bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of V-V and V-R, T energy transfer measurements in mixtures containing HF
Authors: Bott J. F. , Cohen N.
Published: February 2004

A pulsed HF chemical laser has been used to excite HF molecules to their first vibrational level. The decay times of the infrared fluorescence from HF(ν = 1) have been used to determine the rate coefficients for energy transfer from HF to various collision partners including H2, D2, N2, O2, DF, HCl, CO2, NO, CO, and HBr. The experiments were performed at temperatures from 450 to 1000°K for most of the molecules. as well as at 295°K. For the higher temperature measurements, the experiments were performed behind a reflected shock wave in a shock tube. The compression heating capability of a shock tube has been used successfully as an alternative to a heated cell for laser-induced fluorescence measurements. The room-temperature probabilities of energy transfer from HF to the various molecules plotted versus energy mismatch fell along two distinct lines: one for homonuclear and one for heteronuclear molecules. The rate coefficients (cubic centimeters per mole second) for the molecules with the smallest energy mismatch had temperature dependences between T−1 and T0 near T = 295°K, while the molecules with larger energy mismatches and correspondingly smaller rate coefficients showed positive temperature dependences. The room-temperature relaxation rates of HF in the presence of the various molecules were measured to be H2, (1.7 ± 0.1) × 10−2; HCl, (1.7 ± 0.1) × 10−2; DF, (7.7 ± 0.4) × 10−2; CO2, (3.6 ± 0.2) × 10−2; D2, (3.1 ± 0.6) × 10−3; N2, (1.52 ± 0.15) × 10−4; O2, (4.5 ± 0.6) × 10−5; CO, (1.8 ± 0.2) × 10−3; HBr, (7.5 ± 1.0) × 10−3: and NO, (6.0 ± 1.0) × 10−3, in units of (μsec torr)−1. These rates represent the total relaxation rate of HF due to both V - V and V - R,T energy transfer. Relaxation rates of some of the chaperone molecules by HF as well as their self-relaxation rates were also measured.
Shear dependence of the viscosities of both nitroethane-3-methylpentane and polystyrene-cyclohexane mixtures in the critical region
Authors: Tsai B. C. , Myers M. , McIntyre D.
Published: February 2004

The shear viscosities of a critical mixture of nitroethane-3-methylpentane were measured near the critical temperature (ΔT values of 0.500 to 0.55°C) over a range of shear rates from 700 to 0.015 sec−1. No shear dependence within experimental error was found at any temperature. The shear viscosities of solutions of polystyrene-cyclohexane near or at the critical composition were also measured at shear rates from 1500 to 0.1 sec−1 and at a ΔT value of 0.24°C. A constant 10% increase in viscosity at low shear was found for mixtures having concentrations near the critical concentration. Consequently the increase cannot be solely attributed to critical phenomena, but must be related to other polymeric phenomena.
Mössbauer effect and thermal analysis of frozen ferrous perchlorate solutions. I
Authors: Cameron J. A. , Keszthelyi L. , Nagy G. , Kacsóh L.
Published: February 2004

Aqueous Fe(Cl04)2 · 6H2O solutions of different concentrations were quickly frozen to liquid nitrogen temperature and the zero-velocity Mössbauer transmission and differential thermoanalytical curves were measured simultaneously as the samples warmed up. The solutions segregated into two phases: one consisting of pure water (phase I), the other composed of ferrous perchlorate molecules and water molecules together (phase II). Phase II was a glasslike material which, above the glass transition temperature, behaved like a supercooled liquid and recrystallized near −80°C. The concentration dependence of the recrystallization was measured.
Radio-frequency spectrum of metastable N2(A3Σu+). II. Fine structure, magnetic hyperfine structure, and electric quadrupole constants in the lowest 13 vibrational levels
Authors: De Santis David , Lurio Allen , Miller Terry A. , Freund Robert S.
Published: February 2004

The hyperfine structure of the A3Σu+ state of N2 has been measured at low magnetic fields ([similar or less-than] 1 G) by means of the molecular beam magnetic resonance method. Resolved transitions between hyperfine levels with quantum numbers (ν,N,J,F,MF) to levels (ν,N,J,F−1, M'F=MFor MF ± 1) have been observed for states with quantum numbers (N,J,F) equal to (0,1,2), (1,2,4), (1,2,3), (2,1,2), and (3,2,4), within each of the vibrational levels, ν = 0–12, and for various vibrational levels of the (3,2,3) and (3,2,2) states. Individual hyperfine frequencies have been measured to an accuracy of ± 10 kHz. The theory needed to calculate and interpret the hyperfine structure in any 3 Σ state is developed in considerable detail. By using degenerate perturbation theory to remove various matrix elements connecting different electronic and vibrational states it is shown that the effective rotational-fine and hyperfine structure Hamiltonians for a particular vibrational level of the A 3 Σ state of N2 can be written, respectively, as Hve(RF−N2) = B̃v N2 + (2/3)1/2 λ̃v T2 (S,S) · T2 (n,n) + γ̃v T1 (N) · T1 (S)and Hve(HF−N2)= α̃v T1 (IT) ·T1 (S) − (5/2)1/2 β̃v T1 (IT) · T1 [T1 (S), T2(n)] + p̃v T1 (N) · T1 (IT) + (3/8)1/2 [open phi] Q̃v T2 (Ia,Ia) ·T2 (n,n) + dv T2 (Ia,Ib) ·T2 (n,n). The parameters ãv,β̃v, Q ̃v, p̃v, and Gv ≡ (2B̃v − γ̃v)/λ̃v have been determined (independently for each level) from the observed molecular beam transitions. dν is calculated independently of the beam data and λ̃v is obtained from Gv by assuming that B̃v and λ̃v are known from optical data. The experimentally determined values for α ̃v, β̃v, Q̃v, p̃v, and Gv along with their experimental uncertainties are given. The parameters can be fit to within experimental error by quadratic power series in (ν + 1/2). Each ν dependent parameter in the above effective Hamiltonian consists of a number of both first order (diagonal) and second order terms. It is concluded that in most cases second order terms (arising from matrix elements off diagonal in electronic and vibrational states) are not negligible compared to the present experimental error. However, for α ̃v, β̃v, and Q̃v, such second order terms represent only a minor contribution.
Absolute total cross sections for Li-molecule scattering
Authors: Dehmer Patricia , Ury George , Wharton Lennard
Published: February 2004

Absolute total scattering cross sections were measured for 7Li scattered by D2, N2, CO, CO2, CH4, and SF6 over a range of Li beam velocities of 0.75–4.75 × 105 cm/sec corresponding to a range of relative kinetic energies of 0.04–0.33 eV for Li–D2 to 0.02–0.79 eV for Li–SF6. In the observed cross sections random experimental errors were less than 1.5% and systematic errors were between −0.3% and +1.4%. Two spherically symmetric potentials, the Lennard-Jones (12,6) and the Buckingham-Corner were fit to deconvoluted and statistically smoothed data using a non-linear least squares fitting routine. For each Li-molecule system a satisfactory fit could be obtained with standard deviations of approximately 1%–2%. The best fit potentials gave accurate values for the average long range attractive part of the potentials over the range of limiting impact parameters. Evidence from high resolution differential cross section experiments is introduced that indicates that there should be relatively little damping of the glory features of the total scattering cross sections for the Li-molecule systems studied here, and hence the ability of spherical potentials to reproduce the data is not surprising.
Vibronic interactions, resonance Raman spectra and bond strengths for the radical anion salts of tetracyanoethylene
Authors: Hinkel Jerald J. , Devlin J. Paul
Published: February 2004

Raman spectra for the intensely colored salts of the tetracyanoethylene radical anion with sodium and potassium cations confirm previous assertions that the infrared salt spectra are completely dominated by vibronic interaction effects. As expected, strong Raman scattering has been observed at frequencies coincident with the intense infrared bands which have been assigned to totally symmetric modes activated by an ``electron-vibration'' moment. The scattering intensities of the symmetric stretching modes (ν1, ν2, and ν3) reveal a complex dependence on excitation frequency which is qualitatively consistent with the observed vibronic structure of the electronic absorption band. By confirming the assignment of several of the radical anion internal modes, the Raman data have also permitted the evaluation of reliable stretching constants for comparison with the neutral molecule force constants and quantum chemical predictions of bond order changes. New data and a subsequent force constant analysis have required the reassignment of
Recombination rate measurements in nitrogen
Authors: Douglas-Hamilton D. H.
Published: February 2004

A method of generating an atmospheric pressure high-electron-density plasma with arbitrary electron temperature is described and applied to measurement of electron ion recombination rates in N2. The recombination rate for N2 is shown to be independent of pressure in the region investigated and is given as function of E/N and electron temperature.
Bounds to dispersion energy coefficients
Authors: Abdulnur Suheil F.
Published: February 2004

Starting from the second-order perturbation energy expression and utilizing inner projection and operator inequalities techniques, easy to evaluate expressions for the bounds to dispersion energy coefficients are obtained in terms of ground state sum rule values of the separated atoms for two sets of basis functions. The resulting bounds are narrower than those obtained starting from the Casimir-Polder integral formula and bounding each of the polarizabilities in that expression by using either the present technique and basis set or the [1,0] Padé approximants. The bounds obtained here from the larger basis set are of comparable quality to those reported using Gaussian quadrature or the [2,1] Padé approximants to bound the polarizabilities in the Casimir-Polder formula. A derivation of the Kramer-Herschbach combination rule from one of the bounds is also presented.
LCAO-MO-SCF calculations using Gaussian basis functions. XI. BeNe and BeAr. Desirable criteria for atomic contraction coefficients for molecular formation and valence-shell correlation
Authors: Kaufman Joyce J.
Published: February 2004

Ab initio LCAO-MO-SCF calculations of the lowest 1Σ+ states of BeNe and BeAr showed that the systems were both repulsive. Population analyses indicated that there was only a very small amount of π electron density transferred from the rare gas π orbitals to the empty π orbitals on the boron. Examination of the SCF gross atomic populations of both the occupied and unoccupied orbitals led to several interesting observations. First, it seems possible to identify, merely from the SCF gross population analyses, which virtual molecular orbitals will correlate uniquely certain of the occupied molecular orbitals. This could be very useful in enabling one to truncate expeditiously a set of virtual orbitals. Second, several choices for contracting an 11s 6p atomic Gaussian basis set for first row atoms and a 17s 12p atomic Gaussian basis set for second row atoms better suited to describe molecular formation and virtual orbitals for valence shell configurations are suggested.
Semiclassical approximations for scatterings by nonlocal potentials. I The effective-mass method
Authors: Gerber R. B.
Published: February 2004

A semiclassical theory for the scattering of a particle by a nonlocal potential is developed with the purpose of applying it to several aspects of atomic collisions. The scheme that we construct is based on the replacement of the Hamiltonian with the nonlocal interactions by an approximate Hamiltonian that includes a certain local potential and an effective mass that depends on the distance of the particle from the origin of the potential. This is followed by the introduction of either the JWKB or the Eikonal approximation in the form familiar in potential scattering theory. The dependence of the approximate semiclassical wavefunctions and phase shifts on the effective mass is studied and effects owing to the variation of the latter quantity with the coordinates are discussed. A treatment is provided for cases where the effective mass has a zero or a pole. Appropriate ``connection formulas'' are derived for the determination of the correct JWKB solution in regions that lie in the neighborhood of points at which such a zero or a singularity occurs. It is pointed out that zeros of the effective mass can lead to pronounced resonances and to barrierlike effects. Since any multichannel collision process can be discussed in terms of equivalent one-body equations involving nonlocal potentials, the semiclassical scheme we develop is applicable to inelastic and rearrangement processes as well as to elastic ones. Applications of this method to atomic collision theory will be described in a forthcoming publication.
Dependence of vicinal H–H coupling constants in substituted ethanes on potential function characteristics to internal rotation. II. Application to ABX PMR spectrum of 1,1,2-trisubstituted ethanes of the type XCH2–CHXY
Authors: Lin Wei-chuwan
Published: February 2004

The three-spin system of 1,1,2-trisubstituted ethanes of the type XCH2–CHXY exhibits either a typical complex ABX or a deceptively simple ABX proton spectrum depending on the nature of substitution groups X and Y and also on the nature of solvent. A theory governing the change of the vicinal coupling constants in such an ABX spectrum was developed in terms of the potential function characteristics to internal rotation. Based on rotational averaging and on the simple model of internal rotation about the C–C axis, a refined Karplus equation for the vicinal H–H coupling constant could yield the analytical expressions, each of which, respectively, describes the explicit functional dependence of the ratio and of the individual vicinal coupling constants on internal rotation parameters α, β, and γ. Where α is related to the ethane barrier, β to the maximum interaction energy between two unlike bonds C–X and C–Y, and γ to the maximum interaction energy between two identical C–X bonds. These expressions permit experimental determination of γ at a given temperature with the values of α and β known from literature. The determined values of γ for three different compounds of the type BrCH2–CHBrY in the medium of the same solvent were found to be in complete agreement with one another. A similar agreement was also obtained for another group of compounds of the type ClCH2–CHClY. Other physical parameters of internal rotation, viz., barrier, energy difference between rotamers, etc., can be expressed by α, β, and γ, and can be easily evaluated.
Long-range intermolecular forces in crystalline solids
Authors: Rafizadeh Hamid A.
Published: February 2004

Expressions for the multipole interaction elements of the dynamical matrix are obtained using the rigid molecule approximation and the Coulomb interaction between the composite ions of the molecules in an ionic molecular crystal. It is shown that this formulation includes the electronic polarization effects. The monopole, dipole, quadrupole, and octupole contributions are calculated for model crystals of simple cubic structure having linear and tetrahedral molecules as basis. The effect of multipole interactions is found to be very significant. The neglect of multipole interactions in the calculation of translation coefficients of the lattice with linear molecule basis introduces errors as large as 30% along the [q00] direction. A similar calculation with the more complex tetrahedral molecule basis shows an increase in the errors to as large as 240%. In general the magnitude of multipole coefficients is seen to increase with the increasing complexity of the molecular basis.
Negative-charge production by hydrogen atoms in Ar, Kr, Xe, CO, CO2, and CH4 in the energy range 80–2000 eV
Authors: Dehmel R. C. , Meger R. , Fleischmann H. H. , Steinberg M.
Published: February 2004

Experimental cross sections for negative-charge production by neutral hydrogen atoms in the energy range 80eV–2keV in Ar, Kr, Xe, CO, CO2, and CH4 are reported. In all cases, a smooth increase of the cross section with energy is observed, from values of about 10−17 cm2 at 80 eV to a few times 10−16 cm2 at 2kev.
T
4 dependence of the nuclear quadrupole resonance frequencies in solids. II
Authors: Schempp Ellory , Silva P. R. P.
Published: February 2004

Analyses of experimental data for NQR frequency shifts as a function of temperature reveal a dominant T4 dependence at sufficiently low temperature, T ⪝ 20°K, in accord with a recent prediction. The results indicate the necessity of adding a Debye term to the usual Bayer expression. The coefficient of the Debye term is shown to vary with TD−5; preliminary results indicate that values of the Debye temperature TD may be obtained from low temperature NQR data.
Dissociation of carbon dioxide behind reflected shock waves
Authors: Dean Anthony M.
Published: February 2004

The apparent dissociation rate of CO2 has been measured by monitoring infrared emission from dilute CO2/Ar mixtures behind reflected shock waves. These experiments covered the temperature range of 3700–5500 °K and a pressure range of 500–800 torr. The Arrhenius parameters (in units of cubic centimeters molecule−1· second−1) of k1 are: log A=−9.98 ± 0.09 and Ea=84.72 ± 1.84 kcal/mole. The effect of impurities was minimized by keeping background pressures in the shock tube below 5 × 10−5 torr. Additional runs with 150 and 465 ppm CH4 added to 1% CO2/Ar mixtures were also made. Assuming CH4 was the only impurity in those runs, numerical integration calculations of the likely mechanism were performed. Quantitative agreement with the experimental results was obtained using literature values for all rate constants and the value of k1 reported above. These results strongly suggest that the impurity levels in the ``clean'' CO2/Ar system were indeed low (∼ 10 ppm) and thus could not account for the anomalously low value of Ea. This amount of impurity can raise the activation energy for the dissociation by less than 3 kcal/mole. It is suggested that Ea for the dissociation under these experimental conditions is thus less than 90 kcal/mole.
On an evaluation of the accuracy of the uniform semiclassical approximation for differential elastic scattering cross sections
Authors: Mullen J. M. , Thomas B. S.
Published: February 2004

The uniform approximation to the differential elastic scattering cross section is extended to allow direct comparison of approximated cross sections with cross sections computed by exact evaluation of the partial wave sum using WKB phase shifts. Results of calculations are presented and an assessment is made of the accuracy and utility of the uniform approximation.
Time resolution and characteristics of a broadband picosecond continuum and light gate
Authors: Varma C. A. G. O. , Rentzepis P. M.
Published: February 2004

A broadband continuum which last a few picoseconds can be generated in isotropic materials such as liquid H2O or D2O by single picosecond pulse excitation. It is demonstrated that the blue part of the spectrum is delayed relative to the red portion. A spectral analysis reveals a stimulated inverse Raman band around 260 cm−1 to the blue of the first anti-stokes emission. We offer two alternative explanations for this observation. The open time of the light gate is shown to depend on various parameters and in the case of a CS2 shutter, it may be extended over much longer time intervals than the pulse duration. At the same time we have observed depolarization and isotropic scattering of the interrogating light.
Water molecule interactions. Stability of cyclic polymers
Authors: Lentz Barry R. , Scheraga Harold A.
Published: February 2004

Ab initio LCAO-SCF molecular orbital calculations have been carried out with an extensive basis set to determine the stabilization energies of a cyclic trimer, a cyclic tetramer, and various noncyclic oligomers of water. The cyclic trimer is shown to be less stable than the noncyclic one. It is concluded that appreciable nonadditive effects are not present in cyclic polymers of water and that these structures show no special stability (compared to noncyclic ones) other than that to be expected from their extra hydrogen bond. Finally, the results of these and similar calculations are used to calculate the lattice energy of ice I, which agrees well with the experimental value.
Raman spectra and structure of B2F4 in the gaseous and solid states
Authors: Durig J. R. , Thompson J. W. , Witt J. D. , Odom J. D.
Published: February 2004

The Raman spectra of B2F4 have been recorded from 25 to 1500 cm−1 with the sample in both the gaseous and crystalline states. An assignment of the normal vibrations of the molecule in the planar form is presented. No evidence could be found for the conversion from the D2h form in the solid to a nonplanar D2d form in the gas as had been previously reported. It appears that the rule of mutual exclusion is retained in the spectra for the vapor and liquid states and that the molecule has D2h symmetry in all physical states. The optically active translations and librations have been observed in the low frequency infrared and Raman spectra of the solid, respectively. Intermolecular force constants have been calculated.
Relaxation of the proton spin dipolar energy in hexagonal ice
Authors: Bruno G. F. , Pintar M. M.
Published: February 2004

The relaxation time of the proton spin dipolar energy, T1D in hexagonal ice was measured to be 35 μsec at −24°C. Within the accuracy of the experiment (±9%), no anisotrpy was observed when the crystal was rotated around the b axis. Measurements of the spin-lattice relaxation time in the rotating frame T1ρ are reported for different rf fields, H1 at −2.4 and −24°C. At the lower temperature, at H1 of 7 G, T1ρ was anisotropic ([inverted lazy s] 24%) if the crystal was rotated around the b axis. This anisotropy is primarily a result of the anisotropy of the proton dipolar specific heat. The Slichter-Ailion parameter p was calculated for rotational jumps accompanying the ultra slow diffusion of the water molecule. If two protons only are considered (one water molecule), the parameter p is isotropic and equals −0.2. The calculation was made also for the two water protons and two first neighbors. The isotropic average of this p is −0.05 if rotational jumps around two axes are excluded. If the ice lattice is simulated by using groups of four protons, p remains very small. It varies between −0.07 and 0.00 if the crystal is rotated around its b axis. At −24°C, using the calculated p and the experimental T1D, we estimate the correlation time for the diffusion to be 37 ± 6 μsec.
Relaxation of vibrationally excited HF in levels v=1 and v=2. II. By CH4, C2H6, C3H8, C2H2, and C2H4
Authors: Anlauf K. G. , Dawson P. H. , Herman J. A.
Published: February 2004

The rate constants for the vibrational deactivation of HF(v = 1,2) by CH4, C2H6, C3H8, and C2H2 were measured by monitoring the decay of HF† rotation-vibration emission in a fast flow system. For these hydrocarbons the energy transfer processes are very efficient. In the case of C2H4 the rate constant could only be estimated.
Relationship between the metal ionization energies and the chlorine K—x-ray absorption of some transition metal chlorides
Authors: Sugiura Chikara
Published: February 2004

The K absorption spectra of chlorine in CrCl2, CuCl2, and ZnCl2 have been obtained with a 50-cm bent-quartz-crystal vacuum spectrograph. Results are evaluated by comparing the obtained spectra with the chlorine K absorption spectra of MnCl2, FeCl2, CoCl2, and NiCl2 reported previously. Chemical shifts are also found for the first absorption maximum and discussed in relation to the ionization energies of the monovalent metal ions. The chemical shifts are accounted for in terms of the change of the ionization energies.
Vibrational spectrum of MoF5
Authors: Acquista Nicolo , Abramowitz Stanley
Published: February 2004

The infrared spectrum of matrix isolated MoF5 as well as the Raman spectra of the liquid and polycrystalline species have been observed. The use of double boiler Knudsen cells has facilitated a vibrational assignment for monomeric MoF5 based on a trigonal bipyramid (D3h) structure.
On the strengths of the Fourier components of gas-surface interaction potentials
Authors: Goodman Frank O.
Published: February 2004

Earlier calculations of the interaction potential energy of a gas atom with a solid, as a function of position of the gas atom [F. O. Goodman, Phys. Rev. 164, 1113 (1967)], are used to estimate the strengths of the Fourier components (in other words, the diffraction strengths) of gas-surface interaction potentials. The fcc(001) surface is discussed as it is relevant to the usual experiments involving LiF. Each Fourier component of potential is related to a reciprocal lattice vector of the surface, and it is concluded that the diffraction strengths decrease rapidly with increasing reciprocal lattice vector length. Essentially, at least for the purposes of calculations of diffracted intensities, the only nonnegligible diffraction strengths are those associated with the eight smallest nonzero reciprocal lattice vectors; the values of the nonnegligible diffraction strengths are estimated.
Single crystal Raman spectrum of the external phonons in 5-bromotetrazole
Authors: Baglin F. G.
Published: February 2004

The six Raman active external phonons in 5-bromotetrazole have been assigned by observing four different Raman tensor elements, a(ca)c, a(cb)c, a(ba)c, and a(bb)c. In particular, the librational and translational phonons have been identified and approximate normal modes have been described for them. These results are compared to earlier work on L-alanine and imidazole single crystals. No disorder phenomena were observed in 5-bromotetrazole as in L-alanine. Harmonic force constant calculations confirm the structural prediction that, at K̄=0, no hydrogen-bond influences should be exerted on the external phonon frequencies. To our knowledge this work represents the first unambiguous single crystal Raman study of a hydrogen-bonded ring compound.
35Cl pure quadrupole resonance in acetylated glycopyranosyl chlorides. Relation between chlorine nuclear quadrupole coupling constant and molecular conformation
Authors: Guibé Lucien , Augé Jacques , David Serge , Eisenstein Odile
Published: February 2004

Nuclear pure quadrupole resonance of the chlorine atom bound to carbon atom C1 in several hexo- and pentopyranosyl derivatives has been detected. Observed resonance frequencies are distributed over two groups, centered, respectively, at 35.535 and 35.123 MHz. The two groups can be related to the two possible positions, axial and equatorial, of the chlorine atom bound to the anomeric carbon. The interpretation is supported by general rules of conformational analysis and by conclusions derived from the study of the equilibrium between conformers in solution. An all electron, ``ab initio'' calculation of molecular wavefunction, carried out on a simplified model (2-chlorotetrahydropyran) similar to the molecules under study, yields electronic densities on each atomic orbital, especially those of chlorine, as well as bond indexes for both axial and equatorial conformations. Values of the chlorine electric field gradient, as deduced from the computed populations with the help of the Townes and Dailey theory, are consistent with the variation of the experimental frequencies between axial and equatorial compounds.
Three-atom scattering in gas-phase electron diffraction. II. A general treatment
Authors: Wong T. C. , Bartell L. S.
Published: February 2004

Intramolecular multiple scattering of electrons by polyatomic gas molecules is investigated with the aid of Glauber's theory of high energy elastic scattering. The key to a simpler and more rapidly convergent expression for dynamic scattering corrections is found in a propitious transformation of variables. An analytical representation of the corrections averaged over molecular rotations and vibrations is presented in a form suitable for routine electron diffraction analyses of molecular structure. Magnitudes and practical considerations in analyses are briefly discussed.
Determination of rotational relaxation rates by measurement of the time dependence of saturation in microwave spectroscopy
Authors: Brittain A. H. , Manor P. J. , Schwendeman R. H.
Published: February 2004

A spectrometer for measuring the time dependence of a microwave transition is described. The instrument uses the Stark effect to turn the absorption on and off, and an electronic integrator to obtain the desired signal-to-noise ratio. The qualitative features of the time-dependent spectra as a function of sample pressure, microwave power, and microwave frequency are described. A numerical procedure, based on an equation previously derived [J. Chem. Phys. 57, 3511 (1972)] for extracting the pressure-dependent relaxation rate is outlined. The results of application of the method to the determination of relaxation rates for the J = 1 ← 0 and J = 2 ← 1 transitions in OCS, and the J=3, K=3 inversion transition in NH3 are detailed. In all three cases it is found that the pressure-dependent relaxation rates are very similar to those implied by linewidth measurements. The implications of this result are discussed.
Radiationless transitions in isolated molecules
Authors: Lin S. H.
Published: February 2004

The radiationless decay rate constant of a single vibronic state and the equilibrium average nonradiative decay rate constant of an isolated molecule have been shown to be obtainable from the appropriate inverse Laplace transforms of the thermal average rate constants. An expression of the nonradiative decay rate constant of a single vibronic state, including the frequency changes, has been derived and has been compared with that obtained by Nitzan and Jortner and with that obtained by Heller et al. The microcanonical average rate constant has been shown to be to be derivable from the thermal rate constant by replacing β[β = (kT)−1] in the thermal rate constant by the corresponding β* of the isolated system, which is to be determined from the energy of the system.
The mechanism of shear induced structural changes in liquid crystals—cholesteric-polymer solutions
Authors: Marsh D. , Pochan J. , Erhardt P.
Published: February 2004

The reflectance spectra and rheological properties for a cholesteric liquid crystal-polyisobutylene solution, have been obtained as a function of mechanical shear. The optical data are explained in terms of a layered structure consisting of tilted and untilted helical Grandjean texture and a dynamic focal-conic texture. At low shear rates < 1.72 sec−1, this system behaves optically and rheologically as a normal mixed cholesteric system. At greater shear rates, the structural reinforcing properties of the polyisobutylene cause optical and rheological behavior different from that observed in mixed cholesteric and cholesteric-nematic mixtures. The most striking effect of the polyisobutylene is its facility to disrupt the shear induced focal-conic component, causing relaxation to the Grandjean texture in a way that is similar to raising the temperature or releasing the surface constraints on the system.
Molecular theory of the translational Stokes-Einstein relation
Authors: Kivelson Daniel , Jensen S.J. Knak , Ahn Myong-Ku
Published: February 2004

A molecular-statistical derivation is presented for the Stokes-Einstein expression for the translational diffusion constant for a Brownian (large) particle. The friction constant is expressed in terms of a correlation function of the forces on the particle, and this correlation function is related to the correlation function of pressure fluctuations in a volume equal to that of the particle. Whereas the forces are those on the particle surface, the pressure fluctuations are a property of the liquid solvent. The amplitude of the pressure fluctuations can be obtained from fluctuation theory and the time dependence can be obtained from hydrodynamics, which in turn can be derived from molecular-statistical considerations. Although the exact numerical factors cannot be obtained, the linear dependence of the friction constant on the radius of the Brownian particle is derived. Finally, a discussion of the diffusion constant for small diffusing particles is presented.
Nonuniform resonance Raman effect in diphenylpolyenes
Authors: Schmid E. D. , Brosa B.
Published: February 2004

The Raman intensities (RI) of the aromatic CH stretching vibrations (near 3000 cm−1) and the ring vibrations (near 1600 cm−1) have been determined for some diphenylpolyenes. Using argon ion and He–Ne laser excitation the RI's of the 1600 cm−1 ring vibrations show the expected near-resonance type behavior whereas the RI's of CH stretching vibrations are independent of the exciting frequencies. This result can be interpreted by assuming that the RI's of the CH stretching vibrations are determined only by a σ part of the scattering tensor, i.e., this CH bond property is independent of the π-electron system.
Rotational correlation motion in liquid and adsorbed water
Authors: Klier K.
Published: February 2004

The rotational correlation functions of liquid water, of water adsorbed on a silica surface, and of water contained in a zeolite cavity have been determined from the infrared spectra of these systems. In all cases except in critical water and zeolite water, the rotational motion of water molecules is strongly vibrationally perturbed, which results in a periodic acceleration and slowing down (modulation) of the rotary motion. First order perturbation theory shows that the frequency of this modulation is determined by the difference between the average perturbation of the excited and ground vibrational levels. The average modulation frequencies are compared with those of the intermolecular bands of water and of the librations of ice. It is shown that tailing of vibration-rotation bands to low frequencies, observed in infrared and Raman bands of liquid water and to a lesser degree, also in adsorbed water, can be attributed to an attractive perturbation of the rotary motion, which is thought to be a precursor to an oriented hydrogen bond.
Optical Zeeman spectra of Am3+, Cm3+, and Nd3+ in CaF2
Authors: Stacy J. J. , Edelstein N. , McLaughlin R. D. , Conway J. G.
Published: February 2004

The optical Zeeman rotation spectra were taken of some selected transitions in Am3+, Cm3+, and Nd3+ embedded in CaF2. Only symmetry sites arising from tetragonal compensation could be positively identified, although there was evidence for the existence of lower symmetries.
Studies of viscous drag in binary liquid mixtures by quasielastic light scattering
Authors: Jamieson A. M. , Walton A. G.
Published: February 2004

Previous low angle quasielastic light scattering measurements of diffusion coefficients of binary systems of small molecules are prejudiced by errors from the spread in scattering vector introduced by finite sample volume or finite aperture size. A high power laser heterodyne spectrometer has been assembled which permits observation of spectra at scattering angles far from those at which finite volume errors arise. The characteristics of this system have been investigated and are described. The spectrometer has been used to determine the mutual diffusion coefficients of binary mixtures of primary alcohols in nitrobenzene and carbon disulfide. The effects of concentration and chain length on viscous drag in these systems have been studied. To demonstrate the influence of hydrogen bonding on diffusion the mutual diffusion coefficient in binary systems of hexane in nitrobenzene and hexane in carbon disulfide has also been measured. Finally an estimate has been made of the diffusion coefficient in the acetone/carbon disulfide system previously studied.
Mossbauer spectra of trispyrrolidylcarbodithioates of Cr(III), Co(III), Ga(III), and In(III) doped with Fe(III). Evidence of cross relaxation between Fe(III)–Cr(III)
Authors: Krzeminski Stephen F. , Straub Darel K.
Published: February 2004

Mossabauer spectra have been measured at 298, 78, and 4.2°K on chromium (III), cobalt(III), gallium(III), and indium(III) trispyrrolidylcarbodithioates containing 1–35 at.% iron(III). At 4.2°K the usual six line pattern due to magnetic hyperfine splitting is observed for the iron(III) doped diamagnetic matrices. However, for the paramagnetic chromium (III) matrix, a five line spectrum is found at iron concentrations of 1–18 at.%, indicating a spin-spin relaxation between iron(III) and chromium(III) ions.
Stabilization calculations on a N2− resonance
Authors: Eliezer I. , Moualem A.
Published: February 2004

Stabilization calculations were made on the Σg+2 state of N2−, which may be responsible for the elastic electron scattering resonance at 11.48 eV. A binding energy of 0.21 eV relative to the E3Σg+ Rydberg state was obtained.
MCD behavior of benzene and its derivatives
Authors: Caldwell D. J. , Eyring H.
Published: February 2004

A general method for correlating data from CD and MCD spectra is formulated. The origin dependence of the MCD terms is resolved by minimization of appropriate terms in the Lagrangian density expression. Approximate summation techniques are developed for magnetic and natural optical activity. The salient features of the MCD spectra of benzene derivatives are analyzed. The observed opposite signed magnetic rotational strengths of (o,p)- and m-directors is accounted for by a variation calculation which includes electron donor and acceptor wavefunctions based on occupied and unoccupied substituent orbitals. The uniqueness of the alternating signed benzene spectrum as compared with most hexasubstituted derivatives of D6h symmetry is rationalized on the basis of the vibrational modes of E2g symmetry for carbon-carbon bond stretching and bending. The importance of comparable vibronic and electronic effects is emphasized in the anomalous behavior of the B2u and B1u bands for low symmetry derivatives.
On the cavity field in a nonlinear dielectric
Authors: Bordewijk P.
Published: February 2004

The cavity field is calculated for a nonlinear dielectric. This field appears to be inhomogeneous. Its average value is used for the calculation of the saturation term in the dependence of P on E. The resulting expression differs up to 20% from the expression used until now.
Molecular theory of the glass transition phenomenon
Authors: Tobolsky Arthur V.
Published: February 2004

A molecular theory of the viscoelastic behavior of organic glasses is presented. This is a damped lattice model, where the friction factor is calculated from the Cohen-Turnbull equation. The normal coordinate treatment is approximated by classical Debye theory. A simple result is derived with no arbitrary parameters.
Radiative and predissociative lifetimes of the A 2Σ+ state of OH
Authors: Sutherland R. A. , Anderson R. A.
Published: February 2004

Lifetime measurements have been made on the A 2Σ+ state of OH by the delayed coincidence technique in conjunction with an interrupted rf discharge through water vapor. Lifetimes are reported for rotational states up to K=29 and K=20 in the ν=0 and ν=1 vibrational levels, respectively, and on the unresolved levels of ν=2. A predissociation, previously predicted from relative intensity measurements, resulting from a curve crossing by the repulsive 4Σ− state, was observed for the rotational states above K=23 of ν=0, for those above K=14 of ν=1, and for all those of ν=2. These lifetime data are discussed qualitatively in terms of the electronic-rotational perturbation matrices and the vibrational overlap integrals.
Electronic structure of unstable intermediates. II. The electronic structure of NNC, NCN, NCC, and CNC
Authors: Thomson Colin
Published: February 2004

Ab initio LCAO MO SCF calculations of the equilibrium bond lengths in the linear molecules NNC, NCN, NCC, and CNC have been carried out, using DZ and DZ+P Slater orbital basis sets. The results are in reasonable agreement with experiment. Population analyses of the wavefunctions show these are very sensitive to the basis set used.
Energy transfer processes in monochromatically excited iodine. VIII. Quenching by I atoms
Authors: Schweid A. N. , Steinfeld J. I.
Published: February 2004

Quenching of I2 (B3Π0u+, v′=25) by I(2P3/2) atoms has been measured in a fluorescence experiment at elevated temperatures. The I2*–I quenching cross section is (120±45) Å2. This very large cross section is attributed to the formation of long-lived I3 collision complexes. Vibrational relaxation of I2* by I atoms is not observed.
Singlet exciton migration and energy transfer in pyrene doped naphthalene
Authors: Powell Richard C.
Published: February 2004

Time resolved spectroscopy measurements of the fluorescence intensities of pyrene doped naphthalene crystals were used to investigate host sensitized energy transfer in this system. A time dependent energy transfer rate is observed and these results are interpreted in terms of a generalized random walk formulation for the migration of singlet excitons. This leads to a value of about 1.5× 10−10sec for the exciton hopping time at room temperature. The results also imply the existence of extended trapping regions surrounding each activator and indicate the importance of including greater than nearest neighbor steps in the random walk. These results are compared to similar ones obtained on anthracene and tetracene doped naphthalene crystals. The temperature dependence of the energy transfer rate in pyrene doped naphthalene is consistent with thermal defect scattering and trapping effects similar to those seen in other doped naphthalene crystals.
Multi-quantum scattering processes in radiationless relaxation of electronically excited ions in crystals
Authors: Fong Francis K. , Wassam William A.
Published: February 2004

Radiationless relaxation of electronically excited ions in crystals is shown to arise from five contributing phonon scattering processes which involve Δν=0, ±1, and ±2 quantum changes in the promoting phonon mode. From quantitative comparisons between theory and experiment for several transitions in LaF3:Er3+, LaCl3:Dy3+, LaBr3:Dy3+, and LaCl3:Nd3+, it is found that significant contributions to the radiationless transitions are made only by the Δ ν=+1 and +2 processes, and that of these two, the Δ ν=+2 process is by far the more important. The maximum energy phonon mode is found to be the dominant mediating mode which plays the dual role of promoting the radiationless transition and of accepting the scattered energy which results from the relaxation process. The energy gap involved in the transition is effectively modified by the addition or subtraction of Δν quanta of the promoting phonon energy in a hindered or an assisted process, respectively. In the assisted (hindered) process, electronic relaxation is accompanied by a simultaneous absorption (emission) of Δν quanta in the promoting mode, and the scattered energy which must be accepted by the lattice is accordingly diminished (increased). This interpretation accounts for the predominance of the Δ ν=+2 relaxation process.
Investigation of triplet state energy transfer in organic single crystals at low guest concentrations and low temperatures by magnetic resonance methods
Authors: Brenner Henry C. , Hutchison Clyde A.
Published: February 2004

The transfer of triplet excitation from phenanthrene guest molecules to naphthalene guest molecules in diphenyl single host crystals was investigated by magnetic resonance methods. Mole fractions of guest molecules in the diphenyl crystals were from 0.014 to 0.003 for phenanthrene and from 0.0077 to 0.0005 for naphthalene. The temperature of the diphenyl crystals was ∼1.7°K. Several types of experiments were employed both to prove the existence of the transfer and to elucidate the nature of the mechanisms and processes which were responsible for it. We were able by use of the results of these experiments, to eliminate several a priori possibilities for the mechanism of transfer. These results also showed that the main energy transfer processes were initiated either by intramolecular intersystem crossing of singlet excited phenanthrene donor molecules to triplet states as high or higher in energy than the lowest triplet exciton band of the host crystal, or by guest host intermolecular intersystem crossing which created host molecules in triplet states. These initial processes were then followed by migration of the triplet excitation through the crystal to the lower lying naphthalene triplet state traps.
Electron paramagnetic resonance absorption in oriented phosphorescent chrysene at magnetic fields below 125 G. II. Multiple orientation of chrysene triplets in p-terphenyl single crystals
Authors: Gerkin Roger E. , Winer Arthur M.
Published: February 2004

Multiple electron paramagnetic resonance absorptions by phosphorescent chrysene-d12 in single crystals of p-terphenyl-h14 have been investigated at static magnetic fields below 50 G and at ∼77°K. It has been demonstrated that the observed multiplet structure (corresponding to seven triples of zero-field transitions) arises from multiply oriented chrysene-d12 triplet states. Four types of experiments giving qualitative and quantitative information concerning these multiple orientations are characterized, and results from each type are presented. The orientations of the inequivalent chrysene-d12 triplet magnetic fine-structure tensor axes with respect to each other and to the p-terphenyl molecular and crystal axes have been quantitatively determined from data presented here and previously [R. E. Gerkin and A. M. Winer, J. Chem. Phys. 56, 1359 (1972)]. The dihedral angle between the two translationally inequivalent triplets required by the host structure for each of the seven sets of guests ranges from 50° to 58°, in contrast to the dihedral angle of 69° for the host p-terphenyl. The various chrysene-d12 triplet tensorial axes are oriented to within ∼5°–∼15° of the corresponding host reference axes and, somewhat surprisingly, these three tensorial axis sets (A, B, C) show magnitudes of misalignment comparable to each other.
Doppler broadening of OI 1304 Å multiplet in dissociative excitation of CO2 and O2
Authors: Poland H. M. , Lawrence G. M.
Published: February 2004

Emission of the atomic oxygen triplet at 1304 Å produced by electron impact on O2 and CO2 was passed through an absorption cell of thermal O(3P) at 300°K and peak optical depths near 2000. The transmission of the cell varied from 18% and 75%, depending on electron voltage, gas, and viewing angle. Interpretations of the Doppler broadening effect were made in terms of approximate linewidth, dissociation energy, and excited state symmetry.
Multistate kinetics in non-steady-state nucleation of water on gaseous ions
Authors: Kortzeborn Robert N. , Abraham Farid F.
Published: February 2004

We have numerically computed the multistate kinetics for the non-steady-state nucleation of water vapor onto gaseous ions for a few supersaturation ratios. The calculations include: (1) the complete time-dependent evolution of cluster concentrations; (2) the ``currents'' which describe the rate of nearest-neighbor transitions for cluster growth or decay; (3) the depletion of ions in the system as they are used in cluster formation and leave the system as drops; (4) an over-all picture of how the system relaxes for various cluster sizes.
Polymer conformational statistics. II. Characteristic function of the rotational-isomeric model
Authors: Fixman Marshall
Published: February 2004

The probability distribution of the end-to-end vector for the rotational-isomeric model of polymer chains is discussed in terms of the characteristic function. The characteristic function for a chain of N bonds is shown to be calculable as an expectation value, in the space of a single bond vector b, for the Nth power of an operator on b. This operator is given a finite (truncated) matrix representation and the characteristic function is evaluated numerically. For polymethylene the characteristic function calculated from the rotational-isomeric model is found to be in good agreement with the much simpler worm model.