bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering by an r−2n Potential in the Born Approximation and Application to Dipole-Quadrupole Scattering
Authors: Ganas P. S.
Published: February 2004

By using the Born approximation, an analytic formula is derived for the phase shifts δL for scattering by a potential with an r−2n tail. The low-energy properties of the phase shifts are discussed, and an expansion of tan δL in powers of k is presented. The dipole-quadrupole r−8 potential is discussed as a special case.
Torsional Barriers in the Methyl Substituted Ethylenes
Authors: Durig J. R. , Hawley C. W. , Bragin J.
Published: February 2004

The far-infrared spectra have been recorded from 350 to 33 cm−1 for propene, cis-2-butene, trans-2-butene, isobutene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene, in the gaseous and solid states (−190°C). The Raman spectra of the liquids have also been recorded in the same frequency range. The bands corresponding to the torsional modes are assigned as appearing at 226; 195; 233 and 219; 183 and 144; 219 and 178; and 227, 201, 194, and 153 cm−1, in the infrared spectra of propene, trans-2-butene, isobutene, cis-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene, respectively, in the solid state. The corresponding barriers to internal rotation are 2.68, 2.21, 3.24, 1.82, 2.45, and 2.25 kcal/mole.
On the Coupling Scheme in Uranyl Complexes
Authors: Görller-Walrand C. , Vanquickenborne L. G.
Published: February 2004

Simple theoretical considerations of the ligand field type have been applied to the electronic structure of insular uranyl complexes. The study of the consequences of equatorial ligation is used as a means to test the applicability of different coupling schemes for the isolated uranyl ion. From the analysis of the spectra of a large number of different uranyl complexes of Dnh symmetry, it was previously shown how the effect of equatorial ligation consists in lifting certain degeneracies of the free uranyl electronic energy levels and introducing variations in the corresponding transition probabilities. In this note the equatorial field operator is successively applied to uranyl wavefunctions derived in a Russell-Saunders approximation, in an ω -ω coupling approximation, and in an intermediate scheme. Only Russell-Saunders coupling allows a satisfactory explanation of the observed splitting and intensity pattern.
Thin Film Reflection Spectroscopy. I. Determination of Optical Constants of Amorphous Selenium and As2Se3
Authors: Bock Jan , Jen Su Gouq
Published: February 2004

The reflectivity spectra of thin films of amorphous As2Se3 and Se have been obtained. The films were deposited on aluminum substrates and had a range of thickness from 2 to 50 μ. The frequency range covered by these spectra was from 650 to 40 wavenumbers (15 to 250 μ). Two methods have been used to determine the optical constants, N and K, from the reflectivity spectra. The first employs a single equation nonlinear regression analysis on the radiant reflectance equation. The second method uses a two equation maximum likelihood analysis on the real and imaginary parts of the amplitude reflectance equation coupled with a Kramers-Kronig analysis of the phase angle. The real and imaginary parts of the complex dielectric constant, the absorption coefficient, the energy loss function and the transverse and longitudinal vibrational frequencies are then determined from the optical constants.
Thermodynamics of Rare-Earth-Carbon Systems. IV. The Lutetium-Carbon System
Authors: Guido M. , Balducci G. , De Maria G.
Published: February 2004

The vaporization of the lutetium dicarbide-carbon system has been investigated by the Knudsen effusion-mass spectrometric technique over the temperature range 2100 to 2600°K. Lu(g) partial pressures, dissociation energies for LuC2(g) and LuC4(g) molecules, and the standard heat of formation for LuC2(s) were obtained.
Correlation Functions for a Mixture of Gaussian Molecules
Authors: Helfand Eugene , Wasserman Zelda
Published: February 2004

The Mayer series for the pair correlation functions of the Gaussian mixture has been determined to ninth power of the density (11-point graphs). The model is a mixture of A and B in which the AA and BB interaction potentials are zero. The AB interaction is such that the Mayer f function, exp (−vAB/kBT) −1, is a negative Gaussian. The direct correlation functions and radial distribution functions are evaluated using Padé approximants. Comparison is made with solutions of the Percus-Yevick and hypernetted chain equations.
Molecular Beam Electric Deflection and Resonance Spectroscopy of the Heteronuclear Alkali Dimers: 39K7Li, Rb7Li, 39K23Na, Rb23Na, and 133Cs23Na
Authors: Dagdigian Paul J. , Wharton Lennard
Published: February 2004

Molecular beam electric resonance spectra for several heteronuclear alkali dimers have been obtained for the |MJ|=0→ 1 transition in the J = 1, v=0 state in a supersonic beam. Values of the ground vibronic Stark coefficient μ02/B0 and the nuclear quadrupole coupling constants eqQ were obtained. The values of μ02/B0 were (2.269± 0.002)× 10−19 cm3 for 39K7Li, (3.697± 0.004)× 10−19 cm3 for 85Rb7Li, and (3.966± 0.004)× 10−18 cm3 for 39K23Na. Badger's rule was used to estimate B0 and to determine the following values for the molecular electric dipole moment: μ0(39K7Li)=3.45± 0.1 D, μ0(85Rb7Li)=4.00± 0.1 D, and μ0(39K23Na)=2.76± 0.1 D, where the errors arise from the uncertainties in the rotational constant. Electric deflection was used to obtain a value of μ2/B for Rb23Na of (6.6± 0.5) × 10−19 cm3 and hence 3.1± 0.3 D for the dipole moment, while rf spectroscopy with power broadening was employed with 133Cs23Na to obtain (1.81± 0.02) × 10−18 cm3 for μ02/B0 and hence 4.75± 0.2 D for μ0. The translational and rotational temperatures in the supersonic beams were estimated from velocity scans and quadrupole voltage scans. An ionic model is used in a heuristic interpretation of the dipole moment results.
Effects of Screening and Polarization on Vibration-Rotation Properties of H2
Authors: Hayes Stuart F. , Beckel Charles L.
Published: February 2004

Eight simple models of H2 in the ground state are examined through use of Dunham's formulas, numerical integration of the vibrational Schrödinger equation, and the WBK energy condition. These models provide four examples for studying the effects of variable screening and four examples for the effects of polarization on vibration-rotation properties. At small v, variability of the screening parameter α correlates with positive curvatures of the ΔG and Bv curves; i.e., for the four models with α =1 both curvatures are negative, while both curvatures are positive for the four cases with α variable. The dominance of the quartic potential coefficient a2 in determining near-equilibrium ΔG and Bv curvatures is pointed out. Near dissociation, the presence of polarization causes positive curvature of these two curves. In showing this, large fictitious values of the reduced mass are employed to provide several vibrational levels very close to the dissociation limit. The Dv curves have a pronounced minimum, similar to that of the experimental curve, for α variable but not for α =1. In addition, the values of Dv and Hv are much closer to experiment for α variable than for α =1.
Manifestations of Anharmonicity in the Specific Heat of Crystalline 63Cu
Authors: Stromberg T. F. , Balestri R. J. , Overton W. C.
Published: February 2004

Accurate measurements of the specific heat of a high purity single crystal of 63Cu have been carried out for T<50°K. The data are analyzed in terms of deviations from the specific heat of a physically realistic phonon model for 63Cu. The sixth neighbor general-force model determined for normal Cu at 49°K by neutron diffraction measurements has been adapted to 63Cu by a scaling method. Precision calculations of phonon spectra were done for both general-force and simple Leighton models. A statistical analysis shows deviation curve features are statistically significant with a minimum close to that of the theoretical quartic anharmonic contribution. Smoothed experimental Cp and Cv data are given for crystalline 63Cu.
Dissociation of Molecular Ions Formed by Charge Exchange in an In-Line Tandem Mass Spectrometer
Authors: Lifshitz C. , Tiernan T. O.
Published: February 2004

Dissociations of the molecular ions of several alkanes, alcohols, and ketones, formed in charge-exchange collisions were studied using an in-line tandem mass spectrometer. The effects of both incident ion translational energy and collision chamber temperature upon the observed dissociations were examined. For most of the molecules investigated, the extent of fragmentation of the molecular ion increases as the kinetic energy is raised, indicating that energy is being converted from the translational modes into target excitation. The magnitude of this energy conversion seems to be rather small. Higher collision chamber temperatures also lead to more extensive fragmentation, presumably owing to increased vibrational excitation. In certain cases, notably methanol and 2-hexanone, an increase in the translational energy of incident ions having recombination energies near the onset of known excited ionic states of these molecules results in an increase in the relative intensity of the molecular ion product. This is interpreted as indicating the formation of long-lived excited electronic states of the molecular ion which do not revert to the ground state via radiationless transitions. Charge-exchange spectra obtained in the present study are compared with breakdown graphs previously determined from similar experiments in perpendicular-type tandem mass spectrometers, and also with the results of photoionization experiments and calculations based on the quasiequilibrium theory.
Vibrational Spectra of the Mercuric Halides Associated with Dioxane and Benzene
Authors: Brill T. B.
Published: February 2004

Far ir and Raman measurements of the mercuric halides dissolved in dioxane and benzene along with solid state HgX2-dioxane data are reported. Dipole moment measurements have suggested that the mercuric halides dissolved in dioxane and benzene are either bent with angles between 140°–160° or have a charge transfer of 0.07–0.15 electrons from the donor to the acceptor molecule. The vibrational spectra here suggest that the HgX2 retains near linearity, the X–Hg–X angle probably being greater than 175°, and that the amount of charge transfer is not unusually large.
Translational Diffusion Coefficients of Plane-Polygonal Polymers: Application of the Modified Oseen Tensor
Authors: Yamakawa Hiromi , Yamaki Jun-ichi
Published: February 2004

The translational diffusion coefficient of a plane-polygonal polymer is investigated in the Kirkwood-Riseman scheme following the procedure of Paul and Mazo with the use of the modified Oseen tensor for the finite bead model. Required summations over indices are exactly carried out with the aid of a digital computer. It is pointed out that the mathematical singularities or zeroes can occur in both cases of the Oseen tensor and the modified Oseen tensor, but never appear within the physically possible range of the strength of the hydrodynamic interaction if the beads are assumed to obey Stokes' law. The correct asymptotic solution is also obtained and the results are compared with those for a continuous rigid ring.
Energy Distribution Among Reaction Products. IV. X+HY (X ≡ Cl, Br; Y ≡ Br, I), Cl+DI
Authors: Maylotte D. H. , Polanyi J. C. , Woodall K. B.
Published: February 2004

The distribution of vibrational, rotational, and translational energies (symbolized by V′, R′, and T′) have been obtained for the products of the isotopic pair of reactions Cl + HI → HCl + I and Cl + DI → DCl + I. The experimental method was the ``arrested relaxation'' variant of the infrared chemiluminescence technique. Detailed rate constants k(V′, R′, T′) are reported in the form of contour plots for these reactions. The total detailed rate constants into specified vibrational quantum states for Cl+HI (summed over the rotational levels of each v′ level) are k(v′ = 1) = 0.22, k(v′ = 2) = 0.35, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.74; and for Cl + DI, k(v′ = 1) ≈ 0.08, k(v′ = 2) = 0.14, k(v′ = 3) = 0.35, k(v′ = 4) = 0.73, [k(v′ = 5) = 1.00], k(v′ = 6) = 0.05 [relative to the highest rate constant k(v̂′) = 1.00, in each case]. Preliminary energy distributions are also reported for the products of two other reactions, Cl + HBr → HCl + Br and Br + HI → HBr + I, in the X + HY → HX + Y family (X and Y are halogen atoms). The members of this family of reactions channel a substantial fraction of the energy available to the products into vibrational and rotational excitation, and only a small fraction into relative translation. For the Cl+HI and also the Cl+DI reaction the fractions are f̄V′ + f̄R′ (= 0.71 + 0.13) = 0.84; in contrast to f̄T′ = 0.16. As a corollary there is a marked inverse correlation between vibrational and rotational excitation in the reaction products. Despite the fact that the detailed rate constants into specified product quantum states [k(v′, J′)] are markedly different for the isotopic pair of reactions, the fractional conversion of the available energy into vibration, rotation, and translation are in close agreement (to ∼ ± 1%). This close parallelism in f̄V′, f̄R′, f̄T′ is in accord with predictions from classical trajectory studies. It indicates the usefulness of such calculations even for the case of reactions which yield products with widely spaced (vibrational and rotational) quantum levels.
Energy Distribution Among Reaction Products. V. H + X2 (X ≡ Cl, Br), D + Cl2
Authors: Anlauf K. G. , Horne D. S. , Macdonald R. G. , Polanyi J. C. , Woodall K. B.
Published: February 2004

The ``arrested relaxation'' infrared chemiluminescence technique has been used to obtain the distribution of vibrational, rotational, and translational energies (V′, R′, and T′) in the products of the exothermic reactions (i) H + Cl2 → HCl + Cl, (ii) its isotopic analog D + Cl2 → DCl + Cl, and (iii) H + Br2 → HBr + Br. Detailed rate constants k(V′, R′, T′) are reported in the form of contour plots for these three reactions. The total detailed rate constants into specified vibrational quantum states (summed over the rotational levels of each v′ level) are: (i) for H + Cl2, k(v′ = 1) = 0.28, [k(v′ = 2) = 1.00], k(v′ = 3) = 0.92, k(v′ = 4) = 0.1, k(v′ = 5) = 0.05, k(v′ = 6) = 0.005 [the values for v′ = 5 and 6 are from P. D. Pacey and J. C. Polanyi, J. Appl. Opt. 10, 1725 (1971)]; (ii) for D + Cl2, [k(v′ = 1) ∼ 0.1], k(v′ = 2) ≈ 0.3, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.9, k(v′ = 5) = 0.3, k(v′ = 6) = 0.06; (iii) for H + Br2, [k(v′ = 1) = 0.03], k(v′ = 2) = 0.18, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.99, k(v′ = 5) = 0.2, k(v′ = 6) ≤ 0.002. All of these reactions exhibit a comparatively low fractional conversion of the total available energy into internal excitation of the new molecule. The mean fractions entering vibration plus rotation are (i) for H + Cl2, f̄V′ + f̄R′ ( = 0.39 + 0.07) = 0.46; (ii) for D + Cl2, f̄V′ + f̄R′ ( = 0.39 + 0.10) = 0.49; (iii) for H + Br2, f̄V′ + f̄R′ ( = 0.55 + 0.04) = 0.59. The relatively inefficient conversion of reaction energy into vibration is thought to arise from the combined effect of ``repulsive'' energy release and a light attacking atom. As in the case of other isotopic pairs of reactions there is a close parallelism in k(V′) though not in k(v′) between the members of the pair (H+Cl2 and D+Cl2 in the present case). The increased fractional conversion of the available energy into vibration for H+Br2 as compared with H+Cl2 is indicative of a less-repulsive potential-energy surface. This is in accord with expectation, based on the change in barrier height and consequent change in barrier location on the energy surface. These reactions exhibit only a very small increase in product rotational excitation with decreasing vibrational excitation. It follows that the translational energy of the products is markedly greater for successively lower v′ states.
Energy Distribution Among Reaction Products. VI. F+H2, D2
Authors: Polanyi J. C. , Woodall K. B.
Published: February 2004

The infrared chemiluminescence (``arrested relaxation'') approach has been applied to the measurement of initial vibrational, rotational, and translational energies (V′, R′, and T′) in the products of the exothermic reactions F + H2 → HF + H and F + D2 → DF + D. Detailed rate constants k(V′, R′, T′) are reported as contour plots. The total detailed rate constants into specified vibrational quantum states (summed over the rotational levels of each v′ level) are: (i) for F + H2, k(v′ = 1) = 0.31, [k(v′ = 2) = 1.00], k(v′ = 3) = 0.47; (ii) for F+D2, k(v′ = 1) = 0.28, k(v′ = 2) = 0.65, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.71. Both reactions convert the total available energy quite efficiently into internal excitation of the new molecule. The mean fractions entering vibration plus rotation are: (i) for F+H2, f̄V′ + f̄R′ (= 0.66 ± 0.08) = 0.74; (ii) for F + D2, f̄V′ + f̄R′ ( = 0.66 + 0.08) = 0.74. The fractional conversion of available energy into vibration is comparable to that for the Cl+HI reaction (Part IV of this series) and markedly greater than that for H+Cl2 (Part V). It seems probable that the energy release is predominantly ``repulsive'' in all these reactions, but is more efficiently channeled into product vibration if the attacking atom is heavy (Cl+HI, F+H2). As in the case of other isotopic pairs of reactions (Parts IV and V of this series) there is a parallelism in k(V′) though not in k(v′) between the members of the pair. The present reactions exhibit only a small increase in product rotational excitation with decreasing vibrational excitation (— Δ R̂′ / Δ V′ more closely resembles that for the H+Cl2 reaction than that for the reaction Cl+HI). It follows that the translational energy of the products is markedly greater for successively lower v′ states.
Optical Absorption of NaMnF3
Authors: Srivastava J. P. , Mehra Anjani
Published: February 2004

Optical absorption of a NaMnF3 single crystal has been studied at 300°K and 80°K. The scheme of fitting the band positions involves four parameters B, C, Dq and α. With α fixed at its free ion value (76 cm−1) the values of B, C, and Dq at 80°K are found to be 845, 3040, and 775 cm−1, respectively. Vibrational progressions are observed in the fine structure of some of the bands at 80°K from which approximate vibration frequencies of the crystal have been determined and compared with those of other perovskite fluorides. Some of the bands observed above 35 000 cm−1 are identified with the simultaneous electronic excitation of Mn2+ ion pairs.
Nuclear Magnetic Relaxation Study of Formic Acid. Isotope Effect and Carbon-13 Relaxation
Authors: Ozawa Hiroshi , Arata Yoji , Fujiwara Shizuo
Published: February 2004

The transient recovery after adiabatic inversion has been observed separately for the magnetizations of the C12 – H, 13C–H, and O–H protons of formic acid. A large difference was observed between the decay constants for the C12–H and C13–H protons. It has been concluded that this difference is due to (1) flip of the 13C spin resulting in an exchange of the two C13–H proton signals, and (2) intramolecular dipolar coupling between the 1H and 13C spins. The above results were used along with the nuclear Overhauser effect data to estimate the 13C spin-lattice relaxation time. It was also shown that the difference in relaxation times between the C12–H and C13–H protons is primarily due to the intramolecular dipolar coupling between the 1H and 13C spins.
Ionization of Argon by Electron Impact
Authors: Crowe A. , Preston J. A. , McConkey J. W.
Published: February 2004

The ionization efficiency curves for Ar+ and Ar2+ have been measured for electron energies from threshold to 300 eV. Structure in the Ar+ curve has been confirmed and arguments and evidence are put forward to support the view that this structure is due to production of the ion via various channels (in particular the autoionization channels) rather than to ``competition'' between the Ar+ and Ar2+ channels as has been suggested recently.
γ Radiolysis of Gaseous Carbon Dioxide at High Densities
Authors: Yoshimura M. , Chosa M. , Soma Y. , Nishikawa M.
Published: February 2004

The γ radiolysis of gaseous carbon dioxide has been investigated at 50 ± 1°C over the density range of 0.2 to 0.6 g/ml. At density of around 0.5 g/ml, G(CO) from pure carbon dioxide showed a very marked increase. Addition of SF6 at these densities efficiently reduced G(CO). From this it appears that formation of carbon monoxide results mostly from charge neutralization. Examination of the mechanisms in the radiolysis of carbon dioxide in gas and liquid phase, and a calculation on a simple model indicate that this neutralization is of geminate character. Upon addition of hydrocarbons which react with oxygen atoms as well as the addition of both hydrocarbons and SF6, G(CO) passed through a maximum and reached the value of 2.2 at higher concentrations of hydrocarbons, independent of density. It was interpreted that (1) the positive ions involved in neutralization are probably clustered CO2 + in agreement with the above inference, and that (2) there are at least two species responsible for the rapid re-oxidation of CO.
Optical Activity of Vibrational Transitions: A Coupled Oscillator Model
Authors: Holzwarth G. , Chabay Ilan
Published: February 2004

The infrared optical activity arising entirely from molecular vibrational transitions is estimated by a coupled oscillator model for dimerlike molecules of high symmetry, such as diketopiperazines. Information on molecular geometry and experimental measurements of the absorption intensities of the monomer normal modes are sufficient to evaluate the rotational strengths. It is shown that rotational strengths of vibrational modes can be as large as 10−42 esu2 · cm2 (10−4 D ·μB).
Quenching of Infrared Chemiluminescence: Rates of Energy Transfer from HF (v ≤ 5) to CO2 and HF, and from DF (v ≤ 3) to CO2 and HF
Authors: Airey J. R. , Smith I. W. M.
Published: February 2004

The intensity of HF (and DF) infrared chemiluminescence from vibrationally excited molecules produced in the chain reaction H + F2 → HF + F; F + H2 → HF + H (and its deuterium analogue) has been studied as a function of the concentration of added CO2 and HF. Using a steady-state analysis rate coefficients have been determined for transfer of vibrational energy from HF (v ≤ 5) and DF (v ≤ 3) to (vibrationally cold) CO2 and HF. The results are discussed in terms of possible mechanisms for energy transfer and the importance of the processes in chemical lasers.
Photogeneration in Trinitrofluorenone-Poly(N-Vinylcarbazole)
Authors: Melz Peter J.
Published: February 2004

Experimental results for the field dependence of the photogeneration efficiency are interpreted in terms of a two step process. The first step involves autionization of the photon-excited bound state into a continuum state, and has efficiency φ0. The second step depends strongly on the applied field and involves separation of the electron-hole pair by diffusion under the influence of their mutual Coulomb attraction and the applied field. The photogeneration efficiency for the system 0.06 mole 2,4,7-trinitro-9-fluorenone to 1 mole of the poly (N-vinylcarbazole) monomer has been determined in the field range from 104 to 5×105 V/cm for temperatures from 4 to 50°C. The experimental results are compared to the predictions of the Onsager theory of geminate recombination, which is thought to describe the second step in the process. The field dependence of the photogeneration efficiency is used to determine that the yield into the auto-ionized state φ0 is approximately 0.23, and the initial electron-hole separation r0 is 25 Å. The increase in photogeneration efficiency observed upon increasing the trinitrofluorenone content is attributed to an increase in r0 rather than φ0, but it is the high φ0 for this system which results in higher intrinsic photogeneration efficiency than that of anthracene.
Electron Spin Resonance Study of PH4 Trapped in Solid Krypton
Authors: McDowell C. A. , Mitchell K. A. R. , Raghunathan P.
Published: February 2004

The ESR spectrum of the PH4 radical, produced by the vacuum uv photolysis of phosphine in solid krypton, is reported for the first time. The spectrum centered at g=2.002 is consistent with four equivalent hydrogens, and shows only isotropic hyperfine splittings (ap = 973.8 ± 2.0 G and aH = 21.0 ± 2.0 G). The observed equivalence of the hydrogens contrasts with the spectra reported previously for PF4. A treatment of the energies of configurations for PH4 with the CNDO molecular orbital method indicates the optimum geometry to be C2v with HPH angles equal to 162° and 97°; additionally, the energy barrier to pseudorotation through a C3v intermediate is estimated to be relatively low (approximately 6 kcal mole−1), and this leads to the possibility that the equivalence of the hydrogens is due to internal tunneling motions.
Monte Carlo Trajectory Calculations of the Three-Body Recombination and Dissociation of Diatomic Molecules
Authors: Shui Ven H.
Published: February 2004

The modified phase-space theory of reaction rates has been applied to the problem of the three-body recombination and dissociation of diatomic molecules. The results illustrate the important influence of the weak attractive minimum in the third-body interaction potential and the effect of barrier penetration for recombination at low temperatures. The system N2+Ar was used as a typical illustrative example, and good agreement was obtained between the theoretical predictions and the experimental measurements of the reaction rate coefficients over the temperature range 200–12 000°K. The recrossing factor and the nonequilibrium factor were obtained from Monte Carlo trajectory calculations for states near the dissociation limit. The trajectories were sampled within the reaction zone with a weight proportional to the equilibrium reaction rate, and numerically integrated in both timewise directions to determine the complete histories of the collisions. A simple, separable function for the equilibrium transition rate R(εi, εf) from initial energy states εi to final energy states εf, which could be characterized by three parameters, was obtained to fit the numerical data and was used to solve the steady-state master equation. Distributions of the trajectories with respect to energies and impact parameters are presented, and several typical trajectories are shown to illustrate the important features of the collisions. The contribution to the over-all reaction rate from the ``complex mechanism'' was also obtained.
Carrier-Exciton Interactions in Crystalline Anthracene
Authors: Wakayama Nobuyuki , Williams Digby F.
Published: February 2004

Quenching of delayed fluorescence by injected holes and electrons is observed when either monomolecular or bimolecular exciton processes afford the dominant exciton decay mechanism. With small triplet exciton densities, injected carriers reduce the triplet exciton lifetime, and hence the delayed fluorescence intensity. With high triplet exciton densities this effect is unimportant; however, the over-all triplet-triplet annihilation rate constant is found to increase while the singlet component of the annihilation rate constant decreases in the presence of charge carriers. These effects are discussed in terms of triplet pair formation and annihilation.
Decay of Pair Correlations in Hard Sphere Fluids
Authors: Perry P. , Throop G. J.
Published: February 2004

Using exact results for one dimension and the Percus-Yevick equation for three dimensions, we have calculated the asymptotic form of the pair correlation function for hard sphere fluids. Results are given for the inverse correlation length, period and phase of oscillations, as well as the amplitude. Numerical values are given for three dimensions.
Isobaric versus Canonical Ensemble Formalism for Monte Carlo Studies of Liquids
Authors: King Harry F.
Published: February 2004

The Metropolis Monte Carlo method is one of two main approaches to computer simulation of liquid properties. It has virtually always been employed within the canonical ensemble formalism. By including density as one of the variables for the random walk, the Metropolis method becomes applicable to the analysis of a closed, isothermal, isobaric system (isobaric ensemble conditions). The analysis is directed toward equilibrium properties of classical models of dense polyatomic liquids such as water. Density, compressibility, constant pressure heat capacity, enthalpy and coefficient of thermal expansion are obtained directly in terms of mean values and variances of a two-dimensional distribution, g(U, V) of random walk steps. The method appears to be well suited to the study of liquids in the vicinity of the triple point.
Repulsive Potentials of Atomic Ions, Atoms, and Molecules
Authors: Spears Kenneth G.
Published: February 2004

The repulsive potentials of all alkali (+) and halide (−) ions are determined by combining the available gas phase alkali halide data, ion-rare-gas scattering data, and ion-H2O bond energy data. Computation of ion-H2O bond energies with an electrostatic model allows a self-consistent test of scattering data and potential combining rules. Knowledge of the individual ion potentials allows computation of anisotropic molecular repulsive potentials from bond energy data. The anisotropic potentials of H2O and one component of the N2 potential are computed. The ion repulsive potentials also allows testing rare-gas scattering data for consistency of radial dependences; Kr and Ne potentials may need additional scattering measurements.
Ion-Neutral Bonding
Authors: Spears K. G.
Published: February 2004

Electrostatic calculations of bond energy are made for a variety of ion-neutral systems, and where possible the calculations are compared with experimental results. An independent semiempirical determination of ion repulsive potentials allows accurate calculation of bond energies for H2O molecules clustered to all alkali (+) and halide (−) ions; the cases of one and two H2O molecules are computed here. Contrary to previous estimates on these systems, the ion-quadrupole energy is small and there is very little, if any, covalent bonding in F− · H2O. Bond energies and entropies of association are computed for alkali (+) and F− ions with O2, N2, and CO2; the results yield predictions of equilibrium constants. Relative bond strengths of these neutrals with any one ion are determined by the ion-quadrupole energies. The bond energies of Mg2+, Ca2+, and Ba2+ with O2, N2, CO, CO2, N2O, and H2O are approximated. The molecular hyperpolarizability is very important in the bonding of doubly ionized atoms and is capable of explaining several anomalies in experimental termolecular association rate constants. The bonding of molecular ions is discussed and the O2+ repulsive potential is derived and used to compute the O2+ · H2O bond energy.
Infrared Spectrum and Force Constants in CH3CD3
Authors: Eggers D. F. , Wilson H. W.
Published: February 2004

The gas-phase infrared spectrum of CH3CD3 has been observed under moderately high resolution. Three of the E fundamentals were sufficiently resolved so that a clear-cut choice of the RQ0 transition was possible. Band centers were obtained for all fundamentals, and combinations and overtones below 3000 cm−1 were also measured and assigned. Experimental Coriolis zetas were deduced from Q branch spacings in four of the E fundamentals. Theoretical values of the vibration frequencies and Coriolis zetas were computed from three different potential functions. The constrained hybrid orbital force field of Duncan was shown to agree best with experiment.
Invariant Expansion. II. The Ornstein-Zernike Equation for Nonspherical Molecules and an Extended Solution to the Mean Spherical Model
Authors: Blum L.
Published: February 2004

The Ornstein-Zernike equation for fluids with nonspherical molecules obtained in a former publication [L. Blum and A. J. Torruella, J. Chem. Phys. 56, 303 (1972)] is written in coordinate space as a convolution matrix equation. A rather simple property of the angular coupling coefficients of our former work allows us to write the Ornstein-Zernike equation in irreducible form, as a set of uncoupled matrix equations, of rather small size. A generalization of Baxter's form of the Ornstein-Zernike equation to matrices allows us to write a formal solution to the mean spherical model of neutral hard spheres with almost arbitrary electrostatic multipoles. This is an extension of Wertheim's solution for dipoles [J. Chem. Phys. 55, 4291 (1971)]. The formal solution consists in showing that the direct correlation function inside the hard core is a polynomial in the interatomic distance r. The coefficients of the polynomials are obtained by solving a set of quadratic matrix equations. The class of potentials that admit this kind of a solution is larger than the electrostatic multipole interaction but does not include some cross interactions like the dipole-quadrupole interaction.
Optimized Cluster Expansions for Classical Fluids. I. General Theory and Variational Formulation of the Mean Spherical Model and Hard Sphere Percus-Yevick Equations
Authors: Andersen Hans C. , Chandler David
Published: February 2004

Computationally convenient theoretical methods for calculating the thermodynamic properties and pair correlation functions of a classical multicomponent fluid are presented. The Mayer cluster series for the Helmholtz free energy and pair correlation function are transformed using topological reduction to more compact forms involving a renormalized potential. Then the convergence of the two series is improved by an optimal choice of the renormalized potential. The result is two rapidly convergent series which are useful both for ionic solutions and for simple liquids with short range intermolecular forces. When these series are truncated, very accurate and convenient approximations are obtained for both types of fluids. Another set of results is a variational formulation of the mean spherical model and hard sphere Percus-Yevick equations for the pair correlation functions of multicomponent fluids. The variational formulations greatly facilitate the process of solving the equations numerically. Each of these results can be extended to models for molecular fluids with only a moderate increase in computational effort.
On the Quenching of O(1D) by N2 and Related Reactions
Authors: Fisher E. R. , Bauer Ernest
Published: February 2004

As an extension of earlier work on the quenching of electronically excited alkali metal atoms by N2 and CO, that uses a model of curve crossing involving an ionic intermediate state, here we treat the quenching of O(1D) by N2, a process which proceeds by curve crossing of covalent states. The model is also applied to the vibrational relaxation of N2 in collision with O(3P) atoms and to the unimolecular decomposition of N2O. The order of magnitude of the rate constants for all three processes can be explained by the present model, using the same value of the electronic coupling potential for the curve-crossing process; this value is significantly larger than the corresponding value for isolated O(3P) and O(1D) atoms. In the quenching of O(1D) by N2, the electronic-vibrational coupling is weak, channeling less than 5% of the electronic quantum into vibrational levels of N2, but the quenchant N2 is likely to be rotationally excited. The vibrational relaxation of N2 by oxygen atoms arising due to curve crossing rather than to adiabatic (Landau-Teller) collisions has a significant activation energy, ∼0.8 eV, so that the rate coefficient for vibrational relaxation due to curve crossing is expected to show a strong temperature dependence and to dominate at temperatures above 600°K.
Number Dependence of Small-Crystal Thermodynamic Properties. I
Authors: Hoover William G. , Hindmarsh Alan C. , Holian Brad Lee
Published: February 2004

The approach of small-crystal thermodynamic properties to the large-crystal limit of thermodynamics is studied numerically. We calculate the number dependence of the vibrational entropy for two- and three-dimensional crystallites by direct integration of the canonical partition function. A simple functional representation of the data shows that small-crystal entropies lie within 10k of the predictions of macroscopic thermodynamics.
Potential Constants of Iron Pentacarbonyl from Vibrational Spectra of Isotopic Species
Authors: Jones Llewellyn H. , McDowell Robin S. , Goldblatt Maxwell , Swanson Basil I.
Published: February 2004

The vibrational spectra of Fe(12C16O)5, Fe(13C16O)5, and Fe(12C18O)5 have been observed. Most of the fundamentals have been assigned, with some changes from earlier results in the literature. Potential constants have been calculated by constraining many of the interaction constants to values estimated from analogous constants of the hexacarbonyls. The results indicate that the axial CO bonds are stronger than the equatorial CO bonds. This implies that the axial MC bonds are weaker than the equatorial MC bonds, though the calculated MC potential constants are not significantly different.
Infrared Spectrum of Matrix-Isolated Nitrate Ion
Authors: Tsuboi Masamichi , Hisatsune I. C.
Published: February 2004

The infrared spectra of the nitrate ion isolated in KI, KBr, KCl, NaBr, and NaCl matrices have been examined in the 4000–400 cm−1 region and analyzed. The results indicated that the site symmetry of such a nitrate ion is C3ν. Some anharmonicity constants have been determined, and they were found to be essentially independent of the matrix. The harmonic frequencies, on the other hand, were shifted to higher frequencies as the lattice constant of the matrix was decreased. The fundamental bands showed Lorentz band shapes, and the temperature dependence of their bandwidths allowed an estimation of the potential barrier to reorientation of the nitrate ion in the host matrix. In the KI matrix, bands assignable to combinations of an internal vibrational mode with localized lattice modes have also been observed.
Brownian Motion of N Interacting Particles. I. Extension of the Einstein Diffusion Relation to the N-Particle Case
Authors: Murphy T. J. , Aguirre J. L.
Published: February 2004

The analogs of the Smoluchowski equation and the Einstein diffusion relation for the case of N interacting Brownian particles are derived by a method of the Chapman-Enskog type from the N-particle analog of the Fokker-Planck equation. Explicit expressions are given for the friction tensors and the diffusion tensors in the long-range limit.
Extraction of Scattering Information from Bound-State Configuration-Interaction Computations: Elastic Electron-Hydrogen Scattering
Authors: Murtaugh Terence S. , Reinhardt William P.
Published: February 2004

Using the fact that for complex energies the Fredholm determinant, D(z), for the partial wave Lippmann-Schwinger equation may be constructed using only square integrable (L2) basis functions, electron-hydrogen-atom elastic phase shifts are computed using input generated from a standard bound-state Hylleraas program. The necessary numerical analytic continuation needed to take the z=E+iε limit is performed by the pointwise rational-fraction method and yields the phase shift over a continuous range of energies from a single major computational step. No integrals over non-L2 functions are needed for the computation.
Nitrogen-14 Nuclear Quadrupole Resonance Study of Lithium Hydrazinium Sulfate
Authors: Hastings R. N. , Oja Tõnis
Published: February 2004

Nitrogen-14 nuclear quadrupole resonance (NQR) transition frequencies of the NH2 group of the hydrazinium ion in lithium hydrazinium sulfate have been measured as a function of temperature from 4.2 to 360°K. The usual treatment of temperature dependence, which considers the effect on the transition frequencies of molecular oscillations about the principal field gradient axes, is generalized by considering oscillations about an arbitrarily oriented axis system. This generalization leads to the determination of the orientation of the field gradient axes in the NH2 group, and to a clarification of the existing model of the dynamics of the hydrazinium ion. It is found that between 40 and 320°K the NH2 group undergoes small oscillations about the N–N axis whose amplitude increases linearly with temperature. Above 320°K the amplitude of these oscillations increases more rapidly than a linear function. It is also found that above 150°K, proton exchange in the H–N–H plane of the NH2 group takes place rather than rigid rotation of the protons about the bisector of the H–N–H angle. The linear increase of oscillation amplitude with temperature between 40 and 320°K is found to be inconsistent with the Bayer theory, unless and ad hoc assumption is made about the temperature dependence of the oscillation frequencies.
Carbon-13 T1 Measurements under Proton Coupled and Decoupled Conditions
Authors: Alger Terry D. , Freeman Ray , Grant David M.
Published: February 2004

A theoretical treatment is presented of carbon-13 spin-lattice relaxation observed with and without proton decoupling, with particular emphasis on the influence of dissolved oxygen. It is shown that the recovery of carbon-13 magnetization after population inversion does not follow a pure exponential in the absence of proton irradiation, and contains terms involving proton transition probabilities. This apparent carbon-13 relaxation time can differ significantly from the relaxation time measured under proton decoupled conditions, tending to be longer when measured by pulse methods (which excite all the spin multiplet components) and shorter when measured by adiabatic rapid passage (where only one multiplet component is normally affected). Experimental results for benzene are used to illustrate the importance of these effects including the presence of dissolved oxygen. The significantly larger effect of oxygen on the apparent relaxation times, observed without proton decoupling, can be explained on the basis of the oxygen's greater direct influence on the proton transition probabilities.
van der Waals Interaction between Two Diatomic Molecules
Authors: Roberts P. J.
Published: February 2004

An expansion is derived for the van der Waals r−6 interaction between two homonuclear diatomic molecules. The result is presented for the more general potential r−2n−2, n=0, 1, 2, ··· in two different forms, one being an integral representation, the other an infinite series in inverse powers of the distance between the molecular ``midpoints'' when this distance exceeds the common ``length'' of either molecule.
Collision Dynamics of Three Interacting Atoms: The Faddeev Equations
Authors: Micha David A.
Published: February 2004

An approach to atom-diatom collisions is developed in terms of sums of spin-dependent atomic pair interactions. Elastic, inelastic, atom-exchange, and dissociative collisions are simultaneously considered within the Faddeev formalism, neglecting electronic excitation or ionization. These events may be described as successions of pair-encounters where atomic spins are coupled in singlet or triplet states. At high energies a justification is given for the ``spectator stripping'' model for the reaction A+BC → AB+C and the corresponding probability amplitude is obtained. It is also found that the first correction to this model involves a ``displacement'' mechanism and an effective interaction between A and C.
Dielectric Constant and Molar Polarizability of Compressed Gaseous and Liquid Fluorine
Authors: Straty G. C. , Younglove B. A.
Published: February 2004

In this paper we present accurate wide-range measurements of the dielectric constant of saturated liquid fluorine from 70 to 140°K and of compressed fluid fluorine at temperatures between 100 and 300°K at pressures to 21 MN/m2(1 MN/m2=9.8692 atm=145.038 psi). The data are combined with previously measured densities to determine the molar polarizability and its dependence on density and temperature. The density range examined extends to nearly 3 times the critical density. The molar polarizability is found to increase initially with density and then decrease. Current theories of the dielectric constant are found to give satisfactory qualitative interpretation of the density dependence of the molar polarizability but do not give satisfactory quantitative predictions.
EPR Study of Diphenylnitroxide in Benzophenone
Authors: Lin Tien-Sung
Published: February 2004

A complete anisotropic EPR study of diphenylnitroxide imbedded in a benzophenone single crystal is presented. The 14N hyperfine tensors are Txx=1.9, Tyy=3.6, Tzz=23.8 G. The g tensors are gxx=2.0092, gyy=2.0056, gzz=2.0022, where x, y, and z lie along the N–O axis, the line drawn between the centers of phenyl rings, and a direction perpendicular to the x and y axes, respectively. The isotropic values obtained from the molten mixed crystal, a supercooled liquid, are aN=9.77 G, g=2.0055, a1H=a3H=1.86 G, a2H=0.87 G. The study implies that the unpaired π* electron is delocalized into the phenyl rings. The bonding character of the radical is discussed.
Doppler Broadening of Positron Annihilation Photons in Silver Halide Crystals Following High Energy Implantations of C5+, N5+, O6+, and S6+
Authors: Leber R. Eric , Lambrecht Richard M.
Published: February 2004

The Doppler broadening of positron annihilation photons detected by a Ge(Li) detector was employed to probe the interactions of positrons in high purity AgCl and AgBr (95%)+AgCl sheet crystals that had been exposed to 1011-1013 ions cm−2 of implanted 12C5+, 14N5+, 16O6+, or 32S6+. The narrowing of the Doppler broadened spectrum varied with the implanted ion, the concentration of the dopant, and the composition of the halide crystals. The decrease in linewidth is attributed to the electronic environment of the defects, and an increased probability of annihilation of near-thermal positrons with conduction electrons relative to annihilation with core electrons.
Electric Resonance Spectroscopy of Hypersonic Molecular Beams
Authors: Dyke T. R. , Tomasevich G. R. , Klemperer W. , Falconer W. E.
Published: February 2004

A hypersonic nozzle beam (Mach 19) of HCN molecules was studied by electric resonance spectroscopy. Translational temperatures of 4°K and rotational temperatures of 64± 30°K were found from a 283°K nozzle source. The monoenergetic character of the beam and the rotational cooling lead to an order of magnitude increase in signal-to-noise ratios. The absence of an appreciable velocity dispersion and a homogeneous radiation field allowed a critical comparison with theoretical two-level resonance lineshapes. An SF6 diluent was used to reduce the beam velocity by one-half and increase spectral resolution over a thermal (effusive) source. SF6 vibrational relaxation was observed. Chemically interesting species can be formed: ArXe, XeHCl, (HCl)2, (HCN)x, and (HF)x.
Concept of Activation Energy in Unimolecular Reactions
Authors: Gilbert R. G. , Ross I. G.
Published: February 2004

An exact expression is derived, valid for all pressure regions, for the activation energy of a unimolecular reaction. Because of the reaction, the distribution of reactant molecules among vibrational levels deviates from a Boltzmann distribution; this deviation is explicitly taken into account. In the high-pressure limit, the expression reduces to a well-known form: Eact=〈EK〉 / 〈K〉−〈E〉, due originally to Tolman. In the low-pressure limit our expression contains terms which do not appear in Tolman's formalism. These are a term EM which depends on the deviation from a Boltzmann distribution, and a term EQ which arises from the thermal average of energy-dependent vibrational cross sections. It is shown that the low-pressure expression for Eact does indeed yield an energy fairly close to the energy at which conversion from reactant to product occurs. An approximate analytic expression for Eact is obtained for the case that the cross sections for vibrational energy transfer can be approximated by a truncated harmonic oscillator model. A numerical study of the thermal decomposition of N2O, using SSH theory to evaluate collision rates, shows that both EM and EQ make important contributions to the final value of Eact. It is also shown that the steady-state approximation can lead to serious error in calculating low-pressure rate constants and activation energies at high temperatures.