bluuebunny/crossref_metadata_2025 huggingface dataset:
Two center variationally determined scattering amplitudes
Authors: Lurie B. N. , Rosenthal C. M.
Published: February 2003

Varitionally determined elastic scattering amplitudes arising from the interaction of a structureless particle with two separated Yukawa force centers are reported in this study. The parameters involved include R, the vector separating the centers; k02/2, the energy of the particle; kj and kf, the wave vectors of the incoming the outgoing particles, repsectively; and g, the interaction strength. Numerical values for the T matrix elements are tabulated and plotted for a variety of these parameters. Comparison is also made with three other nonvariational approixmations to this problem.
Fluorine-19 FT–NMR studies of CF3-containing systems dissolved in smectic liquid crystal solutions
Authors: Montana Anthony J. , Appleman Bernard R. , Dailey Benjamin P.
Published: February 2003

The fluorine-19 shielding anisotropies of CF3Cl, CF3Br, CF3I, and CF3CCl3 have been determined from analyses of fluorine NMR spectra in partially ordered smectic liquid crystal solutions. The high degree of orientation and increased solubility produced in the smectic phase leads to measurements of σ∥−σ⊥ for each of these systems to relatively high accuracy. The anisotropies obtained for the trifluorohalomethanes are found to increase in the order: CF3Cl, −13.4±0.5 ppm; CF3Br, 2.7±0.3 ppm; CF3I, 16.8±0.2 ppm. The quantity σ∥ is approximately constant for each of the CF3X molecules studied. This feature permits an estimate of the shielding and spin–rotation constants of CF4.
Analysis of torsional spectra of molecules with two internal C3v rotors. II. Far infrared and low frequency Raman spectra of dimethylether isotopes
Authors: Groner P. , Durig J. R.
Published: February 2003

The torsional far infrared and Raman spectra of gaseous CH3OCH3, CD3OCH3, and CD3OCD3 are presented. They are analyzed using a computer program which is based on the results of an extensive investigation of the isometric groups and of the symmetry groups of the rotation–internal rotation Hamiltonians of a series of semirigid two-top models. Four or more Fourier coefficients of the potential functions in two variables could be determined for each isotope. Strong evidence was found for Fermi-resonance-type interactions with the COC bending mode.
Rotational relaxation times for benzene-h6 and -d6 in very viscous media at 77 K
Authors: Durnick T. J. , Kalantar A. H.
Published: February 2003

Phosphorescence lifetime and polarization measurements have been made for C6H6 and C6D6 in a range of 3-methylpentane/2-methylbutane glasses at 77 K. The rotation times about the in-plane axes are, within experimental error, independent of isomer and consistent with comparable data. The rotation time in 3-methylpentane is long (≳200 s). No photo-orientation effects are found. The possibility of phosphorescence depolarization is discussed for various other processes resulting in a net rotation.
Mixed crystal spectroscopy of 1,3-diazaazulene
Authors: Small G. J. , Burke F. P.
Published: February 2003

The 4500 Å 1B1?1A1 absorption and fluorescence systems of 1,3-diazaazulene are analyzed in three host crystals, naphthalene, quinazoline, and p-dichlorobenzene. Extensive vibronic coupling activity by a1 and b1 fundamentals is discussed in terms of the assignments for the higher energy excited states. The mirror symmetry breakdown between the absorption and fluorescence spectra is marked and while the fluorescence spectrum is medium independent, a portion of the totally symmetric vibrational structure in the absorption spectrum is strongly dependent on the medium. The overall mirror symmetry breakdown is attributed to both intrastate and interstate Duschinsky excited state normal coordinate rotations, interferences between allowed and forbidden transition moments, and the vibronically induced moving level effect.
High kinetic energy N+ ions from decay of doubly ionized N2
Authors: Stockdale J. A. D.
Published: February 2003

N+ ions from the process e+N2→N22++3e→N+ +N++3e have been searched for by a coincidence method in which N+ ions were detected at 90° to crossed N2 and pulsed electron beams. Measurements were made for incident electron beam energies of 100, 150, and 300 eV. At electron energies of 150 and 300 eV, a comparison of calculated accidental and measured coincidence time-of-flight distributions indicates the presence of N+ ions with kinetic energies in the region from 5 to 14 eV from the double ionization process above.
Luminescence and hydrogen bonding in quinoline and isoquinoline
Authors: Anton Mary F. , Moomaw William R.
Published: February 2003

A purification scheme has been developed which is capable of separating the two isomers quinoline and isoquinoline. The emission spectra of the purified compounds were measured at 77 K in a 3-methylpentane (3MP) glass and in a 3MP glass with small amounts of hydrogen bonder added. The hydrogen bonders used were hexafluoroisopropanol (HFIP), trifluoroethanol (TFE), and absolute ethanol (EtOH). An upper limit on the ratio of fluorescence to phosphorescence quantum yields has been set at 20 ppm for quinoline in 3MP, which is 1–2 orders of magnitude smaller than previously reported. Isoquinoline still fluoresces in 3MP, which we believe to be caused by a residual hydrogen bonder not removed by the purification scheme. The excitation and lifetime data obtained suggest that the phosphorescence in these compounds is originating in a nonhydrogen-bonded species, while the fluorescence is originating in a hydrogen-bonded species, regardless of solvent. A new emission has also been detected in the presence of small amounts of hydrogen bonder. This violet fluorescence is believed to be the result of an excited state protonation of the heterocycle. The ground state is believed to be nonprotonated, but strongly or ’’closely’’ hydrogen bonded. A summary of impurity induced absorption and luminescence data obtained by other authors is included to help clarify the spectral properties of quinoline and isoquinoline.
Far infrared magnetic resonance in FeSiF6⋅6H2O and Fe(SPh)42−
Authors: Champion P. M. , Sievers A. J.
Published: February 2003

The technique of far infrared magnetic resonance is used to investigate the zero-field splittings of the spin quintet associated with the lowest orbital state of high-spin ferrous iron. Two examples are discussed in detail: the ’’axial’’ compound, ferrous fluosilicate, and the ’’rhombic’’ compound, tetrakis thiophenolate Fe(II). The data are analyzed within the context of the spin Hamiltonian, and values of D and E are directly obtained from the spectra using a closed form solution of the eigenvalue problem. The application of this technique to the high-spin ferrous forms of biomolecules such as the heme and iron-sulfur proteins is also discussed.
Localization in exchange perturbation theory
Authors: Chipman Daniel M.
Published: February 2003

A new formalism is developed for exchange perturbation theory by applying a localization criterion to remove much of the arbitrariness associated with the definition of the primitive wavefunction. In contrast to Adams’ method, which is based on a certain energy-related localization, our prescription is based on a direct spatial localization of the primitive function by maximizing its overlap with a given reference function. If our primitive function is constrained only by requiring that one of its symmetry projections yield an exact eigenfunction, then the wavefunction and energy coincide through first order with that of the Eisenschitz–London (EL), and Hirschfelder–van der Avoird (HAV) methods, and through the second order with the Murrell–Shaw–Musher–Amos (MSMA) method, while differing in the third and higher orders. If, instead, the primitive function is constrained by requiring that all of its symmetry projections yield exact eigenfunctions, then it coincides in first order with that of the Distinguishable Electron Method (DEM) developed by Kirtman and co-workers. Our analysis then provides a new justification of the first order terms in the EL–HAV, MSMA, and the DEM expansions, and of the second order terms in the MSMA expansion, and also provides soundly based extensions to higher orders.
ESR and ENDOR studies on the structure of primary oxidation products in irradiated α-amino acids
Authors: Muto Hachizo , Iwasaki Machio , Takahashi Yukiko
Published: February 2003

Combining the ESR and ENDOR techniques, the primary oxidation products responsible for the complex ESR spectra of irradiated single crystals of α-glycine and α-aminoisobutyric acid have been identified as deprotonated cations formed from loss of one electron and one of the amino protons. For both the α-amino acids, the species preserves the geometry of the main frame of the undamaged molecule except for the amino proton, which is supposed to be transferred to the neighboring CO2 group through the shortest hydrogen bond. Although the chemical structure of the species is H2NCH2CO2 for glycine and H2NC(CH3)2CO2 for α-aminoisobutyric acid, the unpaired electron is delocalized over the main molecular frame and occupies the in-plane orbitals. The electronic nature of the species may be represented, say for glycine, by the superposition of [H2N+=CH2]CO2 ⋅−, [H2N⋅⋅⋅CH2]CO2, H2Ṅ+—CH2CO2 −, and H2N–CH2–C〈OO⋅. The species exhibits a characteristic negative g shift because of the contribution from the first electronic structure. The similarity of the g shift suggests that the oxidation product in α-alanine possess essentially the same structure.
Vibrational deactivation and atom exchange in O(3P)+CO(X 1Σ+) collisions
Authors: Kelley J. D. , Thommarson R. L.
Published: February 2003

A quasiclassical Monte Carlo averaged trajectory study of the ground-state O, CO collision system is presented. An ’’effective’’ adiabatic potential surface is constructed using pertinent theoretical and experimental data. Vibrational deactivation rates for CO(v=1, 3) and atom exchange rates for CO(v=0, 1, 3) are calculated and compared with experimental data. The high-temperature (400 K<T<2000 K) and low-temperature (270 K<T<400 K) CO deactivation data, and the low-temperature (300 K<T<400 K) atom exchange data are all fit reasonably well by the calculation. However, comparison of the deactivation data to the atom exchange data suggests that at temperatures below 400 K an additional nonadiabatic mechanism may be contributing to the overall deactivation rate.
Microwave spectra of 13CH3 12CD3 and 12CH3 13CD3 and the C–C bond length of ethane
Authors: Hirota Eizi , Matsumura Keiji , Imachi Misako , Fujio Mizue , Tsuno Yuho , Matsumura Chi
Published: February 2003

We observed the J=2←1, K=1 transitions of two doubly labeled ethanes 13CH3 12CD3 and 12CH3 13CD3, which were contained in natural abundance in a CH3CD3 sample. The measured frequencies were subsequently made more accurate using enriched samples. Assuming the centrifugal distortion constants DJ and DJK, which were determined for 12CH3 12CD3, we calculated the B0 constants to be 16 088.428±0.030 and 16 251.914±0.030 MHz for 13CH3 12CD3 and 12CH3 13CD3, respectively. By combining these with the B0 of 12CH3 12CD3(16 474.438±0.030 MHz), we derived the rs distance of C–C to be 1.526131±0.000083 Å, where the error was due to uncertainties of the rotational constants. We also calculated the rz(C–C) distance to be 1.5312 Å in 12CH3 12CD3 by transferring Kuchitsu’s rz(C–H), rz(C–D), ϑz(CCH), and ϑz(CCD). We evaluated the dipole moments of the two species from the Stark effects to be 0.01067±0.00010 D and 0.01094±0.00011 D for 13CH3 12CD3 and 12CH3 13CD3, respectively, which were to be compared with 0.01078±0.00009 D of 12CH3 12CD3.
Hyperpolarizabilities of the nitroanilines and their relations to the excited state dipole moment
Authors: Oudar J. L. , Chemla D. S.
Published: February 2003

We have measured the second and third order hyperpolarizabilities of the three nitroaniline isomers and of two related molecules. For some isomers the intramolecular charge transfer is found to cause a very large enhancement of the second order polarizabilities. We present a theory relating this contribution to the first excited state of energy, oscillator strength, and dipole moment of the molecules. Experimental results are accounted for with an excellent accuracy.
Nuclear relaxation in coupled spin systems dissolved in a nematic phase—the AX and A2 spin systems
Authors: Courtieu Jacques M. , Mayne Charles L. , Grant David M.
Published: February 2003

Relaxation in coupled AX(13CHCl3) and A2(12CH2Cl2) spin systems has been studied in a nematic solvent. The process is modeled as intramolecular dipole–dipole interactions plus other mechanisms that are treated collectively as external random magnetic fields. The AX system provides evidence that extreme narrowing arguments are valid for small molecules dissolved in liquid crystals. Also, values of spectral densities show that relaxation by the intramolecular dipole–dipole mechanism and by the combined external random field mechanisms are of equal importance for proton longitudinal relaxation whereas the former mechanism dominates the carbon-13 relaxation. Important details of the A2 system are discussed for the first time with the two relaxation observables that are obtained when superposition of the transitions is eliminated by the anisotropic solvent. Extreme narrowing is assumed, and the relative importance of the various mechanisms is discussed. The random field type mechanisms, which include intermolecular dipole–dipole interactions with the solvent, are shown to be dominant. So the intramolecular model commonly used to account for the frequency dependence of proton T1 in nematic liquid crystals does not obtain for small molecules dissolved in a nematic phase.
Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. III. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K with fields to 90 kG along the a crystal axis
Authors: Fisher R. A. , Brodale G. E. , Hornung E. W. , Giauque W. F.
Published: February 2003

The heat capacity of a 3.930 cm diam spherical single crystal of neodymium ethyl sulfate 9 hydrate (NES) has been measured with stabilized fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the a crystal axis. This axis is in the isotropic ab plane which is perpendicular to the c axis. The temperature range was from 0.5 to 4.2 °K. After small adjustments were applied for the nuclear polarization of the protons, plus 143Nd (12.20%) and 145Nd (8.30%) isotopes, an effective zero of electronic and lattice entropy was found at 1.25 °K and 90 000 G. These isoerstedic entropy changes derived from the heat capacity series were interconnected by 43 series of adiabatics corrected to isentropes. The heat capacity in zero magnetic field was found to be CH=0=2.27×10−3/T2 −8.45×10−5/T3+1.13×10−3T3+2.15×10−5T5 gibbs/FW below 4 °K, where the first two terms are due to the hyperfine states of 143Nd and 145Nd. The magnetic moment was measured by the potentiometric method at the above fields and temperature ranges used for heat capacities. The saturation limit of the temperature-dependent moment was 5694 G⋅cm3/FW, corresponding to ga=g⊥=2.039. The temperature-independent magnetic susceptibility, χa=0.00576 cm3/mole NES. These values may be compared with our previously measured gc=g∥ =3.594 and χc=0.00341 cm3/mole NES. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment, and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5–4.2 °K. These data will be used as starting references for investigating the properties of NES in the region below 0.5 °K, with the assistance of calorimetric heat introduction. Comparison of the magnetic moment and heat capacity data with an ionic crystal field model, with a dipolar molecular field, using parameters derived from the measured data, gives general good agreement.
Absolute rate of the reaction of Cl(2P) with methane from 200–500 K
Authors: Whytock D. A. , Lee J. H. , Michael J. V. , Payne W. A. , Stief L. J.
Published: February 2003

Rate constants for the reaction of atomic chlorine with methane have been measured from 200–500 K using the flash photolysis–resonance fluorescence technique. When the results from 14 equally spaced experimental determinations are plotted in Arrhenius form a definite curvature is noted. The results are best represented by a statistically evaluated least squares three-parameter fit given by k=5.44×10−19 T2.50 exp(−608/T) cm3 molecule−1 s−1. Over the range 299–500 K, the data are well represented by the Arrhenius expression k= (18.4±2.8) ×10−12 exp(−1545±52/T) cm3 molecule−1 s−1, while the corresponding expression for the 200–299 K range is k= (6.51±0.79) ×10−12 exp(−1229±27/T) cm3 molecule−1 s−1. The error limits are the standard deviations of the least squares fit.. The results are compared to previous work and are theoretically discussed.
A laser Raman study of the stress dependence of vibrational frequencies of a monocrystalline polydiacetylene
Authors: Mitra Vijay K. , Risen William M. , Baughman Ray H.
Published: February 2003

The applicaiton of a tensile stress to a monocrystalline fiber of a polydiacetylene, an extended-chain polymer, causes the Raman-observed C≡C and C=C in-chain vibrational frequencies to decrease linearly with elongation. The polymer studied, poly-HDU, results from the solid state polymerization of R–C≡C–C≡C–R, where R=–CH2OCONHC6H5. This experimental relationship between bond frequency shifts and deformation is analyzed by calculating bond force constant changes as a function of macroscopic stress. It is shown that possible effects due to stress-induced changes in electron delocalization in this fully conjugated polymer are negligible and the principal contributions to the bond frequency shifts are due to bond anharmonicity. Models which assume that the entire effect is due to bond anharmonicity produce calculated dependencies of ν (C=C) and ν (C≡C) upon fractional elongation, which are in good agreement with that observed.
The barriers for abstraction and exchange in H+HCl
Authors: Dunning Thom. H.
Published: February 2003

A b initio configuration interaction calculations on the barriers to reaction for HHCl (abstraction) and HClH (exchange) potential energy surfaces are reported. (AIP)
Model for trapped electrons in nonpolar glassy solids. II. The case of six octahedrally located nearest neighbors
Authors: Nishida Masahiko
Published: February 2003

For trapped electrons in nonpolar alkane glasses we investigate the case in which the nearest-neighbor molecules are aymmetrically arranged in an octahedral fashion, based on a model including exchange interaction. A comparison with the case of tetrahedrally located nearest-neighbors which was published is discussed. (AIP)
The excited states of ethylene
Authors: Mulliken Robert S.
Published: February 2003

On the basis of a review of existing experimental evidence, theoretical calculations, and other theoretical considerations a table of the observed excited states of ethylene is constructed, with assignments of essentially all lower-energy excited states to definite electron configurations, provided the observed V←N spectrum corresponds to a single transition. The probable alternative that it corresponds to an overlapping of two transitions mixed by twisting leads to difficulties in the assignments.
Quantum scattering theory of relaxation phenomena. Coupled states calculations of rotational relaxation and spectral line shapes in He–H2 gas mixtures
Authors: Goldflam Rudolf , Kouri Donald J.
Published: February 2003

The recently developed coupled states theory of relaxation phenomena of Goldflam and Kouri is tested against the close coupling results of Shafer and Gordon for the He–H2 gas mixture. Predictions of pressure broadening (line widths and shifts) and NMR spin-lattice relaxation cross sections are shown to agree extremely well with the close coupling results, in contrast to the previous expectations for the accuracy of the CS theory for such phenomena.
Dynamics of gas–solid interactions: Calculations of energy transfer and sticking
Authors: Shugard Mary , Tully John C. , Nitzan Abraham
Published: February 2003

A classical mechanical generalized Langevin formalism is applied to the study of gas–surface collisions. Procedures are described for constructing generalized friction and fluctuating forces which accurately represent the motion of real solids, and which can be conveniently implemented in a classical stochastic trajectory calculation. Energy transfer computed using this approach for He–W collisions is in excellent agreement with results of a quantum mechanical distorted wave calculation employing the same phonon density of states. The method is further applied to the study of residence times and sticking probabilities. Results indicate that the stochastic trajectory approach is feasible and capable of accurate simulation of gas–surface collision phenomena.
Measurements of 15N, 1H, and 13C, 1H direct couplings in natural abundance from proton NMR spectra of s-triazine in the nematic phase
Authors: Marchal J. P. , Canet D.
Published: February 2003

A method using proton FT NMR and double irradiation has been used in order to obtain 1H– 15N and 1H– 13C direct couplings of unlabelled s-triazine in the nematic phase. These couplings allow a complete structural determination. Large distortions of the aromatic ring with respect to hexagonal geometry are observed.
Statistical mechanics of helical wormlike chains. III. Scattering functions
Authors: Fujii Motoharu , Yamakawa Hiromi
Published: February 2003

The scattering function for the helical wormlike chain is evaluated by the use of the Hermite polynomial expansion of the distribution function, and its general behavior is studied. The convergence of this series is first discussed; upper and lower Tchebychev bounds for the exact scattering function are also examined. Recalling that the model may be regarded as a hybrid of the three extreme forms of rod, random coil, and regular helix, the results are then compared with the scattering functions for these forms. Thus, it is understood that the scattering function for the helical wormlike chain exhibits first coil-like and then helical damped-oscillatory or rodlike behavior as the scattering angle is increased. A comparison of theory with experiment is made for the small-angle scattering of x-rays and neutrons by tactic and atactic poly(methylmethacrylate) chains.
Statistical mechanics of helical wormlike chains. IV. Persistence vectors
Authors: Yamakawa Hiromi , Fujii Motoharu
Published: February 2003

The persistence vector of the helical wormlike chain is defined and evaluated as a function of chain length. It is compared with the persistence vector of a rotational isomeric state model with a determination of the model parameters, taking as examples polymethylene, poly(dimethylsiloxane), isotatic and syndiotactic polystyrene, and isotactic and syndiotactic poly(methylmethacrylate) chains. It is then found that there is good agreement between the persistence vectors of the continuous and discrete models if the directions of the initial tangent and curvature vectors of the former, relative to the first and second bonds of the latter, are chosen properly. The difference between them is at most of the same order of magnitude as the bond length.
The electronic structure and positron annihilation characteristics of positronium halides [X−;e+]. II. Two-photon annihilation
Authors: Farazdel Abbas , Cade Paul E.
Published: February 2003

The basic characteristics of two-photon positron annihilation from the ground- and first-excited states of [F−;e+], [Cl−;e+], [Br−;e+], and [I−;e+] are calculated. The properties of interest are the annihilation rate Γ, the orbital components to the annihilation rate Γnl, and the angular correlation N (ϑ) for two-photon annihilation. The two states considered are the ...ns2np61s+, 2S and the ...ns2np62p+, 2P states of [X−;e+] and all computations presented are based on the Restricted Hartree–Fock wavefunctions for the [X−;e+] states published elsewhere. These results are compared with experiment from various sources and an assessment of the potential role of the [X−;e+] 2S and 2P states is attempted. These results serve to limit the speculation on the role of [X−;e+] bound-state positron systems in the two-gamma annihilation from alkali halide crystals. The calculated lifetimes for the 2S states are 1.7, 4.0, 5.0, and 6.8 nsec for [F−;e+], [Cl−;e+], [Br−;e+], and [I−;e+], respectively. These RHF results obviously place too little electron density at the position of the positron and hence give lifetimes which are at best an upper limit to the true lifetimes (these lifetimes are too high by a factor of about ten). The angular correlation data for the [Cl−;e+] system provides an apparently striking confirmation of the recent experimental identification of a stable chloride/positron system by study of the angular correlation from aqueous solutions by Mogensen and Shantarovich.
Mössbauer spectroscopy of KrF2 and KrF2⋅MF5 (M=As, Sb)
Authors: Holloway J. H. , Schrobilgen G. J. , Bukshpan S. , Hilbrants W. , de Waard H.
Published: February 2003

Mössbauer spectra of KrF2 and the recently synthesized compounds α- and β- [KrF]+[AsF6]− and [KrF]+[SbF6]− have been measured using the 9.4 keV transition of 83Kr produced in the decay of an 83RbF source. The results for the values of quadrupole coupling strengths and the isomer shifts indicate that the Kr–F bonding in all compounds studied is very similar. A slight increase of the quadrupole coupling in going from KrF2 to F–Kr–F–MF5 can be interpreted in terms of a shortening of the average Kr–F bond length. A very accurate value, Qex/Qgr=1.958±0.002 for the ratio of the quadrupole moments of the 9.4 keV state and the ground state has also been derived from the measurements.
Studies in molecular dynamics. XVI. Fluctuation driven resonance
Authors: Alley W. E. , Alder B. J.
Published: February 2003

The natural fluctuations in a system of hard spheres that is placed between closely spaced parallel hard walls lead to resonance for those wavelengths which correspond to the spacing, or integer fractions thereof. The temporal behavior of this resonance is shown to be quantitatively equivalent to the autocorrelation function of the appropriate sum over modes of longitudinal currents which are calculated separately by molecular dynamics for a periodic system at an equivalent density. The decay of this resonance is also analyzed in terms of hydrodynamic and kinetic theory, and the regions of their validity is delineated.
Effect of a dissolved gas on the homogeneous nucleation pressure of a liquid
Authors: Forest T. W. , Ward C. A.
Published: February 2003

An isothermal decompression technique has been used to measure the pressure at which homogeneous nucleation of bubbles occurs in solutions of nitrogen in ethyl ether. Droplets of the ethyl ether–nitrogen solution were suspended in a host liquid by flowing the host liquid at a rate which just countered the buoyancy of the droplets. The system was then decompressed until nucleation occurred. The presence of the dissolved nitrogen in the ethyl ether was observed to raise the pressure at which nucleation occurred. The extent of the increase corresponds closely with that which has been previously predicted.
Theoretical studies of atmospheric triatomic molecules: A
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i
t
i
o equations of motion excitation energies for valence states of the configuration 1π3g2π1u in CO2
Authors: England Walter , Yeager Danny , Wahl Arnold C.
Published: February 2003

Polarized and unpolarized basis set equations-of-motion vertical spectra are presented for the five lowest valence states of CO2. In addition to the traditional solution method, an iterative diagonalization scheme is used to solve the renormalized matrix equations. The equations-of-motion methods depend on the basis set in much the same fashion as conventional SCF, MCSCF, and CI methods. The iterative diagonalization changes the excitation energies by ∼0.2 eV. The final polarized basis spectrum is the most accurate available for CO2.
Determination of exchange parameters of Cr3+ pairs in MgAl2O4 by optical measurements
Authors: van den Boom H. , van Dijsseldonk A. J. J. , Henning J. C. M.
Published: February 2003

The emission and luminescence excitation spectra of nearest-neighbor Cr3+ pairs in spinel MgAl2O4 have been studied. Analyses of these spectra yield the (4A2, 4A2) ground state level splittings. They are described by −JS̄1⋅S̄2+j (S̄1⋅S̄2)2, with S1=S2=3/2, J=−(29±3) cm−1, and j=−(3±2) cm−1. A couple of transitions to the first excited pair state (4A2, 2E) have been observed in the excitation spectrum; however, the data are insufficient to determine the parameters describing the exchange splittings of the excited state.
Crossed-beam study of the reactions H3+(Ar,H2)ArH+ and ArH+(H2,Ar)H3+
Authors: Blakley C. R. , Vestal M. L. , Futrell J. H.
Published: February 2003

The dynamics of the reactions H3+(Ar,H2)ArH+ and ArH+(H2,Ar)H3+ were studied over the initial relative translational energy from 0.87 to 9.7 eV and from 0.18 to 6.7 eV, respectively. The reactions were found to proceed via direct mechanisms at all energies studied. Energetic data are presented that suggest H3+ is not rapidly relaxed vibrationally upon collision with H2 as previously thought. Rather than being relaxed within a few collisions, the lower vibrational states probably are relaxed with a rate constant on the order of 10−12 cm3 molecule−1⋅sec−1.
A calculation of the electron detachment energy of NO2−
Authors: Andersen Earl , Simons Jack
Published: February 2003

The equations-of-motion (EOM) method was used to calculate the detachment energy of NO2−, including correlation and relaxation effects. Enough of the SCF-level potential energy surface of NO2− was calculated to compute the thermodynamic electron affinity of NO2. The 2A1 potential surface of NO2 was obtained by adding the computed vertical detachment energy to the potential surface of NO2− at the corresponding geometry where the highest occupied molecular orbital was of a1 symmetry. The calculated vertical detachment energy of NO2− at its equilibrium geometry was 2.66 eV. Using the calculated potential energy surfaces and the reported values for the vibrational energy differences between NO2 and NO2−, the thermodynamic electron affinity of NO2 was calculated to be 2.25 eV, which compares very well with Lineberger’s experimental value of 2.36±0.1 eV.
Chemiluminescence from the electronic excited states of the cesium atom in the cesium–fluorine reaction system
Authors: Hall Lawrence H.
Published: February 2003

The chemiluminescence of the cesium–fluorine reaction system has been analyzed spectroscopically to give steady-state populations of the excited electronic states of the cesium atom. By correcting for cascade of excitation the primitive populations have been calculated, and these indicate a statistical distribution of electronic excitation. A phase space calculation of the distribution of electronic excitation agrees satisfactorily with experiment. Quantum yield measurements and nitrogen-gas quenching experiments have also been performed to elucidate the reaction mechanics. It appears that the pumping mechanism involves the reaction of Cs with F2 to create vibrationally excited CsF, which then transfers its energy to Cs in a V–E process.
Medium perturbations of atomic extravalence excitations
Authors: Messing Itzhak , Raz Baruch , Jortner Joshua
Published: February 2003

In this paper we present the results of an experimental study of the lowest 1S0→3P1 extravalence electronic excitation of atomic xenon in dense supercritical and subcritical fluid argon over the density range 0.1–1.4 g⋅cm−3, spanning the temperature region 80–300°K. Solvent perturbations were characterized in terms of the spectral shift, the linewidth and the first and the second moments of the absorption band. These energetic parameters exhibit a weak temperature sensitivity and a strong density dependence. The experimental data were analyzed in terms of the semiclassical theory of line broadening extended to account for guest–host and host–host correlations and incorporating realistic pair potentials in the ground and in the excited electronic states. The semiclassical theory results in manageable expressions for the first and for the second moments of the absorption band which are expressed in terms of a difference guest–host interaction potential together with the solute–solvent and the solvent–solvent radial distribution functions. The theory provides a semiquantitative account for the weak temperature dependence and for the marked density dependence of the energetic parameters specifying solvent perturbations and was utilized to extract quite reliable information concerning the excited state Xe(3P1)+Ar(1S0) potential.
Statistical mechanics of nonspherical molecules. VIII. Hard-core models
Authors: MacRury Thomas B. , Steele William A.
Published: February 2003

Calculations of some properties of systems composed of nonspherical hard-core molecules are presented. The intermolecular interactions are modeled by representing each molecule as an assemby of overlapping hard spheres. The specific cases treated include: triangles; planar squares; and linear arrays composed of three, four, and five spheres. The basic statistical property computed is exp(−potential energy/kT) for various values of separation distance and molecular orientation; the results are presented by calculating the distance dependence of the coefficients in the expansion of this quantity in a set of orthogonal functions of the Eulerian orientation angles for each molecule. A number of average properties are calculated with the aid of this function, including: second virial coefficients; the angular correlation contribution to the depolarized light scattering of dilute gases; and the deviation from the Clausius–Mosotti equation (for the dielectric constant of nonpolar fluids) that is linear in density. The properties of these fluids at high density are also calculated by invoking the blip-function theory, as adapted to nonspherical molecules, to calculate molecular pair corrleation functions and the equation of state. Comparisons are made with the scaled-particle equation of state for nonspherical hard-core molecules, and the pair correlation functions are used to calculate angular correlations, depolarized light scattering, and one of the terms contributing to the deviation from the Clausius–Mosotti equation for dense fluids.
Reaction rate of electrons with scavengers in nonpolar liquids
Authors: Tachiya M.
Published: February 2003

The reaction rate of electrons with scavengers in nonpolar liquids is formulated using the time-dependent perturbation theory. The rate constant is expressed in terms of the electron attachment spectrum of the scavenger, which is experimentally obtainable. The correlation of the rate constant with so-called V0, which has been experimentally observed, is satisfactorily explained by the present theory.
ESR study of molecular jumps of manganese(II) impurity in single crystals of Cs2HfCl6 and Cs2ZrCl6
Authors: Maniv S. , Reuveni A. , Luz Z.
Published: February 2003

Electron spin resonance spectra at 35 and 9.3 GHz of Mn2+ impurity ions in single crystals of Cs2HfCl6 and Cs2ZrCl6, from 12 to about 400 K are reported. Below ∼60 K the spectrum consists of a superposition of a number of anisotropic subspectra due to crystallographically equivalent Mn2+ species. Each subspectrum consists of five fine structure bands, due to the different (m−1↔m) transitions, split into six hyperfine components. The spin Hamiltonian of the Mn2+ species in this temperature range is characterized by isotropic g and hyperfine tensors (g=2.004, A=77.0 G) and an almost axially symmetric zero field splitting (ZFS) tensor (D=470 G and E=3 G). It is suggested that the Mn2+ impurity that gives rise to these subspectra consists of MnCl3−5 ions with nearly tetragonal symmetry. The various subspectra correspond to MnCl3−5 ions whose principal ZFS tensor components point along different crystallographic axes. As the temperature is raised above 60 K conspicuous changes occur in the spectrum over an extremely wide range of temperatures: The m≠1/2 fine structure components first broaden and eventually disappear in the noise, while the m=1/2 transitions, due to the different sites, coalesce to give a singly, slightly anisotropic, hyperfine sextet. At high temperatures the full intensity of the spectrum emerges again to give a sharp isotropic sextet. The temperature dependence of the spectrum over the whole temperature range studied can be quantitatively interpreted in terms of a dynamic model in which the major ZFS tensor axis undergoes random jumps between the three crystallographic cubic directions. A general theory for the ESR line shape in the presence of such a process is derived for the case that the ZFS interactions is small compared to the Zeeman energy. Simple and explicit equations are derived for the linewidth and frequency shift in the slow jump limit for the m≠1/2 as well as the m=1/2 fine structure bands. For the fast jump limit the appropriate relaxation matrix is also derived. This theory is then used for a quantitative analysis of the experimental spectra in the CsHfCl6 and CsZrCl6 crystals, and values for the jump rate and the magnetic parameters as function of temperature are derived. It is found that as the temperature is raised from 60 to about 400 K the g value changes from 2.004 to 2.006 and D decreases monotonically from 470 to 330 G. In this temperature range the jump rate changes by about four orders of magnitude and it can be characterized by an Arrhenius plot with the following kinetic parameters: (1.τ)(300 K) =3.5×1011 s−1, ΔE=1.4 kcal/mol. Possible mechanisms for the jump process are discussed.
Vibrational energy transfer in HF–HCN, DF–HCN, and H2–HCN mixtures
Authors: McGarvey John A. , Friedman Nina E. , Cool Terrill A.
Published: February 2003

Measurements of probabilities for vibrational energy transfer are presented for the temperature range 240–450 °K for HF–HCN and DF–HCN gas mixtures. Energy transfer probabilities in these mixtures exhibit a strong inverse temperature dependence over this temperature range. Rate measurements are also given for vibrational energy transfer in H2–HCN mixtures at 298 °K. The present results suggest the feasibility of cw chemical laser operation in HF–H2–HCN mixtures on the 3.85 μ HCN(001) →HCN(010) band.
Raman study of vibrational dephasing in liquid CH3CN and CD3CN
Authors: Schroeder J. , Schiemann V. H. , Sharko P. T. , Jonas J.
Published: February 2003

The Raman line shapes of the ν1(a1) C–H and C–D fundamentals in liquid acetonitrile and acetonitrile-d3 have been measured as a function of pressure up to 4 kbar within the temperature interval 30–120 °C. Densities have also been determined. From the isotropic component of the vibrational Raman band shape the vibrational relaxation times have been obtained as a function of temperature and pressure (density). The experimental results can be summarized as follows: (i) as T increases at constant density ρ, the vibrational relaxation rate (τvib)−1 increases; (ii) at constant T as density is raised τvib−1 increases; (iii) at constant pressure the T increase produces higher τvib−1, however, the change is more pronounced for the CD3CN liquid. Isotopic dilution studies of the CH3CN/CD3CN mixtures shows no significant effect on (τvib−1). The experimental data are interpreted in terms of the Kubo stochastic line shape theory and the dephasing model of Fischer and Laubereau. The results based on Kubo formalism indicate that dephasing is the dominant relaxation mechanism and that the modulation is fast. The isolated binary collision model proposed by Fischer and Laubereau for vibrational dephasing reproduces the essential features of the density and temperature dependence of the (τvib)−1 and suggests that pure dephasing is the dominant broadening mechanism for the isotropic line shapes studied. In the calculation the elastic collision times were approximated by the Enskog relaxation times.
Antiferromagnetism in a mixed-valence iron fluoride heptahydrate (Fe2F5⋅7H2O) and related compounds
Authors: Jones E. R. , Hendricks M. E. , Auel Theo , Amma E. L.
Published: February 2003

Magnetic susceptibilities of mixed metal fluorides of the type Fe(III)M(II)F5⋅7H2O, where M=Fe, Co, Ni, or Zn, were measured from 2.3 to 295 °K with a vibrating-sample magnetometer at an applied field of 10 kOe. Antiferromagnetic transitions were observed in Fe2F5⋅7H2O, TN=3.0±0.2 °K, and in FeCoF5⋅7H2O, TN=3.42±0.10 °K. Deviation from Curie–Weiss behavior was observed in FeNiF5⋅7H2O at temperatures below 10 °K suggesting a possible ordering at temperatures below 2.3 °K, the lowest temperature obtained in this experiment. FeZnF5⋅7H2O and the related compound Al(III)Fe(II)F5⋅7H2O were paramagnetic down to 2.3 °K while FeF2⋅4H2O became antiferromagnetic at 3.4±0.15 °K.
The surface composition of Au–Sn alloys determined by Auger electron spectroscopy
Authors: Overbury S. H. , Somorjai G. A.
Published: February 2003

The Auger spectra of clean and equilibrated Au–Sn alloy ingots of bulk composition ranging between 50 and 99 at% Au have been obtained. The intensity ratios of Auger peaks of various different energies were normalized by comparison with the corresponding intensity ratios from pure Au and Sn. The normalized intensity ratios are used to obtain the surface atom fractions by applying a model which takes full account of the attenuation of the Auger electrons. It is found that for a one phase alloy with overall composition of 50 at% Au there is little or no segregation at the surface, while for a one phase alloy with bulk composition of 86 at% Au there is marked segregation of Sn (surface monolayer composition of about 43 at% Au). For the alloys of bulk compositions between 50 and 86 at% Au in which both phases are present, the surface composition is given by applying the lever rule to the one phase surface compositions. For 1 at% Sn dissolved in the Au lattice there is also considerable enrichment of the surface with Sn (surface monolayer composition of about 46 at% Au). These surface compositions are related to the properties of the bulk phase diagram and are explained by the interplay of the differences in atomic size and in heats of sublimation of pure Au and Sn and of the heats of mixing of the alloys.
The temperature dependence of ’’single collision’’ bimolecular beam–gas chemiluminescent reactions. II. Experimental studies
Authors: Gole J. L. , Preuss D. R.
Published: February 2003

We consider ’’single collision’’ bimolecular beam–gas chemiluminescent reactions in which a metal beam formed effusively intersects a tenuous atmosphere of oxidant gas (10−4–10−6 torr) resulting in the emission of visible radiation from excited electronic states of the reaction products. From recently derived relationships which allow the determination of the temperature dependence for the observed chemiluminescence we deduce upper bounds for ΔH vaporization (ΔHsub). In addition, for systems in which ΔH is accurately known through independent studies Eexp may be evaluated. Derived relationships are demonstrated experimentally through studies of ten bimolecular reactions. We consider the reaction of strontium atoms and fluorine molecules. Here, reaction occurs with one internal state of the metal atom (ground 1S0 states). ΔHsub(Sr), Eexp(SrF, C2Π), and Eexp(SrF, D2Σ+) are determined by monitoring the chemiluminescence from the SrF C2Π and D2Σ+ excited electronic product states. By combining the determined activation energies with reasonable estimates of relative frequency factors for the C2Π and D2Σ+ states we deduce that the D2Σ+ state of SrF is long lived (metastable). Results are also presented for the reactions of Sc, Y, and La with O2, NO2, and N2O. Here the metal beams are characterized by a substantial internal state population. The effect of the internal state population characterizing the metal beams is analyzed. We deduce an upper bound for ΔHvap (Sc, Y, La) from the nine reactions studied. Eexp for formation in the v′=0 level of the ScO and YO A2Π states, and the v′=0 level of the LaO C2Π state, is deduced for the three possible oxidations with O2, NO2, and N2O. The resultant experimentally determined activation energies are compared with those expected on the basis of mechanistic models used to describe the oxidation reactions of Group IIIB atoms.
Nuclear magnetic resonance line shapes in lyotropic liquid crystals and related systems
Authors: Bloom M. , Burnell E. E. , Roeder S. B. W. , Valic M. I.
Published: February 2003

The shapes of NMR absorption lines, free induction decays, and Jeener echoes in systems such as lyotropic liquid crystals have been investigated theoretically and experimentally. For a system having an axis of symmetry for the molecular motion which makes an angle ϑ with the external magnetic field, the secular part of the dipolar Hamiltonian 〈ℋd〉 (ϑ) is proportional to (1/2)(3 cos2ϑ−1). This leads to the characteristic logarithmic absorption line shape for nonoriented systems. The experimental consequences are illustrated with measurements on nonoriented samples of potassium palmitate–water in the lamellar liquid crystal phase.
Low-temperature rotational relaxation in gaseous H2 and D2
Authors: Ramaswamy Ramakrishna , Rabitz Herschel , Green Sheldon
Published: February 2003

Various potentials have been used for generating scattering cross sections for rotational transitions in hydrogen isotope systems. Low-temperature rates were calculated and the relaxation times compared with the results of sound absorption experiments. It is seen that the existing potentials could still be improved since they do not exactly reproduce the experimental results.
Molecular orbital correlation diagrams for He2, He2+, N2, N2+, CO, and CO+
Authors: Ermler Walter C. , Mulliken Robert S. , Wahl Arnold C.
Published: February 2003

After a preliminary check with He2 and He2+, self-consistent field calculations have been carried out for the nitrogen and carbon monoxide molecules and some of their positive ions for the range of internuclear distances from about 1.5 times equilibrium down to 0.01 bohr. To adequately describe the passage from the separated to the united atom limits, basis sets comprised of even-tempered expansions of Slater type s and p functions were centered at each nucleus and at a point midway between them. This three center procedure is compared with that of reoptimizing basis functions at each internuclear distance. It is found that the three-center approach almost completely obviates the need of the polarization functions which must be added if a two-center approach is used. The correlation diagrams for nitrogen and carbon monoxide and the first positive ions of each symmetry type are all similar in shape, especially for the innermost orbitals. Ionization potential curves plotted on the diagrams for the neutral systems are nearly parallel to the corresponding orbital energy curves. This indicates that Koopmans’ theorem is consistent at all distances and implies that correlation diagrams for neutral molecules should be reasonable approximations to the ionization potential curves. For the most easily ionized orbital of both N2 and especially CO, the ionization potential has a remarkably low value at about one-third the equilibrium separation. To adequately describe this orbital an extra s function having a smaller zeta than the smallest one in the united atom basis set was required. This implies that merely using the optimized basis sets for the separated and united atoms in a three-center procedure is scarcely acceptable in the region where the outermost orbital energy has the lowest value.