bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Quenching of OH(2Σ+) in Flames and Its Significance in the Interpretation of Rotational Relaxation
Authors: Carrington Tucker 
Published: January 2005

The quenching of fluorescence of electronically excited OH(2Σ+) molecules in the burnt gases above a lean acetylene-oxygen flame burning at a pressure of 3.5 mm Hg has been measured for resolved rotational lines. From these data the lifetime in this flame of the 2Σ+ state with respect to electronic quenching collisions is found to be 0.45×10—7 sec, about one-tenth of the radiative lifetime of the free molecule. Quenching measurements as a function of pressure and composition give cross sections for quenching by O2, CO2, and H2O of 7, 16, and 35 A2. These values exceed by a factor of 10 or more the cross sections to be expected for simple exchange of rotational with translational energy. For argon the quenching cross section is less than 2 A2.
The large cross sections for quenching by the flame gases, and the resultant short lifetime of electronically excited OH molecules in the flame mean that these molecules undergo a radiationless loss of electronic energy in collisions before they have time for either a radiative transition or a collision leading to simple rotational energy transfer. The rotational distribution in the electronic spectrum emitted by OH in flames is thus determined almost exclusively by collision processes involving transfer of electronic energy. Rotational temperatures derived from these distributions bear in general no direct relation to the translational or rotational temperatures which may be associated with the other species in the flame, and are determined principally by specific excitation processes.
Deuterium Isotope Effect in the Reaction of Hydrogen Molecules with Chlorine Atoms and the Potential Energy of the H2Cl Transition Complex
Authors: Bigeleisen Jacob , Klein Fritz S. , Weston Ralph E. , Wolfsberg Max 
Published: January 2005

The relative rates of reaction of H2 and HD with chlorine atoms have been measured over the temperature range of 243–350°K. In this temperature interval, the ratio of the second-order rate constants, R=kH2/ΣkHD,is equal to (1.24∓0.03) exp (490±6/RT). A search was made for HD after an unequilibrated mixture of H2 and D2 was half converted to hydrogen chloride by photochemical reaction with Cl2. From the failure to detect 0.02% HD in the unreacted hydrogen, a lower limit is set for the ratio of the rate constants of the reactions H+Cl2→ lim k16HCl+Cl and H+HCl→ lim k17H2+Cl.
It is shown that the pre-exponential factors in R for the HD experiments and in the analogous experiments on HT are in quantitative agreement with theoretical calculations for either linear or triangular transition states, subject to the sole restriction that k(HD+Cl→HCl+D) is approximately equal to k(HD+Cl→DCl+H). An intercomparison is made between the experimental difference in activation energies between H2, HD, HT, and D2 for reaction with chlorine atoms and theoretical calculations for linear and triangular transition states. With the most favorable potential function for H2Cl, the maximum deviation between ΔEexp‡ and ΔEtheor‡ is fifteen percent. Inasmuch as there are more experimental data than parameters necessary to construct the potential function of H2Cl, the agreement between theory and experiment constitutes a positive test of the transition state formulation of the effect of isotopic substitution on the rates of chemical reactions.
Kinetics of the Deposition and Dissolution of Silver
Authors: Despic A. R. , Bockris J. O'M. 
Published: January 2005

Galvanostatic measurements, made on spherical silver electrodes in highly purified aqueous acid solutions of silver perchlorate at current densities up to 10 amp cm—2, gave overpotential as a function of time and Faradaic current density at constant total current. Variables were total current density, concentration of silver ions and state of the electrode surface.
The theory of the surface diffusion kinetics was developed to encompass high current density regions and the surface adion concentration (cad0) evaluated.
A theoretical analysis of the steady state of surface diffusion control of the metal-ion exchange reaction shows that the current is distributed nonuniformly between growing sites, with constant potential over the electrode surface.
An equation previously developed by Rojter, Juza, and Polujan has been modified and shown to be applicable to galvanostatic transients when the transfer reaction is rate controlling. The symmetry factor β, of electrode kinetics, is shown to be potential dependent, and, in systems of sufficiently high i0 values, to tend to zero at high overpotential. This results in a limiting current density for a transfer controlled process. The tendency towards such a current was observed and shown to be quantitatively consistent with the discussion of β.
New Method for the Measurement of Microwave Integrated Line Intensities and Line Widths
Authors: Dymanus A. , Dijkerman H. A. , Zijderveld G. R. D. 
Published: January 2005

A method is described for the measurement of microwave line widths and integrated intensities with Stark-modulation spectrometers. The method makes use of a property that the peak intensity αmax,meas, measured at a given Stark field E, depends, under certain conditions, only on the half-width a and the peak intensity αmax. In the present investigation, the method has been used with a Stark cavity spectrometer employing ``antimodulation'' techniques which were described in an earlier paper. Experimental procedure, and the possibilities of the method are illustrated by measurements on two lines arising from the J=1→2 rotational transition of the 16O12C32S molecule in the ground state, and in the excited bending-vibrational state (l-doublet). The measured integrated intensity of the ground-state line of (103±3.5)10—5 cm—1 sec—1 at 1 mm Hg agrees well with the theoretical value of 101.5·10—5 cm—1 sec—1. The half-width constant of the ground-state line and of the l-doublet line was found to be 6.27±0.18 and 6.17±0.23 Mc/mm Hg, respectively. From the measurements on the various mixtures of OCS and N2, a value of 4.36±0.12 Mc/mm Hg has been obtained for the collision broadening factor for OCS molecules with N2 molecules.
The present method is applicable to sharp (also weak) lines of which the Stark splitting pattern is quantitatively known.
Mechanics of Atomic Recombination Reactions
Authors: Bunker Don L. 
Published: January 2005

A treatment is developed by means of which it is possible to calculate an equilibrium constant for the formation of a collision complex from a pair of chemically interacting atoms. For iodine atoms, this leads to a value of the rate constant for I+I+M→I2+M, if the mechanism is 2I⇌I2*(1Σ), I2*+M→I2+M. The rate constant so calculated agrees with that obtained by a statistical procedure [J. Keck, J. Chem. Phys. 29, 410 (1958)].
The calculation also furnishes enough information about the mechanical details of collisions so that the contribution of molecular states other than 1Σ to recombination may be deduced. As a result a fairly conclusive discussion may be given of the plausibility of the various detailed mechanisms thus far suggested. A most likely mechanism and a possible calculation based on it are proposed.
Dissociation of C6H5T Following Beta Decay
Authors: Carlson Thomas A. 
Published: January 2005

The relative abundance of the various charged fragments formed following beta decay of mono tritiated benzene was measured with a specially designed mass spectrometer. In nearly every case the C–He bond was ruptured, the charge remaining with C6H5+. In 28% of the events the C6H5+ species were further excited to produce more than 30 different charged fragments. Comparison of this spectra with the electron impact data on benzene is made to arrive at an estimate of the energies involved in the initial excitation and the results are found to be in essential agreement with those of other tritiated hydrocarbons. The molecular excitation of benzene following beta decay is then shown to result probably from a sudden electronic perturbation following the formation of the doubly charged He3 nucleus.
Some results on the dependence of the collection efficiency of a given ion on its kinetic energy are also discussed.
Multiple Trapping Sites for Hydrogen Atoms in Rare Gas Matrices
Authors: Foner S. N. , Cochran E. L. , Bowers V. A. , Jen C. K. 
Published: January 2005

Hydrogen atoms have been stabilized in nonequivalent lattice sites in matrices of the rare gases at liquid helium temperature. Electron spin resonance spectra of H atoms in argon, krypton, and xenon show that at least two trapping sites are involved in each case. In a neon matrix, H atoms have been stabilized in only one site. Attainability of the various trapping sites apparently depends on the initial energy of the H atom, a simple doublet spectrum being obtained when the atoms are deposited from the gas phase, while multiple trapping spectra are obtained when the atoms are produced by photolysis in the solid.
The hyperfine coupling contants and the electronic g factors for H atoms trapped in the various matrix sites have been determined. The deviation of the hyperfine coupling constant from the free-state value is positive in some cases and negative in others. The experimental results are in good agreement with theoretical predictions. A complex multicomponent H atom spectrum was obtained by photolysis of HI in xenon. The subsplitting in the spectrum is attributed to magnetic hyperfine interactions with matrix nuclei (Xe129 and Xe131). The nature of the trapping sites in rare gas matrices is discussed. Evidence for trapping in substitutional sites and octahedral sites is presented.
Raman Spectra of Metal Carbonyl Compounds. II. Raman Spectra, Structure, and Force Constants of Cobalt and Iron Tetracarbonylate Anions
Authors: Stammreich H. , Kawai K. , Tavares Yara , Krumholz P. , Behmoiras J. , Bril S. 
Published: January 2005

The Raman spectra of the ions Co(CO)4—, Fe(CO)42—, and HFe(CO)4— have been studied in aqueous solutions of the corresponding sodium salts. The spectra of Co(CO)4— and Fe(CO)42—, excited by the helium radiations 5875.6 and 6678.1 A are in full agreement with the expected Td symmetry of these ions; all observed frequencies were assigned to fundamental vibrational modes. A normal coordinate treatment was carried out under the assumption of a simplified valence force field model making use of only two interaction constants. The values of the fundamental frequencies of the tetrahedral ions, calculated by means of the potential constants of this model, were found to be in satisfactory agreement with the observed Raman shifts.
The Raman spectrum of HFe(CO)4—, put in correlation with that of Fe(CO)42—, points strongly to a C3v symmetry of the former ion.
Vibronic Calculations in Benzene
Authors: Albrecht Andreas C. 
Published: January 2005

A group-theoretical reduction incorporating normal-coordinate parameters is applied to obtain expressions for the oscillator strengths of forbidden B2u, B1u, and E2g transitions in benzene in terms of the minimum number of electronic integrals. The simplification obtained encourages the testing of wave functions within the Herzberg-Teller framework as well as empirical evaluation of the theory. An investigation is made of the possible effect of isotopic substitution on forbidden intensities. The group-theoretical reduction is carried out for 1,4 dideuterobenzene, sym-benzene-d3, 2,3,5,6-tetradeuterobenzene, benzene-d6, and a hypothetical molecule p-di-X-benzene (where (X) = 20 and C—X = 1.40 A). It is observed that the B2u and B1u transitions are very insensitive to mass effects independent of the nature of the electronic functions. On the other hand, E2g transitions may or may not show a significant sensitivity depending on the details of the wave functions. By way of illustration, oscillator strengths are calculated for all compounds for B2u, B1u, and two E2g transitions using conventional benzene ASMO functions and published integrals. The distribution of oscillator strengths among all active normal modes is given for benzene, benzene-d6, and p-di-X-benzene. It is found that especially for the E2g transitions the distribution among normal modes is considerably more sensitive to mass effects than is the total oscillator strength.
A general expression is given for the temperature dependence of ``forbidden'' transition probabilities.
Effect of Pressure on the M Center in Alkali Halide Crystals
Authors: Minomura S. , Drickamer H. G. 
Published: January 2005

The effect of pressure to 52 800 atm has been measured on the M band in NaCl, KCl, KBr, and KI, and on the R2 and N bands in KCl. In general, the band peak shifts to higher frequency with increasing pressure for all bands. At the phase transition from fcc to sc there is a blue shift in KCl, but a red shift in KBr and KI. It is suggested that the shift corresponds to a balance between contraction and polarizability effects. From an Ivey-type relation, it would seem that the M center is somewhat less compressible than the F center.
There is a marked increase in intensity of the M center in the potassium halides in going through the phase transition from the fcc to the sc lattice.
Radiolysis of Cyclohexane. I. Pure Liquid Cyclohexane and Cyclohexane-Benzene Solutions
Authors: Freeman G. R. 
Published: January 2005

The radiation chemistry of pure liquid cyclohexane and of cyclohexane-benzene solutions has been investigated. The cyclohexane radiolysis system appears to contain at least two distinct activated species, one of which (c-C6H12″) is subject to ``protection'' by benzene while the other (c-C6H12′) is not. The approximate yields of these two species, determined by kinetic analysis, are G(c-C6H12″) = 3.0±0.4 and G(c-C6H12′) = 2.5∓0.4. In addition to the usual products, cyclohexylcyclohexadiene and dicyclohexadiene have been measured in the cyclohexane-benzene system. A mechanism has been proposed to explain the formation of the major products and the variation of their yields with benzene concentration.
A limiting case calculation for the upper limit of the rate constant for energy transfer between molecules in the present system (1013—1014 liters mole/sec) agrees well with a similar calculation, recorded in the literature, for energy transfer in organic solution scintillators. Another limiting case calculation shows that the rate constant for energy transfer might also be considerably smaller than the above value.
Total Collision Cross Sections for the Interaction of Molecular Beams of Cesium Chloride with Gases. Influence of the Dipole-Dipole Force upon the Scattering
Authors: Schumacher Hugo , Bernstein Richard B. , Rothe Erhard W. 
Published: January 2005

Total cross sections (Q) for the interaction of beams of CsCl with a number of molecules were measured using an apparatus of ca 4′ angular resolution in which the temperature of the scattering gas could be varied from 200°—735°K. The temperature dependence of Q was studied for Ar, CH4, CH2F2, CHF3, CF4, NO, H2S, NH3, and for cis- and trans-CHCl=CHCl. Relative values of Q at 300°K were measured for eight additional gases.
The data were correlated using the Massey-Mohr theory, assuming an intermolecular potential V(r) = —C/r6, so that Q=b(C/vr)2/5, where vr is the relative velocity and b a known constant; the potential constant C was estimated from formulas for the dispersion, dipole-induced dipole, and dipole-dipole forces.
For the nonpolar gases the observed small temperature dependence of Q agrees within experimental error (±3%) with that expected from the temperature dependence of vr. The theoretical values of Q differ by a nearly constant factor from the experimental results; thus relative cross sections (Q*) are predicted with fair accuracy.
For the polar gases the Q's are large, decreasing significantly with increasing temperature. Because of the large dipole-dipole interaction, the approximate theoretical treatment (based on the limiting temperature-dependent dipole-dipole contribution to C) accounts only semiquantitatively for the observations.
Diffusion in a Linear Lattice
Authors: Plesner Igor W. 
Published: January 2005

Diffusion in crystals by a vacancy mechanism is described by a model consisting of an isotope and a vacancy imbedded in a linear lattice of harmonic oscillators. Assuming a 6–12 potential between defects and lattice atoms, the anharmonic interaction is explicitly calculated. The usual approximation of assuming this interaction to depend linearly on the frequency is shown to be valid as long as the Debye approximation for the frequency spectrum is applicable.
The lattice with defects is analyzed using the formalism developed by Brout and Prigogine. In order to solve the equations, the concept of localized modes is introduced. The localized mode is approximated by the oscillation of the defect (isotope) in the lattice. The justification for this is investigated by a method due to Montroll and Potts.
The diffusion constant is calculated and shown to depend on the fourth power of the defect frequency. This is in agreement with an earlier result by Klemens, but deviates appreciably from the usual first power dependence.
Crystal Structure of β-Ga2O3
Authors: Geller S. 
Published: January 2005

The crystal structure of β-Ga2O3 has been determined from single-crystal three-dimensional x-ray diffraction data. The monoclinic crystal has cell dimensions a=12.23±0.02, b=3.04±0.01, c=5.80±0.01 A and β=103.7±0.3° as originally reported by Kohn, Katz, and Broder [Am. Mineral. 42, 398 (1957)]. There are 4 Ga2O3 in the unit cell. The most probable space group to which the crystal belongs is C2h3—C2/m; the atoms are in five sets of special positions 4i: (000, ½½0)±(x0z). There are two kinds of coordination for Ga3+ ions in this structure, namely tetrahedral and octahedral. Average interionic distances are: tetrahedral Ga–O, 1.83 A; octahedral Ga–O, 2.00 A; tetrahedron edge O–O, 3.02 A; and octahedron edge O–O, 2.84 A. Because of the reduced coordination of half of the metal ions, the density of β-Ga2O3 is lower than that of α-Ga2O3 which has the α-corundum structure. Also the closest approach of two Ga3+ ions in β-Ga2O3 is 3.04 A which is considerably larger than the closest approach of metal ions in the sesquioxides with the α-corundum-type structure and, in agreement with the results of thermodynamic measurements, the β phase appears to be the structurally more stable one.
The average Ga–O distances in the structure seem to account for the fact that although the Ga3+ ion is substantially larger than the Al3+ ion its quantitative preference for tetrahedrally coordinated sites when substituted for Fe3+ ion in the iron garnets is very nearly the same as that of the Al3+ ion.
The structure accounts for a recent result obtained by Peter and Schawlow from paramagnetic-resonance measurements on Cr3+-ion-doped β-Ga2O3, namely that the Cr3+ ion substitutes for the Ga3+ ions in a single set of equivalent octahedral sites.
The magnetic aspects of the β-Ga2O3 structure are discussed and it is shown that a possible Fe2O3 isomorph could be expected to be at least antiferromagnetic with a Néel temperature of about 700°K Furthermore, a knowledge of the β-Ga2O3 structure and of the nature of site preferences of the Ga3+ and Fe3+ ions in the garnets lead to a prediction regarding the structure of the ferrimagnetic crystals of formula Ga2—xFexO3 recently discovered by Remeika.
Electron Coupling of Nuclear Spins. IV. Temperature Dependence in Substituted Ethanes
Authors: Schug John C. , McMahon Paul E. , Gutowsky H. S. 
Published: January 2005

The proton-proton coupling constant, AHH′, in H–C–C′–H′ groups is known to depend upon the dihedral angle, φ. Previous valence-bond calculations by Karplus have given the result that AHH′≅A0cos2φ+B.This relation is used to estimate the effects upon the average coupling constant of torsional vibrations and reorientations about the C–C′ bond. For substituted ethanes, it is found that torsional vibrations produce a modest temperature dependence, of opposite sign for the trans and gauche coupling. However, for molecules in which the potential function, V(φ), has threefold symmetry, rotational averaging leads to a cancellation of the vibrational effects, giving a temperature independent value, 〈AHH′〉, for the average coupling. This prediction has been verified in experiments on ethyl nitrate for which 〈AHH′〉 was found to have a constant value of 6.92 cps over a 100° temperature range.
When there is an energy difference, ΔE, between trans and gauche forms, ΔE determines the sign and magnitude of the temperature dependence of 〈AHH′〉; however, corrections for the vibrational effects appear desirable if accurate values of ΔE are to be obtained from such experiments. The temperature dependence of 〈AHH′〉 could not be calculated analytically for any but the simplest potential functions and simplest approximations to the torsional motions. However, it was found that the detailed form of V(φ) has but a slight effect on the results. 〈AHH′〉 is, of course, more sensitive to the functional form of A(φ).
Evidence for Internal Rotation in the Fine Structure of the Infrared Absorption of Oxygen in Silicon
Authors: Hrostowski H. J. , Alder B. J. 
Published: January 2005

Interpretation of the spectra of silicon saturated with oxygen highly enriched with O18 confirms that oxygen is located in an interstitial site. The over-all features of the absorption indicate that the oxygen is in a nonlinear Si2O configuration. The fine structure in the asymmetric Si–O stretching vibration and its temperature dependence can be largely explained by motion of the oxygen in a potential barrier with six-fold symmetry. A symmetry analysis of this process predicts additional structure some of which has now been observed under higher resolution. The spectra of oxygen contaminated silicon containing 2% germanium corroborate our explanation of the fine structure.
The potential barrier hindering rotation of the oxygen about the axis joining its two bonded silicons has been ascribed to the surrounding silicon lattice. Calculation of the potential shows that as the oxygen rotates it can also wobble. Since the fine structure indicates that the ground-state splitting due to rotation is near 2 cm—1, the barrier hindering rotation is about 200 cal/mole. Calculation of this barrier then indicates that the maximum wobble angle is 0.2° and the Si–O–Si angle near 150°.
New Type of Freezing-Point Apparatus. Freezing Points of Dilute Lanthanum Chloride Solutions
Authors: Scatchard G. , Vonnegut B. , Beaumont D. W. 
Published: January 2005

A new type of freezing-point apparatus is described that reduces the errors of previous types. The freezing-point depressions of aqueous lanthanum chloride solutions up to 0.04 m are adequately expressed by the Debye-Hückel approximation for ions with a=6.15 A plus a very small linear term. The ``higher terms'' are computed by combining the equations of Mayer and Kirkwood, using the tables of Poirier, and are found to be very small in this case.
The parameters for the calculation of the activity of water from freezing point depressions, for the Debye-Hückel theory, and for the Kirkwood parameter Bik are redetermined, and the more general use of Bik is discussed.