bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin contamination in unrestricted Hartree-Fock calculations
Authors: Schug John C. , Phillips Donald H.
Published: February 2004

We have treated several pi-electron doublets by both the unrestricted Hartree-Fock method and the restricted approximation of Longuet-Higgins and Pople. For two of the molecules, which contain oxygen heteroatoms, serious spin contamination occurs in the UHF wavefunctions and this negates the usefulness of the single annihilation procedure that is often used for spin-density calculations. The restricted approximation provides a convenient alternative, especially because configuration interaction is easily taken into account.
Adsorbate interactions on a Pt(110) surface. II. Effect of sulfur on the catalytic CO oxidation
Authors: Bonzel H. P. , Ku R.
Published: February 2004

The interaction between adsorbed sulfur and oxygen on Pt(110) was investigated and found to be strong resulting in a Langmuir-Hinshelwood-type surface reaction with SO2 as the reaction product. The kinetics of this surface reaction were studied as a function of initial sulfur coverage, partial pressure of oxygen, and temperature. For low coverage of sulfur, θ < 0.28, the reaction was quite fast while for higher sulfur coverages, 0.28 < θ < 0.75, the reaction became very slow. In this latter range, the reaction proceeded inhomogeneously and gave rise to a nonuniform distribution of adsorbed sulfur. The distribution of sulfur was scanned in two dimensions across the surface by Auger electron spectroscopy with a lateral resolution of about 0.02 cm. The same technique permitted an estimate of the surface diffusion coefficient of sulfur on Pt(110) at 450°C of 3 × 10−7 cm2/sec. In a steady state experiment the rate of CO oxidation was measured by mass spectrometry as a function of the sulfur coverage. In the region 0 ≤ θ < 0.28, this rate decreased to near zero as (1 − κθ)2, with κ = 3.5 as the surface coordination of sulfur. For θ > 0.28 the CO2 formation was indistinguishable from the background CO2 level. It appears that within the region θ < 0.28, the CO2 formation rate is solely governed by the rate of dissociative adsorption of oxygen.
Electron spin resonance of Gd3+ in glasses of the soda-silica-yttria system
Authors: Nicklin R. C. , Johnstone J. K. , Barnes R. G. , Wilder D. R.
Published: February 2004

The electron spin resonance of the Gd3+ ion has been studied in two series of glasses having the molar compositions 6SiO2:5Na2O: x (Gd2O3 + Y2O3) with 0 ≤ x ≤ 0.5 and 500SiO2: x Na2O:1Gd2O3 with 2.5 ≤ x ≤ 494. The spectra were nearly independent of temperature and sample composition, but varied strongly with microwave frequency in the range 5.4–38.4 GHz. The data were interpreted in terms of the spin Hamiltonian for a strong cubic crystal field and also in terms of the usual rhombic spin Hamiltonian H = g 0β H · S + D[Sz2 − (1/3)S  (S + 1)] + E(Sx2 − Sy2) with S = (7/2). Computer calculations were made yielding all possible effective g values for this latter Hamiltonian for all physically distinct combinations of the crystal field parameters when the Zeeman field H was restricted to the x, y, or z direction. The resonance features were related to three distinct sites for the Gd3+ ion. The spectra are indicative of a chemically heterogeneous glass matrix composed of soda-rich, silica-rich, and diffuse transition regions. The heterogeneities were found to exist over the entire range of compositions studied. Variations in the resonance intensity associated with the soda-rich region suggest the existence of a very well-defined substructure within the region. The data indicate that the substructure is related to the fundamental structural features of the possible crystalline compounds which can exist within the composition range.
Non-Gaussian theory of rubber elasticity
Authors: Kumbar Mahadevappa
Published: February 2004

Non-Gaussian theory for rubber elasticity has been developed using the distribution function which was proposed for the excluded volume problem. An equation of state which is based on a very simple model yields remarkably good results when the non-Gaussian parameters are adjusted. A distribution function for network study has been suggested. The computed simple shear-strain curve also closely agrees with that of the experimental curve predicting the relationship to be nonlinear. The equations for swelling phenomenon have been derived using the non-Gaussian network concept.
Chemical potentials and related thermodynamics of sodium-ammonia solutions
Authors: Ichikawa K. , Thompson J. C.
Published: February 2004

Data on the temperature and composition dependence of the chemical potential of Na in Na–NH3 solutions obtained from an electrochemical cell are reported. The cell used a bridge electrode of sodium beta-alumina. A variety of thermodynamic parameters are calculated and estimates are given for the critical exponents α, γ, and δ. Particular attention is paid to the concentration fluctuations 〈(Δ x)2〉 which provide indications of clustering in these and other solutions.
Effect of density on the Raman scattering of molecular fluids. I. A detailed study of the scattering polarization, intensity, frequency shift, and spectral shape in gaseous N2
Authors: Wang C. H. , Wright R. B.
Published: February 2004

This paper reports the density dependent Raman study of N2 (and CO) up to 480 amagat. The study not only extends the previously reported spectral bandwidth study of N2 to higher gas density but also includes the polarization, frequency shift, and integrated intensity measurements. The results of the spectral moment analysis of the depolarized spectrum are also discussed.
δ-function model potential for the calculation of pair correlation energies in atoms
Authors: Alper Joseph S.
Published: February 2004

Pair correlation energies for first-row atoms are calculated using an attractive δ-function potential and the original Slater orbitals. This model potential is the simplest short-range attractive pair potential and several semiquantitative results can be easily derived using it. Analogs of Hund's rules are applied to pair correlation energies. The model distinguishes between transferable and nontransferable pairs and is able to account for the Z (nuclear charge) dependence of the nontransferable pairs quite well. It does not reproduce the dependence of the nontransferable pairs on N (the number of electrons) accurately because this dependence involves all of the electrons in the shell and so cannot be treated by means of a simple pair model involving only one pair of electrons.
Primary processes in excited β-napthol systems: A pulsed laser photolysis study
Authors: Kläning U. K. , Goldschmidt Ch. R. , Ottolenghi M. , Stein G.
Published: February 2004

Using a pulsed N2 laser the rates of formation of solvated electrons, and triplet molecules were measured for β-naphtholate, β-naphthol, and β-naphthyl-methyl-ether in solution. The rate of electron formation is higher than the rate of vibrational relaxation to the lowest excited singlet state, from which intersystem crossing occurs. Quantum yields of triplet formation and rate constants for intersystem crossing were obtained from measurements of fluorescence yields, lifetimes and relative yields of triplets in oxygen free and oxygen containing solutions. For β-naphthol in a high viscosity solvent the sum of the quantum yields of formation of solvated electrons and of population of the lowest excited singlet state is unity whereas the sum is less than unity in low viscosity solvents, indicating that the lowest excited singlet state of β-naphthol is populated by charge recombination in high viscosity solvents but not in low viscosity solvents. A calculation of the energetics yields a maximum charge separation of 5 Å, a value consistent with the occurrence of effective charge recombination.
Van Vleck perturbation treatment of short-range atomic interactions in H2+ and HeH++
Authors: Chang Shih-Yung
Published: February 2004

A modified version of Van Vleck perturbation theory, the distinguishable electron method, is applied to short-range diatomic interactions in H2+ and HeH++. Starting with united-atom wavefunctions φoa and φob at two centers, a and b, as two degenerate states, each wavefunction is corrected to first order in charge-shifting perturbations, Zb(1/ra−1/rb) and Za(1/rb−1/ra), where Zi is the nuclear charge and ri is the electron-nucleus distance. The final molecular wavefunction, correct to first order in charge-shifting perturbation, is then obtained by solving a secular equation; this is facilitated by making use of molecular symmetry and electron-nucleus cusp conditions. For a one-electron diatomic molecule the wavefunction Ψ to first order in charge-shifting perturbation is shown to have the form Ψ = (Za/Z) [φoa+λZbf(ξ, η, Z, R)] + (Zb/Z)[φob+λZaf(ξ, −η, Z, R)], where Z is the sum of nuclear charges, λ is the ordering parameter, and f is a function of Z, R, and confocal elliptic coordinates defined by ξ = (ra+rb)/R and η = (ra−rb)/R. Application of the method to the ground states of H2+ and HeH++ gives better convergence than do the one-center calculations. The total energies evaluated to second order compare favorably with exact values for R < 1.0 a. u. in the case of H2+ and for R < 0.75 a. u. in the case of HeH++. The physical interpretation of the charge-shifting processes is discussed and the method is compared with that of Byers-Brown and Power.
Quantum theory of elastic and inelastic scattering of atoms by solid surfaces
Authors: Goodman Frank O. , Tan Whee-Keng
Published: February 2004

The theory of scattering of atoms by solid surfaces is extended in the following three areas: (1) elastic scattering (atom diffraction) in the absence of inelastic scattering, (2) inelastic scattering (atom-phonon scattering) in the absence of diffraction, and (3) a combination of diffraction and inelastic scattering. The elastic scattering theory is developed to the point where it is possible to interpret experimental results on up to 60 diffracted beams; the starting point is the theory of Cabrera, Celli, Goodman, and Manson [Surf. Sci. 19, 67 (1970)]. The results are applied to experimental data on the helium-lithium fluoride system. The inelastic scattering theory is extended to a consideration of phonon scattering about the diffracted beams; the starting point is the theory cited above and that of Goodman [Surf. Sci. 30, 1 (1972)]. The results are applied to experimental data on the helium-silver and helium-lithium fluoride systems.
Brownian motion of N interacting particles. II. Hydrodynamical evaluation of the diffusion tensor matrix
Authors: Aguirre J. L. , Murphy T. J.
Published: February 2004

For two Brownian particles of arbitrary shapes, expressions in the form of infinite sums are obtained for the translational friction tensors using the method of hydrodynamic reflections. From the generalized Einstein relation which gives the diffusion tensors in terms of the friction tensors, we show that in the absence of long-range forces among the Brownian particles, the self-diffusion constant is of the form D = D0 + D1′c lnc + D1c + ···, where c is the concentration of the Brownian particles. For the case of two identical spheres, the friction tensors are evaluated up to fourth order in the ratio of the radius a of the spheres to the distance between them. The diffusion tensors and the numerical value of D1 are then evaluated in the same approximation; D1′ is found to be zero.
EPR spectra of spin labels in lipid bilayers
Authors: Schindler Hansgeorg , Seelig Joachim
Published: February 2004

Assuming a probability function P(θ)α exp{(−q/RT)cos2Θ} for the orientation of the chain segments in a lipid bilayer, a quantitative theory for the spin label spectra of such systems is developed. Only three parameters, namely two energy parameters q3 and q1 and the correlation time τ20 are required to yield perfect agreement between experimental and theoretical spectra for correlation times up to 3 × 10−9 sec. In calculating the EPR spectra pseudosecular and nonsecular contributions to the linewidth are included, since especially the former exert a distinct influence on the spectra. Also discussed are the effects of tilt angle and spread angle. The theory is applied to the anisotropic motion of the fatty acid spin label I (13.2) in a decanol-sodium decanoate bilayer. Between 44 and 8°C the correlation time is found to increase exponentially from 1.0 × 10−10 to 4.0 × 10−10 sec with an activation energy of 6.84 kcal mole−1. The energy parameters q3 and q1, which determine the order parameters S3 and S1, remain constant in the same temperature range (q3 = −2.9 kcal mole−1; q1 = 1.7 kcal mole−1). The average orientation of the chain segment is perpendicular to the bilayer normal. Below 8°C a phase transition occurs and the chain segments become gradually tilted. At −8°C the correlation time has increased to 2.8 × 10−9 sec and the chains are now tilted by approximately 18° from the bilayer normal. From the correlation time the translational diffusion constant can also be deduced. At 21°C a value of Dtrans = 1.5 × 10−6 cm2 sec−1 is obtained for the lipid molecules in the decanol-sodium decanoate bilayer. In vesicles of dimyristoyl-L-α-lecithin at 21°C the analysis of the spectrum yields a correlation time of 2.5 × 10−9 sec and a diffusion constant of the lipid molecules of Dtrans = 3.6 × 10−8 cm2 sec−1.
Resonance Raman spectrum and vibrational analysis of the ozonide ion in the argon matrix-isolated M+O3− species
Authors: Andrews Lester , Spiker Robert C.
Published: February 2004

Beams of alkali metal atoms and ozone molecules at high dilution in argon were condensed on a tilted copper wedge at 16°K and were examined by argon and krypton plasma laser excitation. Very intense bands shifted 1010 cm−1 below the exciting lines showed small alkali metal effects and appropriate oxygen-18 shifts for assignment to the v1 symmetric oxygen-oxygen mode of the ozonide ion in the M+O3− species. The intense fundamental and a regular progression of overtones out to 4v1 suggest that these spectra are probably due to the resonance Raman effect. Vibrational analysis for six isotopic ozonide species produced the oxygen-oxygen force constant 4.18 ± 0.11 mdyn/Å. The spectroscopic value for the heat of atomization of the ozonide ion calculated from the vibrational constants ω1 = 1028.2 cm−1 and X11 = 4.95 cm−1 for Cs+O3− is 153 kcal/mole, which agrees well with the thermodynamic value.
Valence excited states of CH. I. Potential curves
Authors: Lie George C. , Hinze Juergen , Liu Bowen
Published: February 2004

Ab initio CI calculations have been performed over a wide range of internuclear distances (1.00–20.00 bohr) to obtain the potential curves for the first five valence excited states of CH; X2Π, a4Σ−1, A2Δ, B2Σ−, and C2Σ+. Results, with known experimental values in parentheses, are Re(X2Π) = 2.113 (2.116) bohr, Re(a4Σ−) = 2.053 bohr, Re(A2Δ) = 2.083(2.083) bohr, Re(B2Σ−) = 2.216(2.20) bohr, Re(C2Σ+) = 2.100(2.105) bohr; De(X2Π) = 3.51(3.63) eV, De(a4Σ−) = 2.84 eV, De(A2Δ) = 1.90(2.01) eV, De(B2Σ−) = 0.23(0.40) eV, and De(C2Σ+) = 0.78(0.94) eV. Potential maxima of heights 1284 and 3228 cm−1 are calculated for the B2Σ− and C2Σ+ states, respectively. These maxima are attributed to avoided curve crossings. The a4Σ− state, not observed experimentally, is estimated to lie between 0.62 and 0.76 eV above the X2Π state.
On the vibroelectronic Raman effect
Authors: Kane-Maguire C. , Koningstein J. A.
Published: February 2004

The theory of a new Raman effect is presented where changes occur in the electronic and vibrational quantum numbers. Theory predicts that such an effect is governed by trace scattering and to first order only totally symmetric vibrations are involved. The experimental data are in good agreement with the theoretical predictions.
Energy gradients in extended Hückel theory: Application to cyclopentane
Authors: Ferguson T. R. , Beckel C. L.
Published: February 2004

An energy gradient method for determining stable molecular configurations using extended Hückel theory is applied to cyclopentane. Bond lengths are constrained. Models with as many as twenty-five degrees of freedom are studied, with results showing that past assumptions concerning C–H bond orientations are reasonable. Free pseudorotation is predicted. Computed puckering amplitudes (0.40–0.47 Å) and the barrier to planarity (4–14 kcal/mole) are compared to other published results. Comparisons between molecular orbitals in the planar and puckered forms indicate that the dominant factor in the barrier to planarity is bond eclipsing.
Proof of a fundamental theorem in the many-electron theory for atoms and molecules
Authors: Hertia D. I. , Ivanov A.
Published: February 2004

In this work the cluster-function development for a many-electron function of Sinanoğlu's works is rigorously derived and generalized. More specifically, this development is given for the open shell cases, described by a function which contains internal correlation effects. The special case of closed shells is a very simple consequence of the more general formula obtained here.
Effects of bundling in a lattice gas model of liquid crystals
Authors: Sheng Ping
Published: February 2004

Phase transition properties in a lattice gas model of liquid crystals, consisting of rigid rods with attractive, anisotropic, nearest-neighbor interaction, are calculated with the method of Guggenheim-Flory-DiMarzio lattice statistics. It is shown that in this model the properties of the isotropic-anisotropic phase transition are altered by a bundling phenomenon, in which parallel molecules are grouped into energetically favorable clusters of various sizes. The bundling of molecules increases the density at which the isotropic-anisotropic phase transition occurs and decreases the values of the accompanying density and order parameter discontinuities at the transition. The cases where the molecular length to breadth ratio l = 5, 10 are calculated and illustrated.
Ab initio calculations of potential energy surfaces in the complex plane. I. General theory and one-electron example
Authors: Morokuma Keiji , George Thomas F.
Published: February 2004

A general theory for ab initio calculations of potential energy surfaces for complex values of nuclear coordinates, R, is developed. The motivation for this development stems from the interest of the collision theorist in the analytic continuation of potential energy surfaces into the complex R plane. Ab initio calculations at complex R involve the diagonalization of a complex, non-Hermitian, electronic Hamiltonian, which results in biorthogonal eigenvectors. We apply the theory to a simple model system of two potential curves with an avoided crossing for real R, and investigate their crossing and electron distributions in the complex R plane. We carry out ab initio LCAO MO calculations on the one-electron system HeH++, and focus on two particular potential curves with an avoided crossing for real R. We discuss the general problems associated with MO calculations of many-electron polyatomic systems for complex nuclear coordinates.
Molecular collisions. XIX. The distorted wave approximation to atom-rigid symmetric top rotational excitation
Authors: Russell Dennis , Curtiss C. F.
Published: February 2004

In Paper XVII of this series an exact formalism describing nonreactive collisions of vibrating polyatomic molecules was developed. The present work specializes this formalism to the case of an atom-rigid symmetric top collision. A distorted wave approximation is developed which is appropriate for a symmetric top in which the moment of inertia about the symmetry axis is much smaller than that about the remaining principal axes. The solution obtained is then expressed in terms of the generalized phase shift formalism.
Electron scattering from diatomic molecules in the first Born approximation
Authors: Liu J. W.
Published: February 2004

The differential cross sections for electron scattering from the diatomic molecules H2 and N2 in the first Born approximation, using molecular wavefunctions, have been calculated. The molecular wavefunctions for H2 and N2 were in the form of a Slater determinant(s) with one-electron Slater-type orbitals (STO's). For the purpose of simplifying the calculation the STO's involved in all two-center, but not one-center, integrals were expanded in Gaussian-type orbitals (GTO's). The result of the calculation for H2, using a configuration interaction (CI) wavefunction containing 97% of the binding energy, leads to agreement with existing experimental data. The calculated scattered intensity for H2 can be considered as the most accurate one for comparison with experiment at the 1% accuracy level. This accuracy is a result of the approximate wavefunction containing 1% less energy than the total experimental energy. For the case of N2 the double ξ exponent wavefunction of Richardson was used. It was found that the scattered intensity of the electron-nuclear bonding charge density is very sensitive to the choice of molecular wavefunction used. This study represents the most definitive calculation of the two-electron effects in total scattered intensity so far reported. The total result, including both one- and two-electron terms, was found to be in qualitative agreement with experiment.
Reduced partitioning procedure in configuration interaction studies. II. Excited states
Authors: Bartlett Rodney J. , Brändas Erkki J.
Published: February 2004

Within the configuration interaction (CI) domain a multidimensional partitioning procedure is employed to provide a high-order, nonlinear perturbation approach for the treatment of several states of the same symmetry. Two alternative methods are derived, one of which treats the states simultaneously, while the second permits one to focus on a single selected state. In either case, the results are given as a series of converging upper bounds to the full CI energies. The ``selective'' process has been applied the lowest 1Σ+ states of the HeH+ molecular ion to obtain potential curves. In all cases the first-order solution, which is related to a geometric formula, accounts for about 60% of the energy increment between the full CI and unperturbed result, while an eight- or lower-order solution yields at least 99.9%. Due to the rapid convergence, only small matrices need to be diagonalized to reproduce the full CI eigenvalues.
Axially isotropic Cartesian tensors
Authors: Reznik A. A. , Hollingsworth C. A.
Published: February 2004

Some general properties of three-dimensional Cartesian tensors (of any rank) which are invariant under the point groups C∞, C∞ y, C∞ h, and D∞ h are obtained. A method is described for obtaining the relationships between the nonzero components of these invariant tensors and is illustrated by application to tensors of ranks six and seven. It is shown how the corresponding relationships for tensors of ranks lower than six can be obtained from tables in the literature. The results are applied in a treatment of nonlinear susceptibilities of an axially isotropic system.
Vacuum-ultraviolet photolysis of ethylene oxide
Authors: Kawasaki Masahiro , Ibuki Toshio , Iwasaki Masahiro , Takezaki Yoshimasa
Published: February 2004

The photochemical primary processes of ethylene oxide in the vacuum ultraviolet region have been studied with emphasis on the dependence on energy. It has been found that the decomposition into methyl and formyl radicals is the main process while the decomposition into ethylene and oxygen atoms is also important at shorter wavelengths. 1470 Å1744 Å1783 ∼ 1845 ÅC2H4O+ h ν→ CH3+CHO(CO+H)111(I)→ O+C2H4(C2H2+H2)0.70.10.1(II)→ H2+(CH2CO)0.10.1···(III)→ CH3CHO0.2······(IV)→ CH2+HCHO0.2······(V)The formation of excited ethylene in Process (II) which decomposes into acetylene and hydrogen has been suggested.
Ionization energies of doubly and triply ionized rare earths
Authors: Sugar Jack , Reader Joseph
Published: February 2004

Values for the ionization energies of the doubly and triply ionized rare earth atoms have been derived from interpolated spectroscopic properties of the 4fNns series, and from interpolated energy intervals relating the first series member, 4fN6s, to the ground state. The results in eV are La III19.1774(6)Tb III21.91(10)IV 39.79(20)Ce20.198(3)IV 36.758(5)Dy22.79(30)41.47(20)Pr21.624(3)38.98(2)Ho22.84(10)42.48(32)Nd22.14(30)40.41(20)Er22.74(10)42.65(21)Pm22.32(36)41.09(32)Tm23.68(10)42.69(20)Sm23.43(30)41.37(38)Yb25.03(2)43.74(20)Eu24.70(32)42.65(32)Lu20.9596(10)45.19(2)Gd20.63(10)44.01(35)Hf33.33(2)The values for the doubly ionized atoms agree to within ∼ 1% with those deduced from thermodynamic measurements on lanthanide oxides. A value for the ionization energy of Gd II of 12.09(8) eV was determined by using new spectroscopic data for Gd II and Gd III.
Vibronic coupling. VII. Magnetic circular dichroism of trimers, aromatic hydrocarbons, and porphyrins
Authors: Perrin Marilyn H.
Published: February 2004

Vibronic wavefunctions for trimers are used to calculate the A and B parameters characteristic of MCD spectra. In the weak-coupling limit both the A and the B parameters are zero for s = 0 states and nonzero for s = ±1 states. In the strong-coupling limit, the vibrationally induced 0–1 transition has nonzero A and B parameters, but the spectrum is dominated by the B term. Vibronic wavefunctions for cyclic polyenes are used to calculate the A and B parameters for the electronically forbidden, vibronically allowed 0–1 transitions in closed-shell aromatics and porphyrins. In 4n +2-atomic systems, the 0–1 transition for the B1u state has a small A term, vibronic in nature, and a B term that dominates the spectrum. The parameters are calculated for benzene, 18-annulene, coronene, and triphenylene. In the E2n−1 electronic state of a 4n-atomic system with 4n+2 electrons, there are two vibronic states that are made allowed by excitation of one quantum of either of two nontotally symmetric vibrations. There is a novel magnetic interaction between these two vibronic states. A model 16-membered polyene is used to calculate the A and B parameters for the metal and free-base porphyrins. In the metal porphyrins, the two A parameters are of opposite sign and each is of opposite sign to its corresponding B parameter. The MCD spectrum for each of the two 0–1 transitions in the Q state of the metal porphyrins is dominated by the A term. The free-base spectrum is also discussed. This simple and intuitive model gives calculated values that compare well with the experimental ones.
Optical and magnetic resonance spectra of inorganic molecular crystals-uranium borohydride [U(BH4)4] in hafnium borohydride [Hf(BH4)4]
Authors: Bernstein E. R. , Keiderling T. A.
Published: February 2004

The electronic absorption spectra of U(BH4)4 as a guest in Hf(BH4)4 host crystals are reported. Optical spectra, from the charge transfer or f-to-d cutoff at approximately 2900 Å to the low energy limit due to host molecular vibrations at approximately 2.0 μm, have been obtained at 300, 77, and 2°K for mixed crystals of U(BH4)4/Hf(BH4)4 and U(BD4)4/Hf(BD4)4. From temperature effects, deuteration shifts, and intensity patterns, over 20 possible forced electric dipole crystal field electronic origins have been identified. Several molecular vibrations have been identified built on these origins and, based on physically reasonable arguments, are tentatively associated with specific vibrational symmetries and motions of M(BH4)4 type molecules. Attempts to obtain EPR spectra between 2 and 77°K are discussed. Zeeman spectra in fields of up to 93.5 kG for the region 4000–7500 Å have been used to aid in the identification of both ground and excited electronic crystal field states. Calculations, based on a free ion and cubic crystal field parameterized Hamiltonian, are employed to assign electronic origins. The spectra are best fit to a crystal field model Hamiltonian whose two parameters A60 〈 r6〉 and A40 〈 r4〉 have their signs determined from considerations of 12 negative point charges at the hydrogen positions. Implications of these crystal field and vibrational analyses for actinide spectroscopy are discussed.
Radiative and radiationless decay processes in rhodium(III) ammine complexes
Authors: Thomas T. R. , Watts R. J. , Crosby G. A.
Published: February 2004

Luminescence quantum yields and lifetimes of a series of rhodium(III) halopentammines have been determined at 110°K in water-methanol glasses. Deuterium substitution of the solute-solvent mixture is found to enhance the luminescence lifetimes significantly. The weak and strong coupling mechanisms for radiationless processes are compared, and it is concluded that these complexes are examples of the weak coupling mechanism in spite of the large Stokes shifts found in their emission spectra. The radiative lifetimes of the series of complexes are interpreted on the basis of a spin-orbit-coupling model for dd luminescence. The effect of perdeuteration on the luminescence lifetime of trans-dibromotetra(pyridine)rhodium(III) bromide is reported and compared with the effect of deuteration of the water-methanol solvent system. A large enhancement of the luminescence lifetime is observed in both cases.
Raman spectra of water in rare earth chloride solutions
Authors: Mundy W. C. , Spedding F. H.
Published: February 2004

Raman data were obtained for both polarizations of the OD stretching vibrations of HDO in six or seven concentrations of aqueous solutions of LaCl3, GdCl3, and LuCl3 in which 5 mole% of the water was D2O. For comparison, data were also obtained for the OH stretching vibrations of HDO in GdCl3 which had 95 mole% deuterated water. The rare earth salt concentrations of these solutions were approximately 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5m. All of these data were taken at room temperature. Cation dependent effects were observed in the peak positions and half-widths of the water bands for high solution concentrations. A differential analysis technique was developed which allowed the identification of distributions of frequencies associated with water molecules which were clearly affected in different ways by the rare earth and chloride ions.
Microwave optical double resonance spectroscopy with a cw dye laser: BaO X1Σ and A1Σ
Authors: Field Robert W. , English Alan D. , Tanaka Takehiko , Harris David O. , Jennings Donald A.
Published: February 2004

A tunable, single frequency, continuous wave, dye laser has been used to optically pump various lines of the BaO A 1Σ-X 1Σ electronic transition. Microwave optical double resonance (MODR) spectra are recorded as changes in the intensity of dye laser induced photoluminescence. Fourteen microwave rotational transitions in the X 1Σ (ν = 0,1) and A 1Σ (ν = 0–5) states of 138Ba16O and one transition in the A 1Σ (ν = 1) state of 137Ba16O have been observed. Partially deperturbed rotational constants obtained for BaO A 1Σ are B(ν) = 0.25832(2) − 0.001070(5) (ν + 1/2) cm−1. Two physical models are described which account for microwave optical double resonance effects in the strong (nonlinear) and weak (linear) optical pumping limits. Observed changes in photoluminescence polarization caused by excited state microwave transitions are predicted by a semiclassical transition dipole model. A three level steady state kinetic treatment of microwave optical double resonance indicates that the BaO MODR transitions reported in this paper are observed near the strong optical pumping limit. It is shown that for most allowed transitions in diatomic molecules a 100 mW single frequency, dye laser is sufficiently intense to significantly deplete rotational levels of the electronic ground state with respect to neighboring rotational levels and to cause the populations of the depleted ground state and optically pumped excited state levels to become comparable.
Theoretical solution enthalpies of divalent impurities in the alkali halides
Authors: Bowman Robert C.
Published: February 2004

The solution enthalpies of divalent cations, in the limit of infinite dilution, have been calculated with the Mott-Littleton model and the Born-Mayer potential for the impurity host interactions. The theoretical values obtained for the alkali fluorides indicate the solution enthalpy increase with both the ionic radius and mass of the divalent impurity. This dependency has been experimentally observed in the NaCl and KBr crystals. The effects of variations in both the parameters representing the ionic interactions and the defect model have been investigated. Revised values for the Sr++ and Ba++ impurities in the alkali chlorides, which were previously reported, are also presented.
On a unified treatment of molecular interactions at finite temperatures
Authors: Baer S. , Ben-Shaul A.
Published: February 2004

The by now standard expression for the free energy of interaction of a pair of molecules in terms of molecular susceptibilities at imaginary frequencies follows from a straightforward perturbation expansion of the statistical operator exp(− βH) and from the possibility to express the terms in the expansion in terms of intramolecular charge density correlations at imaginary times.
Spectra and structure of small ring compounds. XXVIII. 2,3-Dihydrofuran and 2,3-dihydrothiophene
Authors: Durig J. R. , Carter R. O. , Carreira L. A.
Published: February 2004

The low frequency Raman spectra for 2,3-dihydrofuran and 2,3-dihydrothiophene have been recorded in the region of the ring puckering vibrations. Only Δν = 2 transitions were observed beyond the region of the rotational envelope for both molecules. The observed transitions in the Raman effect for 2,3-dihydrofuran are in good agreement with the frequencies inferred from the previously reported infrared data. The data indicate that the 0 → 1 transition lies at 19.5 ± 0.5 cm−1 and the molecule is puckered with a barrier of 83 cm−1 to planarity. The previously unreported ring puckering transitions of 2,3-dihydrothiophene have been reasonably well reproduced by the potential V(X) = 6.40 × 105X4 − 2.89 × 104X2 giving a barrier to planarity of 325 cm−1. These direct observations are in disagreement with the midinfrared difference band series previously reported.
Vapor-phase far-infrared spectrum and double minimum potential function of trimethylene oxide
Authors: Jokisaari J. , Kauppinen J.
Published: February 2004

The far-infrared spectrum of trimethylene oxide has been investigated with high resolution and accuracy. A good agreement between the observed and the calculated origins of the ring-puckering vibration bands was achieved with the potential function V(ξ) = 60 (−0.3235ξ2 + 0.1010ξ4 + 1.45 × 10−4 ξ6) cm−1 in the harmonic oscillator representation.
Intrinsic photoconduction in anthracene single crystals: Electric field dependence of hole and electron quantum yields
Authors: Chance Ronald R. , Braun C. L.
Published: February 2004

For electric fields up to 2 × 104 V/cm applied normal to the a b plane of virgin anthracene crystals, both the hole and electron photocarrier quantum yields increase linearly with field. Field-dependence plots exhibit a slope to intercept ratio of 3.1 × 10−5 cm/V, a value which is in quantitative agreement with that predicted by Onsager's theory of geminate recombination. In nonvirgin crystals, sharply reduced photocarrier quantum yields at low fields are found to result from recombination of free carriers with oppositely charged trapped carriers left behind in the excitation region from previous experiments. The free carrier-trapped charge recombination rates are found to be diffusion controlled.
Crystal spectrum of promethium 3 + in LaCl3
Authors: Baer Wolfgang , Conway John G. , Davis Sumner P.
Published: February 2004

The absorption spectrum of Pm3+ in LaCl3 was measured between 12 000 and 28 000 cm−1 for both sigma and pi polizations. Free ion crystal field energy level calculations were made and the line groups 5F1, 5F2, 5F3, 5S2, 5F4, 5F5, 3K6, 5G3, and 5G2 identified. Crystal field parameters were determined from the energy splittings in the first four line groups. Their values are B02=145 cm−1, B04=−320 cm−1, B06=−650 cm−1, and B66=450 cm−1. For these groups the exact free ion energy levels were calculated and the free ion parameters determined. Their values are F2 = 412.5 cm−1, F6 = 7.6 cm−1, and ζ = 977 cm−1.
Self-diffusion and rotational correlation times in liquid acetylene
Authors: Scheie C. E. , Peterson E. M. , O'Reilly D. E.
Published: February 2004

Coefficients of self-diffusion have been measured in liquid C2D2; the data are represented by D = (6.37 ± 1.65) × 10−3 exp [− (1.96 ± 0.11)/R T] cm2 sec−1. Deuteron spin-lattice relaxation time data are represented by T1 = (4.04 ± 0.57) × 101 exp [− (1.26 ± 0.08)/R T] sec. The diffusion coefficient data are interpreted by means of a quasilattice model for self-diffusion which yields a pre-exponential factor of 5.2 × 10−3 cm2 sec−1. Rotational correlation times are computed from the T1 data and interpreted in terms of the quasilattice random flight and the dynamically coherent rotation models for molecular rotation. Both models give reasonably good agreement with experiment.
Ion-molecule equilibria in mixtures of N2 and Ar
Authors: Teng Harry H. , Conway D. C.
Published: February 2004

Equilibrium constants for the reactions 2N2+N2+=N4++N2 (I); N4++Ar=ArN2++N2 (II); ArN2++Ar=Ar2++N2 (III) have been determined mass spectrometrically. The reactions were studied as a function of E/P and temperature in a drift tube. It was found that ΔSI° = −16.2 ± 2.9 eu and ΔHI° = −24.4 ± 2.1 kcal/mole at 723°K. By extrapolation of enthalpy data to 0°K, the bond energies, D0(AB+), were found to be 25.9 ± 2.1, 26.2 ± 2.2, and 27.8 ± 2.2 kcal/mole for N2–N2+, Ar–N2+, and Ar–Ar+, respectively. When presumably more accurate literature data for Reaction (I) were used, the D0(AB+) for the same series were found to be 24.3, 24.5, and 26.3 kcal/mole. With literature data for Reaction (I) ΔSII° = 3.57 ± 0.06 eu, ΔHII° = −0.549 ± 0.026 kcal/mole, ΔSIII° = 1.87 ± 0.08 eu and ΔHIII° = 2.16 ± 0.03 kcal/mole at 298°K. Various models were used to determine the model dependence of the quantities derived from the equilibrium constant data. The ΔHn°, ΔSn° and D0(AB+) values are only weakly dependent on the assumed bond length and weak mode vibrational frequency distribution of the ion-molecule complex. However, D 0(Ar–N2+), ΔSn°, and ΔHn° (n = II or III) would be significantly different if Ar–N2+ were T shape rather than linear as assumed.
Thermal energy electron attachment rate constants for some polyatomic molecules
Authors: Davis F. J. , Compton R. N. , Nelson D. R.
Published: February 2004

Rate constants for the attachment of thermal energy electrons to a number of polyatomic molecules are reported. The attachment rate constants αw are determined in an electron swarm experiment under zero electric field conditions where the electrons have a Maxwellian energy distribution corresponding to the temperature of the nonattaching diluent gas. Various diluent gases were used, and no significant differences in the attachment rate constants were found. Corrections to the attachment rate constant measurements due to electron diffusion are small and are taken into account. Thermal energy attachment rate constants are reported for the following molecules (attachment rate constants are given in parentheses in units of cubic centimeters per second): SeF6(1.27 × 10−9), CCl4 (3.55 × 10−7) C7F14(4.0 × 10−8), C6F6(1.06 × 10−7), C7F8(2.42 × 10−7), C6F10(3.13 × 10−7), C5F8 (1.18 × 10−7), C4F8(1.11 × 10−8), C8H8(7.7 × 10−10), and SO2F2(5.8 × 10−10). Upper limits to the attachment rates for the following molecules were obtained using pure gases: CF4, C2F6, C3F8, CClF3, CHF3, CHClF2, C2H2F2, C2H4F2, C2ClF5, and TeF6. An upper limit of ∼3 × 10−12 cm3/sec for the thermal electron attachment rate constant for HC1 in a mixture with N2 as a carrier gas is reported and is more than 100 times smaller than a previously reported value.
Vibration-vibration equilibration in laser excited CH3F and CH3F-X mixtures
Authors: Grabiner Frederick R. , Flynn George W. , Ronn A. M.
Published: February 2004

The infrared fluorescence risetime of the ν1,ν4 C–H stretching modes of CH3F has been measured in CH3F-rare-gas mixtures after pumping of the ν3 C–F stretching modes with a Q-switched CO2 laser. The pressure-dependent rate of rise was found to be 122 ± 25 msec−1 · torr−1 in pure CH3F. The effect of rare gases on this rate process was also studied and found to be consistent with a vibration-vibration filling mechanism for ν1,ν4 involving a small amount of energy transfer (≤ 75 cm−1) into the translational/rotational degrees of freedom.
Thermodynamics of multicomponent systems. The quasichemical approximation
Authors: Hagemark K. I.
Published: February 2004

Thermodynamic functions to the second order in terms of the nearest-neighbor interactions are derived for a multicomponent system. Expressions for the energy of mixing ΔE, the excess free energy GE, and the partial excess free energy of mixing of the component r, ḠrE, are derived. The expressions are an improvement over the regular solution model, particularly in calculating phase boundaries.
Energy distribution and cross section for photoionization in polar liquids
Authors: Aulich Hubert , Delahay Paul , Nemec Ladislav
Published: February 2004

A method is devised for the experimental determination of the dependence of the cross section on photon energy for bound-continuum transitions of species dissolved in polar liquids of low vapor pressure. The method is based on the determination of energy distribution curves (EDC) for photoelectron emission (PEE) into the gas phase above the solution. Theoretical analysis covers EDC distortion by electron-molecule collisions in the gas phase and resulting experimental requirements; derivation of a general equation for EDC's; criterion for the superposition of the descending segment of EDC's at different photon energies; and determination of cross section. Experimental results on PEE by the anthracene anion radical A− in hexamethyl phosphoric triamide include the effect of pressure on EDC's from 0.4 × 10−3−3.4 × 10−3 torr at different photon energies and the effect of photon energy on EDC's at 0.4 × 10−3 torr from 475 to 240 nm. Analysis of data covers effect of pressure; validity of the method for obtaining cross sections; determination of the cross section for transition to the continuum; correlation with the PEE process via autoionization. The approach developed here may prove feasible for a variety of systems.
On the reactions of N2 with O
Authors: Delos John B.
Published: February 2004

Unimolecular decomposition of N2O, quenching of O(1D) by N2, and vibrational relaxation of N2 in the presence of O(3P) are all believed to occur by the same curve crossing mechanism. This mechanism is examined making use of a complete theory of curve crossings that we have developed earlier. Good agreement with experiment is found for the unimolecular decomposition rate. The simple curve crossing mechanism does not explain the observed O(1D) quenching rate; this rate must be due to complex formation and/or additional crossings. At high temperatures, the calculated vibrational relaxation time is in good agreement with experiment, but at low temperatures there is a serious, unexplained discrepancy.
Electric dipole moment of the A 2Π state of CN as measured by level anticrossing spectroscopy
Authors: Cook Thomas J. , Levy Donald H.
Published: February 2004

The dipole moment of the electronically excited A 2Π state of the CN radical has been measured as 0.56±0.03 D by analyzing the electric field dependence of the level anticrossing spectral linewidth. The theory of the Stark effect in this system is developed and it is shown that the broadening depends upon two parameters: the A 2Π dipole moment and the electric dipole transition moment between the A 2Π and B 2Σ+ states. The spectral linewidth is rather insensitive to the value of the transition moment and this quantity is not well determined from the experimental data.
Delayed emission from organic mixed crystals: Phosphorescence spectrum of biphenyl guest-carbazole host mixed crystal
Authors: Misra T. N. , Mandal Krishnagopal
Published: February 2004

The phosphorescence spectrum of a biphenyl guest-carbazole host mixed crystal with guest concentration 10−2 mole/mole has been investigated in the temperature range 15–90 °K. At 15 °K the spectrum consists of three superimposed spectra, the most intense one being that of biphenyl guest with the origin at 22 986 cm−1. The two other spectra have been attributed to emission from traps T1 and T2. Emission from shallow trap T1 has its origin at 24 572 cm−1 and that from deep trap T2 at 23 552 cm−1. A tentative vibrational analysis of the spectra has been made. It has been observed that at very low temperature the guest and the two traps are all populated. As the temperature is raised, the shallow trap T1 is depopulated and emissions from the deep trap T2 and the guest are observed. On further increase of temperature T2 is also depopulated and the emission is wholly of biphenyl.
Electrostatic Hellmann-Feynman theorem applied to long-range interatomic forces. The hydrogen molecule
Authors: Steiner Erich
Published: February 2004

The use of the electrostatic Hellmann-Feynman theorem for the calculation of the leading term in the 1/R expansion of the force of interaction between two well-separated hydrogen atoms is discussed. Previous work has suggested that whereas this term is determined wholly by the first-order wavefunction when calculated by perturbation theory, the use of the Hellmann-Feynman theorem apparently requires the wavefunction through second order. It is shown how the two results may be reconciled and that the Hellmann-Feynman theorem may be reformulated in such a way that only the first-order wavefunction is required.
Photon impact studies of C2HCN and CH3CN in the vacuum ultraviolet; heats of formation of C2H and CH3CN
Authors: Okabe H. , Dibeler V. H.
Published: February 2004

A photodissociation process to produce CN B2Σ from C2HCN and CH3CN has been studied as a function of incident wavelength. Threshold photon energies required for the production of CN B2Σ from C2HCN and CH3CN are 9.41 ± 0.04 and 8.52 ± 0.03 eV, respectively, from which D0 (C2H–CN) ≤ 6.21 ± 0.04 eV and D 0(CH3–CN) ≤ 5.32 ± 0.03 eV are obtained. The photoionization yield curves have been measured for the C2HCN+ and C2H+ ions. Threshold photon energies obtained for the production of CN B2Σ, C2HCN+, and C2H+ from C2HCN lead to the following thermochemical values; I.P.(C2HCN) = 11.64 ± 0.01 eV, I.P.(C2H) = 11.96 ± 0.05 eV, Δ H f0°(C2HCN) ≥ 85 ± 1 kcal mol−1 (355 ± 4 kJ mol−1). Δ H f0°(C2H) = 127 ± 1 kcal mol−1 (531 ± 4 kJ mol−1) and D0 (C2H–H) = 5.38 ± 0.05 eV. Δ H f0°(C2H) obtained is in good agreement with the recent value obtained directly from a study of the high temperature reactions of graphite with hydrocarbons. Δ H f0°(CH2CN) ≥ 14 ± 1 kcal mol−1 (59 ± 4 kJ mol−1) derived from D0 (CH3–CN) agrees within the stated error limit with the value obtained recently by bomb calcorimetry. The fluorescence efficiency vs incident wavelength curves for C2HCN and CH3CN show several peaks corresponding to Rydberg states indicating that the process is predissociative. The absorption coefficient of C2HCN has been measured in the vacuum ultraviolet. The photoionization yield curve for C2HCN+ shows at least two Rydberg series converging to vibrationally excited C2HCN+ ions.
Unitary transition probabilities for atom-atomic oscillator collisions
Authors: Liu W. S.
Published: February 2004

A unitary treatment, based on the work of Cabrera, Celli, Goodman, and Manson [Surface Sci. 19, 67 (1970)], of multiple quantum transition probabilities for the collision of an atom with an atomic oscillator is studied. The theory is applied to the collision of helium with a tungsten atomic oscillator and compared with both exact quantum results and semiclassical results. It is shown that multiple quantum transitions have appreciable magnitude and cannot be ignored in calculating the thermal accommodation coefficients.