bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the fishery in river communities in the low‐Solimões/high‐Amazon region
Authors: BATISTA V. S. , INHAMUNS A. J. , FREITAS C. E. C. , FREIRE‐BRASIL D.
Published: February 2003

Questionnaires were used to collect data from the low‐Solimões/high‐Amazon region, Brazil, between December 1992 and February 1994. Gillnets, fishing rods and castnets were the preferred gear used. Gillnets were used throughout the year whilst other gears were used only in certain periods of the year. The fish caught tended to supply family needs but a high proportion were sold in regional markets. Curimatã (Prochilodus nigricans), pacu (various Myleinae) and ruelo (young Colossoma macropomum) were the most frequent species caught. Around 50% of the fish caught in these fisheries was consumed fresh, and the remainder was stored under ice or salted. Fish is the most important source of animal protein for this region, with an annual mean consumption rate of 550 g capita−1 day−1. The fishery has changed from a subsistence to a commercial scale, which was associated with increasing cattle ranching activities. This may have serious social and economic implications.
Probing the binding site of 800‐nm bacteriochlorophyll in the membrane‐linked LH2 protein of Rhodobacter capsulatus by local unfolding and chemical modification
Authors: Buche A. , Ellis G. , Ramirez J. M.
Published: February 2003

The aim of this study was to investigate the function of βHis20 in the spectral behavior of the 800‐nm bacteriochlorophyll (Bchl) of the Rhodobacter capsulatus LH2 protein. In this context, the 800‐nm Bchl of the membrane‐linked LH2 was used as an intrinsic probe to follow the reversible, denaturant‐elicited unfolding of the neighboring protein region. This band was reversibly shifted to ≈ 770 nm by acidic pH, suggesting that the environment of the pigment, responsible for its native red shift, was significantly disturbed by the protonation of a chemical group. The reversible acid‐induced blue shift was only observed in the presence of unfolding agents (urea and guanidinium chloride). Thus, dismantling of the protein structure facilitated exposure of the basic group to the medium. The acid–base titrations of the spectral shift indicated an apparent pK ≈ 6.1, a value consistent with His imidazole being the protonatable group responsible for the acid‐induced band shift. The pK values of free N‐terminal amino groups are higher and not expected to be lowered by their local environment in the unfolded state of the protein. A similar blue shift of the 800‐nm Bchl band was caused by the modifier diethyl pyrocarbonate, which is known to carboxylate the imidazole group of His and free amino groups. It is also shown that the Fourier transform Raman spectrum of diethyl pyrocarbonate‐treated LH2 preparations lacks the weak mode at 1695 cm−1, suggesting that it should be assigned to the B800 Bchl.
The Sendai virus membrane fusion mechanism studied using image correlation spectroscopy
Authors: Rocheleau Jonathan V. , Petersen Nils O.
Published: February 2003

The mechanism of Sendai virus membrane fusion to cultured cell membranes was studied. Viral lipids were labeled with the lipophilic dye, 4‐(4‐(dihexadecylamino)styryl‐N‐methylquinolinium iodine) (DiQ), and viral proteins were labeled using fluorescein isothiocyanate (FITC). The redistribution of these probes from the virus to cultured cells was followed using the technique of image correlation spectroscopy. This technique assayed the intensity change and the redistribution of these probes as fusion progressed from a more to less aggregated state. The lipid probe DiQ dispersed into the membrane of the target membrane at both 22 and 37 °C, while the FITC‐labeled proteins dispersed only at 37 °C. Simultaneous labeling of virus with both of these probes showed that at 37 °C their redistribution proceeded at different rates. These data were consistent with the formation of a hemifusion intermediate during the fusion process.
Born–Oppenheimer type wavefunctions and the virial theorem for H2+ and D2+
Authors: Eaves John O. , Epstein Saul T.
Published: February 2003

Numerical calculations are presented which confirm earlier order of magnitude estimates of the extent to which the virial theorem is not satisfied by Born−Oppenheimer type wavefunction.
Collinear quantum mechanical treatment of the heavy−light−heavy mass combination: Cl+HBr→HCl+Br
Authors: Baer Michael
Published: February 2003

Quantum mechanical calculations were performed on the Cl+HBr collinear system. An LEPS potential surface with Sato coefficients was used in the calculations. (AIP)
Hot band and isotopic structure in the resonance Raman spectrum of bromine vapor
Authors: Baierl P. , Kiefer W.
Published: February 2003

The fine structure of the fundamental region of the bromine resonance Raman spectrum is presented. It is analyzed in terms of isotopic splitting of the species 79Br2, 79Br 81Br, and 81Br2. (AIP)
In–out decomposition for inelastic collisions as subdynamics. III. Perturbation theory and the semiclassical limit
Authors: Shipsey Edward J.
Published: February 2003

A new representation for the subdynamics is given such that the resultant coupling matrix becomes identical with the semiclassical expression away from turning points. A perturbation theory is developed which also reduces to semiclassical theory away from the turning points. The subdynamic perturbation expression is therefore capable of making up for the deficiencies of the semiclassical theory at the turning points. A numerical illustration is given.
Deuterium spin–lattice relaxation in ferroelectric triglycine sulfate
Authors: Stepi?nik J. , Slak J.
Published: February 2003

The ND3 deuteron spin−lattice relaxation time has been studied near the ferroelectric phase transition in single crystal triglycine sulfate. The results confirm proton−discorder motion in the hydrogen bond between glycine II and glycine III ions but they cast doubt upon the hypothesis concerning critical flipping of the glycinium I ion. Evidence is presented indicating faster hindered rotation of the glycinium I ND3 group compared to that of such groups at the other glycine ions.
ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H
Authors: Kim J. K. , Theard L. P. , Huntress W. T.
Published: February 2003

Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H2 by CH+, CH2+, CH4+, N+, NH+, NH2+, NH3+, O+, OH+, H2O+, CO+, N2+, C2+, and C2H+ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O+, CO+, and N2+, a large fraction of collisions between these ions and H2 are not reactive. The rate constants measured range from a low of (3±1) × 10−13 cm3/sec for the NH3+−H2 reaction to (1.73±0.04) × 10−9 cm3/sec for the N2+−H2 reaction. These values compare to the Langevin value of about 1.5 × 10−9 cm3/sec for collisions between these ions and H2. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H2 (CH5+, CH3+, NH4+, H3O+, H2S+, H3S+). The only exchange reaction observed was for collisions between CD3+ ions and H2, for which a rate constant of (5.1±0.5) × 10−10 cm3/sec was measured.
Study of electric field gradient parameters and quadrupole splitting of rozenit
Authors: Garg V. K. , Liu Y. S.
Published: February 2003

Low symmetry effects of the Fe2+ ion sites in FeSO4⋅4H2O (rozenit) on the electronic level splitting and the electric field gradient have been considered. Direct lattice sum calculations were performed to obtain the EFG and the multipole moments due to charges associated with all lattice points. The calculated temperature dependence of quadrupole splitting is in good agreement with the experimental values taken from 77 to 300°K. The direction of the maximum field gradient at various temperature is calculated to be nearly in the crystallographic axis b. The ground orbital state is a mixture from the first excited state.
Far infrared collision-induced spectrum in gaseous methane. I. Band shape and temperature dependence
Authors: Birnbaum George
Published: February 2003

The far infrared collision−induced spectrum in CH4 is observed in the region 20−600 cm−1 at temperatures between 163 and 296 K. These results are compared with a synthetic spectrum computed from the theory of Ozier and Fox giving the integrated intensity of the absorption resulting from rotational transitions of the octupole−induced dipole in colliding pairs of molecules. Although such a calculated spectrum accounts for the gross features of the experimental bands, they predict too little absorption in the low and high parts of the band.
g tensor of triplet benzophenone
Authors: Sharnoff Mark , Iturbe Elsa B.
Published: February 2003

Optically detected high field EPR measurements are reported on pure orthorhombic single crystals of normal and deuterium−enriched benzophenone. The results are used to obtain the molecular and excitonic spin Hamiltonians, and these are examined in turn to derive information concerning spin−orbit coupling matrix elements between the metastable triplet state and other levels. It is found that the metastable triplet interacts about as strongly with the nσ* configuration as with the ππ* configuration, suggesting that each of the spin sublevel energies of 3ππ* is affected about as strongly by spin−orbit coupling as by direct magnetic dipolar interaction. It does not seem possible, however, to reconcile the g tensors with semiempirical LCAO MO theory based on SCF calculations for the normal state. The molecular g values are gx = 1.9990±0.0006, gy = 1.9994±0.0006, and gz = 2.0097±0.0006. The principal z axis coincides with the direction of the carbonyl bond, while the x and y axes make angles of 60°±2° and 30°±2° respectively, with the plane of the carbonyl group. The principal values of the molecular fine−structure tensor are X = −2137.3±0.3 MHz, Y = −896.3±0.5 MHz, and Z = +3033.7±1.0 MHz. The principal z axis of this tensor also coincides with the carbonyl bond, but its remaining principal axes are rotated by about 10° from the x and y axes of the g tensor. The direction of rotation is such as to diminish the inclination of the yz plane to the plane of the carbonyl group. The principal axes of tensors characterizing the triplet excitons coincide with the crystralline a, b, and c axes. The principal g values are ga = 2.0002±0.0003, gb = 2.0085±0.0003, and gc = 2.0013±0.0003, while the corresponding fine−structure principal values are A = −819.4±0.4 MHz, B = +2639.9±0.2 MHz, and C = −1820.1±0.4 MHz. It is demonstrated that the excitonic spin Hamitonian is consistent with the average of the magnetically inequivalent molecular Hamiltonians.
A quantum ergodic theory approach to unimolecular fragmentation
Authors: Nordholm Sture , Rice Stuart A.
Published: February 2003

Projection operator techniques are used to separate the complete Hilbert space of a molecular system into parts corresponding to bound and continuum states. The equation of motion of the amplitude associated with an initial excitation of the molecule is then formulated; this equation of motion contains memory effects. Although formally exact, its utility lies in the approximations suggested by its structure. Drawing on recent studies of intramolecular relaxation, a Markovian approximation is formulated and the properties of the model so defined investigated by numerical solution. The decay rate for the model is found to depend strongly upon the nature of the initial excitation, and to correlate with the ergodicity or lack of ergodicity of the initial excitation. When the prepared state is nonergodic, or nearly so, there is a delay in the decay of the molecule. When the state initially prepared is ergodic, there is no such delay. Intermediate cases are also found. It is argued that the formal analysis permits the development of better models and of more sophisticated treatments of the competition between intramolecular relaxation and molecular fragmentation, but that the simple model discussed contains the qualitative elements of importance in such processes.
Zero field splitting of the triplet state of porphyrins. II
Authors: Langhoff Stephen R. , Davidson Ernest R. , Gouterman Martin , Leenstra Willem R. , Kwiram Alvin L.
Published: February 2003

The zero field splitting (zfs) for porphyrin is calculated for possible transitions b2u(π), a1u(π), a2u(π) → eg(π*). Calculations are done with pi−electron orbital coefficients determined from extended Hückel calculations on the deprotonated dianion, the free base, and the acid dication. The spin dipole−dipole couplings are evaluated exactly using a Gaussian−lobe expansion. The calculations are compared to the reported zfs of zinc and free base porphin and to the zfs reported herein of Zn etioporphyrin in various lattice sites in an octane matrix and of Zn tetraphenylporphin. The calculations fit experimental D and E values within 10% under the following assumptions: (i) For Zn etioporphyrin and Zn porphin the triplet state is 3[a1u(π) → eg(π*)], but for Zn tetraphenylporphin it is 3[a2u(π) → eg(π*)]; (ii) the larger value for D observed in free base porphin is due to configuration interaction between these two transitions; (iii) variable axis directions set up by the lattice crystal field cause the variation in E value observed for Zn porphin and Zn etioporphyrin in the various lattice sites.
Electrical conductivity in biological semiconductors
Authors: Kaplan T. A. , Mahanti S. D.
Published: February 2003

We propose and study a simple quantum−mechanical model Hamiltonian which describes the physical picture of the ’’conformon’’ recently discussed by Kemeny and Goklany. We find an activation entropy which is consistent with the proper Arrhenius behavior only in certain temperature ranges; this entropy may also give the enormous enhancement observed in the prefactor of the conductivity. Our model leads naturally to a possibitlity for overcoming the expected decrease in mobility due to the very mechanism (large conformational change) for obtaining the large entropic enhancement. Namely, the conformational change may be associated with localized holes, whereas an appreciable mobility may result from electrons which are rather delocalized. A simple mechanism leading to compensation is also briefly discussed.
Thermodynamic properties of NpO(g)
Authors: Ackermann R. J. , Rauh E. G.
Published: February 2003

The thermodynamic properties of NpO(g) were determined by mass−spectrometric studies of two isomolecular exchange reactions of the type M(g) + M′O(g) = M′ (g) + MO(g) involving the gaseous atoms and monoxides of lanthanum and yttrium. In one series of determinations, both reactions were studied simultaneously. The standard free energy of formation of NpO(g) is given by ΔGf° (NpO,g) = −12890 −13.73T (cal mol−1) over the temperature range 1660−1980 K. An uncertainty of ±1 kcal mol−1 is estimated. The derived thermodynamic properties of NpO(g) suggest the existence of low−lying electronic states in the gaseous molecule. The total volatility of neptunium−bearing species over the univariant system, NpO2(s) + Np(l) + vapor, was measured by the mass−effusion method, and the partial pressures of NpO(g) obtained therefrom were used to confirm the accuracy of the isomolecular results and to derive the standard free energy of formation of NpO2(s): ΔGf° (NpO2,s) ? −256000 + 40.4 T (cal mol−1).
A
b i
n
i
t
i
o study of the electronic structure and hyperfine coupling properties in simple hydrocarbon radicals. II. Short-range and long-range interactions in alkyl free radicals
Authors: Ellinger Y. , Subra R. , Levy B. , Millie P. , Berthier G.
Published: February 2003

Nonempirical calculations of the ground−state energy, proton and carbon−13 coupling constants of methyl, ethyl, n−propyl, and cyclopropyl radicals have been performed in the frame of spin−restricted LCAO−SCF open−shell and first−order double−perturbation theories. The rotation barrier is negligible for the ethyl radical. The two barriers of the n−propyl radical are, respectively, 0.3 kcal/mole (0.4 exptl) and 4.7 kcal/mole for the rotations about the Ċ−Cα and Cα−Cβ bonds. The cyclopropyl radical is found to be nonplanar with an out−of−plane angle of 41° and an inversion barrier of 3.80 kcal/mole. For the equilibrium conformations, the computed carbon−13 splittings of the radical carbon of methyl (1), ethyl (2), n−propyl (3), and cyclopropyl (4) are +31.04, +37.90, +37.72, and +138.83 G, respectively; the theoretical α −carbon−13 splittings are −18.14 (2), −17.15 (3), and −8.35 G (4); the β −carbon−13 splitting is +11.8 G for the stable conformation of the n−propyl radical. The calculated coupling constants are negative for α hydrogens, namely −31.03 (1), −33.82 (2), −34.34 (3), and −9.20 G (4); they are found positive for β hydrogens, i.e., +16.8 (2), +23.58 (3), and 12.12 G (4); the γ couplings of the freely rotating hydrogens of the n−propyl radical are negative −0.21 G. The variation of these couplings with conformational and torsional effects has also been investigated. The radical carbon−13 splitting is quite insensitive to rotations of substituents but increases markedly with out−of−plane deviations at the radical site. The coupling constants of α nuclei aHα, aCα are also insensitive to conformational modifications. For β atoms, the contact hyperfine splittings are found to follow the relation aβ=B0+B2 cos2ϑ independently of the chemical nature of the nuclei, B0 being negative if vibronic effects are neglected. Long−range couplings in γ position are generally negative, except in the region depicted by the so−called W−plan arrangement. The role of delocalization and spin polarization is discussed for each kind of coupling. It is shown that intrabond excitations of the CH→CH* type dominate the spin polarization at the proton in all positions, while inner−shell excitations are found to be essential in the case of the radical carbon.
Brillouin, Rayleigh, and depolarized Rayleigh scattering studies of polypropylene glycol. I
Authors: Huang Y. Y. , Wang C. H.
Published: February 2003

A comprehensive light scattering study of an important polymer—polypropylene glycol, HO−[CH(CH3) −CH2O]n−H—having an average molecular weight of about 425 (PPG 425) was carried out. From the polarized spectra, the velocity and attenuation coefficient of the longitudinal hypersound as a function of temperature were determined. Measurements of the velocity and attenuation coefficient indicate the presence of molecular relaxations between 250−390°K. A maximum in the sound attenuation vs temperature curve was observed. The Landau−Placzek ratio over a wide range of temperatures was also measured and compared with the theory of Litovitz and co−workers on the relaxing molecular liquid over a wide temperature range. Depolarized scattering studies were also carried out. The molecular reorientation time and activation energy are determined from the spectral linewidth measurement as a function of temperature. Depolarization ratios (ρv and ρh) were determined. The Krishnan effect was observed at temperatures below 296°K.
Photochemical decomposition of sodium chlorate
Authors: Herley P. J. , Levy P. W.
Published: February 2003

The photolysis of powdered NaClO3 exposed to 254 nm light has been investigated using unirradiated crystals and material subjected to 60Co gamma−ray irradiation. Pressure versus time curves for all samples increase monotonically and eventually exhibit a constant rate of oxygen gas evolution. The curves appear to contain one saturating exponential component and one linear component. This final stage approximates a second order dependence on light intensity. This dependence can be attributed to the photolytic generation of additional decomposition sites. Gamma−ray irradiation increases the variation from the observed almost second order dependence, decreases the magnitude of the exponential component, and decreases the time required to reach the final stage and the steady state rate. Irradiation also produces color centers and a shift in the apparent optical absorption edge. These observations are consistent with a previously developed phenomenological theory.
Primary radiation damage in thymidine
Authors: Box Harold C. , Budzinski Edwin E.
Published: February 2003

Several primary radiation products produced by ionizing radiation in the nucleoside thymidine have been stabilized at 4.2°K; two have been identified by ESR−ENDOR spectroscopy. One of these products is formed by reduction of the thymine ring. The other product results from the loss of a hydrogen atom from the 5′−hydroxy group.
Magnetic and thermodynamic properties of Mn(NH4)2(SO4)2⋅6H2O below 1°K and at fields up to 24000 G parallel to the b axis
Authors: Fritz J. J. , Clark J. T. , Cesarano J.
Published: February 2003

The heat capacity of Mn(NH4)2(SO4)2⋅6H2O has been measured directly in fields of 0, 1400, 2800, 6800, 12600, 16800, and 22300 G, from 0.4 to 1°K, along with observation of magnetization both isothermally and isentropically. Temperatures, entropies, and heat capacities have been derived for the region between 0.1 and 0.4°K, where direct measurements were not possible. Deviations from ideal behavior have been interpreted in terms of nuclear spin polarization of 55Mn and of (electronic spin) exchange.
Calculation of vibronic structure of the π→π* transition of t
r
a
n
s- and c
i
s-stilbene
Authors: Warshel A.
Published: February 2003

The calculations of the vibronic structure of the first singlet π→π* transition of cis− and trans−stilbene are presented as a step in the detailed study of photoisomerization reactions. In order to obtain the vibronic transition intensities we calculate the equilibrium geometries and vibrational modes of the ground and excited electronic surfaces. The calculated vibronic transition intensities of trans−stilbene are in good agreement with the observed ones. The calculated torsional contributions enable us to assign some of the lines in the spectrum of trans−stilbene and suggest the possibility of deviations from planarity in the ground state equilibrium conformation. The observed diffuse structure of the π→π* transition of cis−stilbene is reproduced and the contributions to photoisomerization of torsional and out−of−plane modes are considered.
Dielectric second virial coefficient of polar gases and their binary mixtures
Authors: Datta K. K. , Seal Parag , Barua A. K.
Published: February 2003

An attempt has been made to interpret the second dielectric virial coefficient of (CH3)2O and the interaction virial coefficient of the polar gas mixtures CHF3+(CH3)2O by using the series expansion method of Buckingham and Pople. For the pure component (CH3)2O the agreement between experimental and calculated values of Bε is fairly satisfactory as had been previously obtained for CHF3. For the mixture, reasonably good agreement between experimental and calculated values of Bε12 has been obtained only by varying the force parameters widely from their respective combination rule values. The calculation of energy of pairing shows that hydrogen bonding probably plays a very important role in this system, in agreement with the suggestion of Barnes and Sutton.
Microwave spectrum of propionic acid. I. Spectrum, dipole moment, barrier to internal rotation, and low-frequency vibrations of c
i
s-propionic acid
Authors: Stiefvater Otto L.
Published: February 2003

From its rotation spectrum propionic acid (CH3CH2COOH) is shown to exist predominantly in a cis−conformation in which the methyl group eclipses the carbonyl bond and with the hydroxyl hydrogen between the two oxygen atoms. The dipole moment of this rotamer is μ = 1.55±0.03 D (μa = 0.19 D, μb = 1.54 D). From the variation of its components under isotopic substitution the dipole moment deviates by (5.3±1.5) ° from the C = O bond toward the hydroxyl group. The barrier hindering internal rotation of the methyl group has been determined for four isotopic forms with the result V3 = 2340±30 cal/mole for CH3CH2COOH and CH3CH2COOD and V3 = 2370±30 cal/mole for CH3CD2COOH and CH3CD2COOD. Satellite spectra from 24 different vibrational levels have been analyzed by double resonance techniques. The five lowest vibrational modes of cis−propionic acid have been assigned: C−C torsion at 64±3 cm −1, CH3 internal rotation at 190.4 cm−1, CCC deformation at 270±15 cm−1, with tentative vibrational assignments of δ (CCO) at 530±30 cm−1, τ (OH) at 547±20 cm−1.
Test of Born approximation on the 60 eV autoionized transition in helium
Authors: Dillon Michael A. , Lassettre Edwin N.
Published: February 2003

The 60.3 eV autoionization transition of helium has been studied by electron spectroscopy. The discrepancy between experiment and a theory based on the Born approximation greatly exceeds experimental error. (AIP)
A systematic and graphical method for generating the kinetic equations governing the growth of aggregates
Authors: Perelson Alan S. , DeLisi Charles
Published: February 2003

We present a systematic method for deriving differential equations which govern the kinetics of formation of large aggregates from two types of multifunctional monomers. The problem of formulating the dynamic equations is complicated by the fact that there can be an arbitrarily large number of different species, each of different composition and with different numbers of reactive sites. It is shown that aggregates can easily be represented by graphs. Graphical methods are then used to simplify a number of counting problems and to derive two parameters which totally describe the reactive state of an aggregate. All possible reactions between aggregates are tabulated in terms of these parameters and the kinetic equations describing the aggregation phenomena are systematically derived.
Effective potential study of the rotational excitation of HD by collision with H2
Authors: Chu Shih-I
Published: February 2003

The effective potential formalism of Rabitz is extended to a general potential expressed in terms of relative or body-fixed coordinates and applied to the study of the H2–HD rotationally inelastic collisions. The H2 and HD molecules are treated as rigid rotors and their interaction potential is derived from the H2–H2 potential. Long-range quadrupole–dipole and quadrupole–quadrupole interactions are also considered. Quantum-mechanical close-coupling calculations for three-dimensional collisions of para-H2 and ortho-H2 with HD are performed up to E=0.20 eV. The general features of the rotational excitation cross sections of HD are examined and their sensitivity to certain aspects of the potential are analyzed. In particular, the different roles of the short- and long-range anisotropies are illustrated. It is found that the degree of anisotropy is meaningful only in relation to the magnitude of the ’’effectively’’ spherically symmetric part of potential. The rate constants for pure rotational transitions of HD are presented in the temperature range of 5 to 800 °K. The relation of these results to the quantitative interpretation of the thermal balance of interstellar clouds is pointed out. We have also calculated the rotational relaxation times for the lowest two levels of HD, which could be examined and compared with future sound absorption experiments to assess the accuracy of the H2–HD interaction potential.
Rate constants for the reactions of O2+(a 4Πu) ions with N2, Ar, CO, CO2,H2, and O2 at relative kinetic energies 0.04–2 eV
Authors: Lindinger W. , Albritton D. L. , McFarland M. , Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: February 2003

Rate constants for the reaction of O+2(a 4Πu) metastable ions with N2, Ar, CO, CO2, H2, and O2, which do not react with O+2(X 2Πg, v=0) ground-state ions, have been measured for the relative kinetic energies 0.04–2 eV in a flow-drift tube. With the exception of O2 and CO, most of the rate constants are near the respective Langevin limits. The rate constant for the reaction with CO exhibits a pronounced minimum at 0.3 eV; the other reactions show much less variation with energy. Up to 2 eV, quenching of the a 4Πu metastable state to the X 2Πg ground state of O+2 appears to be small compared to the reactive losses of O+2(a 4Πu) ions. The reactive process is charge transfer, except for CO and H2. For CO, CO+ and CO+2 are formed roughly in the ratio 5:1 and for H2, only O2H+ is formed.
Analysis of the ground term energy levels for triply ionized neodymium in yttrium orthovanadate
Authors: Karayianis N. , Morrison C. A. , Wortman D. E.
Published: February 2003

An investigation has been made of the 4I ground term of Nd3+ in YVO4. Wavelength and polarization measurements of the absorptions in the wavelength range 0.8–2.6 μm were used to establish energy levels for the 4F3/2, 4I9/2, 4I13/2, and 4I15/2 multiplets. These data were correlated with reported spectra in the literature, and an energy level scheme was obtained that identifies 25 out of the possible 26 ground term levels. By diagonalizing the Hamiltonian H = 𝒥 λn (L⋅S)n + 𝒥 B+km Ckm in an LS basis and performing a least squares calculation, an rms deviation between calculated and experimental energy levels of 4.01 cm−1 was obtained. The parameter values giving this fit are λ1=293.74, λ2=−2.454, λ3=0.0389, B20=−135.7, B40=625.9, B60=−1169.5, B44=1023.9, and B64=−251.4 cm−1. Theoretical values of g∥ = −0.915 and g⊥ = 2.379 are in good agreement with Ranon’s reported values of g∥ = ±0.915 and g⊥ = 2.348 for the ground state; thus the ground state symmetry property was determined to be Γ7,8 in S4 notation or Γ7 in D2d.
Dispersion energies in systems of two closed shell atoms and/or ions
Authors: Winslow George H.
Published: February 2003

A semiempirical device for the calculation of the coefficients in the dispersion energy expansion for interaction between two closed shell atoms or ions is described. Summation is over all electrons. Averages of powers of electron radial coordinates are calculated with Slater-type functions. Effective quantum numbers and screening constants were determined so as to reproduce a set of like-atom rare gas dipole–dipole coefficients. These are used to extend the calculations to coefficients for unlike rare gas and ion–ion interactions, to higher multipole coefficients for those interactions, and to polarizabilities and diamagnetic susceptibilities. The effective one level energies, numbers of polarizable electrons, and accuracy of combination rules, all as determined by these calculations, are examined. Since the principal interest here is extension to ionic crystals, discussion of a questionable lattice sum for dipole–dipole interactions is appended.
Collision integrals for soft, nonspherical molecules in terms of spherical Ω* integrals
Authors: Verlin Jerome D. , Matzen M. Keith , Hoffman D. K.
Published: February 2003

A new formulation of the classical kinetic theory of dilute gases composed of molecules with rotational structure is given which closely parallels that for structureless molecules. The matrix elements of the collision operator are expressed as integral moments of a generalized collision cross section 𝒥. It is shown that a suitable approximation for the momentum dependence of 𝒥 leads to expressions for the matrix elements which can be written in terms of the familiar spherical Ω* integrals.
Temperature dependence of thermal diffusion in CO isotopic gas mixtures
Authors: Verlin Jerome D. , Matzen M. Keith , Hoffman D. K.
Published: February 2003

The temperature dependence of thermal diffusion in several different isotopic gas mixtures of CO is investigated theoretically and the results are compared with experiment. The temperature range includes the inversion temperatures for all mixtures. Thermal conductivity and diffusion coefficients are also calculated. The basis of the study is a previously presented theory which provides expressions for classical collision integrals for molecules with rotational structure in terms of spherical Ω* integrals.
Study of the low-temperature ’’transition’’ in ice Ih by thermally stimulated depolarization measurements
Authors: Johari G. P. , Jones S. J.
Published: February 2003

Thermally stimulated depolarization (TSD) current has been measured in polycrystalline H2O and D2O ice in the temperature range 77–260 K and at pressures of about 1 bar and 1.2 kbar. Three peaks in current have been observed at about 1 bar at a heating rate of 0.0023 K sec−1, the smallest of which appears at 110.4 K and 123.8 K in H2O and D2O ice, respectively. An increase in heating rate shifts the current peaks to higher temperatures, as does an increase in pressure. From an analysis of the current–temperature plots, the dielectric permittivity and the relaxation times have been obtained. It is shown that the current peak occurring at the lowest temperature is due to the relaxation of frozen-in orientation polarization of water molecules in ice and does not indicate a thermodynamic transformation to a ferroelectric phase. The equilibrium dielectric permittivity of H2O ice has been measured in the range 98–119 K by charging the ice for many days and then obtaining the stored charge by TSD technique. The equilibrium dielectric permittivity shows no approach to a ferroelectric ordering at 98 K. The heterocharge in an ice electret of ∼ 105 C V−1⋅F−1 is largely due to the polarization which gives rise to the high-temperature TSD current peaks. Aging reduces the magnitude of this polarization substantially. The mechanism of this polarization is not clear. The homocharge was seen in one sample of ice as a negative depolarization current. It is proposed that the TSD technique should be useful for the detection of very slow phase transformation in dipolar materials.
Configuration interaction studies of O3 and O+3. Ground and excited states
Authors: Hay P. Jeffrey , Dunning Thom. H. , Goddard William A.
Published: February 2003

We report the results of extensive configuration interaction calculations (double ζ basis) on the ground and 15 excited states of ozone and the eight lowest states of the ozone positive ion. The studies on ozone are carried out as a function of both bond length and bond angle. We find that three excited states of ozone may be bound with respect to the ground states of O2 and O. Additional information is provided on the ring state (60 ° bond angle) previously reported. Two of the excited states of ozone are known spectroscopically and the ionization potentials of the first three states of O+3 are now known experimentally. These experimental results are in good agreement with the theoretical calculations.
Ionization in the track of a high-energy electron in hydrocarbon liquids; study of positive and negative ion scavenging using nanosecond pulse radiolysis
Authors: Zador Erika , Warman John M. , Hummel Andries
Published: February 2003

The lifetime distribution of the charged particles in the track of a high-energy electron in cyclohexane and isooctane has been considered. Results on the decay of biphenyl ions in solutions of biphenyl obtained by means of pulse radiolysis with nanosecond time resolution have been compared with lifetime distributions calculated from the concentration dependence of the steady state scavenging, using recently determined absolute rate constants for reaction of excess electrons and mobilities of the charged species. The discrepancy is relatively small for cyclohexane but large for isooctane. It is concluded that the scavengers considerably affect the initial spatial distribution of the charged species in the track. The kinetics of the reaction of the positive species in cyclohexane and isooctane with biphenyl, TMPD, and pyrene has been considered. It has been concluded that the mobile positive species in cyclohexane reacts with pyrene with a rate constant of 5×1011 mol−1⋅s−1, and has a lifetime of 50 ns. In isooctane no evidence for the existence of a mobile positive species has been obtained.
Low resolution microwave spectroscopy. I. The structural significance of the band spacing
Authors: Farag Maya Swamy , Bohn Robert K.
Published: February 2003

Compounds which are nearly symmetric tops, have ∼20 mtorr vapor pressure and have a sizeable dipole moment along the a axis display band microwave rotational spectra under low resolution conditions. The frequencies of the band maxima are adequately represented by a symmetric rotor type equation, ν = (B + C)(J + 1). From calculated spectra it is shown that the B + C value defined above exceeds the ground state effective rotational constant B0 + C0. Low resolution B + C values and high resolution B0 + C0 values are compared for nineteen species. B + C differs from B0 + C0 by less than 2% in all cases and less than 0.8% for molecules with κ < −0.8. Empirically it is found that (B + C)/(B0 + C0) − 1 = ν/ν0 − 1 = 0.025(±0.005)(1 + κ), where k is the asymmetry parameter and ν0 is the hypothetical symmetric rotor frequency, (B0 + C0)(J + 1). This empirical relation allows B0 + C0 to be estimated from B + C with an uncertainty of only a few tenths of a percent.
Low resolution microwave spectroscopy. II. The conformation of 2,2,2-trifluoroethyl vinyl ether
Authors: True Nancy S. , Bohn Robert K.
Published: February 2003

The low resolution microwave spectrum of gaseous 2,2,2-trifluoroethyl vinyl ether displays an intense series of a-type bands and a weak b-type series which identify the species to have an s-cis-planar configuration, τ (C=C–O–C) = 0° and τ (C–O–C–CF3) = 180° [Fig. 1(b)]. This confirms the determination by Charles, Cullen, and Owen based on infrared evidence and analogy to unsubstituted ethyl vinyl ether. No other species is observed which excludes any significant population of an s-trans-planar species, τ (C=C–O–C) = 180° and τ (C–O–C–CF3) = 180° [Fig. 1(d)]. Any other species significantly present in the vapor would have to be relatively nonpolar, i.e., have τ (C–O–C–CF3) < 90°.
Theoretical model for fluorescence in gases subject to continuous infrared excitation
Authors: Parenti R. R. , Whitney J. F. , Artman J. O.
Published: February 2003

The emission from gaseous molecular systems subject to continuous excitation in the infrared has been modeled on a computer. The effects of collisionally induced transitions are specifically included through adaptation of an existing analysis by Rapp. In its present form, the computer program is capable of determining the fluorescence of a single polyatomic gas as well as simulating quenching by a noble gas. Potentially, the program is capable of handling as many constituents, energy levels, and laser ’’pumps’’ as desired. Computations for a 20 level system require about one minute of computer time on a Univac 1108. Specific results are given for excitation at 10 W/cm2 by a CO2 laser for ozone, ammonia, and ethylene, each at 10 Torr and also for ethylene quenched by argon. We conclude that (1) the occurrence of fluorescence at frequencies above the laser frequency is a natural consequence of the collisional energy transfer mechanism, (2) states separated by small differences in energy or by small quantum number intervals are stongly coupled by collisions, (3) fluorescence from certain levels associated with strong absorption peaks is predicted to be weak, and (4) true laser-induced fluorescence is weak compared to simple thermal emission from the laser-heated gas.
NMR study of CuAl2: 27Al, 63Cu, and 65Cu quadrupole and anisotropic shift interactions
Authors: Torgeson D. R. , Barnes R. G.
Published: February 2003

The nuclear magnetic resonance spectra of 27Al, 63Cu, and 65Cu have been studied in a polycrystalline specimen of the intermetallic compound CuAl2 of the C16 structure type at room temperature between 3 and 40 MHz. The 27Al spectra yield to interpretation in terms of a completely anisotropic Knight shift and an asymmetric nuclear electric quadrupole interaction. The observed field separations of the several 27Al quadrupole satellite spectral features at fixed frequencies yield values of the lowest quadrupole frequency νQ = 420.2(8) kHz and asymmetry parameter η = 0.413(9). The 27Al satellite features also yield the three Knight shift parameters Kx = 0.159(1) %, Ky = 0.153(2) %, and Kz = 0.148(10) %. Excellent agreement has also been obtained between observed 27Al central line shape and the theoretical shapes of J. F. Baugher, H. M. Kriz, P. C. Taylor, and P. J. Bray, J. Magn. Reson. 3, 415 (l970). The 63Cu and 65Cu central lines exhibit a strong second and a fourth order quadrupole splitting with νQ(63Cu) = 7.54(17) MHz and νQ(65Cu) = 7.05(18) MHz. An analysis of the copper Knight shift is also presented.
A flasch photolysis–resonance fluorescence study of the formation of O(1D) in the photolysis of water and the reaction of O(1D) with H2, Ar, and He −
Authors: Stief Louis J. , Payne Walter A. , Klemm R. Bruce
Published: February 2003

The relative importance of two primary processes in the photolysis of water, H2O+hν → H+OH d in Processes I and II, respectively. The initially formed O(1D) was deactivated to ground state O(3P) prior to detection via resonance fluorescence. The relative quantum yields for Porcesses I and II are 0.89 and 0.11 for the wavelength interval 105–145 nm and ?0.99 and ?0.01 for the wavelength interval 145–185 nm. Rate constants at 300 °K have been determined relative to that for Reaction (1), O(1D)+O2 → O(3P)+O2 decrease in O signal as a function of H2, Ar, or He pressure for the following reactions: O(1D)+H2 → H+OH % (2), O(1D)+Ar → O(3P)+Ar e−1⋅s−1, we obtain the following results: %k2 = (2.5±1.5) ×10−10, k3 = (8±4) ×10−13, and k4 < 5×10−14 cm3 molecule−1⋅s−1.
Relaxation in the 1A
u state of glyoxal. I. Collision-free lifetimes of single vibrational levels
Authors: Beyer R. A. , Zittel P. F. , Lineberger W. C.
Published: February 2003

Collision free lifetimes are reported for 26 single vibrational levels of the 1Au state of glyoxal (CHOCOH). A nitrogen laser-pumped tunable dye laser is used to excite primarily single vibronic levels of glyoxal in the pressure range 10−5–10−1 Torr. The resulting fluorescence can either be spectrally resolved to provide single vibronic level observation or the entire 1Au emission can be detected. The fluorescence is time-resolved with 100 nsec resolution, and two or more decades of decay are typically observed. A detailed discussion of the apparatus and techniques is presented. Evidence is presented for very rapid rotation and vibration collisional energy transfer, and implications of these effects on extrapolated zero-pressure lifetimes are discussed. By observing an entire vibronic band, effects of rapid rotational redistribution on observed loss rates can be minimized, and thus by varying the total glyoxal pressure, one can determine single vibronic level loss rate constants. Such data are presented for 26 vibronic levels, with cross sections which range from gas kinetic to seven times faster than gas kinetic. These collisional loss rate constants are dominated by vibrational relaxation; an observable but less important loss channel is collision induced intersystem crossing. Implications of these data are discussed.
Relaxation in the 1A
u state of glyoxal. II. Collisional quenching
Authors: Beyer R. A. , Lineberger W. C.
Published: February 2003

Cross sections are reported for collisional quenching of low-lying levels of the 1Au state of glyoxal by 24 collision partners at 297 °K. The quenching cross sections varied from 1 to 22 Å2 with polar collision partners exhibiting the larger cross sections. The quenching rate constants were determined by measuring the time-resolved decay of laser-excited glyoxal, as a function of quench gas pressure. Studies of 3Au state production for five of these gases indicate that the principal collisional loss channel from the 1Au state is to the 3Au state. The derived quenching cross sections are well parameterized by several differing quenching models, not all of which should be valid in this case; such correlations have predictive value, but cannot be taken to verify the quenching model.
Huggins coefficient for the viscosity of polymer solutions
Authors: Freed Karl F. , Edwards S. F.
Published: February 2003

A theory of the Huggins coefficient for the viscosity of polymer solutions (under Θ conditions) is presented that is free of improper integrals. The theory is explicitly applied to the Gaussian chain model and yields the value πζ (2)/[ζ (3/2)]2 = 0.757, where ζ is the Riemann zeta function.
Experimental evidence for the rough hard sphere model of liquids by high pressure NMR
Authors: DeZwaan J. , Jonas J.
Published: February 2003

The NMR 19F spin–lattice relaxation times, self-diffusion constants, and densities have been measured in liquid CCl3F as a function of temperature and pressure. Since spin–rotation interactions provide the dominant relaxation mechanism for fluorine nucleus, the analysis of the T1 data yields the angular momentum correlation time τJ. The density dependence for the spin–rotation relaxation data enables us to calculate the effective hard sphere diameter for liquid CFCl3. In turn these diameters are used in calculation of the self-diffusion constants applying the rough hard sphere model for molecular liquids as recently proposed by Chandler. Our experimental results provide evidence for (i) relationship between τJ and the Enskog relaxation time τE; (ii) validity of the rough hard sphere model for fluids; and (iii) the dependence of diffusion constants upon density in agreement with molecular dynamics calculations by Alder et al.
Magnetothermodynamics of gadolinium gallium garnet. III. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K, with fields to 90 kG along the [110] axis
Authors: Brodale G. E. , Hornung E. W. , Fisher R. A. , Giauque W. F.
Published: February 2003

The magnetic moment of a 2.44 cm diam spherical single crystal of gadolinium gallium garnet has been measured with stabilized fields of 500, 1000, 2500, 5000, 10 000, 12 500, 15 000, 20 000, 25 000, 40 000, 65 000, and 90 000 G along the [110] crystal axis, over the range 0.5 to 4.2 °K. The magnetic moment reached saturation at 90 kG and 0.35 °K. The heat capacity was measured over the 0.5–4.2 °K temperature range and the above fields except that 500 and 1000 G were omitted and zero field included. The zero of electronic and lattice entropy was located at 90 kG and magnetic saturation. Temperatures were measured versus field on 36 adiabatics, corrected with respect to entropy. These provided multiple intersections with the isoerstedic heat capacity curves, so that the entropy could be evaluated over the entire temperature and field ranges of the investigation. The saturation moment was found to be M[110] = 38 963 G⋅cm3/mole Gd3+, equivalent to g[110] = 1.993. This may be compared with the previous similar measurements M[100] = 39 059 and M[111] = 38 979 G⋅cm3/mole Gd3+, corresponding to g[100] = 1.998 and g[111] = 1.994. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its differential isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization, have been tabulated over the ranges 0–90 kG and 0.5–4.2 °K.
129I Mössbauer studies of iodine in the +1 and +3 oxidation states
Authors: Jones C. H. W.
Published: February 2003

The 129I Mössbauer spectra of I(pyridine)2ClO4 and -NO3, I(thiourea)2I, I(acetate)3, a possible phosphate derivative II-phosphate, and I2O4 are reported. Comparisons of the results of these experiments with those of previous workers raise questions concerning the use of simple models in interpreting 129I Mössbauer data.