bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of inverted populations in chemical lasers by temperaturelike distributions: Gain characteristics in the F + H2 → HF + H system
Authors: Ben-Shaul A. , Hofacker G. L. , Kompa K. L.
Published: February 2004

With the aid of the temperature parameters characterizing product state distributions in a number of chemical reactions, frequently used concepts in chemical laser studies can be expressed in a compact form. The assumption of a rotational-translational microcanonical equilibrium in the product atom-diatom system leads to simple expressions for population inversions and gain factors. (However, the equilibrium assumption is not necessary; the expressions will retain their simple form also when the vib-rotational distributions are more specific.) The main advantage is that of using only one or two parameters instead of different vibrational and rotational temperatures for every transition. Two special situations are considered in detail: (a) a nonrelaxed initial product population and (b) a vibrationally nonrelaxed but rotationally thermal population. As a specific example, the HF laser with F + H2 → HF + H as the pumping reaction is studied. Rate equations governing the emission of different laser transitions are solved. In the solution, cascading and pumping effects are considered but not rotational or vibrational relaxation. The detailed rate constants of HF formation in different vib-rotational levels used in the calculation are those which lead to equipartition (microcanonical equilibrium) of rotational and translational energies. Comparison with experimental results indicates that the model calculations are in agreement with some chemical laser and trajectory studies which show initial population peaked at some high rotational states. The chemiluminescence measurements for low reagents energies show relatively lower peaks.
Ring-puckering vibration of μ-aminodiborane
Authors: Gaylord A. S. , Pringle W. C.
Published: February 2004

The ring-puckering vibrations of μ-aminodiborane and ND2–B2H5, NH2–B2D5, and ND2–B2D5 have been investigated. The 0 → 1 transitions are assigned to the Q branches at the frequencies 337.6, 333.6, 244.6, and 243 cm−1, respectively. The potential function for this vibration is V(Z) = 8.695 × 105Z4 + 6.859 × 104Z2 (cm−1), where Z is the displacement coordinate in angstroms. Inclusion of terms in the kinetic energy to account for the dependence of the reduced mass on coordinate suggests that the vibration involves equal bending about the diagonals in the ring-hydrogen analogs and bending about the B-B diagonal in ring-deuterium molecules. The concept of torsional-strain energy in ring molecules is introduced.
Absorption of ultrasound in liquid NH3 and ND3
Authors: Bowen D. E.
Published: February 2004

Data on the absorption of ultrasound in liquid NH3 and ND3 as a function of frequency and temperature are presented. These data indicate that the absorption is both frequency and temperature independent for frequencies above 30 MHz at a value two times the classical value. There is a relaxation occurring at the lower frequencies indicated by an increase in the absorption coefficient as the frequency is lowered. This is interpreted to be a thermal relaxation and not a structural relaxation, which is what might be expected for an associated liquid such as NH3.
Quantum mechanical first Born binary encounter theory of electron impact ionization. II Electron Compton scattering
Authors: Bonham R. A. , Tavard C.
Published: February 2004

The first Born binary encounter theory of electron Compton scattering is developed. The theory includes the relationship between the usual x-ray Compton profile and its electron scattering counterpart including corrections for scattering from pairs of target electrons (a correction also necessary in the x-ray case at small scattering angles) and for exchange and interference scattering. In addition correction terms are derived for the difference between the complete first Born treatment and the binary encounter model. The corrections in the angular range of 10°–60° at an incident electron energy of 25 keV are shown to be negligible. The target electron pair corrections at an incident electron energy of 25 keV are important only for small angle scattering for the lighter elements (< 7° for He) but may extend to larger angles for the heavier elements (< 30° for Ar). Exchange and interference between exchange and direct scattering become significant at the 1% accuracy level at a scattering angle of 4° at the same incident energy. Between 4° and 45° interference between the exchange and direct amplitude dominates the correction term which can amount to 25% of the direct scattering contribution at 35° although it largely vanishes at 45°. Beyond 45° the pure exchange terms rapidly dominate the scattering with increasing angle, and relativistic corrections become increasingly important. In this region the theory can break down and it is suggested that accurate experimental data could be helpful in arriving at a detailed description of the exchange process. A definition for an electron Compton profile including exchange and interference corrections from which the one-electron target momentum density can be extracted is suggested. The theory is also compared with recent experimental work for the case of He, and predictions for the scattered electron intensity as a function of energy loss and scattering angle are made for He at an incident electron energy of 25 keV.
Cluster expansions for hydrogen-bonded fluids. I. Molecular association in dilute gases
Authors: Andersen Hans C.
Published: February 2004

The cluster expansion method of Mayer is formulated in a way that is convenient for calculating the equilibrium pair correlation function of hydrogen-bonded fluids. The topological properties of cluster diagrams for these fluids is investigated, and a cancellation theorem is presented which permits the neglect of certain types of diagrams in these cluster expansions. A method is presented for renormalizing the hydrogen bond in such expansions, and a technique for summing the graphs which define the renormalized hydrogen bond is discussed. The present paper deals only with low density gases, and future work will extend the results to dense liquids.
Cluster beams of hydrogen and nitrogen analyzed by time-of-flight mass spectrometry
Authors: Gspann J. , Körting K.
Published: February 2004

Hydrogen and nitrogen clusters originating from condensing supersonic nozzle flows are studied by a special version of time-of-flight mass spectrometry. The molecular weights of the clusters to be investigated range from 103 to more than 106 and are determined from the change of the cluster speed which is effected by a longitudinal electric field after ionization of the clusters by electron impact. Clusters with up to four positive charges can be distinguished, and the probability for multiple ionization as a function of the electron energy is given for hydrogen clusters containing 6.5 × 104 molecules and for nitrogen clusters containing 1.2 × 104 molecules. Formation of singly charged negative cluster ions of both gases is observed for the first time and becomes more probable with increasing cluster size. While neither fragmentation nor evaporation as a result of the ionization process is observed, beams containing two fractions of masses prior to ionization are found at certain conditions of the cluster beam generation. Except for such cases, the distribution of sizes of singly charged clusters can be derived if the measured narrow speed distribution of the cluster beam is assumed to be valid also for each separate cluster size.
NMR of alternate linear chains of inequivalent nuclei coupled by indirect exchange interaction. II. Computation for a finite chain
Authors: Ayant Y. , Belorizky E. , Casalegno R. , Gagnaire D. , Taieb M.
Published: February 2004

The NMR spectrum of a linear chain containing two types of spin 1/2 nuclei, with slightly different chemical shifts 2δ, and coupled by a scalar exchange interaction J between nearest neighbors is studied theoretically. Expressions for the first ten moments of the spectrum are given. Spectra for a cyclic chain limited to eight spins are computed and the results are compared with those of a previous Green's function theory of the line shape giving an approximately Lorentzian shape in the weak field region. The case where J = δ, for which the line is almost Gaussian, is also analyzed.
Nuclear magnetic relaxation in molten salts. I. Spin-lattice relaxation time of 23Na in molten sodium nitrate
Authors: Harold-Smith Duane
Published: February 2004

The spin-lattice relaxation time (T1) of 23Na in molten sodium nitrate has been measured at 8.0 and 22.3 MHz from the melting point (309°C) to 600°C using a pulse spectrometer. T1 was found to be independent of frequency over this range and equal to about 50 × 10−3 sec. 1/T1 was a linear function of 1/D (where D is the rate of diffusion of Na+); but 1/T1 did not go to zero when 1/D was extrapolated to zero, as predicted by the Bloembergen-Pound-Purcell model. All of these observations can be explained assuming the quasilattice random flight (QLRF) model and a quadrupolar relaxation mechanism. Relaxation by dipole-dipole interactions and by paramagnetic impurities are both shown to be completely negligible. The correlation time τc is obtained from the temperature dependence of 1/T1 and found to agree with the value obtained from compressibility and thermal expansitivity data. The electric field gradient at the Na+ nucleus is also calculated from the relaxation time and shown to be in excellent agreement with the value estimated from the radial distribution function of the melt. Upper and lower limits are given for the lifetime of the diffusing species, NaNO3.
Singlet-triplet energy differences calculated from generalized oscillator strengths
Authors: Lassettre Edwin N. , Dillon Michael A.
Published: February 2004

Using a one-electron model, the difference in energy, ES — ET, between a singlet state (obtained by exciting one electron from a nondegenerate closed-shell ground state) and the corresponding triplet is shown to be (in atomic units) equal to (π gW)−1 ∫000K2f dK where f is the generalized oscillator strength for excitation to the singlet state, W is the excitation energy, g is the degeneracy of the excited singlet state, and K is the change in wave vector on collision. This relationship is tested for several states in helium and carbon monoxide for which both ES — ET and f are known. Calculated and observed values of ES — ET differ, on the average, by about 15%, the discrepancy being due no doubt to the one-electron approximation. Where high accuracy is not required (and singlet-triplet energy differences are difficult to obtain in other ways) the method may be of value since the position of the triplet is obtained from experimental measurements performed exclusively on the singlet excitation at high kinetic energies.
Photolysis of nitrogen dioxide
Authors: Jones I. T. N. , Bayes Kyle D.
Published: February 2004

Relative quantum yields for the photolysis of NO2 to give NO have been measured at 5 or 10 nm intervals in the range of 295 to 445 nm, and also at several longer wavelengths. The behavior of the quantum yield as a function of photon energy can be separated into three distinct wavelength regions. At all wavelengths shorter than 398 nm the quantum yield is almost constant and independent of NO2 pressure in the range 0.5–4 torr. Hence, by comparison with previous work, the photodissociation probability of NO2 remains close to unity for photolysis by all wavelengths shorter than the dissociation limit at 398 nm. At wavelengths longer than 430 nm, there is a small quantum yield for NO formation which decreases slowly with increasing wavelength. Quenching studies and variations in light intensity show that these small yields are caused by reaction of an electronically excited NO2 molecule with ground state NO2. In the wavelength region between 400 and 430 nm, the quantum yield falls abruptly. Isotopic exchange experiments involving oxygen-18 confirm that free oxygen atoms are produced in this region, even though the energy of the photolyzing quantum is less than the NO2 dissociation energy. Recent fluorescence yield measurements quantitatively complement the present photodissociation quantum yields. A previously suggested model, in which the ground state rotational energy of NO2 supplements the photon energy, gives only fair agreement with the experimental quantum yields. A slight reduction in the accepted value for the dissociation energy of NO2 would improve the agreement between theory and experiment, although differences would still remain.
Comparative SCF and CI studies of NH3 and PH3
Authors: Petke J. D. , Whitten J. L.
Published: February 2004

A comparative study of geometry, bonding, and physical properties of NH3 and PH3 utilizing both SCF and CI techniques is presented. One-electron physical properties of both molecules are examined for several basis sets; properties calculated for NH3 are in good agreement with experimental values, while for PH3 only fair agreement is obtained. In PH3 phosphorus d orbitals are found to contribute directly to sigma bonding. In NH3, however, nitrogen d orbitals produce an angular effect which tends to reduce the calculated HNH internuclear angle to a value significantly closer to the experimental angle than is predicted in computations where d orbitals are not employed. Configuration interaction does little to improve the agreement of calculated properties with experimental values, but does lower the total energy significantly. Factors influencing the difference in geometry of the two molecules are discussed.
Polarized-orbital valence-bond calculations on the ground state properties of H5+
Authors: Salmon W. I. , Poshusta R. D.
Published: February 2004

Ab initio calculations were made on H5+ in order to predict its equilibrium geometry, binding energy, vibrational frequencies, and enthalpy of formation. The method was based on a valence-bond configuration interaction wavefunction built from linear combinations of Gaussian basis orbitals and polarized by Sambe's method. Optimization of nonlinear parameters was handled by a conjugate directions procedure derived from Powell's and Zangwill's work. H5+ was found to have a C2ν geometry in agreement with Esterfield and Linnett and with Huang, Schwartz, and Pfeiffer. The binding energy was estimated to be approximately De = 0.1 eV and the enthalpy of formation from H3+ and H2 to be about ΔH = − 3.3 kcal/mole, which is the same order of magnitude as experimental measurements. The importance of doubly occupied structures and of polarization was assessed from our wavefunctions.
Group theory for matrix isolated molecules in static crystal fields
Authors: Miller Ralph E. , Decius J. C.
Published: February 2004

The group theory is solved for molecules of any symmetry matrix isolated at a site in a crystal field of any symmetry. As the potential barrier to rotation of the molecule relative to the host crystal is raised, certain symmetry operations become decreasingly ``feasible'' in the sense of Longuet-Higgins. Using correlation methods the symmetry species of the rotational states are determined from the free rotation limit to any of the librational limits. Examples of linear, symmetric, and spherical rotors are given. From the symmetry of states and the dipole and polarizability tensors, selection rules are applied to predict spectra in the infrared and Raman effect.
Atomic Z expansions and electronic structure of molecules. II. The limits of the molecular one-center scheme
Authors: Horák Zdeněk J. , Šišková Jaroslava
Published: February 2004

The first-order variational principle for energy is used to determine the effective charge and position of the virtual hydrogenlike atom imitating the ground states of the H2+ and HeH2+ ions. In this way the ordinary one-center scheme, placing in H2+ the virtual atom halfway between the two protons, is justified only for internuclear distances ρ smaller than a certain critical distance ρc(H2+) = 1.2633259 bohr. With increasing ρ the variational principle places the virtual center closer and closer to one of the protons, which necessarily leads to the two-center approach, if symmetry requirement is obeyed; in HeH2+, however, the two-center approach would introduce an overcomplete set for any ρ. According to the variational principle the virtual and the real nucleus have to coincide in the ``off-center hydrogen,'' which provides exact energy of this system. For the hydrogen molecule in the ground state, the critical internuclear distance is ρc(H2) = 1.7358046 bohr, which justifies earlier one-center calculations done near the equilibrium distance ρe = 1.4 < ρc(H2). With the virtual hydrogenlike atom treated as an unperturbed system, the corresponding perturbation scheme is carried to second order of energy, generalizing the formulas of Hauk et al and Levine. As a result, the variable location of the virtual center improves convergence of the perturbation expansion.
Electron spin resonance study of liquids during photolysis. XVI. Kinetics of radicals showing emission from tartaric acid
Authors: Livingston Ralph , Zeldes Henry
Published: February 2004

Several free radicals are formed during continuous photolysis of aqueous solutions of tartaric acid, one of which is HOOCCH(OH)CH(OH), radical A. This radical has eight hyperfine lines which are in emission in concentrated solutions of tartaric acid where the radical lifetime is short and which appear in absorption in dilute solutions where the lifetime is longer. The photolytic light source was interrupted with a rotating sector in order to study kinetic behavior. When the light is turned on, radical A always gives a transient signal in the direction of emission before steady state is achieved. There is also a transient when the light is turned off. This behavior has been studied in several concentrations of tartaric acid, a phenomenological theory developed for the shape of the curves, the chemical lifetime of the radical evaluated, and the thermal relaxation time measured. The electron spin states are polarized at the time the radical is formed, and the degree of polarization is − 0.142 (difference of populations of spin states divided by the sum) as compared to 0.00076 for thermal equilibrium. The lifetime of radical A is limited by its transformation to HOOCCHCHO, radical C, by an acid catalyzed rearrangement. Kinetic data on radical C show a large inductive effect due to consecutive, slow chemical reactions. When oxalic acid is added to the system there is electron transfer from various radicals in solution to the oxalic acid giving a reduced form of oxalic acid, radical D. Although this radical always appears in absorption at steady state, the sector results show initial polarization in the emissive direction before steady state is reached. The polarization of A transfers to the oxalic acid in forming radical D.
Configuration interaction calculation of elastic electron-atom scattering phase shifts: Application to e-He scattering
Authors: Murtaugh Terence S. , Reinhardt William P.
Published: February 2004

The problem of electron-atom scattering is discussed using a Fredholm approach and a method developed for calculating the partial-wave Fredholm determinant using only square integrable basis functions and standard bound-state configuration interaction techniques. Problems arising due to wavefunction antisymmetry and use of inexact target states are discussed. S-wave elastic e-He phase shifts are computed as an example of the method.
Electron transfer band in the chlorine K-x-ray absorption spectra of some transition metal chlorides
Authors: Sugiura Chikara
Published: February 2004

The chlorine K absorption spectra of PdCl2, CdCl2, and FeCl3 have been obtained with a 50-cm bent-quartz-crystal vacuum spectrograph. A prominent absorption maximum has been detected at the threshold and is interpreted in terms of the electron transfer model. Results are evaluated by comparing the obtained spectra with the chlorine K absorption spectra of the first-transition metal dichlorides reported previously. Chemical shifts are found for the first absorption band and discussed in relation to the ionization potentials of the metal ions and the lattice energy. The chlorine K absorption spectra of the chlorides are discussed in relation to the crystal structure.
Variation-perturbation treatment of the molecular interaction energy in H2+
Authors: Nee Tsun-Shi , Parr Robert G. , Chang S. Y.
Published: February 2004

A new variation-perturbation method is developed to treat the interatomic interactions in one-electron diatomic molecules at all distances. For a diatomic molecule with nuclear charges Za and Zb a variable charge-shifting perturbation is defined as (Zb − ζ)/ra − Zb/rb, where ra and rb are the distances from the electron to the two nuclei. The adjustable parameter ζ, when determined variationally, leads to a small perturbation at all distances. Limiting cases are ζ = 0 and ζ = Zb at zero and infinite separations, respectively. The method is tested by calculations of the ground-state energy of the hydrogen molecular ion, for which the first-order wavefunction is obtained in closed form. Following the procedure of Chang [J. Chem. Phys. 59, 1790 (1973)], both one- and two-center calculations are performed. The results compare favorably with the exact values and converge correctly to the appropriate united- and separated-atom limits. The largest deviation occurs near the equilibrium distance, where the relative error of energy, in the case of two-center treatment, is 0.6%. Several other variational calculations are reported using various united- and separated-atom functions as the basis set. Extension of the perturbation method to HeH+ is briefly discussed.
Mechanism of thermal energy gas phase charge exchange reaction: He+· + N2
Authors: Kemper Paul R. , Bowers Michael T.
Published: February 2004

Thermal energy charge transfer between He+· and N2 has been investigated using ion cyclotron resonance (ICR) spectroscopy. The N+/N2+· ratio has been measured as a function of total pressure, reaction time, He+· kinetic energy, and He/N2 mixing ratio. The strong dependence of the N+/N2+· ratio on the above parameters indicates the majority of the initially formed (N2+·)* ions from the charge transfer reaction must have lifetimes at least 10−4−10−3 sec. A complete reevaluation of the mechanism for the reaction is required to explain these surprising results. A new mechanism is proposed that is consistent with all known existing thermal energy experimental work and with the latest theoretical calculations.
Infrared band contours and potential functions for the perpendicular vibrations of CF3Cl, CF3Br, and CF3I
Authors: Hoskins L. C. , Lee C. J.
Published: February 2004

The infrared band contours of the perpendicular vibrations of CF3Cl, CF3Br, and CF3I were measured in the infrared spectra, and the Coriolis constants for these vibrations were evaluated by a computer-simulation procedure that calculates the band shape as a function of the molecular parameters. The Coriolis constant for the ν5 band of CF3Br was evaluated by an analysis of the partially resolved Q branches in the high-resolution spectrum. With the vibrational frequencies and Coriolis constants as input data, the E -species force constants of the general harmonic potential function were evaluated. Two different force fields were found for each molecule that exactly fit the experimental data.
Vibrational relaxation of carbon monoxide using a pulsed discharge
Authors: Powell H. T.
Published: February 2004

A cw probe laser is used to monitor the time-dependent gain on vibrational transitions of CO following a short-pulse transverse discharge in a cell at room temperature. The initial vibrational distribution of excited CO produced by the discharge is measured, and the subsequent relaxation, producing gain on some bands, is used to determine vibrational transfer rates for the relaxation processes CO(ν) + CO(ν = 0) → CO(ν − 1) + CO(ν = 1), 2 ≤ ν ≤ 15.
Internal vibrational modes and hydrogen bonding in mixed crystals of HCN and DCN
Authors: Friedrich H. B. , Krause P. F.
Published: February 2004

Infrared spectra of the internal modes of mixed crystals of HCN and DCN have been studied as a function of composition. The variation of the normal mode frequencies as the composition changes cannot be explained by dipolar coupling alone, but long range coupling constants were required to enable a normal mode calculation to fit the observed spectra. The absolute absorption intensities of the internal modes were found to be independent of composition. The dramatic changes in the infrared intensities of the internal stretching modes which occur upon condensation are ascribed to a charge transfer mechanism which is characteristic for hydrogen-bonded systems.
Raman spectra of gases. VIII. Ring puckering in diborane
Authors: Carreira L. A. , Odom J. D. , Durig J. R.
Published: February 2004

The Raman spectra of gaseous 11B2H6, 10B2H6, and B2D6 have been recorded from 0–3000 cm−1. The ν = 0 → 2, ν = 1 → 3, and ν = 2 → 4 ring puckering transitions have been observed for the 11B2H6 isotopic species at 753.7, 776.1, and 795.6 cm−1, respectively. The ν = 0 → 2 ring puckering transitions of the 10B2H6 and B2D6 species have been observed at 756.6 and 531.0 cm−1, respectively. The least squares fit of these data yields the ring puckering potential function V(X) = 6.50 × 105X4 + 7.30 × 104X2. The intensity of the Δν = 2 ring puckering transitions is shown to be due to electrical anharmonicity rather than mechanical anharmonicity or Fermi resonance. The observed gerade fundamentals are found to agree reasonably well with those found earlier from Raman investigations of the liquids.
Nuclear resonance and magnetic susceptibility study of platinum-Group IVa compounds
Authors: Weaver H. T. , Quinn Rod K. , Baughman R. J. , Knauer R. C.
Published: February 2004

Low temperature nuclear magnetic resonance measurements of the Knight shift and spin-lattice relaxation time (T1) have been made for 195Pt, 29Si, and 119Sn in the compounds PtSi, PtGe, PtSn, Pt2Si, and Pt2Ge. Bulk susceptibilities of these compounds were measured in the 4–300 °K temperature range. In all cases the 195Pt Knight shift was found to be positive and the bulk susceptibility negative, although d -electron effects were evident. Both 29Si and 119Sn exhibited metallic behavior in that the Knight shifts were moderate in size and T1T = constant. Analysis of the data suggests that Si and Sn contribute conduction electron states in number at least equal to the Pt states.
Propagation of electromagnetic waves in anisotropic crystals: A simple model for the angular dependence of exciton energies
Authors: Fulton Robert L.
Published: February 2004

The effects of the long range dipole-dipole interactions on the current-current correlation functions of anisotropic crystals are evaluated for a simple model of an anisotropic crystal. We show that the resulting angular dependence of exciton energies in anisotropic crystals agrees with that given by Fox and Yatsiv and is necessary for the validity of the constitutive relations commonly used with the Maxwell equations. As a consequence, excitons are implicit in the Fresnel equations of classical optics.
Polyene spectroscopy: The lowest energy excited singlet state of diphenyloctatetraene and other linear polyenes
Authors: Hudson Bruce S. , Kohler Bryan E.
Published: February 2004

Optical absorption and emission spectra at liquid helium temperatures of solutions of all-trans-1,8-diphenyloctatetraene in single crystals of bibenzyl and polycrystalline n-paraffin matrixes are presented which show an excited singlet state at a lower energy than the 1Bu state responsible for the strong absorption of all linear polyenes. The transition from the ground state to this level has an oscillator strength of about 0.05. The location of this low energy weak transition removes a number of discrepancies between the expected and observed fluorescence properties of diphenyloctatetraene. The observed vibronic pattern is consistent with the Raman spectrum which is also reported. Substantial indirect evidence is presented which indicates that many, and perhaps all, linear polyenes have a similar ordering of excited states. A review of the available information on diphenylpolyenes is presented. A correlation of the oscillator strength of the fluorescence transition as deduced from the emission lifetime with the separation of the low energy excited states for a number of polyenes is noted. The implications for the photochemistry of linear polyenes including the visual chromophores are pointed out.
Clustering in supercooled water
Authors: Rasmussen D. H. , MacKenzie A. P.
Published: February 2004

The specific heats and densities of supercooled water and heavy water have been measured from the respective melting points to the respective homogeneous nucleation temperatures. The calorimetric measurements indicate structural contributions to the differences between the specific heats of the liquids and the corresponding crystals. These ``structural specific heats'' are exponential functions of the supercooling. The results are interpreted in terms of Frenkel's heterophase fluctuation theory. It is concluded that, during supercooling, water molecules tend to form icelike clusters incorporating six or more monomers.
Solvent reorganization around a ``giant dipole'' molecule
Authors: Struve W. S. , Rentzepis P. M. , Jortner Joshua
Published: February 2004

The fluorescence risetimes of the 1La and 1Lb excited states of p-dimethylaminobenzonitrile (DMAB) in ethanol and methylcyclohexane following irradiation at room temperature by the fourth harmonic (2650 Å) of a Nd3+ glass laser were measured directly using picosecond spectroscopy. The onset of 1Lb fluorescence, governed by prior vibronic relaxation in both polar and nonpolar solvents, occurs within 7–20 psec after the exciting pulse. The 1La fluorescence, characterized by a noticeably longer risetime of [inverted lazy s] 40 psec at room temperature, yields directly the solvent orientational relaxation time in the field of the 1La state's large dipole moment ([inverted lazy s] 23 D). This measured relaxation time is consistent with a modification of the Debye theory of viscosity-limited solvent reorganization.
Structure of the dimers of HCl and DCl trapped in monatomic matrix and near infrared absorption
Authors: Girardet C. , Robert D.
Published: February 2004

A detailed analysis of the various possible configurations of the two molecular axes of the HCl and DCl dimers trapped in a monatomic matrix is presented following the ranges of the intermolecular distance. The calculation of the intensity and frequency of the corresponding vibration-orientation absorption bands is performed. Particular attention is paid to the vibrational dependence of the molecular parameters in the solid medium. The consistency of the comparison with the experimental data for the various noble gas solid matrices and for different temperatures and concentrations confirms the interpretation of the spectra following the above analysis. Thus, the existence of intermediate stages called ``pseudodimers'' between the monomer and the dimer is demonstrated. For the ``dimers'', where the molecules are nearest neighbors, the nearly orthogonal configuration previously obtained by the present authors in an a priori calculation of the far infrared absorption is shown to be also suitable.
Photoelectron spectra from some autoionizing states of O2 near the ionization threshold
Authors: Tanaka Ken-ichiro , Tanaka Ikuzo
Published: February 2004

The photoionization efficiency curve of O2 and the vibrational distributions of photoelectrons from seven autoionizing states in the region of 0 ∼ 1.40 eV above threshold have been obtained. The apparatus used was composed of a vacuum ultraviolet monochromator, a quadrupole mass spectrometer, and a retarding-field electron-energy analyzer. The vibrational distributions of photoelectrons from autoionizing states were clearly different from those of calculated Franck-Condon factors for the direct ionizing transition. The classification of the autoionizing states in this region is incomplete as yet; thus, that of Price and Collins was employed in calculation of Franck-Condon factors for the autoionizing transitions. By comparison of the observations with the calculations the optimum values of internuclear spacing, re of the H, H′, and M progressions were determined to be 1.33 ± 0.01, 1.32 ± 0.01, and 1.28 ± 0.01 Å, respectively. The re value of the M progression significantly deviated from the calculated value using the empirical relation of renωe = const. This deviation and the results of more detailed comparison of the observations with the calculations presented the problem of the classification of the autoionizing states especially in the case of the M progression.
Mössbauer study of quinquevalent gold compounds
Authors: Kaindl G. , Leary K. , Bartlett Neil
Published: February 2004

The recently synthesized Au(V) complex fluorides of the form A+ AuF6− with A = Xe2F11+, XeF5+, and Cs+ have been studied by Mössbauer spectroscopy with the 77.3 keV gamma resonance of 197Au. The values obtained for isomer shift and electric quadrupole interaction are in harmony with the assigned oxidation state Au(V), as well as with the octahedral shape of the AuF6− anion.
Negative ENDOR study of an x-ray irradiated crystal of N-acetylglycine
Authors: Helms H. A. , Suzuki Ikuo , Miyagawa Ichiro
Published: February 2004

The negative ENDOR technique was used to study an x-ray irradiated crystal of N-acetylglycine at room temperature. Within the 8–25 MHz frequency range, signals from at least 13 different types of protons were detected. This is in sharp contrast to the case of a conventional ENDOR technique, which detected a signal from only one type, in addition to a broad signal which was difficult to interpret. It was shown that the proton from the ruptured C–H bond is trapped in the immediate vicinity of the damaged molecule. It was also shown that the wavefunction of the paramagnetic electron extends significantly over the neighboring molecules.
Assignment of ν2 (E) and ν4 (F2) of tetrahedral species by the calculation of the relative Raman intensities: The vibrational spectra of VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4
Authors: Weinstock N. , Schulze H. , Müller A.
Published: February 2004

A new method has been developed to assign the frequencies ν2(E) and ν4(F2) in tetrahedral molecules and ions. The method employs the calculation of the relative Raman intensities and has been applied to VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4. The assignment of the frequencies has been further confirmed by measuring the infrared and Raman spectra of some of the ions and molecules in the same solvent. A more complete spectrum of TcO4− than earlier reported in the literature has been given.
Anomalous isotope effect in the H bonds of acetic acid dimers
Authors: Bournay Jacques , Marechal Yves
Published: February 2004

Measurements of the integrated intensities of the νO–H ... O, νO–H, and νC=O bands of acetic acid CH3COOH in the vapor phase (where H-bonded dimers are in equilibrium with non H-bonded monomers), together with measurements of the intensities of the corresponding bands in CH3COOD, have been performed at various pressures and temperatures. It has been found that the transition probability P O–H ... O for the 0 → 1 transition of the stretching motion νO–H ... O of the H atoms in the H-bonds of (CH3COOH)2 was 2 times greater than the corresponding probability νO–D ... O in (CH3COOD)2. This value was determined with a precision better than 10%. The ratio PC=O ... H/PC=O ... D of the transition probabilities for the νC=O ... H and νC=O ... D modes in (CH3COOH)2 and (CH3COOD)2 was found to be equal to 1.25, with a precision better than 10%. The same ratios were found in CD3COOH and CD3COOD. These results are quite puzzling and have not yet been interpreted (by comparison, the ratio P O–H/P O–D of the transition probabilities for the free νO–H and νO–D modes in the monomers was found to be equal to 1.3). This ``anomalous'' ratio P O–H ... O/P O–D ... O seems hardly to be understandable on the basis of anharmonicity considerations alone, and it is suggested, after a critical examination of the possible origins of this effect, that the H bonds are not adiabatic. This would imply that the motion of the H atoms along the H bonds induces electronic transitions.
Lattice-dynamical calculations on some rigid organic molecules
Authors: Filippini Giuseppe , Gramaccioli Carlo M. , Simonetta Massimo , Suffritti Giuseppe B.
Published: February 2004

Several physical-chemical properties in crystals formed by ``rigid'' organic molecules have been calculated by means of different semiempirical atom-atom potential functions. For nine different substances, vibration frequencies, dispersion curves, and ``crystallographic'' temperature factors have been evaluated, and as an example the density of states for two of them are also reported. Experimental data are in excellent to fair agreement with results obtained by use of ``Williams IVa'' functions; some of these results can be advantageously used for libration correction of bond lengths that are determined by x-ray or neutron diffraction. Among the examined substances, some anomalies are found for pyrene crystals, which confirm in this case a rather unusual way of packing.
In-out decomposition for inelastic collisions as subdynamics
Authors: Shipsey Edward J.
Published: February 2004

A new in-out decoupling scheme is derived by means of a phase derivative matrix introduced into the adiabatic canonically transformed close coupled equations for inelastic scattering. The new decomposition is analyzed by means of a slight generalization of the subdynamics introduced by Prigogine and co-workers in nonequilibrium statistical mechanics.
The hydrated proton H+(H2O)n. III. A neutron diffraction study of deuterated paratoluene sulfonic acid monohydrate, D3O+CH3C6H4SO3−, and an analysis of the effect of deuteration on oxonium ion geometry
Authors: Finholt James E. , Williams Jack M.
Published: February 2004

Crystals of D3O+CH3C6H4SO3− (DPTSA) are isomorphous with those of H3O+CH3C6H4SO3− (PTSA), and the detailed molecular geometries of the two compounds are very similar. Deuteration causes an increase in the O–O distance in each of the three (H3O+ · · · 03S−) hydrogen bonds, ef. 2.529(8) (the numbers within parentheses here and throughout the paper are the estimated standard deviations in the least significant digits) to 2.537(4), 2.545(8) to 2.549(4), and 2.522(8) to 2.537(4) Å. The height of the oxonium ion pyramid increased from 0.322(4) to 0.334(3) Å, and the H–O–H bond angles decreased an average of 0.6° to 108.6(3), 110.3(4), and 110.2°(4)°, respectively. Deuteration does not change the average O–H distance in the oxonium ion. The individual changes are small enough to be of doubtful significance. A total of 1732 independent, three dimensional intensities were measured using a neutron wavelength of 1.142(1) Å. The crystals are monoclinic, space group P21/c, with unit cell dimensions a = 5.885(2), b = 7.461(3), c = 20.148(7) Å, and β = 97.89(1)°. The unit cell contains four molecules. The structure was refined by full-matrix least-squares procedures varying anisotropic thermal parameters for all atoms, an isotropic extinction correction factor, the scale factors (S), and the deuterium scattering amplitudes. The final deuterium scattering amplitudes indicated that the oxonium ion was 90% deuterated. It was also shown that only the oxonium ion hydrogen atoms were replaced by deuterium. Final values of 0.053 for R(FO2) and 1.24 for σ1, the ``goodness of fit'' parameter, were obtained.
Self-consistent extended Hückel theory. I
Authors: Kalman Barry L.
Published: February 2004

A self-consistent extended Hückel theory has been constructed. A new off-diagonal approximation is presented. Results from calculations using the consistent extended Hückel method compare favorably to extended Hückel, iterative extended Hückel, CNDO, nonempirical, and experimental results.
The Gerrine Water Striders of Australia (Hemiptera: Gerridae): Taxonomy, Distribution and Ecology
Authors: Andersen Nils Møller , Weir Tom A.
Published: February 2004

Water striders or pond skaters belonging to the subfamily Gerrinae are common inhabitants of various types of fresh water throughout eastern and northern Australia. The present paper deals with the 13 species (in 5 genera) known from Australia. Redescriptions or descriptive notes, illustrations, and keys to adults and nymphs of all species are provided and their distributions recorded and mapped.Tenagogerris pallidusand T. femoratus (both from Northern Territory and Western Australia), Tenagogonus australiensis (Queensland), Limnometra ciliodes (Queensland, Papua New Guinea and Irian Jaya), and Limnogonus fossarum gilguy (Northern Territory, Queensland, South Australia, Western Australia, Indo-Malayan Archipelago, and West Pacific to Samoa and Tonga) are described as new. Limnometra poliakanthinaNieser & Chen is synonymised with L. cursitans (Fabricius) and Hydrometra australis Skuse (= Limnometra skusei Torre-Bueno) with Limnogonus luctuosus (Montrouzier). The evolution and zoogeography of Australian water striders are discussed. Finally, we discuss the ecology of the gerrine water striders of Australia in relation to our present knowledge about habitats, phenology, wing polymorphism, and association between species.
Revision of the Australian Ameroseiidae (Acarina: Mesostigmata)
Authors: Halliday R. B.
Published: February 2004

The Australian fauna of Ameroseiidae (Acarina) is revised. Six genera and 11
species are recognised, including four new species:
Brontispalaelaps marianneae, sp. nov., from the wings of
a moth in Queensland, Epicriopsis walteri, sp. nov.,
from forest litter in New South Wales and Queensland,
Hattena floricola, sp. nov., from
Correa flowers in Victoria, and
Hattena incisa, sp. nov., from mangrove flowers in the
Northern Territory. A key to genera and species is provided.
Edbarellus Manson, 1974, is synonymised with
Hattena Domrow, 1963.
Above- and below-ground biomasses of two species of mangrove on the Hawkesbury River estuary, New South Wales
Authors: Saintilan Neil
Published: February 2004

Above- and below-ground biomasses of two species of mangrove, Avicennia marina and Aegiceras corniculatum, were estimated in a range of intertidal environments along the Hawkesbury River. Estimates of biomass of Avicennia communities in freshly accreted brackish substrata were in the order of 40 kg m–2, the highest figure ever recorded for temperate mangrove communities. The above-ground biomass communities of each species declined with increasing substratum salinity, whereas root/shoot ratios increased with increasing substratum salinity.
Reproductive cycle and size-dependent spawning of female spiny lobsters (Panulirus japonicus) off Oshima Island, Tokyo, Japan
Authors: Minagawa Megumi
Published: February 2004

Reproductive biology of the spiny lobster
Panulirus japonicus was histologically examined by
monthly sampling between March 1993 and September 1994 at Oshima Island, near
Tokyo. P. japonicus had a well defined reproductive
cycle. Yolk accumulation became manifest in February and ovaries grew rapidly
in March. Females spawned from late April to mid August and were ovigerous to
mid September. Of large females with a carapace length (CL) of ≥47 mm,
93% were estimated to spawn twice during the spawning season. Size at
which 50% of females reached sexual maturity was estimated to be 41.8
mm CL, as calculated from a logistic model. Some individuals considered to be
primiparous showed delayed vitellogenesis and were estimated to spawn only
once during the season.
Diet of the Feral Cat (Felis catus) in Central Australia
Authors: Paltridge Rachel , Gibson David , Edwards Glenn
Published: February 2004

Feral cats (Felis catus) occur throughout central Australia. In this study, we analysed the stomach contents of 390 feral cats collected between 1990 and 1994 from the southern half of the Northern Territory. Cats fed on a wide variety of invertebrates, reptiles, birds and mammals, including animals up to their own body mass in size. Mammals were the most important prey but reptiles were regularly eaten in summer and birds were important in winter. Invertebrates were present in the diet in all seasons. Carrion appeared in stomach samples during dry winters only and this has implications for future control of feral cats.
Evaluation of Iophenoxic Acid as a Biomarker for Swamp Wallabies (Wallabia bicolor)
Authors: Fisher P. M. , Marks C. A.
Published: February 2004

The potential of iophenoxic acid (IPA) as a systemic biomarker for use in feeding and diet studies of swamp wallabies (Wallabia bicolor) was investigated. Groups of captive wallabies were administered IPA doses of 0, 15 and 30 mg kg–1. Baseline concentrations of plasma iodine were compared with samples taken at 24 h, 48 h, 4 days, 6 days and 20 days after dosage. Plasma iodine in wallabies dosed with IPA was elevated by 70.43–331 times pre-dosage concentrations at 24 h and was not significantly different from pre-dosage concentrations in all wallabies by four days. The demonstrated short persistence of marking in swamp wallabies differs markedly from most studies of eutherian species and indicates that IPA is unsuitable for use as a biomarker for field-based studies of swamp wallabies.
Emergency room utilization in Copenhagen: a comparison of immigrant groups and Danish-born residents
Authors: Norredam Marie , Krasnik Allan , Sorensen Tine Moller , Keiding Niels , Michaelsen Jette Joost , Nielsen Anette Sonne
Published: February 2004

Background: The aim of the study was to investigate whether utilization of the emergency room differed between immigrant groups and Danish-born residents in Copenhagen, Denmark. Methods: The authors compared the number of emergency room contacts during 1997 among different ethnic groups in the study population. Data were provided by the Statistical Office of the Municipality of Copenhagen. The study population consisted of 183,478 citizens residing in the catchment area of Bispebjerg Hospital in Copenhagen on 1 January 1998. ``Contacts'' included 22,026 visits made to the emergency room at Bispebjerg Hospital during 1997. Both the study population and ``contacts'' were characterized by gender, age, income, and country of birth. The immigrants comprised nine ethnic groups according to country of birth. Data were analysed by Poisson regression comparing rate ratios. Results: Persons born in Somalia, Turkey, and ex-Yugoslavia had higher utilization rates of emergency room than Danish-born residents. All other non-Western-born residents had utilization rates similar to Danish-born residents. Persons born in other Western and European countries showed a tendency towards less utilization. Conclusion: Higher utilization rates among some immigrant groups may be explained by disparities in health or lack of knowledge about the Danish healthcare system as well as barriers to seeking primary care including language, fear of discrimination, and low satisfaction with primary care. The challenge remains to identify these causal relations, and to find out why utilization patterns vary between immigrant groups.