bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron spin polarized triplet state energy transfer in mixed organic single crystals at low temperatures
Authors: Brenner Henry C.
Published: February 2004

Transfer of photoexcitation from phenazine guest molecules to anthracene guest molecules in diphenyl single host crystals at 1.7°K, producing anthracene triplet species, was investigated by electron paramagnetic resonance methods. The triplet spin lattice relaxation rates were slow enough compared to depopulation rates so that preferential populating of the individual triplet sublevels of phenazine and anthracene could be observed. It was found that the long axis zero field state was populated fastest in both donor and acceptor, indicating that spin polarization was conserved in the transfer. This information was used along with several other experimental results to elucidate the nature of the processes responsible for the phenazine to anthracene transfer. It was concluded that the transfer took place either by means of a Dexter exchange process between triplet phenazine and unexcited anthracene, or by production of diphenyl triplet excitons from phenazine excited singlet species, and subsequent exciton migration and population of anthracene acceptor triplet traps. This latter route was suggested by the observation that singlet excitation of phenazine populated diphenyl-h10 triplet traps in a mixed diphenyl-d10/h10 host crystal.
Dynamics of the O+–H2 reaction. II. Reactive and nonreactive scattering of O+(4S3/2) at relative energies above 13 eV
Authors: Gillen Keith T. , Mahan Bruce H. , Winn John S.
Published: February 2004

We report velocity vector distributions for the reactive and nonreactive scattering of O+ by H2, D2, and HD in the relative energy range 13–50 eV. Essentially no very small angle reactive scattering is observed for any of these systems. In the lower and intermediate parts of the energy range, the product of the O+(D2, D)OD+ reaction reaches a maximum intensity near 50°, and decreases somewhat at larger angles. This shape is maintained but with decreasing intensity from 15–30 eV relative energy. At higher energies, the distribution moves to larger angles and the intensity continues to drop. From 13–20 eV, OH+ from O+–HD collisions peaks near 35°, and has little intensity at larger angles, while the corresponding OD+ product rises to a broad miximum near 90°, and is only slightly less intense at larger angles. At relative energies above 13 eV the nonreactive scattering of O+ has a major component that corresponds to the elastic impulsive scattering of O+ from one atom of the target. Nonreactive scattering from HD shows two peaks which correspond to impulsive O+–H or O+–D collisions. The experimental results are compared to the predictions of a model in which reaction occurs as the result of those sequences of two-body hard sphere interactions which lead to bound product molecules. The general forms of the product angular distributions and their dependence on the isotopic composition of the target are fairly well represented by the model. For other features such as the experimental energy dependence of the total cross section (σ ∝ Erel−7/2) and the corresponding isotope effect, the model is less successful. A convenient velocity vector diagram method is given which allows a simple, edifying analysis of product angular distributions to be made with a compass and straightedge.
Investigation of the ESR spectra of Cu2+ in K2Co(SO4)2 · 6H2O
Authors: Sastry B. A. , Sastry G. S.
Published: February 2004

Electron spin resonance studies have been carried out on Cu2+ doped K2Co(SO4)2 · 6H2O at different temperatures. The resolution of the spectrum is found to be maximum at about 210 °K and the electric field symmetry around Cu2+ at this temperature is found to be rhombic having the spin-Hamiltonian constants, gz = 2.330 ± 0.005, gx = 2.227 ± 0.005, gy = 2.053 ± 0.005, Az ≃ (60 ± 2) × 10−4 cm−1, Ax ≃ (52 ± 2) × 10−4 cm−1, and Ay ≃ (59 ± 2) × 10−4 cm−1. These spin-Hamiltonian parameters are found to be temperature dependent. The linewidth of the copper hyperfine lines are found to increase with decreasing temperature which is most probably brought about by the superposition of a very broad Co2+ line on Cu2+ hyperfine line.
MC-SCF. I. The multi-configuration self-consistent-field method
Authors: Hinze Juergen
Published: February 2004

The general multi-configuration self-consistent-field (MC-SCF) method is presented with no restrictions on the types of configurations participating in the expansion of the total wavefunction. The general coupled Fock-like equations for the ``best'' orbitals to be used in such a multi-configuration wavefunction are derived. Formally these coupled nonlinear equations are decoupled with the use of projection operators and transformed into a pseudoeigenvalue problem. Several general methods, based on orbital transformations and on the use of the generalized Brillouin theorem, are presented for solving the coupled nonlinear Fock like equations for the determination of the MC-SCF orbitals. The formalism presented is applicable not only to the ground state of a given system, but also to any excited state, yielding an upper bound to the true energy of the desired state.
Accurate analytic matrix elements for anharmonic oscillators using quantum mechanical commutator relations and sum rules
Authors: Tipping R. H.
Published: February 2004

An expression connecting the vibration-rotation matrix elements of various powers of the internuclear displacement from equilibrium for 1Σ-state diatomic molecules is derived via quantum mechanical commutator relations. This expression can be solved by an iterative procedure and used to generate the diagonal elements. For off-diagonal elements, additional information available through sum rules is necessary in order to obtain explicit results. To illustrate the power and accuracy of the present method, selected matrix elements of H2 have been computed and will be compared with previous numerical results.
NQR in the complexes of trimethylindium with Group Vb trimethyl derivatives
Authors: Patterson Dennis B. , Carnevale A.
Published: February 2004

The 115In NQR parameters, and those for the Sb isotopes and 75As, in the 1:1 complexes of Me3In with Me3N, Me3P, Me3As, and Me3Sb are reported. These data are discussed in the light of those for the analogous series of Me3Al complexes, and the available thermodynamic data, and are concluded to be consistent with a small amount of (d-d)π bonding in the Me3In complexes with Me3P and its heavier congeners.
Electric dipole moment and energy in H2–H2 and H2–H collisions
Authors: Patch R. W.
Published: February 2004

The dipole moment and its derivative with respect to H2 internuclear distance were calculated for H2–H2 and H2–H collisions in the adiabatic approximation. A full configuration-interaction model with a minimum basis set of Slater orbitals was assumed in each case. Linear, planar perpendicular, rectangular, and staggered configurations with intermolecular distances from 2.5 to 5.5. bohr were used for H2–H2. For H2–H some preliminary calculations were made with three models for linear and isosceles configurations. An optimized-orbital-exponent model was then selected for linear, scalene, and isosceles configurations with intermolecular distance from 1 to 4 bohr. For H2–H2 and H2–H the interaction energies were slightly high. However, the dipole moments were in reasonable agreement with treatments for large intermolecular distance, with one minor exception.
Static dielectric properties of polar solutions with nonpolar solvent
Authors: Omini M.
Published: February 2004

The dielectric behavior of a polar substance dissolved in a nonpolar liquid is studied by treating the system of induced dipoles as a dielectric continuum, in which the permanent dipoles of the solute are embedded. The interaction between permanent dipoles (consisting of an electrostatic plus a short range potential energy) is explicitly introduced into a linearized Boltzmann equation to study the correlation between dipoles at a given temperature. The theory is applied to a solution of chlorobenzene in benzene and of acetone in carbon tetrachloride: In both cases the experimental data are in good agreement with the behavior predicted by the theory.
Arsenic monofluoride (AsF, 3Σ): Dissociation enthalpy, ionization potential, electron affinity, dipole moment, spectroscopic constants, and ideal gas thermodynamic functions from a Hartree-Fock molecular orbital investigation
Authors: O'Hare P. A. G. , Batana Alicia , Wahl Arnold C.
Published: February 2004

Accurate Hartree-Fock wavefunctions were computed by the matrix expansion method of Roothaan for the ground state (3Σ) of AsF at several internuclear separations. The equilibrium internuclear separation (re) was deduced to be 1.72 Å based on a Dunham analysis. It is concluded that the most probable value for D0o (AsF) is 4.2 ± 0.2 eV. The vertical ionization potential and electron affinity are 9.4 ± 0.2 and and 1.1 eV, respectively. It is believed that the computed electric dipole moment is too large, and an amended value of 1.75 D is recommended, with the negative end of the dipole at the fluorine atom. At re, the quadrupole moment measured from the center of mass is −2.44 × 10−26 esu · cm2; however, the reliability of this result is uncertain. Ideal gas thermodynamic functions have been calculated for the temperature range 0–1000°K, based on the formulas of statistical mechanics. Koopmans' theorem yields 18.1 eV for the second ionization potential. A brief discussion of the bond enthalpies of AsF+, AsF2+, and AsF− is also included. Estimates have been made of the first and second ionization potentials of SbF (8.4 and 16.3 eV) and BiF (7.3 and 16.6 eV).
Fundamental equation of state of liquid nitromethane to 100 kbar
Authors: Lysne P. C. , Hardesty D. R.
Published: February 2004

Shock-compression experiments were performed on specimens of nitromethane for several values of initial temperature. From these data, a continuum of Hugoniots centered at any initial temperature between the atmospheric pressure freezing and boiling states was obtained. The energy-pressure-volume equation of state then followed from a combination of the known variation of energy with temperature along the atmospheric pressure isobar and the Hugoniot jump relations. The energy-entropy-volume equation was generated by a numerical integration of the coupled differential equations governing the entropy and temperature variation along a Hugoniot. This work is believed to constitute the first totally experimental determination of the equation of state of a liquid in the 100 kbar region.
Comparison of semiclassical, quasiclassical, and exact quantum transition probabilities for the collinear H + H2 exchange reaction
Authors: Bowman Joel M. , Kuppermann Aron
Published: February 2004

Using the classical (CSC), primitive (PSC), and uniform (USC) semiclassical expressions for transition probabilities given by Miller and co-workers, we have calculated the reactive and nonreactive 0 → 0 and 0 → 1 transition probabilities for the collinear H + H2 exchange reaction. Comparison with previously calculated exact quantum and quasiclassical results for the reactive and nonreactive 0 → 0 transitions reveals that the semiclassical approximations are not very good, especially the CSC and PSC ones. All three semiclassical probabilities for the reactive 0 → 0 transition exceed unity in the collision energy range from 0.0 to 0.2 eV above the quasiclassical reaction threshold. This feature coupled with the failure of any of the semiclassical approximations to produce the marked quantum effects present in this transition causes these results to be less accurate than the corresponding quasiclassical ones. For the reactive and nonreactive 0 → 1 transitions the USC results are in qualitative agreement with the exact quantum ones and are better than the standard quasiclassical results. However, the reverse quasiclassical results are almost as good as the USC ones for these transitions. A probable reason for the inability of the USC expression to produce the strong oscillations observed in the exact quantum results is that the latter are due to interference between direct and resonant (i.e., compound state) processes whereas the present formulation of the semiclassical method does not encompass such phenomena. A comparison of the total reaction probabilities obtained by the USC and quasiclassical methods with the exact quantum one indicates that the USC result is more accurate than the quasiclassical one, except at collision energies less than 0.50 eV. This improved accuracy is due to a partial cancellation of errors in the contributing 0 → 0 and 0 → 1 USC reactive transition probabilities.
Generalized molecular distribution functions
Authors: Ben-Naim A.
Published: February 2004

Molecular distribution functions are concerned with the probability densities of observing a set of n particles at some specified locations. The generalized molecular distribution functions ``load'' the n particles with additional information, which may include or exclude their locations. It is argued that the study of these functions may provide a new insight into the local properties of the molecules in the liquid state. A sample of computed generalized molecular distribution functions by the Monte Carlo technique is presented. The singlet and the pair distribution functions for coordination number (CN) and binding energy (BE) were computed for simple, spherical particles in two dimensions. Further examples of the singlet, distribution functions for nonspherical, waterlike particles are also reported, and some topics relevant to the mixture model approach to the theory of liquid water are discussed.
Study of hydrogen diffusion in tantalum hydrides by inelastic neutron scattering
Authors: Rush J. J. , Livingston R. C. , de Graaf L. A. , Flotow H. E. , Rowe J. M.
Published: February 2004

Neutron inelastic scattering spectra have been measured as a function of temperature and scattering angle for α-TaH0.15 and for Ta2H in its α and β1 phases. The widths of the quasielastic peaks vs momentum transfer (Q) have been derived and compared with several models for hydrogen diffusion. The results suggest the dominance of tetrahedral jumps in the diffusion process, although no completely satisfactory theoretical fit was obtained. Residence times τ between 1.6 (340°C) and 4.0 (148°C) psec for TaH0.15 and between 2.4 (300°C) and 7 (153°C) psec for Ta2H were derived from the fit of the observed widths to the tetrahedral model. These results indicate a significant concentration dependence of the diffusion rates in α-TaHx, with activation energies for diffusion of 10.4 ± 1.2 kJ/mol in TaH0.15 and 15 ± 1.2 kJ/mol for Ta2H. ``Effective'' mean square amplitudes of proton vibration of 0.02–0.04 Å2 were obtained from the Q dependence of the quasielastic peak intensities, in reasonable agreement with the values predicted from relatively crude vibration frequency distributions obtained from our inelastic scattering spectra in the α phase. Our results are compared in detail with previous neutron results on VHx and NbHx. On the basis of this comparison it is tentatively concluded that the very high ``Debye-Waller factors'' obtained for VHx and some other hydrides are related to high hydrogen diffusion rates.
Vacuum ultraviolet absorption spectra of dimethylsulfide, dimethylselenide, and dimethyltelluride
Authors: Scott John D. , Causley G. C. , Russell B. R.
Published: February 2004

The vapor phase absorption spectra of dimethylsulfide, dimethylselenide, and dimethyltelluride are reported for the 40 000–80 000 cm−1 vacuum ultraviolet spectral region. Three Rydberg series for each compound were assigned which converge on the ionization potentials of 8.706 ± 0.010, 8.400 ± 0.010, and 7.926 ± 0.010 eV for dimethylsulfide, dimethylselenide, and dimethyltelluride, respectively. These ionization potentials and corresponding Rydberg series members are assigned as originating from the central atom valence p orbital, which is perpendicular to the plane of the molecule. A correlation of the ionization potentials calculated for these molecules to ionization potentials of corresponding rare gases is presented. The term values of Rydberg members of the dimethyl chalcogens are also correlated to the term values of allowed atomic Rydberg series in the rare gases, thus atomic nomenclature is used in the assignment of the molecular Rydberg series. Higher energy absorptions in the spectra of dimethylselenide and dimethyltelluride are assigned as originating from a nonbonding orbital of a1 symmetry localized on the central atom. In the three spectra, vibrational progressions are analyzed with respect to ground state totally symmetric vibrational frequencies. Utilizing Franck-Condon factors and harmonic oscillator potentials, the excited state geometry changes were found to be similar, where the C–X–C (X=S, Se, or Te) bond angles are essentially unchanged and the C–X bond distances are changed approximately 0.040 Å from the ground state bond lengths for all three compounds.
Enskog dense gas theory for soft potentials
Authors: Brinser George B. , Condiff Duane W.
Published: February 2004

Making use of equilibrium correlation functions and cluster functions, a soft potential analogue of the Enskog dense gas Boltzmann equation for hard spheres is derived by neglecting dynamical correlations due to multiple collisions. The equation is shown to reduce to the proper rigid sphere limit, and it is solved by the method of Chapman and Enskog. Expressions for the kinetic and collisional transfer contributions to shear viscosity, bulk viscosity, and thermal conductivity are developed in terms of multidimensional integrals.
Flow-drift technique for ion mobility and ion-molecule reaction rate constant measurements. II. Positive ion reactions of N+, O+, and H2+ with O2 and O+ with N2 from thermal to [inverted lazy s]2 eV
Authors: McFarland M. , Albritton D. L. , Fehsenfeld F. C. , Ferguson E. E. , Schmeltekopf A. L.
Published: February 2004

The positive ion-molecule reactionsN++O2→ NO++O→ O2++N,N2++O2→ O2++N2,O++O2→ O2++O,O++N2→ NO++N,were measured in a newly constructed flow-drift tube apparatus. Reactions (a), (b), and (c) were measured from thermal energy to approximately 2 eV ion kinetic energy in the center of mass. Reaction (d) was measured from 0.3–3 eV ion kinetic energy. The data agree well with previous thermal values at low energies and agree well with beam data at the highest energy. In the case of all the reaction except (a), there is an initial decrease of the rate constant with increasing energy followed by an increase.
Geometry and vibrational spectra of the alkaline earth dihalides. III. MgCl2, CaCl2, SrCl2, and BaCl2
Authors: White David , Calder G. V. , Hemple S. , Mann D. E.
Published: February 2004

The infrared spectra of MgCl2, CaCl2, SrCl2, and BaCl2 trapped in solid krypton matrices at 20 °K are reported. From precise measurements of changes in the vibrational modes on isotopic substitution, a linear configuration for MgCl2 and CaCl2 is confirmed and an apex angle of 120° is established for SrCl2. For BaCl2 the bond angle has been estimated at 100°. Using a valence force field we have obtained a set of force constants from the measured fundamental frequencies as well as approximate values for the anharmonic corrections to some of the vibrational modes. The statistical entropies calculated from the vibrational frequencies and molecular geometries are in excellent agreement with the thermodynamic measurements.
Neutron quasielastic scattering study of SH− reorientation in rubidium hydrosulfide in the intermediate temperature trigonal phase
Authors: Rowe J. M. , Livingston R. C. , Rush J. J.
Published: February 2004

The reorientation of (SH)−ions in the trigonal phase of RbSH has been investigated by neutron quasielastic scattering at 373 and 393 K. The quasielastic peaks show a distinct two-component (elastic and broadened) structure, the behavior of which is used to establish that the ions are reorienting between two equilibrium sites (presumably by 180° flips along the trigonal axis) with average times between reorientation of 5.4 ± 0.4 psec and 4.0 ± 0.4 psec at 373 and 393 K. Mean square amplitudes of hydrogen vibration are determined from the momentum transfer dependence of the total intensity, and found to be higher than that found in the high temperature fcc phase, even though the rate of reorientation is an order magnitude faster in the cubic phase.
INDO-MO calculation of the titanium halides
Authors: Truax D. R. , Geer J. A. , Ziegler T.
Published: February 2004

A nonempirical INDO-MO scheme is described and ground state configurations are determined for the titanium halides TiCl4, TiBr4, and TiI4. Photoelectron spectra calculated for TiCl4 and TiBr4 were compared with experimental spectra and with other MO methods. The photoelectron spectrum of TiI4 is predicted.
Proton-enhanced NMR of dilute spins in solids
Authors: Pines A. , Gibby M. G. , Waugh J. S.
Published: February 2004

The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain in power sensitivity as compared with conventional observation of the rare spins approaches NII(I+1)γI2/NSS(S+1)γS2, or ∼ 103 for S = 13C, I = 1H in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High-frequency resolution of the S -spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.
Carbon-13 chemical shielding tensors in single-crystal durene
Authors: Pausak S. , Pines A. , Waugh J. S.
Published: February 2004

The method of proton-enhanced nuclear induction spectroscopy [A. Pines, M. G. Gibby, and J. S. Waugh, J. Chem. Phys. 59, 569 (1973)] has been employed to find the eigenvalues and eigenvectors of the chemical shift tensors for the various 13C nuclei in a single crystal of durene (1, 2, 4, 5-tetramethylbenzene). For each type of carbon the trace of the shielding tensor, Trσ agrees well with the isotropic shift σi found from spectra of liquid solutions. The well-known tendency of σi to be smaller for aromatic than for aliphatic carbon is found to be ascribable largely to the very small shielding which occurs for the former when the applied field is in the plane of the ring and tangent to it at the C atom in question. The CH3 carbons have much less anisotropic shielding than do the ring carbons. The rather close coincidences between nominal bond directions and the eigenvectors of σ suggest that nonbonded interactions in the crystal play an unimportant role.
Electron diffraction study of the thermal decomposition of BrCCl3
Authors: Leggett T. L. , Kohl D. A.
Published: February 2004

The thermal decomposition of bromotrichloromethane was studied in the gas phase by electron diffraction. An oven was incorporated into the sample inlet system of a conventional photographic plate unit to decompose the sample. Three different diffraction patterns were recorded and analyzed. A peak in the radial distribution curve corresponding to a normal carbon-bromine bond was absent. However, in order to satisfy stoichiometry requirements and to match the areas of all of the peaks, it was necessary to introduce species with an abnormally long carbon-bromine bond length. For each of the three diffraction patterns, the major components in the scattering volume were found to be mixtures of BrCCl3/BrCCl2/CCl4/CCl3, C2Cl4/C2Cl6, and BrCl/Br2. Except for the C–Br bond, all distances and angles had normal values. A plausible explanation of the lengthening (∼ 0.15 Å) of the C–Br bond is that a long-lived excited state of BrCCl3/BrCCl2 was formed as an intermediate in the reaction.
Mössbauer effect studies of transferrin
Authors: Spartalian K. , Oosterhuis W. T.
Published: February 2004

Mössbauer effect experiments with 57Fe in transferrin at p H 7.5 exhibit paramagnetic hyperfine structure and show no difference between the two iron sites. The spectra have been analyzed in terms of a spin Hamiltonian with zero field splitting of the electronic states D = 0.15 cm−1, E/D = 0.31; the magnetic hyperfine coupling Ax :Ay :Az = 221:215:223 kOe/unit spin, respectively. The quadrupole splitting Δ E = 0.75 mm/sec. The effect of ligand nuclear moments is observed in the zero field Mössbauer spectrum. Mössbauer data were also taken with 151Eu but no hyperfine splitting was observed.
NMR line shapes for a tunneling two proton system: A model for the CH2D group
Authors: Johnson Charles S.
Published: February 2004

NMR spectra are calculated for a two proton system where rotation is hindered by a potential barrier having threefold symmetry. This system is a model for the CH2D group in certain compounds. The powder spectra obtained are dependent on the tunneling splitting h νT when this splitting is the same order of magnitude as the frequency of the dipolar interaction. As νT increases for the torsional oscillator the spectra do not approach the limit found for rapid random rotation; but instead they show three pairs of transitions for each orientation of the symmetry axis. However, the classical spectra are recovered for the plane rotor states with angular momentum quantum number m > 1.
Direct rate measurements showing negative temperature dependence for reaction of atomic oxygen with cis-2-butene and tetramethylethylene
Authors: Davis D. D. , Huie R. E. , Herron J. T.
Published: February 2004

Reported in this paper are the first direct rate measurements showing a negative temperature dependence for the reaction of ground state atomic oxygen with cis-2-butene and tetramethylethylene. Wide variations made in the experimental conditions (e.g., total pressure, O atom concentration, and olefin concentration) of these two systems have shown that the measured rate constants were uninfluenced by secondary reactions. The absence of any dependence of the measured rate constants on total pressure at several temperatures indicate that the reactions investigated were bimolecular processes. When expressed in the form of an Arrhenius equation, the observed negative temperature dependence results in an apparent negative activation energy, i.e., kcis-2-B=(9.69± 0.96)× 10−12exp (319± 63 cal mol−1/RT) and kTME=(5.58± 1.07)× 10−12 exp (1570± 120 cal mol−1/RT). Units are in cubic centimeters per molecule seconds. If a threshold energy of 0.0 cal mole−1 is assigned to the reaction of O(3P) with TME, the temperature dependence of the pre-exponential term for a rate expression of the form k =A(T)exp(−E0/RT),E≥ O) is calculated to be T−2. These new results are discussed in terms of both collision and transition state theories.
Absolute rate constant for the reaction OH+NH3→NH2+H2O
Authors: Stuhl F.
Published: February 2004

The kinetic behavior of OH radicals in the presence of a large excess of NH3 has been studied by pulsed photolysis. The OH radicals were produced by vacuum-uv photolysis of H2O and were monitored by resonance fluorescence. The rate constant for the reaction of OH with NH3 was determined to be 1.5(± 0.4)× 10−13 cm3 molecule−1· sec−1 at 298°K. The significance of this result is discussed with regard to atmospheric chemistry.
Proton spin relaxation in methyl substituted aromatic radical ions. A formula for the CH3 proton NMR linewidth
Authors: de Boer J. W. M. , Arick M. R. , de Boer E.
Published: February 2004

The proton relaxation has been studied in methyl substituted aromatic radical ions in solution. The linewidth parameter T2 of the protons in such radicals is governed by two intramolecular interactions, namely, the Fermi contact interaction and the anisotropic dipolar interaction. For the methyl protons the interactions are modulated in time by both internal rotation and tumbling of the whole molecule in solution. Equations have been derived to account for the effect of these motions on the CH3 proton linewidth. The resulting formulas are used to analyze the NMR proton linewidths for the anion of 3, 3′-dimethylbiphenyl.
Collisional deactivation of the c 1π and A 3π states of imino radicals
Authors: Kawasaki Masahiro , Hirata Yoshinori , Tanaka Ikuzo
Published: February 2004

The photolysis of ammonia-d0 and -d3 was studied at each of the three wavelengths, Lyman-α (121.6 nm), Kr resonance lines (123.6, 116.5 nm), and Xe resonance lines (147.0, 129.6 nm). For Lyman-α, Kr resonance lines, and 129.6 nm, NH(c 1π) emission was observed. In the Kr sensitization, both NH(c 1π) and (A 3π) emissions were detected. In the direct photolysis, the effects of Xe, Kr, Ar, He, H2, and N2 as foreign gases were studied. Xe and Kr caused the intersystem crossing of NH and ND(c 1 π → A 3π) to occur. Electronic quenching of NH or ND(c 1π) was also observed for Xe, Kr, H2, and N2. The cross sections for intersystem crossing and quenching are presented. H2, N2, He, and Ar caused no intersystem crossing of NH and ND(c 1π). Neither He nor Ar quenched the emission from NH and ND(c 1π).
Ionization in the track of a high-energy electron in liquid cyclohexane; pulse radiolysis of solutions of biphenyl in cyclohexane
Authors: Hummel A. , Luthjens L. H.
Published: February 2004

In order to study the ionization in the track of a high-energy electron in liquid cyclohexane, the lifetime distribution of the charged species is considered, with and without solutes present that can react with the species and change their mobility. Calculations of the lifetime distributions of the ions are presented, which have been made on the basis of the assumption that the precursors of the ion scavenging reactions can be considered as classically diffusing ions, initially present as pairs of oppositely charged species in each other's field. The calculations are compared with the lifetime distributions of biphenyl ions in solutions of biphenyl in cyclohexane with and without other solutes present, as determined by nanosecond pulse radiolysis. It is concluded that the precursor of the positive biphenyl ion is a positive species, which is considerably more mobile than a molecular ion.
ν1 + ν3 combination band of 32S16O2
Authors: Corice R. J. , Fox K. , Tejwani G. D. T.
Published: February 2004

The infrared-active vibration-rotation band ν1 + ν3 of sulfur dioxide has been measured with moderately high spectral resolution. Quantum number identifications of spectral lines were made by comparison with theoretically computed spectra which include the effects of centrifugal distortion. The band center for ν1 + ν3 was determined to be 2499.60 ± 0.10 cm−1. An absolute band intensity has also been measured in this work, and the magnitude of the dipole moment derivative ∂2μa/∂ Q1∂ Q3 was evaluated.
Porphyrins. XXVII. Spin-orbit coupling and luminescence of Group IV complexes
Authors: Gouterman Martin , Schwarz Frederick P. , Smith Paul D. , Dolphin D.
Published: February 2004

Luminescence studies are reported on compounds M(IV)X2P: M is Si, Ge, Sn, Pb; X is F, Cl, Br, I, OH, benzoate; P is etioporphyrin or octaethylporphin. (One tetraphenylporphin is reported for comparison.) We find fluorescence yields 2 × 10−1 ≥slant φf ≥slant 2 × 10−4; phosphorescence yields 7 × 10−2 ≥slant φp ≥slant 3 × 10−3; and phosphorescence lifetimes 100 msec ≥slant τp ≥slant 1 msec. The contrasting vibronic envelopes of phosphorescence for octaethylporphin and tetraphenylporphin derivatives is explained by attributing the former to transitions 3Θ± 1 → 1ΘGND and the latter to 3Θ± 9→ 1ΘGND, where ± 1 and ± 9 are pseudoangular momentum quantum numbers. The spin-orbit interaction is calculated by the extended Hückel model, and it is found that the ligands have far more effect than the metal, in agreement with the data. However a simple relation between decay rates and spin-orbit coupling fails quantitatively, and the extended Hückel model appears to exaggerate the contribution of the ligand to the spin-orbit coupling.
Monte Carlo calculations of reaction rates and energy distributions among reaction products. IV. F+HF(ν) → HF(ν′)+F and F+DF(ν) → DF(ν′)+F
Authors: Wilkins Roger L.
Published: February 2004

Rate constants are calculated for the vibrational relaxation HF(ν) and DF(ν) molecules by F atoms with ν = 1, 2, 3, and 6. Three-dimensional classical trajectories of the collision dynamics of these reactions were calculated by means of a modified London-Eyring-Polanyi-Sato (LEPS) potential energy surface used to calculate rate constants for the reactions between H atoms and F2 molecules, and D atoms and F2 molecules. The Monte Carlo procedure is used to start each collision trajectory. By means of this calculation, it is predicted for the reactant HF molecule in the ν = 2, J = 8 state that 13.3% of the mean fraction of available energy will become rotation in the product HF, 80.7% will become vibrational energy in the product HF, and 6% will become relative translational energy of the products. As the vibrational energy of the reactant HF molecule increases the mean fraction of available energy that becomes rotational energy increases slightly. For example, if the reactant molecule HF is in the ν = 6, J = 8 state, it is found that the mean fraction of available energy that will become rotational energy in HF is 15.8%, 75.3% will become vibrational energy in HF, and 8.9% will become translational energy in the product. Two different methods are used to calculate the rate constants kν→ν−1 for the de-excitation of vibrationally excited HF molecules by F atoms. The main mechanism for the de-excitation of vibrationally excited HF or DF molecules by F atoms is vibration-rotation energy transfer. Multiple quantum transitions occur in the de-excitation of higher (ν ≥slant 3) vibrationally excited states of HF molecules by F atoms. Chemical effects provide an important mechanism for the efficient vibrational relaxation of HF and DF molecules by F atoms. Rate constants are provided for many reactions that have not been measured experimentally.
Experimental technique for direct measurement of interaction second virial coefficients
Authors: Hall Kenneth R. , Eubank P. Toby
Published: February 2004

An experimental technique is proposed in which a normal Burnett PVT apparatus is used to make direct measurements of the interaction second virial coefficient, Bij. Required information includes observable temperatures and pressures and pure component compressibility factors (or densities). The pure component second virial coefficients and the mixture composition are not required. Interaction virial coefficients determined by this method are shown to be more accurate than by previous techniques and are only slightly less accurate than pure component second virial coefficients measured in the same Burnett apparatus.
Reduction of Cu(II) at high pressure
Authors: Wang P. J. , Drickamer H. G.
Published: February 2004

In a series of previous papers it has been demonstrated that Fe(III) reduces to Fe(II) with increasing pressure in many compounds. The process of electron transfer from a ligand nonbonding orbital to a metal 3d orbital has been related to the location, half-width, and shift with pressure of charge transfer peaks in the optical spectrum. In this paper we present studies on six complexes of Cu(II), in five of which measurable reduction to Cu(I) is observed at high pressure. The reduction correlates with the location and shift of peaks with substantial charge transfer character.
Matrix spectroscopy of Ag, Ta, W, and Mo trapped in Ar and Xe using a triode sputtering source
Authors: Schoch F. , Kay E.
Published: February 2004

Atomic species of tungsten, molybdenum, and tantalum were extracted from a triode sputtering source and subsequently trapped in xenon and argon matrices at 10 °K. It is shown that this approach is particularly convenient for matrix isolation spectroscopy of materials which are difficult to vaporize. Good correlation with the gas spectrum is obtained for the strong spectral features. There is evidence that some spectral features are greatly enhanced in the matrix spectra over those in the gas spectra. Using silver/xenon as a prototype system it is shown that a wide range of plasma conditions can be used without aggregation. However, certain plasma conditions are identified which lead to weak spectra of silver dimers. Spectral shifts due to matrix effects are found to be W/Ar = 850 cm−1, W/Xe = 700 cm−1 for ν̄⊥ < 37 000 cm−1 and 0 cm−1 above, Mo/Ar = 2650 cm−1, Mo/Xe = 1150 cm−1, Ta/Xe = 980 cm−1 for ν⊥ < 33 000 cm−1 and - 3230 cm−1 above. In the spectrum of Ta/Xe a remarkable red shift of 3230 cm−1 for energies above 33 000 cm−1 is observed. This is in sharp contrast to the Ta spectrum in argon, where a surprisingly consistent perturbation of approximately 1000 cm−1 to the blue is observed.
Molecular reorientational motion in liquid acetonitrile: Raman band shapes, diffusion constants and activation energy of reorientation
Authors: Griffiths James E.
Published: February 2004

Isotropic I α(ω) and anisotropic I β(ω) Raman band shape analyses of the ν1(a1) fundamentals in liquid CH3CN and CD3CN are reported. The ν2 and ν4 fundamentals are complicated by secondary structure and therefore were not studied in detail. Values of the perpendicular rotational diffusion constants D⊥, derived from the ν1(a1) fundamentals of both isotopic species are in good agreement with those obtained using NMR relaxation and dielectric methods and in addition agree closely with values calculated from microviscosity theory. The latter is based upon a model which involves a connection between the rotational and translational motions in liquids. In this model, reorientations perpendicular to the C3 axis proceed by small step Brownian diffusion and D⊥ (Raman) for CD3CN yields an activation energy for liquid state molecular reorientations perpendicular to the C3 symmetry axis of 2.0 ± 0.3 kcal/mole, in good agreement with existing NMR and microviscosity values. Comparison of Raman data and results reported here with available infrared results reveals that the D⊥(ir) values are too high by a factor of 2. The source of the infrared errors is discussed.
Centrifugal distortion effects in the microwave spectrum of trans-propylene imine
Authors: Su Chun Fu , Beeson E. L.
Published: February 2004

Centrifugal distortion effects in the microwave rotational absorption spectrum of trans-propylene imine have been investigated. Mesurements of transitions for J numbers up to 40 have been made. Centrifugal distortion coefficients have been evaluated as follows: dJ=(−4.57 ± 0.17) × 10−3MHz, dJK=(2.00 ± 0.70 ) × 10−2MHz, dK=(7.2 ± 1.3) × 10−2MHz, dEJ=(1.228 ± 0.031) × 10−6, dEK=(−5.0 ± 1.2) × 10 −6. The rotational constants have been re-evaluated.
Dynamics of solvation of an excess electron
Authors: Rentzepis P. M. , Jones R. P. , Jortner Joshua
Published: February 2004

We have utilized the techniques of picosecond spectroscopy to study the localization of an excess electron in water. Quasifree electrons were generated by the photoionization of the ferrocyanide anion in aqueous solutions at 2650 Å. Time resolved absorption of the localized electron was monitored continuously from 1.06 μ to 5300 Å, while time and energy resolved absorption was monitored in the range 3100–9000 Å by a broad continuum of picosecond duration. Optical absorption of the initially localized electron in the infrared (1.06 μ) is observed within 2 psec after the generation of the quasifree electron. The optical absorption band evolves in time, shifting from lower to higher energies, and the ``normal'' absorption of the hydrated electron is developed in ∼4 psec.
Effect of horizontal fields on the thermomagnetic gas torque
Authors: Scott Gifford G.
Published: February 2004

When a heated cylinder having a vertical axis of rotation is suspended in a rarefied polyatomic gas, application of a vertical magnetic field produces a torque resulting in a turning of the cylinder. In this ``ordinary'' thermomagnetic gas torque effect, molecular precession occurs about the vertical direction. Addition of a horizontal magnetic field component tips the precession axis to a nonvertical direction. If the cylinder axis is maintained vertical, the nonvertical field produces two interesting effects: (1) the magnitude of the total field for maximum torque is increased (qualitatively indicating an increase in angle of precession between molecular collisions); and (2) the measured maximum vertical torque is found to be larger than the calculated vertical component.
Fluorine chemical shielding tensors and crystal structure of potassium tetrafluorophthalate
Authors: Griffin R. G. , Yeung H.-N. , LaPrade M. D. , Waugh J. S.
Published: February 2004

The 19F shielding tensors of the two aromatic fluorines of potassium tetrafluorophthalate (KTFP) are reported. The results indicate that the most shielded elements of the tensors lie perpendicular to the carbon ring in agreement with previous powder studies and, of the two in-plane components, the more shielded is along the CF bond. The results also show that the ``ortho effect'' of Karplus and Das is not simply additive in the case of KTFP. Such additivity has been assumed by Nehring and Saupe in their liquid crystal study of fluorine shielding tensors in multifluorobenzenes.
Ionization energies of the neutral actinides
Authors: Sugar Jack
Published: February 2004

Values for the ionization energies of the neutral actinides have been derived by utilizing interpolated spectral properties of these atoms. The results in electron volts are Ac: 5.17(12); Th: 6.08(12); Pa: 5.89(12); U: 6.05(7); Np: 6.20(12); Pu: 6.06(2); Am: 5.993(10); Cm: 6.09(2); Bk: 6.30(9); Cf: 6.41(10); Es: 6.52(10); Fm: 6.64(11); Md: 6.74(12); No: 6.84(12).
Relaxation of the V=4,5,6,7, Σg+ vibrational levels of carbon monoxide studied by laser absorption
Authors: Chackerian C. , Weisbach M. F.
Published: February 2004

The vibrational relaxation of individual vibration rotation levels of carbon monoxide behind incident shock waves of carbon monxide has been studied by the method of laser absorption. For the particular vibrational states (V = 4–7) and temperature range (2500–5500 °K) studied, we conclude that the characteristic relaxation times are in excellent agreement with those obtained via previous measurements of ``bulk'' gas properties. Further, the data furnish strong corroboration of the idea that the individual levels are in Boltzmann vibrational equilibrium during the relaxation process.
Raman spectra of gases. VII. Barriers to planarity in 1,4- and 1,3-cyclohexadiene
Authors: Carreira L. A. , Carter R. O. , Durig J. R.
Published: February 2004

The Raman spectra of gaseous 1,4- and 1,3-cyclohexadiene have been recorded between 80 and 3300 cm−1. A band at 216 cm−1 in the 1,4-cyclohexadiene spectrum has been assigned to the ring-puckering mode which is only consistent with D 2h (planar) configuration. A series of Q branches appearing at ∼195 cm−1 has been assigned to the low frequency twisting mode in 1,3-cyclohexadiene. The assignment of these lines to a double minimum potential function leads to a barrier to planarity of 1099 ± 50 cm−1. The CH2 stretching modes of 1,4-cyclohexadiene have been reassigned in light of the gas phase Raman data and a tentative vibrational assignment is given for the observed Raman lines of 1,3-cyclohexadiene.
Energy loss neutron inelastic scattering spectra of HCrO2 and HCoO2
Authors: Temme F. P. , Waddington T. C.
Published: February 2004

The energy-loss neutron inelastic scattering spectra for HCoO2 and HCrO2 are reported in the range 300–1400 cm−1 (optically), and the far infrared spectra of the compounds in the range 50–400 cm−1. The data obtained combined with that from other techniques provide supporting evidence for Snyder and Ibers' assignment of a symmetric hydrogen bond in HCrO2.
Some formal results in the quantum theory of molecular scattering
Authors: Snider Neil S.
Published: February 2004

The two-potential formula for the transition matrix was employed to generalize some results in the formal theory of molecular scattering which were previously derived from R -matrix theory. Most important, the quantum mechanical analog of Wigner's classical expression for an upper bound to the rate constant of a chemical reaction was generalized to apply to a reaction with any number of product molecules. In addition to removing the restriction inherent in R -matrix theory, that only two entities emerge from the collision, the generalized results are free of difficulties connected with choices, necessary in R -matrix theory, of internal and external regions, boundary conditions, and external wavefunctions.
Vibrational relaxation of OCS in HBr, HCl, and rare gaseous mixtures
Authors: Hopkins Barbara M. , Baronavski Andrew , Chen Hao-Lin
Published: February 2004

The laser-excited vibrational fluorescence technique has been used to study the rates of vibrational relaxation of the asymmetric stretching mode (00 °1) of OCS and HBr (V = 1) in rare gaseous mixtures. The relaxation rates measured at 296 °K show cross sections of OCS (000 1) vibrational relaxation as σOCS–H2 = (3.1 ± 0.3) × 10−20cm2, σOCS–He = (1.3 ± 0.1) × 10−20cm2, σOCS–Ne = (2.2 ± 0.2) × 10−20cm2, σOCS–Ar = (4.3 ± 0.4) × 10−20cm2, σOCS–HBr = (2.4 ± 0.3) × 10−18cm2, and σOCS–OCS = (3.8 ± 0.5) × 10−17cm2. The relative efficiency for deactivation by rare gases has only a slight dependence on the collisional reduced mass, with a peak closer to Ar. It is possible that during OCS-rare-gas collisions, vibrational energy is transferred mostly into nearby vibrational energy levels and little is transferred into translation. The rate of intermolecular V → V energy transfer between hydrogen halides and OCS (00 °1) vibrations gives cross sections of σHBr → OCS = (1.2 ± 0.1) × 10−16cm2 and σHCl → OCS = (1.2 ± 0.1) × 10−17cm2.
Eigenfield expansion technique for efficient computation of field-swept fixed-frequency spectra from relaxation master equations
Authors: Belford R. L. , Belford G. G.
Published: February 2004

If the Hamiltonian and Liouville operators of a spectral intensity problem are functions of a field parameter x computation of the intensity as a function of x requires, in effect, inversion of a different large matrix for each value of x. Here we show that when the Liouville operator is a polynomial in x, with operator coefficients, solution of one generalized eigenvalue problem followed by a single solution of a system of linear equations yields the intensity for all x. This formulation promises to save large amounts of computational time, particularly for electron paramagnetic resonance problems involving large zero-field splittings.
Spin-orbit coupling effects on the zero field splitting of (π, π*) triplet states of conjugated enones
Authors: Jones Claude R. , Maki August H. , Kearns David R.
Published: February 2004

The optically detected paramagnetic resonance transitions of five cyclic conjugated enones have been observed in zero field. The |E|/h c parameters are small and nearly invariant for series, but the |D|/ h c parameters range from 0.22 to 0.30 cm−1. Simple theory suggests that both spin-spin dipolar interactions and spin-orbit interactions make significant contributions to the ZFS. The large variation in the ZFS of these enones is primarily due to the dependence of the spin-orbit interaction on the energy gaps between the 3(π, π*) state and the 1(n, π*) and 3(n, π*) states.
Vibration-to-rotation energy transfer in hydrogen fluoride: Effects of the dipole-dipole and hydrogen-bond interactions
Authors: Kyu Shin Hyung
Published: February 2004

The importance of the dipole-dipole and hydrogen-bond interactions in the vibration-to-rotation energy transfer in hydrogen fluoride molecules is investigated in the temperature range of 300 to 4000°K. The collision trajectory and collision time are evaluated for the over-all potential energy constructed from the sum of the exponential (Morse-type) and dipole-dipole interaction functions. Good agreement between the present calculations and experiment is found over the entire temperature range.