bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular charge transfer reactions of monosubstituted benzenes at low energies
Authors: Bregman-Reisler H. , Rosenberg A. , Amiel S.
Published: February 2004

Cross sections for the symmetrical and exoergic asymmetrical charge transfer reactions of a series of monosubstituted benzenes were measured for primary-ion kinetic energies between 30 and 150 eV. In this energy range, the charge transfer cross sections of all the reactions were found to be larger than the gas-kinetic collisional cross sections, and their velocity dependence typical of resonant processes. These features seem to indicate that transitions to excited levels occur with high probability. The momentum transfer and the conversion of translational to internal energy in all the reactions was low, as expected for reactions having large impact parameters. In contrast to atomic and diatomic systems, no systematic difference was observed between symmetrical and asymmetrical processes, and molecular parameters other than the ionization potential of the system were found to affect the cross section. For a given projectile ion the cross section increased with the polarizability of the target molecule. This increase is associated with the deformation and lowering of the potential barrier. The nature of the projectile ion affected the magnitude of the cross section to about the same extent as did the target molecule, and this seems to be related to the energy defect of the reaction and to the dimensions and complexity of the projectile ion.
Electron energy loss spectroscopy of acetone vapor
Authors: Huebner Russell H. , Celotta R. J. , Mielczarek S. R. , Kuyatt C. E.
Published: February 2004

High resolution, inelastic electron scattering data can provide new spectroscopic information on the electronic structure of polyatomic molecules. Features in the acetone energy loss spectrum from 0 to 15 eV obtained for 100 eV incident electrons correspond to vibrational, electronic discrete, and electronic continuum excitations. These data are compared with optical measurements in a wide spectral region extending from the infrared to the vacuum ultraviolet. A comprehensive interpretation of the energy loss spectra is attempted with the use of photochemical and photoelectron data, as well as quantum-chemical calculations in the literature. Three Rydberg series with quantum defects of 1.03, 0.81, and 0.315 join onto bands previously discussed in terms of transitions to valence orbitals. These series converge to an ionization limit of 9.705 eV in good agreement with previous optical determinations. Dissociative continua underlie the Rydberg region and give rise to a variety of neutral products observed in recent photolysis work. Broad features in the ionization continuum appear to correlate generally with higher ionization potentials observed by photoelectron spectroscopy. Apparent oscillator strengths derived from the energy loss data for the bands at 4.4 and 6.35 eV and for a region (9.7–11.78 eV) of the ionization continuum agree very well with the photoabsorption measurements. Integrated oscillator strengths of 0.46 below 9.7 eV and 3.93 below 15 eV were derived from the electron impact data.
Spectra of manganese(IV) hexafluoride ion (MnF6=) in environments of O
h and D3d symmetry
Authors: Helmholz Lindsay , Russo M. E.
Published: February 2004

The visible and near ultraviolet spectra of MnF6= have been observed in solid solutions in Cs2GeF6 and K2GeF6 in which the site symmetries of the hexafluoride ion are Oh and D3d, respectively. At liquid helium temperatures these spectra show sharp line absorption corresponding to electric and magnetic dipole transitions. The electric dipole transitions are vibronically allowed and correspond to the excitation of the three ``u'' vibrations of an octahedral, XY6 molecule. These are observed combined with the a1g completely symmetrical vibration and, we have assumed, with certain of the lattice vibrations. The assignments given for the 4A2g→2Eg and 2T1g transitions are reasonably straightforward. For the first spin allowed transition, 4A2g→4T2g, it is necessary to assume a reduction in the spin-orbit coupling parameter by a factor of about 10 to account for the observations. We have not observed the transition to the 2T2g state, and the higher lying quartet 4T1g appears as a poorly resolved progression corresponding to va1g ≈ 460 cm−1.
Emission spectra of solid rare-gas alloys
Authors: Gedanken Aharon , Raz Baruch , Jortner Joshua
Published: February 2004

In this paper we present the results of an experimental study of the α-excited vacuum ultraviolet emission spectra of xenon-argon, xenon-krypton, krypton-argon, xenon-neon, krypton-neon, and argon-neon solid alloys in the temperature range 6–40°K. Three mechanisms for electronic energy transfer to single impurity states and to impurity pairs were considered: (1) energy transfer from vibrationally relaxed homonuclear diatomic molecule of the host to Xe/Ar and to Xe/Kr impurity states; (2) energy transfer from the host vibrationally excited homonuclear diatomic molecule to Kr/Ar impurity states; and (3) energy transfer via impurity ionization or the formation of metastable states in neon alloys. The single impurity emission bands originating from the lowest Wannier states exhibit large red Stokes shifts reletive to the corresponding absorption bands, being close to the corresponding gas-phase transitions, and thus manifest the effect of medium relaxation around single impurity states. A similar effect is exhibited for diatomic molecules in pure solids and for excited impurity pairs. Qualitative information has been obtained regarding efficient nonradiative relaxation processes between high Wannier impurity states. The emitting single impurity state involves in most cases the lowest lying, optically allowed, excited state. We have observed multiple trapping sites for the single impurity and for the impurity pairs in solid Ar and Kr but not in Ne. The population of these trapping sites is determined by the deposition temperature. Finally, spectroscopic evidence is obtained for the existence of heteronuclear rare-gas XeKr* and ArKr* diatomic molecules.
Photoelectron spectra of OCSe, SCSe, and CSe2
Authors: Frost D. C. , Lee S. T. , McDowell C. A.
Published: February 2004

The HeI photoelectron spectra of OCSe, SCSe, and CSe2 have been measured and the electronic states associated with the various observed ionization potentials have been assigned. Comparison of the measured Franck-Condon transition probabilities with those calculated theoretically enables us to determine the geometries of the molecular ions studied.
Nonequilibrium gas reaction kinetics: The nonvanishing effect of vanishing products
Authors: Fitzpatrick J. M. , Desloge E. A.
Published: February 2004

Vanishing quantities of the products of a chemical reaction are found in general to have a nonvanishing effect on the system's ``normal state.'' The generality of this effect, previously observed by Pyun and Ross, is established through the use of a slightly altered expansion of the velocity distribution function. Each coefficient of this new expansion measures the contribution by one particular species to the perturbation of the entire system. The effect of ignoring small quantities of the products is determined for a particular simple system. An approximate solution to the Boltzmann equation for this system is obtained by the moment method, and the relaxation of this solution to the normal solution is confirmed. The resultant correction to the perturbation of the reaction rate is found to be considerable, but because of the small size of the perturbation, the correction to the rate itself is negligible.
Monte Carlo simulation of simultaneous bulk, grain boundary, and surface diffusion
Authors: Brandt W. W.
Published: February 2004

The diffusion of a sorbate in a solid body bisected by a narrow straight grain boundary has been simulated using a combination of the so-called floating random walk Monte Carlo technique and a modified technique of that sort, particularly applicable to the study of random walks inside narrow grain boundaries. The results have been compared to the published solutions obtained from deterministic methods. Complex composite processes involving simultaneous bulk, grain boundary, and surface diffusion have been simulated as well, using the techniques so developed, so as to show that the computations are quite feasible, even though at this point the results cannot always be verified by comparison to known solutions.
NMR investigation of certain hydrated fluorosilicates
Authors: Muthukrishnan K. , Ramakrishna J.
Published: February 2004

Proton and fluorine NMR were investigated in the temperature range 90–425 °K in the hexahydrated fluorosilicates of Zn, Cu, Mn, Co, and Ni and in the tetrahydrated CuSiF6 to obtain information about the internal motions in these solids. Second moment transitions were observed at widely different temperatures for the different substances, and these are ascribed to the onset of reorientation of the M(H2O)62+ and SiF62− octahedra. The correlation frequency and the potential barrier hindering the motion were calculated in all the cases. Apart from the narrowing taking place at higher temperatures, the Co salt showed a change in the line structure at 248 °K, where a phase transition was reported from magnetic susceptibility measurements. Studies on the single crystals of ZnSiF6 · 6H2O and NiSiF6 · 6H2O showed that there are three nonequivalent p-p vectors, and after the transition they all become equivalent, with the M(H2O)62+ octahedron reorienting about the fourfold axes.
Kinetic isotope effects in the reaction of fluorine atoms with molecular hydrogen. II. The F + HD/DH intramolecular isotope effect
Authors: Persky Avigdor
Published: February 2004

The intramolecular kinetic isotope effect in the reaction of fluorine atoms with HD molecules, F+HD→kF+HDHF+D,F+DH→kF+DHDF+H,was measured as function of reaction temperature in the range of 159–413 °K. The measured isotope effect can be expressed as an Arrhenius-type equation: kF+HD/kF+DH = (1.26 ± 0.02) exp[(70 ± 6)/RT]. Experiments were carried out in a fast flow system with direct mass spectrometric analysis of reaction products. The experimental results for kF+HD/kF+DH, as well as results for kF+H2/kF+D2 which were reported in an earlier publication, are compared with calculations based on transition state theory, using empirical and semiempirical models.
Proton NMR and covalency parameters of ruthenium(III) hexaammine
Authors: Waysbort Daniel , Navon Gil
Published: February 2004

The NMR signal of the ammine protons of the Ru(NH3)63+ ion was directly measured by a wide line technique at various temperatures. A non-Curie behavior of the paramagnetic chemical shift was observed and the ligand pseudocontact interaction suggested by Kurland and McGarvey was used for its interpretation. The contact hyperfine interaction with the ammine protons was found to be A = 5.9 MHz. The covalency parameter was calculated as λ = 0.33, but after allowing for cross-term spin densities it was reduced to 0.28. The NMR relaxation times are discussed in terms of the ruthenium proton distance and the electronic spin relaxation times of the Ru(NH3)63+ ion.
Hydrodynamic properties of ring macromolecules with increasing chain stiffness and excluded volume
Authors: Kumbar Mahadevappa
Published: February 2004

The Bloomfield-Zimm and Simon version of the Rouse-Bueche-Zimm spring-bead model has been used to investigate the effect of local chain stiffness and excluded volume in circular macromolecules. The local chain stiffness is accounted through the second-nearest-neighbor interactions. The calculations are made using the normal coordinate method of Zimm. Since the dynamic properties of interest depend only on the sum and the square of inverse eigenvalues, these sums have been computed for N = ∞ (N being the number of chain elements) as a function of chain stiffness and the excluded volume. These sums decrease as either the chain stiffness or the excluded volume increases. The Flory parameter Φr(× 1023) is computed as a function of increasing chain stiffness and excluded volume, and it is concluded that this parameter slightly depends on molecular weight in the low-molecular-weight range due to chain stiffness. However, such dependency vanishes in high-molecular-weight range. The behavior of this parameter as a function of excluded volume and the chain stiffness is similar to that of the linear molecules. The effect of excluded volume is more pronounced than the chain stiffness, which was also found to be true in linear macromolecules. The ratio of S chain to S ring has been investigated. This ratio remains constant as chain stiffness increases and slightly increases as excluded volume increases. The Mandelkern-Flory-Scheraga parameter slightly decreases as chain stiffness increases and increases as excluded volume inceases. This parameter as well as the sedimentation ratio do not depend on molecular weight in high-molecular-weight range, however, depend on molecular weight in low-molecular-weight range due to chain stiffness. The increasing behavior with excluded volume has been explained in terms of coil expansion and suggested that the chain stiffness may play a greater role in the ring molecule compared to the linear molecule. It is also suggested that the chain stiffness may have a greater influence when the coil is in the status of high expansion. The particle scattering functions have also been studied with increasing chain stiffness and excluded volume. These functions have been derived for low and high angles. The computation is carried out for N = 20 (N being the number of scattering centers), and the scattering functions for ring and linear molecules are compared. It is concluded that the ring scattering functions are higher than those of the linear scattering functions. The effect of excluded volume or chain stiffness is more pronounced at higher angles than the lower angles.
Dependence of extrema in the generalized oscillator strengths on momentum transfer and effective nuclear charge for atomic transitions
Authors: Miller Kenneth J.
Published: February 2004

Generalized oscillator strengths f(K) for one-electron atomic transitions involving atoms in the first through third rows of the Periodic Table are studied within the first Born approximation. A one-electron model employing hydrogenlike orbitals is used with appropriate effective nuclear charges. For single electron excitations, the Born matrix element f(K) = 2Δ E|∫ φb*e iK· rφadV|2/K2 can be scaled to yield a reduced generalized oscillator strength f (κ) which depends on the ratio of effective nuclear charges ζ(final)/ζ(initial), and a reduced momentum transfer κ = K /ζ(initial). Transitions to a Rydberg series exhibit extrema in f(K) which are nearly the same for all members of the series, whereas excitations to different series exhibit a different number and positioning of the extrema. This behavior suggests that trends in generalized oscillator strengths can be used as an experimental tool to probe various types of transitions and to unravel Rydberg series. Comparison of theoretical calculations with available experimental results yields good agreement and new experimental goals are suggested.
Vibronic splitting of Γ8 electronic states of Ir+4 in single crystals of Cs2ZrCl6 at 4.2 °K
Authors: Massuda Rachel , Dorain Paul B.
Published: February 2004

Single cubic crystals of Cs2ZrCl6 containing Ir+4 exhibit two absorption bands with extensive vibronic structure at 4.2 °K. Two progressions in the symmetric stretch mode (ν1) show a splitting of the absorption lines as a function of the number of quanta of the ν1 mode. Analysis shows that the electronic transitions must be from the ground Γ7(2T2g, t2g5) state to excited Γ8 quartet states, which are coupled to a threefold degenerate vibration mode of symmetry Γ4 or Γ5 and n modes of the ν1 mode. Zeeman measurements at 70 kG confirm the assignment for one progression. Arguments are presented to show that the threefold degenerate vibration mode corresponds to the transverse components of the ν4(Γ4u) mode of the face-centered cubic lattice.
Angular dependence of 23P and 33P excitation of He by electron impact
Authors: Ojha S. P. , Tiwari P.
Published: February 2004

Differential scattering cross sections for excitation of helium by electron impact from its ground state to its 23P and 33P excited states have been calculated using the Ochkur approximation at four incident electron energies in the range 55.5–500 eV for scattering angles between 0° and 80°. Results are compared with other theoretical and experimental data.
Some calculated quantities in the radiation chemistry of molecular hydrogen: Average energy per ion pair and numbers of singlet and triplet excitations per ion pair
Authors: Jones W. M.
Published: February 2004

The average energy (W) expended per ion pair (ip) in hydrogen and the numbers of molecular singlet (R2) and triplet (R3) excitations per ion pair were calculated for electrons of up to 1500 eV energy and extrapolated to high energy limits. Experimental and theoretical cross sections were used. Calculations were made for a secondary electron energy distribution based on measurements of Opal, Beaty, and Peterson at 500 eV and for the Gryzinski distribution. For each distribution calculations were made for two assumptions concerning dissociative ionization. For the preferred calculation (experiment-based secondary electron distribution for ordinary ionization and zero kinetic energy for electrons formed in dissociative ionization) the results at high energies are W = 36.8 eV/ip, R2 = 1.06 (includes dissociative excitation), and R3 = 0.359. The experimental value of W is 36.3 eV/ip.
On the theory of fluorescence decay experiments. II. Statistics
Authors: Isenberg Irvin
Published: February 2004

Emission data is assumed to be obtained by monophoton equipment, and analyzed by the method of moments. It is assumed that the random errors result from fluctuations in the number of counts and that the fluctuations are governed by a multinomial distribution. Expressions are obtained for the variance of a decay time, the total number of counts needed to bring the error below a given value, and the total number of counts needed to resolve two closely spaced decays in the presence of other decays.
Resonant Raman scattering from cytochrome c: Frequency dependence of the depolarization ratio
Authors: Collins David W. , Fitchen D. B. , Lewis Aaron
Published: February 2004

The depolarization ratio has been measured for several peaks in the resonant Raman spectrum of horse heart ferrocytochrome c (reduced) using six argon and krypton ion laser lines near resonance with the β absorption band. The depolarization ratio is observed to be a strong function of laser frequency so that previous mode symmetry assignments for heme proteins based on data at a single frequency are unreliable. For the anomalously polarized peaks (ρl > 3/4), the depolarization ratio increases to a maximum when the laser frequency is midway between the α and β absorption bands. These data are compared with a theoretical expression for the dispersion derived using perturbation theory to treat mixing of the D4h basis states. Quantitative estimates of the relative contributions of the different symmetry representatives are obtained.
Effect of ozone on the vibrational relaxation time of oxygen
Authors: Parker J. G. , Ritke D. N.
Published: February 2004

Measurement of the relaxation time of a mixture containing 38 mm of O3 in 35 atm of O2 gives a relaxation frequency of 720 cps amounting to a shift of 545 cps above the value obtained for pure O2. Theoretical interpretation of the result suggests that the vibration-vibration transfer rate from O3 to O2 is considerably slower than the corresponding rate for CO2 to O2.
Pressure dependence of the near-infrared absorption in ZnS:Cr crystals
Authors: Kelley C. Stuart
Published: February 2004

Data are reported that indicate a pressure dependence of the shape of the 0.7 eV optical absorption in ZnS:Cr crystals, consistent with an increasing peak intensity and peak energy and decreasing half-width and oscillator strength as the hydrostatic pressure increases. These effects are interpreted by crystal field theory and a normal-coordinate treatment of the vibrationally assisted 5T2 → 5E transition within the Cr2+ impurity. The electric-dipole moment associated with this transition decreases with increasing pressure.
Temperature dependence of near resonant vibration → vibration energy transfer in HCl–D2 mixtures
Authors: Hopkins Barbara M. , Chen Hao-Lin , Sharma Ramesh D.
Published: February 2004

Laser-excited vibrational fluorescence measurements have given rates for nearly resonant vibrational energy exchange between HCl and D2 molecules over the temperature range of 196–343°K. The energy transfer cross section σν ν shows an inverse temperature dependence; namely, decreases as temperature increases. The magnitude and temperature dependence of these cross sections could be fit by first order calculations based on quadrupole-quadrupole, and dipole-quadrupole interactions. The rates of vibrational deactivation of HCl by He were found to increase with temperature. However, the results on HCl self-relaxation also show an inverse temperature dependence over this temperature range studied. This enhancement observed at lower temperature is probably caused by the attractive chemical forces exerted between HCl molecules.
Application of an empirical equation of state to the critical region of methane and argon
Authors: Gielen H. , Jansoone V. , Verbeke O.
Published: February 2004

The equation of state for the critical region of simple fluids proposed by Verbeke et al. is, with other options for the parameters, applied to methane and argon. The data on methane reported by Jansoone et al. are reanalyzed with this equation. In order to apply the equation in the critical region of argon the data of Verbeke et al. are utilized and expanded with additional new data. It is demonstrated that the proposed equation can be useful in the further investigation of the equation of state in the critical region of simple fluids.
Self-avoiding random walks, circle and star graphs, and a group of singular matrices
Authors: Eichinger B. E.
Published: February 2004

The self-avoiding random walk problem in d -dimensional space is efficiently treated by use of a class of graphs of great generality, called circle graphs. Matrices associated with these graphs are shown to be submatrices of the matrix belonging to the complete star on the circle. The latter matrix possesses an interesting group property which is dependent on the notion of the generalized inverse. The self-avoiding random walk problem is solved to all orders by graphical expansion, and a concise prescription suitable for numerical calculation of the coefficients is given. It is suggested that an analytical solution would be obtained from consideration of the properties of determinants of matrices in the generalized group.
Fluctuations and noise in kinetic systems. II. Open ensembles at equilibrium and steady state
Authors: Chen Yi-der
Published: February 2004

We consider the noise and fluctuations of an open ensemble of independent systems each of which can exist in a set of discrete states {0, 1, 2,..., x}. By an open ensemble we mean that the systems in the ensemble may be exchanged with one or more reservoirs. We derive the noise power spectrum of the quantity N=Σi=0x aiNi as a function of rate constants of the kinetic rate equations (αij for the transition i →j, etc.). N i is the number of systems of the ensemble in state i and the a i 's are constants. This paper and a previous one [Y. Chen and T. L. Hill, Biophys. J. (to be published)] form a complete noise analysis for discrete linear kinetic systems and may be used in differentiating various kinetic schemes in complex biological problems. Also obtained is a Poisson distribution function for the number of systems of an open ensemble at cycling steady state (that is, some transition rate constants among the system states do not obey the Wegscheider relation). This extends the usual steady state results on open ensembles in which the Wegscheider relation holds.
15N magnetic shielding anisotropies in 15N15NO
Authors: Bhattacharyya Pranab K. , Dailey Benjamin P.
Published: February 2004

The 15N magnetic shielding anisotropies in nitrous oxide (15N15NO) have been determined using a pulsed FT NMR spectrometer. The shielding anisotropies obtained from the temperature dependence of the nematic phase chemical shifts are 512 ± 10 ppm (central 15N) and 369 ± 15 ppm (end 15N). The values obtained from the nematic-isotropic phase difference method are 505 ± 10 ppm (central 15N) and 366 ± 10 ppm (end 15N). Theoretical estimates of the anisotropies from the so-called atom dipole method are also reported. The indirect scalar coupling constant has been assigned to be negative. The signs of the 15N spin-rotation constants are predicted to be positive.
Reduced 4f-5d electrostatic interaction of Tm2+ in SrCl2
Authors: Alig R. C. , Duncan R. C. , Mokross B. J.
Published: February 2004

The visible absorption and emission spectra of Tm2+ in SrCl2 sharpen at low temperatures and exhibit marked vibronic structure. The 4f12 3H6 5deg excited states account for these transitions. The splitting of these states is almost entirely due to the 4f-5d electrostatic interaction. For theory and experiment to agree, the free-ion electrostatic interaction must be multiplied by 0.6. This suggests a strong nephelauxetic (cloud-expanding) effect for the 5d electron on the divalent lathanides.
Study of the structure of molecular complexes. V. Heat of formation for the Li+, Na+, K+, F−, and Cl− ion complexes with a single water molecule
Authors: Kistenmacher H. , Popkie H. , Clementi E.
Published: February 2004

In order to obtain the heat of formation ΔH, for the ion-water complexes previously studied in the Hartree-Fock approximation in the first three papers of this series, we have computed the normal frequencies of the complexes, the zero-point energy correction to ΔH, and the molecular extra correlation energy. The main contribution to ΔH is due to the Hartree-Fock binding; the least important contribution results from the correlation effects. The Hartree-Fock binding varies from about 35 kcal/mole (Li+–H2O) to about 12 kcal/mole (Cl−–H2O); the zero-point correction is between 1 and 2 kcal/mole; and the molecular extra correlation correction is less than 1 kcal/mole. The computation of ΔH is analyzed in order to estimate upper and lower bounds. We conclude that the calculated ΔH values are accurate to about 2.0 kcal/mole. Experimental data support this conclusion. In the Appendix, the potentials for water-ion complexes have been presented in the form of a simple analytical expansion. The expansion has been obtained by fitting the Hartree-Fock computed energies for the water-ion complexes.
Effects of polymorphism on the Raman-active longitudinal acoustical mode frequencies of n-paraffins
Authors: Khoury F. , Fanconi B. , Barnes J. D. , Bolz L. H.
Published: February 2004

Raman spectroscopic measurements on the orthorhombic and monoclinic crystalline forms of n-C36H74 and n-C94H190 show that the frequencies of the longitudinal acoustical modes depend on the orientation of the chain axis relative to the planes containing the terminal methyl groups as well as the chain length. The frequency differences between the orthorhombic and monoclinic forms of a given n-paraffin depend on the magnitude and direction of the regular stagger between neighboring end groups in the monoclinic forms. It is concluded that these frequency differences are most likely associated with variations in end group packing associated with differences in crystalline form. The implications of these observations to the use of Raman spectroscopic data to characterize the morphology of chain-folded polyethylene crystals are discussed.
Vibrational spectra and structure of methyl chloroformate and methyl chloroformate-d3
Authors: Katon J. E. , Griffin M. G.
Published: February 2004

The infrared spectra of methyl chloroformate and methyl chloroformate-d3 are reported in the liquid and solid phases in the region 4000–50 cm−1. The liquid phase Raman spectra of these compounds are also reported. It is found that the two compounds readily crystallize as oriented polycrystalline films when cooled in contact with cesium iodide windows. The polarized infrared spectra obtained with these films make possible an improved vibrational assignment for the light compound and a good first assignment for the deuterium-substituted analog. The results are most consistent with a planar cis structure and there is no indication of the existence of a second conformer. No clear cases of crystal splitting are observed.
Structural implications of the microwave spectrum of hexafluoropropene
Authors: Jacob E. Jean , Lide David R.
Published: February 2004

Analysis of the microwave spectrum of hexafluoropropene, C3F6, has yielded rotational constants for the ground vibrational state of 2557.88, 1255.033, and 987.082 MHz. Assignments have also been made on the first four excited states of the CF3 torsional mode and on the first excited state of another low-lying skeletal mode. A rough estimate of 350 cm−1 has been obtained for the barrier to internal rotation of the CF3 group. The ground-state moments of inertia are consistent with the expected geometry of the molecule, in which all atoms are coplanar except for two equivalent F atoms in the CF3 group.
Atomic oxygen oscillator strengths in the autoionization region. I. The absolute strength of the 5s′ lines
Authors: Van Tassel R. A. , Huffman R. E. , Roebber John L.
Published: February 2004

A curve-of-growth method was used to determine the absolute oscillator strength and other line parameters of the autoionized transition OI:2s22p43P2→ 2s22p3(2D5/2,3/20) 5s′ 3D3,2,10. This method was used because the spectral width of the lines is far less than the bandwidth of the spectrometer. Neither lifetime nor emission measurements are applicable because depopulation of the upper state occurs predominantly by autoionization. The atomic oxygen concentrations were detemined by means of the O–NO2 titration. Sets of curves of growth were computed on the basis of the separation of the three levels, 3D3,2,10, as observed with a spectrograph, tabulated values of the relative line strengths based on L–S coupling, and consideration of the different broadening mechanisms operating under the conditions of the experiment. This included consideration of the configuration interaction of the upper states with the adjoining ionization continuum. Comparison of the experimental curve with the computed curves gives f = 0.0021, Σgf = 0.019, and Γ = 0.01 Å, resulting in an autoionization lifetime τ of 2 × 10−11 sec.
Nonorthogonal atomic self-consistent field orbitals
Authors: Raffenetti Richard C. , Ruedenberg Klaus
Published: February 2004

A method is presented for determining nonorthogonal linear combinations of accurate self-consistent field atomic orbitals which are analogous to nodeless minimal-basis-set Slater-type atomic orbitals. The utility of such nonorthogonal basis orbitals is discussed in terms of applications to molecular calculations.
Even-tempered atomic orbitals. V. SCF calculations of trialkali ions with pseudoscaled, nonorthogonal AO bases
Authors: Raffenetti Richard C. , Ruedenberg Klaus
Published: February 2004

Ab initio self-consistent-field calculations are reported for the triatomic alkali ions H3+, Li3+, Na3+, Li2H+, Na2H+, LiH2+, NaH2+, Li2Na+, LiNa2+, and their diatomic and monatomic dissociation products. Equilibrium conformations are determined and regularities in the interatomic distances are elucidated. Dissociation energies are calculated and all species are predicted to be stable by more than 30 kcal/mole, with the exception of LiH2+ and NaH2+ for which an SCF binding energy of less than 5 kcal/mole is found. Population analyses are discussed. Available experimental information is correlated with the theoretical findings. The calculations are carried out using basis sets of pseudoscaled even-tempered contracted Gaussian atomic orbitals which are found to perform very well.
High frequency dielectric response of dipolar liquids
Authors: Lobo Roberto , Robinson John E. , Rodriguez Sergio
Published: February 2004

The dynamical dielectric response of a condensed system of molecules with permanent electric dipole moments is studied. We start from the dynamical extension of the Onsager theory developed by Nee and Zwanzig, but generalized so as to be applicable at high frequencies. Specifically, we retain inertial terms and introduce relaxation effects in a way valid in a high frequency limit. The dielectric function obtained incorporates a diversity of both collective and single-particle behavior, consistently, over the entire range of frequencies below those of intramolecular excitation. It is noteworthy that not only is a collective mode, or dipolar plasmon, exhibited, but that its frequency is also a resonance of the single-dipole motion. The properties of the dielectric function are analyzed and illustrated in detail, and specific applications are made to water, to hydrogen chloride, and to chloroform.
Numerical results on two-body and (two + three)-body lattice dynamics of CaF2, SrF2, and BaF2
Authors: Ra O/.
Published: February 2004

Utilizing semiempirical two-body and (two + three)-body force fields, respectively, two distinct sets of shell-model calculations are reported on the crystal dynamics of CaF2, SrF2, and BaF2. The central force computations cover longwave properties, dispersion curves, specific heat, and thermal expansion. Also included are numerical results for mean square amplitudes as calculated conventionally and, in addition, by a new computational device which circumvents the need for diagonalizing the dynamical matrix in uninformative regions of k space. On comparing theory and measurement it appears, as expected, that the two-body potentials cannot alone account quantitatively for the experimental findings. The discrepancies, which decrease in the order CaF2, SrF3, and BaF2, probably do not prevent the models from being suitable for various orientational lattice dynamics calculations, say theoretical defect work. The calculations predict different branch pairings at the intersection of symmetry elements in the Brillouin zone for the three alkaline-earth fluorides, the CaF2 realization of compatibility requirements being confirmed by available neutron results. In the BaF2 case the predicted, but as yet unmeasured, dispersion relations exhibit a complete separation of optical and acoustic branches; the latter bearing a strong resemblance to those typical of monoatomic fcc lattices. The numerical work based on (two + three)-body force fields is limited to exploratory calculations concerning the longwave optical properties. Although indicating that Löwdin forces originating in both cation-anion as well as anion-anion overlap may be important, static Heitler-London values for overlap charge approximated by point charges are not suitable for rectifying the two-body shell models. However, in anticipation of a refined theory, present and previous formulas concerning three-body contributions may be useful when treated as adjustable adjunctions to the central force equations of motion.
Microwave radiometric investigation of vibrational relaxation in low pressure nitrogen discharges
Authors: Sahni Omesh , Jennings W. C.
Published: February 2004

A novel technique based on the coupling between electrons and molecular vibration levels has been used to investigate the temporal buildup of vibrational energy during the active period of pulsed N2 discharges. The radiometric technique monitors the decay of the electron average energy Ūe in the afterglow of a discharge excited by voltage pulses of variable duration. Since the electron distribution function in the N2 afterglow is often non-Maxwellian, Ūe is determined by first calculating the electron velocity distribution function from microwave measurements of the collisional broadening of the radiation temperature of electron cyclotron emission. If the quasi steady state value of Ūe [⪞] 0.5 eV in the afterglow, the electrons are essentially in thermal equilibrium with the molecular vibrational levels. Thus, the measured effective electron temperature can be taken as a direct measure of the vibrational temperature achieved in the active period. Results of this first low pressure study yield an effective electron superelastic de-excitation rate between 6 and 7 × 10−9 cm3/sec, a room temperature surface catalytic efficiency of ≈ 10−2 for deactivation at Vycor walls with pressure in the neighborhood of 1 Torr, and a normalized effective collision frequency for vibrational excitation by electrons of ≃ 10−8 cm3/sec.
Electrical resistance of the system isobutyric acid-water near the critical point
Authors: Stein Arnold , Allen Guy F.
Published: February 2004

The electrical resistance of sealed solutions of isobutyric acid-water at the critical composition were measured in the reduced temperature range (ε = T/Tc − 1)3.3 × 10−7 ≤ ε ≤ 6.6 × 10−2 using a Jones ac bridge and lock-in amplifier. Temperatures were controlled and measured to ± 0.0001°C. The temperature derivative of the resistance exhibits a strong divergence very close to Tc so that dR/dT [inverted lazy s] ε−d, where 0.56 ≤ d ≤ 0.77 depending on which of the several methods of data analysis presented are used. A mechanism is proposed which relates this strong divergence to the weak anomaly in the shear viscosity near Tc.
Reaction rate constant for 2N2(A 3Σu+)→N2(C 3Πu) + N2(X1Σg+, ν′ > 0)
Authors: Hays G. N. , Oskam H. J.
Published: February 2004

Absolute emission intensities of the Vegard-Kaplan and second positive bands were measured during the decay period of plasmas produced in nitrogen for pressures varying from 1 to 3 torr. The reaction rate constant k for the metastable-metastable energy pooling reaction N2(A3Σu+) + N2(A 3Σu+) → N2(C3Πu) + N2*(X) was found to be k = (2.6−1.4;+2) × 10−10cm3sec−1per molecule in nitrogen plasmas at 300°K. The value of k for a plasma temperature of 98°K was, within experimental errors, equal to the value obtained at 300°K.
On some aspects of the first-order centrifugal distortion constants in polyatomic molecules
Authors: Müller A. , Mohan N. , Alix A.
Published: February 2004

A detailed study of the extremal properties and the signs of the first-order centrifugal distortion constants is reported. It is shown unambignously that the signs of tαααα (α = x, y, or z) and tαβαβ (α and β in cyclic order correspond to x, y, or z) are always positive. Analysis of the force field corresponding to the extremal values of the centrifugal distortion constants is also reported. Mass effect on these constants in isotopically substituted molecules has been studied by using the first-order perturbation theory. Some properties of certain matrices of θ and φ characterizing the centrifugal distorsion constants are also discussed. For many XYZ (C∞ν)-type molecules, it was found that the experimental value of DJ lies in the neighborhood of the solution corresponding to the condition that θ22 and tαααα are maximum.
Dispersion contributions to surface energy
Authors: Mahanty J. , Ninham B. W.
Published: February 2004

The concept of dispersion self-energy of a molecule or atom of finite size in an inhomogeneous dielectric medium is developed. The self-energy, which is always finite and its dependence on distance from an interface dividing two media, is evaluated. The surface energy of the interface is obtained in terms of the self-energies of all the molecules of the medium. The resulting expression is shown to reduce in suitable approximation to forms similar to those derived by Fowkes and by Craig.
Bound-free transition of trapped electrons in polar matrices
Authors: Fueki Kenji , Feng Da-Fei , Kevan Larry
Published: February 2004

The photon energy dependence of the bound-free transition probability for trapped electrons in polar matrices is calculated for ice, ethylene glycol-water (50/50), 2-propanol, 2-methyltetrahydrofuran, diisopropylamine, and triethylamine. A hydrogenic model is used for the transition probability, and the necessary parameters are calculated from a semicontinuum potential model. Both distorted wave and plane wave approximations are made. The calculated results are in reasonable agreement with the available experimental data on the photon energy dependence of photobleaching and photoconductivity efficiencies for trapped electrons in several matrices and support the assignment of bound-free transitions to these processes. Distinct trends with matrix polarity are reproduced by the calculations.
F + H2, D2, HD reactions: Chemical laser determination of the product vibrational state populations and the F + HD intramolecular kinetic isotope effect
Authors: Berry Michael J.
Published: February 2004

Relative gain coefficients of individual HF†(DF†) laser transitions in the F + H2, D2, HD chemical lasers have been measured by a grating selection technique. Product vibrational population inversions Nν/Nν−1 were calculated from these measurements. The results indicate a complete parallelism in product vibrational energy content in the four room-temperature isotopic reactions, modified only by a threshold effect for HF†(ν = 3) production in the F + HD reaction and by secondary mass effects in the HF-producing VS DF-producing reactions. A room-temperature measurement of the intramolecular kinetic isotope effect in the F + HD reaction is reported. Lastly, evidence is presented for highly efficient energy-transfer processes [V → V′: HF†(ν = 3) + HD(ν = 0) → HF†(ν = 2) + HD†(ν = 1) and E → V: I*(5 2P1/2) + HF†(ν) → I(5 2P3/2) + HF†(ν + 2)].
Overhauser effect on saturated lines of an AX spins system: 13C−1H in chloroform
Authors: Duplan J. C. , Briguet A. , Delmau J.
Published: February 2004

When saturating fields are successively applied at resonance frequencies of an AX spins system, the populations of the energy levels change towards new equilibrium values. The transient decay of a saturated line is used, in the case of chloroform, to obtain information about the relaxation of carbon-13.
Thermal energy positive ion reactions in a wet atmosphere containing ammonia
Authors: Fehsenfeld F. C. , Ferguson E. E.
Published: February 2004

Rate constants for reactions of H+(H2O)n with NH3 for n = 1−4 have been measured at 296°K. Rate constants for NH4+ (H2O)1,2 with NH3 and the rate constant for NO2+(H2O) + NH3 → NH4+ + HNO3 have also been measured. A number of equilibrium constants for reactions of the form NH4+(NH3)x(H2O)y + NH3 ⇄ NH4+(NH3)x +1 (H2O)y − 1 + H2O have also been measured at 296°K. All of the measurements have been carried out in a flowing afterglow system.
Single crystal electron paramagnetic resonance study of tris (octamethylpyrophosphoramide) copper (II) perchlorate
Authors: Koch Richard C. , Joesten Melvin D. , Venable John H.
Published: February 2004

Single crystal EPR spectra of tris(octamethylpyrophosphoramide) copper (II) perchlorate have been obtained at 90 °K. The results are correlated with x-ray structural data and evidence is presented in support of a model in which three g tensors are related by the trigonal axis of the unit cell. The model is consistent with the dynamic-static Jahn-Teller theory proposed by Abragam and Pryce which assumes the presence of three mutually perpendicular tetragonal distortions of equal energy.
Primary processes of the photolysis of ethylenimine at Xe and Kr resonance lines
Authors: Kawasaki Masahiro , Iwasaki Masahiro , Ibuki Toshio , Takezaki Yoshimasa
Published: February 2004

The direct and sensitized photolyses of ethylenimine vapor at Kr and Xe resonance lines have been studied. The hydrocarbon products are ethylene, ethane, methane, and small amounts of acetylene, propane, and n -butane. Other products detected are hydrogen, ammonia, and the dimers of ethylenimino radicals. The effect of added oxygen or ethylene has also been investigated. Emphasis being laid on the formations of methyl radicals, ethylene, and acetylene, the quantum yields of primary processes are determined as follows; (CH2)2NH + h ν → C2H4 + NH [I], CH3 + (H2CN) [II], and C2H2 + (NH3) [III]; at Xe resonance lines φI = 0.36, φII = 0.41, φIII = 0.028; at Kr resonance lines φI = 0.22, φII = 0.13, φIII = 0.028. Xe and Kr sensitized photolyses have also been studied. A very slight difference in the product distribution between the direct and sensitized photodecompositions has been observed.
Electron drift and Hall mobility in γ-irradiated 10M NaOH glassy alkaline ice
Authors: Huang T. , Eisele I. , Kevan L.
Published: February 2004

The drift and Hall mobility of electrons in 10M NaOH glassy alkaline ice has been studied to determine the relevant charge transport mechanisms in this disordered system. The electrons are photoexcited to a conduction state after being trapped in the matrix at 77 K by γ irradiation. The dominant electron scattering mechanisms have been deduced from variation of voltage and temperature, and it appears that electron transport in this matrix is well characterized by a band model. Field dependent mobilities are observed and indicate that hot electron effects exist. In the field independent mobility region, the limit of which depends on temperature, the dominant mechanism is scattering by acoustical and optical phonons. This holds above 77 K and probably to much lower temperatures. In the field dependent mobility region, the dominant mechanism is ionic species scattering, notably by O−, at lower temperatures, and acoustical and optical phonon scattering at higher temperatures. The dividing temperature decreases with increasing field and is ∼50 K at 4 kV cm−1. At constant temperature versus field, the mobility is dominated by phonon scattering in the field independent mobility region, by ionic species scattering in the initial part of the field dependent mobility region, and by phonon scattering again at high fields. Drift mobility, Hall mobility, and photoconductivity results all interrelate and give a consistent picture of electron transport in 10M NaOH. The super-Ohmic photocurrents, previously observed, are seen to be due to dominance of ionic species scattering. The temperature and field dependence of the mobility is satisfactorily predicted by a simple band model and the mobility magnitude is at least semiquantitatively predicted. However, the critical field, at which hot electron effects occur, is predicted to be too high by the band model.
Thermodynamics of lithium-isotope-exchange reactions. IV. Exchange between the isotopic metals and solid fluorides
Authors: Hall John C. , Silvester Leonard F. , Singh Gulzar , Rock Peter A.
Published: February 2004

This paper reports our results for the direct experimental determination of the equilibrium constant for the lithium-isotope-exchange reaction 7Li(s) + 6LiF(s) = 6Li(s) + 7LiF(s). This reaction was studied in electrochemical double cells without liquid junction of the type 7Li(s)|7LiF(s)|KBF4(pc)|6LiF(s)|6Li(s), where pc represents the solvent propylene carbonate. The experimental value of the equilibrium constant for this reaction is K = 1.10 ± 0.01 (296°K). We also report here our results for a complete Born-von Kármán lattice calculation of the equilibrium constant for the above reaction. The calculated result is K = 1.082 at 298.15°K. The above reaction exhibits the largest lithium isotope effect that has been found experimentally.