bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Resonance Powder Patterns of the Second-Order Nuclear Quadrupole Interaction in Solids with Asymmetric Field Gradient
Authors: Narita Koziro , Umeda Jun-ichi , Kusumoto Hazime
Published: January 2005

Numerical calculations of the powder pattern of the central component shifted by the second-order nuclear quadrupole interaction in solids have been performed for various values of the asymmetry parameter, η. Shape functions have been obtained in units of (νQ2/6νL) (a—¾) for η=0.1, 0.2, ···, 1.0, at 0.1 intervals. Also, positions of special points such as infinities and steps of the shape function have been determined as functions of η. Effects of the dipolar broadening of the single-crystal resonance upon powder patterns have been estimated for the case of η=0.5. Influences of anisotropic magnetic shift were also discussed on powder patterns obtained experimentally. These relations are useful for simple and rapid determinations of η and νQ from the second-order powder pattern.
Flow Birefringence of DNA Molecules
Authors: Osborne C. F.
Published: January 2005

A calculation is made to determine whether the flowing of DNA molecules in water solution would produce a measurable anisotropy in the refractive index of the solution. Using the time-dependent Hartree method, a one-parameter solution is obtained for the degree of anisotropy. Finally an estimate of the anisotropy is made.
Wavelength Dependence of the Quenching of Iodine Fluorescence
Authors: Steinfeld Jeffrey I.
Published: January 2005

The variation of the quenching efficiency of various gases (He, Xe, NO, CO2, C2H4, C6H6, I2) with energy of excitation was measured for the iodine B→X fluorescence. The correlation of efficiency with the parameter αμ½, previously found, was confirmed over a range of vibrational states. States of v′≤7 appear to be ``unquenchable'', and a fluorescence stabilization effect appears as a departure from the Stern—Volmer law. This is attributed to the absence of repulsive electronic states below the seventh vibrational level of I2. Anomalously large quenching cross sections are found for several species (NO, CO2); however, there is no conclusive evidence for a complex formation mechanism.

Using these data, it was possible to locate approximately the repulsive states of I2 relative to the B state. The magnetic quenching rate can be computed to good accuracy from simple LCAO—MO wavefunctions, using first-order time-dependent perturbation theory. The collision-induced quenching can be completely explained on the basis of a van der Waals-type interaction.
Rotational Analysis of Some Bands of the Triplet←Singlet Transition in Formaldehyde
Authors: Raynes W. T.
Published: January 2005

Using the absorption frequencies measured by Robinson and DiGiorgio, a rotational analysis of the 0+←0 and 1+←0 bands of the 3A2←1A1 transition in H2CO has been performed. Each band contains a number of overlapping subbands which are themselves made up of several branches consisting of individual rotational lines. Despite the overlapping, it was found possible to give assignments to a large number of lines. All branches are q-type branches; that is, only ΔK = 0 transitions are observed. The positions of the triplet-state rotational levels relative to the lowest rotational level of the ground vibronic state were obtained with the aid of the very accurate ground-state rotational levels determined interferometrically by Parkin and Poole. These triplet-state levels were found to fit accurately the Hamiltonian proposed by Van Vleck for an asymmetric-rotor molecule in a triplet electronic state provided that further terms were added to take account of rotational distortion.

Values of the rotational constants, rotational distortion constants, and spin-interaction constants of the 3A2(0+) and 3A2(1+) states have been determined. The rotational constants for the 3A2(1+) state are as follows: A = 8.6275 (±0.0008) cm−1; B = 1.1491 (±0.0001) cm−1; and C = 1.0343 (±0.0001) cm−1. The results for the 3A2(0+) state are very similar. From these constants it is possible to show that the equilibrium nuclear geometry of formaldehyde in this state is highly nonplanar, the geometrical parameters having the following values: r(C–H) = 1.10 Å; r(C–O) = 1.28 Å; ∠HCH = 118°; out-of-plane angle = 36°. The spin-interaction constants, which determine the extent of the triplet splitting of the rotational levels, take account not only of spin—molecular rotation, spin—orbit, spin—other-orbit, and spin—spin interactions, but also of the effect of rotational asymmetry upon these interactions. The observed relative intensities of the rotational lines agree very well with those predicted by the recent theory of Hougen. In particular, the almost complete absence in the spectrum of transitions to the F2 component of the triplet state is understandable in the light of this theory. As a consequence of the fact that only ΔK = 0 transitions are observed (the theoretically possible ΔK = ±2 transitions were not detected), it is possible to deduce with the aid of Hougen's theory that it is a 1A1 state that, by spin—orbit coupling with the 3A2 state, permits the formally forbidden triplet←singlet bands to occur. This result is in complete agreement with the theoretical deductions of Sidman made some years ago.
Study of Triplet—Triplet Transfer by the Method of Magnetophotoselection. II. Concentration Depolarization
Authors: Siegel Seymour , Goldstein Lester
Published: January 2005

The concentration depolarization of the spectra from Δm=±1 electron paramagnetic resonance (EPR) transitions of photoexcited naphthalene-d8 triplet-state molecules dissolved in ethanol glasses at 77°K has been studied. An analysis of the results is made in terms of triplet-state energy transfer. It is shown that the results are completely consistent with an electron exchange triplet-state energy-transfer mechanism, with the probability of transfer being the same as that found in the case of transfer between unlike molecules. However, for the self-transfer case, back transfer is important and it was included in the analysis. It was also necessary to assume in the theoretical analysis that the rate of transfer between molecules at the effective transfer distance is slow compared to the rate of relaxation of the spin magnetization.

Some preliminary evidence is presented for an appreciable solvent effect on the polarization of the 1La band of naphthalene.
Rayleigh and Brillouin Scattering in Liquids: The Landau—Placzek Ratio
Authors: Cummins Herman Z. , Gammon Robert W.
Published: January 2005

The classical theory of light scattering in liquids leading to the Landau—Placzek ratio for the intensities of the Rayleigh and Brillouin components is reviewed. A simple modification is proposed in which the effect of dispersion is included by defining a hypersonic compressibility βshs=1/(ρvhs2), where vhs is found from the experimentally measured Brillouin shifts. Further modification is presented to account for dispersion in the electrostriction. A modification of the Landau—Placzek equation due to Fabelinskii is discussed and shown to be essentially equivalent to our equation.

The predictions of the ratios are evaluated for 11 common liquids and compared with new experimental values reported in this paper and with other values taken from the literature. It is found that in most cases the dispersion modification leads to ratios in considerably better agreement with the experimental values than does the simple Landau—Placzek equation.

We present our measurements of the ratio of the Rayleigh and Brillouin intensities obtained with an He–Ne laser light source and photoelectric detection. We discuss the experimental technique and the data-reduction procedure. The detection time constant was sufficiently short that contributions to the Rayleigh component from dust were distinguishable from true molecular scattering. The anomalously large central component for water which has been frequently reported in the literature was thus traced to residual dust contamination and was found to be less than 2% of the Brillouin-component intensity when dust was absent.
Kinetics of Rapid Reactions in Liquid Ammonia. The Ammonia—Amide Proton Exchange
Authors: Swift T. J. , Marks S. B. , Sayre W. G.
Published: January 2005

Highly purified liquid ammonia was prepared and the proton magnetic resonance spectrum was recorded as a function of temperature from about −70° to about 35°C. The line shapes were shown to be given quantitatively by the equation derived by Pople and precise values for the nitrogen—proton coupling constant and the transition probabilities connecting the 14N spin states were measured.

The Bloch equations pertinent to pure 14NH3 were extended to include the possibility of chemical exchange and a means was devised to extract precise values for the rate constants for the exchange process.

Solutions of KNH2 in NH3 were prepared by the decomposition of potassium—ammonia solutions with platinum black and the kinetics of the ammonia—amide proton exchange were studied as a function of temperature and concentration. The bimolecular rate constant for the exchange was found to be 1.51×107 liter/mole·sec at 25°C, the enthalpy of activation is 4.0±0.5 kcal/mole, and the entropy of activation is −12±2 eu.

This large negative entropy is interpreted in terms of a sizeable reorganization of the solvent structure in the activated complex.
Some Properties of the Quintet-State Carbon Atom
Authors: Lin Sheng Hsien
Published: January 2005

The oscillator strength of the transition 5S20 (2s2p3)↔3P2 (2s22p2) and the lifetime of 5S20 of carbon are calculated by using the wavefunctions obtained by Tubis. The results are f=0.3×10−6 and τ=4×10−3 sec. The hyperfine splitting of 13C in the 5S20 state is estimated as 3×103 Mc/sec.
Electron Spin Resonance of a Gamma-Irradiated Single Crystal of Barbituric Acid Dihydrate
Authors: Bernhard William , Snipes Wallace
Published: January 2005

Free radicals produced in single crystals of barbituric acid dihydrate by ionizing radiation have been identified by ESR spectroscopy and the parameters of the Hamiltonian describing the free radicals have been determined. The stable radical observed at room temperature is formed by loss of a hydrogen atom from C(5) of the original molecule, thus leaving an unpaired electron mainly in a 2pπ orbital on the carbon atom. Within experimental error, the free radicals have the same orientation in the crystal lattice as did the original molecules. Principal values of the g tensor characterizing the resonance were found to be gu=2.0044, gv=2.0056, gw=2.0022. Hyperfine interaction of the unpaired electron with the single hydrogen atom bonded to C(5) of the free radical splits the absorption into a doublet. Principal values of the hyperfine tensor were found to be Ax=11.2 G, Ay=30.0 G, Az=20.4 G. The principal axis systems for the g tensor and the hyperfine coupling tensor coincide. Two sets of satellite lines corresponding to changes in the spin states of one and two neighboring protons concurrent with the change in spin state of the unpaired electron were observed.
Thermal Conductivity of Argon in the Dense Gaseous and Liquid Regions
Authors: Rosenbaum B. M. , Oshen Steven , Thodos George
Published: January 2005

Thermal conductivities for argon in the dense gaseous state were determined at 6.2°, 20.7°, 25.0°, and 48.8°C for pressures up to 10 340 psia, using a coaxial cylindrical cell. These values were found to be in good agreement with thermal conductivities reported by others and when expressed as residual quantities, k—k*, unique relationships resulted with ρR and the (∂PR/∂TR)ρR. These relationships were independent of temperature and pressure and included both the dense gaseous and liquid states.

The Enskog equation for the effect of pressure on thermal conductivity,k/k*=bρ[(1/bρχ)+(6/5)+0.7574bρχ],,has been applied to the data of this study and of others for the dense gaseous and liquid regions, to obtain values of b. These values were found to be independent of pressure and to depend upon temperature as follows: bρc=1.06/TR23. For these calculations, bρχ values were established from PVT data for argon. The experimental values obtained in this study were used to determine (k/ρ)min for each temperature, which were used in conjunction with the Enskog equation to produce thermal conductivities at elevated pressures. Values calculated with (k/ρ)min produced an average deviation of 1.2%, whereas the values resulting from bρc=1.06/TR23 gave an average deviation of 2.0%.
Nuclear Spin Relaxation in Gases and Liquids. V. Liquid Hydrogen
Authors: Deutch J. M. , Oppenheim I.
Published: January 2005

The theory of nuclear spin relaxation in gases and liquids developed by Bloom and Oppenheim is applied to the liquid-hydrogen system. An explicit expression for T1 in terms of correlation functions of the anisotropic intermolecular potential is obtained. Two terms contribute to T1. The first term is independent of the ortho concentration and arises from the anisotropic potential that exists between an ortho molecule and a para molecule or the spherically symmetric part of another ortho molecule. It is suggested that three-particle correlations must be explicitly considered if one is to understand the magnitude and the temperature and density dependence of this term. The second contribution is linear in the ortho concentration and arises from the anisotropic potential between the asymmetric part of two ortho molecules (quadrupole—quadrupole interaction). Theoretical calculation of this term agrees remarkably well with experiment. It is found that a dynamical model of the molecular motions (CAA) is more satisfactory than a diffusion model (DCAA) in the calculation of the quadrupole—quadrupole interaction effects.
Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of the Free Radical CNN
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

Features appearing at 393, 1241, and 2847 cm−1 after photolysis of matrix-isolated cyanogen azide with 2100–2800-Å radiation are shown to exhibit parallel behavior. Isotopic data are consistent with the assignment of these three features as fundamentals of the free radical CNN, produced by the reaction of carbon atoms with molecular nitrogen. Ultraviolet absorptions at 4189 and 3964 Å can also be assigned to CNN. The force constants and thermodynamic properties of CNN have been derived. The carbon—nitrogen bond is found to have approximately triple-bond character and the nitrogen—nitrogen bond approximately double-bond character.
Trapped Electrons in γ-Irradiated 3-Methylpentane at −196°
Authors: Skelly David W. , Hamill William H.
Published: January 2005

The yield of solvent-trapped electrons in γ-irradiated 3-methylpentane at −196° was 0.75 per 100 eV when measured within a few seconds, and diminished to ∼0.6 after 3 min. The quantum yield for bleaching at 950 mμ decreased from 0.8 toward zero with progressive bleaching. Addition of 0.05% biphenyl maintained the quantum yield at >0.8 until more than 90% of the solvent trapped electrons had bleached. The initial quantum yield at λ>1.7μ was ∼0.01, both with and without added biphenyl. There is qualitative correlation between photobleaching and the rate of spontaneous decay.
Photoconductivity of Vitreous Zinc 9-Anthroate
Authors: Plessis L. A. du
Published: January 2005

Vitreous films of zinc 9-anthroate have p-type dark conductivity and photoconductivity and a high density of traps. The photoconductivity spectrum shows a single peak near the long-wavelength edge of the first absorption band. An explanation for this peak is that light of wavelength longer than that of the peak is weakly absorbed, while light of shorter wavelength penetrates only a short distance, producing high concentrations of charge carriers, which rapidly recombine.
Generation of Sound Waves in Liquids Accompanying Two-Photon Absorption
Authors: Rentzepis P. M. , Pao Yoh-Han
Published: January 2005

Depending upon the circumstances, the phenomena which accompany or are the consequences of two-photon absorption may be quite varied. The effects which have been reported to date are luminescence, internal and external photoelectric generation, and initiation of chemical reactions. In this paper, we point out that generation of sound waves may also be expected on a theoretical basis, and we present experimental results which we believe may have demonstrated this effect in liquids consisting of solutions of molecules such as benzanthracene and benzpyrene.
Calculation of Valence States of NO and NO+
Authors: Lefebvre-Brion H. , Moser C. M.
Published: January 2005

The excitation energies for all the valence levels of NO and NO+ have been calculated using approximate Hartree—Fock orbitals found for the ground states of these molecules. In addition spin—orbit coupling constants have been calculated for the 2Π valence states of NO using two different semiempirical methods. We conclude that the valence states which have previously been called ``L 2Π'' and ``P 2Π'' belong to the same electronic system. This is in agreement with the most recent experimental results. It appears likely that the limit of the β series in NO is a 3Π state.
Electron Paramagnetic Resonance Study of Solutions of Europium in Liquid Ammonia
Authors: Thompson D. S. , Hazen E. E. , Waugh J. S.
Published: January 2005

The electron spin resonance spectrum of a solution of Eu in liquid ammonia consists of a single line characteristic of the solvated electron and a complex hyperfine pattern which is shown to arise from Eu2+, 8S7/2 with a small admixture of excited states. T2 for the electron decreases sharply with increasing concentration in contrast with other metal—ammonia solutions, whereas the change in T2 for the Eu2+ is slight. The solutions decompose by a heterogeneous mechanism that involves strong adsorption on the walls of the container.
Kinetic Energies of Products of Ion—Molecule Reactions
Authors: Stanton H. E. , Wexler S.
Published: January 2005

The mean kinetic energies of the ionic products of the reactionsC2H4++C2H4→C3H5++CH3,C2H2++C2H4→C3H3++CH3,CH3++CH4→C2H5++H2have been measured in a mass spectrometer equipped with a cylindrical electrostatic energy analyzer. The translational energies observed in the center-of-mass frame of reference for Reactions (I), (II), and (III) were 0.085±0.05, 0.150±0.05, and 0.056±0.05 eV, respectively. The values are somewhat higher than the mean kinetic energies calculated from statistical theory by two different methods (one using the ``temperature'' approximation of Chupka, the other the semiclassical approximation of Klots), but for Reactions (I) and (III) the difference was less than the experimental error. For the collision complexes formed from these primary ions and molecules, the comparisons suggest that the fractions of the excitation energies that are partitioned among the translational modes of the dissociation products of the complexes are somewhat higher than the fractions estimated from a statistical theory that assumes complete equilibration of the excess energy among the many internal degrees of freedom of the complexes.

Mathematical procedures for examining the kinematics of the ion—molecule collisions and subsequent dissociations of the complexes are described. Included are methods for eliminating the effects of instrumental bias on the experimentally determined translational energies.
Nuclear Magnetic Dipole—Dipole Relaxation Along the Static and Rotating Magnetic Fields: Application to Gypsum
Authors: Look D. C. , Lowe I. J.
Published: January 2005

General formulas are derived for the spin—lattice relaxation times along the static magnetic field (T1) and the rotating field (T1r) due to magnetic dipole—dipole interactions. First-order perturbation theory is used in the calculation, and it is assumed that the spin system can be described by a temperature. The correlation functions that appear in these formulas are evaluated for the case of a spin system in which each spin has just two possible equilibrium positions. The results are used to improve Holcomb and Pedersen's calculation of dipole—dipole spin—lattice relaxation due to the motion of spin pairs that execute 180° rotational flips about their perpendicular bisecting axes. Applying the results to gypsum (CaSO4·2H2O) yields T1=43.4 msec at the minimum of the T1-vs-temperature curve for a static-field strength B0=2348 G. The experimental value is 47±4 msec. Similarly, the calculated minimum of the T1r-vs-temperature curve is T1r=1.86 msec for a rotating-magnetic-field strength B1=20.2 G. The experimental value is T1r=1.9±0.2 msec.
Semiempirical Treatment of Hindered Rotation in Simple Hydrides and Halosubstituted Ethanelike Molecules
Authors: Lowe John P. , Parr Robert G.
Published: January 2005

A semiempirical electrostatic model for internal rotation in certain molecules is developed from the integral Hellmann—Feynman theorem. The model is shown to be capable of rationalizing and predicting barriers to internal rotation in terms of well-established physical and chemical concepts. For simple hydrides containing only atoms from the first two rows of the periodic table (CH3NH2, CH3SH, etc.), the barriers to methyl rotation are shown to be correlated with the electronegativity of the heavy atom (N,S, etc.). Effects due to d and f character in bond hybrids appear to be important only for molecules containing atoms in Rows III and IV of the periodic table. The remarkably low internal-rotation barriers for acetylene derivatives are attributed to the polarizability of the triple bond. The model is consistent with observed changes of the barrier with fluorosubstitution in ethane and methyl silane when inductive effects are included. The sets CH3CH2X and CF3CH2X are examined, and barriers are predicted for SiH3CH2X molecules giving 1.99, 2.44, 2.45, and 2.32 kcal/mole for X=F, Cl, Br, I, respectively. Barriers are also predicted for SiH3CHF2 (2.00), SiH3CF3 (2.42), SiH3SiHF2 (0.85), and SiH3SiF3 (0.81). It is argued that disilane should have a barrier of 1.08 kcal/mole—lower than the barriers for ethane or digermane. The relationship between the shape and the physical source of the barrier is discussed. The model predicts V6≈−0.005V3 for molecules of the type considered. For ethyl fluoride, V6 is predicted to be −16 cal/mole compared to the experimental value of −15 cal/mole. The relations between this model and other theories of the barrier are briefly discussed.
Chemiluminescence in Molecular Beams. Electronic Excitation of Alkali Atoms in Exchange Reactions of Vibrationally Excited Alkali Halides
Authors: Moulton M. C. , Herschbach D. R.
Published: January 2005

Energy transfer by a chemical-exchange process, KBr†+Na→K*+NaBr (where † denotes vibrational excitation and * electronic excitation), has been observed in a ``triple-beam'' experiment. The KBr† was formed at the intersection of crossed beams of K+Br2 and entered a second scattering chamber containing a Na cross beam, where light emitted by K* was observed with a photomultiplier behind an interference filter. The cross section for the exchange process is estimated to be at least 10 Å2. The angular variation of the light intensity agreed precisely with the angular distribution of KBr measured (by a surface-ionization detector) in the same experiment. The light disappeared when propyl iodide was substituted for Br2 (as expected, since the K+PrI reaction exothermicity is well below the threshold for electronic excitation of K). An attempt was also made to observe the nonreactive exchange process, NaBr†+K→NaBr+K* (by interchanging the K and Na beams). However, this was obscured by background light arising from collisions of K with ambient Br2; at present it can only be concluded that the cross section appears to be <10% of that for the reactive exchange process.

The light yield from chemical exchange was about as large when the experiments were repeated with Br2 replaced by ICl. Thus the primary K+ICl reaction must give an appreciable yield of KCl (since the exothermicity is above the threshold for K excitation if KCl is formed but below if KI is formed). In this case, the light intensity falls off more rapidly at wide angles than the angular distribution of the alkali halide. This suggests that the primary reaction also forms KI which scatters mainly at wide angles, whereas the KCl scatters mainly forward with respect to the incident K atoms.
Thermal-Energy Ion—Neutral Reaction Rates. III. The Measured Rate Constant for the Reaction O+(4S)+CO2(1Σ)→O2+( 2Π)+CO(1Σ)
Authors: Fehsenfeld F. C. , Ferguson E. E. , Schmeltekopf A. L.
Published: January 2005

The rate constant for the reactionO+(4S)+CO2(1Σ)→O2+(2Π)+CO(1Σ)+1.5eVis measured to be 1.2±0.4×10−9cm3/sec in a pulsed flowing afterglow system. This reaction violates the Wigner spin-conservation rule and is probably the fastest such reaction to have been observed.
Fast Ion—Molecule Reaction in CO2
Authors: Paulson J. F. , Mosher R. L. , Dale F.
Published: January 2005

The production of O2+ by a second-order ion—molecule reaction in CO2 has been studied in a conventional mass spectrometer. Experiments are described designed to determine whether the O2+ arises from the reactions O++CO2→O2++CO or CO2+(2Σg+)+CO2→O2++2CO.
Hydrogen Bonding of Hydrazoic Acid in Solid Nitrogen
Authors: Pimentel George C. , Charles Stuart W. , Rosengren Kjell
Published: January 2005

The infrared spectrum of hydrogen bonded HN3 dimers in solid nitrogen has been determined. A dimer band at 387 cm−1, assigned to the torsional distortion of the hydrogen bond, indicates the dimer has an open, not a cyclic structure. The hydrogen bond bending force constant is 0.09 mdyn/Å. The hydrogen bond frequency shift in the N–H stretching mode is 150 cm−1, which, by comparison to similar systems, suggests a hydrogen bond energy of about 2 kcal/mole.

The infrared spectrum of monomeric HN3 casts doubt upon the earlier gas-phase assignment of ν6. According to the matrix spectrum, the band center is more likely to be near 588 cm−1.
Distortional Effects on the Ethane Internal-Rotation Barrier
Authors: Sovers O. J. , Karplus M.
Published: January 2005

The importance of vibrational deformations for the barrier to internal rotation in ethane is investigated. Simplified model calculations based on force constant data and empirical nonbonded potenlials yield an eclipsed structure that is more open than the staggered form. It is found that the HCC angle is increased by a few tenths of a degree and the carbon—carbon bond is elongated by a few hundredths of an angstrom. Although these changes in geometry are small, their effect on the internal-rotation barrier may be significant.
Optical Studies of the Photolysis of CO2 at 1470 Å
Authors: Young Robert A. , Ung Alban Y.-M.
Published: January 2005

Experiments have failed to detect radiation from O(1D) at 6300 Å in the photolysis of CO2 and O2 using 1470-Å radiation. From the observed rate of CO formation [which had been expected to equal the rate of O(1D) formation] and the sensitivity of the optical detection, it is concluded that insignificant amounts of O(1D) exist in photolyzed CO2 under these conditions. Measurements on O2 irradiated with 1470-Å light imply that O2 deactivated O(1D) with a rate coefficient greater than 10−12 cm3/sec. From an analysis of the photolysis of mixtures of CO+CO2, CO+O2, and CO+O2+CO2, it is determined that O(1D) complexes with CO2 (probably from CO3) with a rate coefficient greater than 10−12 cm3/sec, that CO3+CO is less than 20% as efficient as O(3P) in producing chemiluminescent radiation, and that O(1D) forms CO3 at least five times more rapidly that it is deactivated to O(3P) by CO2.
Statistical-Mechanical Properties of Small Systems in the Isothermal—Isobaric Ensemble
Authors: Salsburg Zevi W.
Published: January 2005

The exact N dependence is given for the first N − 1 virial coefficients calculated for a system with a finite number, N, of particles in the isobaric-isothermal ensemble. When the specific volume v=V/(N+1) is expanded as a power series in z=p/kT, it is shown that the first N − 1 coefficients are linear functions of (N+1)−1. The explicit results are given for the first six coefficients.
Thermal Diffusion in Almost Lorentzian Mixtures
Authors: Mason E. A. , Smith Francis J.
Published: January 2005

A new approximation is presented for the thermal diffusion factor of an almost Lorentzian gas mixture (m2/m1≪1, x1→1), which has better convergence properties than the Chapman—Enskog approximation. The results are given as the exact Lorentzian results plus correction terms in powers of the small quantity m2/m1. Numerical tables are given for the exp−6, 12–6, 9–6, and 28–7 potentials, and for repulsive exponential and screened Coulomb potentials. It is also shown that it is now possible to give simple formulas by which the thermal diffusion factor can be calculated accurately at all temperatures and compositions of ordinary interest, and for most values of the mass ratio. These formulas are summarized, and checked by comparison with experiment for He–Kr and He–Ar. Reversal of the calculation procedure gives a method for obtaining the ordinary diffusion coefficient from experimental measurements of the composition dependence of the thermal diffusion factor. Agreement with experiment is satisfactory.
Decomposition Processes and Fragmentation Probabilities of W(CO)6 by Electron Impact
Authors: Cantone B. , Grasso F. , Pignataro S.
Published: January 2005

The electron-impact ionization-efficiency curves (I.E.) of Group VI metal carbonyls and of their fragments show that competition can occur between different ionization and fragmentation processes. By analyzing these curves, the whole decomposition scheme of W(CO)6 has been obtained, although the processes involved happen too quickly to give metastable ions. A possibility of calculating the fragmentation probabilities pi as a function of electron energy is shown; for W(CO)6, this gives the information that all the pi have a similar trend in agreement with the proposed decomposition scheme involving only successive CO losses.
Photoconductivity in Rigid Organic Solutions. I. Phenomenology of the Photocurrents
Authors: Johnson G. E. , Albrecht A. C.
Published: January 2005

Dilute solutions of several benzene derivatives in 3-methylpentane solvent display three types of photocurrent when examined in their rigid, amorphous state at 77°K. There is the primary steady-state photocurrent seen only when illuminating in the absorption region of the solute molecule. Following ionization in this ``primary'' spectral region (and never before) two new induced signals are seen. One is characterized by a photocurrent spike which is excited in the near infrared or higher energies. It is a transient signal which, once destroyed at any wavelength, can be seen again only after further primary irradiation. The second induced signal appears to have a threshold in the near-ultraviolet region but at energies definitely below the onset of solute absorption. This signal is also basically transient. However, its decay is so slow compared to the decay of the spike signal, that it appears rather as a pseudo steady-state photocurrent. It is found that oxygen exerts its influence primarily on the spike signal with a strong quenching effect. A volt—ampere study is reported. At the higher fields Poole's law is seen to hold. Ohm's law holds at lower fields. The parameter characterizing Poole's law is shown to be independent of solute and wavelength of primary excitation. It rather reflects any given preparation of the rigid solid. The Poole's-law behavior can be removed by bathing the sample with near-infrared light during the volt—ampere studies. The Poole's-law behavior is also destroyed when the viscosity of the solid, at 77°K, is reduced by use of a two-component solvent. A model is discussed which succeeds in rationalizing these observations. Basic to the model is that (1) the charge carrier is the electron, (2) the solid matrix contains sites (neutral) which trap electrons so firmly that their thermal mobilization is negligible, and (3) the photoionized system contains, homogeneously dispersed, the long-range attractive Coulomb wells of the immobile cations—products of the photoionization, and (4) there is a very short-lived mobile state of the electron. To explain the volt—ampere behavior and viscosity effects, a substructure is assigned to the mobile state of the electrons. It is proposed that this state consists of electrons trapped somewhat deeper than kT which are thermally activated into a condition of ``maximum mobility'' — the closest condition to a conduction band in this amorphous solid. Sufficiently intense fields aid in the activation of these electrons to the state of maximum mobility, while reduced viscosity permits thermal saturation of this state by diminishing the shallow trap depths.
Long-Range (Retarded) Intermolecular Forces
Authors: Meath William J. , Hirschfelder Joseph O.
Published: January 2005

The Casimir and Polder retarded dipole—dipole energy of interaction between two ground-state (non-degenerate) atoms is expressed in terms of sine and cosine integrals. This result should be accurate for all interatomic separations R. In the range of moderately large separations (discussed in the preceding paper), where the charge distributions do not overlap and where R is small compared to λ/0=(αΔε)−1, the Casimir and Polder results can be expanded in the form Eint=R−6C6+α2R−4W4+α3R−3A+α4R−2B+···.This expansion is only accurate for R/λ/0<0.6. Here α is the fine-structure constant. The R−6C6 term is the usual London dispersion energy. The α2R−4W4 term was obtained in the preceding paper by taking the expectation value of the Breit—Pauli Hamiltonian using the wavefunction for the two-atom system corrected for the classical electrostatic dipole—dipole interactions. Thus, at least in the dipole—dipole approximation, the Breit—Pauli Hamiltonian gives the energy of interaction accurate through O(α2). For large values of R/λ/0, the interaction energy is expanded in the series Eint=α−1R−7D+α−3R−9F+α−5R−11G+···.This large R expansion is only accurate for R/λ/0>5.0.
Ultraviolet Fluorescent and Absorption Spectra of S2 Isolated in Inert-Gas Matrices
Authors: Brewer L. , Brabson G. D.
Published: January 2005

The 3Σu−←3Σg− transition of S2 has been observed in absorption in Ne and in fluorescence in Ne, Ar, Kr, Xe, and N2 matrices. The strongest bands observed in fluorescence belong to the (0, v″) progression as the result of rapid vibrational deexcitation of the 3Σu− state. T00=31 680, 31 350, 30 900, 30 780, and 31 480 cm−1, respectively, for S2 in the five matrices. Unlike the other matrices, argon yields very sharp fluorescent bands, having a width of 15 cm−1. The frequency of the forbidden infrared vibration transition has been calculated from the fluorescent data, and is found to differ from the observed infrared spectrum.
Approximate Self-Consistent Molecular Orbital Theory. III. CNDO Results for AB2 and AB3 Systems
Authors: Pople J. A. , Segal G. A.
Published: January 2005

The approximate self-consistent molecular orbital theory with complete neglect of differential overlap (CNDO) presented in earlier papers has been modified in two ways. (a) Atomic matrix elements are chosen empirically using data on both atomic ionization potentials and electron affinities. (b) Certain penetration-type terms, which led to excess bonding between formally nonbonded atoms in the previous treatment, have been omitted. The new method (denoted by CNDO/2) has been applied to symmetrical triatomic (AB2) and tetratomic (AB3) molecules, for a range of bond angles. The theory leads to calculated equilibrium angles, dipole moments, and bending force constants which are in reasonable agreement with experimental values in most cases.
Some New Applications of the FE Theory to the Spectra of Linear Unsaturated Compounds
Authors: Olszewski S.
Published: January 2005

A linear FE model with electron—electron and electron—core interaction appeared to be fairly accurate in reproducing the experimental data for (i) lowest excited singlet—triplet separation in polyenes, (ii) twisting frequencies of ethylene, and (iii) location of the absorption maxima in cumulenes. For calculations of (i) and (ii), electron—electron interaction has been assumed to play the dominant role. With the same assumption made, cis—trans isomerization of polyenes was found to be easier with long chains than with short. It also is easier about a central double bond in the chain than about an outer double bond. In the case of a single double bond, an important part of the energy path in isomerization is that for the triplet state; however, the role of triplet states in isomerization should diminish rapidly with an increase in the number of double bonds in the chain. With ethylene as the example, the effect of pi-electron correlations in the FE model was briefly investigated, and the correlation for the perturbation calculus of an order higher than the first was found to be in the FE model much less important than in the LCAO theory. No empirical parameters other than the fundamental atomic constants and the length of the FE path of a given molecule were used in the calculations.
Structure of Alpha GeTe
Authors: Goldak J. , Barrett C. S. , Innes D. , Youdelis W.
Published: January 2005

The parameters in the crystal structure of α-GeTe were determined by least-squares analysis of intensity data obtained with an automatic x-ray powder diffractometer. The rhombohedral cell containing 4 Ge and 4 Te atoms has a=5.996±0.001 Å, α=88.18°, and the single atom-position parameter x=0.237±0.002. The displacement of one sublattice with respect to the other from the relative position that would correspond to the NaCl structure (i.e., x=0.250) corroborates the predictions, based on band calculations, of Cohen, Falicov, and Golin.
On the Nonconfirmation of the Dual Emission Properties of Biphenylene
Authors: Hochstrasser Robin M. , McAlpine Robert D.
Published: January 2005

It is shown that the previously reported dual emission properties of biphenylene are most likely caused by an impurity that absorbs around 2800 Å, and emits fluorescence at 3000 Å and phosphorescence at 4100 Å.

The first two electronically excited states of biphenylene are discussed briefly in terms of low-temperature mixed-crystal studies in polarized light.
Kinetics of the Reaction D+H2=HD+H
Authors: Ridley B. A. , Schulz W. R. , Le Roy D. J.
Published: January 2005

The reaction D+H2=HD+H has been studied in the gas phase in the temperature range 274° to 468°K. By attributing the curvature in the Arrhenius plot to quantum-mechanical tunneling and interpreting the results in terms of absolute reaction rate theory the rate constant was given by the expression k3=3.63×1015T−12Γexp(−9.40×103/RT). The results obtained previously for the reaction H+p-H2=o-H2+H fitted the equation k1=1.18×1015T−12Γ exp(−9.21×103/RT). The tunneling factors Γ were calculated on the assumption of a truncated parabolic barrier and gave almost identical values for the force constant of the asymmetric stretching vibration of the complex. The results are compared with recent theoretical calculations.
Force Fields for Some Group VI Hexafluorides
Authors: Abramowitz Stanley , Levin Ira W.
Published: January 2005

The Coriolis zeta constants were determined for the infrared-active F1u modes of SF6 and TeF6 from gas-phase band contour measurements. The Coriolis data were applied toward determining the general force fields for thes Group VI hexafluorides.
Shock-Tube Determination of the C2(A 3Π→X 3Π) and CF(A 2Σ+→X 2Π) Band-System Oscillator Strengths
Authors: Harrington J. A. , Modica A. P. , Libby D. R.
Published: January 2005

Reflected-shock gas mixtures of C2ClF3, CF4, and C2F4 in excess argon were used to produce emission spectra of the C2(A 3Π—X 3Π) and CF(A 2Σ+—X 2Π) band systems. Absolute intensities of these electronic transitions were measured at several different wavelengths. Spectral data analyzed with equilibrium C2 and CF concentrations based on current JANAF heats of formation of the CF2 and CF radicals yielded for the Swan system the oscillator strength f(0, 0) in emission, 0.017±0.005 and for the CF system, 0.046±0.014. By reduction of the same data with recent shock-tube heats of formation, the oscillator strength f(0, 0) for the Swan system was 0.028±0.009 and that for the CF system, 0.0051±0.0015.
Ionization of Liquids by Radiation. I. Methods for Determination of Ion Mobilities and Ion Yields at Low Voltage
Authors: Hummel Andries , Allen A. O.
Published: January 2005

Experimental methods are described in detail for determination of ion mobilities and of the zero-field conductivity induced by irradiation of insulating liquids with x rays. The yield of separated ions is thereby obtained with an accuracy of ±11% and is found to be 0.10 ion pairs per 100 eV for hexane at 23°C.

The physical processes resulting from absorption of high-energy radiation are less well understood for liquids than for gases. Though it has long been thought that most ions produced in liquids disappear immediately by initial recombination, with only a small fraction of the excitation events leading to real charge separation, no actual measurement of the yield of separated charges was available when we first undertook to make this determination (late in 1961). From the magnitude of this value for different liquids and its dependence on temperature we may hope to deduce something about the behavior of slow electrons in liquids and the geometrical distribution of the radiation-induced electric charges.
Infrared Spectra of HCl, DCl, HBr, and DBr in Solid Rare-Gas Matrices
Authors: Mann D. E. , Acquista N. , White David
Published: January 2005

The infrared absorption spectra of HCl, H35Cl, DCl, HBr, and DBr isolated in solid rare-gas matrices in the range 4°—20°K are presented. The influence of temperature, dilution, deposition rate variations, as well as the presence of certain impurities, on the spectra are also reported and discussed.

In the fundamental region the spectra normally consist of a few relatively narrow bands or lines which show reproducible and fully reversible variation of intensity and bandwidth with change of temperature. The presence of certain dopants, e.g., N2, in the halide—noble-gas mixture leads, under suitable deposition conditions, to the replacement of the temperature-dependent features by much narrower temperature-insensitive lines at somewhat shifted frequencies.

The temperature-dependent features have been identified as individual rotation—vibration lines of the matrix-isolated diatomic molecules. Their separations are significantly less than those of the corresponding lines in the free molecule spectra, thereby indicating the existence of hindered molecular rotation in the matrix. The barrier to rotation is interpreted in terms of two different models for the molecule-lattice interactions and their limitations discussed.

The temperature-insensitive lines show no rotational structure, and are normally obtained when N2 or certain other dopants are present in the gas mixtures from which the matrices are formed at 20°K. They do not appear if the deposition is carried out at 4°K. It is suggested that the rotational quenching may be attributed to the formation of loose couples between halide and N2 molecules during the condensation process.
Microwave Spectrum, Vibration—Rotation Interaction, and Potential Function for the Ring-Puckering Vibration of Trimethylene Sulfide
Authors: Harris David O. , Harrington Howard W. , Luntz Alan C. , Gwinn William D.
Published: January 2005

The microwave spectrum of the ground and first four excited states of the ring-puckering mode of trimethylene sulfide has been observed and assigned. From an analysis of the perturbations to the rotational spectrum arising from the coupling of the internal angular momentum with the over-all rotation of the molecule, the separation between the lowest two vibrational levels was determined to be 8229 Mc/sec. Three mixed vibration—rotation transitions have been observed, and give the more accurate value of 8232.5±0.4 Mc/sec (0.27461 cm−1) for this separation. From the vibration—rotation interaction and the relative intensities of certain lines, the potential function governing the vibration has been determined to be 7.0207Q4−87.7581Q2 cm−1, where Q is the coordinate describing the vibration. The height of the barrier to the planar configuration is 274.2±2 cm−1. The agreement between the far-infrared spectrum that was calculated using this potential function derived from microwave data, and that which was recently observed by Borgers and Strauss, is very good.

On the basis of a dynamic model for the ring-puckering motion in which the atoms move along curvilinear paths with no bond stretching, the coupling constant between the over-all rotation and the internal angular momentum was calculated. It was found to be 170 Mc/sec compared to the experimental value of 176 Mc/sec. The importance of treating the vibrational dependence of the off-diagonal elements of the inertial tensor as being equivalent to vibrational angular momentum is stressed.
1
A
2←1A1 Transition of Formaldehyde
Authors: Henderson J. R.
Published: January 2005

The 1A2←1A1 system of HCHO is explained as vibronic transitions between the pure 1A1 ground state and an excited state which is a superposition of the 1A2, 1B1, and 1B2 states. It is shown that vibronic interaction through the ν4, ν5, and ν6 normal modes couples the excited electronic states. Through symmetry arguments, one comprehensive theoretical treatment explains the parallel bands as magnetic-dipole transitions between the ground state and the 1A2 component of the excited state, while the perpendicular bands are interpreted as transitions to the 1B1 and 1B2 components of the mixed excited state. Intensity ratios of Type B/Type A bands are explained quantitatively through calculations of excited-state vibrational wavefunctions.
Interaction of Thermal Electrons with Polarizable and Polar Molecules
Authors: Christophorou L. G. , Hurst G. S. , Hadjiantoniou A.
Published: January 2005

Drift velocities w were measured for thermal electron swarms traveling through gases and gas mixtures. The w data are used to calculate average cross sections for momentum transfer, σ's, which are assumed to have a v−1 and a v−2 dependence for nonpolar and polar molecules, respectively. An effort is made to correlate the experimental values of σ with the molecular polarizabilities and/or the molecular dipole moments. The theoretically predicted correlations are discussed and compared with our experiments. Simple theories of long-range forces agree reasonably well with the experimental data; the agreement between theory and experiment is better when the theory avoids the use of the Born approximation. Various factors proposed to account for the observed differences between the experimental data and the simple theory of short-range inductive forces are discussed, and the conclusion is drawn that detailed theoretical consideration must be given to each nonpolar molecule before agreement with experiments can be achieved.
Vibrational Spectrum of Methyl Arsine
Authors: Harvey Albert B. , Wilson M. Kent
Published: January 2005

The infrared spectra of CH3AsH2, CH3AsD2, CD3AsH2, and CD3AsD2 have been investigated from 250 to 4000 cm−1 in both the vapor and solid states. The Raman spectra of all four compounds in the liquid phase have been recorded. A complete vibrational assignment and normal coordinate calculation have been carried out. A large repulsion exists between the approximately degenerate pair of methyl wagging vibrations and the approximately degenerate twisting and wagging motions of the AsH2 group. The far-infrared spectrum of CH3AsH2 has a broad, weak band centered at about 185 cm−1 which is assigned to the torsional vibration.