bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermolecular Potential and Lattice Dynamics of the CO2 Crystal
Authors: Suzuki M. , Schnepp O.
Published: February 2004

The lattice dynamics of solid CO2 has been treated throughout the Brillouin zone. The molecular librational degrees of freedom have been treated by the use of Eulerian displacement coordinates. The potential model assumes the molecule represented by two centers of interaction (diatomic model) and each molecular pair interaction term is written as a sum of 6–12 terms between interaction centers on different molecules. The three parameters of the potential are obtained by fitting to the five optic modes, from the crystal energy, and by invoking the condition of zero uniform stress. It is found that the interaction between translational and librational degrees of freedom is large inside the Brillouin zone. The low temperature specific heat was calculated and found to agree well with experimental data. In an appendix, the applicability of the classical harmonic oscillator treatment to small molecular solids is discussed, and it is concluded that this approach is justified for solid CO2.
Vacuum-Ultraviolet Lasing Action Observed in CO: 1800–2000 Å
Authors: Hodgson R. T.
Published: February 2004

Stimulated emission has been observed on Q and R branch lines of five bands of the CO fourth positive group (A 1Π → X 1Σ+) in the wavelength range 1810–1970 Å. Superradiant 1.5-nsec 6-W pulses were produced using a Blumlein circuit parallel plate transmission line discharging through a tube containing carbon monoxide at 60 torr pressure. The order of appearance of the lines and their relative intensities are in agreement with a simple model. The model supposes single electron impact excitation of the ground state molecules to the lowest energy excited singlet state, followed by stimulated emission of those transitions of highest gain to the initially unpopulated, highly excited vibrational levels of the ground electronic state. No stimulated emission from highly perturbed rotational levels is seen.
Continuous Wave Carbon Monoxide Chemical Laser
Authors: Wittig Curt , Hassler J. C. , Coleman P. D.
Published: February 2004

A cw carbon monoxide chemical laser is discussed. Experimental results are given for a longitudinal flow system in which partially dissociated oxygen, in a helium carrier, is mixed with carbon disulfide in an optical cavity to produce vibrationally excited CO. Laser action occurs in highly excited vibrational levels of CO with the transitions originating from v=10 and v=9 being strongest. The system is analyzed using a static model with the result that the vibrational level pairs that exhibit the strongest laser action have average population densities that are roughly equal under lasing conditions. A dynamic model is proposed that invokes chemical excitation and V-V relaxation as the dominant excitation and relaxation processes, respectively. Calculations using this model explain limitations imposed on the system by the fluid mixing geometry and agree qualitatively with experiment.
Dissociative Excitation of Vacuum-Ultraviolet Emission Features by Electron Impact on Molecular Gases. II. N2
Authors: Mumma M. J. , Zipf E. C.
Published: February 2004

Atomic-nitrogen multiplets which radiate in the vacuum ultraviolet have been excited by electron impact on N2. Their excitation cross sections have been measured over the energy range from threshold to 350 eV. The transition arrays, mean wavelengths, and cross sections for dissociative excitation of these multiplets at 100 eV are: N (2p34S0−2p23s4 4P) 1200 Å− 6.70 × 10−18 cm2 ± 18%; N[2p3 2D0−2p2(1D)3s′2D] 1243 Å−1.45 × 10−18 cm2 ± 22%; and N (2p3 2D0−2p23s 2P) 1493 Å−2.53 × 10−18 cm2 ± 21%. In addition, the cross sections of the following multiplets have been measured at 100 eV only: N (2p3 2D0−2p24s 2P) 1177 Å−5.16 × 1019 cm2 ± 22%; N (2p3 2D0−2p23d 2D) 1164 Å−1.63 × 10−19 cm2 ± 23%.
Effect of Metastable O+(2D) on Reactions of O+ with Nitrogen Molecules
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2004

Laboratory measurements indicate that the metastable ions of O+ in reaction with N2 in the low-energy range (14 eV) react to form principally N2+, while the ion—molecule reaction to form NO+ has a very small probability. The ground-state O+ ion reacts mainly to form NO+. The abundance of metastable O+ 2D ions was determined using the observation that O+(2D)+N2 has a small cross section for forming NO+. The ion energy dependence for both reactions has been measured within the energy range 1.0–500 eV.
Theory of Semiclassical Transition Probabilities for Inelastic and Reactive Collisions. II Asymptotic Evaluation of the S Matrix
Authors: Connor J. N. L. , Marcus R. A.
Published: February 2004

The asymptotic evaluation of the integral representation for an S matrix element in a previously developed semiclassical theory of molecular collisions is considered. The integral representation is evaluated asymptotically by the method of Chester, Friedman, and Ursell to give a uniform approximation for the S matrix element which is valid for classically accessible and classically inaccessible transitions. The results unify and extend those previously derived, which were restricted to the simple semiclassical and Airy function cases. A comparison is made with the simple, Airy, and uniform semiclassical approximations that occur in Miller's semiclassical theory of molecular collisions. Although the starting point of the two theories is different, it is concluded that their asymptotic results are essentially identical. In addition, a simpler derivation of the integral representation for an S matrix element from the semiclassical wavefunction is given, one which avoids the use of Green's theorem.
Semiclassical Transition Probabilities (S Matrix) of Vibrational—Translational Energy Transfer
Authors: Wong W. H. , Marcus R. A.
Published: February 2004

Uniformized coordinates and an integral expression for the semiclassical S matrix, derived elsewhere, are described and applied to vibrational transition probabilities. The expression obeys microscopic reversibility. The numerical results are compared with the exact quantum mechanical results of Secrest and Johnson.
Electron Affinities from Endothermic Negative-Ion Charge-Transfer Reactions. II. O2
Authors: Tiernan T. O. , Hughes B. M. , Lifshitz C.
Published: February 2004

Electron-transfer reactions of negative ions were studied utilizing an in-line tandem mass spectrometer. Cross sections were measured as a function of translational energy for the reactions of D−, O−, S−, SH−, Cl−, Br−, and I− with O2. All of these reactions exhibit thresholds, their cross sections rising sharply with increasing energy above onset. The low energy tails of the electron-transfer cross sections which are observed are shown to be caused by Doppler broadening of the effective center-of-mass energy, owing to the thermal motion of the target molecules. Center-of-mass energy distributions were calculated for several of the reactions (O−, S−, Br−, and I−) using an approximate one-dimensional treatment of the collisions. These energy distributions were convoluted with various trial threshold functions, and the calculated curves were fitted to the experimental cross sections to obtain the true energy thresholds. Within the limits of error of this method, thresholds derived for the various reactions yield a consistent lower limit for the electron affinity of O2 of 0.45 ± 0.1 eV.
Intermolecular Potentials from Crossed Beam Differential Elastic Scattering Measurements. III. He+He and Ne+Ne
Authors: Siska P. E. , Parson J. M. , Schafer T. P. , Lee Y. T.
Published: February 2004

High-resolution differential cross sections for elastic scattering extending to wide scattering angles for He–He and Ne–Ne have been measured at two collision energies in the thermal range. The experiments were carried out by crossing two supersonic nozzle atom beams at right angles and detecting the atoms scattered in the plane of the beams with a rotatable electron-bombardment mass-filter universal detector. The results are analyzed to yield information on the interatomic potentials for these systems using a realistic and flexible potential function, and comparison is made with previously proposed potentials. For He2, a somewhat ``harder'' low-energy repulsion than that of most such potentials is inferred, while for Ne2 the potential well depth found is ∼ 30 % larger than earlier estimates and in good agreement with a preliminary spectroscopic finding.
Chemistry of Nuclear Recoil 18F Atoms. VI. Approximate Energetics and Molecular Dynamics in CH3CF3
Authors: Krohn Kenneth A. , Parks Norris J. , Root John W.
Published: February 2004

Energetics and molecular dynamics results are reported from an extensive set of high energy recoil 18F experiments with CH3CF3. Based upon thermochemical evidence alone, substantial fractions of the primary hot F-for-H, F-for-CH3, and F-for-CF3 reaction products are indicated to involve minimum excitation energies of 7.9 ± 0.2, 9.3 ± 0.1, and 3.5 ± 0.2 eV, respectively. The primary F-for-F reaction products in CH3CF3 do not exhibit unimolecular decomposition via a carbon—carbon bond scission mode in apparent violation of RRKM theoretical predictions. The primary F-for-H products decompose both via β elimination of HF and via carbon—carbon bond scission in apparent accord with theory. More than one kind of microscopic dynamics is involved in the primary hot F-for-H and F-for-CH3 processes in CH3CF3 and in the primary hot F-for-F process in CF4. Direct, concerted, and collusive dynamics are required for the higher energy reaction modes for these processes.
Expansion for the Quantum Second Virial Coefficient Using Hard-Sphere Basis Functions
Authors: Derderian Edmond J. , Steele William A.
Published: February 2004

Following the general approach to the calculation of the quantum second virial coefficient first developed by Wigner and Kirkwood, an expansion in powers of h2 is derived for B(T) using hard-sphere basis functions rather than the free particle functions used in the Wigner—Kirkwood calculation. A variational method is utilized to determine the hard sphere diameter that gives the best second virial coefficient. Computed values of B(T) which are presented here indicate that a considerable improvement over the Wigner—Kirkwood calculation is obtained, both in the direct (Boltzmann statistics) and in the exchange virial coefficient.
Long-Range Polarizability of the Helium Diatom
Authors: Certain Phillip R. , Fortune Patrick J.
Published: February 2004

The coefficients A6∥ and A6⊥ of R−6 in the long-range expansion of the helium diatom polarizability tensor have been computed with the result A6∥ = 60.09 a.u. and A6⊥ = 28.43 a.u.
On One-Dimensional Model for Exchange Forces
Authors: Damburg R. J. , Propin R. Kh.
Published: February 2004

A one-dimensional Schrödinger equation with the potential U(x) = (1 / 8R2)(x2 − R2)2 is considered. Asymptotic expansions for eigenvalues Eg,u = E0 ∓ 12ΔE for large R are presented. It is shown that the quantity ΔE obtained by means of the LCAO approximation exhibits incorrect behavior in the limit of large R. Comparisons of asymptotic formulae with results of numerical calculation are given.
Molecular Orbital Investigation of CF and SiF and Their Positive and Negative Ions
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

Accurate Hartree–Fock self-consistent-field wavefunctions have been computed for CF, CF+, and CF− at several internuclear separations by the Roothaan expansion method. Similar wavefunctions were also computed for SiF, SiF+, and SiF− at the parent molecule internuclear separation. A Dunham analysis of the energy curves for the three CF species yielded values for the spectroscopic constants. Other properties deduced in the present research include the first and second ionization potentials, electron affinities, and dipole and quadrupole moments for CF and SiF. The dipole moment calculated for CF is consistent with a charge distribution corresponding to a C−–F+ configuration. In addition, the correlation energies of a number of light-element diatomic fluorides have been deduced from literature data and from results given in the present paper. It appears that the correlation energy increment between adjacent diatomic fluorides is virtually constant for molecules of the first row of the periodic table.
Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First-Row Atoms
Authors: Dunning Thom. H.
Published: February 2004

Contracted [5s3p] and [5s4p] Gaussian basis sets for the first-row atoms are derived from the (10s6p) primitive basis sets of Huzinaga. Contracted [2s] and [3s] sets for the hydrogen atom obtained from primitive sets ranging in size from (4s) to (6s) are also examined. Calculations on the water and nitrogen molecules indicate that such basis sets when augmented with suitable polarization functions should yield wavefunctions near the Hartree–Fock limit.
Luminescent Piezoelectric CdSiP2: Normal Probability Plot Analysis, Crystal Structure, and Generalized Structure of the AIIBIVC2V Family
Authors: Abrahams S. C. , Bernstein J. L.
Published: February 2004

CdSiP2 is a typical member of the AIIBIVC2V family with chalcopyrite structure. The x-ray scattering for luminescent and nonluminescent material is essentially identical: The atomic order at the Cd and Si sites is at least 99.8% complete. The lattice constants of this tetragonal crystal are a = 5.680 ± 0.001 and c = 10.431 ± 0.003 Å at 298°K. The space group is I4̄2d, and there are four formulas per unit cell. A total of 2370 reflections from a nonluminescent crystal, and 2156 from a luminescent CdSiP2 crystal, were measured with PEXRAD. Least squares refinement, based on 320 symmetry-independent reflections from both crystals, led to a final agreement factor of 0.047. Normal probability plot analysis shows the least squares derived standard deviations to be underestimated by a factor of 3.0, and the two sets of measured structure factors to possess a small parallel bias. The bond angles about the Si atom do not differ significantly from the regular tetrahedral angle of 109.47°. Regular tetrahedral bond angles about Si were previously observed in ZnSiP2. The assumption that the BIV atom in all members of the AIIBIVC2V family maintains a regular tetrahedral valence angles leads to the relation: x = 0.5 − (c2 / 32a2 − 11 6)1/2, where x is the atomic coordinate of the CV atom at position x1418. The predicted interatomic distances for a wide group of family members are both internally consistent and in excellent agreement with measurement on ZnSiP2 and CdSiP2. The experimental Cd–P distance is 2.561 ± 0.002 Å, and Si–P is 2.247 ± 0.002 Å. The CdSiP2 characteristic temperature θ is 282°K, and representation is ΠPP(4̄2m).
Magnetic Rotation Spectra of the A 2Σ+ − X 2Πi Transition of OH and OD
Authors: Nanes R. , Robinson D. W.
Published: February 2004

The magnetic rotation spectrum of the (0, 0) band of the A 2Σ+ − X 2Πi transition of OH (3064 Å) and OD (3065 Å) was photographed at high resolution along with the Zeeman and zero-field absorption spectra. All twelve branches of both bands appeared with measurable intensities for the two magnetic fields used, 1300 and 2700 G. In each band the P1 and Q1 branches were the most intense, requiring only minutes of exposure compared to the four hours necessary for some weak branches. Several of the MRS lines (particularly in the OD spectra) revealed multiple structure where the individual Zeeman components appear unresolved in absorption. Interpretation was achieved by a computer-aided synthesis of the spectra. Calculations were based on the classical formulas for the dispersion of the refractive index and absorption coefficient near resonance, and thus included the effects of both magnetic optical rotation and circular dichroism. After corrections for instrumental broadening, the calculations gave good agreement with experiment.
Far-Infrared Collision-Induced Absorption in CO2. I. Temperature Dependence
Authors: Ho W. , Birnbaum G. , Rosenberg A.
Published: February 2004

Accurate measurements of collision-induced absorption in CO2 are made at a number of temperatures in the range from − 40 to 60°C in the wavelength region 7–250 cm−1. Direct evidence for the separation of the pure translational band from the rotational–translational band is obtained at all temperatures. This and other aspects of the band shape are discussed. Over the entire temperature range, the experimentally determined Kramers–Kronig integral is found to be in good agreement with the theoretical value, i.e., the static dielectric constant. This agreement is achieved only when the contribution of the quadrupole–quadrupole energy in the radial distribution function, of particular importance for CO2 because of its large quadrupole moment, is calculated accurately. A value of the quadrupole moment is obtained, (4.5 ± 0.2)10−26 esu, which is in satisfactory agreement with that obtained by the method of Buckingham and Disch, which does not depend on a knowledge of intermolecular force constants. Induction due to higher multipole moments and the overlap interaction is considered.
Calculation of Collision-Broadened Linewidths in the Infrared Bands of Methane
Authors: Tejwani G. D. T. , Varanasi P.
Published: February 2004

Anderson–Tsao–Curnutte theory of collision-broadened spectral lines has been extended to octopolar molecules, and the results are applied to the rotational lines in the ν3 band of methane. Calculated half-widths are in excellent agreement with the high-resolution measurements of Varanasi for self-broadening and broadening by N2, O2, H2, and He. The theory has also been applied to CO lines broadened by CH4 and to CH4 lines broadened by HCl. The excellent agreement with experimental data in both the cases leads to the estimate of Ω = 5.0 × 10−34esu·cm3 for the octopole moment of CH4.
Direct Calculation of First- and Second-Order Density Matrices. The Higher RPA Method
Authors: Simons Jack
Published: February 2004

We present a procedure for approximately determining the first- and second-order density matrices of pure-state N-fermion systems. A higher random-phase approximation is used to derive a method in which the resulting density matrices are approximated self-consistently in an iterative scheme. As test calculations, the method is applied to the ground states of the helium, lithium, and beryllium atoms. The possibility and importance of obtaining error bounds involving the density matrices are discussed.
Production of Light by Collisions of 2.5–490 eV He+ with N2: NI, N2+ Second Negative, and Unresolved Emissions between 1200 and 3200 Å
Authors: Holland Redus F. , Maier William B.
Published: February 2004

The production of light in collisions between He+ and N2 has been studied at primary ion energies, E, between 2.5 and 490 eV. Strong emissions are present between 1200 and 3200 Å, and spectra have been obtained for spectral resolutions between 1.5 and 16 Å. NI emissions, N2+ second negative (2N) emissions, and strong, unresolved emissions have been found. The total cross section for producing the emission between 1200 and 3200 Å is of the order of 10−16 cm2. For E <̃ 40 eV, the cross section for producing the unresolved emissions is greater than the cross section for producing the N2+(2N) emissions. The cross section for production of the NI emissions decreases with decreasing E and vanishes near the threshold energies expected for NI emission produced by He++N2→N++N+He. With decreasing E, total cross sections for the N2+(2N) and unresolved emissions increase. Apparent populations of the vibrational levels of the N2+(2N) parent state depend differently on E; in particular, for E = 490 eV the υ′ = 1 and 2 levels are the most highly populated, and for E = 4.5 eV the υ′ = 3 and 4 levels are the most highly populated. The electronic transition moment of the C 2Σu+ → X 2Σg+ transitions, which produce the N2+(2N) emissions, varies considerably with the wavelength of the emitted light.
Generalized Boltzmann Equation for Molecules with Internal States
Authors: Snider R. F. , Sanctuary B. C.
Published: February 2004

The general form of the Boltzmann collision operator is discussed. It is argued that this should be the natural transition (super-) operator for a binary collision that is defined analogous to the ordinary transition operator in collision theory. Properties of the collision term are discussed, in particular pointing out its general nonhermiticity and nondefiniteness as well as its behavior under parity, rotations, and time reversal. In general, there is no H theorem.
F-Aggregate Centers in Sodium Chloride. I
Authors: Jun Moo Jin , Neubert Theodore J.
Published: February 2004

Thermal aggregation of electron excess color centers in NaCl, x irradiated at 80°K, was studied by observation of changes in optical absorption in pulse annealing experiments. An initial 80 h x irradiation introduced large concentrations of F, F′ and positive hole centers. As annealing temperatures were raised (80 → 235°K) recombination of thermally released positive holes with electrons in F centers produced α centers. Thermal aggregation of F centers occurred above 240°K when α centers become mobile. M+ centers (F2+) form and disappear and M centers (F2) increase rapidly in number near 265°K as a result of the reactions F + α → F2+ and F2+ + e → F2. R+ centers (F3+) form by the reaction F2 + α → F3+ below 320°K and disappear slowly by the reactions F3+ + e → F3 and F3+ + heat → F2 + α, above 330°K. Optical absorption band maxima at 80°K are: M+, 1.22 eV (1015 nm); M1, 1.74 eV (713 nm); R+, 1.80 eV (690 nm); R1, 2.28 eV (543 nm) and R2, 2.07 eV (600 nm). N1 and N2 band systems were observed but were not studied in any detail. M+ centers also were formed by direct ionization of M centers by 300-nm light. The concentration, however, was low because of a counterbalancing of photoionization and electron capture processes. R+ centers were formed in x-irradiated NaCl by excitation with light absorbed in the R2 band. They could be transformed back to R centers by x-irradiation or F center bleaching.
Tracer Diffusion and Shear Viscosity for the System Isobutyric Acid–Water near the Critical Mixing Point
Authors: Allegra Joseph C. , Stein Arnold , Allen Guy F.
Published: February 2004

Tracer diffusion coefficients of 14C isobutyric acid in mixtures of isobutyric acid–water have been measured over the entire concentration range at ε = 3.9 × 10−4 above the critical point using the diaphragm cell technique. No anomaly was detected. The temperature dependence of the shear viscosity coefficient for mixtures of critical composition was determined over the temperature range 6.7 × 10−6 < ε < 2.8 × 10−2 by a closed capillary viscometer. These data were carefully analyzed in terms of a general power law equation. This analysis suggests that the excess viscosity may not diverge as the critical point is approached from the one-phase region. Severe rounding occurs for ε < 5 × 10−5.
ESR Study of Gamma-Irradiated Single Crystals of Potassium Bicarbonate at 77°K
Authors: Holmberg Robert W.
Published: February 2004

Several paramagnetic centers are formed when single crystals of KHCO3 or KDCO3 are gamma irradiated at 77°K. Their magnetic properties were studied using electron spin resonance. The two centers formed predominantly were identified as the free radicals (HCO3)2−·and ĊO33−. Lesser amounts of HCO3· were found trapped in two different sites in the crystal. When the crystals are warmed to room temperature (or when irradiated at room temperature), another radical with properties like ĊO2− is formed.
α-γ
Transition in Solid Nitrogen and Carbon Monoxide at High Pressure
Authors: Raich J. C. , Mills R. L.
Published: February 2004

We have examined the stability of the experimentally observed γ phase of solid nitrogen in order to test the validity of various forms of the intermolecular potential for N2. It was found that a Lennard-Jones repulsive potential between nonbonded atoms fails to explain the stability of the tetragonal γ phase, whereas a parametric, shape-dependent, hard-core potential gives a satisfactory account of this high-pressure phase of solid N2. The behavior of solid nitrogen-15 is discussed briefly. On the basis of the hard-core potential one would predict that a γ phase also exists for carbon monoxide, although at a very much higher pressure.
Effect of Rotation and Thermal Velocity on the Anisotropy in Photodissociation Spectroscopy
Authors: Jonah C.
Published: February 2004

In connection with photodissociative spectroscopy, where one studies the anisotropy of the velocity vectors of photodissociated fragments, one can derive an expression for the anisotropy of flux depending on the angle between the transition dipole moment and the direction of travel of the dissociated fragment. The formulas derived here correct the simple derivations for the effect of rotation and finite dissociation velocity. The loss of anisotropy for a finite velocity is proportional to the ratio of thermal energy to translational dissociation energy.
Study of the Anomalous Paramagnetic Relaxation Observed at Low Fields in a Kramers Pair Salt
Authors: Douglas E. C. , Davids D. A.
Published: February 2004

Measurements of the paramagnetic relaxation rate were made for various concentrations of Fe+++ ions in K3Co(CN)6 (0.2–1.0 at.%) at low-field values (60–650 Oe) and low temperatures (1.24 < T < 1.38 °K) using the direct-observation sampled-recovery technique. The results obtained were found to be concentration dependent and to display at the higher concentrations a double exponential dependence on time. This behavior is at variance with the single-ion Kronig–Van Vleck theory that has been shown to apply at higher fields. It is shown that this behavior can be attributed to the existence of numerous alternate relaxation paths that involve exchange coupled clusters of magnetic complexes.
Relative 14C–13C Kinetic Isotope Effects
Authors: Stern Marvin J. , Vogel P. Christian
Published: February 2004

Model-reaction calculations are used to show that relative 14C–13C kinetic isotope effects, defined as r=ln(k12/k14)/ln(k12/k13), should, within the framework of the presently accepted statistical-thermodynamic theory of such effects in the harmonic approximation, generally be restricted to the range 1.8≤r≤2.0. Significant deviations from this range may occur when the individual 14C and 13C kinetic isotope effects are of unusually small magnitude and/or are associated with easily detectable temperature-dependence anomalies. Reported cases of experimental values of r significantly outside the 1.8–2.0 range are examined with regard to the model-reaction calculations. It is concluded that, if the reported effects in four of the five such cases are real, additional complications, not considered in the basic theory as usually applied, must be operative. The results of this study are in accord with, and qualify only slightly, a conclusion reached by Bigeleisen almost two decades ago.
Interaction Second Virial Coefficients in Binary Systems
Authors: Khoury Fouad , Robinson D. B.
Published: February 2004

Interaction second virial coefficients of some binary gas mixtures are higher than either of the pure component values within certain temperature ranges. For other systems and temperature ranges the interaction second virial coefficient is lower than the pure component values. Conditions under which these situations may occur are investigated in terms of the intermolecular potentials and force constants, and examples from literature experimental data are given.
Self-Diffusion Coefficients and Rotational Correlation Times in Polar Liquids. II
Authors: O'Reilly D. E. , Peterson E. M.
Published: February 2004

Self-diffusion coefficients and rotational correlation times have been measured in several polar liquids by pulsed nuclear magnetic resonance techniques. Self-diffusion coefficients are reported for CH3OH, CH3NO2, (CH3)2CO, C6H5NO2, and C6H5Cl; proton, deuterium, and chlorine-35 relaxation times are given for these liquids. Deuteron quadrupolar coupling constants for the deuterated molecules were measured directly for the solids at low temperature. Methyl groups in CH3OH, CH3NO2, and (CH3)2CO have correlation times that are considerably shorter than the correlation time for the tumbling of the entire molecule. The Ivanov theory of large amplitude molecular jumps is generalized to the case of two kinds of jump about different axes and an explicit expression for the over-all correlation time is given. The pre-exponential factors of the methyl group correlation times appear to change drastically in CH3OH and CH3NO2 upon melting. Rotational correlation times for molecular tumbling are in good agreement with those calculated from quasilattice random flight model. In methanol there is evidence that rotation of the molecule about the OH bond direction occurs more rapidly than the over-all tumbling of the molecule. Molecular rotation also appears to be anisotropic in nitrobenzene as evidenced by a factor of 2 difference between the nitrogen and deuteron rotational correlation times. The pressure dependence of the intramolecular relaxation rate in C6H5Cl reported by Bull and Jonas is also shown to be in reasonable agreement with the prediction of the quasilattice model.
New Approximations to the Regular Solutions. I
Authors: Gokcen N. A. , Chang E. T.
Published: February 2004

It has been shown by the method of statistical mechanics that the existing first approximation to the regular solutions is incorrect. The correct approximation has been obtained by finding the distribution function for a given number of bonds between the unlike molecules in solution. Equations have been derived to represent the excess Gibbs energy (Gibbs free energy), enthalpy, and entropy of mixing of binary systems. Calculated and experimental results are compared to show the usefulness of derived equations.
Calculation of Chemical Reaction Rates by the R-Matrix Method
Authors: Crawford Oakley H.
Published: February 2004

The application of Wigner and Eisenbud's R-matrix theory to chemical reactions is tested by calculation of reaction probabilities in collinear H+H2 collisions. Conclusions are drawn concerning resonances, statistical reaction theories, and the calculation of reaction cross sections.
Spin Echoes in Multi-Half-Spin Systems: Demodulation and High Resolution
Authors: Tokuhiro Tadashi , Fraenkel Gideon
Published: February 2004

Carr-Purcell spin-echo (CPSE) experiments have been carried out with typical examples of homonuclear AX, homonuclear A3X, heteronuclear ABX, and homonuclear AA′XX′ systems respectively, in order to compare the recently developed theory with experiment. An examination of the theory has been undertaken to predict conditions when spin-echo patterns and the extraction of information therefrom are simplified. These involve two markedly different rf power levels. When H1 is high, at certain values of tcp (the time interval between adjacent 180° pulses), ``decoupling'' and ``double resonance'' of the CPSE have been demonstrated in a homonuclear AX system. For instance, in an AX system, when tcp is an integer multiple of 12 JAX the CPSE of the same sign show simple exponential decay instead of the usual modulated pattern. For intermediate rf power when H1 is of the same order as the internal chemical shift, a density matrix approach has been developed to choose experimental conditions when magnetically nonequivalent nuclei in homonuclear systems may be pulsed selectively. Under these conditions of high resolution, spin-echo experiments and theory for homonuclear AaXx systems show no modulation in both Aa and Xx groups. This provides a method for measuring separately T1 and T2 of chemically nonequivalent nuclei in the same molecule. Such experiments have been carried out on the title compounds. In dichloroacetaldehyde T2 for the aldehyde, hydrogen is independent of tcp, whereas T2 for the CHCl2 hydrogen varys with tcp. Furthermore, the T1's for the two protons are different. It is concluded that proton chlorine scalar coupling in the CHCl2 group is responsible for these effects. A similar effect takes place in 1-chloro-1-fluoroethylene.
Raman Spectra of the High-Temperature Phase of Polycrystalline NaBF4
Authors: Quist Arvin S. , Bates John B. , Boyd George E.
Published: February 2004

Raman spectral studies on polycrystalline NaBF4 at temperatures a few degrees above and below its phase transition at 245°C show abrupt changes in the splitting of the degenerate ν2 (e) and ν4 (f2) vibrational modes. The spectrum of the high-temperature solid phase indicates the presence of a highly symmetric effective field about the BF4− ion similar to that previously observed in melt spectra. A complete disordering of the fluoride ion positions must be assumed for the spectral results to be consistent with recent x-ray data on crystalline NaBF4 powders at 265°C which have been indexed in the hexagonal system.
Determination of Models for Collision-Induced Polarizability by the Method of Moments
Authors: Levine Howard B. , Birnbaum George
Published: February 2004

The form of the function giving the variation of the induced anisotropic polarizability with interatomic separation in a pair of interacting atoms is obtained by the method of moments. The spectrum of depolarized light in gaseous Ar, Kr, and Xe and the second Kerr virial coefficient of Ar, used to convert relative to absolute scattered light intensities, are used in this analysis. The coefficients in the model for the induced anisotropy, β (x)=(6A2σ−3) [x−3+(y/6) x−p], where A is the polarizability of a single isolated atom, σ is the atomic diameter, and x=r/σ, are for Xe, for example, p=9.6 and y/6=−0.957. These results clearly demonstrate that short-range interactions have an important effect on the induced anisotropy.
Argon Matrix Infrared Spectrum of the ClO Radical
Authors: Andrews Lester , Raymond James I.
Published: February 2004

The matrix reaction of dichlorine monoxide with alkali metal atoms at high dilution in argon produces absorptions due to the appropriate alkali metal chlorides and bands near 995 and 850 cm−1 which show the calculated oxygen isotopic shift for a ClO diatomic species and are independent of the alkali metal used to generate the reaction. The 995-cm−1 feature has an appropriate chlorine isotopic counterpart for ClO. Experiments altering the concentrations of Cl2O and lithium atom reactants identify the 995-cm−1 absorption as the vibrational fundamental of ClO and the 850-cm−1 band as ClO perturbed by another molecule, perhaps the Cl2O precursor. This assignment is consistent with the conclusions of earlier matrix isolation studies of ClO species. The high Cl–O force constant in the chlorine oxide free radical is rationalized in terms of (p–p) π bonding.
Electron Spin Resonance of a Trinuclear Vanadyl Pyrophosphate Complex
Authors: Hasegawa Akinori
Published: February 2004

Vanadyl pyrophosphate (1:1) complex was revealed to be trinculear with a formula of Na6(VOP2O7)3· 12H2O by measurements of ESR, magnetic susceptibility, and molecular weight. The ESR spectrum of the aqueous solution consists of 22 lines at intervals of about 36.4 G and has a g value of 1.966. This spectrum was in good agreement with that predicted theoretically for the trinculear complex with three unpaired electrons coupled by spin exchange interactions. A ring model was proposed to be the most probable one for the complex.
Dissociative Excitation of O2 in the Vacuum Ultraviolet by Electron Impact
Authors: Ajello Joseph M.
Published: February 2004

The emission cross section of the 1304-Å resonance triplet (3S0→3P) of atomic oxygen produced by dissociative excitation of O2 by electron impact was measured from threshold to 300 eV. The peak cross section is at 100 eV with a value of 3.00×10−18 cm2. The relative emission cross section of the 1356-Å multiplet (5S0→3P) of atomic oxygen was also determined. The peak cross section for the 1356-Å multiplet at 100 eV is at least 1.65×10−18 cm2.
Temperature-Dependent Raman Study and Molecular Motion in l-Alanine Single Crystal
Authors: Wang C. H. , Storms R. D.
Published: February 2004

Spectral line intensities and shapes of Raman lines in an oriented single l-alanine crystal were studied in detail at temperatures ranging from 120 to 300°K. It has been found: (1) Although most of the vibrational modes are polar, the effects of long-range electrical force on the internal vibration modes are not large. For the lattice modes, the electric dipolar interaction tends to induces coupling between modes of different symmetries; (2) the molecular configuration of an l-alanine molecule in crystal remains unchanged in the 120–300°K temperature range although crystalline strain and ahnarmonic interaction between molecules significantly affect the Raman spectral lines; (3) for temperature above 220°K, the line shape of the −NH3+ torsional mode becomes a sensitive function of temperature. The linewidth study of this mode shows that the breaking of a second H bond is an important mechanism for broadening the torsional mode at T above 220°K.
Electron Paramagnetic Relaxation and EPR Line Shapes of Manganous Ion Complexes in Aqueous Solutions. Frequency and Ligand Dependence
Authors: Reed George H. , Leigh John S. , Pearson John E.
Published: February 2004

Line shapes of electron paramagnetic resonance spectra of manganous ion in various ligand environments have been examined at two microwave frequencies, 9.1 and 35 GHz. From the observed differences in line shape at two microwave frequencies and the theoretical expression for relaxation of sextet state ions, the correlation times for processes modulating the zero-field splitting (zfs) interaction and the magnitude of the effective zfs were evaluated. For all complexes which were examined the correlation times were in the range 3×10−12−9×10−12sec at 300°K. Two types of zfs are distinguished, a transient zfs which is related to the relaxation processes and a static zfs. In this regard there appears to be no simple relation between the transient zfs as obtained from relaxation studies and the static zfs as obtained from solid-state spectra. The large static zfs for MnEDTA gives quasi-solid-state features to the solution EPR spectra of this complex.
Radio-Frequency Spectrum of Phosphine (PH3)
Authors: Davies P. B. , Neumann R. M. , Wofsy S. C. , Klemperer W.
Published: February 2004

The electric resonance spectrum of phosphine (PH3) was measured at zero electric field for three rotational states, J=4, 5, and 7 with K=3. In addition, the J=K=2 and J=K=1 spectra were observed at several values for the electric field. The dipole moment (debye) is 0.57395±0.0003. The magnetic hyperfine constants (kilohertz) are cα=−114.90±0.13, cβ=−116.38±0.32 for the spin—rotation interaction of the 31P nucleus, and ζ α=8.01±0.08,ζβ=7.67±0.19 for the spin—rotation interaction of the 1H nuclei. The α constant is the mean interaction in the x and y directions, and the β constant is the interaction about the molecular z axis. No inversion doubling was observed (Δ〈1 kHz). The K=3 levels have K-doubling fine structure as predicted by Nielson and Dennison, but the magnitude does not agree with their formula.
Trapped Electron in the Irradiated Single Crystal of Ice Doped with Some Impurities: Its Formation and Photobleaching at 77°K
Authors: Kawabata Keisuke
Published: February 2004

It is found that single crystals of ice doped with 10−4–10−2M ammonium fluoride and alkali fluoride color considerably by gamma ray irradiation at 77°K. Their spectra all are the same as the one in the pure crystal (the peak is at 6400 Å), and the largest optical density is about 6 times as high as that in the pure crystal. These enhanced absorptions represent an increase of the concentration of the trapped electrons in the doped samples. D2O crystals doped with NH4F show a similar increase, having the same spectrum as that in pure D2O crystal (the maximum yield is about 10 times of that in the pure H2O crystal). The increased electrons are not due to those produced in the locally amorphous parts. Other samples doped with such impurities as NH4Cl, NH4OH, KCl, NaOH, etc., do not show such coloring. Trapping sites for these electrons are considered. Photobleaching of the pure and the doped crystal shows simple and uniform decays and the original spectrum is almost unchanged by the stimulation at any wavelength. The spectrum represents only one species trapped in one definite form of potential. The trapped electron in the pure and the doped crystal show a low bleaching efficiency for the wavelength corresponding to the peak of the spectrum. Wavelength dependence of the bleaching quantum efficiency shows a steep rise from roughly 5000 Å to the higher energy side. The peak of the optical absorption spectrum is a transition to the bound state. The asymmetrical tail in the high energy side of the spectrum corresponds to the transition to the higher excited levels, bound or in the continuum.
Infrared-Active Optical Phonon Vibrations in Anhydrous Lanthanide Chlorides and Bromides
Authors: Basile L. J. , Ferraro J. R. , Gronert D. , Quattrochi A.
Published: February 2004

Twelve anhydrous lanthanide chlorides and eleven anhydrous lanthanide bromides have been investigated in the far-infrared region, and the infrared-active optical phonon modes determined. The number of experimentally found infrared-active optical phonon vibrations show close agreement with the number of vibrations predicted by solid-state selection rules. The far-infrared regions are observed to be diagnostic for the particular structural type involved. Spectroscopic results are in agreement with x-ray studies for these substances.
Partial g-Sum Rule, a Tool for Interpreting Impurity Ion Spectra
Authors: Karayianis N.
Published: February 2004

It is shown that one can define signed g∥ for spaces of atomic wavefunctions characterized by the crystal quantum numbers μ and −μ if these spaces are disjoint with respect to the crystal field interaction. In general, the states in these spaces will be pairwise degenerate and will be split by a magnetic field along the axis of symmetry of the crystal. Within a Russell—Saunders approximation, traces of the Zeeman interaction for each q, μ pair in a given JLS multiplet are calculated, where q is related to the q-fold field of the point group symmetry of the crystal field. The partial g-sum rule, that these traces are approximately invariant even when substantial term and J mixing are present, is tested by comparing various g sums to theoretical and experimental results reported in the literature. It is shown that the partial g-sum rule provides a useful tool that can aid in the analysis of spectra without resorting to involved calculations. Examples of such applications are discussed, and tables are given for the partial g sums for each q, μ pair over every J multiplet of the terms in pn, dn, and fn configurations.
Reactions of Metastable Nitrogen Atoms
Authors: Lin Chorng-Lieh , Kaufman Frederick
Published: February 2004

The line absorption technique was applied to the kinetic study of the two metastable atomic nitrogen states N (22D) and N (22P) in a flowing afterglow system. The optical absorptions of the NI 1493-Å (2p32D−3s2P) and 1743-Å (2p32D−3s2P) transitions were used for the quantitative measurement of N (22D) and N (22P) concentrations. Deactivation of N (2D) and N (2P) by the Pyrex tube wall was found to be very efficient, i.e., occurs at nearly every collision. The second-order rate constants at 300°K for the removal of N (2D) by O2, N2O, CO2, NO, N2, Ar, and He were found to be (6±2)×10−12, (3.5±1.2)×10−12, (5±2)×10−13, (7±2.5)×10−11, (1.6±0.7)×10−14, (1±0.6)×10−16, and ≤ 1.6×10−16 cm3 sec−1, respectively. It was established that the process for the first three reactant gases results in chemical reaction rather than physical quenching.
Isomeric Forms of Dinitrogen Trioxide in a Nitrogen Matrix
Authors: Varetti Eduardo L. , Pimentel George C.
Published: February 2004

When dinitrogen trioxide is formed in a nitrogen matrix, it displays a vibrational spectrum very similar to that of the gas-phase, asymmetrical molecule (asym-N2O3). On near-infrared irradiation at 20°K, however, this structure is converted into an isomeric form with absorptions at 1689.7, 1661.0, 969.4, 704.3, 387.4, and 365.5 cm−1. Both 15N and 18O labeling show that this isomer (sym-N2O3) has conventional, nitrite-like bonding and an extended, symmetric configuration, O=N–O–N=O. The spectral region responsible for the matrix-photolytic conversion of asym-N2O3 into sym-N2O3 is 7000–9000 Å, a region in which asym-N2O3 absorbs (maximum, near 7200 Å). The sym-N2O3 can be converted quantitatively back into asym-N2O3 through irradiation in the ultraviolet region, 3700–4800 Å. Ultraviolet absorption features at 3630, 3810, and 3980 Å appear in the spectra of matrix samples during infrared-photolytic production of sym-N2O3. These features disappear during the ultraviolet conversion of sym-N2O3 back into asym-N2O3, so they are assigned to sym-N2O3; they must account for this ultraviolet photolytic process. Through bond energy arguments, the symmetric nitrite-like structure of sym-N2O3 is judged to be no more than 5± 10 kcal less stable than the asymmetric form.
Geometry and Infrared Spectra of Matrix-Isolated Rare-Earth Halides. I. LaF3, CeF3, PrF3, NdF3, SmF3, and EuF3
Authors: Wesley R. D. , DeKock C. W.
Published: February 2004

The infrared absorption spectra (40–800 cm−1) of the trifluorides of lanthanum, cerium, praseodymium, neodymium, samarium, and europium isolated in solid argon, krypton, and nitrogen matrices have been obtained. For LaF3, CeF3, SmF3, and EuF3 only the asymmetric stretching mode and the bending modes were observed; these molecules are assigned a planar configuration. For PrF3 the symmetric and asymmetric stretching modes were observed together with the bending modes; PrF3 is accordingly assigned a pyramidal configuration. At present the spectrum of NdF3 cannot be satisfactorily interpreted, but a number of possibilities are explored. Using a valence force field approximation, force constants have been derived from the measured fundamental frequencies and the infrared-inactive symmetric stretching frequency of the planar molecules has been estimated. Statistical entropies have also been calculated from the vibrational data and molecular geometries and are compared with third-law values.
Self-Consistent Field Theories of the Polymer Excluded Volume Problem. I Edwards' Functional Integral Approach
Authors: Freed Karl F.
Published: February 2004

Edwards' formal function integral approach to the polymer excluded volume problem is reinvestigated in order to further elucidate the underlying simple physical principles and to generalize the results. The functional integral representation is shown to be equivalent to a hierarchy of equations which resembles the standard many body problems. Edwards' self-consistent field (SCF) theory of excluded volume follows upon introduction of the appropriate Markovian approximation into the lowest member of the hierarchy. The use of this approximation in the next member leads to a SCF theory which is almost identical to that which follows from Reiss' variational approach. These two approximations are also directly obtained from the functional integral representation where special emphasis is placed upon showing how the chain end point(s) become(s) the origin(s) of the SCF. Comparisons are made between the results of these formal theories and both Reiss' approach and some diagrammatic approaches to the polymer excluded volume problem.