bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivation of the DIPR model for reactive scattering
Authors: Marron Michael T.
Published: February 2004

The classical model for reactive scattering proposed by Kuntz, Mok, and Polanyi is derived from the viewpoint of a pseudo-hard-sphere model which satisfies conservation of momentum constraints. Derivation of the DIPR equations is considerably simplified by (a) viewing the model in an impulsive framework and (b) casting it in a coordinate system different from the original derivation. The model admits analytical expressions for the angular distribution of products and the final translational energy distribution. A method for introducing potential information is described in terms of net momentun transfer and weighting collision configurations.
14N nuclear quadrupole resonance in compounds containing N–O bonds. I. Oximes
Authors: Sauer Enrique G. , Bray P. J.
Published: February 2004

The nitrogen-14 nuclear quadrupole resonance spectra at 77°K of thirteen oximes are reported and analyzed in the framework of the Townes and Dailey theory. The results obtained suggest that in most cases the π charge at the nitrogen atom is sufficiently large to allow a positive coupling constant for the nitrogen atom. A weak dependence between the distribution of σ charges and the π charge at the nitrogen atom was observed and is interpreted as arising from hydrogen bonded intermolecular interactions.
Photolysis of monochlorobenzene in gas phase
Authors: Ichimura Teijiro , Mori Yuji
Published: February 2004

Monochlorobenzene vapor has been photolyzed in the presence of ethane at 184.9, 206.2, 228.8, and 253.7 nm. The products benzene, ethylene, and n-butane were detected. Quantum yields were found to be dependent on the excitation wavelength, while they were independent of the pressure of ethane above 30 torr. The possible reaction mechanism is discussed and the decomposition rate of the C–Cl bond in the molecule is estimated.
Vibrational relaxation times of oxygen in the pressure range 10–110 atm
Authors: Parker J. G. , Ritke D. N.
Published: February 2004

Measurements of the vibrational relaxation times and sound velocities of oxygen have been carried out at room temperature over the pressure range 10–110 atm. Over this pressure range not only are the effects of vibrational relaxation evident but also of significance are real gas effects. The observed dependence of sound velocity on pressure is in good agreement with theory. Variation of the relaxation frequency with pressure does not exhibit the linear dependence expected on the basis of binary collisions. Extrapolation of the data suggests that in the limit of vanishing pressure, the product p0τv>6(−2) sec·atm. Use of a semiempirical formula combining both the expected high and low pressure dependence of τv suggests in the limit of vanishing pressure that p0τv→ 9.76(−2) sec·atm. Both of these are significantly longer than previously determined values.
Velocity dependence of electronic to vibronic energy conversion for Hg(63 P2) in molecular collisions
Authors: Krause H. F. , Datz S. , Johnson S. G.
Published: February 2004

The de-excitation of metastable mercury atoms (63P2→63P1) by collisions with H2, D2, N2, NO, and CH4 has been studied in a modulated crossed beam experiment. The molecular beam was velocity selected and the photon emission at 2537 Å was studied vs the molecule speed. From these measurements, quenching cross sections vs initial collision energy are derived. These results, which are discussed in terms of two existing theories, suggest that quenching occurs when electronic-vibrational terms of the quasimolecule intersect.
Calculation of Grüneisen parameters of polymers
Authors: Curro John G.
Published: February 2004

In a polymer there exist a large number of degrees of freedom; however, only the translational modes have appreciable volume dependence. This fact leads to low values of the Grüneisen parameter defined by (T)γ=V(∂ P/∂ E)V, since much of the internal energy is stored in the volume independent degrees of freedom. Assuming only the translational modes are volume dependent, the formula (T)γ= γ0CTR/CV is derived, where γ0 and CTR/CV are the Grüneisen parameter and heat capacity fraction for translation. The translational Grüneisen parameter γ0 is calculated from a cell model and the translational heat capacity fraction is estimated for polystyrene and polymethyl methacrylate. The Grüneisen parameters of these polymers are then calculated from the above formula. These results agree with Grüneisen parameters obtained from available data on thermal expansion, heat capacity, and compressibility at high temperatures. At low temperatures the cell model predicts that γ0→ 3.16 as T→ 0. Further low temperature data is needed to assess the accuracy of the theory in this region.
Phonons in disordered molecular solids: Raman spectra of heavily doped mixed crystals of benzene and perdeuterobenzene
Authors: Hong Hwei-Kwan , Kopelman Raoul
Published: February 2004

Raman spectra of mixed crystals of benezene-h6 and benzene-d6 have been studied throughout the whole concentration range (0%–100%). They are discussed in the virtual crystal limit, suitable for small trap depths. It is shown that within this limit: (1) All the phonons are delocalized in mixed crystals; (2) k-designation is still valid, and (3) no appreciable broadening is expected in mixed crystals. In particular, because the trap depths are the same for all three rotations in benzene mixed crystals, it is further inferred that: (1) There is a one-to-one correspondence between the mixed crystal absorption and the pure crystal absortion; (2) spectral line positions depend on the concentration linearly; and (3) the normal coordinates in the mass (or moment of inertia)-weighted coordinates remain unchanged from benzene-h6 to mixed crystals to benzene-d6. All these conclusions are supported by the experimental data. More general cases, where trap depths are different for different degrees of freedom, are also discussed. Implications of the phonon delocalization in isotopic mixed crystals to the interpretation of phonon sidebands of electronic spectra of isotopic mixed crystals are also pointed out.
Infrared reflection from longitudinal modes in anisotropic crystals
Authors: Decius J. C. , Frech Roger , Brüesch Peter
Published: February 2004

In anisotropic crystals belonging to the tetragonal, hexagonal, trigonal, and orthorhombic systems it is often found that naturally occurring faces are normal to the transition dipole direction for vibrational modes which are reasonably well separated in the spectrum. Strong reflectivity from such faces of waves with transverse magnetic polarization at finite incidence angles is found at frequencies above that of the longitudinal mode. Experimental data for this configuration are presented for the ν2 and ν3 carbonate vibrations in calcite. Theoretical curves are calculated as a function of incidence angle and damping constant, and the special utility of this type of experiment is discussed.
Study of the reactions H2+ + He→HeH++H and HeH+ + H→H2++He using crossed beam techniques
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2004

The proton transfer reactions H2+ + He→HeH++H and HeH+ + H→H2++He have been studied in the laboratory energy range 1–25 eV. The first process, which is endothermic for ground state reactants, has been studied over the indicated energy range with different degrees of vibrational excitation present in the H2+ particles. Below 9 eV, the reaction is found to depend strongly on vibrational energy while above this energy the reaction cross sections appear to depend mainly on the kinetic energy of the reactants. The exothermic reverse reaction exhibits a 1 / ν dependence in the low-energy region indicating an ion-dipole mechanism. Methods of measuring the degree of dissociation obtained in forming the hydrogen atom beam are discussed.
Novel two-photon radiative interaction operators from relativistic theory for Rayleigh scattering and for spin-dependent Faraday rotation
Authors: Chiu Ying-Nan , Brown Samuel H.
Published: February 2004

The quantum field theoretic treatment of Akhiezer and Berestetskii is generalized to a Dirac electron in a time-dependent electromagnetic field (versus static electric field). From the Hamiltonian a unique set of Hermitian, time-dependent interaction operators applicable to two-photon, as well as one-photon, processes are obtained. Some of the two-photon interaction operators have not been considered in literature. This is in contrast to more conventional treatments which obtained two sets (instead of one) of apparently equivalent interaction operators with each set containing a non-Hermitian term for both time-dependent and time-independent fields. The two sets of interaction operators obtained from the conventional treatment differ in order (i.e., i E·Π vs i Π·E) and are only applicable to one-photon processes. When applied to two-photon processes, the said operators are non-Hermitian due to the noncommutation of quantized electromagnetic fields (in Π and in E) which also makes the ordering of the operators important. We examine in detail two of the newly obtained Hermitian two-photon interaction operators, one related to iE·Π and one is spin dependent and proportional to S·Π×E. The first-order matrix elements for the two-photon processes of simultaneous absorption and emission are calculated. It is found that one matrix element corresponds to a new mechanism for first-order Rayleigh scattering. This matric element is comparable in magnitude to the conventional first-order matrix element in the x-ray region. The other matrix element corresponds to a new mechanism for magnetic optical rotation (Faraday effect) due only to spin of the electron and is applicable to molecular radicals with nonsinglet spin multiplicity. In the microwave region, this new matrix element appears to be comparable in magnitude to the matrix element for conventional magnetic optical rotation. Both operators are of potential astrophysical interest because of the various radiation processes in space.
Solvent effects on electronic spectral oscillator strengths
Authors: Abdulnur Suheil F.
Published: February 2004

The effect of long-range dispersion forces on the conversion from the total integrated absorption of an allowed solute transition in solution to the corresponding unperturbed oscillator strength in the isolated solute is investigated. As an illustration of this effect, calculations are performed on the 1s → 2p transition of an H solute in a variety of inert and other gases. The commonly used Lorentz field correction factor (n02+2)2/9n0 is shown to be of minor importance compared to an additional ``IMF'' factor arising from the intermolecular forces between the solute and the solvent molecules and the translational fluctuations between the induced moments. While the former factor is always greater than one, the latter can be greater than as well as less than unity. Implications regarding more complex solutes are considered.
Calculation of molecular ESCA spectra by the multiple-scattering-Xα method
Authors: Connolly J. W. D. , Siegbahn H. , Gelius U. , Nordling C.
Published: February 2004

The recently developed multiple-scattering method has been applied to the solution of the approximate SCF (Xα) equations. Through the concept of the transition state, it is possible with this method to estimate the ionization energies measured in electron spectroscopy (ESCA) experiments. Comparisons with experimental ionization energies for several small molecules (i.e., CF4, NH3, N2, CO, NO, CO2, N2O, C3O2) show in general, better agreement than semiempirical orbital energies and about the same as ab initio MO-LCAO-SCF orbital energies.
High-field level-crossing and Stark studies of the A 2Σ+ state of OD
Authors: Weinstock E. M. , Zare R. N.
Published: February 2004

We have carried out a high-field level-crossing experiment on the ν = 0, N=1, J=3/2 ot the OD A 2Σ+ state. A precise measurement of the magnetic fields at which three crossovers are observed permits a determination of the three hyperfine constants b = 110.4 ± 2.6 MHz, c = 22 ± 14 MHz, and eQq = 0.09 ± 0.05 MHz (3σ). In addition, we have applied a static electric field parallel to the magnetic field and observed a shift in the location of the high-field level crossings from which we calculate the dipole moment of this excited state to be 1.72 ± 0.10 D (3σ). A comparison of these structural parameters is made with ab initio calculations.
Heat transfer in nucleation theory
Authors: Salpeter E. E.
Published: February 2004

In nucleation theory the rate of growth of droplets near the ``critical size'' is needed as a function of the supersaturation ratio and of the equilibration time for heat transfer to the carrier gas. If the droplet is sufficiently small, the latent heat deposited when one molecule is added heats the droplet sufficiently for the evaporation rate to be increased appreciably. It is shown that the net growth rate is ``exponentially small'' when the heat transfer rate is moderately slow, unless the supersaturation ratio exceeds a critical value. Approximations are derived for this small growth rate under various conditions.
``End effects'' in thermogravitational thermal diffusion. Thermal diffusion factors for the carbon tetrachloride-cyclohexane system
Authors: Stanford David J. , Beyerlein Adolph
Published: February 2004

Thermogravitational thermal diffusion separations are studied for carbon tetrachloride-cyclohexane mixtures as a function of temperature difference using an apparatus without reservoirs. There is a very small negative temperature difference dependence of 0.25% per °C which is in excellent agreement with Horne and Bearman's phenomenological theory of thermogravitational thermal diffusion [J. Chem. Phys. 46, 4128 (1967); 49, 2457 (1968)]. This is in contrast to the large positive temperature difference dependence of 1% per °C observed for an apparatus with reservoirs. These contrasting results substantiate the earlier conjecture of Beyerlein and Bearman that temperature difference effects are the result of ``end effects.'' Thermal diffusion factors, α1, at 25°C calculated as a function of carbon tetrachloride mole fraction using the experimental separations and Horne and Bearman's theory are α1 = − 1.837 + 0.181 X1 with a standard error of 1.7%. This is within 1% of Anderson and Horne's pure method results [J. Chem. Phys. 55, 2831 (1971)]. Agreement with other independent work ranges from 1% to 5%. It is concluded Horne and Bearman's theory provides an accurate description of thermogravitational thermal diffusion.
Far-infrared spectra of ring compounds. XIII. The spectrum and structure of 1,4-dioxacyclohexadiene-2,5
Authors: Lord R. C. , Rounds T. C.
Published: February 2004

The far-infrared absorption spectrum of gaseous 1,4-dioxacyclohexadiene-2,5 in the range 230–20 cm−1 consists of a regular series of Q-branches decreasing in intensity toward high frequency. They have been assigned to various transitions of the B2u ring bending mode and from them the potential function V(x) of a one-dimensional Hamiltonian has been evaluated: V(x) in cm−1= 0.2949× 104 x2+0.2930× 106x4. in which the variable x is the usual ring bending coordinate. This expression of V(x) results from a fixed reduced mass of 99.64 amu. When the reduced mass is allowed to vary with x, higher-order kinetic energy terms are introduced into the Hamiltonian and a slightly different potential function is obtained: V(x) in cm−1= 0.8251× 103x2+0.4702× 106x4. The latter treatment gives somewhat better agreement between calculated and observed Q-branch frequencies. Results of a normal coordinate calculation for the 24 vibrations of dioxadiene are also presented.
Nonorthogonal configuration interaction study of the ground state of BeH2
Authors: Hosteny R. P. , Hagstrom S. A.
Published: February 2004

A series of configuration interaction (CI) calculations are carried out on the Σg+1 ground state of the BeH2 molecule using a nonorthogonal one-electron basis of elementary symmetry orbitals formed from real Slater-type orbitals. A number of different atomic-orbital basis sets are used. For the largest basis, a calculated energy of −15.8478 hartree at an equilibrium Be–H bond distance of 2.52 bohr is obtained with an optimized 80-term wavefunction. Based on previous estimates of the Hartree-Fock energy and the present results, this figure represents approximately 55% of the total correlation energy of the molecule, which is estimated to be −0.140 hartree. Using potential curves obtained from this wavefunction, the fundamental symmetric and asymmetric vibration frequencies are calculated to be 2083 and 2497 cm−1, respectively. The related force constants are also given. There are no experimental data available for comparison. The computed wavefunctions are discussed and comparisons made with elementary valence bond functions.
Charge density study of diamond
Authors: Stewart Robert F.
Published: February 2004

Generalized x-ray scattering factors are applied to published x-ray powder measurements of diamond for a charge density analysis. The Debye-Waller parameter (0.140±004A2) is substantially lower than published results based on the Hartree-Fock atomic scattering factor (.206±.003A2). The electron content in the atomic octapole and hexadecapole electron density moments are in agreement with other analyses. The contribution of the valence electron density to the gradient of the electric field gradient is 〈Vxyz〉= 1.5± 0.2× 1032joules m −3 coul −1. The components, from a similar contribution, of the gradient of the gradient of the electric field gradient are 〈Vα α α α〉= 5.3± 1.5× 1042 J m−4· C−1 and 〈Vα α β β〉= −(1/2)〈Vα α α α〉. The analysis also has provided some guide lines for the application of generalized x-ray scattering factors to organic molecular crystals.
General contraction of Gaussian atomic orbitals: Core, valence, polarization, and diffuse basis sets; Molecular integral evaluation
Authors: Raffenetti Richard C.
Published: February 2004

Generally contracted Gaussian basis functions are defined as those for which each contracted function may have a nonzero contribution from each primitive Gaussian. Alternatives for choice of such bases are tested and guidelines proposed. The basis is compared with standard methods in current use and is shown to be superior in terms of energy lowering obtained per additional basis function beyond a minimal number. A new program for computation of the required multicentered integrals is described.
Infrared determination of C for phosphine via perturbation-allowed Δ |k − l|= ± 3 transitions in the 3ν2 band
Authors: Maki Arthur G. , Sams Robert L. , Olson Wm. Bruce
Published: February 2004

The 3ν2(A1) and 4ν2−ν2(A1) infrared bands of PH3 have been measured with high resolution. In the ν2=3 state an interaction between the K and K±3 levels gives rise to perturbation allowed ΔK = 3 transitions through a weak high order interaction. Since only one component of the K = 3 levels is of the proper symmetry to interact with the K = 0 levels there is a splitting of the K = 3 levels. Also detectable is the splitting of the K = 3 levels of the ground vibrational state. The measurements have been combined with microwave measurements to give accurate values for the ground state rotational constants B0, C0, D0J, D0JK, D0K, H0J, H0JJK, and H0JKK. The absence of observable inversion effects sets an upper limit of about 0.02 cm−1 for the inversion splitting of the 4ν2 level.
Steady state theory of hot atom reactions
Authors: Keizer Joel
Published: February 2004

A simple steady state theory of hot atom reactions is developed based on the Boltzmann equation. The solution to this equation is approximated by a local Maxwell distribution involving the temperature of the hot atoms and steady state distributions are calculated by determining steady values of the hot atom temperature. General considerations imply the existence of steady state distributions with temperatures just below the ambient temperature and a simple model calculation indicates that very reactive systems should have steady or quasisteady states at temperatures much higher than ambient. An application of the theory to a photochemical reaction is shown to be compatible with more extensive computer calculations. If a hot atom distribution becomes steady, it is shown that the loss of hot atoms can be described by a pseudo-first-order rate equation with a rate constant differing from the equilibrium rate constant only by the appearance of the steady state temperature.
Vibrational relaxation in CO2/O2 mixtures
Authors: Bass H. E.
Published: February 2004

The acoustic absorption in mixtures of CO2 and O2 has been measured for 90%, 80%, and 70% concentrations of O2 at 300 °K. The absorption has been analyzed to extract the rate of energy transfer between the vibration of the bending mode of CO2 and the O2 vibration and the rate at which O2 de-excites the bending mode of CO2 in a v-t process. The rate constants for the v-t de-excitation of the bending mode of CO2 by O2 was found to be about the same as de-excitation by CO2. The v-v exchange between CO2 and O2 increases only slightly from 1.6 × 105 (sec atm)−1 at 300 °K to 2.5 × 105 at 600°K.
Wigner distribution and reduced distribution functions
Authors: Shalitin D.
Published: February 2004

Some general properties of the equilibrium Wigner distribution function are discussed. An invariance law under Galilean transformation is obtained for systems with no external forces. The reduced distribution functions in configurational, momentum, and phase space are studied, with emphasis on the correlations of the velocities among themselves and between them and the configurational coordinates. It is shown that up to linear terms in h2, the reduced distribution can be derived from a Hamiltonian with momentum-dependent potential.
Temperature dependent Raman study of molecular motions and interactions of CH3 I in the liquid phase
Authors: Wright R. B. , Schwartz M. , Wang C. H.
Published: February 2004

The polarized and depolarized components of the 524 cm−1 Raman band in liquid methyl iodide were measured between 196 and 300°K. A technique, utilizing the isotropic scattering intensity, allowed the separation of reorientational line broadening of the anisotropic spectrum from the broadening due to other processes. The reorientational correlation times derived from the anisotropic Raman spectrum were found to agree well with those obtained by other techniques throughout the temperature range studied. The temperature dependence of the isotropic correlation times was opposite to that predicted by current theories of vibrational relaxation and collisional broadening. The depolarization ratio was also measured as a function of temperature and is seen to vary quite markedly. The depolarized low frequency spectra of methyl iodide were also studied and the results were fit to a theoretical expression for collision induced scattering to obtain values for the linewidth parameter Δ. The temperature dependence of Δ proved to be opposite from that predicted by theory and is qualitatively similar to the temperature dependence of the isotropic linewidths, indicating that the same broadening mechanism is probably present in both spectra.
Inelastic neutron scattering study of the ``rotator'' phase transition in n -nonadecane
Authors: Barnes John D.
Published: February 2004

A simple kinematic model for rotational jump diffusion of a normal alkane about its long axis (circular random walk model) is developed. Inelastic neutron scattering data obtained on the Fermi chopper time-of-flight instrument at the National Bureau of Standards reactor using an incident neutron wavelength of 2.47 Å (Δ λ/λ ≃ 3.8 %) are compared with the predictions of the model. Data taken below the temperature of the ``rotator'' phase transition in n -nonadecane (295 °K) show no quasielastic scattering due to diffusive motions. Data taken in n -nonadecane in its disordered solid phase show quasielastic scattering consistent with the circular random walk model. Estimates for values of the model parameters of 3.5 psec. for τ1 and N ≥ 8 are obtained.
Kinetic study of electronically excited phosphorus atoms, P(32DJ, 32PJ), by atomic absorption spectroscopy. II
Authors: Acuna A. U. , Husain D. , Wiesenfeld J. R.
Published: February 2004

Electronically excited phosphorus atoms in the P(32DJ) and P(32PJ) states have been generated in the gas phase by pulsed photolytic irradiation and monitored by means of absorption spectroscopy using attenuation of atomic resonance radiation. The kinetic decay of these two low-lying, optically metastable states has been studied in the presence of the following collision partners: Ar, Kr, Xe, N2, CO, NO, Co2, N2O, PCl3, CH4, and C2H4, and second-order constants are reported for the removal processes at 300°K.
Dielectric relaxation of 1-alkenes
Authors: Crossley John
Published: February 2004

Dielectric constants and losses have been measured for 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, and 1-octadecene as pure liquids at up to 10 frequencies between 1 and 140 GHz at 25°C. The mean relaxation times, τ0, and viscosities, η, increase significantly with increasing chain length; however, the parameter τ0/η reaches a maximum for 1-dodecene and then decreases with increasing chain length. The results are compared with those obtained for other n-alkyl compounds containing a polar end group.
Glory scattering in molecular collisions. III. Collisions between indistinguishable molecules
Authors: Biolsi Louis
Published: February 2004

An extended distorted-wave treatment is used to obtain formal expressions for the total cross section when two indistinguishable rigid diatomic molecules, with orbital and nuclear spin angular momenta, collide. Explicit expressions for the cross section are obtained through second order, including the lowest order inelastic effects. An expression for the total inelastic cross section is also given. The results are compared with the corresponding results when distinguishable molecules collide.
On optical polarization measurements in liquid crystals
Authors: Sackmann E. , Möhwald H.
Published: February 2004

``Compensated'' nematic mixtures of cholestryl derivatives are very well suited as anisotropic solvents for optical polarization studies in the ultraviolet since these compounds are transparent to about 240 nm and can be homogeneously oriented by dc electric fields. Such mixtures have been prepared in a temperature range between 20 and 100 °C by only slight changes in the composition. Polarization experiments have been performed both in the liquid state above room temperature and in the ordered frozen state below −30 °C. The degree of absorption polarization has been calculated as function of the elements εxi of the molar extinction coefficient tensor and the average orientations (order parameters Sxi xi) of the solute molecular axes xi. For symmetric molecules all elements εxi (λ) and order parameters can be determined. Results of our polarization studies of anthracene, chrysene and a charge transfer complex are presented. Moreover, it is shown that measurements of the circular dichroism, observed in the absorption region of solute molecules incorporated in a helical fashion in cholesteric phases, yields a very simple method to determine relative polarization directions. By comparing the absorption polarization and (or) the circular dichroism spectra with the fluorescence polarization spectrum the position of weak hidden bands can be detected with good accuracy. The long wavelength edge of the 1Lb transition of anthracene has been located in this way at about 29 000 cm−1.
Measurement of hyperfine structure in CH2F2 by beam maser spectroscopy
Authors: Kukolich S. G. , Wang J. H. S. , Ruben D. J.
Published: February 2004

High resolution measurements of hyperfine structure on the 303→ 212, 423→ 514, 523→ 616, and 615→ 524 rotational transitions in CH2F2 were made using a molecular beam maser spectrometer. The components of the fluorine spin-rotation tensor obtained from the data are Maa(F)=−20.4± 1.0 kHz, Mbb(F)=−4.9± 0.5 kHz, and Mcc(F)=−13.1± 0.5 kHz. Components of the hydrogen spin-rotation tensor are Maa (H)=6.5± 3.0 kHz, Mbb(H)=1.0± 1.4 kHz, and Mcc(H)=0.3± 1.3 kHz. Precise values for the rotational transition frequencies are also reported. Relations between the spin-rotation tensor and the magnetic shielding tensor for CH2F2 are discussed. Combining the experimental spin-rotation tensor with the diamagnetic shielding tensor from the atom-dipole model, leads to the determination of the magnetic shielding tensor σaa=407 ppm, σbb=390 ppm, σcc=217 ppm, and σAv=338 ppm.
Vibrational relaxation in the HF–HCl,HF–HBr,HF–HI, and HF–DF systems
Authors: Ahl Jeffrey L. , Cool Terrill A.
Published: February 2004

The laser-excited fluorescence method has been employed to determine rate constants for vibrational energy transfer (V → V, R) and deactivation (V → R, T) processes in the HF–HCl,HF–HBr,HF-HI, and HF–DF systems at temperatures of 300 and 350°K. The rates exhibit a marked inverse temperature dependence indicative of strong attractive (hydrogen-bonding) intermolecular forces. Energy transfer from HF to HI appears to occur by a double vibrational quantum transition in HI.
On the possible existence of hydrogen ions in solid rare-gas crystals
Authors: Cohen Simon S. , Ron Arza
Published: February 2004

Bondybey and Pimentel [J. Chem. Phys. 56, 3832 (1972)] have reported infrared absorptions in the spectra of rare-gas solids doped with hydrogen. Some possibilities as to the nature of the absorbing species, such as H and D neutral atoms and H− and D− ions, are suggested by the authors of the latter paper. We discuss the possibility that H− and D− ions are the species responsible for the observed data.
Diffusion and chemical oscillations—theory and calculations on a mechanism for the bromate-cerium-malonic acid system
Authors: Clarke Bruce L.
Published: February 2004

An approach to the calculation of the boundary of stability of chemically oscillating systems with diffusion has been developed. The method uses the fact that the Routh-Hurwitz stability criterion has an absolute minimum of zero at the boundary of stability. The condition for this minimum can be used to obtain the shape of the boundary of stability in concentration space, the wavelength and frequency of the undamped perturbation, and the oscillating normal modes of the reaction system. The method is developed using a model mechanism derived from the one discussed by Glansdorff and Prigogine for the bromate-cerium-malonic acid instability. The difficulties to be encountered if this method is extended to the much more complicated mechanism of Noyes, Field, and Körös appear great. Calculations done for the model mechanism produced a boundary of stability with a very complex shape which was dependent on only two parameters and would serve to verify the reaction mechanism.
Dynamical aspects of helix-coil transitions in polypeptides. I
Authors: Tanaka Toyoichi , Soda Kunitsugu , Wada Akiyoshi
Published: February 2004

A dynamical theory for the helix-coil transitions in polypeptides with finite length, which has the following specific features, is presented. (1) It includes size effects which result in the broadening of a critical slowing down (enlargement of the relaxation time of helix-coil transition near its critical temperature). [M. Suzuki, Prog. Theor. Phys. 43, 882 (1970)] (2) It is formulated to give a clear physical picture for the relaxation modes from the final equations. (3) It is directly applied to experiments which measure physical quantities concerning a helical length and its orientation, such as dielectric dispersion, the Kerr effect, light scattering, sonic dispersion or T-jump method. The relaxation spectra for dielectric dispersion are given.
Photostability and molecular structure
Authors: Otterstedt Jan-Erik A.
Published: February 2004

Photostability, defined as the inverse of the quantum yield of a photochemical reaction, is assumed to be proportional to the rate of internal conversion. The rate of internal conversion is inversely proportional to the energy difference between the first excited state and the ground state. In intramolecularly hydrogen-bonded π systems, the photoexcited enol form rearranges itself to an excited keto form. SCF LCAO MO calculations indicate that the energy difference between the first excited state and the ground state is smaller in the keto form than in the enol form. Experiments are reported in support of these theoretical considerations. Weak, strongly red-shifted fluorescence is observed at 77°K for several photostable quinazolines, pyrimidines, quinolines, pyrazines, benzotriazoles, and benzophenones with an o-hydroxyphenyl group in ortho position to a ring nitrogen or a carbonyl group. For some compounds a moderately red-shifted fluorescence is observed as well. No phosphorescence is detected. None of the compounds fluoresce at room temperature. When intramolecular hydrogen bonding is destroyed by, e.g., methylation, the compound shows phosphorescence and moderately red-shifted fluorescence. With data from the literature, the increase in photostability due to enol-keto tautomerism in the excited state is estimated. The increase agrees well with the experimental results.
Iterative perturbation calculations of ground and excited state energies from multiconfigurational zeroth-order wavefunctions
Authors: Huron B. , Malrieu J. P. , Rancurel P.
Published: February 2004

A method is proposed to calculate the effect of configuration interaction by a Rayleigh-Schrödinger perturbation expansion when starting from a multiconfigurational wavefunction. It is shown that a careless choice of H0 may lead to absurd transition energies between two states, at the first orders of the perturbation, even when the perturbation converges for both states. A barycentric defintion of H0 is proposed, which ensures the cancellation of common diagrams in the calculated transition energies. A practical iterative procedure is defined which allows a progressive improvement of the unperturbed wavefunction ψ0; the CI matrix restricted to a subspace S of strongly interacting determinants is diagonalized. The desired eigenvector ψ0 of this matrix is perturbed by the determinants which do not belong to S. The most important determinants in ψ1 are added to S, etc. The energy thus obtained after the second-order correction is compared with the ordinary perturbation series where ψ0 is a single determinant. For the ground state, this procedure includes, besides the whole second-order correction, the most important terms of the third and fourth orders. The question of orthogonality of excited states is discussed. This technique, hereafter called CIPSI, has been tested on the ground and several excited states of H2, Ne, and MgO, showing both a rapid convergence of the calculated transition energy and the importance of correlation effects on transition energy.
String-plucking model for vibrational excitation of molecules
Authors: Gordon Robert J. , Kuppermann Aron
Published: February 2004

A ``string-plucking'' model has been developed to describe the translational to vibrational energy transfer between an atom and a harmonic oscillator in terms of the time-dependent force constant and equilibrium distance of the molecule. The model is compared with exact classical trajectory calculations of collinear and ``breathing sphere'' collisions involving repulsive exponential or Lennard-Jones interaction potentials. In the adiabatic limit for simple collisions (i.e., in the absence of multiple collisions produced by a light middle atom or a deep potential well), the energy transfer predicted by the model is in good agreement with the exact trajectory results. In the case of the Lennard-Jones potential, both model and exact calculations predict that the effect of decreasing the initial kinetics energy is to increase the fractional energy transfer up to 100%. For breathing sphere collisions with a Lennard-Jones potential, the model correctly predicts a sharp decline in energy transfer at a critical impact parameter which is found in the exact trajectory calculations to equal the rainbow impact parameter. For simple collisions with either potential both model and exact calculations show that the effect of increasing the vibrational energy is equivalent to diminishing the initial radial kinetic energy by an equal amount. The model is also compared with the Landau-Teller, Nikitin, and Attermeyer-Marcus theories, and their regions of validity are explored.
Momentum transfer and total scattering cross sections for ions with polar molecules
Authors: Dugan J. V. , Magee J. L.
Published: February 2004

The scattering of ions by polar molecules has been studied using numerical techniques. Because of the long range potential of interaction the scattering cross sections are very large. The total scattering cross section and rotational energy transfer cross section are of the order of thousands of Å2 for the cases studied. The momentum transfer cross sections are 1.3 to 2.0 times the capture cross sections in contrast to the σm/σc=1.105 for Langevin collisions. However, the scattered intensity I(θ) at impact parameters less than 20Å can be quite anisotropic because of the nature of single reflection collisions.
Low temperature chiral nematic liquid crystals derived from β-methylbutylaniline
Authors: Dolphin D. , Muljiani Z. , Cheng J. , Meyer R. B.
Published: February 2004

The synthesis and some basic physical properties of three new liquid crystals are reported. Each of these compounds has been synthesized in both pure chiral and racemic versions. It is demonstrated that a mixture of the chiral and racemic versions of a compound produces a chiral nematic liquid crystal which behaves as a one component system in which the torsion of the helical structure varies linearly with composition, while other thermodynamic properties are independent of composition.
Laser scattering measurements of droplet growth in binary mixtures. I. H2O and air
Authors: Vietti M. A. , Schuster B. G.
Published: February 2004

Droplet growth rates in a Wilson cloud chamber were measured in an air-H2O medium. Growth rates were accurately determined in the size range 0.45–10 μm by detection of oscillations in the intensity of polarized light scattered at 30° from a He–Ne laser source. Pressure and initial temperature were measured in the chamber for use in the computation of three droplet growth theories for comparison to experiment. Experiments were conducted in supersaturations ranging from 1.49 to 3.45.
Semiclassical theory of rearrangement and exchange collisions
Authors: Chan Eu Byung
Published: February 2004

A semiclassical theory of rearrangement and exchange collision processes is developed as an extension of the semiclassical theory of inelastic collisions reported in the earlier papers in this series. The uniform WKB solutions are again used to obtain the WKB solutions of a set of intergrodifferential equations that describe the relative motions of the collision fragments in various channels. The solutions obtained are free of the turning point difficulty characteristic of the usual WKB solutions and thus most suitable for various calculations. The S matrix is constructed from the WKB solutions and given in terms of quadratures involving Airy functions. Approximation of the S matrix thus constructed is also discussed along with a discussion on a possibility of exploiting curve crossings.
Kinetic study of electronically excited phosphorus atoms, P(3 2DJ, 3 2PJ), by atomic absorption spectroscopy
Authors: Acuna A. U. , Husain D. , Wiesenfeld J. R.
Published: February 2004

Electronically excited phosphorus atoms, P(32DJ) and P(32PJ), generated by pulsed photolytic initiation, have been monitored photoelectrically in absorption by attenuation of atomic resonance radiation. Rate constants for the collisional deactivation of these two atomic states are reported for the gases H2, O2, and PCl3 and the resulting rate data discussed in terms of the effects of spin and orbital symmetry in the collision intermediate.
Theoretical development of a virial relationship for spatially defined fragments of molecular systems
Authors: Bader R. F. W. , Beddall P. M. , Peslak J.
Published: February 2004

The original statement of the proposal that a molecular charge distribution can be spatially partitioned by a particular surface into fragments whose average kinetic and potential energies obey the virial relationship, involves an arbitrary choice of origin for the definition of the nuclear virial. A development of the fragment virial relationship is presented here which closely parallels Slater's derivation of the molecular virial theorem. This development provides an independent condition for the determination of the origin and demonstrates that it is determined by a property of the system. The surface which partitions the charge distribution ρ(x) of the total system into fragments (A) and (B) is defined by the gradient vector ∇ρ(x), passing through the point at which ρ(x) attains its minimum value between a pair of adjacent nuclei. The consequences of the restraints which the fragment virial relationship places on a molecular system are discussed with reference to the question of the transferability of the spatially defined fragments between different systems and with respect to the possibility of imposing the restraints directly in the calculation of the properties of a system.
On a nearly proton-ordered structure for ice IX
Authors: La Placa Sam J. , Hamilton Walter C. , Kamb Barclay , Prakash Anand
Published: February 2004

Single-crystal neutron diffraction shows that ice IX, the low-temperature modification of ice III, has an almost completely proton-ordered structure in which the ordered component contains two types of water molecules, type 1 in a site of no point symmetry, and type 2 on a twofold axis, each forming four hydrogen bonds in a three-dimensional framework. The configuration of the water molecules is slightly but significantly altered from that of water vapor. Independent O–D distances, which do not differ significantly from one another, average 0.982± 0.003 Å (corrected for thermal motion), and are increased by 0.012 Å over the vapor value. The shift in O–D stretching frequency ν1 from vapor to ice IX corresponds to a slope dν1/dr≅ −20 000 cm−1. Å−1, which agrees with the slope predicted from spectroscopic anharmonicity constants. D–O–D bond angles (104.7± 0.4°, 106.0± 0.2°) are not decreased from the vapor value (104.5°) despite the smaller O··· O··· O angles into which the water molecules donate protons (98.2°, 100.8°); the same effect occurs also in ice II and oxalic acid dihydrate. The ordered molecules are oriented into the available O··· O··· O angles that differ the least from 104.5°, but the orientation is not completely symmetrical in relation to these angles so that the H-bond bend angles are substantially larger than the minimum possible. Observed amplitudes of thermal vibration, interpreted in terms of rigid-body motion of the molecules, indicate that restoring forces for H-bond distortion are approximately isotropic, ignoring the low-symmetry molecular environments. The amplitudes correspond to appropriate average vibrational frequencies. About 4% of the deuterons in the structure are not in the ordered sites, but occupy the alternative sites that also provide hydrogen bonding. The retention of this partial disorder may be an effect of quenching through the transition range from ice III to ice IX, or it may be an inherent feature of the ice IX structure as achievable experimentally.
Mass spectrometric studies of tetrafluorohydrazine and the difluoroamino radical
Authors: Foner S. N. , Hudson R. L.
Published: February 2004

A mass spectrometer with a collision-free modulated molecular beam sampling system was used to obtain the mass spectrum of N2F4 and to study ionization and dissociation processes in NF2 and N2F4. The mass spectrum of N2F4 differs significantly from previous studies, particularly in regard to the N2F4+/NF2+ ion intensity ratio, indicating that considerable decomposition had occurred in earlier work. Surprisingly, dissociation of N2F4 into NF2 radicals at 300°K at very low pressures, for which the degree of dissociation should be almost 100% at equilibrium, was found to be a slow process, an N2F4 molecule readily surviving the order of 105 wall collisions without decomposing. To obtain substantial conversion of N2F4 into NF2, it was necessary to send the sample through a heated line. Appearance potentials were determined for selected ions from N2F4 and NF2 and the relevant processes identified. The bond dissociation energy D(F2N–NF2)= 0.94± 0.1 eV= 21.6± 3.2 kcal/mole was directly obtained from the appearance potentials of the NF2+ ion from NF2 and N2F4. Other thermochemical energies measured in this study include: D(NF–F)= 3.15± 0.10 eV= 72.8± 2.3 kcal/mole, I.P.(N2F4)= 12.00± 0.1 eV, I.P.(NF2)= 11.76± 0.1 eV, and I.P.(NF)= 12.24± 0.1 eV.
Molecular beam determination of alkali ion-rare gas potentials
Authors: Powers T. R. , Cross R. J.
Published: February 2004

Scattering cross sections have been measured for K+ and Na+ on He, Ne, Ar, Kr, and Xe over the LAB energy range of 40–1000 eV. The data have been analyzed to give intermolecular potentials for these systems in the range of thermal energies to ∼ 0.2 eV. The He and Ne systems could be fit with a purely repulsive wall. For the heavier rare gases the strong attractive ion-induced-dipole force contributed measurably in our energy range. The potentials are harder than the corresponding neutral alkali systems with well depths roughly ten times as large.
Temperature dependence of the rates of ion-molecule collisions
Authors: Buttrill S. E.
Published: February 2004

Momentum transfer collision rate constants have been obtained from ion cyclotron resonance linewidths over a temperature range of 200–425°K. The systems studied were CH5+ in methane, N2+ in N2, H3S+ in hydrogen sulfide, and CH2F+ in methyl fluoride. Collision rates measured at room temperature are in agreement with previous ion cyclotron resonance results and, in the case of N2+ in N2, with dc mobility experiments. For relative ion energies of approximately 0.08 eV, the collision rate constants for CH5+ in CH4 and CH2F+ in CH3F decrease substantially with increasing temperature. This fact shows that the ion-neutral interaction is strongly dependent on the rotational state of the neutral molecule. The frequently used locked dipole approximation to the ion-neutral potential, V(r) = −e2α/2r4−ep/r2, is completely inadequate for describing these experiments since it does not include any orientation or rotational state dependent terms.
Alkali metal intercalates of molybdenum disulfide
Authors: Somoano R. B. , Hadek V. , Rembaum A.
Published: February 2004

Natural molybdenite and single crystals of MoS2 grown by chemical vapor transport were intercalated with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Stoichiometries and x-ray data of all intercalates were determined and a complete indexing of the x-ray patterns of K0.4MoS2 and Rb0.3MoS2 was achieved. The x-ray results show insignificant changes in the ao axis and considerable expansion of co axis after intercalation (Δco : 6.745, 2.704, 4.286, 4.899, and 7.312 Å for Li0.4MoS2, Na0.3Mos2, K0.4MoS2, Rb0.3MoS2, and Cs0.3MoS2, respectively). All intercalated crystals were superconducting (Tonset: 3.7, 4.1, 6.1, 6.25, and 6.30 for Li0.4MoS2, Na0.3MoS2, K0.4MoS2, Rb0.3Mos2, and Cs0.3MoS2, respectively). The superconductivity is believed to be due to an electron transfer from the alkali metal to an empty band of MoS2, resulting in an increase in electron density as well as in the density of states at the Fermi surface.