bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Diffusion in Isotopic 16O2–18O2
Authors: Mathur B. P. , Watson W. W.
Published: February 2004

The isotopic thermal diffusion factor α0 has been measured for a 90% 16O2–10% 18O2 symmetrical mixture, using both the conventional two-bulb apparatus and the trennschaukel. The values are in the average temperature range of 125–440°K. We find that α0 is negative below about 135°K, while at higher temperatures there is good agreement with the literature values (α0 = 0.45 at 450°K). The low-temperature results (below 200°K) are similar to the findings of Raman et al. for 14N2–15N2, and the recent measurements of Stevens et al. on the isotopic mixtures of methane. Theoretical calculations according to the Chapman–Enskog theory using an Exp-6 potential (α = 17, ε/k = 132.0°K) agree well with the experimental values in the temperature range 260–440°K. At low temperatures the agreement is rather poor. Since even at 78°K as many as five rotational states are excited in this molecule, inelastic collisions must play an important role over the entire temperature range. At our low temperatures, with a fair fraction of the gas at 78°K, the possible incipient polymerization in O2 may, to some extent, be responsible for the negative values of α0.
First-Order Intensity Perturbations for the Vibration–Rotation Lines of Asymmetric Rotor: Theory and Application
Authors: Braslawsky J. , Ben-Aryeh Y.
Published: February 2004

A general theoretical treatment of intensity perturbations is given for the vibration–rotation lines of asymmetric rotor. The nonlinear XYX molecules are specially treated, and for this case a new formula is derived for the correction F factors of the intensities. A good agreement is obtained with other authors for the bands ν1 and ν2 of H2O;, and new information is derived for the band ν3 of the same molecule.
Gas-Phase Structure of XeF2
Authors: Reichman Sandor , Schreiner Felix
Published: February 2004

The ν3 region of the spectrum of XeF2 at 560 cm−1 was studied under high resolution. The analysis of the band gives ν0 = 560.101 cm−1, B0=0.11350 cm−1, α3 = 3.31 × 10−4 cm−1, and X23 = −1.44 cm−1. The xenon–fluorine bond length obtained from B0 is 1.9773 ± 0.0015Å.
Dirac Delta Functions in the Laplace-Type Expansion of rnYlm(θ, φ)
Authors: Kay Kenneth G. , Todd H. David , Silverstone Harris J.
Published: February 2004

The theory of generalized functions and Fourier transforms is used to derive the Laplace-type expansion for r12nYlm(θ12, φ12). This approach leads naturally to a general formula for the Dirac delta-function terms which occur when n≤−3 and n − l is odd.
Semiempirical Energy Surface for H3
Authors: Salomon Mark
Published: February 2004

A semiempirical potential-energy surface has been generated from the London equation by evaluating the Coulomb and exchange integrals using a method which takes into account the effective orbital overlap as a function of internuclear distance. A single adjustable parameter is used to fit the calculated activation energy to the observed value. The surface is symmetrical and very flat over the saddle-point region, which leads to much lower values for the probability of H-atom tunneling through the barrier.
Photoionization, Absorption, and Fluorescence of CS2
Authors: Cook G. R. , Ogawa M.
Published: February 2004

Absolute absorption and photoionization coefficients of CS2 have been measured in the 600–970-Å region. A 1-m radius Seya–Namioka-type scanning vacuum-ultraviolet monochromator was used with the Hopfield helium continuum source as a background and with photoelectric detection of the dispersed radiation. A number of peaks in both the absorption and photoionization spectra were observed at wavelengths that agree well with a higher resolution photographic spectrum. The total continuum underlying the band structure has been estimated as well as the fraction due to absorption and to ionizations. Fluorescence was observed when the wavelength of the incident radiation was shorter than 976.5 Å. A brief discussion of its origin is given.
Molecular Collisions. X. Restricted-Distorted-Wave–Born and First-Order Sudden Approximations for Rotational Excitation of Diatomic Molecules
Authors: Fenstermaker R. W. , Curtiss C. F. , Bernstein R. B.
Published: February 2004

Although a number of approximation methods have been widely used in the field of molecular rotational excitation and scattering, their interrelationships and ranges of applicability have not always been clearly established. The present work is a comparison of several of these approximations. Considered are the time-independent treatments such as the distorted wave approximation (DWA), the restricted distorted wave (RDW) and the RDW–Born approximations, and the time-dependent ones such as the sudden approximation (SA), full trajectory and straight-line limit, and the first-order perturbation approximations. Equivalence is demonstrated between the RDW–Born and first-order SA, and convenient analytical forms are presented for the resulting transition probabilities.
Time-Dependent Concentration Fluctuations of Polystyrene in Cyclohexane
Authors: Chu B. , Kuwahara N. , Tamsky M.
Published: February 2004

We report the effects of long-range correlation for a critical mixture of polystyrene (Mn≈392 000) in cyclohexane at small temperature distances from the phase separation temperature (T − Tp < 1.5°) by means of quasielastic light scattering. The estimated coherence length for the polystyrene–cyclohexane system from Rayleigh linewidth studies is somewhat smaller than that from angular dissymmetry measurements if we assume that the temperature dependence of the molecular-interaction range remains unchanged from static to dynamic phenomena.
Study of the Geometry and Spectra of the Allylic Systems by Ab Initio Methods
Authors: Peyerimhoff Sigrid D. , Buenker Robert J.
Published: February 2004

Ab initio SCF MO and CI calculations are reported for the allyl cation, radical, and anion and also for their cyclopropyl isomers. A large series of SCF calculations is employed to study the relationship between the position of the hydrogen atoms of C3H5+ and the magnitude of its CCC skeletal internuclear angle. The differences in the molecular geometry and heights of various rotational barriers observed between the cations and the related neutral species allene and cyclopropene are subsequently explained in terms of changes in electronic configuration induced upon protonation of these C3H4 systems. Analogous geometrical phenomena for the neutral C3H5 systems and the allyl anion are investigated via Koopmans' theorem. Finally the electronic spectrum of the allylic systems is studied by means of a large CI calculation in which excitations involving σ MO's are given explicit consideration; the results of this treatment are seen to differ markedly from those obtained by semiempirical π-electron calculations, especially in that many of the low-lying excited states obtained herein are found to result from the σ → π category of electronic transitions.
Photoelectron Emission by Solutions
Authors: Baron Bill , Chartier Pierre , Delahay Paul , Lugo Roberto
Published: February 2004

A detailed experimental study is reported of electron photoemission at a solution–nitrogen interface by aqueous solutions of potassium or sodium ferrocyanide. Old work on this problem is briefly reviewed as well as similar studies with organic systems and alkali metals in liquid ammonia. The following topics are covered: outline of experimental methods; variations of collected current with field strength and gas pressure; dependence of electron drift velocity in gases on field strength and pressure; plot of the reciprocal of current against the reciprocal of electron drift velocity; application of this plot to the determination of the emitted current and the average velocity and energy of electrons at emission; dependence of emitted current on field strength and possible explanations based on the photoelectric Schottky effect and/or field penetration in solution; correlation with double layer structure; spectral response for the collected current and determination of the threshold at 236 mμ for 0.1M K4Fe(CN)6; correlation with absorption band for charge transfer to solvent; influence of ionic valence and spectral shift.
Molecular Dynamics of Weakly Coupled Electric Dipoles on a Rigid Lattice. II. The Dielectric Response Function
Authors: Bellemans A. , Köhler M. , Gancberg M.
Published: February 2004

The dielectric response function of a finite two-dimensional system of dipoles is evaluated numerically by the method of molecular dynamics. The dipoles are located on the sites of a rigid square lattice and are only allowed to rotate; the specimen itself is circular and includes 101, 193, or 421 dipoles. Two types of coupling are considered: (a) dipolar interactions and (b) classical exchange interactions favoring either parallel or antiparallel alignment. The corresponding response functions are largely different in each case. For dipolar interactions they differ rather little from the response function corresponding to zero coupling and the influence of the long-range part of the potential seems negligible. On the contrary, exchange interactions lead to response functions which deviate strongly from the zero-coupling limit, even when the coupling is rather weak. The Fourier transforms of these response functions and the corresponding Cole–Cole diagrams are constructed and discussed as well.
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Level of Pr3+ in Crystal Matrices and Energy-Level Parameters for the 4f2 Configuration of Pr3+ in LaF3
Authors: Carnall W. T. , Fields P. R. , Sarup R.
Published: February 2004

The absorption spectrum of Pr3+ in LaF3, LaCl3, CaF2, Pr(Y)Cl3·6H2O, and Pr2(SO4)3·8H2O was investigated. Evidence for the S01 level in Pr3+:LaF3 at 46 986 cm−1 is presented; this level was not observed directly in absorption in any of the other matrices studied. An analysis of the 13 observed levels in Pr3+:LaF3, based in part upon a re-examination of the experimentally observed crystal-field components of certain levels, gave the following electrostatic, spin–orbit, and configuration-interaction parameters: E1 = 4559.0, E2 = 21.954, E3 = 467.75, ζ4f = 744.44, α = 15.294, β = − 669.02, γ = 1411.8, with an rms deviation= 33 cm−1.
Internal-Rotational Spectra of Methylamines. II. The Fundamental Torsional Band of CH2DNH2
Authors: Tamagake Keietsu , Tsuboi Masamichi , Hirakawa Akiko Y.
Published: February 2004

The infrared absorption spectrum of CH2DNH2 gas has been examined in the 310–80-cm−1 region. A relatively simple fine structure observed in the 300–260-cm−1 region was assigned to that of the fundamental band designated as n = 1 ← 0, where n is the vibrational quantum number of the torsional oscillation of the CH2D group with respect to the amino group. It is shown that, in the ground state (n = 0) and in the first excited state (n = 1), there are well-defined trans and gauche rotational isomers and that each of the gauche levels at n = 1 splits into two with a separation of about 2.8 cm−1 due to the resonance between the two equivalent gauche positions. It is shown, on the other hand, that, in the higher excited states with n ≥ 2, the internal rotation couples strongly with over-all rotation, so that the fine structures of the hot bands (n = 2 ← 1, 37 ← 2, etc.) are apparently complicated. Such an energy-level structure of the internal rotation in CH2DNH2 is mainly attributable to the situation that the mode of coupling of the torsional oscillation with other vibrations is different in the trans and gauche forms, rather than to the situation that the moments of inertia are the functions of the internal-rotation angle (x).
Phase Diagrams to High Pressures of the Univalent Azides Belonging to the Space Group D4h18-I4 / mcm
Authors: Pistorius Carl W. F. T.
Published: February 2004

The high-pressure phase diagrams of CsN3, TlN3, RbN3, and KN3 were studied by means of differential thermal analysis and volume displacement. These substances decompose explosively near ∼ 460°C even at high pressures. CsN3, TlN3, and RbN3 each have a new high-pressure transformation with a volume change of ∼ 3.5% near 6 kbar at 25°C. The transition pressures increase with temperature. In the case of CsN3 this transition line meets the tetragonal/bcc transition line at a triple point at 173°C, 8 kbar. The resulting CsN3 III/bcc phase boundary was followed to 37 kbar, where it is terminated by explosive decomposition. The TlN3 tetragonal/bcc boundary was followed to 20 kbar, where it is also terminated. The melting curves of KN3 and TlN3 were followed only to ∼ 5 kbar, where they are terminated.
Ground-State Molecular Constants of Hydrogen Telluride
Authors: Moncur N. K. , Edwards T. H.
Published: February 2004

The ground states of the five isotopic species H2130Te, H2128Te, H2126Te, H2125Te, and H2124Te have been analyzed by simultaneous least-squares fits of ground-state combination differences formed from the four bands ν1 + ν2, ν2 + ν3, 2ν1, and ν1 + ν3. Values have been obtained for the ground-state constants A, B, C, the four centrifugal distortion taus, and the empirical term HK added to the second-order Hamiltonian, for each of these species.
Infrared Spectra and Geometry of TiF2 and TiF3 in Rare-Gas Matrices
Authors: Hastie J. W. , Hauge R. H. , Margrave J. L.
Published: February 2004

From an infrared study of gaseous TiF2 and TiF3 species isolated in neon and argon rare-gas matrices values of the symmetric and antisymmetric vibrational frequencies were obtained. Bond-angle measurements for TiF2, made using the isotope shift method, indicated a value of 130° ± 5°. This result has been rationalized in terms of possible electronic configurations for TiF2. Equilibrium constants for the reaction 2TiF3(g)+Ti(s)→3TiF2(g) were measured and combined with calculated free-energy-function data to indicate the stability of TiF2.
Studies of Heisenberg Spin Exchange in ESR Spectra. I. Linewidth and Saturation Effects
Authors: Eastman M. P. , Kooser R. G. , Das M. R. , Freed J. H.
Published: February 2004

A compact general theory for the effect of Heisenberg spin exchange on ESR linewidths and saturation parameters is detailed. The effects of Heisenberg exchange on the linewidths of the tetracyanoethylene anion (TCNE−) radical and the di-tert-butyl nitroxide (DTBN) radical in both dimethoxyethane (DME) and tetrahydrofuran (THF) are investigated. From comparative studies of linewidth as a function of temperature and of radical concentration, TCNE− in DME is shown to undergo strong exchange with a second-order rate constant of 4.1 ± 0.6 × 109M−1·sec−1 at 15°C. The TCNE− radical in THF exhibits an anomalous concentration-dependent linewidth effect when compared to the theory and to the experiments employing DME as the solvent. The uncharged DTBN radical shows similar spin-exchange properties in both solvents. Possible mechanisms for the anomalous linewidth effect are discussed. The effect of spin exchange on the saturation parameters of the TCNE− radical in DME is investigated in detail, and the experimental results are shown to agree, within experimental error, with the theory developed. Electron–nuclear dipolar and electron–electron dipolar relaxation effects are discussed in terms of their (small) contributions to the experimentally determined relaxation times.
Upper Bounds on Many-Channel Scattering Phase Shifts by an Adiabatic-Type Approximation
Authors: Gerber R. B. , Karplus M.
Published: February 2004

An approximate equation for the treatment of atom–atom collision problems is proposed, based on the assumption that in the closed channels nuclear kinetic energy is negligible compared with the electronic energy. It is shown that this approximation yields upper bounds on the exact scattering phase shifts when the collision energy lies below the lowest nonadiabatic resonance level. To test the quality of this approximation, three model problems, all of them involving two coupled channels one of which is closed, are introduced. Each of these models is solvable exactly, solvable in the ordinary adiabatic approximation (which provides lower bounds on the phase shifts) and solvable within the new approximation. The accuracy of the results obtained is discussed with special reference to its dependence upon the form and strength of the interactions involved.
Total Energy in Iterative Hückel Theories
Authors: Jug Karl
Published: February 2004

The relationship between the operator F for the MO's and the operator H for the total energy is studied through an expansion technique. Various cases are discussed. The Wolfsberg–Helmholz approximation is found to be an improper choice if applied to the elements of F directly. However, it may be incorporated into F via introduction into H.
Transient of One-Carrier Injections in Polar Liquids
Authors: Atten P. , Gosse J. P.
Published: February 2004

The transient space-charge-limited current technique developed in crystals is made to fit polar liquids: First, from a theoretical point of view the injection is no longer only limited by space charge, the electrode–liquid contact being non-Ohmic; second, from an experimental point of view, the electric field distribution is at every moment determined by means of the electro-optic Kerr effect, and known ions are injected by permselective membranes. Applying this technique makes it possible to estimate the mobility of different carriers injected into different polar liquids and brings out high mobility values of about 2 × 10−3 cm2 V−1·sec−1. Account is taken of the influence of bulk liquid motion to explain the high values of ionic velocities obtained.
Density Effects on the Transport Coefficients of Gaseous Mixtures
Authors: Bennett David E. , Curtiss C. F.
Published: February 2004

A modified Boltzmann equation for mixtures, which includes the effects of collisional transfer and three-particle collisions, is presented. This equation is then solved by a perturbation expansion. General expressions for the fluxes are derived, and the transport coefficients are expressed in terms of the perturbation coefficients. Finally, the various integrals encountered in the development are evaluated numerically.
Dufour Effect in Liquid Mixtures
Authors: Rastogi R. P. , Yadava B. L. S.
Published: February 2004

The Dufour effect in the liquid state has been investigated for 10 systems. Dufour coefficients have been estimated from the experimental data. The values of Dufour coefficients have been compared with those for thermal-diffusion coefficients estimated from the known data on the soret coefficient using measured values of diffusion coefficients recorded in the paper.
New Approach for Evaluating Lattice-Configurational Thermodynamic Properties
Authors: Douglas Thomas B.
Published: February 2004

As a generalization of earlier work of the author [J. Chem. Phys. 40, 2248 (1964); 45, 1080 (1966)] a completely noncombinatorial method is derived which gives for any state the exact thermodynamic properties of a system of particles on a lattice infinite in one dimension. The method appears to be essentially equivalent to, but somewhat simpler in development and application than, the matrix method used for the same problems recently. Interaction of unit configurations is explicitly considered only at lattice boundaries, leading directly to a set of independent algebraic equations giving the complete solution for a specified state. Two simple examples are given to which alternative combinatorial procedures can be readily applied without approximations, yielding identical explicit results. The general method first given is modified for the imposition of artificial density constraints, and as an illustration it is shown how this variation improves markedly, over the range of disordered densities, the convergence to an infinite plane of the hard-core square-lattice fluid with nearest-neighbor exclusion.
Low-Energy Electron-Impact Study of the 12–14-eV Transitions in Nitrogen
Authors: Williams Albert J. , Doering John P.
Published: February 2004

A high-resolution low-energy electron spectrometer has been constructed and used to study the nitrogen energy-loss spectrum in the 12–14-eV region. The relative intensities of the υ′ = 2, 3, and 4 bands of the b 1Πu←X1Σg+ transition between 12.65–12.84 eV and the intense 12.92-eV composite transition have been studied in detail at primary energies from 15–50 eV and scattering angles of 1°–40°. The relative intensities of the bands of b 1Πu←X1Σg+ up to υ′ = 4 were found to remain invariant with respect to changes in primary energy and scattering angle. However, the ratio of the 12.93-eV peak to the 12.84-eV b 1Πu←X1Σg+ (4 − 0) transition decreased by a factor of 3, with increasing scattering angle from 1° to 40°, independent of primary energy. The strong angular dependence of the relative intensities for these transitions suggests that the differential-scattering cross section for the p′1Σu+ Rydberg state at 12.93 eV is much more strongly peaked in the forward direction than that for the b 1Πu state. The effect of multiple scattering on these transitions was investigated. At low energies, the intensity of a peak at 13.2 eV increased relative to the b 1Πu bands with increasing scattering angle. There may be a singlet–triplet transition at this energy.
Thermodynamic Anomalies of a van der Waals Helium–Nitrogen Solution at the Critical Point of Pure Nitrogen
Authors: Dalton B. J. , Barieau Robert E.
Published: February 2004

For a van der Waals He–N2 solution, it is shown that in the limit of the infinitely dilute solution of He in N2 (with the exception of the heat capacity at constant volume which is zero everywhere for a van der Waals fluid) all relative partial molal thermodynamic properties of He are infinite at the critical point of pure N2; all relative partial molal thermodynamic properties of N2, with the exception of the chemical potential and the heat capacity at constant pressure, exhibit a finite, nonzero singularity at the critical point of pure N2, and the limiting value of the singularity, as a function of the concentration of He, depends on the path by which this critical point is approached. It is also shown that these same general conclusions are valid for any van der Waals binary mixture and are expressible in terms of the constants appearing in the equation of state itself.
Method of Local Configuration Interaction Applied to Electronic Systems. Hydrogen Atom and Hydrogen Molecule Ion
Authors: Rothstein Stuart M. , Welsch James E. , Silverstone Harris J.
Published: February 2004

The local configuration interaction method, a way to solve the Schrödinger equation without evaluating integrals, is applied to two electronic systems: the hydrogen atom and the hydrogen molecule ion. The exact energies are reproduced for both systems. The H2+ is treated both as a separable and nonseparable problem. The convergence to the exact energy is seen to be slower than for a variational calculation with the same basis.
Calculation of NMR Free Induction Signals for Nuclei of Molecules in a Highly Viscous Medium or a Solid–Liquid System
Authors: Woessner D. E. , Snowden B. S. , Meyer G. H.
Published: February 2004

A general solution of the isotropic rotational diffusion equation applied to NMR transverse magnetization of molecules containing two identical spin-one-half nuclei is used to obtain the spin–echo amplitudes in one, two, and multiple 90° pulse sequences. Numerical calculations using the rotational correlation times (or rotational diffusion coefficients) appropriate to a highly viscous medium are used to evaluate the observable NMR decay parameters (T2* and T3*). For rapid motion this general calculation gives the well-known results for secular contributions to transverse relaxation. In the limit of slow motion, the shape parameter (BT3*) of the spin–echo amplitude at 2τ is found to depend on the cube root of the product of the splitting constant (B) and the rotational correlation time (τc). The relevance of this formalism to solid–liquid systems is also demonstrated.
Deuteron Quadrupole Coupling Constants of Hydrogen-Bonded Systems
Authors: Olympia P. L. , Fung B. M.
Published: February 2004

A discussion of the electron distribution in the hydrogen-bond system, O1–D···O2, in relation to the first-order density matrix and the deuteron quadrupole coupling constant (DQCC), is presented. It is shown that the valence-bond wavefunction of Coulson and Danielsson is only qualitatively useful. For the computation of the DQCC, a four-electron, three-basis orbital model appears to be inadequate. Theoretical values for DQCC which are somewhat comparable to experiment over a certain range of hydrogen-bond length, O1···O2, is presented. These values are obtained with a 13-electron molecular-orbital model with sp3 hybrid orbitals. On the basis of the theoretical results the relation between the isotope effect and the DQCC is discussed. The empirical relationship between DQCC and the D···O2 bond distance proposed by Soda and Chiba and the effect of hydrogen-bond symmetry on DQCC are also examined.
ESR Studies on the Molecular Motion of the Broken End of Polyoxymethylene
Authors: Moriuchi S. , Kashiwabara H. , Sohma J. , Yamaguchi N.
Published: February 2004

The temperature dependence of the ESR line shape of the polyoxymethylene radical ∼CH2–O–H2C· is observed. In order to estimate the linewidths of the observed spectra, the spectra are simulated by using the computer, based on the theory of the line shape of an amorphous sample. The correlation times are determined from the empirical linewidths thus obtained, and the activation energy for the motion of the broken end of the polyoxymethylene molecule is evaluated from the temperature variation of the linewidth. The motion of the broken end is discussed in relation to the other types of molecular motion of the polyoxymethylene molecule.
Comparative Test of Approximations for Calculation of Energy-Level Densities
Authors: Forst W. , Prášil Z.
Published: February 2004

Two molecular models, one representing a “small” molecule and the other a “large” molecule, both with several free rotors, are used to test, by comparison with exact count, seven approximation formulas for the calculation of density of harmonic vibration–rotation states, at energies between 1000 and 20 000 cm−1. The techniques of the classical approach, the Laplace transform, steepest descents, and symmetric functions are represented among the seven formulas. Also shown is the effect of the various approximations on the energy dependence of the computed unimolecular rate constant, and on ion breakdown curves calculated by the statistical theory of mass spectra. It is concluded that the techniques of the Laplace transform [J. Chem. Phys. 46, 3736 (1967)] and steepest descents, as formulated in an Appendix, yield the best all-around approximation, while a semiclassical-type formula [J. Chem. Phys. 41, 1883 (1964)] requires least computational effort and still gives excellent results in most cases. In an Appendix, the method of steepest descents is generalized and its connection with the Laplace transform noted.
Interpretation of Crystal-Field Parameters in the Rare-Earth-Substituted Garnets
Authors: Newman D. J. , Stedman G. E.
Published: February 2004

Crystal-field parameters of Yb3+, Eu3+, Tm3+, Sm3+, Dy3+, and Er3+ ions in various garnet lattices have been analyzed using a development of the superposition model proposed by Bradbury and Newman. This effects, in principle, the separation of the crystal-field contributions of the different coordinated O2− ions and determines power laws and the angular distortion near substituted ions. A realistic separation of the contributions to the n = 4 parameters is obtained even when no allowance is made for local distortion. However, owing to their greater angular sensitivity, the contributions to the n = 6 parameters can only be separated if local angular distortions of up to 9° are allowed for. Results derived for single-ligand parameters and power laws are in good accord with theoretical results obtained for other rare-earth systems.
EPR of Ru3+ in LuAlG and LuGaG
Authors: Offenbacher E. L. , Miller I. A. , Kemmerer G.
Published: February 2004

EPR data were determined at 4.2°K for Ru3+ impurities located at the octahedral sites of two lutetium garnets and yield the following g values: g‖ = 3.161, g⊥ = 1.136 in LuGaG and g‖ = 2.907, g⊥ = 1.286 in LuAlG. From these data the dependence of the trigonal field parameter υ on polar angle is derived and represented by a quadratic function of the angular distortion of the ideal octahedron. From this dependence it is concluded that the observed trigonal fields can not be explained as arising from the superposition of a positive point-charge field onto a larger negative field of the ligands.
Metastable Ions in the Mass Spectra of CD3CH3 and C2H6
Authors: Löhle U. , Ottinger Ch.
Published: February 2004

The mass spectra of CD3CH3 and C2H6 were searched for metastable transitions using a mass spectrometer with high sensitivity. With a detection limit of about 3 × 10−8 of the total ionization, 54 metastable transitions in CD3CH3, and 19 in C2H6 were found. All of these were checked for possible collision-induced contributions by admitting krypton to the analyzer tube. The CH3CD3 decompositions are classified as (a) C–C ruptures, (b) H2, HD, and D2 eliminations, and (c) loss of an H or D atom. The first category provides information about D–H scrambling. The rate constant for D–H scrambling prior to C–C rupture is 5 × 104 sec−1 for parent ions, but very much larger in fragment ions, with the possible exception of CH2CD2+. The second category gives information about the isotope effect between H2, HD, and D2 loss. Compared to the loss of H2, the elimination of HD is diminished about fivefold and that of D2 by a factor of about 150. In the parent ion much less (if any) D–H scrambling occurs prior to the HD elimination than prior to the C–C rupture, in accord with the expected dependence of the scrambling rate on internal energy. Practically no H2 and D2 loss from the parent ion is found, indicating that the mass-28 ion of ethane has the ethylene structure. The H and D losses provide only a few, but very convincing, examples of the strong isotope effect which suppresses D loss in the presence of H by a factor of at least 600. Furthermore, evidence is seen for a secondary isotope effect which slows down the loss of H from CH2CD2+ as compared to C2H4+.
On the Unrestricted Hartree–Fock Wavefunction
Authors: Nakatsuji Hiroshi , Kato Hiroshi , Yonezawa Teijiro
Published: February 2004

The unrestricted Hartree–Fock (UHF) wavefunction is analyzed and interpreted in configuration-interaction (CI) language. The results of the present study are as follows. (i) The UHF wavefunction includes only one type of the singly excited configurations [Eq. (20)], and thus the correlation effects included are very limited ones, compared with the usual CI treatment. (ii) The weight of the lowest contaminating spin function, included in the UHF wavefunction, decreases with increasing spin multiplicity. (iii) The annihilation of the lowest contaminating spin function little affects the electron density distributions and other physical quantities, the operators of which commute with the annihilation operator. (iv) In the UHF method, the “spin-appearing” (spin-polarization and spin-delocalization) mechanisms are clearly divided, and an approximate method to separate these contributions is generalized, and some discussions about spin annihilation are made.
Molecular g Values, Magnetic Susceptibility Anisotropies, Molecular Quadrupole Moments, and the Second Moment of the Electronic Charge Distribution in OCF2, CH2CF2, cis-CHFCHF, and CH2F2
Authors: Blickensderfer Roger P. , Wang J. H. S. , Flygare W. H.
Published: February 2004

The rotational molecular Zeeman effect is observed under high resolution and high magnetic fields in OCF2, CH2CF2, cis-CHFCHF, and CH2F2. The absolute values of the molecular g values (gaa, gbb, and gcc) and the signs and magnitudes of the magnetic susceptibility anisotropies [(2χaa − χbb − χcc) and (2χbb − χaa − χcc)] in the principal inertial axes are obtained and listed. Arguments are presented to show that all molecular g values are negative leading to the molecular quadrupole moments. For ease of comparison, the values are given below in an arbitrary x, y, and z axis system. The x and y axes are in the heavy-atom molecular plane, and the x axis bisects the FCF angle in all of the molecules. The units of χ are 10−6 erg/G2·mole and the units of Qxx are 10−26 esu·cm2. OCF2CH2=CF2cis-CHF=CHFH2CF2gxx− (0.0568 ± 0.0006)− (0.0421 ± 0.0005)− (0.0296 ± 0.0003)− (0.0411 ± 0.0004)gyy− (0.0747 ± 0.0004)− (0.0466 ± 0.0004)− (0.1015 ± 0.0009)− (0.0725 ± 0.0006)gzz− (0.0328 ± 0.0006)− (0.0119 ± 0.0004)− (0.0158 ± 0.0002)− (0.0398 ± 0.0004)(2χxx − χyy − χzz)+ (1.6 ± 0.9)− (2.3 ± 0.6)− (1.6 ± 0.3)+ (0.8 ± 0.4)(2χyy − χxx − χzz)+ (5.3 ± 0.6)+ (7.7 ± 0.5)+ (5.7 ± 0.4)− (3.9 ± 0.5)Qxx− (3.7 ± 0.7)+ (2.4 ± 0.5)+ (3.0 ± 0.3)+ (1.9 ± 0.3)Qyy− (0.2 ± 0.5)− (0.9 ± 0.4)− (1.7 ± 0.4)− (4.1 ± 0.4)Qzz+ (3.9 ± 1.1)− (1.5 ± 0.8)− (1.3 ± 0.5)+ (2.2 ± 0.6)

The diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in second moment of the electronic charge distributions are computed from the above results and the known molecular structures. The above results are used along with additivity relations for the second moment of the electronic charge distribution to give estimates of the diamagnetic and total magnetic susceptibility tensor elements.
Mössbauer Studies of Iron Organometallic Complexes. VII. The Iron (−II) Tetrahedral Compounds
Authors: Mazak R. A. , Collins R. L.
Published: February 2004

Magnetic perturbation was used to determine the electric-field gradient parameters Vzz and η for several tetrahedral Fe(− II) compounds. Because of the spherical symmetry of the 3d10 configuration, only ligand dispositions and strength are measured. Distortions from tetrahedral symmetry are sensitively measured by the magnitude of η.
Band Structures of Metal-Free Phthalocyanine in the β Phase
Authors: Chen Inan
Published: February 2004

The excess electron and hole-band structures of β-metal-free phthalocyanine are calculated with the tight-binding approximation, using the Hückel molecular orbitals obtained previously by this author. The heteroatomic nature of the molecule is emphasized, and hence a new form of molecular potential, which reflects the nonuniform distribution of the pi electrons in the molecule, replaces the Goeppart–Mayer–Sklar potential used in previous band-structure calculations of hydrocarbons. The interaction between the two electron bands formed from the two nearly degenerate lowest empty molecular orbitals has also been considered. The resulting band structures are qualitatively similar to those of anthracene, but with more pronounced anisotropy in the bandwidths. The velocity tensors 〈υiυj〉 and 〈υiυj / | υ |〉, where υ is the group velocity and υi, υj are its components, associated with a particular band are computed from the band structures for different values of vibronic overlaps. The applicability of the simple band model of charge transport is discussed.
Light Scattering from Polydisperse Rods and Gaussian Coils. II. Spectral Distribution of the Pure Translational Term
Authors: Pecora R. , Tagami Yukiko
Published: February 2004

Calculations of the effects of polydispersity on the spectral distribution of terms broadened solely by translational diffusion in the light scattered from dilute solutions of rigid rods and Gaussian coils have been performed. It is assumed that the degree of polydispersity follows Schulz's distribution and that the translational diffusion coefficient depends on molecular weight through the standard relation, D = CM−a, where C and α are constants. Tables of the spectra are given in reduced form for both rods and coils for α = 0.50, 0.75, and 1.00.
Low-Energy Electron-Diffraction Studies of the Adsorption of Unsaturated Hydrocarbons and Carbon Monoxide on the Platinum (111) and (100) Single-Crystal Surfaces
Authors: Morgan A. E. , Somorjai G. A.
Published: February 2004

The interaction of simple aliphatic hydrocarbons and carbon monoxide with Pt(111) and Pt(100) surfaces, at gas pressures ≤ 1 × 10−7 torr, has been studied using low-energy electron diffraction (LEED), mass spectrometry, flash desorption, and work-function (φ) measurements. The Pt(111) substrate was characterized by a (1 × 1) diffraction pattern while a (5 × 1) surface structure was visible on Pt(100). In contrast to the saturated hydrocarbons, all the other gases used (CO, C2H2, C2H4, C3H6, 1,3-butadiene and the isomeric butenes) were readily chemisorbed on both substrates. Relatively large decreases in φ resulted from the chemisorption of the unsaturated hydrocarbons while a small increase in φ was measured due to the adsorption of CO. A (2 × 2) surface structure was produced on the (111) face by all of the unsaturated hydrocarbons studied, with the exception of isobutylene which exhibited a larger unit mesh. Although C2H2 and C2H4 produced a C(2 × 2) structure on the (100) face of platinum, the adsorption of the other hydrocarbons was disordered. The necessity of close packing of the olefins appeared to be responsible for the presence of ordered structures on the Pt(111) surface and for their absence on Pt(100). The results of these structural studies indicate that the carbon atoms are sp2 hybridized in the adsorbed state. The chemisorption of CO resulted in the appearance of a C(4 × 2) structure on both (111) and (100) surfaces. This structure was transformed by electron-beam desorption into a (21/2 × 51/2)R45° structure on the Pt(100) surface. Three bonding states of CO were apparent on this substrate whilst only one was detected on Pt(111). A simple model can rationalize these differences.
Electron Nuclear Double Resonance in an Organic Molecule in a Triplet Ground State. Spin Densities and Shape of Diphenylmethylene Molecules in Diphenylethylene Single Crystals
Authors: Hutchison Clyde A. , Kohler Bryan E.
Published: February 2004

The electron nuclear double resonance spectra of the protons in diphenylmethylene molecules in the ground triplet state in a single crystal of 1,1′-diphenylethylene have been studied. The values, in the fine structure principal axis system, of the components of the proton–electron hyperfine interaction tensor have been determined and tabulated. Both the values of the 7 distinguishable spin densities and the molecule geometry, which give best fit to the measurements, have been given. Calculations made by the method of intermediate neglect of differential overlap have been compared with the experimental results.
Xenon Sensitized Photolysis of Carbon Dioxide
Authors: Stief L. J. , De Carlo V. J. , Payne W. A.
Published: February 2004

The xenon-sensitized photolysis of CO2 has been examined and contrasted with the direct photolysis at the 1470-Å Xe resonance line. In the Xe-sensitized system, the following results were obtained: the quantum yield for CO production φCO equals 2 at low pressure of CO2; φCO decreases toward unity upon addition of several gases whose relative efficiencies are as follows: CO2=1.00, Xe=0.90, He=0.14, Kr=0.06, and C2F6=0; complete recovery of O2 (O2 / CO = 0.50) is always achieved. The principal reactions required to explain these results are: Xe+hv→Xe*, Xe*+CO2→Xe+CO+O(1D)†, O(1D)†+CO2→CO3*, CO3*→CO+O2, CO3*+M→O(3P) or O(1D)+CO2+M. where O(1D)† represents electronically excited atomic oxygen containing excess kinetic energy. The high efficiency of He in this system (0.14) compared to that previously established for O(1D) with no excess kinetic energy (0.02) lends support to participation of O(1D)† in the Xe-sensitized photolysis of CO2.
Theory of Electron Transport in Disordered Systems: The Nearly Free-Electron and Nearly Bound-Electron Limits
Authors: Fischer Sighart , Rice Stuart A.
Published: February 2004

Electron dynamics in a liquid metal is studied in the nearly free-electron and nearly bound-electron limits including in both cases coupling of the electron motion to collective translational excitations of the ion-core fluid. The kinetic equations descriptive of both limits are of Boltzmann form provided that the fluctuations in the band width are smaller than the bandwidth and that the bandwidth is larger than the average phonon frequency. The translational excitations of the ion-core fluid lead to extra temperature dependences of the transport coefficients. In the nearly free-electron limit this contribution is small and the Ziman theory is recovered. In the nearly bound-electron limit the contribution to the temperature dependence of, say, the conductivity by coupling to translational excitations of the ion-core fluid is important.
Formation of N2O− via Ion–Molecule Reactions in N2O
Authors: Chantry P. J.
Published: February 2004

The production of O−, NO− and N2O− by electron impact on N2O has been studied as a function of pressure in the range 10−6 to 5 × 10−3 torr, using a quadrupole mass filter. The respective linear, quadratic, and cubic pressure dependences observed for these ions and their relative signals are consistent with the following reaction sequence and cross sections: e+N2O → O−+N2,O−+N2O → NO−+NO (3 × 10−16cm2), NO− + N2O → N2O− + NO (1 × 10−16cm2).. An alternative explanation of the data in terms of the three-body reaction converting O− to N2O− is rejected due to the implausibly large coefficient required to explain the data. No other reactions were detected. Discrepancies between the present results and those of other workers are discussed quantitatively. It is suggested that N2O− formation by the presently proposed reaction may well be endothermic, accounting for its nonappearance in systems used to study thermal energy reactions.
Negative Ions of N2O and CO2
Authors: Bardsley J. N.
Published: February 2004

Temporary negative ions of N2O and CO2 are important in several processes. Recent experiments have given much information about these ions. For N2O− the shapes of the potential-energy surfaces for the three lowest states can be inferred from the available experimental information. For CO2− two alternative sets of surfaces are consistent with the present knowledge.
Magnetic Resonance Study of the Dissociation of Peroxydisulfuryl Difluoride into Fluorosulfate Radicals
Authors: Stewart R. Allan
Published: February 2004

Broadening of the NMR line of 19F in peroxydisulfuryl difluoride, S2O6F2, was investigated between 40 and 100°C. The linewidth contribution from fluorine “exchanging” between the diamagnetic peroxide and paramagnetic SO3F radicals was separated from other linewidth contributions by simultaneously observing stable, inert pyrosulfuryl fluoride, S2O5F2. The concentration of fluorosulfate radicals as a function of temperature was obtained from EPR measurement by comparison of spectral intensity with that of a sample containing a known number of spins. The NMR chemical shift ΔωR of the SO3F radical was estimated from the isotropic hyperfine splitting constant A = 9.2 G, which was determined by EPR from the peroxide at liquid-nitrogen temperature under uv irradiation. The activation energy Ea = 25.0 kcal/mole for the reversible, thermally controlled reaction S2O6F2⇆2SO3F was found from the temperature variation in width of the single fluorine NMR line observed. Equations developed by Swift and Connick and Luz and Meiboom were employed.
Quantum Vibrational Transition Probabilities in Atom–Diatomic Molecule Collisions
Authors: Cheung Agnes S. , Wilson David J.
Published: February 2004

A generalization of the method of Shuler and Zwanzig is shown to permit the calculation of the scattering matrix for collinear atom–diatomic molecule systems having rather general intermolecular potentials. The procedure is related to the method of invariant imbedding. It is then applied to the calculation of transition probabilities for a harmonic oscillator molecule interacting with the bombarding atom via a hard-sphere potential with a “step”—i.e., V(y) = ∞, y < σ0; V(y) = V1, σ0 ≤ y < σ1; V(y) = 0, σ1 ≤ y, where y is the distance between the bombarding atom and the nearest end of the molecule. The dependence of the transition probabilities on the height (depth) and width of the potential step is studied. Resonance effects on the transition probabilities were observed; these involve the De Broglie wavelength of the collisional motion and the width of the potential step. Application of this approach to diatomic–diatomic collisions is out-lined.
Theory of the Second Virial Coefficient of Polymer Solution
Authors: Imai Satoshi , Temple William B.
Published: February 2004

The second virial coefficient A2 has been derived from Fixman's boson method. The result shows that A2 becomes constant at high molecular weight in good solvents. Thus this theory can predict the experimental observations by Sotobayashi–überreiter, and the cs0 dependency of A2 of polyelectrolyte.
Energetics of the Collision-Induced Dissociations C2H2+→C2H+ + H and C2H2+→H+ + C2H
Authors: Yamaoka Hitoshi , Dông Pham , Durup Jean
Published: February 2004

The energetics of the collision-induced dissociation of fast C2H2+ ions into C2H+ + H and H+ + (C2H) are determined from the measurements of the translational energy of the fragments and from the study of the influence of ionizing electron energy, incident ion energy, delay between production of the ions and collision, and nature of the target used. Evidence is given for the occurrence of three different processes: (i) electronic excitation to a dissociative state, (ii) adiabatic dissociation following momentum transfer, and possibly (iii) collision-induced predissociation, processes (i) and (iii) giving rise to C2H+ + H and process (ii) to H+ + C2H. The adiabatic correlations between the states of C2H2+ ions and of their fragments are discussed.
Quantum Mechanics of the H+H2 Reaction: Investigation of Vibrational Adiabatic Models
Authors: Wyatt Robert E.
Published: February 2004

The effects of reaction-path curvature and angular-momentum state on reactive H+H2 collisions are investigated for the rotating linear model: three atoms constrained to a line with the line free to rotate in three-dimensional space. Three vibrational adiabatic approximations to the quantum-mechanical scattering problem are investigated after introducing Marcus' natural-collision coordinates. Calculations based upon the Porter and Karplus H3 surface are presented for the following reaction properties: local vibrational and translational energy, reaction probabilities, and reaction cross sections. Tunneling, the internal centrifugal effect, and the energy dependence of reaction coordinates are also considered.
Luminescence Kinetics Following Pulse Irradiation. II. DNA
Authors: Lillicrap S. C. , Fielden E. M.
Published: February 2004

The spectra and decay kinetics of the luminescence of calf-thymus DNA following irradiation by 4.3-MeV electrons are reported over a temperature range from 93° to 400°K. The emission is followed from 2 μsec to 1 sec after the start of a 1.6-μsec electron pulse. All the emission spectra observed can be accounted for by the presence of three components with emission peaks at 350, 410, and 470 nm. Emission at 93°K exhibits only 350- and 470-nm components which can be clearly resolved. Apart from the decay of the 350-nm component at 93°K, which follows a reciprocal time–power law, none of the emission decay curves at any temperature can be fitted to a simple mathematical function. It is shown that much if not all the phosphorescence in the temperature range studied results from the trapping of excitation energy. Above 200°K the depths of the traps responsible are distributed about a mean of 0.36 eV and this conclusion is confirmed by thermoluminescent studies. In addition to the decay above, at 93°K the emission at times less than 50 μsec after irradiation depends on the previous dose history of the sample and a possible explanation is presented.