bluuebunny/crossref_metadata_2025 huggingface dataset:
Relaxation of Excited States in Cr(III) Complexes
Authors: Camassei F. Diomedi , Forster Leslie S.
Published: February 2004

The quantum yields of luminescence and E3 lifetimes have been determined as a function of temperature for Cr3+ in the crystalline hosts, K3Co(CN)6, NaMgAl(C2O4)3·9H2O, C(NH2)3Al(SO4)2·6H2O(GASH), C(NH2)3Al(SO4)2·6D2O(GASD), AlCl3·6H2O, and AlCl3·6D2O. The effect of structure and environment on the nonradiative transitions has been assessed. For a given complex, the probability of the nonradiative E2→A42 transition may or may not depend upon environment. In all cases, only phosphorescence is observed at low temperatures, but upon warming, the aquo complexes fluoresce. Depopulation via T42 is the dominant thermal relaxation process of E2.
Relationship between the Experimental Hamiltonian and the Point Symmetry of a Paramagnetic Species in a Crystal
Authors: Rae A. D.
Published: February 2004

The ESR spectrum of a paramagnetic species in a single crystal is considered. Relationships between the Laue symmetry of the species, the Laue symmetry of the crystal, and the number of species observable in specific directions is derived. The application to experiment is discussed.
Quantum-Mechanical Hamiltonian for Triatomic Chemical Reactions
Authors: Shipsey Edward J.
Published: February 2004

Parabolic coordinates are introduced in the triatomic problem. An angular variable is defined in this coordinate system which has the same geometrical interpretation with respect to products as with respect to reactants. Distance variables are introduced in a natural way and they asymptotically approach those appropriate for the separated reactants or products.
Cotton–Mouton Effect through an Absorption Band
Authors: Boccara A. C. , Ferre J. , Briat B. , Billardon M. , Badoz J. P.
Published: February 2004

Cotton–Mouton dichroism was measured for an aqueous solution of europium trichloride. The experiment was performed at room temperature through the visible F70→D51 absorption band. A phenomenological theory is given for the results thus obtained. The spectroscopic splitting factor of the excited state is determined and is shown to be in close agreement with that obtained independently through Faraday effect measurements. Optimal experimental conditions are pointed out for further work in the field.
Gas-Phase Electron Resonance Spectra of SF and SeF
Authors: Carrington Alan , Currie Gavin N. , Miller Terry A. , Levy Donald H.
Published: February 2004

The electron resonance spectra of the gaseous radicals SF and SeF have been detected and analyzed. The derivation of an effective Hamiltonian which operates in the rotational subspace of the ground vibronic state is described. Use of this Hamiltonian yields the rotational constants, the fine-structure splittings, and the axial components of the 19F hyperfine interaction for both radicals.
Vacuum-Ultraviolet Study of Liquid H2O and D2O
Authors: Verrall R. E. , Senior W. A.
Published: February 2004

Vacuum-ultraviolet spectra of liquid D2O and H2O have been obtained at several temperatures in the wavelength range 1300–1750 Å. Because of the very large extinction coefficient of water in this region, the absorption spectra were obtained from very thin liquid films. The results show that the vapor–liquid shift is to the blue by some 7000 cm−1. The spectra are discussed in terms of the effect of temperature on hydrogen-bonding properties of the liquids in the ground state and the nature of the electronic transitions from which they arise.
van der Waals Constant between Alkali and Noble-Gas Atoms. II. Alkali Atoms in Excited States
Authors: Mahan G. D.
Published: February 2004

The van der Waals constant C6 is calculated for interactions between alkali and noble-gas atoms. Values are given for the case that the alkali atom is in an excited state.
Electronic Structure of the Lithium Hydride Molecule Ion
Authors: Lin C. S.
Published: February 2004

A generalized valence-bond calculation of the lithium hydride molecule ion gave the total energy − 7.758855 a.u. at R = 3.736 a.u. Possible behavior of the potential-energy curve in the region 3.60–4.25 a.u. is discussed. Based on its behavior, the reason this molecule ion has not been experimentally established is explained and a possible method of producing it is suggested. Electron-density distribution and planar-density distribution are calculated and analyzed in comparison with the lithium hydride molecule.
Atomic Integrals Containing rijp Correlation Factors with Unlinked Indices
Authors: Perkins J. F.
Published: February 2004

The S states of multielectron atoms can be calculated by use of Rayleigh–Ritz expansions, each term of which is a product of Slater-type functions, riaexp(− αri), and a single two-electron correlation factor of the form rijp. This requires convenient (preferably algebraic, rather than numerical integration) methods for evaluating the five types of energy and normalization integrals which arise. Formulas for some of these integrals, including the relatively difficult linked-index three-electron integral, have been given previously. For each of the four nonlinked-index integrals, there is given herein an explicit, computer-programmable formula in which the expansion parameters are treated as input arguments. Practicality of the formulas was demonstrated by preparation of a fortran computer program which was used to evaluate sample integrals. Some differencing error is involved, but typically results in loss of only two or three significant figures.
Raman Spectra of Hydrogen and Deuterium Halide Crystals
Authors: Ito Mitsuo , Suzuki Masako , Yokoyama Tohru
Published: February 2004

The crystal Raman Spectra of HCl, DCl, HBr, and DBr have been observed for the lattice and intramolecular vibrational regions. The results for the intramolecular region indicate that the crystal structure of the low-temperature orthorhombic phase is C2v9 − Pn21a with four molecules in a unit cell, containing nonplanar hydrogen-bonded zigzag chains. However, the nonplanarity of the chain is so small that it is not sensitively reflected to the spectra of lattice vibrational region. As a result, the lattice vibrational bands may be assigned adequately based on a planar structure C2v12 − Bb21m, which is the structure determined by neutron diffraction measurement. Normal coordinate calculations have been made by using several kinds of intermolecular potentials. A central force field which assumed dispersion and repulsion forces and dipole–dipole forces failed to explain the observed lattice frequencies. A potential which assumed hydrogen bonding explicitly gave a reasonable fit of the calculated frequencies with the observed ones. The calculations showed that the hydrogen bond involved is relatively weak and high frequencies of the rotational lattice vibrations in spite of the weakness of the hydrogen bond are due simply to a small value of the moment of inertia of the molecule. The Raman spectra of the high-temperature cubic phase showed no strong band in the lattice region and very broad bands in the stretching region. From the results obtained, a model for the molecular reorientational motions in the cubic crystals has been proposed, in which the molecule in the crystal is bound to one of the equilibrium orientational positions, but reorients at random from one equilibrium position to the other before the molecule as a whole completes one cycle of translational oscillation. This model seems to explain the experimental data available.
Chlorine NMR in CsNiCl3 and CsCuCl3
Authors: Rinneberg H. , Haas H. , Hartmann H.
Published: February 2004

The analysis of 35Cl NMR measurements in single crystals of CsNiCl3 and CsCuCl3 at room temperature yielded the quadrupole coupling and magnetic shift tensors at the chlorine positions. For the two inequivalent sites in CsCuCl3 the following parameters were found: v35= 11.249 Mc/sec, η = 0.389 (general position), and v35q = 10.701 Mc/sec, η = 0.131 (special position), and for CsNiCl3: v35q = 8.349 Mc/sec, η = 0.387. The calculated hyperfine constants along and perpendicular to the metal–chlorine bonds are in CsCuCl3: A‖ = 21.3, A⊥ = 3.0 (Clgen) and A‖ = 17.7, A⊥ = 3.9 (Clspec) and in CsNiCl3: A‖ = 8.0, A⊥ = 2.4 (all in units 10−4 cm−1). The hyperfine constants are compared to MO calculations. The 63Cu and 65Cu NMR has been observed and partially analyzed.
Equation-of-State Measurements in Compressed Argon
Authors: Crawford R. K. , Daniels W. B.
Published: February 2004

A weighting technique used in obtaining experimental P–V–T data for argon at high pressures is described. The data for fluid argon at pressures from 0.2 to 6.3 kbar and temperatures from 95° to 210°K are presented, along with melting data for argon in this range. The entropy and energy of argon are derived from these data. Recent theoretical calculations are compared with the results, and a discrepancy between the calculated and experimental values for the energy is discussed.
Collision Broadening of Rotational Absorption Lines. IV. Pressure Broadening of the Ammonia Inversion Spectrum
Authors: Murphy Joseph S. , Boggs James E.
Published: February 2004

The collision broadening of the NH3 inversion spectrum was investigated within the framework of an earlier proposed theory of pressure broadening. The original treatment must be modified before application to NH3 to allow for the fact that NH3 has two closely spaced energy levels, the inversion doublet, with all other levels very widely spaced. This situation results in a “two-level resonance” system which greatly affects the linewidth. In general, the agreement between the calculated and experimental values is very good although the calculated values tend to be slightly smaller. Molecular quadrupole moments for N2 and H2 are determined from linewidth data for broadening of NH3 inversion lines and are in excellent agreement with values determined by other methods.
Ultrasonic Relaxation and the Volume Change during Internal Rotation in 1,1,2-Trichloroethane
Authors: Crook K. R. , Wyn-Jones E.
Published: February 2004

Ultrasonic absorption measurements have been carried out in solutions of 1,1,2-trichloroethane in various solvents. The observed relaxation has been attributed to the perturbation of the equilibrium between the trans and gauche rotational isomers. The concentration dependence of the relaxation parameters have served as an indirect check on the assumptions used in developing the ultrasonic theory. These results were used with those from a recent NMR study to calculate the volume change during isomerization, ΔV / V. This quantity had values in the range 1%–3% showing that the assumption used in deriving the enthalpy difference ΔH from ultrasonic data (ΔV / V)(Cp / θ) ≪ ΔH is not justified. (Cp is the specific heat at constant pressure and θ the coefficient of thermal expansion.) The temperature dependence of the relaxation time was found to be approximately the same as the pure liquid.
Photoionization of High-Temperature Vapors. V. Cesium Halides; Chemical Shift of Autoionization
Authors: Berkowitz J.
Published: February 2004

From the thresholds for photodissociative ionization of cesium halide molecules, results have been obtained for the dissociation energies of the diatomic molecules. The values of D0 obtained are CsCl, 105.6 ± 1.6 kcal/mole; CsBr, 96.2 ± 1 kcal/mole; CsI, 82.3 ± 1 kcal/mole. For D0(CsF), the interpretation is in doubt. The dissociation energies of the molecular ions CsBr+ and CsI+ have also been measured, as have the heats of formation of Cs2F+, Cs2Cl+, and Cs2Br+. Several autoionization peaks have been observed in the ionization efficiency curves of the cesium halides, somewhat displaced in energy from their positions in atomic cesium. In particular, the (5p)66s → (5p)5(6s)2 transition, which occurs at 12.306 eV in atomic cesium, is shifted to 12.1, 12.4, 12.5, and 12.6 eV, for CsF, CsCl, CsBr, and CsI, respectively. These peaks are also present in the ionization efficiency curves of the dimer ions. Some consequences of these results are discussed.
Glory Scattering of Lithium by a Series of Molecules. II. Fluorocarbons and Hydrocarbons
Authors: Rothe Erhard W. , Helbing Reinhard K. B.
Published: February 2004

The velocity dependence of the total cross section has been measured for the scattering of lithium-7 by 26 fluorocarbon and hydrocarbon molecules, and by CH3F, CH2F2 and CHF3, in the velocity range from about 1–4 km/sec. This work is similar to that described in a previous paper in which the scattering was from 13 diatomics. Potential parameters were derived for these systems. The quenching of the normal glory pattern may be qualitatively correlated with the geometric structures of the scatterers. Glory scattering persists even for rather complex molecules (e.g., CF3–cyclo-C6F11). The saturated fluorocarbons may be roughly thought of as rare gases of varying shape. The data are in reasonable agreement with previous work, although our interpretation differs.
Hyperfine Spectrum of NaCl by Molecular-Beam Electric Resonance
Authors: Cederberg J. W. , Miller Carl E.
Published: February 2004

The hyperfine spectrum of NaCl has been observed at very low field using the molecular-beam electric resonance method. The Hamiltonian is expressed in a representation in which the combined quadrupole term is diagonal when the quadrupole interaction constants of the two nuclei are equal. The analysis of the spectrum then gives for the constants X+ ≡ [(eqQ)Na + (eqQ)Cl] / 2, X− ≡ [(eqQ)Na − (eqQ)Cl] / 2, c+ ≡  (c1 + c2) / 2, c3, and c4 the values (in kilohertz) for 23Na35Cl: X+ = − 5658.0 ± 0.1, X− = − 16 ± 50, c+ = + 0.51 ± 0.01, c3 = + 0.22 ± 0.02, and c4 = + 0.05 ± 0.03 for v = 0; X+ = − 5716.3 ± 0.5 and X− = + 116 ± 20 for v = 1; X+ = − 5772.6 ± 0.7 and X− = + 235 ± 12 for v = 2; and X+ = − 5828 ± 1 and X− = + 340 ± 15 for v = 3. Lines have also been observed corresponding to 23Na35Cl, J = 2, and 23Na37Cl, J = 1.
Decay of Correlations. II. Relaxation of Momentum Correlations and Momentum Distributions in Harmonic Oscillator Chains
Authors: Oppenheim Irwin , Shuler Kurt E. , Weiss George H.
Published: February 2004

We have studied the relaxation of the n-particle momentum distribution function fn(pn; t) and the corresponding n-particle Ursell function Un(pn; t) for both an isolated infinite chain of coupled harmonic oscillators and an infinite chain of coupled harmonic oscillators in contact with a heat bath. The time development of the Ursell function gives us the desired information on the decay of initial momentum correlations. For both of these systems we have found the asymptotic relaxation laws fn(pn; t) − fn(0)(pn) ∼ f1(p; t) − f1(0)(p) and Un(pn; t)→0 as [f1(p; t) − f1(0)(p)]n, where the superscript zero denotes the equilibrium distribution. The momentum correlation function Un(pn; t) thus goes to zero (no correlations) much more rapidly than the n-particle distribution function approaches its equilibrium value. These results are identical with those obtained by us previously for initially correlated, noninteracting many-particle systems in contact with a heat bath and by Glauber for the relaxation of spins in an Ising lattice. It is interesting to speculate on the reason for this identity of results in such apparently different relaxation models, but no answer can be provided as yet.
Molecular-Beam Measurements of the Emission Spectrum and Radiative Lifetime of N2 in the Metastable E 3Σg+ State
Authors: Freund Robert S.
Published: February 2004

Electron-impact excitation of a molecular beam of nitrogen was used to produce the metastable E 3Σg+ state. This state, which lies 11.87 eV above the ground state, has recently been observed in a number of electron-impact experiments. This paper reports the emission spectrum from the molecular beam, and identifies three forbidden electronic transitions, E 3Σg+ → A 3Σu+, E 3Σg+ → B 3Πg, and E 3Σg+ → C 3Πu. Approximate absolute transition probabilities are determined. The radiative lifetime of the E state is 270 ± 100 μsec, and the equilibrium internuclear distance is 1.16 ± 0.02 Å.
Calculation of the Vibrational Intensities of F2CO
Authors: Segal Gerald A. , Bruns Roy , Person Willis B.
Published: February 2004

The CNDO/2 calculations of the dipole-moment derivatives with respect to the vibrational symmetry coordinates of F2CO, ∂p / ∂Sj, are carried out in order to determine which of the possible sets of values found from the experimental intensity data is most likely to be correct. Reasonable agreement is obtained with one of the many sets of values and an unambiguous assignment is possible. The signs of the dipole-moment derivatives with respect to the normal coordinates are thereby fixed. The inadequacy of the bond-moment model for the vibrational intensities of this molecule is discussed.
Positive Surface Ionization of Na, NaCl, NaBr, NaI, and LiCl on Rhenium and on Oxygenated Rhenium Surfaces
Authors: Persky Avigdor
Published: February 2004

Results are reported for the ionization of sodium, sodium halides, and lithium chloride on rhenium and on oxygenated rhenium surfaces. The oxidation of a rhenium surface was found to cause an increase in its work function. As a result the ionization efficiencies for sodium and sodium halides incident on this surface are increased from about 0.20 to unity. The efficiency for lithium chloride is also increased to a value probably close to unity. The oxide layer which is formed even at low air pressures (5 × 10−7 torr) seems to be stable only up to about 1650°K.
Geometries of O4+, O4−, and N4+ by an Approximate SCF–MO Theory Which Considers Intermolecular Differential Overlap
Authors: Conway D. C.
Published: February 2004

We have found that the CNDO/2 (semiempirical SCF–MO) theory does not properly account for the long-range repulsive interactions in O2–O2 (S = 2) and O2–O2+ (S = 32). This results in the O2–O2 interaction potential being zero at O–O separations of 2.3–3.5 Å and the O2–O2+ bond energy being much too large. The CNDO/2 method has been modified by considering sp-type integrals to account for charge–quadrupole and charge–atomic polarization interactions. In addition, differential overlap is considered and multicenter integrals are approximated for intermolecular interactions. This is a semiempirical method in which the adjustable constants are fixed by the quadrupole moments of O2 and N2 and the O4+ bond energy. The interaction energies of O4+, O4−, and N4+ are computed for structures of C2 symmetry as a function of θ and R. The equilibrium dissociation energies De (kcal) at Re (Å) and θe are as follows: O4+, 11.66, 2.03, − 67°; O4−, 8.49, 2.08, − 71°; N4+, 34.7, 2.04, O°. The computed O2–O2 interaction potential is in reasonable agreement with the experimental results for the repulsive part of the van der Waals potential.
Mössbauer Effect of 129I in Pyridine Complexes of Iodine Monohalides
Authors: Wynter C. I. , Hill J. , Bledsoe W. , Shenoy G. K. , Ruby S. L.
Published: February 2004

The values of isomer shift and quadrupole interaction at the 129I nucleus in IBr and ICl complexes with cyclic nitrogen bases have been measured. These have been used to estimate σ and π bondings in these complexes. All these complexes exhibit a linear N–I–X (X≡Cl, Br) linkage. Although the bromine complexes show a systematic dependence of the isomer shift on the basicity of the complexing cyclic amines, no such trend is observed in chlorine complexes.
Thermoluminescence of ZrO2
Authors: Bettinali C. , Ferraresso G. , Manconi J. W.
Published: February 2004

The thermoluminescence of ZrO2 samples, both pure and doped with titanium, irradiated with low doses of x rays has been studied. The glow curve of ZrO2(Ti) exhibits, in the temperature range 100° to 350°K, four main peaks all having the same spectral composition. The pure ZrO2 presents a similar glow curve but having a luminous intensity about 2 × 103 times lower than that of the doped material. These data indicate that Ti4+ ions act as thermoluminescent centers. Activation energies were calculated by means of the initial rise method and also by using the shape of the isolated peaks. The electron traps probably are related to oxygen vacancies. In fact, the luminous intensity increases when the vacancy concentration increases, and the activation energies calculated from the dielectric constant are close to the activation energies obtained from glow peak data. The build-up curves indicate that the vacancies, acting as trapping centers, exist prior to the irradiation and are probably of the same type for all of the thermoluminescent peaks.
Quantum Mechanical Second Virial Coefficient of a Lennard-Jones Gas. Helium
Authors: Boyd M. E. , Larsen S. Y. , Kilpatrick J. E.
Published: February 2004

The quantum-mechanical second virial coefficients of Lennard-Jones 3He and 4He gases with the De Boer parameters have been obtained over the complete temperature range from near absolute zero to the classical region. A formalism separating the virial into direct (Boltzmann) and exchange (spin and quantum statistics) contributions has been employed. The calculation is based on phase shifts except at the very highest temperatures where a Wigner–Kirkwood method has been used. Examination of the exchange term shows in detail the rapid suppression of the statistical effects with rising temperature, their contribution dropping to less than 0.001 cm3 by 7°K (4He). Comparison of the high-temperature (Boltzmann) results with those obtained by a third-order Wigner–Kirkwood expansion shows excellent agreement down to about 50°K for 4He and 60°K for 3He. The Wigner–Kirkwood expansion is shown to be unsuitable for determining the behavior of the exchange terms. Finally, results are compared with the available experimental data.
C
2υ
Potential Energy Surfaces for Seven Low-Lying States of CH2
Authors: O'Neil Stephen V. , Schaefer Henry F. , Bender Charles F.
Published: February 2004

Ab initio calculations have been carried out at 28 C2υ geometries for the lowest A11, 1A2, 3A2, 1B1, 3B1, 1B2, and B23 states of CH2. The basis set used was of the contracted Gaussian type with four s and two p functions on carbon and two s functions on hydrogen. In all calculations except A11 the SCF configuration plus all singly and doubly excited configurations were included (holding the K shell frozen), and the iterative natural orbital procedure was used to obtain an optimum set of orbitals. For the A11 state a two configuration SCF calculation was used as the starting point for the configuration interaction calculations. In a preliminary communication we predicted the triplet ground state of CH2 to be bent, and this prediction has since been justified experimentally by Bernheim et al. and by Wasserman et al. For the A11 state the ab initio geometry is r = 1.13 Å, θ = 104°, compared to experiment, r = 1.11 Å, θ = 102°. For the B11 state the predicted geometry is r = 1.09 Å, θ = 144°, as opposed to experiment, r = 1.05 Å, θ ∼ 140°. The four other states investigated, A21, 3A2, 1B2, and B23, are all unstable with respect to a carbon atom plus a hydrogen molecule, and it is concluded that there are only four bound non-Rydberg states of CH2. The B13–1A1 splitting, unknown experimentally, is predicted to be 7770 cm−1 (0.96 eV). The calculated A11–1B1 splitting is 7860 cm−1 (0.97 eV), compared to the experimental value 7100 cm−1 (0.88 eV). The wave-functions are discussed and three-dimensional plots of the potential surfaces are presented.
Semiempirical Correlation of Potential Parameters
Authors: Stwalley William C.
Published: February 2004

The similar potential hypothesis (SPH)—that proportionality constants relating observables to potential parameters are roughly equal in chemically similar systems—yields ratios of potential parameters for a variety of systems. These ratios, obtained simply from even primitive data, agree well with ratios obtained from accurate but far more laborious potential inversion analyses (which require a great deal of high quality data). These ratios are shown to be more consistent with reciprocal combination rules for Z ≡ εrm and ε than are the corresponding geometric and arithmetic combination rules.
Electron Correlation in the Lowest Σ+1 State of Beryllium Oxide
Authors: Schaefer Henry F.
Published: February 2004

Ab initio first-order wavefunctions, which include electron correlation, are reported for the lowest Σ+1 state of BeO. A contracted Slater function basis of better than double-zeta plus polarization accuracy was used, resulting in 157 configurations, constructed from 569 distinct Slater determinants. Practical convergence in form of the molecular orbitals was obtained using the iterative natural orbital procedure. Considerable emphasis is placed on obtaining the correct dissociation behavior, in the present case to a two-configuration (1s22s2and 1s22p2) wavefunction for S1 Be plus a slightly better than Hartree–Fock wavefunction for the D1 state of oxygen. The calculated dissociation energy is 6.58 eV, compared to the Hartree–Fock value, 4.13 eV, and the spectroscopic value recommended by Gaydon 6.69 ± 0.4 eV. The other spectroscopic constants represent a substantial improvement over the Hartree–Fock values and are all within 10% of experiment. The dominant configurations in the wavefunction are presented, and it is seen that, contrary to the suggestion of previous workers, the 1σ22σ23σ24σ25σ21π2 is not particularly important near the equilibrium internuclear separation. The natural orbital occupation numbers complete our picture of the electronic structure of Σ+1 BeO.
ESR Study of Irradiated Glycine at Low Temperatures
Authors: Sinclair James
Published: February 2004

Single crystals of glycine, glycine-d3, and glycine-d2 have been x irradiated at liquid-nitrogen temperatures and the paramagnetic fragments produced examined as a function of temperature by electron spin resonance techniques. The radicals observed in the temperature range 77–300°K include: ĊH2N+H3, N+H3CH2ĊOO−(H), ĊH2COO(H), ṄH2+CH2COO−, and N+H3CHCOO−. The production of these radicals can be rationalized by a sequence of reactions which involve initially formed cation and anion radicals.
Radial Expansion of 3d Orbitals and the Near Degeneracy of the A41g and E4g Excited States of Octahedral Mn(II) Complexes
Authors: Lohr Lawrence L.
Published: February 2004

The relationship between the wavefunctions for mostly 3d molecular orbitals and the energies of the nearly degenerate A41g and E4g excited states of octahedral Mn2+ complexes is investigated from two points of view. First, the expressions relating the energy splitting to the degree of covalency have been extended within the framework of the intermediate neglect of differential overlap (INDO) approximation to include the large but previously neglected two-center Coulomb integrals and all ligand one-center Coulomb and exchange integrals. The results resemble those previously obtained in their inability to account for the spectral assignment of the E4g state below E41g for the MnF64− complex in the salts KMnF3, RbMnF3, and MnF2. Second, the assumption of identical metal-ion repulsion integrals for the eg and t2g molecular orbitals is discarded in a simple analysis of an all-electron molecular SCF calculation for the MnF64− complex. While both the eg and t2g orbitals contain a metal-ion d orbital that is expanded relative to that for the free Mn2+ ion, the slightly greater radial expansion for the t2g orbital is shown to qualitatively account for the observed ordering of the A41g and E4g states.
Symmetry and Conformation of the Cycloalkanes
Authors: Pickett Herbert M. , Strauss Herbert L.
Published: February 2004

The conformations of the cycloalkanes and related molecules are expressed in terms of a symmetry-adapted set of coordinates. The coordinates measure the deviation of the molecule from a planar regular structure. Use of these coordinates leads to relatively simple expressions for the conformational energy and to a method for finding possible paths for free pseudorotation. We conclude that conformations with low symmetry are more likely to pseudorotate with low energy barriers than are conformations with high symmetry. Selection rules for electric dipole transitions among the energy levels characteristic of pseudorotation are derived. The conformational energy surface is discussed in detail for a number of the smaller cycloalkanes. Description of the conformation of very large rings in terms of our coordinates is expected to be incomplete and our method will consequently not be applicable to these rings.
Nonequilibrium Contributions to the Rate of Reaction. IV. Explicit Time-Dependent Solutions
Authors: Shizgal B.
Published: February 2004

The explicit time dependence of the corrections to the equilibrium rate of reaction and the equilibrium rate of change of the temperature in one-component monatomic systems is obtained by integrating the nonlinear Boltzmann equation with a moment method. The calculations are carried out for the model systems employed in the earlier studies. For sufficiently small values of the ratio of the elastic and reactive relaxation times (τE / τR ≲ 10−2), it was found that in a time τE the time-dependent corrections increased rapidly from zero to an asymptotic value. For times greater than τE, the asymptotic values of the corrections increased or decreased slowly and approximately linearly with time. The maximum values of the corrections as a function of time (in instances where a maximum value was obtained) were compared with the corresponding result obtained employing the Chapman–Enskog solution of the Boltzmann equation. This qualitative comparison indicates that for τE / τR ≈ 10−2 the Chapman–Enskog result differs from the present result by 10%. For τE / τR ≈ 10−4, the deviation between the two results is reduced to 1%–3%. In the limit as τE / τR → 0, the present results coincide exactly with the Chapman–Enskog result.
Ultraviolet Absorption Spectra of Transition Metal Atoms in Rare-Gas Matrices
Authors: Mann D. M. , Broida H. P.
Published: February 2004

Absorption spectra from 2200 to 4000 Å have been obtained of chromium, manganese, iron, cobalt, copper, nickel, tin, and palladium atoms trapped in argon matrices at 4.2°K and of iron and copper in krypton and xenon matrices at 4.2 and 20°K. Observed transitions were found to correlate with gas phase transitions, under the assumption of a matrix and atomic configuration dependent shift of the atomic transitions. Energy shifts of the transitions were inversely proportional to matrix atom size. Configurations with an odd number of 3d electrons were shifted less than those with an even number. Within a given configuration, the transitions at higher energies were shifted more than those at lower energies. A Lennard-Jones potential was unsuccessful in generating the observed energy shifts caused by the interaction between the trapped atom and the matrix. Atom diffusion and resultant aggregation within the matrix both during the condensation of the solid from the gas phase and during warming was found to be a significant effect. Oscillator strengths, calculated from observed spectra, were from 10 to 100 times less than gas phase values.
One-Center rij Integrals Over Slater-Type Orbitals
Authors: Sims James S. , Hagstrom Stanley A.
Published: February 2004

Expressions are derived for the integrals which arise in calculations of atomic wavefunctions of four or more electrons, utilizing the method of explicit introduction of interelectronic distances rij into a configuration interaction wavefunction (subject to the restriction of at most one rij per configuration). The approach followed in the derivations is similar to one followed by Öhrn and Nordling for three electron integrals; however, in extending the Öhrn and Nordling scheme to four electrons for a basis of s, p, and d Slater-type orbitals, numerical snags are encountered which have been obviated by an Euler transformation on certain of the auxiliary integrals.
Kinetic Salt Effects on the Aquation Reaction of the Azidopentaaquochromium (III) Ion and Predictions of the Mayer Theory
Authors: Indelli A. , De Santis R.
Published: February 2004

The rate of the reaction of aquation of the azidopentaaquochromium (III) ion has been measured at two different concentrations of hydrogen ion in the presence of a number of salts. The values of k1 and k0 of the equation kobs = k1 [H+] + k0 + k −1 [ H+ ] −1 + k −2 [ H+]−2were calculated and both show positive salt effects and obey the Olson-Simonson rule. Calculations performed using the Mayer theory in the approximation `` DHLL+ B2'' have shown that at high dilution both these effects can be rationalized using appropriate values of the distances of closest approach. The possibility of using this form of the Mayer theory for extrapolation purposes is suggested. The use of different distances of closest approach for different pairs of ions does not lead to any inconsistency.
Pressure Shifts in Properties of Solvated Electrons in Alcohols and Water
Authors: Robinson M. G. , Jha K. N. , Freeman G. R.
Published: February 2004

Pressure shifts of the optical absorption maxima of solvated electrons are, respectively, in electron volts per kilobar and nanometers per kilobar: in water 0.053 and −19; in ethanol 0.062 and −20; in methanol ∼ 0.05 and −15. The half-width of the absorption spectrum of esolv− in water is increased from 0.9 eV at 1 bar to 1.2 eV at 3.8 kbar. In both ethanol and methanol the half-lives are reduced by pressure. In ethanol Δ V‡ (esolv− → ROsolv− + H) = − 16 cm3 mol−1. In water Δ V‡ (esolv− + S → S−) ≈ −1 cm3 mol−1.
Pulse Radiolysis of Liquids at High Pressures. I. Absorption Spectrum of the Hydrated Electron at Pressures up to 6.3 kbar
Authors: Hentz Robert R. , Farhataziz  , Hansen Earl M.
Published: February 2004

A system for study of the pulse radiolysis of liquids at pressures up to 6.9 kbar is described. With this system the optical absorption spectrum of the hydrated electron has been measured at 29 ± 3° C and applied pressures in the range 0–6.3 kbar. The spectrum shifts monotonically to shorter wavelengths with increase in applied pressure from 0 to 6.3 kbar. The transition energy at the absorption maximum, Emax, increases from 1.71 to 2.00 eV, and the bandwidth at half-maximum increases by ∼ 28 %. It is concluded that the extinction coefficient at the absorption maximum decreases by ∼ 18 % and, therefore, that the oscillator strength shows little or no pressure dependence. Values of Emax obtained in the present work and from a published study of the temperature dependence show a monotonic increase with increase in the static dielectric constant, Ds. It is suggested that the correlation between Emax and Ds is a consequence of a predominant influence on the structure of eaq− of an attractive force determined by the local dielectric constant of the first solvation shell. Being determined in a similar manner by the same physical factors, Ds and the local dielectric constant change in the same direction.
Optical Bleaching and Deviations from Beer—Lambert's Law of Solutions Illuminated by a Ruby Laser. I. Cryptocyanine Solutions
Authors: Andorn M. , Bar-Eli K. H.
Published: February 2004

The deviations from Beer—Lambert's law of solutions of cryptocyanine were measured when the solutions were illuminated by a giant ruby laser pulse. The transmission-intensity curves show quite unambiguously that a second absorption from an excited state is needed to explain the experimental results. It is also shown that under steady state conditions it is the number of absorptions and not the detailed level scheme that governs the behavior of the system. The transmitted pulse was shown to be narrower than the incident one in an amount depending on incident intensity. Using the two absorption steady state mechanism, the change of shape could be explained and calculated. The decay rates and absorption cross sections were calculated for two models—the one which assumes absorption from an excited singlet, and the other which assumes absorption from the lowest triplet state. The blue fluorescence of cryptocyanine is explained in terms of our results. A level scheme based on the known spectrum fits with the suggested model.
Replacement Partition Function for Small Crystals in Homogeneous Nucleation Theory
Authors: Nishioka Kazumi , Shawyer R. , Bienenstock Arthur , Pound G. M.
Published: February 2004

The replacement partition function was calculated for small fcc crystals by numerical normal mode analysis using exactly the same model, which considers nearest-neighbor interactions only and neglects the surface relaxation and thermal expansion, to compute all the necessary quantities. A method of calculating the surface free energy of a small crystal from data on the macroscopic surface was introduced. The numerical value of the replacement partition function thus computed was, for example, 108 at T=2θ and for n=87. This is considerably larger than the value estimated for a crystal so far, which is 102-−04 at T=2θ and for n ≅ 100. This result suggests the need of further work both in numerical calculation and in theoretical studies.
Microwave Spectrum, Molecular Structure, Force Field, and Dipole Moment of Thiocarbonyl Selenide, SCSe
Authors: Hirose Chiaki , Curl R. F.
Published: February 2004

The microwave spectrum of SCSe was observed in the (0, 1±1, 0) and (0, 2±2, 0) vibrational states. The transitions observed were: J=7←6, 8←7, and 9←8 for 80Se and 78Se species, and J=8←7 and 9←8 for 76Se and 82Se species. It was not possible to observe directly the transitions of the ground state, but ground state rotational constants extrapolated from the two vibrationally excited states are 2043.310, 2060.321, 2078.190, and 2027.113 MHz for 32S12C80Se, 32S12C78Se, 32S12C76Se, and 32S12C82Se, respectively. These values differ considerably from those reported previously. The vibration-rotation constant α2 and the l-type doubling constant ql are also obtained as α2 = − 4.133, −4.169, − 4.215, and − 4.116 MHz, and ql=1.005, 1.021, 1.041, and 0.996 MHz for 32S12C80Se, 32S12C78Se, 32S12C76Se, and 32S12C82Se, respectively. The centrifugal distortion constant Dj was determined to be 0.163 and 0.22 kHz for 80Se and 78Se species. The molecular force field was calculated from ql to be fC–Se = 5.72, fC–S = 7.97, frr′ = 0.59, and fα/r1r2 = 0.20 mydn/Å. The dipole moment in the (0, 2±2, 0) state was measured to be 0.031 D.
Optical Studies of Energy Levels in Eu(OH)3
Authors: Cone R. L. , Faulhaber R.
Published: February 2004

The energy levels of Eu(OH)3 have been determined from the absorption and fluorescence spectra at 4.2 and 77°K. A crystal field analysis of the 7F manifolds, including intermediate coupling and the J-mixing effects of the crystal field, gave best agreement for B20 = 211 cm−1, B40 = −72 cm−1, B60 = −52 cm−1, and B66 = 611 cm−1. The above parameters also gave a good fit to the 5 D manifolds. Using these crystal field calculations and the free ion level structure of Carnall, Fields, and Rajnak, it was possible to identify nine levels in the 5L8 and 5L9 levels, which were found directly below and above the 5D4 manifold and are strongly mixed with it. The over-all rms deviation for the levels in the 7F, 5D, and 5L manifolds was 4.9 cm−1. The above crystal field parameters have been compared with previous results for other rare earth hydroxides: Gd(OH)3, Tb(OH)3, Dy(OH)3, Er(OH)3, Gd3+:Y(OH)3, Tb3+:Y(OH)3, Ho3+:Y(OH)3, and Er3+:Y(OH)3. Phonons in the rare earth hydroxides are discussed briefly, with results presented from the vibronic transitions in Eu(OH)3 and the phonon Raman effect in Tb(OH)3.
Observations of Triplet-State Radicals in Irradiated Single Crystals of Carbazide
Authors: Reiss Keith , Gordy Walter
Published: February 2004

The ESR of carbazide (NH2NHCONHNH2) after γ irradiation at 77°K exhibits signals corresponding to an effective g value of 4 in addition to the components centered at g=2. These half-field lines correspond to second-order Δ Ms= ± 2 transitions of a spin triplet state which result from isotropic exchange couplings of electronic spin centers located on two NH fragments, probably on the ṄH–NH–CO–NH–ṄH biradical but possibly on NH2–NH–CO–NH–ṄH–NH2–NH–CO–NH–ṄH radical pairs. An analysis of the anisotropic dipolar coupling tensor yields the principal values D∥ = 665.0 G and D⊥ =−332.5 G. There are two distinguishable biradical orientations for which separate spectra occur. Except for this difference in orientation the biradicals are identical. The mean value, R=4.37 ± 0.04 Å, is found for the separation of the exchange coupled electron spins. In addition to the biradicals, the related radical NH2NHCONHṄH and other unidentified radicals having only one unpaired electron are observed. These latter species greatly exceed the number of biradicals formed. Analysis of the temperature dependence of the biradical half-life by isothermal annealing gave the activation energy for the decay to be Ea=0.165  eV. The radicals having single unpaired electrons were also observed to be thermally unstable, though not so much so as the biradicals.
Collision Induced Infrared Absorption of Gaseous Nitrogen at Low Temperatures
Authors: Sheng De T. , Ewing George E.
Published: February 2004

The collision induced infrared absorption spectrum of gaseous nitrogen was studied over the temperature range 77–297°K. The integrated absorption coefficient depends quadratically on the gas density and indicates as have previous studies on this and other nonpolar diatomic molecules that the transition inducing mechanism involves a two molecule interaction. A profile analysis of the absorption band at various temperatures assigns the observed features to colliding pairs of freely rotating nitrogen molecules. No evidence for bound state dimers was found although our data do not preclude their existence. Since the integrated absorption coefficient is related to the intermolecular potential, a comparison between the theoretically calculated and experimentally measured values at different temperatures provides a means for studying the potential. It was found that the Lennard-Jones potential was adequate from 297°K to about 130°K with the traditionally accepted σ and ε/k parameters, but for lower temperatures the agreement with spectroscopic measurements was poor. The discrepancy can be accounted for by realizing that the Lennard—Jones potential is isotropic, but at low temperatures angularly dependent quadrupole interactions become relatively more important and need to be included in the description of the total intermolecular interaction.
Electron Spin Resonance Line Shapes in Partially Oriented Systems
Authors: Nordio Pier Luigi , Busolin Paola
Published: February 2004

The relaxation theory for paramagnetic molecules dissolved in liquid crystals, having the same elongated shape of the solvent molecules so as to act as probes of their dynamical behavior, has been revised. The diffusion equation is solved as a series expansion of Wigner rotation matrix elements, employing a simplified orientating potential, and the solution is used to evaluate the effects of the molecular fluctuations on the electron spin resonance line shapes. The irreducible components of the dipole and g interaction tensors relax with a spectrum of characteristic times, which are functions of an alignment parameter and cause any contribution to the linewidth to vanish in the limit of complete ordering.
Nanosecond Time-Resolved Emission Spectroscopy of 1-Anilino-8-Naphthalene Sulfonate
Authors: Chakrabarti Saroj K. , Ware William R.
Published: February 2004

Nanosecond time-resolved emission spectroscopy and fluorescence lifetime measurements are reported for 1-anilino-8-naphthalene sulfonate. Time-dependent spectral shifts are observed that are interpreted in terms of dipole reorientation of the solvent around the electronically excited molecule. Both the radiative and nonradiative transitions probabilities are observed to be strongly solvent dependent.
Study of the Lifetimes of Individual Vibronic States of the Isolated Benzene Molecule
Authors: Spears Kenneth G. , Rice Stuart A.
Published: February 2004

In this paper we report measurements of the lifetimes of 22 vibronic states of benzene and the relative quantum yields of fluorescence for transitions originating from these states. The measurements, which are all made in the free molecule limit, are used to test the theory of radiationless processes. It is found that the available theory provides a moderately good description of the observations. Our principal observation is that the nonradiative lifetime of the prepared state decreases with increasing excitation over the origin in such a way that the decrement in nonradiative lifetime per quantum of vibrational energy is approximately constant. The excitation of progressions in low frequency out-of-plane modes decreases the nonradiative lifetime per unit energy more than do excitations of progressions in, say, the totally symmetric mode. We also discuss the pressure dependence of the lifetime of a prepared state and its relationship to molecular properties.
Concept of Minimum State Density in the Activated Complex Theory of Bimolecular Reactions
Authors: Wong W. H. , Marcus R. A.
Published: February 2004

In some bimolecular reactions, for example, certain low potential-energy barrier reactions, the saddle-point choice for the position of the activated complex is vague and sometimes incorrect. In these and in some others a different choice is needed. The concept of minimum state density for this purpose, its relation to adiabatic transition state theory and to the maximum free energy criterion, are discussed. It is shown how it may be applied to bimolecular reactions using microcanonical activated complex theory for these reactions.
Matrix-Isolated Silane. Infrared Spectra
Authors: Wilde R. E. , Srinivasan T. K. K. , Harral Richard W. , Sankar S. G.
Published: February 2004

The infrared spectra of silane and its deuterated species isolated in solid neon, argon, krypton, xenon, nitrogen, carbon monoxide, and methane have been obtained. In addition, argon—krypton mixed-matrix studies and oxygen-doping experiments have been done. It is shown that silane occupies at least two types of defect sites. There is no evidence for free or nearly free rotation of silane in any of the matrices.
Role of the Attractive Potential in Gas—Surface Interaction Theory
Authors: Goodman Frank O.
Published: February 2004

To study quantum mechanically the role of the attractive potential in gas—surface interaction theory, a one-dimensional ``oscillating repulsive wall'' model is presented. Results are obtained for a rather general form of the attractive potential by combining a WKB method with a distorted-wave Born approximation and the one-phonon approximation; the analysis is restricted to monatomic gas molecules. Discussions of the validity of the method lead to the expectation, or at least to the hope, that it may give a reasonably realistic description of some gas—surface interactions. It is concluded that considerable care should be taken when gas—surface interaction potentials which incorporate long-range exponential attractive behavior (such as the commonly used Morse potential) are used in discussions of low-energy interactions, when transitions of gas molecules into their bound states at the surface may play important roles. An example of the results is given in the form of an approximate calculation of the adsorption probability of a low-energy gas molecule by a cold surface.
Neutron Diffraction Study of Ice Polymorphs under Helium Pressure
Authors: Arnold G. P. , Wenzel R. G. , Rabideau S. W. , Nereson N. G. , Bowman A. L.
Published: February 2004

Neutron diffraction studies of several of the D2O ice polymorphs were made with helium pressures to 3.5 kbar. Volume compressions (ΔV / V) were obtained for ices Ih, Ic, and IX at 2.1 to 2.8 kbar. The equilibrium phase boundaries between ices I–II and I–III in the presence of helium are shifted toward higher pressure values. The crystal structures of ices Ih, Ic, II, and IX at approximately 2.5 kbar are the same as the structures found for these ice forms at atmospheric pressure. A tetragonal structure is indicated for ice III with lattice parameters at − 23°C and 2.7 kbar of a = 6.674 ± 0.015 Å and c = 6.97 ± 0.03 Å. The c / a ratio for ice IX has been found to be 1.000 ± 0.003 both at 1 bar and at 2.8 kbar.