bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonreactive Molecular Encounters
Authors: Levine R. D.
Published: January 2005

Low-energy molecular collisions are discussed from a point of view that emphasizes the role of the internal degrees of freedom of the colliding molecules. The theory centers attention on the mechanism of energy transfer from kinetic energy of relative motion into internal energy and vice versa. It is shown that irrespective of the over-all energy transfer (which may be zero), the collision event proceeds via steps of energy migration between internal and relative degrees of freedom. This feature is absent in the available first-order theories. An approximation scheme which includes this feature even in first order is suggested, and a self-consistent-field scheme where each collision partner moves in the average field of the other partner is discussed.

The migration of kinetic energy into internal degrees of freedom results in the temporary formation of bound states. Such intermediates are of importance in the study of intermolecular forces, vibrational excitations, contact charge-transfer complexes, and three-body recombinations. The collision of two hydrogen atoms is discussed in the adiabatic approximation, where the temporary bound state is due to charge redistribution. The mechanism of three-body recombination is discussed and a recombination rate constant is calculated.
Application of Low-Field NMR to the Unambiguous Assignment of Spin-Coupling Parameters. I. Pentafluoro-Iodobenzene
Authors: Moniz William B. , Lustig Ernest
Published: January 2005

A low-frequency internal-lock spectrometer system, obtained by substitution of a 6.14-MHz rf unit and probe in a Varian HA−100 spectrometer, makes it possible to record high-quality precalibrated 1H and 19F spectra at about 1.5 kG. Since at such field strengths, chemical shifts are reduced by about one order of magnitude compared to usual conditions, determinations of relative signs of coupling constants (J's) and assignment of J's to particular pairs of nuclei can be made in many cases in which this is not possible at 14 or 23 kG due to ``first-order'' characteristics of spectra.

In this way, the relative signs of the three meta JFF's in C6F5I were determined, and the values of −4.95 and −1.22 Hz were unambiguously assigned to J26 and J35, respectively. (These signs are based on ortho JFF<0, as found in a preliminary analysis of the 6.14-MHz spectrum of C6HF5.) In general, low-frequency (∼6 MHz) field-lock NMR spectroscopy yields detailed information on spin coupling constants, when ``non-first-order'' conditions can thus be created.
Microwave Absorption and Molecular Structure in Liquids. LXVIII. Dielectric Behavior at 2.2-mm Wavelength and Intramolecular Motion in Five Substituted Benzenes and Cyclohexanes
Authors: Garg S. K. , Smyth C. P.
Published: January 2005

The dielectric constants and losses of anisole, bromocyclohexane, aniline, N,N-dimethylaniline, and cyclohexanol in the pure liquid state have been measured at 2.2 mm wavelength at temperatures between 20° and 60° and combined with data in the literature to calculate the dielectric relaxation times. Where additional data were needed, measurements were made at wavelengths of 1.2, 3.2, 10.0, and 575 000 cm. A single relaxation region was found for bromocyclohexane, corresponding to dipole orientation by molecular rotation, while cyclohexanol showed three relaxation times like those found for aliphatic alcohols, a long one associated with the hydrogen-bonded structure of the liquid, an intermediate one presumably corresponding to molecular rotation, and a short one corresponding to hydroxyl-group rotation. Anisole gave two relaxation times, one for molecular rotation and one for methoxy-group rotation. Aniline and N,N-dimethylaniline gave two relaxation times, one of the magnitude to be expected for molecular rotation and one so much shorter than the second and shorter relaxation time of anisole as to suggest its association with a molecular-inversion process.
Influence of Paramagnetic Resonance on the Static Susceptibility. The Lattice—Bath Relaxation Time of Neodymium Ethyl Sulfate
Authors: Candela George A. , Mundy Robert E.
Published: January 2005

The spin—lattice—bath relaxation process of neodymium ethyl sulfate was investigated by measuring simultaneously the change in the static susceptibility and the microwave power absorbed at electron spin resonance. This technique can be used at constant temperature to distinguish the spin—lattice process from the lattice—bath process. The relaxation time of neodymium ethyl sulfate was studied at a microwave frequency of 14.5 GHz as a function of temperature, helium-exchange gas pressure, microwave power absorbed, two crystal orientations, and crystal size. At this microwave frequency the energy transfer from the lattice to the bath appears to be the rate-determining process. The dominant lattice—bath relaxation time, τp, is inversely proportional to the square of the bath temperature τpT2=0.20 sec·°K2 but is apparently independent of the crystal size, the helium-exchange gas pressure, and crystal orientation. The experimental data are in essential agreement with the data obtained by other researchers using different methods.
Heat Capacity and Entropy of NiSiF6·6H2O from 0.35° to 4.2°K with Magnetic Fields 0–90 kG Perpendicular to the c axis. The Use of 3He Gas Conduction in Calorimetry
Authors: Hornung E. W. , Fisher R. A. , Brodale G. E. , Giauque W. F.
Published: January 2005

The heat capacity of nickel fluosilicate hexahydrate has been measured over the range 0.35–4.2°K in stabilized magnetic fields of 0, 1, 5, 10, 20, 40, 60 and 90 kG. The field was perpendicular to the crystallographic c axis of the 3.5-cm-diam single crystal. The entropy changes in NiSiF6·6H2O have been accurately tabulated over the ranges 0.35°—4.2°K and 0–90 kG, by combining the heat-capacity data and the change in temperature with field on isentropics. The temperature was measured by means of a carbon thermometer which was also used to introduce calorimetric heat. The total electronic entropy removed to magnetic saturation was Rln3. The substance gave no indication of hysteresis at any field or temperature. At the higher fields and lower temperatures it was necessary to consider a small entropy change due to nuclear magnetization of the hydrogen and fluorine atoms. As a practical rule it has been shown that a 2 mtorr pressure of 3He, which is sufficient to cause liquefaction near 0.3°K, is acceptable in a calorimeter over the range 0.4°—4°K, provided that the ratio of sample surface to volume is small, as, e.g., with a very large spherical single crystal.
Chemiluminescence of CH in the O +C2H2 Reaction : Rotational Relaxation and Quenching
Authors: Brennen W. , Carrington Tucker
Published: January 2005

Rotational distributions of CH (A 2Δ, v=0) were measured at pressures from 0.1 to 8.5 torr in the O+C2H2 reaction in the presence of large excess of N2, Ar, or He. The reaction N+NO→N2+O was used to produce O without O2. Under all conditions the distributions are found to be a superposition of two Boltzmann distributions, one at 1200°—1400°K characteristic of the process leading to the formation of excited CH (A 2Δ), and one which stays close to the temperature of the reactor. Assuming that the observed behavior of the rotational distributions is caused by collisions of excited CH with heat-bath molecules and interpreting the fraction of molecules in this low-temperature distribution as a measure of the extent of relaxation of the initial rotational distribution of excited CH, average relaxation rate constants are derived. With the collision partners mentioned above, 10 to 30 collisions are required for relaxation. A 14-level phenomenological model including only transitions between neighboring rotational levels (K→K±1) fits the experimental distributions well at all pressures studied if the downward rate constants kK−1,K are approximately proportional to exp(−2BK/kT), where B=14.6 cm−1 is the rotational constant for CH(A 2Δ, v=0) and T=360°K. Other models are discussed. Rotational and vibrational distributions for CD(A 2Δ) are also described. Quenching of the CH(A→X) emission by added oxygen was studied quantitatively and the results are consistent with a mechanism in which not CH(A 2Δ) but a precursor to its formation is removed by O2. In the absence of O2 the lifetime of the precursor is determined primarily by the atomic-oxygen concentration.

When an electrical discharge through O2 is used as the source of oxygen atoms for reaction with acetylene, the rotational distribution of CH(A 2Δ) and its pressure dependence is quite different from that described above. When acetylene reacts with the products of a discharge through CO2 with excess CO2 as heat bath, the rotational distribution of CH(A 2Δ) has a Boltzmann form at all pressures, with only the rotational temperature depending on pressure and approaching the gas kinetic temperature at high pressure.
Recoil Tritium Reactions: Studies on the System T +SiH4
Authors: Cetini G. , Gambino O. , Castiglioni M. , Volpe P.
Published: January 2005

Reaction of monosilane with hot tritium atoms was investigated thoroughly, determining the extent of formation of SiH3T, HT, and higher tritiated silanes. A special study was made of the effect of I2 as radical scavenger and the effect of 4He as moderator in order to verify, experimentally, the applicability of the kinetic theory, elaborated by Wolfgang for the reaction of hot atoms, to the examined system. The bond energy of Si–H was also correlated with the variation of the found ratio HT/RT, as compared with the same ratio in the system H+CH4.
Resonant Transfer of Vibrational Energy in Molecular Collisions
Authors: Mahan Bruce H.
Published: January 2005

The cross section for resonant vibration—vibration energy exchange between infrared-active molecules due to the long-range dipole potential is formulated. It is found that despite certain restrictions imposed by rotational selection rules, energy-exchange cross sections may be as much as 0.01 to 0.1 times as large as the molecular gas-kinetic cross section and are greater than those estimated using only an exponential repulsive interaction between molecules.
Molecular Structure of PClF4: Infrared Spectrum, Low-Temperature Raman Spectrum, and Gas-Phase Dipole Moment: Pentacoordinated Molecules. IX
Authors: Holmes Robert R.
Published: January 2005

The vapor-state infrared spectrum (2000–250 cm−1) and liquid-state Raman displacements (Δv=50–1200 cm−1) of PClF4 are reported. The vapor-state electric dipole moment of PClF4 was obtained from a study of the temperature variation of the dielectric constant over the range −68° to −2°. The resulting value is 0.78±0.01 D. The induced polarization is 13.7±0.4 cc. Interpretation of the vibrational data as well as the dielectric data and 35Cl pure quadrupole resonance frequency support the conclusion that the structure of PClF4 is a trigonal bipyramid (C2v point group) with the chlorine atom located at an equatorial site.
Potential Field and Molecular Vibrations of the Trigonal Bipyramidal Model AX3YZ: Pentacoordinated Molecules. X
Authors: Holmes Robert R.
Published: January 2005

The secular equations with angular dependence are derived in terms of the FG matrix system representing the normal vibrations associated with the trigonal bipyramidal model of C3v symmetry. A normal-coordinate analysis of PCl4F and CF3PCl4 both of C3v symmetry is given based on recent infrared and Raman data. The symmetry coordinates adequately represent the normal modes except for ν4, ν6, and ν7 where appreciable mixing is indicated.
EPR Spectrum of Cr3+: K2NaCo(CN)6
Authors: Schechter D. , Rosenthal Jack
Published: January 2005

The EPR spectrum of Cr3+ in K2NaCo (CN)6 has been examined at room temperature and K-band microwave frequency. The spin Hamiltonian is assumed to have the form Hs=gβH·S+D(Sz2−54)+E(Sx2−Sy2). A general analysis is given for fitting this spin Hamiltonian when the orientation of the crystal-field axes is unknown. The application of this analysis to the experimental data yields g=1.992±0.001, D=0.022±0.001 cm−1, E=0.003±0.001 cm−1.
Study of the Electronic Structure of Molecules. I. Molecular Wavefunctions and Their Analysis
Authors: Clementi Enrico
Published: January 2005

In this paper we have summarized the complete multiconfiguration self-consistent-field theory (CMC SCF LCAO MO or CMC for short) as given from the analysis of Veillard and the author (published elsewhere).

In the analysis of the CMC theory it is shown that the CMC technique allows determination of the pair and pair—pair correlation energy and retains the physical simplicity of the Hartree—Fock functions. The CMC theory differs from usual many-body techniques in so far as it does not take the Hartree—Fock energy as zero-order energy. It has been shown that the CMC wavefunction can be cast in the form of a new type of ``single determinant'' (the ``CMC determinant'') with elements which are different from the standard elements of the Slater determinant. The existence of the CMC determinant provides the formal justification for the use of a single determinant in semiempirical work aiming at exact prediction.

The analysis of the CMC wavefunctions is then continued in terms of a population analysis which to a large extent follows Mulliken's work. Then the energy expression of the SCF MO and CMC techniques are analyzed in terms of bond-energy diagrams. These are special partitions of the total energy with immediate reference to structural chemistry. Finally, the bond-energy diagrams are briefly discussed in their relation to bond-energy transferability, vibrational analysis, and other chemical phenomena. This paper introduces both the notation and the terminology we shall use in describing all-electron computations for the NH3, HCl reaction surfaces, and for pyrrole, pyridine, pyrazine, fluorobenzene, benzene, and a few other molecules presented in the following papers of this series.
Flash Photolysis of Propane
Authors: Griffiths D. W. L. , Back R. A.
Published: January 2005

The flash photolysis of propane has been studied at an average wavelength of 1590 Å and a pressure of 50 torr, with absorbed light intensities between 2 and 15×1021 photons/liter·sec. The primary processes, C3H8+hν→H2+C3H6(~94%),C3H8+hν→CH4+C2H4 (~6%),appear to be virtually the only reactions occurring at low conversion. With increasing conversion, photolysis of propylene becomes important, yielding a variety of secondary products. These observations are compared with earlier studies made at low intensity and shorter wavelengths.
Thermal Diffusion Factor of Argon from Column Operation
Authors: Raman S. , Paul R. , Watson W. W.
Published: January 2005

A 3-m glass hot-wire column has been used to study the separation of argon isotopes. The operational criteria for obtaining maximum enrichment are investigated by using both alternating (ac) and direct (dc) currents to heat the wire and determining the variation of separation factor with pressure, the ratio θ0 of temperature of hot wire to cold wall, and the number of spacers. By the quasitheoretical method outlined by Raman et al., the thermal diffusion factor αT of argon is computed. In accordance with theory, higher θ0 values lead to enhanced separation. When centering of the wire is improved with spacers, dc heating leads to a greater increase in enrichment than with ac. The average value of αT at 280°K over the pressure range of 45 to 75 cm is found to be 0.0112±0.0015.
Electronic Structure of Hexaquo Metal Ions. I. Chromium (III)
Authors: Carlin Richard L. , Walker Ian M.
Published: January 2005

The optical spectra of the hexaquochromium (III) ion in the host crystals of C(NH2)3Al(SO4)2·6 H2O and several isomorphs, and in AlCl3·6 H2O, are presented and discussed. The broad-band spectra have been analyzed to determine trigonal field parameters, and these results are confirmed by the analysis of the fine-line spectra. The off-diagonal element of the trigonal field, v′, is shown to be as large in magnitude as v, and therefore to be of considerable importance in the interpretation of polarized spectra. Evidence confirming the dependence of the ground-state splitting D on the parameter v′ is also presented.
Electronic Structure of Hexaquo Metal Ions. II
Authors: Walker Ian M. , Carlin Richard L.
Published: January 2005

The electronic absorption spectra of the hexaquo ions of trivalent titanium, vanadium, manganese, and cobalt in host crystals of C(NH2)3Al(SO4)2·6 H2O and of (Ti, Al)Cl3·6 H2O are presented and discussed in relation to earlier studies on the hexaquochromium(III) ion in these and related compounds. The broad-band spectra have been analyzed to determine trigonal field parameters, and evidence for further tetragonal splittings of some excited states is presented.
Ultrasonic Relaxation Due to trans—gauche Rotational Isomerism in the Liquid Normal Paraffins
Authors: Piercy J. E. , Rao M. G. Seshagiri
Published: January 2005

The ultrasonic absorption has been measured in liquid normal butane, pentane, hexane, and heptane at frequencies of 5, 15, and 45 Mc/sec over the temperature range from their freezing to boiling points at atmospheric pressure. The absorption was also measured in propane and two mixtures of pentane with propane at a frequency of 45 Mc/sec for temperatures in the range −130° to −50°C. The measurements indicate internal rotation about internal C–C bonds to be the relaxation mechanism and a barrier for the conversion from a gauche to a trans configuration of 3.4±0.4 kcal/mole for n-butane, 4.2±0.4 kcal/mole for pentane, 3.1±0.4 kcal/mole for hexane, and 3.8±0.4 kcal/mole for heptane. They also indicate a difference between the molar volume of gauche and trans isomers of butane which is less than 0.3% and a value for the ratio of the compressional to shear viscosities caused by molecular rearrangement of 1.1 for propane, 6.3 for pentane, 6.2 for hexane, and 5.7 for heptane.
Triplet-State Zero-Field-Splitting Correlations in Substituted Molecules
Authors: Smaller B. , Avery E. C. , Remko J. R.
Published: January 2005

The triplet-state properties of a large number of unsaturated ring compounds have been investigated by optical and electron paramagnetic techniques. Correlative effects have been noted between optical zero-field-splitting (ZFS) shifts and chemical data. Redistribution of spin density due to substituents as evidenced by ZFS shifts appear to be directly related to measures of π charge redistribution using other techniques. For the naphthalene derivatives the dependence of ZFS shift on spin density at substitutional carbon site has been found also to correlate with triplet lifetimes.
Theory for the Infrared Absorption Intensities of the Lattice Vibrations of Molecular Solids
Authors: Schnepp O.
Published: January 2005

A theory is developed for the infrared-transition dipole intensities of the lattice vibrations in molecular solids. For nonpolar molecules like N2 and CO2 the origin of the intensities lies in the nonzero dipole derivatives where the dipole is induced by the molecular quadrupole moment of the neighboring molecules in the lattice. The distortion moment is not taken into account and its neglect is justified on the basis of independent available experimental evidence. For molecular solids composed of polar molecules, the intensity of quasirotational lattice modes is calculated. The results are given in general form and, in addition, dipole-moment derivative sums are evaluated for lattices of factor-group symmetry Th6 appropriate for solid CO2 and approximately for the α phase of N2.
Positive and Negative Self-Surface Ionization of Tungsten and Rhenium
Authors: Scheer Milton D. , Fine Joseph
Published: January 2005

The self-surface ionization of tungsten and rhenium has been investigated with a specially designed mass spectrometer. It has been found that both positive and negative singly charged atomic ions sublime from these metal surfaces in the 1900°—2600°K temperature range. The assumption that these processes can be described by a generalized Saha—Langmuir equation has been shown to be valid. The energies required for positive-ion sublimation were found to be 12.1 and 10.7 eV for tungsten and rhenium, respectively. The negative-ion sublimation energy for rhenium was determined as 12.6 eV and that for tungsten is given by approximately the same value. At 2300°K, the ratio of positive to negative ions evaporating from these surfaces was found to be about 40 for tungsten and about 20 000 for rhenium. These results are consistent with the following estimates for the electron affinities: A(W)=0.50±0.30 eV and A(Re)=0.15±0.10 eV.
Quantum Mechanics of the H2–H2 Interaction. I. A Restricted Valence-Bond Approach
Authors: Magnasco V. , Musso G. F.
Published: January 2005

The short-range intermolecular interaction of two hydrogen molecules in their ground state has been approached by a rigorous valence-bond calculation using a minimal set of four symmetrically orthogonalized 1s atomic orbitals with the orbital exponent fixed to the best variational value for the isolated molecule. All the covalent, singly polar and doubly polar ``formal'' structures which are expected to be relevant in the case of relatively large intermolecular distances have been included in the calculation. Within a given range of separation distances four relative orientations of the two molecules have been considered in order to study the angular dependence of the intermolecular interaction. All the occurring three- and four- center integrals have been evaluated to six significant figures using a three-dimensional numerical integration in confocal elliptic coordinates. Although the quantitative value of the intermolecular potential resulting from this calculation is expected to be as good as it could be for a minimal basis approach, many interesting features of the interaction in the short-range region have been emphasized through a population analysis of the valence-bond (VB) molecular wavefunction made in terms of the original set of nonorthogonal atomic orbitals which allows to describe unambiguously the bonding or antibonding situations within the system. It is found that the charge distributed according to the overlap densities between orbitals belonging to different molecules escapes from the intermolecular region and piles up as an extra charge on the two molecules. A small charge transfer showing a strong angular dependence on the dihedral angle is observed to occur in each molecule along the bond direction. The general discussion suggests that the introduction of localized wavefunctions could be appropriate for understanding the details of the correlation between charge distribution and intermolecular energy and for a partitioning of the energy into significant contributions.
Scattering of Cold Neutrons in Ammonium Carbonate, Ammonium Citrate, and Ammonium Acetate
Authors: Myers Vernon W.
Published: January 2005

Neutron-energy-gain spectra have been measured in (NH4)2CO3, (NH4)2HC6H5O7, and NH4C2H3O2 at 20°C using the Brookhaven slow-chopper facility. Each spectrum exhibits two peaks that are characteristic of optical modes. The spectra of ammonium carbonate and ammonium citrate are similar to those of the body-centered-cubic lattice phase of the ammonium halides in which the ammonium ion has torsional and translational optical vibrations.
Ion—Molecule Reactions in Propane
Authors: Bone L. I. , Futrell J. H.
Published: January 2005

Ion—molecule reactions in propane were studied using mass- and energy-resolved ion beams in a tandem mass spectrometer. The sequence of elementary reactions which lead to C3H8+ and C3H7+ as stable ions was established. Through the use of deuterium-labeled reagents it was established that the parent ions undergo rapid charge-exchange reactions but that the resonance hydride transfer reaction is not observed within sensitivity limitations of the instrument (k<10−12 cm3/molecule·sec). The alkene ions C2H4+ and C3H6+ react with propane by H− and H2− transfer reactions and the relative importance of these modes of reaction depends strongly on ion—neutral relative kinetic energy. Interesting rearrangement processes observed for the relatively low-intensity primary ions C2H3+ and C3H3+ were also studied as a function of ion kinetic energy. In general, atom-transfer reactions are favored over more complex rearrangement processes as ion velocity is increased and, in certain cases, new reaction channels are opened by the conversion of translational energy into internal energy.
Role of Molecular Interaction in Anisotropic Light Scattering by Liquids
Authors: Kielich Stanisℏaw
Published: January 2005

The influence of molecular linear and nonlinear polarizability, anisotropy, shape, radial and angular correlations, and other microscopic factors on anisotropic light scattering is discussed for some models of a liquid within the framework of statistical—molecular theory. An effective optical anisotropy Δ2 is introduced and computed numerically for several liquids from the experimental depolarization ratio Du and optical birefringence constant Bλ; for strongly anisotropic substances, this yields Δ2 values almost twice smaller than those determined from the anisotropic Rayleigh ratio Ranis. Theoretical, numerical computations of Δ2 basing on the ellipsoidal Lorentz and Onsager—Scholte models result in values close to those from Du and Bλ. Finally, the isotropic and anisotropic parts of the refractive index variation due to intense laser light are related, respectively, with the isotropic and anisotropic Rayleigh ratios, by means of which numerical computations are made for various liquids.
Solution Properties of Synthetic Polypeptides. III. Viscosity Behavior of Poly-γ-Benzyl-L-Glutamate in the Helix—Coil Transition Region
Authors: Teramoto Akio , Nakagawa Koichi , Fujita Hiroshi
Published: January 2005

Limiting viscosity numbers [η] and specific rotations [α]578 of five samples of poly-γ-benzyl-L-glutamate (PBLG) (ranging in weight-average molecular weight M̄w from 1.9×104 to 4.0×105) in mixtures of dichloroacetic acid (DCA) and ethylene dichloride (EDC) of various compositions were measured as functions of temperature in the range where the PBLG molecule underwent a thermal transition from a disordered, random-coil state to an ordered helical state. For one sample the measurements of optical rotatory dispersion were made at various solvent compositions and temperatures, and the data were analyzed in terms of the Moffitt plot. When the M̄w of a given sample was above a certain critical value, [η] first decreased (or was kept constant), passed through a shallow minimum, and then increased sharply to a limiting value as the temperature was raised. Below the critical value, the change in [η] with temperature was a monotonic decrease. Irrespective of the molecular weight of the sample, [α]578 increased sharply in a narrow range near 30°C and then gradually leveled off as the temperature was raised. This narrow region coincided with the region where [η] underwent a marked increase. It was found that the helical content fH of a given sample can be evaluated from the reduced mean residue rotation measured at 578 mμ. When the values of [η] obtained under different solvent compositions and temperatures are plotted against the fH values so calculated, the plotted points formed a single composite curve over the entire range of fH. This curve exhibits a quite similar character to the theoretical curves for 〈S2〉 (mean-square radius of gyration) vs fH calculated by Nagai on the statistical-mechanical treatment of helix-forming polypeptides.
Generalized Diffusion Theory of Nonequilibrium Reaction Rates
Authors: Keck James C.
Published: January 2005

A simple expansion procedure is used in conjunction with the detailed balancing condition to show that the linear master equation describing the relaxation of an atomic system in a background of inert atoms can be approximated by an equivalent diffusion equation with appropriate boundary conditions. This equation has the form of the ordinary heat-conduction equation for a medium of variable heat capacity and thermal conductivity and is simplier than the commonly used Fokker—Planck equation. It is expected to be a reasonable approximation under conditions where the changes in the constants of the motion are small in a single collision. A similar equation has been derived by Van Kampen who showed that it implies the phenomenological equations of nonequilibrium thermodynamics. However, he did not consider the boundary condiditions necessary to deal with chemical reactions or phase changes.
Vibrational Energy Transfer in CO2 Lasers
Authors: Moore C. Bradley , Wood Robert E. , Hu Bei-Lok , Yardley James T.
Published: January 2005

Laser-excited vibrational fluorescence measurements have been made on the asymmetric-stretching vibrational level (00°1) of CO2. Vibration→vibration energy-transfer rates from this level due to collisions with CO2 and with a number of other collision partners are presented. The rate of near-resonant exchange of vibrational energy between CO2 and N2 (ΔE=18 cm−1) has been measured. The kinetics of the CO2 laser system are analyzed in terms of a three-level scheme. Observed laser performance is compared with that calculated by use of collisional and radiative coupling rates observed in nonionized gases and of electron activation and deactivation rates estimated from CO2 discharge systems. In accordance with the scheme presented, the relative effectiveness of small amounts of added H2, D2, and He on laser output parallels their effectiveness in deactivating the lower laser level. The criteria for selecting molecules with vibrational-energy-level patterns likely to produce laser systems are outlined. Attempts to produce new continuous-wave lasers in SO2 and HCN are described.
Temperature Dependence of Singlet—Triplet Intersystem Crossing in Anthracene Crystals
Authors: Adolph J. , Williams D. F.
Published: January 2005

The formation of triplet excitons from singlet excitons via a radiationless transition (intersystem crossing) is studied in anthracene crystals. Using blue exciting light with 430 mμ>λ>350 mμ the temperature dependence of the intersystem crossing is found to follow an exponential law with an activation energy of 800±50 cm−1.

It is concluded that this transition starts from a vibrationally excited single state and involves the second triplet state. The total energy of this vibrational state is about 26 100 cm−1 in good agreement with that suggested by Kellogg, 26 050 cm−1, for an excited triplet level.

No emission from the triplet—triplet transition could be observed.
Diffusion Length of Triplet Excitons in Anthracene Crystals
Authors: Williams D. F. , Adolph J.
Published: January 2005

Recently two different experimental principles have been used to determine the diffusion length of triplet excitons and the results have differed by an order of magnitude. Experiments have now been performed using (i) singlet excitation and (ii) triplet lifetime dependence on thickness, and the results are shown to be in accord with results from other techniques. The triplet diffusion length l is shown to be 20±10 μ. Also it is found that l is slightly temperature dependent, with an apparent activation energy of approximately 10−2 eV.
Electron Spin Resonance of Radical Pairs in Single Crystals of Oxalic Acid, Dihydrate and Anhydrous
Authors: Moulton Grace C. , Cernansky M. Pierre , Straw David C.
Published: January 2005

The electron-spin-resonance spectra of free-radical pairs have been observed in single crystals of oxalic acid, both anhydrous and dihydrate, produced by irradiation with 3-MeV x rays at 77°K. The anisotropic dipole—dipole coupling due to the unpaired electrons observed was fit to theoretical curves for unpaired electrons 6.33 Å apart in the dihydrate and 9.93 Å apart in the anhydrous oxalic acid. It is concluded that these electrons are located on the hydroxyl oxygen atoms. In the dihydrate they are in adjacent molecules of the unit cell, and in the anhydrous they are in molecules separated by 1 unit cell length in the b direction plus 1 unit cell length in the c direction.
Electronic Absorption Spectrum of Ferrocene
Authors: Armstrong A. T. , Smith F. , Elder E. , McGlynn S. P.
Published: January 2005

The electronic absorption spectrum of ferrocene has been investigated in the vapor, in liquid solutions, and in glassy matrices. Temperatures used ranged from 420° to 77°K. The absorption spectrum contains at least 11 distinct electronic absorption bands. Three of these appear to be triplet←singlet in nature, and to be made allowed by spin—vibronic perturbations (i.e., spin—orbit coupling of the triplet manifold with vibronically coupled singlets). It is shown that a spin—orbit coupling factor 300≤ζ≤400 cm−1 can account for the observed intercombination intensities. The singlet←singlet absorption spectrum is dominated by one allowed transition at ∼50 000 cm−1 with f∼0.69. It is possible that all other electronic transitions, the 53 000-cm−1 band excepted, are dipole forbidden and obtain intensity by first-order vibronic stealing from the ∼50 000-cm−1 band. The higher-energy absorption bands show vibrational structure, and this structure is analyzed herein; unfortunately, the resolution is restricted by ``molecular'' reasons associated with vibrational ``richness,'' hindered rotations, and vibrational ``hot bands.'' The higher-energy absorption bands are heavily localized on the aromatic rings in contrast to the three low-energy diffuse electronic systems in Regions IV, V, and VI which contain much d-orbital and intramolecular charge-transfer character. No phosphorescence emission of ferrocene has been observed here.
Vacuum-Ultraviolet Photolysis of Solid Propane at 20° and 77°K
Authors: Rebbert R. E. , Ausloos P.
Published: January 2005

The photolysis of CD3CH2CD3, CH3CD2CH3, and C3H8—C3D8 mixtures has been investigated at 1470 Å (8.4 eV), 1236 Å (10 eV), and 1048–1067 Å (11.6–11.8 eV) at both 20° and 77°K. On the basis of the isotopic analysis of the products it is concluded that the following primary fragmentation processes occur: C3H8+hv→C3H7+H→C3H6+H2→C2H6+CH2→C2H5+CH3→C2H4+CH4.Hydrogen, methane, and ethane are mainly formed by elimination processes from a single carbon atom which results in the simultaneous formation of a carbene in each case. In this respect the primary processes occurring in the solid phase are the same as those reported to occur in the gas phase. The elucidation of the primary processes in the condensed phase is facilitated because of the inhibition of secondary decomposition of the internally excited fragments formed in Processes A to E. For instance, the ethylidene and propylidene rearrange quantitatively to ethylene and propylene, respectively.

The occurrence of geminate disproportionation and combination leads to difficulties in determining the relative quantum yields of the primary processes A and D. It could, however, be concluded on the basis of isotopic analyses that the C–H and C–C cleavage processes, A and D, increase in importance when the energy of the incident photon is increased.

Although propane ions, which have an ionization energy of 11.07 eV in the gas phase, must be produced at 1048–1067 Å, no concrete information could be obtained as to the fate of these ions in the solid phase. The data, however, show that decomposition of the superexcited molecules may be the major source of the hydrocarbon products formed at these wavelengths.
Photolysis of Cyclopentane at 1470, 1236, and 1048–1067 Å
Authors: Doepker R. D. , Lias S. G. , Ausloos P.
Published: January 2005

The photolysis of cyclopentane has been investigated at 1470, 1236, and 1048–1067 Å. The primary process, cyclo-C5H10+hv→C5H8+H2 is of major importance at 1470 Å, but its quantum yield diminishes at shorter wavelengths where processes involving C–C cleavage become more predominant. The products formed in the gas-phase photolysis of cyclo-C5D10—H2S mixtures and in the solid-phase photolysis of cyclo-C5H10 indicate that the excited cyclopentane molecule undergoes ring opening to form a 1-pentene molecule. In the gas phase, the internally excited 1-pentene decomposes to form methyl and ethyl radicals. Evidence is also obtained for the occurrence of the dissociative process: C5H10*→C2H4+C3H6 where C3H6 consists of cyclopropane and propylene. At 1048–1067 Å (11.6–11.8 eV), ionization is extensive (ionization potential of cyclo-C5H10=10.5 V). Saturation current measurements yielded a value of 0.64 for ηC5H10/ηNO. On the basis of an isotopic analysis of the propane formed in the photoionization of C5D10–C5H10–O2 mixtures it is shown that the parent ion dissociates as follows: C5H10+→C3H6++C2H4 and that the C3H6+ ions participate in an H2− transfer reaction: C3H6++C5H10→C3H8+C5H8+. Fragmentation of the parent ion diminishes with an increase in pressure. The collisional deactivation process is more pronounced for the perdeuterated than for the perprotonated cyclopentane ion. The data also indicate that a fraction of the parent ions undergoes ring opening to form cis- or trans−2-pentene as a final product.
Vaporization of Dimolybdenum Carbide
Authors: Fries R. J.
Published: January 2005

The vaporization behavior of Mo2C was investigated over the temperature range 2125° to 2550°K by Langmuir experiments utilizing an induction heated, ultrahigh vacuum thermobalance. A congruently vaporizing composition of MoC0.49 was found at temperatures from 2250° to 2300°C. The total evaporation rate increases and the heat of evaporation decreases as the carbon-to-metal ratio of the sample decreases from 0.49 to 0.44.

A mass-spectrometric examination of the evaporate from MoC0.49 did not reveal any MoxCy molecules. Therefore, evaporation by decomposition is assumed. If monatomic gaseous species and unit evaporation coefficients are also assumed, the pressures over MoC0.49 are logPMo(atm)=7.112±0.139−(3.420±0.033) (104/T),logPC(atm)=6.351±0.139−(3.420±0.033) (104/T).

The errors quoted are standard deviations. The heat of formation at 298°K of MoC0.49 is −4.9 kcal/mole from third-law calculations, in good agreement with the −5.5 kcal measured calorimetrically.
Intramolecular Vibration-to-Vibration Energy Transfer in Carbon Dioxide
Authors: Yardley James T. , Moore C. Bradley
Published: January 2005

We have used a vibrational fluorescence technique to study the deactivation of the asymmetric stretching vibration (00°1) of CO2 by intramolecular vibration-to-vibration energy transfer during CO2—rare-gas collisions. The efficiency for deactivation has only a slight dependence on mass, with a peak corresponding to resonance between the duration of the collision and the frequency difference between the vibrational levels involved. We have been able to obtain order-of-magnitude agreement between observed and theoretical transition probabilities only when the mixing of vibrational states of CO2 by Coriolis coupling and anharmonicity is considered.
Self-Consistent-Field Calculations of Bound Electron Pairs in Dielectric Media
Authors: Land R. H. , O'Reilly D. E.
Published: January 2005

The potential for an electron trapping center in a dielectric medium is constructed by a multipole expansion and the effect of electronic polarization of the dielectric included in the electron adiabatic approximation. The Hartree—Fock equations are converted to a set of difference equations, which are solved by a matrix method. For a series of alkali halides, the calculated F and F′ centers s—p excitation energies are generally within 20% of the observed values. Calculations are carried out for the one- and two-electron cavity and one-electron positive-ion trapping centers in liquid ammonia. Calculated heats of solution, pairing energies, and s—p excitation energies are compared with experimental results.
Bis(3-Phenyl−2,4-Pentanedionato)Copper. II. Polarized Crystal Spectra
Authors: Belford R. L. , Carmichael J W
Published: January 2005

Polarized spectra of (001) and (100) faces of the centric chelate bis(3-phenyl−2,4-pentanedionato)copper show four ``d—d'' bands, all principally y polarized. The transitions are of electric-dipole, vibronically allowed, single-molecule origin. From the polarization it is inferred that several vibrations are effective, but that the bulk of the intensity is borrowed from one charge-transfer transition, B3u←B1g in D2h. There is a subtle difference in interpretation between D2h and C2h(x) pseudosymmetry, either of which satisfactorily explains the results. From the temperature dependence of intensities, the two lowest-energy bands (∼15.4 and 16.9 kK) are inferred to be Ag(x2—y2, 3z2—r2)←B1g(xy), and the highest ones (∼19.0 and 20.6 kK) to be B2g(xz) and B3g(yz)←B1g(xy).
Magnetic Rotation Spectrum of the A2Σ+←X2Πr Transition in NO. I
Authors: Robinson Dean W.
Published: January 2005

The γ bands of NO have been found to yield a strong magnetic rotation spectrum. The 0, 0 band of this system has been photographed with a resolution of about 0.3 cm−1, enough to observe some details of the line shapes. Qualitative interpretation of the spectra and the effects of pressure and field strength has been possible solely on the basis of the Faraday effect. The molecule NO appears to be a model case for future detailed study in magnetic rotation spectroscopy, as no profound mysteries have emerged as yet.
Selective Enhancement in Hydrogenlike Molecules with the Rare Gases. II. HD and D2 with Ar and Kr
Authors: Takezawa S. , Innes F. R. , Tanaka Y.
Published: January 2005

Recent work on selective enhancement of the H2 spectrum in Ar and Kr discharges has been extended to HD and D2. Similar phenomena are expected and can be observed in the spectra of these molecules when excited in Ar but not in Kr. The explanation given of the processes involved in the case of H2, namely, resonance fluorescence and collisions of the second kind involving allowed transitions, was supported also by the observed evidence in the present work. Vibration levels in the ground state of HD and D2 were greatly extended and the highest levels which occur in these states can now be estimated at (v= ) 17 and 21, respectively.
On Static and Dynamic Compressibilities of Debye Solids at High Pressures
Authors: Huang Y. K.
Published: January 2005

Investigations show that static compressibility of a Debye solid can be deduced from shock-compression data and vice versa. In this paper three different approaches are considered for the evaluation of static and dynamic compressibilities. Except for the linear law of shock propagation and the Born—Mayer type of energy function, which are semianalytical, all other equations are derived on a full analytic basis. It is of interest to show that the entropy and temperature are implicit functions of shock compression. These implicit functions are then determined in closed form, and they turn out to provide a means for the calculation of thermal properties of the Debye solid at high pressures in terms of purely mechanical parameters. Some calculated results are given according to the pseudo-Hugoniot approach only, and the validity range covers pressures from 104−107 atm and temperatures from 102−103K.
Vacuum-Ultraviolet Absorption Spectrum of Carbon Suboxide
Authors: Roebber John L. , Larrabee J. C. , Huffman R. E.
Published: January 2005

Absorption coefficients of carbon suboxide have been measured from 2000 to 1050 Å photoelectrically and the absorption spectrum has been photographed from 1000 to 600 Å. The background light sources were the H2, He, and Ar continua. The region from 1650–1050 Å is dominated by a ns←π Rydberg series converging to the first ionization potential at 10.60 eV. Diffuse structure on the short-wavelength side of three of the Rydberg bands is probably caused by vibrational progressions in the C=C and C=O symmetric stretching frequencies but may be due to two other fragmentary Rydberg series. Several very strong diffuse bands are present below 1000 Å which have not yet been assigned. A system of 14 bands around 1780 Å may be a vibrational progression in a 400 cm−1 bending mode or a vibrational sequence. Neither the experimental evidence nor theoretical considerations allow a definite assignment to be made. However, the gradual emergence of the vibrational structure from the underlying continuum strongly supports the progression explanation.
Study of the Electronic Structure of Molecules. III. Pyrrole Ground-State Wavefunction
Authors: Clementi E. , Clementi H. , Davis D. R.
Published: January 2005

An SCF LCAO MO ground-state wavefunction is presented for the pyrrole molecule. All electrons, σ and π, are considered, and all the necessary many-center integrals are included in this work. The analysis of the wavefunction reveals that there is a strong two-way charge transfer on the nitrogen atom. (This reopens the problem of the validity of π-electron computations, as discussed in the paper.) The lowest π-electron MO is below the highest σ electron. The hybridization of the σ electrons in the carbon and nitrogen atoms is not s1p2, but deviates strongly for the nitrogen atom and slightly for the carbon atoms.
Study of the Electronic Structure of Molecules. V. All-Electron SCF Wavefunction for the Ground State of Pyrazine
Authors: Clementi Enrico
Published: January 2005

In this work we report on all-electron SCF LCAO MO computation for the ground-state wavefunction of the pyrazine molecule (C4H4N2). As in previous works of this series, we have made use of a ``contracted set'' of Gaussian functions in order to save computational time. All many-center integrals are accurately computed. The two lone pairs on the nitrogen molecule are quite different in character: The lower one is very little delocalized (1.88 electrons on the nitrogen); the second lone pair is as delocalized as the lone pair in pyridine (1.37 electrons on the nitrogens, 0.22 electrons on the hydrogens, and 0.40 electrons on the carbons). Each of the hydrogen atoms has donated 0.27 electrons to the carbons or the nitrogens of the molecule.
Cyclotron Resonance in Gases. II. Cross Sections for Dipolar Gases and for CO2
Authors: Tice Russell , Kivelson Daniel
Published: January 2005

The interaction of dipolar molecules with very low-energy electrons arises almost entirely from the monopole—dipole interaction. These cross sections have been measured by analyzing the widths and shapes of the cyclotron-resonance absorption lines of electrons in a gaseous mixture of N2 and dipolar gases. The electron collision cross sections σD for the dipolar molecules could be reasonably well fitted to the relation σD = 180D2(v0/v)2, where σD is in square angstroms, D is the dipole moment in Debye units, v is the electron velocity, and v0 is the electron velocity of 298°K electrons (1.16×107 cm/sec). A Born-approximation calculation yields the same result with the coefficient equal to 130 rather than 180. CO2 has an anomolously large cross section for a nonpolar molecule. The experimental data is compatible with a cross section that is proportional to v−1, but it can also be fitted by a dipolar cross section with D=0.67 which is set equal to zero for v<5×106 cm/sec. This model corresponds to the physical situation in which the faster electrons see the instantaneous dipole moment due to bending motions in CO2, and the slower electrons feel the interaction over several vibrational periods and hence do not see a net dipole moment. However, estimates based on infrared data indicate that the effective dipole moment should only be about D=0.16 in the ground state. The cross section of N2O also shows evidence of being effected by instantaneous dipole moments.