy2). It is recommended that all future work be reported in the standard system corresponding to the range −1≤3E/D≤0.
Effects of ionizing radiation on tyrosine
Authors: Box Harold C. , Budzinski Edwin E. , Freund Harold G.
Published: February 2004

Two oxidation products and one reduction product were identified in single crystals of tyrosine HCl irradiated at 4.2°K. Both oxidation products are associated with the loss of an electron from the phenol ring of tyrosine. The reduction product is the result of electron addition to the carboxyl group. The identification of these species followed from an analysis of proton hyperfine couplings measured by the ENDOR technique.
Scattering of alkali halides by electrons. III. KI
Authors: Slater R. C. , Fickes M. G. , Becker W. G. , Stern R. C.
Published: February 2004

Scattering of KI by 0.81–15.7 eV electrons has been observed using the molecular beam recoil technique. Center of mass cross section models are adjusted to fit the apparatus space scattering pattern. Absolute total cross sections agree at high energies with the first Born approximation and are a factor of 4 smaller at the lowest energy. At low energies the momentum transfer cross sections are an order of magnitude below theory. The measured cross sections are nominally identical to those measured in CsCl.
Kinetic theory of dimer formation and decay
Authors: Lowry J. T. , Snider R. F.
Published: February 2004

Guided by the equilibrium statistical mechanics of ideal gas mixtures, we postulate a form for the density operator ρ(N) for an N-atom gas consisting of M monomers and D dimers (M +2D = N). The reduced density operators ρ(n) derived from ρ(N) are investigated and it is shown how ρ(1) and ρ(2) are related to the monomer density operator ρf and the dimer density operator ρb. Kinetic equations for ρf and ρb are obtained which include the effects of bimolecular collisions and those termolecular collisions which lead to either dimer formation or dissociation. These equations are ``derived'' from the N-atom von Neumann equation within the philosophy of the Boltzmann equation; that is, assuming molecular chaos before the collision event. This coupled pair of kinetic equations for ρf and ρb is a natural generalization of the Boltzmann equation to include atomic recombination and diatomic breakup in gaseous systems.
Electron scavenging in the radiolysis of supercritical ethane, ethylene, n -butane, and isobutane
Authors: Nishikawa Masaru , Yamaguchi Yoh-ichi , Fujita Kazuo
Published: February 2004

Free ion yields in the radiolysis of supercritical ethane and ethylene at 50°C, and n -butane and isobutane at 170°C were estimated as a function of density from the nitrogen yields observed upon electron scavenging by N2O with the use of the square root model, G(N2)=G(N2)fi + G(N2)gi(A[N2O])1/2. The estimated Gfi in the hydrocarbon gases were in the decreasing order C2H6 > i −C4H10 > n −C4H10 > C2H4 for the density range 0.12–0.24 g/ml. The density-normalized range of electrons estimated from Gfi values decreased sharply with an increase in density for C2 hydrocarbons, while it was practically constant for butanes over the entire range studied (0.12–0.42 g/ml). The variation of A values with density was discussed in terms of the concomitant change in the electron mobilities.
Modified statistical method for intermolecular potentials. Combining rules for higher van der Waals coefficients
Authors: Cohen James S. , Pack Russell T
Published: February 2004

A modification of the Gordon-Kim statistical method for calculating intermolecular potentials is presented, discussed, and shown to give a reasonable estimate of the whole potential curve for both like and unlike pairs of noble gas atoms. Rae's correction to the exchange energy is used, but double counting of the correlation energy is avoided by using the van der Waals energy in lieu of the statistical correlation energy at large internuclear separations. Simple but apparently reliable combining rules for the van der Waals C8 and C10 coefficients are derived and tested. Calculated interatomic potentials are given for all pairs of noble gas atoms.
Residual absorption of 1,1,1-trichloroethane and some related broad band absorption studies
Authors: McLellan C. K. , Walker S.
Published: February 2004

As a result of dielectric work mainly at 70 and 140 GHz and an extrapolation of the data by the Cole-Cole equation to obtain the permittivity of very high frequencies (ε∞) the residual dispersion (ε∞ − n2) of 1,1,1-trichloroethane would appear to be very small indeed at 293 and 318°K. However, the liquid exhibits strong broad band absorption. It would seem, therefore, that either the Poley concept of residual absorption is inadequate for 1,1,1-trichloroethane or that the data at frequencies significantly greater than 140 GHz do not fit a Cole-Cole plot and the resulting extrapolation yields a misleading value of ε∞. The fairly intense far-infrared absorption of 1,1,1-trichloroethane would support the latter as being the case, especially since the ε∞−nD2 at 253°K is ∼0.3, while the absorption intensities of the broad band appear essentially unaltered over the 227–310°K range. Far-infrared studies have also been carried out on 2,2-dichloropropane over a fairly wide temperature range in the liquid and solid phases, and the results support the concept that the broad band absorption in the liquid phase of polar substances may have a large contribution from molecular rotation (which could be somewhat restricted) since for both 2,2-dichloropropane and 1,1,1-trichloroethane, on their passing from the liquid phase to the adjacent solid phase, the half-band width and αmax values do not change appreciably. On further cooling of these solids below the lambda point, the far-infrared spectrum changes appreciably and characteristic lattice bands result which are to be related to the more rigorous order of a lattice and the lack of molecular rotation. No rotator solid phase has been detected for chloroform, and in this case a considerable change occurs between the broad band absorption of the liquid at room temperature and the lattice bands of the solid.
Photogeneration processes in poly (N-vinylcarbazole)
Authors: Pfister G. , Williams D. J.
Published: February 2004

The photogeneration efficiency of holes in films of highly purified poly (N-vinylcarbazole) (PVCA) and of PVCA containing 0.1% by weight trichloroacetic acid (TCAA) has been studied as a function of applied field (5×104−2×106 V/cm) and excitation energy (3.4–5.2 eV), and the influence of extrinsic effects such as aging, ambient and photodecomposition upon the carrier generation efficiency, fluorescence, and absorption has been examined. It is observed that light and aging degrades the film. Possible photo-oxidation processes are discussed. Oxygen is found to reduce the yields for carrier generation and fluorescence. The carrier generation in PVCA becomes less field dependent but more efficient with increasing excitation energy. The addition of TCAA to PVCA reduces the field dependence of the carrier generation, sensitizes it at low fields, but quenches it at high fields. A kinetic model is developed which assumes that the field dependence of the generation yield can be described in terms of the Onsager model for geminate recombination. The essential parameters from this analysis are φ0∼0.14 and ∼0.11 for the primary quantum yield for pure and acid doped PVCA, respectively. For PVCA the separation of the photoexcited electron-hole pair increases from r0∼22.5 Å for excitation into the first singlet state (1S1) to r0∼30 Å for excitation into the third singlet state (1S3). For the acid doped film, we find r0∼30 Å for 1S1 excitation. The kinetic model enables us to relate φ0 to molecular parameters, to account for the reduction of φ0 on doping with acids, and to predict the influence of extrinsic effects upon the spectral dependence of the carrier generation.
The reaction of atomic oxygen with several atmospheric ions
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2004

Cross sections for reactions of atomic oxygen with the ions H+, O+,N+,N2+, O−, and O2− have been measured. The ion energies range from 1 to 500 eV. For all ions, the charge transfer processes have been considered. In addition, for N2+ the ion-molecule reaction leading to production of NO+ has been studied. For the charge transfer reactions in which no accidentally resonant pathway exists, cross sections less than 10−17 cm2 at 1 eV were measured. Where accidental resonance occurs, cross sections larger than 10−16 cm2 at 1 eV were found. For N+, both the ground and excited states of the ion were used in the measurements. The method used to form the atomic oxygen beam is discussed.
Sufficient conditions for fragment and regional virial theorems
Authors: Srebrenik S. , Bader R. F. W.
Published: February 2004

Sufficient theoretical conditions are derived for the satisfaction of the molecular fragment virial theorem of Bader and Beddall [J. Chem. Phys. 56, 3320 (1972)] and of the regional virial theorem of Mazziotti, Parr, and Simons [J. Chem. Phys. 59, 939 (1973)].
Magnetic state of an unusual bacterial heme protein
Authors: Maltempo Martin M.
Published: February 2004

The unusual magnetic properties of the bacterial heme proteins known as the ferricytochomes c′ are explained as arising from ground state heme-iron electronic configurations consisting of quantum mechanical admixtures of an intermediate [S =(3/2)] spin state and a high [S =(5/2)] spin state, coupled via the spin-orbit interaction. The general conditions under which quantum mechanical mixing will occur in ferric heme complexes are discussed, as well as the specific magnetic properties of the ferricytochromes c′. The published magnetic data for the proteins are compared with the magnetic parameters predicted from theory. Ligand field considerations are used to infer a heme-iron configuration at physiological pH which is structurally hybrid between the high and low spin configurations.
Valence shell excitation accompanying photoionization in mercury
Authors: Berkowitz J. , Dehmer J. L. , Kim Y.-K. , Desclaux J. P.
Published: February 2004

The 584 Å photoelectron spectrum of mercury vapor exhibits weak peaks corresponding to formation of the excited (5d)10 (6p) 2P1/2,3/2 ionic states, in addition to the one-electron transitions, which produce the (5d)10 (6s) 2S1/2 and (5d)9 (6s)2 2D5/2,3/2 states of Hg+. Although the 2P1/2,3/2 states are forbidden by the usual shakeup mechanism, they can occur either by a ``conjugate'' shakeup process or by configuration interaction (CI) in the initial state. We present calculations which indicate that the latter is responsible for ∼80% of the 2P1/2,3/2 intensity observed. The 304 Å photoelectron spectrum provides evidence for formation of additional excited ionic states which may have the configuration (5d)9 (6p)2 and/or (5d)9 6s 7s. Our calculations show that the energies of these states are in the region of peaks experimentally observed. The (5d)9 (6p)2 states can be formed by the initial-state CI mechanism, whereas the (5d)9 6s 7s states are attainable via the shakeup process. The probabilities for these two transitions are comparable.