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Volume 72, Issue 1, 01 January 1980

An effective nuclear charge model for the prediction of valence force constants in polyatomic molecules. I
View Description Hide DescriptionThe effective nuclear charges have been defined using the quadratic force constants which are obtained by the application of perturbation theory to homonuclear diatomic molecules. It has been shown that these charges are applicable to the calculation of force constants in heteronuclear diatomic molecules. To make further application of the effective nuclear charges to polyatomic molecules, we have proposed effective intramolecular potential functions founded on the electrostatic theorem, and have attempted to predict the force constants of triatomic molecules. The results show that our method of approach using the effective nuclear charges is useful for the prediction of approximate valence force constants in polyatomic molecules.

Calculation of one‐electron properties of LiH from Xα multiple‐scattering wave functions
View Description Hide DescriptionOne‐electron properties of LiH are calculated from Xα wave functions for a number of parameter sets by use of the charge‐partitioning method. To test the method, the results are compared with the Xα numerical quadrature values of Woodruff and Wolfsberg, with Hartree–Fock and CI results, and with experiment. The charge‐partitioning procedure is found to introduce errors on the order of those in the Xα wave function itself and to improve in accuracy with parameter variations that improve the Xα wave function. The variations of one‐electron properties as functions of the Xα parameters are studied; it is found that these variations can be interpreted in terms of a simple electronegativity picture. Implications of these results for calculations of one‐electron properties of polyatomics are discussed.

Absolute rate constant for the chemiluminescent reaction of atomic oxygen with nitric oxide
View Description Hide DescriptionThe absolute rate constant for light emission from the NO–O reaction has been determined, as a function of wavelength, by using a standard brightness source, which has a surface of uniform brightness. The spectral distribution measured between 0.4 and 1.4 μm is in good agreement with those of the previous studies except for a little difference in the near infrared region. The influence from NO–O_{3}chemiluminescence is demonstrated for atomic oxygen production from O_{2} discharges.

A laser flash photolysis‐resonance fluorescence kinetics study of the reaction Cl(^{2} P) + CH_{4}→CH_{3} + HCl
View Description Hide DescriptionThe technique of laser flash photolysis‐resonance fluorescence is employed to study the kinetics of the reaction Cl(^{2} P) + CH_{4}→CH_{3} + HCl over the temperature range 221–375 K. Chlorine atoms are produced by photolysis of Cl_{2} at 355 nm. At temperatures ? 241 K the apparent bimolecular rate constant is found to be dependent upon the identity of the chemically inert gases in the reaction mixture. For Cl_{2}/CH_{4}/He reaction mixtures (total pressure =50 Torr) different bimolecular rate constants are measured at low (k _{1L}) and high (k _{1H}) methane concentrations. For Cl_{2}/CH_{4}/CCl_{4}/He and Cl_{2}/CH_{4}/Ar reaction mixtures, the bimolecular rate constant (k _{1}) is independent of methane concentration with k _{1}?k _{1L}. k _{1} and k _{1L} are in good agreement with previous results obtained using the flash photolysis‐resonance fluorescence technique while k _{1H} is in good agreement with previous results obtained using the discharge flow‐resonance fluorescence and competitive chlorination techniques. At 298 K the measured bimolecular rate constant is independent of the identity of the chemically inert gases in the reaction mixture and in good agreement with all previous investigations. The low temperature results obtained in this investigation and all previous investigations can be rationalized in terms of a model which assumes that the Cl(^{2} P _{1/2}) state reacts with CH_{4} much faster than the Cl(^{2} P _{3/2}) state. Extrapolation of this model to higher temperatures, however, is not straightforward.

ESR–ENDOR study of x‐irradiated α‐methyl‐D‐glucopyranoside single crystals at 12 K: Influence of hydrogen bonding on primary alcohol group radiation chemistry
View Description Hide DescriptionSingle crystals of α‐methyl‐D‐glucopyranoside x‐irradiated at 12 K contain a primary alkoxy radical. In contrast to the previously characterized primary alkoxy radical found at 77 K, the C–O bond does not significantly reorient. This result, as well as deprotonation of an accompanying primary hydroxyalkyl radical, is explained by the presence of three, instead of the usual two, hydrogen bonds about the O_{6} atom.

High resolution and sub‐Doppler Fourier transform spectroscopy: Iodine molecular fluorescence excited by the 514.5 and 501.7 nm Ar^{+} laser lines
View Description Hide DescriptionFluorescence from the I_{2} B O^{+} _{ u } state, excited by the 514.5 and 501.7 nm cw Ar^{+} laser lines, is recorded using a high resolution Fourier transform spectrometer. Spectra are obtained with both multimode (6 GHz) and single mode (<100 MHz) Ar^{+} lasers, the latter spectra exhibiting reduced Doppler width. B O^{+} _{ u }−X ^{1}Σ^{+} _{ g }fluorescence is recorded at 1 mK precision for v″=10–100, e Q q″ quadrupole constants are obtained (±5%) from measuredlinewidths, broadening of quasibound X ^{1}Σ^{+} _{ g } rotational levels above the rotationless X ^{1}Σ^{+} _{ g }dissociation limit is observed, and perturbations of X ^{1}Σ^{+} v″⩾92 by two previously unobserved long range I_{2} molecular states are detected. These two states, 0^{+} _{ g } and 1_{ g }, which dissociate into two ^{2} P _{3/2} I atoms, are also observed directly in the fluorescencespectrum. This paper presents illustrative examples; constants and a complete analysis will appear subsequently.

On the intermolecular interaction in π‐exciplexes of aromatic hydrocarbons with amines
View Description Hide DescriptionComparison of the energy of exciplex band maxima of aromatic hydrocarbons with dimethylaniline and diethylaniline has been used to study the nature of the intermolecular interaction in these exciplexes. For the interpretation of the results an approximate method is used to compare the zeroth‐order energies of the first locally excited, LE, and charge‐transfer, CT, states of the complexes. It led to the conclusion that even for strongly polar exciplexes the covalent part of the wave function can not be neglected; its weight depends on the energy gap between the first LE state and the ’’pure’’ CT state of the complex, and greatly increases when there is a near degeneracy between the first excited singlet state of the donor and acceptor molecules.

Long time dynamics of swollen rubbers: Optical and mechanical properties
View Description Hide DescriptionThe low frequency dynamics of a swollen network is investigated by means of a many‐body Langevin equation which treats the junctions like slowly moving structural units, as suggested by recent improvements of the equilibrium theory of rubber elasticity. Both the viscoelasticconstitutive equation and the optical autocorrelation function S (k, t) of a junction‐labeled network are then calculated for a model system with very long circuits. Deviations of S (k, t) from exponential behavior and quadratic linewidth are predicted to occur if the scattering wavelength is not much larger than the average distance between adjacent crosslinks. Calculated deviations are shown to be strongly dependent on functionality and swelling ratio. In particular, we predict a remarkable difference between trifunctional and tetrafunctional networks.

Dynamics of spheroid‐cylindrical molecules in dilute solution
View Description Hide DescriptionThe dilute solution dynamics of spheroid–cylindrical molecules, i.e., straight cylinders with oblate, spherical, or prolate hemispheroid caps at the ends, is studied in detail. The translational and rotatory diffusion coefficients and the dynamic intrinsic viscosity are evaluated numerically for short cylinders by determining the frictional force by an orthodox method of classical hydrodynamics. For long cylinders, the Oseen–Burgers procedure is shown to be valid, and the results previously obtained by it are still useful. Thus, empirical interpolation formulas for the transport coefficients above are also constructed to be applied to spheroid–cylinders of arbitrary size. The end effects on the translational and rotatory diffusion coefficients are rather small, while the effect on the zero‐frequency intrinsic viscosity is remarkable, depending appreciably on the shape of the ends, though for relatively short cylinders. In general, for a rigid body of revolution having a plane of symmetry perpendicular to its axis, it is shown that the dynamic intrinsic viscosity may be expressed in terms of the zero‐frequency intrinsic viscosity, the rotatory diffusion coefficient about a principal axis in the symmetry plane, and a newly defined factor, which is also associated with the rotational motion about this axis.

Free energy and radial distribution functions for a model of point defects in AgCl doped with CdCl_{2}
View Description Hide DescriptionThe Helmholtz free energy and radial distribution functions were calculated for impurity and vacancypoint defects in AgCl doped with 1–5 mole % CdCl_{2} at 250 °C. The model assumed a Coulombic interaction except at the nearest‐neighbor separation. The method was a variational solution of the hypernetted chain integral equations. The relation of the calculation method and results to liquid electrolyte solution theory is discussed. The degree of association into nearest‐neighbor vacancy–impurity complexes is not close to zero, contrary to recent suggestions. The results are consistent with the occurrence of triplet (and possibly larger) nearest‐neighbor complexes in addition to the pairs.

Infrared spectrum of the water formaldehyde complex in solid argon and solid nitrogen
View Description Hide DescriptionInfrared spectra of the water formaldehyde complex in argon and nitrogen matrices have been obtained. The complex shifts of the water fundamentals clearly show that water forms a hydrogen bond with formaldehyde. HDO prefers to form a D bond, but a metastable H‐bonded complex is observed in nitrogen matrices below 20 K.

Excitation and deactivation of O(6s ^{5} S) in collisions with N_{2} at above‐thermal energies
View Description Hide DescriptionParameters in the theoretical equation for growth of O(6s ^{5} S) states in an atomic oxygen beam have been determined by fitting the growth equation to values measured for the intensity of 5436 Å emission from the beam as a function of target pressure. In this manner, cross sections for excitation and deactivation of the 6s ^{5} S state in collisions of oxygen atoms with N_{2} were determined for beamenergies from 3.85 to 19.65 keV. A correlation in the energy dependence for the two cross sections was observed.

Inhibition and enhancement of positronium formation in aqueous solutions from the Doppler broadening of annihilation peaks
View Description Hide DescriptionThe Doppler broadened positron annihilation line shapes have been determined in aqueous solutions of various inhibiting and enhancing agents of positronium (Ps) formation : H^{+} _{aq}, NO^{−} _{3}, S^{2} ^{−}, SCN^{−} and the halide ions. The results confirm that the inhibition is made through electron scavenging by H^{+} _{aq} and NO^{−} _{3}, and through positron capture, to form a bound state, by the other ions. The characteristics and yields of the various positron‐containing species in the solutions are inferred from the deconvoluted experimental line shapes. On referring to the lifetime spectroscopy experimental data, it is found that the yields of positronbound states are lower than expected, and the formation of excited states is hypothesized to account for the discrepancy.

Reaction path Hamiltonian for polyatomic molecules
View Description Hide DescriptionThe r e a c t i o n p a t h on the potential energy surface of a polyatomic molecule is the steepest descent path (if mass‐weighted Cartesian coordinates are used) connecting saddle points and minima. For an N‐atom system in 3d space it is shown how the 3N‐6 internal coordinates can be chosen to be the reaction coordinate s, the arc length along the reaction path, plus (3N‐7) normal coordinates that describe vibrations orthogonal to the reaction path. The classical (and quantum) Hamiltonian is derived in terms of these coordinates and their conjugate momenta for the general case of an N atom system with a given nonzero value of the total angular momentum. One of the important facts that makes this analysis feasible (and therefore interesting) is that all the quantities necessary to construct this Hamiltonian, and thus permit dynamical studies, are obtainable from a relatively modest number of a b i n i t i o quantum chemistry calculations of the potential energy surface. As a simple example, it is shown how the effects of reaction path curvature can be incorporated in the vibrationally adiabatic approximation, and application to the collinear and 3 dH+H_{2}→H_{2}+H reaction shows that the tunneling probabilities given within this approximation are considerably improved when these curvature effects are included.

Raman investigation of vitreous and molten boric oxide
View Description Hide DescriptionRaman data have been obtained for vitreous and molten B_{2}O_{3} from −196 to 1594 °C. A ΔH° of 6.4±0.4 kcal/mole boroxol was obtained from the temperature dependence of ratios of integrated Raman intensities. This heat is thought to correspond to the transformation of BO_{3} triangles in boroxol rings, to BO_{3} triangles in a random network. Vitreous B_{2}O_{3} is composed predominantly of boroxol rings, but the boroxol ring concentration decreases with increasing temperature in the melt, and becomes small at temperatures above 1600 °C.

Two large‐amplitude motions in triatomic molecules. Force field of the ^{1} B _{2} (^{1} A′) state of SO_{2}
View Description Hide DescriptionA program has been developed to calculate the energy levels associated with the two large‐amplitude stretching vibrations ν_{1} and ν_{3} of a bent triatomic molecule in which the ν_{3} oscillation occurs in a double minimum potential. Employing the two large‐amplitude Hamiltonian H ^{0} _{ s }(ρ_{1},ρ_{3}) obtained earlier by Brand and Rao. [J. Mol. Spectrosc., 61, 360 (1976)], the vibrational energy levels (v _{1},v _{3} ^{even/odd}) of SO_{2} molecule in its ^{1} B _{2} (^{1} A′) excited state are calculated. The nine parameters of the potential function V _{0}(ρ_{1},ρ_{3}) are then adjusted to give a least‐square fit to the 12 observed vibrational term values corresponding to the levels (v _{1},v _{3} ^{even}) of S^{16}O_{2} and S^{18}O_{2}. A three‐dimensional picture of the potential surfaceV _{0}(ρ_{1},ρ_{3}) using the final set of force constants is also presented. The saddle point of this surface is at (ρ^{O} _{1}=1.5525 Å, ρ^{O} _{3}=0.0 Å) and the absolute minima occur at (ρ^{ e } _{1}=1.5644 Å, ρ^{ e } _{3}=±0.0745 Å). Barrier height, i.e., the height of the saddle point above the absolute minima, is 140 cm^{−1}.

A semiclassical series solution of the generalized phase shift atom–diatom scattering equations
View Description Hide DescriptionA semiclassical series solution of the previously developed operator form of the generalized phase shift equations describing atom–diatom scattering is presented. This development is based on earlier work which led to a double series in powers of Planck’s constant and a scaling parameter of the anisotropic portion of the intermolecular potential. The present solution is similar in that it is a double power series in Planck’s constant and in the difference between the spherical radial momentum and a first order approximation. The present series solution avoids difficulties of the previous series associated with the classical turning point.

The Dufour effect. III. Direct experimental determination of the heat of transport of carbon tetrachloride–cyclohexane liquid mixtures
View Description Hide DescriptionThe heat of transport of carbon tetrachloride–cyclohexane liquid mixtures has been determined directly by Dufour effect experiments. The technique employs a withdrawable ’’liquid gate’’ to create a nonturbulent, sharp diffusionalinterface. The partial differential equations governing the barycentric velocity, composition, and temperature distributions are solved with a Crank–Nicholson implicit numerical scheme. This allows inclusion of the composition and temperature dependence of the thermodynamic and transport parameters. For mean mole fraction of carbon tetrachloride x _{1} between 0.34 and 0.55 and for mean temperature T between 295.13 and 296.43 °K, the best least squares fit of the data for the heat of transport ?*_{1} in kJ mol^{−1} is ?*_{1}=5.82+2.32 (x _{1}−1/2)+0.225 (T−295.82), with a calculated standard error of 0.087. Analysis of the same experiments indicates that the composition dependence of the thermal conductivity κ of the mixture in the specified composition and temperature ranges is best given (in J m^{−1} s ^{−1} K ^{−1} ) by (∂κ/∂w _{1})_{ T,p }=0.0252 (w _{2} ^{1/2}−0.032), where w _{ i } is mass fraction.

Fluorescence kinetics of cadmium and cadmium–mercury molecules
View Description Hide DescriptionThe molecular fluorescence of Cd_{2} and CdHg has been studied experimentally using optical excitation at 266 nm. The 460 nm, 150 nsec band of CdHg(b) is described and related to the cadmium molecular system. A model is proposed to describe the decay of both the pure cadmium and cadmium–mercury systems which involves cadmium trimer, dimer reservoir, and dimer radiating species. Energy spacings and equilibrium constants are derived for these states.

Discussion of the origin of secondary photon and secondary ion emission during energetic particle irradiation of solids. I. The collision cascade
View Description Hide DescriptionSecondary photon and secondary ion emission during energetic particle irradiation of solid surfaces is assumed to arise due to excitation and de‐excitation of sputtered particles originating from a collision cascade induced by the incident projectile. The excitation is postulated to occur by two alternative mechanisms: path (a), where excitation occurs at or very near the surface of the solid due to atom–atom or atom–electron collisions; and path (b), where excitation occurs as the sputtered particle leaves the solid, but is still under its influence so that electron exchange processes are permitted. Once the excited and/or ionized sputtered particle is formed nonradiative de‐excitation processes are then included in the discussion which allow the excited and/or ionized particle to be de‐excited and/or neutralized. The result of these nonradiative de‐excitation processes is shown to provide a possible channel for the formation of new excited ’’daughters’’ by the de‐excitation of the initial excited ’’parent’’. Depending on the initial excitation probability of the parent the new excited daughters are shown to contribute to various energy regions of the excited and/or ionized secondary particle energy distribution. A mathematical formalism is developed based on the neutral sputtered atom energy and velocity distributions assuming a collision cascade origin for these sputtered particles. By including various models for the excitation probability, and the survival probability for excited particles once formed to not undergo nonradiative de‐excitation the resulting energy and velocity distributions of the sputtered excited and/or ionized secondary particles are calculated. These distributions are found to be a function of the emission angle depending on the model assumed for the initial excitation. From this formalism the total excited secondary particle yield may be calculated. The mathematical expressions herein developed may be used to interpret present experimental data in such a manner that the initial assumptions regarding path (a) or path (b) excitation may or may not be substantiated. The formalism also suggests new experiments which can be performed to further test the excitation processes involved in excited and/or ionized secondary particle emission and thereby increase the understanding of the origin of these phenomena.