Volume 48, Issue 1, 01 January 1968

Microwave Spectrum, Structure, Boron Quadrupole Coupling Constants, and Dipole Moment of Difluoroborane
View Description Hide DescriptionThe microwave spectra of H^{10}BF_{2}, H^{11}BF_{2}, D^{10}BF_{2}, and D^{11}BF_{2} have been assigned. Rotational constants are 74 494.82, 10 496.74, and 9181.67 Mc/sec for H^{11}BF_{2} 77 244.25, 10 495.35, and 9221.49 Mc/sec for H^{10}BF_{2} 52 896.09, 10 498.29, and 8740.46 Mc/sec for D^{11}BF_{2} and 54 081.82, 10 496.89, and 8771.57 Mc/sec for D^{10}BF_{2}. The structural parameters obtained from these constants and their estimated uncertainties are , , and . The quadrupole coupling constants have been obtained. The dipole moment is 0.971 ± 0.010 D.

Electron Spin Resonance Spectra of Gamma‐Ray‐Irradiated Phosphate Glasses and Compounds: Oxygen Vacancies
View Description Hide DescriptionThe electron spin resonance spectra of γ‐ray‐irradiated glassy and polycrystalline phosphorus pentoxide and alkali phosphates with molar ratios of phosphorus pentoxide to alkali oxide ranging from 3.33 to 0.625 have been observed at 10 and 35 Gcps and at 300° and 78°K. Well‐resolved hyperfine doublets were observed in each glass or polycrystallinepowder. Additional resonances were also present in all the specimens but these are not discussed. The widths and shapes of the doublets were independent of temperature and only small alterations in the shapes of each component of a doublet were found as a function of frequency. One set of doublets has been discussed elsewhere and is not considered. Those doublets which are discussed are attributed to an electron trapped at a nonbridging oxygen vacancy. Interaction of the electron with the nearest‐neighbor ^{31}P nucleus (100% natural abundance, ) produces the doublet structure. These doublets exhibited isotropic hyperfine interactions ranging from 1880 to 4490 Mcps. The smaller interactions, 1880‐2196 Mcps, were found in glasses and polycrystallinepowders with molar ratios ≤ 1 and the larger interactions, 2630‐4490 Mcps, were found in those with molar ratios > 1. The anisotropichyperfine interaction, , of all the doublets was ≤ 540 Mcps. The defect electron state is assumed to be the nonbonding phosphorus sp hybrid orbital. On the basis of this assumption, the different isotropic hyperfine interactions are attributed to different geometric configurations of the phosphorus ion and the oxygens to which it is bonded. The assumed sp hybridization accounts for most of the electron density. An approximate g value is calculated for the doublets and is found to range from 2.005 to 2.040.

Vibration→Vibration and Vibration→Translation Energy Transfer in Methane‐Oxygen Mixtures
View Description Hide DescriptionA laser‐excited infrared fluorescence technique has been used to study vibration‐to‐vibration energy transfer from O_{2} to CH_{4} and to study vibration‐to‐translation relaxation in O_{2}–CH_{4} mixtures. It is found that 440 ± 40 O_{2}–CH_{4} collisions are necessary to transfer one quantum of vibrational excitation from O_{2} to CH_{4}. Measurements of vibrational relaxation in NO–CH_{4} systems are also given.

Mass‐Spectrometric Investigation of the Primary Processes in the Photodissociation of 1,3‐Butadiene
View Description Hide DescriptionThe primary processes in the 1,3‐butadiene photodissociation are investigated by direct detection of the fragments in a mass spectrometer at pressures of 10^{−4} mm Hg in the reaction chamber. With the special technique used here, collisions do not occur during the time between photon impact and primary‐product detection. The resulting products of illumination with a light continuum between 2200 and 1800 Å, which is produced by a pulsed high‐pressure argon flash lamp, are as follows: C_{3}H_{3} + CH_{3}; C_{4}H_{5} + H; C_{2}H_{4} + C_{2}H_{2}; C_{2}H_{3} + C_{2}H_{3}; and to a small amount, also C_{4}H_{4} + H_{2}. The quantitative probabilities for these five dissociation modes are derived from the measured ion spectrum of the neutral photodissociation fragments that is produced in the ion chamber of the mass spectrometer by electron impact. Some results concerning the original excited state and fragment energies are discussed.

Chemistry of Detonations. I. A Simple Method for Calculating Detonation Properties of C–H–N–O Explosives
View Description Hide DescriptionDetonation pressures of C–H–N–O explosives at initial densities above 1.0 g/cc may be calculated by means of the simple empirical equation , , , detonation velocities by the equation . is the number of moles of gaseous detonation products per gram of explosive, is the average weight of these gases, is the chemical energy of the detonation reaction, and is the initial density. Values of , , and may be estimated from the H_{2}O–CO_{2} arbitrary decomposition assumption, so that the calculations require no other imput information than the explosive's elemental composition, heat of formation, and loading density. Detonation pressures derived in this manner correspond quite closely to values predicted by a computer code known as RUBY, which employs the most recent parameters and covolume factors with the Kistiakowsky‐Wilson equation of state.

Chemistry of Detonations. II. Buffered Equilibria
View Description Hide DescriptionAt low loading densities, values of , , and calculated from the H_{2}O–CO_{2} “arbitrary” show poor individual agreement with estimates of these quantities from the RUBYcomputer code. Nevertheless, when substituted into the equation they lead to detonation pressures which correspond closely to RUBY predictions. That incorrect input information should yield results which are very nearly “correct” is rationalized on the basis that the equilibria whose shifting engenders the changes in , , and are “buffered” in the sense that “errors” in are offset by compensating “errors” in and . As a consequence of the fact that most of the important equilibria in the detonation of C–H–N–O explosives are buffered, calculated (and actual) mechanical properties of detonations appear to be extremely insensitive to exact product compositions. A number of other interesting consequences of these buffered equilibria are discussed.

Chemistry of Detonations. III. Evaluation of the Simplified Calculational Method for Chapman‐Jouguet Detonation Pressures on the Basis of Available Experimental Information
View Description Hide DescriptionIt is shown that the simplified calculational scheme discussed in Parts I and II of this series accomodates the total body of inexact and often self‐contradictory experimental information almost as well as might reasonably be expected of any computational method. Some possibly systematic discrepancies in the reported experimental C‐J pressures are discussed on the basis of methods used to carry out and interpret the measurements in the various laboratories.

Percus‐Yevick Equation Applied to a Lennard‐Jones Fluid
View Description Hide DescriptionAn efficient method of solving the Percus‐Yevick and related equations is described. The method is applied to a Lennard‐Jones fluid, and the solutions obtained are discussed. It is shown that the Percus‐Yevick equation predicts a phase change with critical density close to 0.27 and with a critical temperature which is dependent upon the range at which the Lennard‐Jones potential is truncated. At the phase change the compressibility becomes infinite although the virial equation of state does not show this behavior. Outside the critical region the PY equation is at least two‐valued for all densities in the range (0, 0.6).

Generalized Equation of Motion for a Gas Using the Quantum‐Mechanical Green's Function Technique. I
View Description Hide DescriptionThe quantum‐mechanical Green's function technique of Kadanoff and Baym is extended to include non‐Markowian effects in order to make contact with the results of Prigogine.

Applications of the Quantum‐Mechanical Green's Functions to the Study of Chemical Reactions. II
View Description Hide DescriptionStarting from a field theoretical representation of chemical reactions, the rate equation is developed in terms of the quantum mechanical Green's functions. The equation is valid for non‐Markowian behavior and the approximations that are necessary in order to obtain the conventional (Markowian) rate equation are investigated. The effect of finite collision times is also discussed.

Accurate Perturbation‐Variation Treatment of the Hydrogen Molecule
View Description Hide DescriptionA Rayleigh‐Schrödinger perturbation treatment of electron repulsion in the ground state of the hydrogen molecule is presented. The perturbation energies were accurately determined from Hylleraas‐type variational principles using a 50‐term basis. The perturbation series appears to converge rapidly at the equilibrium distance, in a similar fashion to the series for the united atom, helium, obtained by Scherr and Knight (1963). The electronic energy through fifth order is − 1.88872 hartree, which is comparable with the straight variational result of − 1.88876 obtained by Kolos and Wolniewicz (1964).

Magnetic and Crystallographic Characteristics of Praseodymium Hydrides
View Description Hide DescriptionThe susceptibilities (χ) and lattice parameters are reported for a series of praseodymium hydrides represented by the formula PrH_{ x } in which x varies from 0.99 to 2.57. _{χ} was measured from 4° to 300° and at field strengths up to 21 kOe. The samples are two‐phase for Curie–Weiss behavior is observed for all samples above 100°K with slopes in fairly good agreement with that expected for an assemblage of free tripositive ions. Deviations occur below 100°K. These are two kinds—negative for and positive for The deviations in the first case are small and appear to result from the crystal‐field interaction. The positive deviations are ascribed to a change of valence for Pr from 3 + to 4 +. Magnetic, electrical, and crystallographic evidence is in accord with this postulate. There is no indication of magnetic ordering in the hydrides at 4.2°K.

Yield of Solvated Electrons in the γ Radiolysis of Water + 10% Ethanol: Nonhomogeneous Kinetics of Electron Scavenging in Water
View Description Hide DescriptionThe effect of nitrous oxide concentration over a very wide range, and at low dose, on the radiolysis of the system water + 10% ethanol has been investigated. At very high concentrations compared to approximately 2.7 between 10^{−4} and 10^{−2} Mnitrous oxide. The results are discussed in terms of a nonhomogeneous kinetics model for the scavenging of solvated electrons, with . The free ion yield is . These values apply to both the present system and to pure water. The wide variation in previously reported values of is understandable in terms of the present model. The previously published model for charge scavenging in liquids [J. Chem. Phys. 46, 2822 (1967) ] has been moderately successful in describing charge scavenging in the γ radiolysis of hydrocarbons, alcohols, and water. This emphasizes the earlier suggestion that the behavior of extra electrons in nonpolar and polar liquids differs in degree but not in kind.

Simple Formulas for the Vibrational and Rotational Eigenvalues of the Lennard‐Jones 12‐6 Potential
View Description Hide DescriptionDunham expressed the term values of a generalized rotating vibrator as a double power series in the vibrational and rotational quantum numbers. Eighteen coefficients in this series have been evaluated for the Lennard‐Jones (12‐6) potential. The accuracy of the resulting term‐value formula has been tested by direct numerical solution of the radial equation and was found to be very good. The addition of a few empirical corrections for states lying close to the dissociation limit provides an eigenvalue predictor which is accurate to better than a part per million in the most favorable cases and never worse than a part per thousand. The range covered is from systems with only a single bound state to ones with more than ten thousand, e.g., the iodine dimer. When used to provide trial eigenvalues for Cooley's procedure for solving the radial equation, the predictor successfully discriminates between states separated from each other and from the dissociation limit by less than one part in 10^{5}. Simple formulas have also been derived for the zero‐point energy, the number of pure vibrational states, and the total number of bound states. Finally, it is shown that even fourth‐order WKB terms can make significant contributions for very light systems and that there is no indication that Dunham's series for this potential model fails to converge even for term values lying arbitrarily close to the dissociation limit.

Heat Capacity of Deutero‐Ammonium Bromide from 17° to 300°K
View Description Hide DescriptionThe heat capacity of deutero‐ammonium bromide has been measured from 17° to 300°K. The heat‐capacity curve is characterized by the appearance of two maxima. These are associated with polymorphic transitions in the crystal lattice and with the ordering of the ammonium ion tetrahedra with respect to the two equilibrium positions in the unit cell. The excess entropy associated with the maxima is found to be in agreement with the order‐disorder nature of the upper transition. A frequency of torsional oscillation for the ammonium ion in good agreement with infrared data is obtained from the Debye‐Einstein function representing the heat capacity below 100°K.

Studies of the Nitrogen Afterglow. I. Surface Catalytic Efficiency and Diffusion‐Controlled Decay of Atomic Nitrogen
View Description Hide DescriptionThe temporal behavior of the afterglow light intensity in decaying nitrogen plasmas, as well as that of the number density of N^{+}, N_{2} ^{+}, N_{3} ^{+}, and N_{4} ^{+} ions, was studied in the pressure range of about 0.1 to 1.7 torr. The analysis of the light intensity decay curves resulted in a method of measuring the surfacecatalytic efficiency for the recombination of nitrogen atoms at the plasma boundary. The simultaneous identification of the ions present in the plasma by means of a quadrupolemass spectrometer ensures that the data relate to pure nitrogen as well as to extremely clean surfaces. The values obtained for of molybdenum sputtered on a glass surface decreased with pressure from a value of 0.22 at 0.09 torr to 0.04 at 1.35 torr. The studies also showed that part of the afterglow light emission is due to collisions between metastable nitrogen molecules which are produced in the afterglow by the atomic volume recombination process.

Viscosity and Its Temperature Dependence in Molten BeF_{2}
View Description Hide DescriptionThe viscosity of molten beryllium fluoride has been measured with coaxial‐cylinder viscometers over five orders of magnitude (limits: 979°C, 28.6 P; 574°C, 2.24 × 10^{6} P). Over the experimental range of shear stresses, BeF_{2} behaves as a Newtonian fluid. Like SiO_{2}, its high‐temperature analog, BeF_{2} shows an Arrhenius temperature dependence over several orders of magnitude in viscosity. Reported heat‐capacity data for BeF_{2} and SiO_{2} and the Adam‐Gibbs theory indicate that the Arrhenius viscosity behavior of these liquids may be explained in terms of the configurational entropy which is virtually constant at temperatures above the glass‐transition temperature.

Calculation of the Effect of Non‐Brownian Motion on Some dc Transport Coefficients in Solution
View Description Hide DescriptionEffects of non‐Brownian motion on transport coefficients are found on the basis of a model in which the carrier undergoes random changes of state between two states of different mobility. The transport properties investigated are the electrical mobility, the Hall mobility, and the Onsager slope of the equivalent conductance. On the basis of these examples the relations among certain transport coefficients may be expected to be quite sensitive to the microscopic dynamics of the carrier.

Effect of Electric‐Field‐Gradient Inhomogeneity on Quadrupolar Satellite Intensities in Nuclear Magnetic Resonance Spectra in Solids
View Description Hide DescriptionA simple model of random electric‐field‐gradient inhomogeneity has been incorporated into the usual first‐order treatment of quadrupolar satellites in nuclear magnetic resonance spectra in solids. Observed departures of experimental intensities from those expected strictly on the basis of transition probabilities are satisfactorily accounted for on the basis of this model.

Magnetic Circular Dichroism of Benzene, Triphenylene, and Coronene
View Description Hide DescriptionThe magnetic circular dichroism of benzene, triphenylene, and coronene in regions of absorption (20 000‐45 000 cm^{−1}) are reported. The data support the conventional molecular‐orbital assignments of the absorption spectra. The lowest and states of triphenylene and coronene, respectively, are shown to be little affected by Jahn‐Teller perturbations. Magnetic moments are obtained for these states which are in good agreement with values calculated from the free‐electron network model and from molecular‐orbital wavefunctions if Löwdin orthogonalized atomic basis functions are employed.