bluuebunny/crossref_metadata_2025 huggingface dataset:
Finding the Potential Directly from Scattering Data
Authors: Pritchard David E.
Published: February 2004

I show how to obtain reduced phase variables from the interference structure in elastic scattering. One such curve contains nearly all of the information which may be found from the positions of the supernumerary and glory structure (even though the energy and angle are varied independently in the data). I show that this information is insufficient to determine the deflection function (and hence the potential) uniquely unless additional information is utilized. Three methods are presented for determining the deflection function from the data without the use of parametrized models. The discussion is generalized to the case of resonant exchange.
Raman Spectral Studies of HTO in H2O
Authors: Walrafen G. E. , Blatz L. A.
Published: February 2004

Argon-ion laser Raman spectra have been recorded photoelectrically from a 10 volume % solution of T2O in H2O at temperatures from 26 to 94°C and from a 3.6M ternary solution of NaClO4 in 5 volume % T2O in H2O at 25°C. Laser-Raman spectra were also obtained from a 10 volume % solution of H2O in D2O at temperatures from ·23 to 96°C. At 26°C, a Raman intensity maximum was observed in the OT stretching region from HTO near Δ ν̄=2130 ± 5 cm−1, and a shoulder was apparent near Δ ν̄=2225 − 2250 cm−1. An isosbestic frequency was also indicated for HTO near Δ ν̄=2164 ± 7 cm−1 from 26 to 70°C and for HDO near 3450 cm−1 from ·23 to 63°C. The shapes of the OT and OH stretching contours from HTO and HDO were approximated by two broad Gaussian components using an analog computer, and the resulting plots of log10 (INHB / IHB) vs 1/T, where INHB refers to the high-frequency nonhydrogen-bonded Gaussian component intensity (the shoulder), and IHB refers to the low-frequency hydrogen-bonded intensity (the peak), were characterized by values of about 2.5±0.2 kcal/mole OTO and 2.2±0.3 kcal/mole OHO in resonable agreement with a previous two-Gaussian value of 2.5±0.6 kcal/mole ODO. Two pronounced intensity maxima were also observed in the OT stretching region from the ternary NaClO4 solution near Δ ν̄=2150 ± 5 cm−1 and Δ ν̄=2225 ± 5 cm−1 in general support of the two-Gaussian analysis of the binary solution stretching contours. The ΔHo values corresponding to the disruption of O–T ··· O, O–D ··· O, and O–H ··· O bonds agree despite the facts that the three contour shapes are different and that the nonhydrogen-bonded OT stretching component is, relative to the hydrogen-bonded component, roughly 2 times more intense than the corresponding OD and OH components. The value of ·2.5 kcal/mole hydrogen bond was also found to agree with numerous other experimental ΔHo values, as well as with a recent value from molecular dynamics calculations.
Differential Measurements of Dissociative Charge Exchange, He++CO2
Authors: Coplan M. A. , Ogilvie K. W. , McMillan M.
Published: February 2004

Measurements of the angular distributions and energies of the charged products of the dissociative charge exchange collision between helium ions and carbon dioxide have been made over the range of incident ion energies 100–500 eV. The angular distributions in the laboratory system show two maxima. The average energy of the ions corresponding to the two maxima differ by a significant amount. The data can be explained in terms of two different dissociative charge exchange mechanisms and there is evidence that certain orientations of the carbon dioxide molecule with respect to the helium ion beam are favored in the charge exchange process.
Effect of Resonant Collisions on the Propagation of a Self-Induced Transparency Pulse in SF6
Authors: Wang C. H.
Published: February 2004

Effect of the SF6 pressure on self-induced transparency (SIT) in SF6 was investigated systematically. The study consists of measuring the shape, width, delay time, and intensity of the transmitted pulse (which is a SIT pulse at low SF6 pressure) as a function of SF6 pressure P. The SIT pulse was induced by the nonlinear interaction of a 20-nsec P(20) CO2 laser pulse with the SF6. A theory which includes the homogeneous broadening mechanism was developed for the pulse delay time. For a stationary propagating pulse, it was found that the pulse delay time is related nonlinearly to Q (the ratio of the transiently energy stored energy density to the rate of change of the energy flux density of the field). From the interpretation of the experimental results, it was concluded that, for P>100 μ, the SF6-SF6 resonant collision makes a significant contribution to the departure from SIT. The effect of level degeneracies associated with the high angular momentum of the involved resonant vibrational states is also discussed.
Superposition Assumption. II. High Density Fluid Argon
Authors: Wang Shein-shion , Krumhansl J. A.
Published: February 2004

The triplet correlation function for high density fluid argon was calculated by the Monte Carlo (MC) method with a truncated cube as the basic box. This new box provides us a longer range for the triplet function than the conventional cubic box using the same number of particles; it also provides us better statistics for the same computing time. The MC g(3) at ρ* = 0.80 was found to be very different from the SA prediction. Upon substituting both MC g(3) and SA g(3) into the Born-Green equation, it is found that the result is fair for MC g(3) but very poor for the SA one. We conclude that the Superposition Assumption (SA) is poor at high density.
Density Localization of Atomic and Molecular Orbitals. I
Authors: von Niessen W.
Published: February 2004

A new intrinsic method for the localization of atomic and molecular orbitals is presented, which will be called (charge) density localization method. This new procedure follows an earlier suggestion of Edmiston and Ruedenberg. It is based on the minimization of the sum of the charge density overlap integrals of the orbitals: Σi<j ∫ |〈 r|i〉|2|〈 r|j〉|2d3r, |〈 r|i〉|2 being the charge density of orbitals |i〉. Because of the physical relation between the exchange interaction of wave packets representing fermions and their mutual overlap it is expected that this method is related to the energy localization procedure of Edmiston and Ruedenberg. The density localization method is applied to the atoms Be and Ne, where the four outer shell localized orbitals point to the corners of a tetrahedron. The results are compared with those of other localization procedures. Good agreement is obtained. It is shown in the present and in forthcoming publications that the same physical situation can be described by different but physically equivalent pictures.
Ground State of Gaseous CaO; a Study of the Matrix Spectra of Ca and CaO
Authors: Brewer Leo , Wang J. Ling-Fai
Published: February 2004

The 1P←1S transition of Ca was studied in Kr and Xe at 20°K. The transition was shifted to the blue relative to the gas. The short-wavelength component of the triplet shifted to the blue while the other two shifted to the red upon warming from 18 to 40°K. Codeposited Ca and Mg showed the same triplet structures with no shifts as when deposited individually in Xe thus confirming that the triplet structure is not due to long-range interactions between metal atoms. CaO was synthesized in Kr and Xe by the reaction Ca+2O2=CaO+O3 using 16O2 and 18O2. CaO showed a band system with the 0–0 band in Xe at 20 130 cm−1 and ωe′=890 cm−1. ωe″=794 cm−1 from the infrared spectrum. The matrix spectra do not correspond to any of the analyzed singlet systems of CaO. It is concluded that the X 1Σ state is not the ground state of CaO, which is probably a triplet.
Radiative Lifetime of N2(a 1Πg) and the Formation of Metastable N2(a′ 1Σu−)
Authors: Freund Robert S.
Published: February 2004

A model calculation has been carried out on the intrasystem cascading between the a 1Πg, a′ 1Σu−, and w 1Δu states of N2. Input data to the calculation are spectroscopically determined energy levels and Franck-Condon factors, experimentally determined radiative transition probabilities from each of the three excited states to the ground state, and reasonable estimates of the transition moments between excited states. A set of 21 coupled radiative decay equations is then solved for the populations of the excited state levels. The main conclusions are (1) the a′ 1Σu− metastable state is efficiently populated by intrasystem cascade, (2) the a 1Πg state decays nonexponentially, with an ``apparent'' lifetime shorter than that derived from the oscillator strength for the a 1Πg− X 1Σg+ transition, (3) lifetimes of individual vibrational levels of the a 1Πg state decrease with increasing vibrational quantum number, and (4) decay of a metastable molecular beam is nonexponential and shows an ``apparent'' lifetime which differs from that of the a 1Πg state, due to formation of metastable a′ 1Σu− molecules.
Three-Body Nonadditive Free Energy of Gases Adsorbed on Solids of Arbitrary Electron Delocalization
Authors: MacRury T. B. , Linder B.
Published: February 2004

A general formalism is presented for the nonretarded interaction between three nonoverlapping systems of arbitrary sizes and electron delocalizations. The theory is formulated in terms of response functions and spatially dependent susceptibilities of the noninteracting systems. The three-body nonadditive free energy is worked out in detail and specialized to the interaction between two small nonpolar gas molecules adsorbed on the surface of a solid of arbitrary electron delocalization. Two extreme cases are considered: (1) the electrons in the solid are localized in small polarizable units and (2) the electrons in the solid are completely delocalized. The results are discussed and compared with previously derived expressions.
Photodissociation of CS2 in the Vacuum Ultraviolet; Determination of D° (SC—S)
Authors: Okabe Hideo
Published: February 2004

It has been shown that a major primary photochemical process of CS2 in the vacuum ultraviolet is the reaction, CS2→ lim hνCSA 1Π +S3P2, in apparent violation of the spin conservation rule. From the threshold energy of incident photons required to produce the fluorescence, CS A 1Π -X 1Σ, D0° (SC—S) = 4.463± 0.014 eV or 102.9 ± 0.32 kcal/mole has been obtained in excellent agreement with the value derived previously from the photoionization of CS2. Other related thermochemical data are derived and are compared with those obtained by various methods. The fluorescence excitation spectrum shows peaks corresponding to Rydberg series I and II, indicating that the above reaction is mainly the result of predissociation from Rydberg states. The fluorescence efficiencies became quite small above incident photon energies corresponding to the first ionization potential of CS2. The CS A 1Π fluorescence spectrum produced by the 1236 Å line photolysis shows vibrational levels populated up to v′=5. The absorption coefficient of CS2 has been measured in the region 1200–1400 Å.
Fourier Representation Methods for Electronic Structures of Linear Polymers
Authors: Harris Frank E.
Published: February 2004

A Fourier representation method is presented for calculating the electrostatic energies of classical charge arrays with periodicity in one dimension. Extension of the method to quantum-mechanical systems is then discussed. The classical presentation illustrates mathematical features which must be understood to avoid apparent divergences in the quantum-mechanical formulation.
Hydrogen Bond Studies. LX.* A Single Crystal Neutron Diffraction Study of Trichloroacetic Acid Dimer
Authors: Jönsson Per-Gunnar , Hamilton Walter C.
Published: February 2004

The crystal structure of trichloroacetic acid (CCl3COOH) has been determined by application of direct methods of phase determination to single crystal neutron diffraction data. The structure is monoclinic (P21/c) with cell constants at 22°C: a=6.152(2) Å, b=9.705(4) Å, c=12.020(9) Å, β=124.29(5)°, Dc = 1.830 gcm−3,Dm = 1.81 g cm−3. The value of R(F) for 615 independent reflections is 0.057. There are four molecules, crystallizing as two centrosymmetric, hydrogen-bonded dimers in the unit cell. The bond lengths (corrected for rigid-body motion) are C–O, 1.311(4) Å; C=O, 1.216(4) Å, C–C, 1.546(4) Å, C–Cl (mean), 1.768(3) Å; O–H, 1.013(11) Å. The O··· O distance of the hydrogen bond is 2.666(6) Å, and the O–H···O angle is 176.5(5)°. A rigid-body analysis of the thermal motion indicates a librational amplitude of 10° approximately about the long axis of the dimer, smaller librations about the other two axes, and rms translational amplitudes of 0.20 Å in all directions. The apparent vibrational amplitude of the hydrogen atom along the hydrogen bond is 0.12 Å. This exceeds the value to be expected for a harmonic oscillator with the observed vibrational frequency; substantial anharmonicity is suggested. There is no evidence of disorder.
Infrared Intensity Sum Rule and Effective Charges
Authors: King W. T. , Mast G. B. , Blanchette P. P.
Published: February 2004

By using a Cartesian coordinate system, it is shown that the sum of integrated infrared intensities is given by a very simple expression that depends upon atomic masses, effective charge parameters, and the molecular dipole moment, but is otherwise independent of molecular geometry. The application of this sum rule to the analysis of the intensities of the hydrocarbons reveals that the effective charge parameters are approximately transferable from one molecular system to another, with the possible exception of acetylene.
Internal Motion and Its Pressure Dependence in FeSiF6· 6H2O
Authors: Vaughan R. W. , Nicolaides G. L. , Elleman D. D.
Published: February 2004

Both wideline and pulsed NMR techniques have been used to examine internal motion in FeSiF6· 6H2O. At room temperature and pressure the fluorine-fluorine contribution to the 19F second moment is 0.38± 0.06 G2 and indicates rapid reorientation of the SiF6− − group. The application of pressure slows the internal motion such that rigid lattice values of the 19F second moment are obtained above 50 kbar. Analysis of the second moment within the transition region allows calculation of an activation volume which is 2.4± 0.4% of the molar volume.
Corrections to Vibrational Transition Probabilities Calculated from a Three-Dimensional Model
Authors: Stallcop James R.
Published: February 2004

Corrections to the collision-induced vibration transition probability calculated by Hansen and Pearson from a three-dimensional semiclassical model are examined. These corrections come from the retention of higher order terms in the expansion of the interaction potential and the use of the actual value of the deflection angle in the calculation of the transition probability. It is found that the contribution to the transition cross section from previously neglected potential terms can be significant for short range potentials and for the large relative collision velocities encountered at high temperatures. The correction to the transition cross section obtained from the use of actual deflection angles will not be appreciable unless the change in the rotational quantum number is large.
Thermochemical and Theoretical Investigations of the Sodium-Oxygen System. I. The Standard Enthalpy of Formation of Sodium Oxide (Na2O)
Authors: O'Hare P. A. G.
Published: February 2004

Calorimetric measurements of the enthalpy of hydrolysis of pure sodium oxide (Na2O) are described. Based on the enthalpy of reaction, the standard enthalpy of formation at 298.15°K, Δ Hf298o(Na2O), was calculated to be −414.82± 0.28 kJ mole−1 (−99.14± 0.07 kcal mole−1). The enthalpy of reaction reported in the present study is significantly more exothermic than that determined by previous investigators. This discrepancy is attributed to the probable presence of hydroxide, carbonate, or other contaminants in the earlier sodium oxide samples.
Thermochemical and Theoretical Investigations of the Sodium-Oxygen System. II. Properties of NaO and Its Ions from Hartree-Fock Molecular Orbital Studies
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

Accurate Hartree-Fock wavefunctions, computed by the method of Roothaan, are reported for the 2II and 2Σ states of NaO, for the 3Σ state of NaO+, and for the 3II, 3Σ, and 1Σ states of NaO−. Spectroscopic constants and dipole and quadrupole moments have also been calculated for each of the molecules and ions. Several properties of the Na–O species have been deduced. These properties include the vertical and adiabatic ionization potentials (7.7 and 7.4 eV), electron affinity (1.1 eV), dissociation enthalpy (2.7 eV), several thermodynamic functions for NaO, and the Π 3→Σ1 (1.7 eV) and Π 3→Σ3 (0.2 eV) excitation energies for the NaO− system. Thermodynamic data for selected reactions involving NaO and NaO+ are given, together with a brief discussion of the bond enthalpies in NaO2 and NaO2+.
Volume Contraction During Melting; Emphasis on Lanthanide and Actinide Metals
Authors: Wittenberg Layton J. , DeWitt Robert
Published: February 2004

A review of the volume change during melting indicates that the majority of metals exhibits an average volume increase of 3.8% during this phase transformation. The volume increase is unusually small for La, Pr, Nd, and Np, and is negative for the semimetals plus cerium and plutonium. Based on a free-volume relationship for viscous flow, a close-packed structure for the liquid V l0 was calculated which was nearly the same as the volume of the solid (Vs) at the melting point for a number of close-packed metals, the rare gas solids Ar, Kr, and Xe, the alkali metals, Hg, and the lanthanide metals La and Yb. The value of V l0 was significantly less than Vs for Bi, Ga, Ce, Pr, U, and Pu. Examination of the phase diagrams of Bi, Ga, and Pu revealed that V l0 corresponded to the volume of the phase formed under pressure at which point the slope of the melting curve became zero. The mechanisms postulated for the formation of V l0 smaller than Vs were closer-packing for the semimetals and slight valence increases with corresponding reductions in metallic radii for Ce, Pr, U, and Pu. Additionally, the use of liquid compressibility values correctly predicted the pressures at which the slopes of the melting curves became zero. The Lindemann melting law and extensions derived from it were found to be invalid for all metals which contract during melting.
Pair Correlation Effects for l2 Electrons
Authors: Jankowski K. , Malli Gulzari , Maysilles J. H.
Published: February 2004

The effect of electron correlation on the energy of the terms arising from a pair of d electrons has been investigated by ab initio methods for the 20-electron isoelectronic series: Ti2+, V3+, Cr4+. Pair correlation energies in the monopole (radial) and quadrupole approach within the truncated multipolar expansion pair function method [K. Jankowski, Can. J. Phys. 48, 2707 (1970)] have been obtained together with the pair functions under consideration. Convergence properties of the correlation energy with respect to expansion of the radial part of the correlation factor have been investigated. Multiplet spacings have been obtained and compared with other results. In addition, an attempt is made to compare our results with those obtained by Mires and co-workers [Phys. Rev. 134, A332 (1964); 185, 16 (1969); A 1, 14 (1970)] in a semiempirical way.
Potential Energy Surface Including Electron Correlation for the Chemical F + H2 → FH + H I. Preliminary Surface
Authors: Bender Charles F. , Pearson Peter K. , O'Neil Stephen V. , Schaefer Henry F.
Published: February 2004

Rigorous quantum mechanical calculations have been carried out for about 150 linear and 200 non-linear geometries for the FH2 system. The contracted Gaussian basis set used consisted of four s and two p functions on fluorine and two s functions on hydrogen. The barrier height and exothermicity are poorly predicted by single configuration self-consistent-field calculations. However, the 214-configuration correlated results are in qualitative agreement with experiment (low barrier height and substantial exothermicity). The reaction coordinate is discussed, and pictures of the potential surface are presented. A second series of calculations is being carried out with a larger basis set. These latter calculations yield nearly quantitative agreement with experiment for both the barrier height and exothermicity.
Nonequilibrium Effects in Atomic Recombination Reactions
Authors: Gelb A. , Kapral R. , Burns G.
Published: February 2004

Relaxation in the bromine-argon system is investigated by approximating the time evolution with a sequence of trajectory calculations. Two systems are considered: (a) recombination of bromine atoms via the radical-molecule complex mechanism and (b) rotational relaxation of a rigid rotator in a thermal bath. The phenomenological and equilibrium rate coefficients for recombination at 300°K are computed and compared. Nonequilibrium effects lead to a 19% discrepancy between the two rate coefficients after an initial transient period during which the phenomenological rate coefficient shows a distinct time dependence. Comparison of the rotational relaxation of Br2 and the rigid rotator shows the importance of vibrational-rotational coupling for highly excited molecules. The relaxation time of the vibrationally excited molecules is much greater than that of the rigid rotators.
Trajectory Studies of Atomic Recombination Reactions. II. The Energy Transfer Mechanism and Nonequilibrium Effects
Authors: Clarke A. G. , Burns G.
Published: February 2004

Rate constants for the recombination of bromine atoms in excess of the inert gases helium, argon and xenon have been computed by 3D classical trajectory/Monte Carlo methods. Previous work on the radical molecule complex (RMC) mechanism [J. Chem. Phys. 55, 4717 (1971)] has been extended by the calculation of the recombination rates via the energy transfer (ET) mechanism Br+Br⇌ Br2*, Br2*+M→ Br2+M. Nonequilibrium corrections for the two mechanisms were estimated by computing the fraction of initially formed, highly excited, Br2 molecules which redissociated on subsequent collisions with third body atoms. Rate constants were determined for each mechanism and each third body at 300, 500, 1000, and 1500°K and for argon at 2000°K. The interaction potential between Br and M was assumed to be of the Lennard-Jones form with the following parameters. M = He, ε = 0.5 kcal/mole, σ = 2.5 A; M = Ar, ε = 1.0 kcal/mole, σ = 3.0 Å; M = Xe, ε = 1.0 kcal/mole, σ = 3.5 Å. The RMC mechanism gives rate constants with appreciable negative temperature coefficients, while the ET rate constants vary slowly with temperature. The RMC mechanism is dominant for argon and xenon at low temperatures and the ET mechanism is dominant for argon and xenon at high temperatures and for helium over the whole temperature range studies. The nonequilibrium corrections reduced the rate constants by more than one-half in some cases. The total recombination rates are in good agreement with experiment at low temperatures but above 1000°K they exceed the experimental rates obtained using flash photolysis by a factor not larger than two.
On the Herzfeld Theory of Metallization. Application to Rare Gases, Alkali Halides, and Diatomic Molecules
Authors: Ross Marvin
Published: February 2004

In 1927 Herzfeld proposed a criterion which predicted that an element would become metallic when its molar volume became equal to or less than R, its molar refractivity. We have inspected this criterion by comparing its predictions with calculations on the rare gases and hydrogen, and with high pressure experiments on iodine and the alkali halides, and found it to be surprisingly good.
Crossed Molecular Beam Study of F+C2H4, C2D4
Authors: Parson J. M. , Lee Y. T.
Published: February 2004

Crossed molecular beam experiments on F+C2H4, C2D4 have been performed with a mass spectrometric universal detector. Angular distributions of both substitution and abstraction reaction products were measured. The substitution reaction to form C2H3F (C2D3F) appears to proceed via a long-lived complex, yet the recoil energy of the products has a broad distribution peaking at about half of the energy available. Experimental results for the substitution reaction are compared with the predictions of the RRKM theory of unimolecular decomposition. The discrepencies between them and inadequacies of the theory are discussed. Highly vibrationally excited DF was produced through the abstraction reaction of F+C2D4. DF formed in the forward direction of F motion is primarily in v′=4. The formation of DF(v′=4) also suggests, from the conservation of total energy, that the internal excitation of the other reaction product C2D3 should be very small.
Electron Correlation in Closed Shell Systems. I. Perturbation Theory Using Gaussian-Type Geminals
Authors: Pan Kee-Chuan , King Harry F.
Published: February 2004

The calculation of electron correlation energy in closed-shell atoms and molecules is approached using Rayleigh-Schroedinger perturbation theory with the symmetric sum of Hartree-Fock operators for H0. The alleged advantages of using a VN−1 potential are questioned. Variational equations for first-order pair correlation functions are computed for He, Be, B+ and Ne by expansion in linear combinations of correlated Gaussian-type geminal basis functions containing r122 in the exponent. Such functions form mathematically complete sets, have convenient symmetry properties, and are integrable in closed form. An extensive search for optimum exponential parameters yielded trial functions for each of the ss orbital pairs giving better than 99% of the limiting second-order pair energy using only five basis functions per pair. Similar but less thorough studies of sp and pp pairs in neon are also reported. Careful attention is paid to computational accuracy. An upper bound of −0.3428 a.u. is established on the second-order contribution to the correlation energy in neon.
Pulse NMR Relaxation Study of Liquid Arsine
Authors: Burnett L. J. , Zeltmann A. H.
Published: February 2004

The arsenic-proton and arsenic-deuteron spin-spin coupling constants in AsH3 and AsD3 have been measured using pulse NMR techniques. The accuracy obtainable from this method is found to be comparable to that of other techniques and is applicable in situations where conventional high-resolution measurements are impossible. A comparison of spin couplings in the Group V hydrides shows that in contrast to the situation in the Group IV hydrides, the reduced spin-spin coupling constants are relatively constant with increasing Z. Measurement of the arsenic and deuterium spin-lattice relaxation times over the temperature range +25 to −113°C indicates that the arsine molecule reorients as an almost free rotor at high temperatures. The temperature dependence of the proton spin-lattice relaxation time shows that translational diffusion dominates the relaxation process at low temperatures and that the spin-rotational interaction becomes an important mechanism at the higher temperatures. The magnitude of the intermolecular contribution to relaxation indicates that translational diffusion proceeds via large-size jumps of the order of a molecular diameter rather than by small step diffusive motion. These relaxation data also allow the spin-rotational coupling constant in AsH3 and the deuteron quadrupole coupling constant in AsD3 to be determined.
Energy Level Structure of Trapped Electrons in Methyltetrahydrofuran Glass from Photoconductivity and Optical Bleaching Studies
Authors: Huang Timothy , Eisele Ignatz , Lin D. P. , Kevan Larry
Published: February 2004

Electrons are trapped in γ irradiated methyltetrahydrofuran (MTHF) glass at 77°K. Monochromatic photoexcitation produces photoconductivity and optical bleaching with a threshold near 780 nm (1.6 eV) and a peak near 520 nm (2.4 eV). This transition is linear in light intensity and independent of temperature between 77 and 4.2°K, so it is interpreted as a one photon transition directly to the conduction band or to an autoionizing state. Effective double beam photoexcitation discloses a two photon transition which depends on the light intensity squared. The first photon corresponds to the well-known optical absorption of trapped electrons in MTHF at 1.0 eV. This transition is interpreted as a 1s → 2 p type. The 2p state then presumably crosses to a 2s-type state from which the second photon is absorbed. The wavelength dependence of the second photon transition shows a peak at 950 nm (1.3 eV) and a threshold near 1150 nm (1.1 eV). The temperature of both optical bleaching and photoconductivity under ir photoexcitation shows that population of the 2s-type state involves an activation energy ∼ 0.001 eV. The deduced energy level structure agrees well with theoretical calculations based on a semicontinuum model for trapped electrons in glassy matrices. Compared to more polar matrices like ice, both experiment and theory indicate that in less polar matrices like MTHF the short-range charge-dipole interactions are relatively less important compared to the long range polarization interactions and cause the bound excited states to be relatively more stable and the ground state to be relatively less stable.
Transport Equations of Multicomponent Systems of Polyatomic Molecules. I
Authors: Wu Kuan-Shih Yuan , Snell Fred M.
Published: February 2004

The treatment of the transport phenomena starting with the Liouville equation was first given by Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)] for a one-component system composed of point molecules. The theory has been extended by Bearman and Kirkwood [J. Chem. Phys. 28, 136 (1957)] to multiple-component point-molecule systems and by Dahler [J. Chem. Phys. 30, 1447 (1959)] to a one-component system of diatomic molecules. In the present work, the theory is extended to a multicomponent system composed of polyatomic molecules. The theory treats the translational, rotational, and vibrational motions of fluids but not the electronic motion. From the Liouville equation, the equations of continuity and of linear momentum, angular momentum, and energy transport are developed. The one-particle and pair densities, involving the one-particle and the two-particle distribution functions are expanded in powers of a parameter measuring the small deviations from the state of local thermodynamic equilibrium, but the calculations extend only to the first order in the gradients of the particle densities and temperature. From the general transport equations, the phenomenological equations involving transport coefficients are obtained. These coefficients are formally determined in terms of the laws of intermolecular interaction and of the assumed dependence of the distribution functions on the gradients of the particle densities and of temperature.
Transport Equations of Multicomponent Systems of Polyatomic Molecules. II
Authors: Wu Kuan-Shih Yuan , Lee Paul S.
Published: February 2004

Expressions for the rotational diffusion coefficient, the rotation viscosity coefficients, and the rotational coefficient of heat conductivity are developed for a multicomponent system of polyatomic molecules. In the present work, the same method used in Paper (I) of this series has been followed to obtain the rotational diffusion, viscosity, and heat conduction coefficients of a multicomponent system of polyatomic molecules.
Intermolecular Potentials and Width of Pressure-Broadened Spectral Lines. III. The Rotational Lines of Diatomic Molecules Perturbed by Linear Molecules with High Moment of Inertia
Authors: Giraud M. , Robert D. , Galatry L.
Published: February 2004

Expressions of the differential cross section for diatomic molecules perturbed by linear molecules with high moment of inertia have been derived using a simplified version of the Anderson theory of line shape. The corresponding validity conditions have been presented. The connection with a ``classical description'' of the rotational degrees of freedom of the perturber has been shown. The cases of HF–CO2, HCl–CS2, and HF–CS2 have been studied as characteristic examples.
Dynamics of NO2 Electronic States Excited by a Tunable Dye Laser
Authors: Sackett Philip B. , Yardley James T.
Published: February 2004

A tunable organic dye laser has been used as a narrow band (∼0.8 Å) radiation source to excite NO2 molecules under essentially collision-free conditions in the spectral range 4515–4605 Å. The fluorescence which is observed in a very large cell is decidedly nonexponential, so that the decay function for each experiment is characterized as both nonexponential and exponential, the latter for purposes of comparison with other experiments and for purposes of discussion in standard terms. The lifetimes which are obtained in this way show a marked structural pattern when displayed as a spectrum, with individual values ranging from 62 to 75 μsec for observation of fluorescence at wavelengths longer than 5200 Å. In addition, the dependence of lifetime and nonexponentiality, as well as their spectral variations, on observation wavelength, pressure, and fluorescence observation geometry are investigated over a shorter spectral region. A small amount of high resolution spectral data is reported which seems to indicate the presence of some unresolved, quasicontinuous absorption underlying the obvious bands of the visible spectrum. The effects of restrictive fluorescence measurement geometry on lifetime measurements are explored, with particular attention to other investigations, for which the shorter, nonvarying lifetime observations may be explained. Finally the observed dynamics and spectroscopy of NO2 are discussed in terms of the following hypotheses: (1) Transitions to both the 2B1 and 2B2 electronic states occur together over a large portion of the visible spectrum, (2) both of these excited states are clearly perturbed, and (3) the 2B2 transition is the stronger of the two.
Optical Properties of Liquid Carbon Tetrachloride, n-Hexane, and Cyclohexane in the Vacuum Ultraviolet
Authors: Sowers B. L. , Williams M. W. , Hamm R. N. , Arakawa E. T.
Published: February 2004

The optical properties of three organic solvents, carbon tetrachloride, n-hexane, and cyclohexane are reported from 2.0 to 10.65 eV. Reflectance measurements using a closed cell and transmission measurements using samples as thin as 800 Å were made to determine the optical constants, n and k. The optical absorption is interpreted in terms of molecular excitations of the nonbonding and σ electrons.
Calculation of g Values for O3−, NO22−, and NF2
Authors: Hayden Don W. , McCain Douglas C.
Published: February 2004

Electron spin g values have been calculated for the isoelectronic π radicals O3−, NO22−, and NF2 using an SCF Hartree-Fock type approach with a minimum basis set of Slater type orbitals and a number of excited states for each species. The results show fair agreement with experimental data. In addition, some new experimental data are reported for the ozonide ion, O3−.
Defects in Low Temperature Irradiated Single Crystals of NaClO3: ClO3 Centers
Authors: Vinther O.
Published: February 2004

Defects generated in single crystals of NaClO3 by x irradiation at −247 and −196°C have been studied using ESR and uv spectroscopy. The defects are assigned to: ClO3, ClO2, and O2−. ClO3 is formed in two modifications with different g and A tensors, optical absorption, and thermal stability at −196°C. One modification can be transformed into the other by illumination with light of wavelengths longer than 5500 Å. A mechanism for the light induced decay of ClO3 involving electron transfer from O2− to ClO3 is proposed. Comparison is made between ClO3 formed in NaClO3 and in irradiated perchlorates.
On a Perturbed Hartree-Fock Study of the Magnetic Susceptibility and the 13C and 17O NMR Shielding Constants in Formaldehyde with Slater Basis Sets
Authors: Tokuhiro Tadashi , Appleman Bernard R. , Fraenkel Gideon , Pearson P. K. , Kern C. W.
Published: February 2004

The theoretical study of Flygare et al. on one-electron properties of the formaldehyde molecule is extended to include the paramagnetic susceptibility and the 13C and 17O NMR shielding constants and to investigate their sensitivity to Slater basis-set quality. The Gaussian transform method is used to evaluate the necessary integrals. Using the fully coupled perturbed Hartree-Fock formalism, we find that improvements in the wavefunction produce significant changes in most components of the second-order properties. The best shielding calculations, obtained with a double-zeta Slater set, are within the rather large experimental uncertainties, whereas the agreement between the theoretical and experimental susceptibility results is less satisfactory. The complete paramagnetic tensors are analyzed in terms of MO and AO contributions. Comparisons are made with other ab initio calculations and with simplified forms of the theory.
Square-Well Potential. II. Some Comments on Critical Point Behavior and Scaling Laws
Authors: Kozak John J. , Schrodt I. B. , Luks K. D.
Published: February 2004

Critical exponents are determined for a square-well fluid with σ2/σ1 = 1.85 by solving the Yvon-Born-Green equation in the neighborhood of the critical point, with the superposition approximation used to effect the necessary closure. The results of several numerical studies are reported which serve to establish the reliability of the following values: β = 0.429 ± 0.01, δ = 3.04 ± 0.08, and γ = 0.793 ± 0.002. These results are analyzed in the light of recent experimental and theoretical work on classical fluids.
Polymorphism of the Crystalline Methylchloromethane Compounds. IV. The Crystal and Molecular Structure of Methyl Chloroform at −60° and −145°
Authors: Silver Lawrence , Rudman Reuben
Published: February 2004

The crystal structure of the ordered form of solid methylchloroform (1,1,1-trichloroethane) has been determined from three-dimensional x-ray film data, collected at −60° and −145°. The data revealed no significant structural differences between the solids at these temperatures. The existence of a crystal-lographic phase transition at −68° is thus ruled out. The crystals are orthorhombic, space group, Pnma, with four molecules per unit cell. The lattice dimensions are a=11.53(1) Å, b=8.000(5) Å, c=5.88(1) Å at −60° and a=11.46(1) Å, b=7.890(5) Å, c=5.81(1) Å at −145°. The C–Cl distance is 1.782(16) Å. Analysis of the thermal parameters indicate that at −60° there is a greater degree of librational motion about the C–C axis than at −145°.
Linear Symmetric H4
Authors: Bender Charles F. , Schaefer Henry F.
Published: February 2004

Ab initio calculations have been carried out for the lowest Σg+1 state of H4. A contracted Gaussian basis set of two s and one p functions centered on each atom was used. Self-consistent field (SCF), SCF plus all singly and doubly excited configurations, and full configuration interaction (2172 configurations) calculations were carried out. The results may be pertinent both to the H2+D2 reaction and the problem of the linear antiferromagnetic chain. It is predicted that two H2 molecules may approach to within 1.6 bohr with an energy only 43 kcal above that of the separated molecules. A van der Waals attraction of 22°K is predicted at H2 – H2 center of mass separation 7.1 bohr. Equidistant H4 is predicted to have lowest energy at 1.67 bohr, lying 7.1 eV below the exact energy of four H atoms but 44 kcal above two H2 molecules. The electronic structure of linear equidistant H4 is discussed as a function of H – H separation and no evidence of a Mott transition is found.
Effect of Vibronic Interaction on the Singlet-Triplet Separation in Cyclopentadienyl Cations
Authors: Purins D. , Feeley H. F.
Published: February 2004

Vibronic wavefunctions and energies are obtained for the A1'1, E2'1, and A2'3 states of the cyclopentadienyl cation (C5H5+) and the pentadeuterio and pentachloro derivatives. Strong pseudo Jahn-Teller coupling occurs between the E2'1 and the 3048 cm−1 higher A1'1 electronic states and has the effect of reducing the triplet-singlet excitation energy from 2613 cm−1 to 275 cm−1 in C5H5+. Thus, it is probable that vibrational-electronic interaction is an important factor in determining the relative stabilities of the singlet and the triplet states of these and related systems. Because coupling with the A1'1 state is much stronger than interaction between the two degenerate E1'1 components, the lowest singlet vibronic state of C5H5+ is totally symmetric, in contrast to the benzene anion. Comparison of the results for C5H5+, C5D5+, and C5Cl5+ shows that the extent of vibrational-electronic interaction and vibronic energy lowering are not very sensitive to moderate alterations in force constants and vibrational frequencies. The energy lowering in C5Cl5+, however, may be about 200 cm−1 smaller than in C5H5+ if strong C–Cl, C–C vibration interactions are present. If the pentaphenyl derivative (C5 φ5+) is treated by the point-mass approximation, the vibronic wavefunctions are expected to resemble closely those obtained for C5Cl5+. The major factors determining the relative energies of the singlet and the triplet vibronic states in the C5X5+ cations are the A1'1-E2'1 and the E2'1-A2'3 electronic energy separations. While the latter is smaller in C5 φ5+ than in C5H5+, the two singlets are more widely spaced, so that a smaller vibronic energy lowering results. The energies of the E2'1 and the A1'1 vibronic states are obtained as a function of the A1'1-E2'1 electronic separation.
Reduced Density Matrices for Valence Bond Wavefunctions. II. Symmetry and Reduction Procedures for Square Planar Nets
Authors: Choi Jong H. , Messmer Richard P. , Thorson Walter R.
Published: February 2004

A systematic procedure is described for calculating the reduced density matrices of first and second order for a resonating valence bond wavefunction on square planar nets with Born-von Karman boundary conditions of finite period. The density matrices explicitly display the electron correlation in such a wavefunction, which is a model ground state for a two-dimensional Mott insulator. Because of the extremely large number of contributing valence bond structures, it is essential to utilize their symmetry under the space group for minimum computation. For the totally symmetric singlet state described, density matrix eigenvectors form basis vectors for irreducible representations. The irreducible representations spanned by pair states on the square plane lattice are listed, and a set of irreducible basis vectors for the two-particle density matrix is defined which clearly displays the nature of electron pair correlations in such a system (correlated geminals). The apparatus has been employed in a calculation described in the paper accompanying this one (succeeding article).
Reduced Density Matrices for Valence Bond Wavefunctions. III. Density Matrices for the 4×4 Square Planar Net
Authors: Choi Jong H. , Thorson Walter R.
Published: February 2004

One- and two-particle reduced density matrices have been calculated for a ``resonating'' Heitler-London wavefunction, in a system which is a finite model of a two-dimensional square planar lattice structure (4×4 net of one-electron atoms with Born-von Karman boundary conditions). The Heitler-London wavefunction describes the electronic ground state of a system with a single narrow half-filled band (the Mott insulator). Various measures of electron correlation (pair correlation functions, etc.) are defined and calculated. The intent of these calculations is to provide ``empirical'' guidelines for many-body methods for calculation of Green's functions for one and two particles (reduced density matrices are initial values for the respective Green's functions). Results show that the Heitler-London description is incompatible with several assumptions and widely used models for the Mott insulator. In particular it is found that (a) pair correlations in the Heitler-London ground state remain local even when ``resonance'' of an extremely large number of valence-bond structures occurs; the long range antiferromagnetic ordering obtained in several models of the Mott insulator (the ``two-sublattice'' or ``different bands for different spins'' models) does not occur. (b) The density matrix for the Heitler-London state does not exhibit a BCS type ``pair condensation'', as has been conjectured to describe the Mott insulator in some recent work. Our results strongly suggest that if the Heitler-London description is appropriate, the ``Hubbard Hamiltonian'', which includes only intraatomic pair interactions, does not offer an adequate model of the Mott insulator.
Absolute Specific Photodissociation Cross Sections of CH4 in the Extreme Ultraviolet
Authors: Welch A. R. , Judge D. L.
Published: February 2004

The photodissociation of methane has been studied at 16 different incident wavelengths in the range 555–1242 Å. Absolute partial cross sections have been determined for those processes yielding excited fragments which fluoresce in the range 3500–8000 Å. The fluorescence was dispersed and found to result from the A 2Δ → X 2Π and B 2Σ → X 2Π systems of CH, the b̃ 1B1 → ã 1A1 system of CH2, and the Hα, Hβ, and Hγ transitions of H. Absolute cross sections have been assigned to the processes CH4 + hν → CH(A 2Δ) + H2(X 1Σg+) + H (1 2S1/2), CH4+hν → CH(B 2Σ) + H2(X 1Σg1) + H(1 2S1/2), and CH4 + hν → CH2 (b̃ 1B1) + H2 (X 1Σg+). Emission cross sections have been assigned to the Balmer lines Hα, Hβ, and Hγ. The process CH4 + hν → CH3 (X 2A2″) + H* is believed to be responsible for the Balmer lines. The largest cross section measured, σ = 8 × 10−20 cm2, occurred at 923 Å for the process leading to CH (A 2Δ). Cross sections of this magnitude are three orders of magnitude less than the total peak absorption cross section for methane.
Viscosity and Thermal Conductivity of Moderately Dense Gas Mixtures
Authors: Wakeham W. A. , Kestin J. , Mason E. A. , Sandler S. I.
Published: February 2004

The paper presents a simple, semitheoretical expression for the initial density dependence of the viscosity and thermal conductivity of gaseous mixtures in terms of the appropriate properties of the pure components and of their interaction quantities. The derivation is based on Enskog's theory of dense gases and provides us with an equation in which the composition dependence of the linear factor in the density expansion is explicit. The interaction quantities are directly related to those of the mixture extrapolated to zero density and to a universal function valid for all gases. The reliability of the formulation is assessed with respect to the viscosity of several binary mixtures. It is found that the calculated viscosities of binary mixtures agree with the experimental data with a precision which is comparable to that of the most precise measurements. The method developed in the paper allows us to calculate the viscosity and thermal conductivity of moderately dense binary and multicomponent mixtures of gases. The evaluation of the respective properties in the limit of zero density has been made possible by the law of corresponding states developed by Kestin, Ro, and Wakeham.
On the Microscopic Conditions for Linear Macroscopic Laws
Authors: Cukier R. I. , Shuler K. E.
Published: February 2004

We have investigated the conditions which must be imposed on the microscopic equations of motion to obtain exact linear laws for macroscopic (phase averaged) variables. The starting point in this study has been the lowest order master equation (Pauli equation) which is a linear microscopic equation in the state probabilities with a time-independent transition matrix. Discrete and continuous variable master equations as well as their multivariate generalizations have been considered. In the case of continuum state variables, we have used various Fokker-Planck equations and their corresponding Langevin equations as our starting microscopic equation of motion. In each case the conditions which must be imposed to obtain linear macroscopic transport equations have been derived and discussed. The problem of the derivation of linear macroscopic laws from microscopic laws which are nonlinear in the dynamical variables has been discussed in the context of our results. We find that exact linear macroscopic laws can be derived from microscopic laws only when stringent conditions are imposed on the form of microscopic transition rates.