bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared chemiluminescence investigation of the abstraction reactions between fluorine atoms and unsaturated compounds
Authors: Moehlmann Jon G. , McDonald J. D.
Published: February 2003

The abstraction reaction between fluorine atoms and various olefinic and aromatic substrates has been examined by the arrested relaxation infrared chemiluminescence technique. The relative populations of each rotational–vibrational quantum state of the HF produced in such reactions have been obtained. The fraction of reaction exothermicity entering HF vibration, as well as the relative total cross sections for the substitution and abstraction reactions have been estimated. The results indicate that, typically, about 40% of the exothermicity enters HF vibration, with the HF V=1 state the most likely to be populated, followed by V=2 and V=3.
Concentration dependent solute redistribution at the ice/water phase boundary. I. Analysis
Authors: Gross Gerardo Wolfgang , McKee Chester , Wu Chen-ho
Published: February 2003

The purpose of this work was to find a method suitable for analyzing experimental data of solute redistribution at the ice/water phase boundary at (quasi) equilibrium, when solute transport is controlled by (one-dimensional) diffusion and the distribution coefficient is concentration dependent. A careful study of the models proposed by earlier workers led to the formulation of an approximate log linear solution to the appropriate diffusion and continuity equations. Its validity was checked and justified by a numerical model of the rigorous analytical solutions available for the case of a concentration independent distribution coefficient. The approximate log linear solution is valid nearly over the whole range including the region approaching steady state, but not at the very beginning of freezing. It provides a straightforward method for analyzing experimental solute distribution curves. Its usefulness will be demonstrated subsequently by applying it to experimental data.
Optical excitation in collision of 500–5000 eV H2+, He+, Ne+, Ar+, and N2+ ions with CO2
Authors: Bregman-Reisler Hanna , Doering John P.
Published: February 2003

Electronic excitation of the products of collisions of 500–5000 eV H2+, He+, Ne+, Ar+, and N2+ ions with CO2 has been investigated by a spectroscopic study of the optical emissions from the collision products at wavelengths from 3000 to 6500 Å. For H2+ and N2+ projectile ions,the most important contribution to the observed emissions was from the A 2Πu excited state of CO2+. For He+ and Ne+ impact, however, strong emissions from Oi, Oii, Ci, and Cii in high Rydberg states produced by dissociative ionization of CO2 were observed. Emission from excited molecular dissociation fragments (CO and CO+) was weak in the latter case, but it was possible to identify fluorescence definitely from the d 3Δi and a′ 3Σ+ states of CO and the A 2Π state of CO+ as well as to identify tentatively emissions from the e 3Σ− and b 1Σ+ states of CO. Emissions from the projectile ions or fast neutral atoms produced by charge transfer were also observed. The most intense lines produced with He+, Ne+, and Ar+ projectiles originated from the neutral rare-gas atoms in Rydberg states as high as n=9. Analysis of the results shows that charge transfer, dissociative charge transfer, and direct excitation channels all contribute to the observed emissions, but the relative importance of the various channels is different for different projectile ions.
Cross-relaxation determination of short quadrupolar spin–lattice relaxation rates in solids: Strong mixing in KH2AsO4 and Ag2H3IO6
Authors: Blinc R. , Z̆umer S.
Published: February 2003

The application of dipolar proton (I) spin–lattice relaxation time measurements for the determination of fast quadrupolar spin–lattice relaxation rates on nonresonant S spins, the signals of which are too weak to be measured directly, are discussed in the limit of strong I–S dipolar coupling. The spin–lattice relaxation of the common 1H–75As dipolar reservoir in KH2AsO4 and the common 1H–127I dipolar reservoir in Ag2H3IO6 are used to illustrate the above technique.
Distorted-wave Born calculation of near-resonant energy transfer
Authors: Sharma R. D. , Picard R. H.
Published: February 2003

The distorted-wave Born calculation for transfer of one quantum of asymmetric stretch from CO2 to 14N2 and 15N2 is presented. A spherically symmetric Lennard-Jones 6–12 potential with parameters derived from transport properties is used as distorting potential. The energy transfer is assumed caused by dipole–quadrupole coupling, i.e., interaction involving the transition dipole of CO2 and the transition quadrupole of N2. The results obtained are in excellent agreement with those obtained earlier using a straight path as the trajectory during the intermolecular collision and an empirical recipe for summing over impact parameters.
Pressure broadening of the atomic iodine 52P1/2–52P3/2 transition
Authors: Padrick T. D. , Palmer R. E.
Published: February 2003

Pressure-broadening coefficients for the atomic iodine 52P1/2–52P3/2 transition have been measured for several buffer gases using a laser gain technique. The results in MHz/Torr are as follows: CO2, 7.4±0.7; N2, 6.2±0.8; He, 3.6±0.3; Ne, 4.3±0.4; Ar, 5.1±0.5; Kr, 4.4±0.4; and Xe, 3.0±0.3. These values are compared to those predicted by impact theory.
Lower bound to the energy of complex atoms
Authors: Hertel Peter , Lieb Elliot H. , Thirring Walter
Published: February 2003

There are methods available for calculating rather precise lower bounds for the energy of simple atoms or molecules. If complex atoms or molecules are to be investigated, these methods become inapplicable, or impracticable. Here we propose a new method which, for the above cases, promises to become as accurate as the Hartree–Fock procedure for the upper bound. Although applicable to a wider class of problems, we shall demonstrate it for an atom with N electrons.
Deuterium quadrupole coupling in solid 1,3,5-trichlorobenzene-d3 and 1,2,3,4-tetrachlorobenzene-d2
Authors: Ragle J. L. , Mokarram M.
Published: February 2003

Nuclear quadrupole coupling parameters for 1,3,5-trichlorobenzene-d3 and 1,2,3,4-tetrachlorobenzene-d2 are reported and compared with results for other compounds. No systematic trends were observed. (AIP)
Rates of H+CH3X reactions
Authors: Westenberg A. A. , deHaas N.
Published: February 2003

Rate constants for the reaction H + CH3X → CH3 + HX (X=Br, Cl, F) have been measured over a wide temperature range using a discharge flow reactor, with pseudo-first-order decays of CH3X measured mass spectrometrically and excess H concentrations measured by ESR. Both absolute data (∼±20%) and rate constant ratios (∼±10%) were obtained. k (CH3Br) was measured over 298–996 °K, k (CH3Cl) over 510–998 °K,,and k (CH3F) over 605–871 °K. Arrhenius expressions (k in cm3 mole−1⋅sec−1, E in cal/mole) fitted k (CH3Br) = 2.8×1013 exp(−5300/RT) over 300–800 °K, k (CH3Cl) = 3.7×1013 exp(−9300/RT) over 500–800 °K, and k (CH3F) = 1.8×1013 exp(−9400/RT) over 600–900 °K. The ratio k (CH3Br)/k (CH3Cl) obeyed 0.73 exp(4000/RT) over 600–1000 °K, the data overlapping recent point source flame data of Hart et al. with excellent agreement. The combined results from this work and from Hart et al. on k (CH3Cl)/k (CH3F) fit 1.7 exp(300/RT) over 600–1100 °K.
Optical spectra of Be atoms and Be2 molecules in rare gas matrices
Authors: Brom J.M. , Hewett W. D. , Weltner W.
Published: February 2003

Beryllium atoms, trapped at 4 °K in solid neon, argon, and krypton, showed a strong absorption near 235 nm which is assigned to the resonance transition 1P1 ← 1S0 appearing at 234.86 nm (42 565 cm−1) in the gas phase. Specifically, the absorption occurred at 232.0 nm (43 090 cm−1), 236.0 nm (42 360 cm−1), and 240.5 nm (41 567 cm−1) in Ne, Ar, and Kr, respectively. Excitation to the 1P1 state also led to long-lived emission in Ar and Kr matrices at 465.0 and 464.7 nm with lifetimes of 1.33(8) and 0.095(5) sec, respectively, and is assigned to the spin-forbidden 3P1 → 1S0 emission. In each case an adjoining emission band also appeared at longer wavelengths, which can most probably be attributed to coupling of the electronic transition to matrix phonons. In concentrated matrices, Be2 molecular absorption yielded a progression of bands with the (0,0) band at 350.15(5) nm (28 551 cm−1) in Ne and at 361.30(5) nm (27 670 cm−1) in Ar. In analogy with the similar van der Waals molecules Mg2 and Ca2, these bands are assigned to the A 1Σ+u ← X 1Σ+g transition. The vibrational frequency in the upper state is 489 cm−1 in Ne and 474 cm−1 in Ar matrices. No other molecular electronic transitions were detected out to 50 000 cm−1.
Impact broadening and shift of the Hα line by helium, neon, and argon
Authors: Kielkopf J. F.
Published: February 2003

Observations are reported of the collision broadening and shift of the hydrogen-α line by helium, neon, and argon foreign gases. An analysis of the line profile from a microwave-excited discharge with allowance for Doppler broadening and fine structure yields the effect of foreign gas pressure on the spectral line shape. The classical theory of spectral line impact broadening together with an interatomic potential proposed previously for alkali–noble gas interactions correctly predicts the observed broadening and shift of the line.
Semiclassical theory of spectral line shapes. II. Applications to CO, HCl, and OCS, broadened by inert gases
Authors: Fitz D. E. , Marcus R. A.
Published: February 2003

The semiclassical theory of spectral line broadening developed in the previous paper of this series is used to calculate the half-widths and shifts of nonoverlapping rotational spectral lines of CO, HCl, and OCS, broadened by inert gases. Comparisons are made with the available experimental data and with related theoretical analyses, and reasonable agreement is obtained. The method used applies both to fairly quantum systems as well as to the relatively classical ones. A symmetrized semiclassical expression for Wigner 6-j symbols is given and applied.
Far infrared collision-induced absorption in gaseous methane. II. Determination of the octupole and hexadecapole moments
Authors: Birnbaum George , Cohen E. Richard
Published: February 2003

The octupole and hexadecapole moments of methane are obtained by comparing the experimental and theoretical zeroth spectral moment and the integrated absorption coefficient of the collision-induced far infrared rotation–translation spectrum. The data presented in Part I of this series and the theory summarized in this paper give the values Ω2/σ7 = 4.67×10−16 erg and Φ2/σ9 = 1.56×10−16 erg, from which we obtain the octupole and hexadecapole moments, respectively, ‖Ω‖ = (2.22±0.12) ×10−34 esu⋅cm3 and ‖Φ‖ = (4.8±0.5) ×10−42 esu⋅cm4 for σ=3.758 Å. An argument is advanced as to why it is preferable to report these results in the form Ω2/σ7 and Φ2/σ9, where σ is the molecular diameter parameter appearing in the potential function.
Brillouin scattering of light in a cholesteric liquid crystal
Authors: Wang C. H. , Huang Y. Y.
Published: February 2003

Brillouin scattering was used to study the hypersonic properties of cholesteryl palmitate in the liquid crystal–liquid phase transition region. Contrary to the results of similar measurements by Durand and Rao, no anomalous change in either the velocity or the attenuation of the hypersonic waves was observed at the transition.
Flow–drift tube measurements of kinetic energy dependences of some exothermic proton transfer rate constants
Authors: Lindinger W. , Albritton D. L. , Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: February 2003

The rate constants for several exothermic proton transfer reactions have been measured as a function of relative ion kinetic energy in a flow–drift tube. The reactions include the exothermic proton transfers of O2H+ with N2, CO2, and NH3; H3+, CH5+, COH+, and NH3+ with NH3. The energy range covered is from thermal to about an electron volt. The energy dependences of the proton transfers are of interest in evaluating the reaction efficiency, with both polar and nonpolar neutrals. It is found that the thermal energy rate constants are given reasonably well by the Langevin (nonpolar) or average dipole orientation (polar) collision rate constants in most cases. However the energy dependence of the reaction rate constants is not that expected for the collision rate constant in most cases. It is thus concluded that models assuming a constant reactant efficiency with energy are not always valid.
Nonlinear polarizability of alpha-iodic acid
Authors: Crane G. R.
Published: February 2003

The nonlinear optical coefficient d14 of HIO3 has been remeasured by the wedge technique. The new value dHIO314 = 13.1±1 dKDP36 substantially agrees with values previously determined via phase matched experiments. A probable reason for failure of a simple bond polarizability scheme to predict this coefficient is discussed.
Velocity dependence of the Penning and associative ionization cross sections of Ar atoms by He(2 3S) and He(2 1S) atoms
Authors: Pesnelle A. , Watel G. , Manus C.
Published: February 2003

The velocity dependence of both the Penning and associative ionization cross sections σPI and σAI of Ar atoms by He(2 3S) and He(2 1S) metastable atoms, and of their sum σT = σPI + σAI, is measured in the velocity range 1200–4500 m/sec (30–400 meV) in a crossed-beam experiment by a time-of-flight technique. Characteristic cross-section ratios σAI/σT and σT(singlet)/σT(triplet) are reported along with the relative magnitude of the cross sections σAI, σPI, σT. The measurements clearly show a difference in the reaction mechanisms involving He(2 3S) and He(2 1S). This difference appears not only in the ratio σAI/σT, whose magnitude reaches 19% and 38% for He(2 3S) and He(2 1S), respectively, at the velocity v = 1200 m/sec (30 meV), and in the ratio σT(singlet)/σT (triplet), which increases from 0.5 to 3.8 for velocity decreasing from 4500 m/sec to 1200 m/sec, but also in the different shapes of the σAI and σPI cross sections for He(2 3S) and He(2 1S). The experimental results for He(2 3S) are also compared to theoretical calculations made in the classical impact parameter formulation. The model gives a total ionization cross section σT and partial ionization cross sections σAI and σPI in good agreement with the data. Information on both the coupling width and the He + Ar+ interaction potential well are obtained.
Density functional theory of interacting closed shell systems. II. The determination of charge densities and the Hellman–Feynman theorem
Authors: Harris Robert A. , Heller Donald F.
Published: February 2003

The density functional formalism and the additive density approximation are used to obtain the nonadditive contribution to the electron density of a set of closed shell atoms in the absence of external fields. It is shown that due to the additive density approximation, the Hellman–Feynman theorem is violated when the force on the nucleus is examined. The reason for this violation is discussed.
Radical overshoots and dissociation in methane/air flames
Authors: Bulau James R. , Kaskan Walter E.
Published: February 2003

A discussion is given of the fact that observed radical overshoots in methane combustion imply the existence of dissociation reactions. The fraction of methane molecules which oxidize via a path including a dissociation has been found to approach 0.8 in very rich methane/air flames by observing that radical concentrations tend toward zero as the flames are made richer and approach a limiting equivalence ratio, φl. This finding provides an interpretation of the observation that methane is converted entirely to CO and CO2 at equivalence ratios below φl, whereas above φl unreacted methane persists into the burned gases.
Lifetimes for resonance fluorescence and near resonance Raman scattering
Authors: Mukamel Shaul , Jortner Joshua
Published: February 2003

In this paper we present a quantum mechanical treatment of time resolved resonant and near resonant light scattering from a molecular system. The time resolved decay pattern is characterized by just two types of lifetimes, those specifying the molecular system and those characterizing the light pulse, while the off resonance energy parameter affects the total intensity and, in some cases, the relative intensities of the different decay components. The theoretical results for the ’’isolated’’ molecule are confronted with the recent experimental data of Williams, Rousseau, and Dworetzky [Phys. Rev. Lett. 32, 196 (1974)] for resonance and near resonance photon scattering from I2. Finally, we present a general scheme for handling photon scattering from a multilevel molecular system.
Vibrational relaxation in the ground electronic state of large organic molecules in solution
Authors: Ricard D. , Ducuing J.
Published: February 2003

A new and sensitive method for the study of vibrational relaxation in the ground electronic state of molecules has been applied to dilute solutions of Rhodamine 6G in alcohols. The method takes advantage of the large electronic cross sections to prepare the molecules in vibrationally excited states and probe their return to the ground state. The influence of the solvent on our experimental observations is discussed. A study of the effect of dielectric relaxation and hydrogen bonding on the Stokes shift justifies the interpretation of our results in terms of vibrational relaxation.
Thermal force on a disk in rarefied gas
Authors: McCoy B. J.
Published: February 2003

A theory for thermal force on a finite disk is developed by revising an earlier theory for an infinitely large plate. Coupling between force and temperature gradient is provided as before by constitutive equations relating momentum and heat flux to the second derivative of temperature. Viscosity and thermal conductivity coefficients depend on Knudsen number so as to span the transition regime. The theory includes surface accommodation effects and is in satisfactory agreement with recent experimental data.
Three-dimensional quantum mechanical studies of D+H2 → HD+H reactive scattering
Authors: Tang K. T. , Choi B. H.
Published: February 2003

A three-dimensional quantum mechanical study is made on the reactive scattering of D+H2 → DH+H. The differential and total cross sections as well as the S-matrix elements are obtained from the adiabatic distorted wave model. With the initial molecule H2 in the ground rotational state, we calculated the cross sections for reactions to all possible rotational states of the product molecule DH. The potential used is that of the Porter and Karplus semiempirical surface. The reactive scattering is predominantly backward. However, the peak in the differential cross sections gradually shifts away from ϑ=π as the energy is increased, with higher rotational states shifting more. In the thermal energy region, there is virtually no scattering in forward directions. The reaction is endothermic but only slightly so. Although the 0→0 rotational transition contributes only a small fraction to the total reactive cross section, most product molecules prefer rotational states that are considerably lower than the highest one allowed by energy conservation. Differential cross sections summed over all possible final rotational states are significantly different from that of any one state. Previous three-dimensional quantum mechanical studies on this system are all limited to one final rotational state; these previous results are compared with the result of the corresponding case in the present study. The present results are also compared with the corresponding classical trajectory calculations on the same potential surface. Finally, the experimental measurements of Geddes, Kraus, and Fite are compared with the present results. Qualitatively, there are general agreements. but quantitatively the calculated cross sections are definitely too large as compared with the experimental ones. The most likely cause for this difference is that the potential surface used is ’’too reactive.’’
Multiplet generalized oscillator strengths and inelastic scattering cross sections calculated including the electron correlation effects: Transitions of neutral atoms: Be, B, C, N, and O
Authors: Davis Stephen L. , Sinanoğlu Oktay
Published: February 2003

The generalized oscillator strengths as a function of momentum transfer q and the integrated inelastic cross section as a function of incident electron kinetic energy E are calculated with accurate inclusion of all of the nonclosed shell type correlations in both initial and final states using the new atomic structure theory for excited states of Sinanoğlu for BeI 2s2 1S → 2s2p 1P0, BI 2s22p 2P0 → 2s2p2 2D, BI 2s22p 2P0 → 2s2p2 2P, CI 2s22p2 3P → 2s2p3 3D0, CI 2s22p2 3P → 2s2p3 3P0, CI 2s22p2 3P → 2s2p3 3S0, NI 2s22p3 4S0 → 2s2p4 4P, and OI 2s22p4 3P → 2s2p5 3P0. Some difficult variational problems in these neutral atom states, some of which are not the lowest of their symmetry, have to be and are properly dealt with here. The results show large effects of correlation as compared with Hartree–Fock calculations on both the magnitudes and the shapes of the curves. Similar effects will occur in the electron impact spectra of molecules.
Approximate hindered asymmetric top wavefunctions for atom–diatomic molecule reactions
Authors: Elkowitz Allan B. , Wyatt Robert E.
Published: February 2003

A method for quickly computing approximate hindered asymmetric top rotational wavefunctions suitable for input to the close-coupled scattering equations for one-path atom–diatom collisions is outlined. An approximate form of the Coriolis-asymmetry coupling operator is used before diagonalization of the asymmetric top Hamiltonian in the free rotor basis. Correlation diagrams and wavefunction density plots are shown for a model one-path reaction. Errors made in the approximation are discussed by comparison of the approximate rotor energies with the near exact values.
Radiationless decay in propynal: Dependence upon vibrational state
Authors: Thayer C. A. , Pocius Alphonsus V. , Yardley James T.
Published: February 2003

New time-resolved measurements of luminescence decay rates and intensities for vibronically selected propynal molecules excited by a pulsed tunable dye laser are reported. The observations allow individual determination of the rates for ’’collision-free’’ and collision-induced intersystem crossing and internal conversion from the initially excited 1A″ state. Explicit ’’no parameter’’ calculations of the collision-free decay rates for the vibrationless level based on the Fermi Golden Rule for time-independent perturbations give 0.38×104 sec−1 for internal conversion and 0.59×105 sec−1 for intersystem crossing if the broadening mechanism for the initially prepared levels is primarily radiative. The observed decay rate for intersystem crossing from the vibrationless level is 0.52 (+0.5, −0.25) μsec−1, while that for internal conversion is 0.48 (+0.3, −0.48) μsec−1. Results are also presented for collisional quenching of selected vibronic levels of propynal (1A″) by acetonitrile. The enhancement of quenching rate with vibronic excitation would also appear to agree with theoretical expectations.
Stability of topologically similar chemical networks
Authors: Clarke Bruce L.
Published: February 2003

Theorems are proven which support the view that chemical reaction network topology determines which networks can have unstable steady states and when the steady states are unstable. These theorems make it possible to determine the stability of large networks in certain circumstances by determining the stability of simpler networks with identical topology. Chemical networks are classified as ’’qualitatively vertex stable’’ (QVS), ’’qualitatively vertex marginally stable’’ (QVM), and ’’qualitatively vertex unstable’’ (QVU). Roughly speaking, QVS networks always have stable steady states, QVM networks have linearized dynamics which is marginally stable for all rate constants and constrained concentrations, and QVU networks have unstable steady states for specific parameter ranges. The sense in which the preceding sentence is rough is discussed in the text. It is shown that the linear steady state stability analysis problems for topological similar networks are closely related. A geometrical and graph theoretical approach to the stability problem previously developed by the author is then used to prove a number of theorems establishing in certain cases that topologically similar networks possess identical qualitative vertex stability classifications.
Electronic spectroscopy of t
r
a
n
s-azomethane by electron impact
Authors: Mosher Oren A. , Foster Michael S. , Flicker Wayne M. , Beauchamp J. L. , Kuppermann Aron
Published: February 2003

The electron impact excitation of trans-azomethane (i.e., trans-dimethyl diazine CH3–N–N–CH3) has been studied by both trapped electron (TE) and differential electron scattering (DES) techniques. The nature of the excited state in each of several transitions has been identified by the energy and angular dependences of the excitation cross section. Two previously unreported singlet→triplet transitions are observed with maxima at 2.75 and 4.84 eV. Theoretical calculations on the parent compound, trans-diimide (H–N=N–H), suggest that these are the ? 1Ag→1 3Bg (produced by excitation of an electron from an n+ molecular orbital to a π* molecular orbital) and the ? 1Ag→1 3Bu (π→π*) transitions, respectively. The ? 1Ag→1 1Bg (n+→π*) transition is observed with a peak at 3.50 eV in the DES studies. A strong peak at 6.01 eV in the TE spectra appears as a weak shoulder in the DES studies and is interpreted as either a symmetry-forbidden or Rydberg-like singlet→singlet transition. Allowed singlet→singlet features overlap each other in the transition energy range from 6 to 10 eV. Peaks are seen in the DES spectra at 6.71, 7.8, and 9.5 eV and in the TE spectrum at 8.0 eV. Several significant differences between the TE and the DES spectra are analyzed on the basis of the different nature of the two experiments.
Shift of the emission band upon excitation at the long wavelength absorption edge. II. Importance of the solute–solvent interaction and the solvent reorientation relaxation process
Authors: Itoh Ken-ichi , Azumi Tohru
Published: February 2003

Fluorescence and phosphorescence of quinine and its related compounds such as 6-methoxyquinoline are found to exhibit a red shift when excitation is achieved at the long wavelength edge of the first absorption band, and this anomalous shift is investigated in detail. The anomalous shift is observed not only in room temperature fluorescence, but also in low temperature fluorescence and phophorescence. The term edge excitation red shift (EERS) is introduced. After various plausible interpretations we have suggested a logical mechanism for EERS. In the suggested mechanism, EERS is observed if the solvent reorientation relaxation rate is small compared with the emission rate, and the Franck–Condon solvation energy is reasonably large with respect to solvent orientation. All the experimental observations are satisfactorily interpreted within the framework of the suggested mechanism.
Reanalysis of the density of liquid water in the range 0–150 °C and 0–1 kbar
Authors: Kell G. S. , Whalley E.
Published: February 2003

The change of density of liquid water under pressure has been calculated from the speed of sound u by fitting u−2 as a polynomial in temperature and pressure, integrating with respect to pressure, and allowing for the difference between isothermal and adiabatic compressions. By comparing calculations done by different methods on the same data and on different data it appears that the densities so obtained are accurate to about 20 ppm at 1 kbar. These densities are about 100 ppm greater than the densities obtained by us some years ago by direct measurement of the compressions in the range 0–150 °C and 0–1 kbar relative to a stainless steel vessel. It seems likely that the compressibility of the vessel used in this work is too high by about 0.1 Mbar−1. A correction to the compressibility of the vessel is proposed to bring the densities in the range 0–100 °C and 0–1 kbar into agreement with the values from the speed of sound. The same correction should apply in the range 100–150 °C, and the corrected values appear to be the best available. A hysteresis between the runs at increasing and decreasing pressures is now ascribed to a hysteresis in the position of some nylon washers. The two types of runs have therefore now been analyzed independently, and revised densities are tabulated.
An investigation of nonequilibrium kinetic isotope effects in chemically activated ethyl radicals
Authors: Cowfer J. A. , Michael J. V.
Published: February 2003

The reactions of thermal H and D atoms with C2H4 and C2D4 have been studied in helium diluent at room temperature with a discharge flow system time of flight mass spectrometric apparatus. New absolute measurements of the apparent bimolecular rate constants, under atom excess conditions, for the reactions D+C2H4, H+C2D4, and D+C2D4 have been obtained as a function of pressure. Mechanistic studies have also been carried out for the D+C2H4 and H+C2D4 reactions in the pressure region of 1–5 torr. The observed pressure dependence of the rate constants and the mechanisms for the two mixed cases have been found to differ markedly. The variation in over-all mechanism for the mixed isotope cases, ethyl-d1 and ethyl-d4, and the nonequilibrium kinetic isotope effects for chemically activated ethyl radicals are presented and compared with other work. RRKM theoretical calculations are shown to be consistent with the experimental observations for the four systems.
Mobilities of various mass-identified positive ions in helium and argon
Authors: Lindinger W. , Albritton D. L.
Published: February 2003

Measurements at room temperature with a flow-drift tube have been made of the mobilities of the following mass-identified positive ions: H3+, O+, CO+, COH+, Ar+, ArH+, O2+, O2H+, O2H2+, NH3+, NH4+, CH5+, CO2+, NO+, and N2OH+ in helium and COH+, CO2+, and N2OH+ in argon. The measurements were obtained over the range 2 ? E/N ? 135 Td for helium and 5 ⩽ E/N ? 200 Td for argon (1 Td = 10−17 V⋅cm2). The similarities of the E/N dependence of the mobilities are discussed. The reduced zero-field mobilities obtained here and in other studies of ions in helium and argon are compared to the predicted mobilities of the point-charge, induced-dipole, or ’’Langevin,’’ model. The discrepancies are smaller for the more polarizable argon.
Normal coordinate analysis of the optically active vibrations (k=0) of crystalline magnesium orthosilicate Mg2SiO4 (forsterite)
Authors: Devarajan V. , Funck E.
Published: February 2003

A normal coordinate analysis for the vibrations of the olivine type crystal Mg2SiO4 (forsterite) in the limit k=0 has been carried out to investigate the group behavior of the SiO4 ion and also to identify the ’’external’’ modes. The crystal FG matrix method of Shimanouchi et al. is used with a potential function which combines general valence and short range force constants. Calculations have also been done for the 26Mg isotope. A dipole–dipole interaction model has been introduced through stretch–stretch interaction to account for the correlation field splitting of ν3b of the SiO4 group. Conclusions are also drawn about the nature of different vibrational modes.
Statistical mechanics of interfacial properties of polyatomic fluids. I. Surface tension
Authors: Davis H. Ted
Published: February 2003

General expressions for the surface tension and bulk pressure are derived for a semiclassical polyatomic fluid. The Fowler–Kirkwood–Buff approximation is used to reduce the general surface tension formula to a simple form and to show that the dipole–dipole interactions account for about half of the surface tension of low vapor pressure water.
Rotational nonequilibrium in cw chemical lasers
Authors: Sentman L. H.
Published: February 2003

By including the spontaneous emission term in the radiative transfer equation, an explicit expression for the radiation term in the species equation is obtained in terms of the fluid variables. This formulation is used to study the role of rotational nonequilibrium in cw chemical lasers. It is shown that the phenomena of J shifting and the power being contained in the high J transitions are consequences of the rotational equilibrium assumption. When rotational nonequilibrium is allowed to occur, several J transitions within a given vibrational band lase simultaneously, most of the power is contained in those J transitions that are preferentially populated by the pumping reaction, and the power is decreased by 20%–30% from the rotational equilibrium value. Agreement between the predicted and observed lasing transitions in HF lasers is obtained.
Electronic state of iron in enterobactin using Mössbauer spectroscopy
Authors: Spartalian K. , Oosterhuis W. T. , Neilands J. B.
Published: February 2003

Well-resolved paramagnetic hyperfine structure is observed in the Mössbauer spectra of 57Fe complexed by enterobactin, an iron transport compound found in many enteric bacteria. Spectra were observed under varied conditions of temperature (4.2–77 K) and applied magnetic field (0–6 kOe). The spectra for the high spin ferric ion (S=5/2) are well explained using a spin Hamiltonian with rhombic symmetry including a fourth order term in the electronic spin. This Hamiltonian has partially rhombic symmetry with the ratio E/D = 0.46. An isotropic ESR signal at g = 4.3 is predicted from the spin Hamiltonian if 4a = 3D (1-3 E/D), except when E≡D. A derivation of this relationship is given, which includes the special case of E = D/3, a = 0, previously used as the explanation for the so-called ’’rhombic’’ ESR signal at g = 4.3. The zero field splitting parameters are found to be D = 0.50 cm−1, λ = E/D = 0.46, and μ = a/D = −0.27. The magnetic hyperfine coupling constant is A = 1.51 mm/sec, the quadrupole coupling constant is e2qQ/4 = −0.15 mm/sec, η = 3λ = 1.38, and the isomer shift is +0.28 mm/sec.
Configuration interaction studies of the excited states of water
Authors: Winter N. W. , Goddard W. A. , Bobrowicz F. W.
Published: February 2003

We report the results of extensive configuration interaction studies on 16 excited states of water. These states can be accurately described as corresponding to excitation from one of the highest two molecular orbitals (1b1 or 3a1) of the ground state into either the 3s or one of the three 3p Rydberg orbitals. The results provide the most accurate and consistent treatment of these states to date (within 0.1 eV for all known transitions) and form a reliable basis for the assignment of the photon and electron impact spectra of H2O.
Formal theory of atom–diatomic molecule reactions
Authors: Mittleman Marvin H.
Published: February 2003

Low energy atom–diatomic molecule scattering is formulated in the adiabatic representation. Explicit care is taken to describe the scattering boundary conditions and the Pauli principle correctly. A set of coupled three body equations is obtained for the nuclear motion. Coupling represents ’’hopping’’ from one electronic surface to another. The coupling operator is obtained by a generalization of a method previously used in atom–atom scattering. It has the property of vanishing when the reacting products are well separated and involves the previously introduced electron switching function and a new nuclear switching function.
Photoemission from ice and water surfaces: Quasiliquid layer effect
Authors: Nason D. , Fletcher N. H.
Published: February 2003

Photoemission studies of ice and water have been conducted using uv radiation. The photoemission threshold for both ice near −10°C and water near 10°C is about 1950±50 Å, the emission efficiency for liquid water being about half that for ice. Photoemission from ice decreases steadily with decreasing temperature, apparently without shift in threshold, and vanishes below about −160°C. The results suggest that a waterlike phase is stable on the surface of ice at temperatures above −160°C. It is also concluded that hydroxyl ions which are highly concentrated in the surface phase are responsible for the photoactivity.
Molecular reorientation in liquids by Rayleigh scattering: Pressure dependence of rotational correlation functions
Authors: Dill J. F. , Litovitz T. A. , Bucaro J. A.
Published: February 2003

Results of high pressure study of the depolarized Rayleigh scattering in acetone, benzene, and methyl iodide are presented. The density dependences of the angular velocity and angular position correlation functions are determined. The angular velocity correlation function of each liquid shows a negative overshoot. In addition, benzene at all pressures and methyl iodide at high pressures exhibit additional oscillations in the angular velocity correlation function. The details of the correlation functions are discussed in terms of ''collision interrupted'' models such as the well known J-diffusion model. It is concluded that a more general description than J diffusion capable of allowing incomplete loss of momentum upon collision is needed. The results are compared to studies of reorientation by means of NMR. Finally, the relation between shear viscosity and reorientation in these liquids is discussed.
Charge exchange of rare gas ions: An ion kinetic energy study
Authors: Ast T. , Terwilliger D. T. , Beynon J. H. , Cooks R. G.
Published: February 2003

The charge exchange reaction m++ + N → m+- + N+- has been studied at 8 keV impact energy in a double-focusing mass spectrometer for each combination of the rare gas ions and atoms. The kinetic energy gained or lost by the fast species m has been measured and from this the states of m+- and N+- have been assigned. Generally all the observed peaks correlate with known states of the product ions and the relative intensities of the peaks are in approximate agreement with previously determined cross sections. The Massey ''near-resonance'' criterion is qualitatively applicable. Extension of the work to the study of polyatomic species is reported.
A theory for the thermodynamics and structure of nonuniform systems, with applications to the liquid–vapor interface and spinodal decomposition
Authors: Abraham Farid F.
Published: February 2003

We propose a theory for the description of the thermodynamics and structure of nonuniform fluids. The theory is based on a generalization of liquid-state perturbation theory of uniform fluids and on the Fisk–Widom generalization of the thermodynamic theory of van der Waals and Cahn–Hilliard. The theory is applied to the liquid–vapor interface near the triple point and near the critical point, and to the thermodynamic analysis of the stability of a single phase fluid in the spinodal region (spinodal decomposition). The limitations of the van der Waals/Cahn–Hilliard theory for surfaces and Cahn’s analysis for spinodal decomposition are discussed.
Energy gap law for vibrational relaxation of a molecule in a dense medium
Authors: Nitzan Abraham , Mukamel Shaul , Jortner Joshua
Published: February 2003

In this paper we advance a model Hamiltonian for direct vibrational relaxation of a guest molecule in a host lattice. General expressions for the vibrational relaxation rate constant are derived utilizing the generating function method, elucidating the gross features of this class of multiphonon relaxation phenomena. Explicit theoretical results were obtained for the vibrational relaxation rate in two temperature regions: for moderately low temperatures below the characteristic Debye temperature and in the high temperature limit. In the low temperature range the vibrational relaxation rate exhibits a nearly exponential variation with the order of the multiphonon processes, revealing the energy gap law, an appreciable isotope effect, and a strong temperature dependence. The predicted energy gap law is compatible with the available experimental data.
Effects of oxygen-18 substitution upon electronic relaxation in the 3B1 state of SO2
Authors: Nelson Glenn E. , Borkman Raymond F.
Published: February 2003

We have measured phosphorescence lifetimes and quantum yields of solid S16O2 and S18O2 at several temperatures. Isotopic substitution was found to increase the phosphorescence lifetime of the 3B1 state of solid SO2 at 77 °K from 1.0±0.1 msec to 1.3±0.1 msec, and at 4.2 °K from 8.7±0.1 msec to 9.7±0.4 msec. The quantum yield of solid SO2 at 77 °K was determined to be 0.09±0.01 and at 4.2 °K was determined to be no less than 0.6±0.1. Radiative and nonradiative rate constants for 3B1 → 1A1 relaxation were calculated from our quantum yield and phosphorescence lifetime data. The nonradiative relaxation rate constant was found to be temperature dependent as well as isotope dependent, decreasing by a factor of 20 between 77 and 4.2 °K. At 1.4 °K, where the spin-lattice-relaxation rate is considerably reduced, three lifetime components could be resolved, and the phosphorescence decay time for the dominant spin state τ1 was found to be longer for S18O2 than for S16O2, consistent with our observations at higher temperatures.
Conformal ionic solution theory for additive ternary molten–ionic systems
Authors: Saboungi Marie-Louise , Blander Milton
Published: February 2003

Excess free energies of mixing (ΔAEm) for additive ternary molten ionic systems (AX–BX–CX or AX–AY–AZ) have been calculated from conformal ionic solution (CIS) theory. The CIS theory applies rigorously to ionic systems containing cations (or anions) of different size, whereas quasichemical theory, which is based on a lattice model, cannot be rigorously applied to such systems. Nevertheless, most of the terms calculated from CIS theory have counterparts in quasichemical theory except for asymmetric terms proportional to products of mole fractions of components i and j of the form X2iXj. Such asymmetric terms are known to be significant in molten salt systems. In the expression for ΔAEm calculated to third order [Eq. (20)], all of the coefficients can be evaluated from data on the subsidiary binaries. In the expression for ΔAEm calculated to fourth order [Eq. (33)], one can show that the only term which cannot be evaluated from data on the binaries is probably negligible. Thus the theory permits the calculation of properties of ternaries solely from a knowledge of properties of binaries.
Apparent oscillator strengths for molecular oxygen derived from electron energy-loss measurements
Authors: Huebner Russell H. , Celotta R. J. , Mielczarek S. R. , Kuyatt C. E.
Published: February 2003

Oscillator strengths for O2 from 6 to 14 eV are derived from the energy-loss spectrum of 100 eV incident electrons. Integrated f values for the Schumann–Runge bands and continuum, which span four orders of magnitude in intensity, agree well with high-resolution photoabsorption measurements. Vibrational structure superimposed on the Schumann–Runge continuum, previously assigned to the (3sσg)  3Πg Rydberg state, contributes less than 0.5% to the total oscillator strength determined for that region. These data also yield f values for discrete bands in the region between 9.5 and 14.0 eV, where line saturation problems complicate oscillator strength analysis of the optical data. An oscillator strength sum of 0.198 is obtained for all transitions below the ionization potential at 12.07 eV.
Relative cross sections in electroionization
Authors: Marmet Paul
Published: February 2003

Electron impact ionization efficiency curves showing vibrational states of NO+ and O+2 are presented just above their ionization threshold. These results and other recent ones prove that the competition between different cross sections must be taken into account in order to explain a good many electron impact data.
On the theory of the relaxation matrix and its application to microwave transient phenomena
Authors: Liu Wing-Ki , Marcus R. A.
Published: February 2003

The phenomenological relaxation times T1 and T2 measured in microwave transient experiments are expressed in terms of specific molecular relaxation matrix elements. Conditions for this simple T1, T2 description are also given. The system is described in terms of a kinetic equation for the density matrix, which provides a unified treatment of the microwave transient behavior, spectral line shapes, and double resonance phenomena. Spatial degeneracy of the states and m dependence of T1 and T2 are discussed in detail. The recently developed semiclassical theory of molecular collisions is then applied to obtain expressions for the relevant relaxation times.
Theory of the relaxation matrix and its relation to microwave transient phenomena. II. Semiclassical calculations for systems of OCS and nonpolar collision partners
Authors: Liu Wing-Ki , Marcus R. A.
Published: February 2003

Cross sections corresponding to relaxation times T1 and T2 measured in microwave transient experiments are calculated for systems of OCS and nonpolar collision partners, employing the recently developed semiclassical theory of molecular collisions. Cases in the presence and absence of static Stark field are described. The over-all agreement with existing experimental results is encouraging. Similarities and differences between T1/T2 values in microwave transient experiments and in molecular beam maser experiments are discussed, together with a role of semiclassical collisional selection rules.
Effect of molecular angular momentum on the thermal conductivity of a multicomponent gas mixture
Authors: Biolsi Louis , Mason E. A.
Published: February 2003

The effects of molecular angular momentum (spin polarization) on the thermal conductivity of a multicomponent gas mixture are considered. The Wang Chang–Uhlenbeck approach to the kinetic theory of gases with internal states is used. Formal results are obtained for the thermal conductivity of a gas mixture of uniform composition. These results are given in terms of the quantum mechanical degeneracy-averaged cross section.
The Compton profile of water: Computed from an SCF–MO wavefunction in a double-zeta Gaussian basis set
Authors: Snyder Lawrence C. , Weber Thomas A.
Published: February 2003

The Compton profile of water has been computed by the Dirac transformation of an SCF–MO position-space wavefunction in a double-zeta quality Gaussian basis set. This theoretical Compton profile agrees with the experimental one of Reed and Eisenberger within their estimated experimental error.
Conjugated electron contributions to the second order hyperpolarizability of substituted benzene molecules
Authors: Levine B. F.
Published: February 2003

We present a simple theory which accounts for the magnitude and absolute sign of the second order hyperpolarizability β for substituted benzene molecules in terms of the substituent produced π-electron spectral shifts.