bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy Atom Effect on the Phosphorescence of Aromatic Hydrocarbons. II. Quenching of Perdeuterated Naphthalene by Alkali Halide
Authors: Hofeldt R. H. , Sahai R. , Lin S. H.
Published: February 2004

The effects of varying concentrations of alkali halide, external heavy atom perturber, on the phosphorescent characteristics of naphthalene-d8 were investigated in rigid solutions of ethyl alcohol at 77°K. It was found that the total phosphorescence could be considered as being composed of two phosphorescent species existing in equilibrium with each other: an excited, free naphthalene and an excited, 1:1 complex of perturber and naphthalene. The phosphorescent decay rates of the latter were in the range of 0.3–0.4 sec−1 when complexed with alkali iodides. The phosphorescent characteristics did not depend significantly upon the metal ion associated with the halide, and CsF up to 0.9M did not quench the phosphorescence measurably. The phosphorescent intensities and mean durations were calculated based on the proposed charge-transfer mechanism. The experimental data were correlated very well using this mechanism. The direct spin–orbit interaction mechanism proposed by Lin and Tweed was found to be unimportant in these systems. The phosphorescent state was discussed theoretically from the charge-transfer viewpoint. The triplet state in the donor was considered to be perturbed by spin–orbit and charge-transfer interactions which gave rise to two terms: one involving only charge-transfer interaction and a second, a cross term involving both spin–orbit and charge-transfer interactions. Thus, it is predicted (and observed) that the mixing of the donor triplet arises only when a charge-transfer complex is formed and this mixing will give rise to the heavy atom effect if a heavy atomic species is present in the acceptor. The nonradiative processes were also discussed in the light of this mechanism.
Ozone Ultraviolet Photolysis. II. Quantum Yield at Low Ozone Concentration
Authors: Webster Henry , Bair Edward J.
Published: February 2004

The relative ultraviolet quantum yield was measured at low ozone concentration (∼ 0.2 torr) in order to identify contributing processes under conditions where the Norrish chain mechanism is not expected. The quantum yield in pure O3 and in O3–He mixtures exceeds that in O3–N2 mixtures by a component φx ≈ 2 which is attributed to the products of the O(1D) + O3 reaction. These products decompose ozone with a rate constant k ≤ 107liter/mole·sec and are not affected by a large excess of inert gas. This result tends to rule out O2(3Σu+) as the reactive product.
Vibrational Excitation in a Morse Oscillator
Authors: Lin Jeong-long
Published: February 2004

Vibrational excitation in the system He+H2 is studied theoretically by considering H2 as a rotating Morse oscillator. The anharmonicity of molecular vibration is found to have only a small effect on the 0 → 1 transitions. Vibrational transition probabilities are also found to be insensitive to the rotational energy of the diatom. Following the approach of Mies and Shuler, based on the modified wavenumber approximation, three-dimensional transition probabilities are calculated from one-dimensional results and the steric factor is obtained as a function of the collision energy.
Microwave Spectrum of Methylhydrazine; Rotational Isomerism, Internal Motions, Dipole Moments, and Quadrupole Coupling Constants
Authors: Lattimer Robert P. , Harmony Marlin D.
Published: February 2004

The microwave spectrum of methylhydrazine has been investigated. Two rotamers have been observed, and their spectra have been assigned and analyzed. The ground-state rotational constants of the inner skew rotamer are A = 36 704.37 MHz, B = 9689.70 MHz, and C = 8531.95 MHz, while the values obtained for the outer skew rotamer are A − C = 29 597.20 MHz and κ = − 0.925849. Strong evidence for the conformational identifications was provided by the measured dipole moment components, which were μa = 1.04 D, μb = 1.21 D, μc = 0.46 D for the inner rotamer and μa = 0.26 D, μb = 0.60 D, and μc = 1.70 D for the outer rotamer. Relative intensity measurements indicate that the inner rotamer is more stable than the outer rotamer by 293 ± 23 cm−1. Spectral splittings produced by inversion and methyl tunneling have been observed. Analysis of the latter effect leads to a barrier of V3 = 1329 cm−1 for the inner rotamer. Hyperfine splittings of the inner rotamer spectrum were described by the single set of 14N quadrupole coupling constants, χaa = 4.09 MHz, χbb = 0.69 MHz, and χcc = − 4.78 MHz.
Location of Energy Barriers. III. Effect on the Dynamics of Reactions AB + CD → AC + BD
Authors: Mok M. H. , Polanyi J. C.
Published: February 2004

A previous investigation of the effect of barrier location on the reaction dynamics of reactions A + BC → AB + C (Paper I) has been extended to the four-atom bimolecular reaction AB + CD → AC + BD. “Barrier location” is defined in terms of a 3d “diagnostic” potential-energy surface, namely the surface for reaction by way of rectangular coplanar configurations. Surface I had a barrier displaced by about 0.3 Å into the entry valley (or “approach coordinate”), and surface II had a barrier displaced by the same amount into the exit valley (or “retreat coordinate”). On both surfaces the classical barrier height was Ec = 34–35 kcal mol−1. A total of 22 batches of classical trajectories were run, across these two surfaces. The reacting molecules were free to move in three dimensions, i.e., reaction took place across the full 7d potential-energy hypersurface. The batches differed for the most part in the magnitude and distribution of the reagent energy. The reagent energy was restricted to relative translation (ET), and molecular vibration [(EV)AB and (EV)CD]. It was found that on surface I ET was very markedly more effective than EV in promoting reaction. The converse was true on surface II. This finding parallels that for the three-atom system A + BC → AB + C. In contrast to the three-atom case, a reagent energy substantially in excess of the barrier height, approaching 2Ec, was required in order to obtain significant reaction. These findings applied equally when the masses of the particles were mA = mB = mC = mD, and when they were mA = mB ≪ mC = mD. The equal-mass case differed from the unequal-mass case principally in the fact that the former gave direct reactive encounters (according to the most stringent criterion) whereas the latter gave indirect (or “complex”) ones. For both the equal- and the unequal-mass cases on surface I the greater part of the reagent energy (very largely ET) became internal excitation of the products (EV′ + ER′), whereas on surface II the greater part of the reagent energy (largely EV) became product translation (ET′). (This tendency for the reagent energy to become “transposed” into the complementary degrees of freedom in the products was also noted in Paper I, for the reaction A + BC). For the equal-mass case a test was made on surface II of the effect of distributing the reagent energy so that (EV)AB ≪ (EV)BC; the reactive cross section was somewhat less than for the situation (EV)AB = (EV)BC used in most of this study.
Lattice Dynamics of Sodium Nitrate. A Group-Theoretical Analysis
Authors: Rao K. R. , Trevino S. F. , Logan K. W.
Published: February 2004

The symmetry properties of normal modes of the lattice of sodium nitrate are investigated using group-theoretical techniques. Making use of the formalism of Maradudin and Vosko, the symmetry vectors at several points in the Brillouin zone are determined. The interrelations between elements of the dynamical matrix corresponding to the points have also been obtained.
Application of Many-Body Perturbation Theory to the Hydrogen Molecule
Authors: Schulman Jerome M. , Kaufman D. Neal
Published: February 2004

The hydrogen molecule total energy, polarizabilities, and electron-coupled nuclear spin-spin Fermi interaction are studied by many-body perturbation theory. Two potentials, the Hartree and Hartree–Fock, are considered. Through second order the energies are within several kilocalories per mole of the accurate nonrelativistic values. The Hartree–Fock expansion is reasonably accurate through first order for polarizabilities and gives very good agreement with experiment if a rather simple geometric approximation is used. For the spin–spin coupling constant, good agreement with experiment is obtained using the Hartree potential and considering some second- and higher-order diagrams.
Noniterative Solutions of Integral Equations for Scattering. IV. Preliminary Calculations for Coupled Open Channels and Coupled Eigenvalue Problems
Authors: Sams W. Neal , Kouri Donald J.
Published: February 2004

The homogeneous integral solution formalism developed by Sams and Kouri is illustrated for coupled open channel scattering calculations and coupled eigenvalue calculations. This method for scattering calculations compares favorably, both in accuracy and in computation time required, with the Lester–Bernstein close coupling solution of the differential equations for scattering and the Johnson–Secrest amplitude density method. Preliminary results for coupled eigenvalue integral equations are also encouraging. A simple technique for applying the quantization condition in searching for the eigenvalues of coupled integral equations is presented, and is employed in the calculations reported. Example results are given for 16, 23, and 30 coupled scattering channels and for 1, 2, and 3, coupled integral eigenvalue equations.
Thermal Decomposition of N2O4 and NO2 by Shock Waves
Authors: Zimet Elihu
Published: February 2004

A study of the reactions N2O4 + M⇄2NO2 + M and 2NO2 + M⇄2NO + O2 + M was carried out using the shock-wave method. For the first of these two reactions the rate equation was taken to be d[N2O4] / dt = −kD1[N2O4][M] + kR1[NO2]2[M] based on previous results. For argon as the inert gas M, with a reactant mole fraction less than 0.1, the rate constant was found to be kD1 = 2.2 × 1014exp(− 11 000 / RT) liter/mole·sec. Incorporated in these results was the new application of fully dispersed shock waves and these weak waves were found to produce more accurate results than the conventional use of partly dispersed shock waves. For the second reaction, the rate equation was taken to be d[NO2] / dt = −kD2[NO2]2 − kD3[NO2][M], and with argon as the inert gas the dissociation rate constants were found to be kD2 = 3.0 × 109exp(− 26 900 / RT) liter/mole·sec and kD3 = 3.6 × 1013exp(− 65 400 / RT) liter/mole·sec. An analytical description of the flow fields agreed well with the experimental values which were determined by a light absorption technique.
Infrared Spectra of Matrix-Isolated Hydrogen Sulfide in Solid Nitrogen
Authors: Tursi Anthony J. , Nixon Eugene R.
Published: February 2004

The infrared spectra of H2S in a series of solid nitrogen matrices at 20°K are recorded for the 2500–4000-cm−1 region. From a curve-resolution analysis of the SH stretching region, assignments of peaks are made to monomer, dimer, and polymer species. The H2S dimer absorptions lead to a postulated open structure with a single hydrogen bond. An estimate based on frequency-shift data indicates a hydrogen bond strength of roughly half that found in the matrix-isolated water dimer.
Electron Spin Resonance of Gamma-Irradiated Single Crystal of Dihydrouracil
Authors: Herak J. N.
Published: February 2004

Free radicals in gamma-irradiated dihydrouracil have been identified as –C(5)H2–C(6)H–. Two sets of resonance lines due to two magnetically distinct molecules were observed. From the direction cosines of the α-proton coupling tensor it has been concluded that the N(6) atom, originally significantly out of the plane defined by the atoms N(1), C(2), N(3), and C(4), comes to that plane after the abstraction of a hydrogen atom from C(6). The nonequivalence of the β-proton couplings proves that the C(5) atom remains out of the plane even in the radical form. Calculated bond energies for the four C–H bonds indicate that the H(6′) hydrogen atom should be the most easily removed. That is in agreement with the observations.
Isoelectronic Molecules. II. First- and Second-Order Physical Properties
Authors: Laurenzi Bernard J. , Saturno Antony F.
Published: February 2004

It has been shown that first- and second-order physical properties of isoelectronic molecules are interrelated in a simple way. This follows from the fact that the corresponding first- and second-order operators are homogeneous functions of position and nuclear charge. The results are rigorously true for noninteracting electrons and can be extended to include interelectronic effects as well.
Thermodynamic Properties of a Rigid-Sphere Fluid
Authors: Carnahan Norman F. , Starling Kenneth E.
Published: February 2004

The excess thermodynamic properties for a rigid-sphere fluid have been calculated with an accurate equation of state. Values of (PV / NkT), and (H − H°) / RT, (S − S°) / R, (G − G°) / RT, and (f / P) are reported for a wide range of fluid density.
Self-Consistent Molecular-Orbital Methods. VII. Convergence of Gaussian Expansions of Slater-Type Atomic Orbitals in Calculations of First- and Second-Order Properties
Authors: Ditchfield R. , Miller D. P. , Pople J. A.
Published: February 2004

Least-squares representations of Slater-type atomic orbitals by a sum of Gaussian-type orbitals are used in self-consistent molecular-orbital calculations of first- and second-order properties. Quadrupole moments and electric field gradients are considered as examples of first-order properties. Diamagnetic susceptibilities, magnetic shielding constants, electrical polarizabilities, and nuclear spin coupling constants are calculated using finite perturbation theory. It is shown that, except for nuclear spin coupling constants, the results converge rapidly (with increasing size of Gaussian expansion) to the values appropriate for pure Slater-type orbitals. A comparison of calculated results with experimental data will be made in a future publication.
Absolute Infrared Intensities of the Fundamental Absorption Bands in Solid Cyanogen Halides
Authors: Bandy Alan R. , Friedrich H. Bruce , Person Willis B.
Published: February 2004

Absolute absorption intensities of the three infrared-active fundamental vibrations of each of the cyanogen halides—CICN, BrCN, and ICN—have been measured for crystalline samples, using experimental techniques developed by Hollenberg and Dows. Comparison between integrated intensities obtained with “drawn in” backgrounds and those obtained after integrating the absorption coefficient, κ, obtained from the measured transmittance by a Kramers–Kronig method, shows that the results agree within their estimated experimental uncertainty. The intensities of the stretching fundamentals in the solid phase differ drastically from those in the gas phase, e.g., ν1 for ClCN goes from an estimated 900 darks in the gas phase to 0 in the solid, ν3 increases by a factor of 2 from gas to solid for ClCN, and by a factor of about 4 for BrCN. However, the solid phase intensities of ν2, the bending motion perpendicular to the molecular chains in the solid, are only slightly larger than the gas phase values, indicating that the major perturbation of the vibrational intensities in crystals of these molecules is parallel to the molecular chains. The dipole derivatives with respect to the change in CN and in CX bond lengths (∂μ / ∂ri) have been computed for both gas and solid phases. A resonance structure argument leads to predictions for the signs expected for ∂μg / ∂rCX and ∂μg / ∂rCN, and for the changes expected as a result of intermolecular interactions in the solid phase. This qualitative resonance structure argument (which also successfully accounts for the nuclear quadrupole resonance results) is consistent with only one choice of signs for the ∂μg / ∂Qi and ∂μs / ∂Qi values. An alternative argument, independent of the model for the interaction, also leads to the same conclusion regarding the sign choice, increasing confidence that this choice is correct.
Comments on the Born–Yvon–Green and Kirkwood Hierarchies in Equilibrium
Authors: García-Colín L. S. , Piña E.
Published: February 2004

A compatibility condition is obtained for two functions g(n) and g(n+1) which are simultaneously solutions of the exact Born–Green–Yvon and Kirkwood hierarchies in equilibrium. This condition is shown to be both necessary and sufficient for the functions to be solutions of the hierarchies. Also, the problem of why an approximation introduced into the two hierarchies does not always lead to the same numerical results, is clarified.
Thermodynamic Investigation of Solid Argon–Oxygen Mixtures
Authors: Pace E. L. , Bivens R. L.
Published: February 2004

The heat capacity from 14 to 90°K and the enthalpies of transition and fusion have been measured for argon–oxygen mixtures containing 40.34 and 94.98 mol% oxygen. A comparison of the spectroscopic and calorimetric entropy of the mixtures at their normal boiling points shows a discrepancy equal to the entropy of mixing of the pure components within the experimental error. For the 40.34% mixture, a “hump”-type transition not observed in x-ray work was present in the temperature range from 14–25°K. For the β–γ transition in the 94.98% mixture, positional as well as orientational disorder is occurring. The lattice model of Pople and Karasz for transitions and fusions in solids is entirely inadequate for the argon–oxygen system.
Optical Ionization-Excitation Functions of Zinc, Cadmium, and Mercury by Electron Impact
Authors: Anderson Richard J. , Lee Edward T. P.
Published: February 2004

The cross sections for the production of 16 lines of the Zn(II), Cd(II), and Hg(II) spectra by ionization-excitation collisions between electrons and neutral atoms have been measured over the energy range0–260eV. The spectral lines are characterized by optical excitation functions which reach their maximum values within the energy range 40–90 eV, and by emission cross-section values of approximate, 10−17–10−20 cm2 at 200 eV. Theoretical branching ratios have been calculated and are used with the experimental data to obtain estimates of the 72S1/2 (Hg+), 62S1/2 (Cd+), and 52S1/2 (Zn+) direct excitation cross sections. Corresponding theoretical cross sections are estimated by means of the Born approximation. The cross-section ratios Q(n2P1/2,3/2) / Q(n2D5/2) are calculated for Zn+ (n = 5), Cd+ (n = 5), and Hg+ (n = 7), and the results compared with experiment.
Nonadditivity in the Potential for Pairs of Polyatomic Molecules
Authors: Yorke Ellen D. , De Rocco Andrew G.
Published: February 2004

The question of additivity for the pair potential between collections of harmonic dipole oscillators is examined to the third order of perturbation by the method of Bade. We recover the results of Sparnaay and go on to show that configurations characterized by central symmetry exhibit no net nonadditivity as a result of diple–dipole interactions among the oscillators of each group separately. Suggestions are made concerning the relevance of those results for simple polyatomic molecules and for more general globular systems.
Cryogenic Stability of Small Boron Compounds and Their Energetics Using the MINDO Method
Authors: Ganguli P. S. , Gordon L. P. , McGee H. A.
Published: February 2004

Borane from the pyrolysis of BH3CO survives quenching to 65–67°K and revaporization, but its isolation as a cryoreagent is unlikely since it dimerizes at temperatures corresponding to vapor pressures of about 10−5 torr. The reaction intermediate B4H8 produced in the pyrolysis of B4H10 also survives a cryogenic quench and revaporization. The MINDO molecular orbital method has been successfully applied to some B–H–F compounds, and computational results both affirm the accuracy of earlier energetic data and suggest further fruitful synthetic chemistry.
High Pressure Photoionization Mass Spectrometry. III. Reactions of NO+(X 1Σ+) with C3–C7 Hydrocarbons at Thermal Kinetic Energies
Authors: Searles Stuart K. , Sieck L. Wayne
Published: February 2004

The vapor phase reaction of NO+(X 1Σ+) with C3 through C6 normal, branched, or cyclic alkanes was found to proceed exclusively via an H− transfer mechanism, NO+(X 1Σ+)+RH2→RH++HCO. In addition to (I), C4H9+ was also formed by a second-order process in the reaction with 3-methylhexane. Absolute rate constants were determined for all systems at thermal kinetic energies. Isomers containing tertiary H atoms were found to be the most reactive, exhibiting rate constants on the order of 10+9 cm3/molecule·sec. Isotopic labeling has verified that the tertiary site is involved in the H− transfer reaction in those molecules having both secondary and tertiary H atoms. The rate constants found for n-alkanes and nonsubstituted cycloaklanes fall in the range 10−12–10−10 cm3/molecule·sec. The bimolecular reaction cyclo-C6H11++NO→C6H11NO+ was also noted at higher pressures. No further reaction of the RH+ species generated in (I) was found in any other RH2–NO combination at pressures up to 0.5 torr.
Structure Relaxation at Liquid–Solid Interfaces
Authors: Roy Narendra N. , Halsey G. D.
Published: February 2004

The high-coverage isotherms of Lando and Slutsky for neopentane and tetramethyl silane on gold films are analysed on the basis of a slab model for adsorbed layers. It is possible to fit the data to an inverse cube law for surface energy if a structure relaxation term, as proposed by Adamson and Ling, is introduced. The cube law coefficients so obtained are approximately an order of magnitude larger than the theoretical values.
Energy-Level Scheme for Nd3+ in LiYF4
Authors: Sengupta D. , Artman J. O.
Published: February 2004

Crystal-field parameters appropriate for S4 symmetry were fit to existing data on the I49/2 and I411/2 sublevel splittings of LiYF4:Nd3+. Intermediate coupling wavefunctions obtained previously from fits to the CaWO4:Nd3+ spectrum were used. Although ground-state EPR data were not available in this system, the symmetries of the levels were uniquely assignable from group-theoretical considerations and the available polarization data. The parameter values found are (in cm−1): B02 = 482.7, B04 = − 1452.5, B06 = − 122.1, B44 = − 1222.0, B46 = − 981.9, B4′4 = − 0.3, and B4′6 = − 0.2. The rms deviation of this fit was 10. We calculate ground-state g∥ and g⊥ values of 0.483 and 2.571, respectively. The crystal-field parameters found here are compared with those of CaWO4:Nd3+ and those of the “mirror” ion Er3+ in LiYF4:Er3+. We conclude that simple geometrical considerations as to the algebraic signs of the crystal-field components in these systems may be misleading.
Chemical Applications of Metastable Argon Atoms. IV. Excitation and Relaxation of Triplet States of N2
Authors: Setser D. W. , Stedman D. H. , Coxon J. A.
Published: February 2004

An argon flow system containing about 0.01% of metastable argon atoms (3P2,0) in the absence of other energy carriers is described and characterized. The interaction of these metastable atoms with nitrogen gives radiative transitions of N2 from C(3Πu) → B(3Πg) → A(3Σu+) and finally A(3Σu+) → X(1Σg+). Absolute-intensity measurements, high-resolution spectra, and pressure-dependence data show that independent channels exist for production of C(3Πu) and B(3Πg). Unusual nonequilibrium populations of the rotational levels, the three spin sublevels, and the λ-doublet levels were found for the N2(C3Πu) state. Possible mechanisms responsible for producing these populations are discussed. Study of the dependence of these populations upon pressure permitted evaluation of collisional relaxation within the various levels of N2(C3Πu). It was shown that rotational relaxation mainly occurs by ΔK = ± 1 with a rate constant of 7.4 × 1013 cm3 mol−1·sec−1. The rate constant for electronic quenching of N2(C3Πu) by argon is less than 2 × 1011 cm3 mol−1·sec−1. Relaxation among the three spin sublevels was found to be slower than rotational relaxation.
Excluded-Volume Effect on Helix-to-Coil Transitions in n-Stranded Molecules
Authors: Kumbar Mahadevappa
Published: February 2004

The effect of excluded volume on the probability of ring closure n-stranded molecules has been examined using the distribution function. The ring closure index is calculated as 3γ(n−1) / 2 in three dimensions. For double-stranded molecules the order of phase transition remains the same as in the Gaussian problem, regardless of the effect of excluded volume.
ENDOR Study of X-Irradiated Single Crystals of Ice
Authors: Box Harold C. , Budzinski Edwin E. , Lilga Kenneth T. , Freund Harold G.
Published: February 2004

ENDOR measurements were made on x-irradiated single crystals of hexagonal ice. The ENDOR frequencies yield the hyperfine coupling for the OH radicals produced in irradiated ice. The method is capable of distinguishing between OH radicals produced in three different environments. The principal values of the hyperfine coupling tensors in megacycles per second of the three distinct OH radicals are as follows: AxxAyyAzz(I)− 80.0− 124.4+ 9.2(II)− 81.2− 124.4+ 19.4(III)− 78.2− 126.2+ 15.6 Using ESR spectra in conjunction with ENDOR data, the g tensors were also determined with the following results: gxxgyygzz(I)2.00282.00892.0597(II)2.00312.00892.0571(III)2.00272.00882.0581
Hydroxyl Radical Kinetics by Kinetic Spectroscopy. VI. Reactions with Alkanes in the Range 300–500°K
Authors: Greiner N. R.
Published: February 2004

Flash photolysis and kinetic spectroscopy were used to study the reactivity of OH radicals toward a representative set of alkanes. Previous studies have shown that OH radicals abstract H atoms from alkanes to produce H2O and an alkyl radical. The following formula was found to reproduce accurately all of the observed abstraction rate constants for the 10 model alkanes: ktot = 6.15 × 1011 N1exp(− 1635 / RT) + 14.1 × 1011 N2exp(− 850 / RT) + 12.6 × 1011 N3exp(+ 190 / RT) cc mol−1·sec−1, where N1, N2, and N3 are the respective numbers of primary, secondary, and tertiary H atoms in the alkane, and ktot is the total (in these experiments the observed) rate constant for the abstraction of H atoms from the alkane. Thus, there is a generally applicable frequency factor and activation energy for each of the three types of H atoms found in alkanes. Methane and ethane were somewhat expected exceptions to this rule. Their rate constants are 3.31 × 1012exp(− 3772 / RT) and 1.12 × 1013exp(− 2447 / RT) cc mol−1·sec−1, respectively.
Model Calculations of Transport Coefficients for Diatomic Gases in an External Magnetic Field
Authors: Cooper E. R. , Hoffman D. K.
Published: February 2004

The geometry of rigid, convex molecular models in collision is discussed. Transport coefficients of diamagnetic, diatomic gases are computed in field-free space and in a static field using these models. The calculated transport coefficients are compared with the approximate analytical results of McCourt and Snider and Levi and McCourt. It is shown that the terms odd in the angular momentum make only a small contribution and are, in fact, zero in the approximation of Levi and McCourt. The viscosity is found to provide a more sensitive test of the models than does the thermal conductivity, and the reasons for this are explored.
Contribution to the Study of GdO Band Spectrum
Authors: Suárez Carlos B. , Grinfeld Rafael
Published: February 2004

The band spectrum of GdO has been obtained in a dc arc. New bands have been found between 6250–7500 Å, and in the green region. Two previously known systems in the blue have been confirmed, and four new systems are presented, modifying previous vibrational assignment between the green and red region of the spectrum. The vibrational constants derived are found to lie between 700–1000 cm−1.
Theory of Collisionally Induced Intramultiplet Mixing in Excited Alkali Atoms
Authors: Dashevskaya E. I. , Nikitin E. E. , Reznikov A. I.
Published: February 2004

The theory of intramultiplet mixing in P2 resonance excited states of alkali atoms induced by collisions with noble gas atoms is discussed in connection with various mechanisms of nonadiabatic coupling between molecular states. The semiclassical approach is used, and a high value of the Massey parameter corresponding to 12→32 transitions is assumed. Two coupling regions are found, and it is shown that the main contribution to the total inelastic cross sections for heavy partners is given by the Coriolis interaction at small interatomic distances. Comparison between theory and experiment reveals reasonable agreement. In addition, the validity of the perturbation theory for almost adiabatic collisions is discussed.
Quantum Corrections for the Noncentral Intermolecular Forces to the Second Virial Coefficient of Deuterium Gas
Authors: Singh Y. , Datta K. K.
Published: February 2004

The quantum corrections to the second virial coefficient of simple nonpolar polyatomic gases have been calculated for the noncentral intermolecular forces by taking into consideration the various factors, viz., (1) quadrupole–quadrupole interaction, (2) quadrupole–induced-dipole interaction, (3) anisotropy, and (4) shape factors. Experimental second virial coefficient data in conjunction with the central force parameters determined from viscosity have been used to estimate the quadrupole moment and shape factor of D2 molecule. The quadrupole moment thus obtained is in reasonable agreement with that calculated theoretically.
Ultrasonic Study of Aqueous Solutions of ZnCl2: From Dilute Solutions to Hydrated Melts
Authors: Darbari G. S. , Richelson M. R. , Petrucci S.
Published: February 2004

Longitudinal sound absorption and velocity measurements for aqueous solutions of ZnCl2 in the concentration range 0.5–12M between − 15 and 25°C and in the frequency range 5–250 MHz are reported. A single relaxation process is noticed throughout the entire concentration range. These results are interpreted as due to a chemical relaxation caused by rearrangement between various complex forms of the type ZnCln2−n in accord with findings by Raman spectra. A phenomenological treatment in terms of the compressional moduli adapted for the case of a chemical relaxation and for the condition τυ ≫ τs, τυStr, is applied to the data corresponding to the composition ZnCl2·5H2O, ZnCl2·4H2O, and ZnCl2·2.3H2O. The condition τυ ≫ τs is confirmed by shear velocity measurements on the most concentrated solution. Measurements by changing the ratio Zn:Cl and the nature of the anion prove the specificity of Cl− for the observed relaxation and indicate that probably ZnCl4−2 is the species always involved in the observed process.
Optical Study on the Phase Transitions in KH2PO4 and KD2PO4
Authors: Sato Yoshiki
Published: February 2004

The infrared spectra of the PO4 stretching vibrations have been studied on KH2PO4 and KD2PO4 over a wide range of temperature. A trend of the intensity variation with temperature for these bands is similar in each compound, but is very different between both compounds. An inspection of the intensity behaviors indicates that each PO4 group is attached equivalently by four hydrogen atoms in KH2PO4, and by two deuterium atoms in KD2PO4, above the respective transition points. Namely, each of the hydrogen and phosphorus atoms in KH2PO4 moves in a single-minimum potential well with a flattened bottom, while each of the corresponding atoms in KD2PO4 moves in a double-minimum potential well. Further, non-existence is evidenced for a Slater configuration connected with an energy parameter ε0 in his model. As a result, it is concluded that the displacive and pseudospin models are the most relevant in describing the phase transition mechanisms in KH2PO4 and KD2PO4, respectively.
Molecule–Atom Total Scattering Cross Sections: LiF on Ar, Kr, and N2
Authors: Richman E. , Wharton L.
Published: February 2004

Total quantum-mechanical scattering cross sections of LiF on Ar, Kr, and N2 were measured as a function of collisional velocity in the thermal energy range, to about 1%–2% accuracy, through the use of circular beam geometry and a McLeod gauge to measure target gas density. Good absolute agreement with the Schiff–Landau–Lifshitz elastic scattering theory and the calculated 1/r6 long-range potential was obtained at only the lowest experimental velocities. At higher velocities the cross section is larger than predicted by this theory. No glory undulations were detected. Forces arising from the higher-order multipoles are insufficient to explain the results, but molecular protrusion correlates with the ordering of the deviations observed.
Nonexponential Nuclear Magnetic Relaxation by Quadrupole Interactions
Authors: Hubbard Paul S.
Published: February 2004

Results are presented of calculations showing that the nuclear magnetic relaxation of the longitudinal and transverse components of a spin I are different, but each is the sum of I decaying exponential terms if I is an integer, or the sum of I + 12 decaying exponential terms if I is half an odd integer, if the relaxation is produced by quadrupole interactions for which the correlation time is not short compared to the Larmor period. Expressions for the exponents and coefficients are given in detail for the case I = 32. If the correlation time is short, the expressions reduce to the simple exponential decays calculated by previous investigators.
Rotational Diffusion Tensor of Liquid Methylene Chloride from Its Infrared Spectrum
Authors: Rothschild Walter G.
Published: February 2004

The rotational motion of the three inertial axes of liquid methylene chloride (CH2Cl2, point group C2υ) has been studied by computing the autocorrelation functions through the Fourier inversion of the observed band contours. Three fundamentals [symmetry species a1 (283 cm−1), b1 (895 cm−1), and b2 (1265.5 cm−1)], as well as three summation bands [symmetry species b1 (2308 cm−1, 2414 cm−1) and b2 (2688 cm−1)], one overtone [symmetry species a1 (2525 cm−1)], and one difference band [symmetry species b2 (452 cm−1)], were investigated. The experimental results indicate that the liquid-phase molecules do not obey Debye-type diffusion but, on the contrary, are able to make orientational jumps of 27° – 38° around their inertial axes. The decay of the coherence of the rotational motion takes between 0.6 × 10−12 and 1.1 × 10−12 sec. Further-more, the anisotropy of the rotational motion in the liquid is observed to be about the same as that of freely rotating CH2Cl2 molecules. The results imply that rotational motion is not sensitive to molecular association, weak hydrogen-bond formation, and similar phenomena. A method of adjusting the integration limits of the Fourier transformation to the theoretical value of the second moment of the bands has been applied. Intermolecular torques were estimated.
Calculation of Force Constants of Ethylene by a Semiempirical ASMO–SCF Method
Authors: Machida K. , Nakatsuji H. , Kato H. , Yonezawa T.
Published: February 2004

A semiempirial ASMO–SCF calculation involving all valence electrons was carried out for a number of nuclear configurations of ethylene molecule. From the variation of the ground-state energy on the change of various structure parameters, all the diagonal quadratic force constants in the internal symmetry coordinate system were calculated and compared with those obtained from vibrational spectra. A modification of the Dewar and Klopman's formula including two empirical parameters was used to represent the core repulsion energy. It gave reasonable potential energy curves for the stretching coordinates.
Emission Spectra of O2(1Δg) Trapped in Solid Oxygen at 4.2°K
Authors: Akimoto Hajime , Pitts James N.
Published: February 2004

Emission spectra of the 0–0 band of the Δg1 → Σg−3 system, and the 0–0 and 0–1 bands of the Δg + 1Δg1 → Σg−3 + Σg−3 system of oxygen were observed in pure solid oxygen while a stream of microwave-discharged oxygen was being condensed on a glass surface at liquid-helium temperature. Both the single and double transitions were characterized as induced electric dipole transitions. The lifetime of the O2(1Δg) has been estimated to be <10−6 sec in solid oxygen at liquid-helium temperature.
Rotational Collision Numbers of N2, O2, CO, and CO2 from Thermal Transpiration Measurements
Authors: Malinauskas A. P. , Gooch J. W. , Annis B. K. , Fuson R. E.
Published: February 2004

Thermal transpiration results which were determined at an (assumed) characteristic temperature of 504°K are reported for all of the noble gases and for N2, O2, CO, and CO2. The helium data are found to be anomalous when viewed in terms of the dusty-gas model for thermal transpiration. Application of the model in the zeroth differential approximation yields the following rotational collision numbers for the polyatomic molecules: N2, 6.0; O2, 2.2; CO, 1.3; CO2, 1.9.
On the Relation between Symmetric and Asymmetric Charge Exchange
Authors: Storm David , Rapp Donald
Published: February 2004

A theoretical calculation was made of the cross sections for the processes: Li++Li→Li+Li+, Li++Na→Li+Na+, using hydrogenic 2s traveling orbitals in a two-state approximation. It was found that the general outline of the results found by Rapp and Francis, using a very crude approximate model, remain unchanged in this more rigorous calculation. The main difference between the present results and those of Rapp and Francis is that the cross sections fall off more rapidly at velocities above 5 × 107 cm/sec when traveling orbitals are used. It may be concluded that nonresonant charge transfer does indeed behave like symmetric resonant charge transfer at velocities above that necessary to satisfy the adiabatic criterion υ = ΔEa / h.
Electron Correlation in the Spin–Spin Interaction for l2
Authors: Gibbs R. L.
Published: February 2004

A symmetric two-electron correlation function is coupled by tensor operator methods to the spin–spin Hamiltonian. The matrix elements in the JM representation are calculated using standard tensor operator techniques. The method is applied to the p2 configuration with numerical results for the 2p2P3 state of helium included.
Thermionic Emission by Solutions of Solvated Electrons
Authors: Baron Bill , Delahay Paul , Lugo Roberto
Published: February 2004

Solutions of solvated electrons (generated by dissolution of sodium) in hexamethyl phosphoric triamide in a nitrogen atmosphere exhibit thermionic emission. This process was established on three counts: near-perfect rectification at the solution–gas interface; measurement of the drift velocity of charge carrier in the gas between solution and collector; analysis of electrical conduction in the gas phase. Measured currents were corrected for the Schottky effect and for back scattering of electrons in the gas phase. The dependence of current on sodium concentration was studied from 0.004–0.18 mol liter−1 and from 3.7–11.2°C. The current increased upon dilution. This unexpected result can be explained by assuming variations of the surface potential and interface structure upon dilution. Changes in surface potential of less than 0.1 V, for two simple limiting cases, account for experimental results. The temperature dependence of current yielded an energy of 1.0 eV. This energy includes the work function and contributions from solution and interfacial equilibria. Techniques are described, and ancillary measurements of solution conductivity are reported. This is the first report, to our knowledge, on thermionic emission by solvated electron solutions and by liquid systems at room temperature. Further theoretical and experimental work is suggested.
Infrared Spectra of Methoxyamine and Methoxyammonium Ion
Authors: Nelson H. M.
Published: February 2004

The infrared spectra of CH3ONH2, CH3OND2, CH3ONH3+Cl−, and CH3OND3+Cl− have been obtained in the region 4000–400 cm−1 with the samples in the form of thin crystalline films at liquid-nitrogen temperature. With the exception of the CH3 and NH3+ torsions, all the fundamentals for methoxyamine and methoxyammonium ion have been observed and assigned. Davies and Spiers' assignments for CH3ONH2 have been revised in part and the NH2 twist and wag located. The assignments for CH3ONH3+ ion are readily correlated with those for CH3ONH2 and for both species the assignments for the A′ vibrations are consistent with the product rule.
Magnetothermodynamics of Antiferromagnetic αMnCl2·4H2O. IV. Reversibility Conditions in the a, b, and p Regions with H  ‖ c Axis. Spin Flop, an Inappropriate Term
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2004

Detailed magnetothermodynamic measurements have been made on a 3.934-cm-diam spherical single crystal of α-MnCl2·4H2O, at temperatures below 1.7°K and with fields below 25 kG directed along the c crystallographic axis. Forty-one adiabatics, selected to cross the so-called boundaries in the magnetic regional diagram of antiferromagnetic MnCl2·4H2O were measured. Values of the temperature and magnetic moment along adiabatics were recorded automatically at very close magnetic field intervals. Equilibrium measurements of magnetic moment between 5 and 10 kG were made after the sample had been stabilized at constant field and temperature. The measurements were made by moving the sample slowly with respect to coils to avoid disturbing the equilibrium moment. Heat capacity measurements, supplementing those of Reichert and Giauque [J. Chem. Phys. 50, 4205 (1969)], were made at close intervals of field and temperature across the magnetic regional boundaries. The combined data made it possible to measure the entropy production on adiabatics and to locate the conditions under which it was produced. The gradual cooperative transition between the a and b regions was found to be under the equilibrium control of temperature and field. The reorientation does not occur irreversibly after a definite field enables the process to start. The equilibrium data, and particularly the magnetic moment measurements, show that the polarization in going between the a and b regions occurs over a broad band of fields. Since the word flop implies lack of control, the term spin flop for the gradual transition is quite inappropriate. No evidence was found to support any transition in the phase rule sense in this system and the term magnetic phase diagram is also undesirable usage. The term magnetic regional diagram is suggested for this very useful type of description in order to avoid the purposeless downgrading of a respected term in thermodynamics.
Quenching of Hg(63P) Atoms by Hydrogen and Hydrocarbons
Authors: Vikis Andreas C. , Moser H. C.
Published: February 2004

Mercury atoms in the 63P0 state were produced from the Hg(63P1) state by collisions of the second kind with N2 under steady-state illumination with 2537 Å light in a static system. C2H4 was found to quench Hg(63P0) atoms, with a rate constant of 2.4 × 1013 cc mol−1·sec−1, forming excited C2H4 which decomposes to C2H2 and H2 with a mechanism similar to the Hg(63P1) photosensitized decomposition. The reduction in the yield of this reaction due to the addition of various gases was used to determine cross sections for the deactivation of Hg(63P0) atoms by H2, D2, CH4, C2H6, C3H8 CH3CD2CH3, c-C3H6, C(CH3)4, n-C4H10, and i-C4H10. The quenching cross sections relative to C2H4 are, respectively, 4.94 × 10−2, 4.72 × 10−2, < 1.0 × 10−5, 4.0 × 10−4, 3.9 × 10−3, 3.1 × 10−4, 1.8 × 10−4, 4.3 × 10−4, 6.8 × 10−3, and 2.2 × 10−2. Relative quenching cross sections for some of the preceding were obtained also from measurement of Hg(61P0) induced electron emission from Ag, and the results were in agreement with the first method. In general, Hg(63P0) reactions are similar in nature to other excited metal atom–molecule reactions. However, they exhibit much lower quenching cross sections and a more marked dependence on the strength of the C–H bond than do corresponding Hg(63P1) reactions. The inadequacy of simple models for quenching based solely upon conservation of total electronic angular momentum is discussed. The importance of both total excitation energy and C–H bond energy is shown by a comparison of the quenching cross section of Hg(63P0), Hg(63P1), andHg(61P1) by the alkanes.
Negative Ion Formation in Selected Hexafluoride Molecules
Authors: Stockdale J. A. D. , Compton R. N. , Schweinler H. C.
Published: February 2004

Negative ion formation in gaseous SeF6, TeF6, MoF6, ReF6, and UF6 has been studied as a function of incident electron energy in the region from 0 to ∼10 eV. Negative hexafluoride ions formed by direct electron attachment were observed only in the cases of MoF6 and ReF6. SeF6−, TeF6−, and UF6− were produced by charge exchange with thermal SF6−* and rates for these reactions and for the reaction UF5− + UF6→UF6− + UF5 were measured and are reported here. Electrons having energies close to zero are known to attach to SF6 with a cross section approaching the maximum for s-wave capture. The excited negative ion SF6−* formed in this way has a lifetime of 26 μsec against autodetachment of the electron. An argument based on molecular orbital theory is given for the existence of a Jahn–Teller effect in SF6−. This could provide a means for the coupling between electronic and nuclear motion needed to trap the low-energy electron. Selenium and tellurium lie directly under sulfur in the same column of the periodic table, but the large spin-orbit splittings expected in SeF6 and TeF6 should dominate any Jahn–Teller effect in these otherwise similar molecules. The suggestion that a Jahn–Teller effect provides the coupling mechanism between electronic and nuclear motion is partially supported by the observation that ReF6 (large Jahn–Teller distortion) strongly captures slow electrons to form ReF6−*.
Hyperfine Structure of Thallium Bromide
Authors: Dickinson J. Thomas , Stephenson David A. , Zorn Jens C.
Published: February 2004

The hyperfine structure of the J = 2 and J = 3 rotational states of TlBr has been measured with a molecular-beam electric resonance spectrometer. Hyperfine transition frequencies were measured under conditions of very weak electric and magnetic fields. The linewidth was 500 Hz. The hyperfine interaction constants have been determined for 205Tl79Br, 203Tl79Br, 205Tl81Br, and 203Tl81Br in the first five vibrational states for J = 2. In addition, the interaction constants for J = 3, υ = 0 were determined for Tl79Br and Tl81Br, but it was not possible to resolve the effect of the two thallium isotopes in the J = 3 state. The spectra measured are well described by a hyperfine Hamiltonian containing the bromine quadrupole interaction, the spin–rotation interactions of both the thallium and the bromine nuclei, and both the scalar and tensor parts of the spin–spin interaction between the nuclei. The dependence of the magnetic hfs constants on vibrational state and on isotopic composition shows good agreement with theory. The magnetic octupole interaction of the bromine nucleus in TlBr is negligibly small, and we find no evidence for nuclear polarization or pseudoquadrupole effects.
Ab Initio Calculations of Harmonic Force Constants. III. An Exact Calculation of the H2+ Force Constant
Authors: Bishop David M.
Published: February 2004

The energy, within the Born–Oppenheimer approximation, of the 1sσg state of H2+ is evaluated for internuclear separations of 1.90–2.10 a.u. in steps of 0.01. These energies are used to determine the force constant of H2+ in the 1sσg state; it is found to be 0.102970438 a.u.