bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the absolute sign of the electron spin dipolar and nuclear quadrupolar interactions in molecular excited triplet states
Authors: Tinti D. S. , Kothandaraman G. , Harris C. B.
Published: February 2004

A simple method for determining the absolute sign of the principal component of the zero field tensor or the sign of the nuclear quadruple coupling constant in molecular excited triplet states is outlined for molecules containing half-integral nuclear spins where I > (1/2).
Steady-state kinetic model for solid-fluid reactions
Authors: Taplin John H.
Published: February 2004

The model assumes (i) the reacting solid becomes covered by a coherent coating of solid products and (ii) the reaction may be poisoned by a sufficiently high concentration of outward diffusing material. The three kinetic regimes and their rate controlling processes are linear (surface decomposition of reacting solid), parabolic (inflow of fluid reactant), and joint (dual control by outflow of material and surface decomposition). For a large plane surface the model gives classical tarnishing kinetics plus the possibility of joint kinetics between the linear and parabolic regimes. For a discrete particle the reaction must start and finish linear, but otherwise, may be almost entirely parabolic or joint. For testing experimental data it may be convenient to use the approximation dF/d(tz)= kz(1−F)N/R, where z depends on both regime and particle shape.
Rayleigh-Brillouin intensity ratios in aqueous electrolyte solutions
Authors: Maret Arthur R. , Yeager Ernest
Published: February 2004

Rayleigh-Brillouin intensity ratios have been measured for a number of aqueous electrolytic solutions as a function of concentration. The calculated and experimental intensity ratios are in agreement within the experimental precision for solutions of alkali-metal and alkali-earth halides and nitrates at concentrations up to 3M, thus confirming applicability of simple concentration fluctuation theory for such systems. In solutions of 2–2 sulfates, the observed intensity ratios are significantly higher than the calculated values; the discrepancy remains to be explained although pronounced ionic association may be a factor.
He–Be
2+
interaction energy at small internuclear distances
Authors: Harrison S. W. , Massa L. J. , Solomon P.
Published: February 2004

The He–Be2+ interaction energy for internuclear separations from 0.16 to 0.79 Å has been determined from single-configuration MO-SCF calculations and compared to that deduced by Giffen and Berry from scattering data. The ratio of the calculated to experimental energies varies from 1.45 at 0.16 Å to 1.03 at 0.79 Å. The large discrepancy between theory and experiment for small internuclear separations is similar to that found by Giffen and Berry from a Thomas-Fermi-Dirac calculation of the interaction energy. The MO-SCF interaction is represented to within 10% by a Born-Mayer potential V(R)= 944 exp(−6.23 R) eV with R in angstroms.
Nuclear magnetic resonance studies of smectic liquid crystals
Authors: Luz Zeev , Meiboom Saul
Published: February 2004

Nuclear magnetic resonance measurements in the smectic liquid crystalline phases of seven thermotropic compounds are reported. The compounds investigated are: terephthalbis(butylaniline); ethyl(methoxybenzylidene)amino] cinnamate; diheptyloxyazoxybenzene; octyloxybenzoic acid; dipentylazoxycinnamate; diethylazoxycinnamate; diethylazoxybenzoate. Proton spectra at 100 MHz of the neat liquid crystal molecules, as well as of simple probe molecules dissolved in small amounts in the liquid crystal, were studied in their dependence on temperature and on sample orientation with respect to the magnetic field. The results show that good alignment of the smectic phases can be obtained by cooling from the isotropic or the nematic phase in a magnetic field; once aligned, the smectic planes conserve their original orientation on rotation of the magnetic field. The results are consistent with the following models of the smectic phases: Smectic-A is uniaxial and there is fast rotational and translational molecular diffusion. Smectic-C is similar to smectic-A, except that the molecules are tilted with respect to the smectic layers. A model, in which the direction of tilt is free to reorient, is used to interpret the behavior of the NMR spectra of smectic-C on rotation of the magnetic field. The magnitude of the tilt angle can be estimated from such an interpretation. Two of the compounds studied have a smectic-B phase. In one it is uniaxial, while in the other it is biaxial. The NMR results are consistent with this classification. They also show that molecular diffusion is considerably slower in the smectic-B than in the smectic-A and -C phases: the correlation time is of the order of 10−6 sec. In an appendix the formal theory of molecular orientation in a biaxial liquid crystal is given.
Dissociation energy of CeO2 and Ce2O2 molecules
Authors: Piacente V. , Bardi G. , Malaspina L. , Desideri A.
Published: February 2004

A combination of Knudsen effusion and mass spectrometric techniques has been employed in studying the gaseous species in thermodynamic equilibrium with condensed CeO2 and with condensed Ce–CeO2 mixtures. A thermodynamic treatment of ion currents yields a value of ΔH°298=135±6 kcal mole−1 for the heat of vaporization of CeO2(s). The following reactions: Ce(g)+CeO2(g)⇄ 2CeO(g), (1), Ce2O2(g)⇄ 2CeO(g), (2), have been studied and it has been found that ΔH°298=−19±4 kcal mole−1 and ΔH°298=90±6 kcal mole−1 for Reactions (1) and (2), respectively. Utilizing these heats of reaction, the CeO2 and Ce2O2 atomization energies at 298°K were determined to be D°298(CeO2)=350±15 kcal mole−1 and D°298(Ce2O2)=474±15 kcal mole−1.
Detection of free radicals by an intracavity dye laser technique
Authors: Atkinson George H. , Laufer Allan H. , Kurylo Michael J.
Published: February 2004

A new technique for the detection of free radicals inside the cavity of a dye laser is described. This intracavity absorption phenomenon has two important advantages: (1) It has the potential for quantitative detection suitable for kinetic studies of transient chemical species and (2) It has a high degree of sensitivity. In the present work, the technique is shown to be at least as sensitive as, and most probably several orders of magnitude more sensitive than, previous methods for the detection of transients. It is presently a powerful tool for obtaining high resolution absorption spectra as well as obtaining precise information about the energy distribution of transient species produced photolytically or kinetically. Spectra for both NH2 and HCO (produced flash photolytically) are presented.
Semiclassical studies of planar reactive H+H2
Authors: Tyson John J. , Saxon Roberta P. , Light John C.
Published: February 2004

The semiclassical scattering theory recently developed by Miller [J. Chem. Phys. 53, 1949 (1970)] is applied to the planar reactive scattering of H + H2 to test the accuracy and practicality of the semiclassical technique and to investigate the differences between the quantum and classical results obtained by Saxon and Light [J. Chem. Phys. 56, 3874, 3885 (1971); 57, 2758 (1972)]. Though the semiclassical probabilities agree surprisingly well with the quantum results for some transitions, they do not support the quasiselection rule observed in the quantum calculations, and thus the semiclassical theory does not predict the forward peak characteristic of the quantum differential cross section. Several difficulties involved in applying the semiclassical prescription are discussed, which seem to severely limit the usefulness of this approach.
Production of metastables in ion-molecule collisions
Authors: Haugh Michael J.
Published: February 2004

A second-order process observed in the emission from the A 2Σ states of HCl+ and HBr+ produced by collisions of 2.5 keV He+ ions with HBr and HCl is shown to arise from the formation of fast He metastables in the primary collision. These fast metastables react with the molecules to produce molecule-ions in the A 2Σ state which have a vibrational distribution much different from that expected on the basis of a Franck-Condon excitation. This vibrational distortion has been observed for thermal He metastable reactions with HBr and HCl but has never been observed for fast metastables and is difficult to reconcile with present theory of Penning ionization. The vibrational distribution in HCl+ produced by the fast He metastables is distorted considerably more than that produced by thermal metastables. The cross section for reaction of fast He metastables with HBr is 90× 10−16 cm2. The Ne+ ions reacting with HBr and HCl also produce fast Ne metastables. These react to produce molecule-ions with distorted vibrational distributions. An investigation of Ne+ and He+ reacting with HF shows that no molecular emission is produced. The reaction of Ar+ with HCl to produce Ar metastable has a cross section comparable to the near-resonant charge transfer process producing HCl+ (A 2Σ).
Microcalorimetric determination of the enthalpy of sublimation of benzoic acid and anthracene
Authors: Malaspina L. , Gigli R. , Bardi G.
Published: February 2004

A Calvet microcalorimeter has been utilized to determine the sublimation enthalpy of benzoic acid and anthracene. The vapor pressures measured by Knudsen effusion weight-loss method over the temperature ranges 338–383°K and 353–432°K were, respectively, log10p(torr)=(12.175 ± 0.047) − (4501 ± 17)/T, for benzoic acid, and log10p(torr)=(12.616 ± 0.062) − (5277 ± 24)/T, for anthracene. The Gibbs energy functions for C6H5COOH and C14H10 gaseous molecules have been estimated.
Exact quantum mechanical reaction probabilities and rate constants for the isotopic collinear H+H2 reactions
Authors: Truhlar Donald G. , Kuppermann Aron , Adams John T.
Published: February 2004

Quantum mechanical calculations on three of the collinear H+H2 reactions involving D-substitutions are presented and compared with each other and with previous calculations on the H+H2 reaction itself. The energy at which the reaction probability becomes appreciable is well predicted by the vibrationally adiabatic model. The reaction probabilities at low energies (``tunneling'') are larger than predicted by tunneling through one-dimensional barriers for motion along the reaction coordinate. The deviations of the exact rates from transition state theory with unit transmission coefficient and with transmission coefficients corrected for tunneling and nonclassical reflection are examined. Transition state theory including tunneling is usually very accurate (correct within 20% for rate constants); but the errors are much larger at temperatures below 300°K. Although the main use of the present results is for testing approximate models of reaction, not for comparison with laboratory experiments, it is interesting to note that the isotope effects are in rough agreement with the (noncollinear) experimental ones. The results are used to examine the general validity of treatments of the dynamics which separate effects due to the different modes of motion.
Model calculations of magnetic field effects on diffusion and thermal diffusion coefficients of binary gas mixtures
Authors: Cooper Eugene R. , Dahler John S. , Verlin Jerome D. , Matzen M. Keith , Hoffman David K.
Published: February 2004

Model calculation studies are presented for the effects of an external magnetic field on the thermal and binary diffusion coefficients of a dilute gas of polyatomic molecules. We consider binary isotopic mixtures of N2 and CO and binary mixtures of CH4, CD4, and CF4. Rigid interaction models are employed. In the high field limit we find approximate decreases of 1% in the thermal diffusion coefficient and of 10−3% in the binary diffusion coefficient.
Calculations and estimates of the ground state energy of helium trimers
Authors: Bruch L. W. , McGee Ian J.
Published: February 2004

Variational calculations of the ground state energy of 4He trimers are reported and are compared with the Hall-Post-Stenschke lower bound on the ground state energy. The variational result for the ground state energy for a range of model pair potentials is in the range −0.05 to −0.2 K; the effect of the triplet nonadditive term is estimated to be less than 1% of the contribution of the pair potentials. A study of the variation of the ground state energy of 3 bosons with pair potential coupling constant is also reported for a Lennard-Jones and a Morse potential model. There is no bound spin 3/2 3He trimer; a lower bound is given for the ground state energy of the spin 1/2 trimer and analogy with the boson results is used to argue that the spin 1/2 trimer is probably not bound. This paper contains computational applications of formal results derived elsewhere.
Virial coefficients of argon, methane, and ethane at low reduced temperatures
Authors: Pope Gary A. , Chappelear Patsy S. , Kobayashi Riki
Published: February 2004

Second and third virial coefficients of argon, methane, and ethane have been measured using the recently developed isochorically coupled Burnett method. The reduced temperature range was 0.66 to 1.00. The results were compared with theory using the Kihara potential and potential parameters were determined. The Kihara potential was used directly to yield a CSP correlation for the second virial coefficient. An empirical correlation was developed for the third virial coefficient which covers the reduced temperature range 0.66 to 3.15.
Rotational diffusion of spherical top molecules in liquids. III. Semiclassical rotational diffusion model and the infrared band shapes of CH4 in gaseous and liquid mixtures
Authors: Eagles T. E. , McClung R. E. D.
Published: February 2004

Semiclassical analogs of the extended rotational diffusion models presented in previous papers in this series are investigated. Application of these semiclassical rotational diffusion models to calculation of the v3 band contour of CH4 indicates that these models account satisfactorily for the bandwidths and asymmetries observed in gaseous mixtures of CH4 with helium or nitrogen in the density range 100–1000 amagat, in liquid methane and in liquid solutions of noble gases. The angular momentum correlation times obtained from the application of the semiclassical models are not greatly different from those obtained by application of the classical extended diffusion theory. This observation implies that the asymmetry of the spectral band is quantum mechanical in origin, but a classical analysis of the symmetric part of the band shape leads to essentially the same description of the molecular rotations in fluids as the quantum mechanical models do. The use of Fourier cosine transforms of band shapes to study the reorientation of molecules in liquids is, therefore, justified.
Temperature dependence of several vibrational relaxation processes in DF–CO2 mixtures
Authors: Bott J. F. , Cohen N.
Published: February 2004

A pulsed DF chemical laser has been used to excite DF molecules to their first vibrational level. Decay of the infrared DF fluorescence was used to calculate the vibrational relaxation times of DF due to collisions with itself at temperatures between 468 and 920°K as well as at room temperature. The high temperature data were obtained in a laser-induced fluorescence experiment performed behind a reflected shock wave in a shock tube. The relaxation time of DF(1) due to DF collisions was measured and determined to be 0.063± 0.005μsec · atm at 295°K increasing to 0.36± 0.03μsec· atm at 900°K, which was in agreement with previous shock tube measurements. A measurement of the rate for DF(1)+DF(1)⇄ DF(0)+DF(2) gave a value of kν ν=1.96± 0.2× 1013 cc/mole· sec at 295°K. The rate for the reaction DF(1)+CO2(000)⇄ DF(0)+CO2(001) rate was measured to be 115(μsec· atm−1 at 295°K decreasing to 32± 3(μ sec· atm)−1 at 720°K. Deactivation of CO2(001) by DF was measured to be 8.0± 0.8 (μ sec· atm)−1 at 470°K and 18± 2(μsec· atm)−1 at 295 °K. All of the measured rate coefficients, converted to units of cubic centimeters/mole· second, decreased roughly as T−1 from their values at room temperature.
Frequency dependence of the proton spin relaxation of the dipolar energy in a liquid crystal
Authors: Sharp A. R. , Forbes W. F. , Pintar M. M.
Published: February 2004

The frequency dependence of the proton spin dipolar relaxation time was measured in the range 24–32 MHz at 123, 127, and 131 °C in the nematic phase of the liquid crystal para-azoxyanisole. The experiment shows that in this liquid crystal a relaxation mechanism, too slow to relax the Zeeman energy, contributes to the relaxation of the dipolar energy. The experiment also shows that this relaxation rate does not depend on temperature or frequency within the range studied.
Electronic band structure for istopic mixed benzene crystals
Authors: Netzel Thomas L. , Colson Steven D. , Fox David
Published: February 2004

Calculations, based on a particular model Hamiltonian and the coherent potential approximation (CPA), of the partial densities of states and the k=0 spectral densities are reported for binary mixtures of C6H6/C6H5D, C6H6/C6H4D2, and C6H6/C6D6. The spectral density calculations are compared with the experimental absorptions for the C6H6/C6H5D and C6H6/C6D6 systems. Deviations between theory and experiment for the latter case seem to be more a result of a breakdown in the ideal-mixed-crystal assumption than in the CPA model. There is good agreement between-theory and experiment for the C6H6/C6H5D system. Also, additional experiments to study directly the partial densities of states of binary mixtures are outlined.
Solution of the mean spherical model for a mixture exhibiting phase separation
Authors: Waisman Eduardo
Published: February 2004

We have solved analytically the Lebowitz-Percus Mean Spherical Model (MSM) approximation for a symmetric mixture of two species of particles, constrained to have an equal number of particles of species 1 and 2. In this mixture, like particles interact via a hard sphere potential for r < R, the hard core diameter, and a Yukawa potential −Ae−κ r/r for r > R; unlike particles interact via the same hard spheres potentials (same diameter) and an opposite Yukawa potential Ae −κr/r. We find that for A>0, corresponding to an attraction between particles of the same kind and a repulsion between particles of different kind, that there are no spatially homogeneous solutions of the MSM when θ>θc,θ≡βξε, where β is the reciprocal temperature, ξ the total reduced density of hard spheres and ε≡ Ae−κ R/R. We interpret this to mean the existence of phase separation when θ is above its critical value θc We are able to calculate θc analytically as a function of A, κ, and R. We also find that when A<0 there are always homogenous solutions of the MSM. Finally when κ→ 0 and A=−e2/D, we recover the Waisman-Lebowitz solution of the MSM for hard charged spheres of equal numbers of the +e and −e charged particles and dielectric constant D.
Far-infrared spectra of t-butyl bromide-h9 and -d9 in the liquid and three solid phases
Authors: Bertie John E. , Sunder Sham
Published: February 2004

The far-infrared spectra of the liquid and three solid phases of t-butyl bromide-h9 and -d9 have been recorded between 200 and 10 cm−1. Strong absorption only occurs below 100 cm−1, where the liquid and the two plastic crystal phases, I and II, show a broad featureless band, whose frequency of maximum absorption increases with decreasing temperature. Relaxation processes and mixed translational-rotational vibrations contribute to the band, but the vibrations determine the frequency of maximum absorption. The spectra of solid phase III at 90°K show eight features that are assigned to lattice modes and indicate that the solid is ordered with at least two molecules per primitive unit cell. At 195°K phase III is orientationally disordered.
Estimation of dipole-quadrupole dispersion energies
Authors: Alvarez-Rizzatti Milton , Mason E. A.
Published: February 2004

The calculation of the dipole-quadrupole dispersion coefficient is discussed through a perturbation and a variation method. Accurate combination rules are obtained from both methods, one new and one already known. Further approximations permit computations in terms of accessible parameters. Values are calculated for the interactions of atomic pairs formed from hydrogen, alkali, and rare-gas atoms. A new relation giving the dipole-quadrupole coefficient in terms of the dipole-dipole coefficient and the dipole and quadrupole polarizabilities seems accurate, but needs further testing.
Low frequency Raman-active lattice vibrations of n -paraffins
Authors: Olf Heinz G. , Fanconi Bruno
Published: February 2004

Raman spectra in the frequency range 5–200 cm−1 have been measured for a series of crystalline n -paraffins from n -C5H12 to n -C26H54 and also n -C32H66, n -C35H72, and n -C36H74. It is found that the spectral data may be grouped consonant with crystal structures exhibited by n -paraffins. The data are used to map out portions of the transverse acoustical phonon dispersion curves of the orthorhombic polyethylenelike lattice and of one triclinic crystalline form. A band whose frequency is independent of chain length is observed for the orthorhombic n -paraffins and is assigned to the B3g rotatory lattice mode of polyethylene.
Cooperative optical phenomena. II. Spin-forbidden lifetime of the a 4Π state of nitric oxide
Authors: Zarur George Louis , Chiu Ying-Nan
Published: February 2004

As an additional mechanism for the spin-forbidden a 4Π −x 2Π transition of nitric oxide, we consider the coupling of two nitric oxide molecules and the subsequent cooperative optical transition via a one-photon, spin-allowed, electric-dipole mechanism. The feasibility of such a mechanism arises mainly through the exchange overlap of the orbitals. The coupled composite states of the dimer are constructed by projecting out the over-all permutational symmetry (by antisymmetrization), the spin symmetry (by Clebsch-Gordan vector coupling), and the point-group symmetry of the dimer. For the point-group symmetry, the state functions of the D∞ h dimer are first constructed explicitly and are then combined upon descent in symmetry to give lower point-group (C∞ ν, C2ν, C2h, Cs) state functions. The states obtained agree with the qualitative predictions of Kotani, Mulliken, and Herzberg, who did not give such explicit quantitative wavefunctions as we give. Exchange degeneracy between the Π4 and Π2 states in a dimer also gives rise to many new states not considered before. The oscillator strengths for the transition between the composite states are shown to give lifetimes comparable to experimental results, thus showing that this cooperative mechanism is as important as the conventional spin-orbit interaction mechanism. The relationship between the intensities computed for a given geometry and the importance of such geometry in the dimer is discussed. Potential usefulness of the symmetry analysis and correlation with the composite (intermediate) state in chemical reactions is also discussed.
Dissociative excitation of N2 by electron impact: Translational spectroscopy of long-lived high-Rydberg fragment atoms
Authors: Smyth Kermit C. , Schiavone James A. , Freund Robert S.
Published: February 2004

Nitrogen atoms in long-lived high-Rydberg states have been produced in the dissociative excitation of N2 by electron impact. Four principal features were found in the time-of-flight distributions of the dissociation fragments and in the corresponding translational (kinetic) energy distributions. Appearance potentials and excitation functions were measured for high-Rydberg atoms with known and well-defined translational energies; for the slowest high-Rydberg fragments the excitation function exhibits sharp, resonancelike structure near threshold. The core-ion model of high-Rydberg dissociation, which treats the Rydberg electron essentially as a spectator in the dissociation process, is described and used to interpret the data. Observed dissociation limits are assigned as one fragment being an N+(3P) core surrounded by a high-Rydberg electron and the other fragment being a nitrogen atom or ion. In addition, the high-Rydberg translational energy distributions are in reasonable qualitative agreement with kinetic energy distributions of N+ measured by dissociative ionization experiments. These observations provide substantial support for the core-ion model. The available data on the dissociative core-ion states of N2+ are discussed extensively. However, no unique assignments can be made for the molecular high-Rydberg states which participate in the dissociation processes.
Raman study of Fermi resonance, hydrogen bonding, and molecular reorientation in liquid ammonia
Authors: Schwartz M. , Wang C. H.
Published: February 2004

The Fermi resonance between the ν1 and 2ν4 bands in the polarized Raman spectrum of liquid ammonia was studied as a function of temperature. The resonance interaction was quantitatively analyzed at all temperatures through utilization of the coupled damped oscillator model. The results of this analysis furnish convincing evidence for reversal of the assignment of these bands from that most commonly assumed in the past. An analysis of the temperature dependence of the parameters obtained from the coupled oscillator model (linewidths, uncoupled peak frequencies, and the resonance interaction constant) showed all the results to be self-consistent and in agreement with the behavior which has been found in other strongly hydrogen-bonded systems. The polarized and depolarized linewidths of other bands in the spectrum were examined, and they, too, were found to be consistent, given the strong hydrogen bonding in liquid ammonia.
Measurements of relaxation cross sections for NH3 and OCS with a molecular beam maser spectrometer
Authors: Wang J. H. S. , Oates D. E. , Ben-Reuven A. , Kukolich S. G.
Published: February 2004

Scattering cross sections for beams of NH3 and OCS are measured using a molecular beam maser spectrometer. The scattering gases used are NH3, OCS, CF3H, CH3F, N2, and He. In order to determine elastic and inelastic contributions to relaxation cross sections, measurements are made for (I) scattering of pure inversion or rotational state molecules, (II) scattering of molecules in a coherent superposition state, and (III) scattering of the whole beam in a distribution of rotational states. For dipolar scattering gases the cross sections for superposition states (σII) are significantly smaller than cross sections for pure states (σI). A theory of the scattering is presented in terms of phenomenological Redfield parameters and the S matrix. The theoretical description of scattering is used to separate elastic and inelastic contributions to the measured cross sections.
Generalized hydrodynamics and the depolarized Rayleigh doublet in anisaldehyde
Authors: Alms G. R. , Bauer D. R. , Brauman J. I. , Pecora R.
Published: February 2004

High resolution depolarized Rayleigh light scattering spectra of anisaldehyde (4-methoxybenzaldehyde) at several temperatures are presented. The depolarized q dependent doublet is well resolved at temperatures > 20 °C and disappears as temperature is lowered. Over the temperature range studied (6–79 °C) the value of q 2η/ρΓ22 varies from 0.04 to 1.5. All spectra are found to fit well the form predicted by a ``two-variable'' theory in the low frequency regions studied. It is furthermore concluded on the basis of physical intuition and our previous work on solutions that the spatial Fourier transforms of the transverse velocity density and the second rank orientation tensor density are the appropriate variables.
Depolarized Rayleigh scattering and orientational relaxation of molecules in solution. II Chloroform and nitrobenzene
Authors: Alms G. R. , Bauer D. R. , Brauman J. I. , Pecora R.
Published: February 2004

Measurements of orientational relaxation times of chloroform and nitrobenzene in a variety of solvents have been made by depolarized light scattering. At constant concentration a plot of reorientational relaxation time of nitrobenzene versus solution viscosity was found to fit a straight line with nonzero intercept. The reorientational relaxation time of both solutes increased with increasing solute concentration (at constant viscosity). For nitrobenzene and chloroform, plots of the reorientational relaxation time versus solute concentration were linear. This concentration dependence is attributed predominantly to pair correlations. The ``static'' correlation parameter f and the ``dynamic'' correlation parameter g are determined for both chloroform and nitrobenzene. The carbon-13 spin-lattice relaxation time (T1) for both solutes in solution has also been determined. The reorientational relaxation time of chloroform determined by NMR agrees well with the reorientational relaxation time determined by depolarized light scattering extrapolated to zero solute concentration.
Scattering of fast potassium ions by small molecules
Authors: Amdur I. , Jordan J. E. , Fung L. W.-M. , Hermans L. J. F. , Johnson S. E. , Hance R. L.
Published: February 2004

Measurements have been made of the effective total cross sections for the scattering of potassium ions with energies between 100 and 2350 eV by room temperature O2, N2, CO, NO, CO2, and N2O. The repulsive interaction potentials were deduced from the energy dependence of the cross sections using both the inverse power and exponential representations of the potential function. The results appear to be self-consistent, indicating no measurable difference between the potentials for K+ interacting with O2, N2, NO, or CO, or between the potentials for K+ interacting with CO2 or N2O. Where it is possible to compare with other work, significant differences are found, as happened previously in reports of potentials of K+ interacting with several rare gas atoms. The potentials were compared to those determined in this laboratory by scattering argon beams with the same molecules and the potentials for the two isoelectronic systems were found, in all cases studied, to be essentially identical and actually cross in the energy range studied.
Experimental interaction dipoles for the rare gases
Authors: Bar-Ziv Ezra , Weiss Shmuel
Published: February 2004

Interaction dipoles for He–Ar, He–Kr, He–Xe, Ne–Ar, Ne–Kr, Ne–Xe, Ar–Kr, and Ar–Xe were determined by adjusting the parameters of flexible dipole moment functions to reproduce the experimental collision-induced translational spectra. The present limitations of this approach to interaction dipoles — which to date is the only experimental one available — are discussed.
Computer study of the collective modes of a one dimensional disordered chain
Authors: Bishop Marvin , Berne Bruce J.
Published: February 2004

It is found, on the basis of molecular dynamics experiments, that the density fluctuation of wavenumber k, in a one dimensional disordered chain of Lennard-Jones rods, decays like a damped cosine with frequency ωk and lifetime τk such that the dispersion relation ω = ωk is very similar to that of an harmonic chain and that τk goes as k−1/3 at small k. This latter observation is shown to be consistent with the conjecture that the single particle velocity autocorrelation function behaves asymptotically as t−3. It is concluded that the Lennard-Jones chain does not display a hydrodynamic decay.
NMR in the quadrupole regime: Polycrystalline spectra
Authors: von Meerwall E. D. , Creel R. B. , Griffin C. F. , Segel S. L.
Published: February 2004

NMR in the quadrupole regime for a spin I = 3/2 nucleus involves the transition between the two lowest levels of the nucleus in a strong electric field gradient and an applied magnetic field. The exact theory of the frequency of this transition in the presence of quadrupolar asymmetry and anisotropic chemical shift was presented in earlier papers, in conjunction with experimental results on single crystal samples. This paper studies application of this method to polycrystalline specimens. Perturbation expressions are used to derive the resonant intensity distribution (powder pattern), while histographic techniques are used in the presence of quadrupolar asymmetry (η ≠ 0). The powder pattern is widely distributed over frequency, exhibiting three distinct features (a singularity and two edges), each of which is shown to arise from crystallites whose field gradient tensors have specific orientations with respect to the applied field. Exact theory is easily applied to a study of the field dependence of the transition frequency of each feature. Only two of the aforementioned features were observed in our experiments on powdered paradibromobenzene. The precisely known pure quadrupole transition frequency for this substance was used to increase the precision of the determination of η and of σx and σy, two components of the chemical shift. For practical reasons related to the small magnitude of η in paradibromobenzene, the interpretation of the field dependences of the two observed features could not yield η, σx, and σy independently. The results of this experiment are consistent with earlier work on single crystal specimens, particularly with concurrent work in which η, σx, σy, and σz were independently determined.
Nuclear quadrupole resonance study of phase transition in tetrachloro-p -benzoquinone (chloranil)
Authors: Chihara Hideaki , Nakamura Nobuo
Published: February 2004

The phase transition in chloranil crystal has been studied by measurements of the 35Cl nuclear quadrupole resonance frequency and the spin-lattice relaxation time. The splitting of the resonance line in the low temperature phase was shown to behave as an order parameter of the phase transition. The experimental order parameter and the anomalous behavior of the transition probability (1/T1) near the transition point were interpreted satisfactorily in terms of the librational soft-mode theory which assumes anharmonic coupling between molecular librational modes in the crystal.
Excitation of atomic nitrogen by electron impact
Authors: Ganas P. S.
Published: February 2004

An analytic atomic independent particle model (IPM) is utilized for calculating absolute cross sections for the single particle excitations of atomic nitrogen. The two parameters of the IPM potential are adjusted to reproduce the experimental values of the absolute energies of the 10 excited states 3s-7s, 3p-4p, 3d-5d, and the 2p ground state. Using the Born approximation, we calculate the generalized oscillator strengths (GOS). The GOS are parametrized using convenient analytic forms which lead to analytic total excitation cross sections. The results are compared with Hartree-Fock-Slater calculations and experiment.
Piezoelectric nonlinear optic CuGaS2 and CuInS2 crystal structure: Sublattice distortion in AIBIIIC2VI and AIIBIVC2V type chalcopyrites
Authors: Abrahams S. C. , Bernstein J. L.
Published: February 2004

CuGaS2 and CuInS2 are typical AIBIIIC2VI members of the chalcopyrite structure family. The lattice constants of tetragonal CuGaS2 are a = 5.34741 ± 0.00007 and c = 10.47429 ± 0.00006 Å at 298 °K, and of CuInS2 are a = 5.52279 ± 0.00007 and c = 11.13295 ± 0.00022 Å at 298 °K. Both materials have four formulas in a unit cell with space group I 42d. A total of 984 reflections for CuGaS2 and 1413 for CuInS2 were measured with PEXRAD, and the resulting 134 symmetry-independent CuGaS2 and 310 CuInS2 structure factors, in least-squares refinement, led to final agreement factors of 0.029 and 0.038, respectively. Both materials are slightly nonstoichiometric. Final x coordinates are 0.2593 ± 0.0004 for CuGaS2 and 0.2295 ± 0.0004 for CuInS2. As was also found with AgGaS, these values are significantly different from those expected for a geometrically regular B atom tetrahedron. The resulting sublattice distortion is predictable from a linear sum of atomic electronegativities, which is also used to predict the x coordinate and interatomic bond lengths in 17 other AIBIIIC2VI chalcopyrites. The sublattice distortion in AIIBIVC2V chalcopyrites is generally small, but also significant. The experimental Cu–S distance is 2.312 ± 0.001 Å in CuGaS2 and 2.335 ± 0.001 Å in CuInS2, the Ga–S distance is 2.288 ± 0.001, and In–S is 2.464 ± 0.002 Å. The amplitudes of thermal vibration for the A and B atoms in AgGaS2, CuGaS2, and CuInS2 are essentially isotropic, with considerable anisotropy in the C atom motion.
Thermodynamic equations for tri- or third order critical points
Authors: Bartis James T.
Published: February 2004

Thermodynamic equations which state the criteria which certain thermodynamic derivatives must satisfy at tricritical, or third order critical, points in fluid mixtures are derived. The method used is an extension of Gibbs' original derivation of ordinary critical point equations and, in particular, analyticity about the tricritical point is assumed. In the molar Gibbs free energy representation, the tricritical equations are ∂ μ̃1/∂ x1 = ∂2μ̃1/ ∂ x12=∂3μ̃1/∂ x13=∂4 μ̃1/∂ x14=0, where μ̃1 is related to the chemical potential of component ``1'', x1 is the mole fraction of that component, and the temperature, pressure and chemical potentials relevant to the remaining independent components are held constant during the partial differentiations. General thermodynamic representations are considered, and the results are generalizable to critical points of arbitrary order.
Rate constant for the reaction CO(1Σ+) + O(3P) + CO2 → 2CO2
Authors: Inn Edward C. Y.
Published: February 2004

A technique based on flash photolysis of CO2 followed by chemiluminescent recombination of CO and O has been used to measure the rate of the over-all recombination reaction CO(1Σ+) + O(3P) + M → CO2 + M. At 296 °K, the following third-order rate coefficient for M = CO2 was obtained: kCO2 = 5.4 ± 0.7 × 10−36 cm6 molecule−2 · sec−1. Values for M = CO and AR are derived in which kCO = 4.5 ± 1.0 × 10−36 cm6 molecule−2 · sec−1 and kAr = 9.8 ± 2.0 × 10−36 cm6 molecule−2 · sec−1.
Predictions of the solid helium phase diagram
Authors: Holian Brad Lee , Gwinn William D. , Luntz Alan C. , Alder Berni J.
Published: February 2004

The hcp-fcc phase transition of helium is predicted on the basis of a quantum mechanical, anharmonic, anisotropic cell model calculation. The small heat of transition agrees with experiment within the uncertainty in the knowledge of the pair potential. The phase line is extended beyond present experimental range by introducing lattice dynamics corrections, which are increasingly important at high densities. The phase line is predicted to curve over and intersect the pressure axis at 0 °K at about 20 000 atm. This behavior of the phase line is independent of the quantitative results of the models used here, since the harmonic approximation, which becomes exact in the high-density limit, requires that fcc be stable relative to hcp. Anharmonic lattice dynamic correlations are shown to be essential to the prediction of the bcc-hcp transition. They are introduced here via a correlated cell model. For the highly accurate cell model calculations several numerical methods of solution are compared.
Molecular charge transfer: Experimental and theoretical investigation of the role of incident-ion vibrational states in N2+–N2 and CO+–CO collisions
Authors: Flannery M. R. , Cosby P. C. , Moran T. F.
Published: February 2004

The effect of reactant-ion vibrational energy on total charge-transfer cross sections has been examined for 0.03–2.20 keV N2+–N2 and CO+–CO collisions. A multistate impact parameter treatment was applied to the examination of charge transfer between the above ions occupying various vibrational levels and ground-state neutral molecules. The resulting first-order coupled equations were solved numerically, and convergence of the calculated cross sections was achieved by systematic introduction of additional states to the wavefunction expansion for the total system. The calculated cross sections were weighted according to the vibrational distribution present in the laboratory reactant-ion beam formed by electron impact and the results compared with experiment in which we employed time-of-flight techniques to measure the forward-scattered neutral N2 and CO products. Reactant-ion vibrational state distributions were varied by changing the ionizing electron beam energy in a controlled electron-impact mass spectrometer ion source. The vibrational state population of the reactant-ion beam was estimated from absolute excitation cross sections spectroscopically measured for electron-impact ionization of the above molecules, the squares of the overlap integrals of the respective ground and excited ionized states (where needed), and total electron-impact cross sections for molecular ion formation. The major contribution to the charge-transfer cross sections arises from those reaction channels with large vibrational overlaps and small energy defects with respect to the initial channel. Multistate cross sections for those channels involving near-reasonant states with favorable vibrational overlaps are found to be closely approximated by the low-velocity limit proposed by Bates and Reid. Measured cross sections and their dependence on reactant-ion vibrational state distributions are correctly predicted by the multistate model below approximately 1.5 keV ion kinetic energy. There are, however, indications that competitive, inelastic, electron-transfer processes tend to occur at higher kinetic energies.
ESR study of copper diethyldithiophosphate
Authors: Cowsik R. Kumari , Srinivasan R.
Published: February 2004

ESR investigations are reported in single crystals of copper diethyldithiophosphate, magnetically diluted with the corresponding diamagnetic nickel complex. The spectrum at normal gain shows hyperfine components from 63Cu, 65Cu, and 31P nuclei. At much higher gain, hyperfine interaction from 33S nuclei in the ligand is detected. The spin Hamiltonian parameters relating to copper show tetragonal symmetry. The measured parameters are g∥ = 2.085, g⊥ = 2.025, A63Cu = 149.6 × 10−4 cm−1, A65Cu = 160.8 × 10−4 cm−1, BCu = 32.5 × 10−4 cm−1 and QCu ∞ 5.5 × 10−4cm−1. The 31P interaction is isotropic with a coupling constant AP = 9.6 × 10−4 cm−1. Angular variation of the 33S lines shows two different hyperfine tensors indicating the presence of two chemically inequivalent Cu–S bonds. The experimentally determined hyperfine constants are A 1s = 34.9 × 10−4 cm−1, B 1s = 26.1 × 10−4 cm−1, A 2s = 60.4 × 10−4 cm−1, B2s = 55.5 × 10−4 cm−1. The hyperfine parameters show that the hybridization of the ligand orbitals is very sensitive to the symmetry around the ligand. The g values and Cu hyperfine parameters are not much affected by the distortions occurring in the ligand. The energies of the d-d transitions are determined by optical absorption measurements on Cu diethyldithiophosphate in solution. Using the spin Hamiltonian parameters together with optical absorption results, the MO parameters for the complex are calculated. It is found that in addition to the σ bond, the π bonds are also strongly covalent.
Compressibility of water as a function of temperature and pressure
Authors: Fine Rana A. , Millero Frank J.
Published: February 2004

The isothermal compressibility of water from 0 to 100 °C and 0 to 1000 bar has been determined from Wilson's sound velocity measurements which have been normalized to Kell's 1 atm values. The isothermal compressibilities determined from the sound velocities have been fit, with a maximum deviation in compressibility of ± 0.016 × 10−6 bar−1, to an extended bulk modulus equation V 0P/(V0-VP) = B + A1P + A2P2, where V0 and VP are the specific volume at an applied pressure of zero and P; and B, A1, and A2 are temperature dependent constants. Our specific volume results are in reasonable agreement with the work of Kell and Whalley at low pressures; however, our results at high pressures (1000 bar) disagree by as much as 169 ppm (the average deviation is approximately 115 ppm). A comparison of the compressibilities indicates a parabolic shift in Kell and Whalley's work with a maximum of approximately 0.205 × 10−6 bar−1 at 400 bar and 5 °C. Since the velocity of sound data is extremely reliable (± 0.2 m/sec) and the maximum error in the compressibilities derived from the sound data is within ± 0.016 × 10−6 bar−1, our PVT results based upon the sound data are more accurate than any direct measurements made to date.
Auger electron spectroscopy study of the surface composition of the lead-indium system
Authors: Berglund S. , Somorjai G. A.
Published: February 2004

The Auger spectra of lead-indium alloys (4.53, 9.08, 28.63, 44.62, and 60.49 atom% lead) and of pure lead and indium were monitored in the liquid and solid states. The relative intensities of the lead 92 eV and the indium 403 eV Auger peaks were used to determine the surface composition. The peak intensity ratio proved to be a sensitive detector of the change of surface composition with respect to temperature and bulk composition. The surface layers of the alloys were richer in lead than the bulk, and the surface composition exhibits a temperature dependence similar to that predicted by the ideal monolayer model. Oxygen decreased while carbon increased the surface excess lead concentration. Ion bombardment at 300°K caused appreciable solid state diffusion. This effect was considerably reduced by lowering the temperature to 78°K; however, selective removal of Pb then took place. Auger electron spectroscopy, when coupled with suitable calibration of the peak intensities, should be an excellent technique to study the surface thermodynamics of multicomponent systems.
MC–SCF and CI calculations for the ammonia molecule
Authors: Dejardin P. , Kochanski E. , Veillard A. , Roos B. , Siegbahn P.
Published: February 2004

Multiconfiguration self-consistent field calculations are reported for the ammonia molecule, both with and without symmetry restrictions. Correlation energies of 0.039 and 0.080 a.u. have been obtained, respectively, for the core and the valence shell (without the symmetry restriction). It is found that the MC–SCF method is not stable with respect to the symmetry constraint, as the result of a better description of the left-right correlation. A comparison is made of configuration interaction calculations based either on canonical SCF or MC–SCF or approximate natural orbitals. Comparable values of the correlation energy are obtained from CI calculations which are based on the same number of MC–SCF orbitals or approximate natural orbitals. Analysis in terms of pair correlation energies shows that the approximate natural orbitals achieve less of the intrapair and more of the interpair correlation energy than the MC–SCF orbitals. Strongly occupied natural orbitals are close to the corresponding SCF orbitals, both being more delocalized than the MC–SCF orbitals. The weakly occupied NO and MC–SCF orbitals are comparatively much closer.
Emission spectra of xenon impurity states in solid and liquid krypton
Authors: Cheshnovsky Ori , Raz Baruch , Jortner Joshua
Published: February 2004

In this paper we present the results of an experimental study of electronic energy transfer in xenon-krypton liquid and solid alloys. The α-induced luminescence of these dense systems consists of three emission bands which are assigned to the host Kr*2 molecule, the guest XeKr* heteronuclear molecules, and the Xe2* homonuclear molecule. Electronic energy transfer occurs via dipole-dipole coupling between Kr2* and Xe single impurity states in the liquid and in the solid as well as to impurity aggregates in the solid. The critical radii for energy transfer were evaluated as Rq = 25 Å in the solid at 110 °K and estimated to be Rq ≃ 24 Å in the liquid at 120 °K, while the second order perturbation theory results in the values Rq = 15 Å for the solid and Rq = 21 Å for the liquid. A dramatic decrease of the efficiency and energy transfer with decreasing temperature was observed, which is consistent with the proposed energy transfer mechanism. Some information regarding diffusion controlled reactions in liquid rare gases is reported.