bluuebunny/crossref_metadata_2025 huggingface dataset:
Attachment of Low-Energy Electrons to Oxygen
Authors: Conway D. C.
Published: January 2005

The experimental data on electron attachment in pure O2 and C2H4–O2, CO2–O2, N2–O2, CH4–O2, and He–O2 mixtures are reviewed. The results have been interpreted by a mechanism which is a modification of the Hurst and Bortner extension of the Bloch and Bradbury mechanism. The rate constants in the general rate equation are estimated and the equation is shown to be in general agreement with the reaction orders which have been obtained. The CO2 and C2H4 data lead to a value for the mean life of O2—* against electron detachment of 1×10—9 sec. The various reactions are discussed in some detail. The number of collisions required to stabilize O2—* has been estimated from the experimental data and compared with the theoretical estimate of the rate of vibrational deactivation for each of the molecules studied.
Shock-Tube Study of the Vibrational Relaxation of Nitric Oxide
Authors: Wray Kurt L.
Published: January 2005

The vibrational relaxation time of nitric oxide in NO–Ar mixtures was determined over the temperature range 1500°—7000°K. An ultraviolet absorption technique using 1270-A radiation was employed to monitor the vibrational temperature as a function of time after these mixtures were shock heated to high translational temperatures. P10, the transition probability per oscillator per collision for transition between vibrational levels 1 and 0 calculated from the measured relaxation times ranged from 1.0×10—3 at 1500°K to 2.8×10—2 at 7000°K for NO–NO collisions. Argon is about 1/50 as efficient as NO. The results are compared with the lower temperature (400°—1500°K) work of Robben and with the adiabatic theory of Schwartz, Slawsky, and Herzfeld and the nonadiabatic theory of Nikitin.
Unimolecular Decomposition of Vibrationally Excited Ethane and Ethyl Radicals
Authors: Heller Carl A. , Gordon Alvin S.
Published: January 2005

H or D atoms and ethyl radicals were concurrently produced by the mercury sensitized photolysis of mixtures of H2 (or D2) and diethyl ketone. Combination of an ethyl radical with a hydrogen atom produces vibrationally excited ethane molecules. Their rate of dissociation into methyl radicals relative to stabilization to ethane was studied as a function of pressure of ketone for both H and D.

Similar studies were made of the mercury sensitized reactions of mixtures of D2 or H2 and ethylene, which permitted the measurement of the maximum rates of decomposition of excited ethyl radical and of excited ethane both as a function of pressure and of temperature.

Our results show that vibrational energy is not used in overcoming the barrier for alkyl radical addition to an olefin bond.
Ultrasonic Absorption in an Electrolytic Solution with a Mixed Solvent
Authors: Yun S. S. , Beyer R. T. , Dill M. W.
Published: January 2005

The ultrasonic-absorption coefficient has been measured by pulse techniques in solutions of 0.05 and 0.02 molal MgSO4 for pure-water solvent and for various mixtures of methanol and water, up to 70% methanol by weight. The high-frequency relaxation peak decreases steadily in frequency with increase in methanol, while the height of the peak rises to a maximum and then decreases. An attempt is made to interpret these findings in terms of the dissociation model. Inadequacies in available chemical data prevent a satisfactory detailed comparison with theory.
Transport Properties of Polar-Gas Mixtures
Authors: Mason E. A. , Monchick L.
Published: January 2005

A previously proposed model for the calculation of viscosity, diffusion, and thermal diffusion in dilute polar gases is extended to mixtures. A simple set of combination rules for the potential parameters is discussed. Available data limit the comparison of calculation and experiment to binary mixtures of a polar and a nonpolar gas. The agreement exhibits a success comparable to that obtained for models and combination rules involving only nonpolar gases. It is concluded that the present model and combination rules can be used to describe the transport properties of mixtures with a fair measure of success, and that any attempts to refine the combination rules should await more experimental results of high accuracy, especially results on thermal diffusion and diffusion.
Enthalpy of Formation of Oxygen Vacancies in Barium Oxide
Authors: Holloway H.
Published: January 2005

An estimate is made of the enthalpy of formation of oxygen vacancies in barium oxide. This estimate is derived from known thermochemical data together with published data on defect equilibria and on the electronic work function of barium oxide. The result provides confirmation of previously published calculations based on the method of Mott and Littleton.
Infrared Spectra of Crystalline C2H4 and C2D4
Authors: Dows David A.
Published: January 2005

High-resolution infrared spectra of crystalline ethylene and fully deuterated ethylene have been obtained. Accurate frequencies of all band components observed at 65°K are presented. Appearance of one gas-phase inactive fundamental in the crystal spectrum, and the structures of certain multiplets, shows that the presently accepted crystal structure is not correct. This conclusion is in agreement with that from a previous study under lower resolution.
Organic Liquid Scintillators. III. On the Quantum Yield of Fluorescence and the Quenching of Fluorescence by Oxygen
Authors: Heller Adam
Published: January 2005

Expressions for the quantum yield of fluorescence of aromatic hydrocarbons in benzene and alkylbenzenes have been derived assuming zero internal quenching. These expressions indicate that the molecular quantum yield of fluorescence increases with (a) the lifetime of the first excited singlet state of the solvent, (b) the transition probabilities from the levels of the solute that correspond to the levels involved in the excitation of the solvent [A. Heller, J. Chem. Phys. 35, 1980 (1961)], and (c) the increase in the degree of degeneracy in the solute levels corresponding to those involved in the excitation of the solvent.

Minimum values of the molecular quantum yield of fluorescence of a group of aromatic hydrocarbons have been computed at different concentrations of the solutes. The compounds with the highest values are p-divinylanthracene, perylene, p-quaterphenyl and p-terphenyl.

The dimensions of the excited aggregates that are formed by the exchange interaction between the molecules in liquid or plastic scintillators are estimated from Basile's data for solutions of PBD in polyvinyltoluene [L. S. Basile, J. Chem. Phys. 27, 803 (1957)]. The number of monomer units per aggregate is about 1.2×103 and the radius of interaction about 18 A.

The quenching of fluorescence by oxygen is explained by the existence of π-electron level pairs of almost similar energy difference in the solvent and the solvent—oxygen complex [H. Tsubormura and R. S. Mulliken, J. Am. Chem. Soc. 82, 5966 (1960)], and by the short lifetime of the complex compared with that of the solvent. The latter results from the lower order of symmetry of the complex in comparison with that of the π-electron system in benzene.
Structure of the Triplet Bands of CO
Authors: Carroll P. K.
Published: January 2005

The 3–0 band of the CO ``triplet'' system has been photographed under high resolution and a rotational analysis carried out. The upper state is shown to be 3Δ in agreement with electron-configuration theory and not 3Π as indicated by previous work. The spin structure in the 3Δ state has been studied and the intensity distribution in the branches is discussed. Revised constants for the d3Δ state are given.
Decomposition of (CH3Xe131)+ Following the Nuclear Decay of CH3I131
Authors: Carlson T. A. , White R. M.
Published: January 2005

The charged fragments resulting from the decay of CH3I131 have been measured by a specially designed mass spectrometer. In 70% of the decays, the parent ion CH3Xe+ remained intact in direct contrast to the decay of CH3T in which hardly any CH3He+ was found [A. H. Snell and F. Pleasonton, J. Phys. Chem. 62, 1377 (1958)].

More than 20 other ions were also detected including the doubly charged methyl xenon (CH2Xe)+2. Their relative abundances are discussed in terms of excitation resulting from the sudden change in nuclear charge, and from multiple Auger processes in cases where internal conversion accompanies the decay.
Vibrational Spectra of MoF6 and TcF6
Authors: Claassen Howard H. , Selig Henry , Malm John G.
Published: January 2005

Infrared spectra of gaseous MoF6 and TcF6 from 6–43 μ, the Raman spectrum of MoF6 gas, and an incomplete Raman spectrum of liquid TcF6 are reported. These are interpreted in terms of the octahedral point group 0h. The fundamental frequencies for MoF6 are 741(ν1), 643(ν2), 741(ν3), 264(ν4), 306(ν5), and 190(ν6). For TcF6 they are 705(ν1), 551(ν2), 748(ν3), 265(ν4), 255(ν5) and ν6 has not been determined.

Differences between the spectra of MoF6 and TcF6 are explained as a consequence of orbital degeneracy in the ground state of the latter, in analogy with similar differences in the 5d series.
Diffusion of Transition Metal Ions in Single-Crystal MgO
Authors: Wuensch B. J. , Vasilos T.
Published: January 2005

Diffusion coefficients for transition metal ions in single-crystal MgO have been determined in the temperature range 1000°-1850°C. from concentration distributions obtained with the aid of x-ray absorption analysis and electron microbeam probe spectroscopy. The variation of the diffusion coefficients with temperature yields D0 = 8.83 (10)-5, 5.78 (10)-5, and 1.80 (10)-5 cm2/sec and activation energies for diffusion of 1.81, 2.06 and 2.10 electron volts for Fe2+, Co2+, and Ni2+, respectively. It is found that the activation energy for diffusion increases exponentially with the ratio ionic radius/ionic electronic polarizability for the diffusing cation and that D0 increases exponentially with the cation radius cubed. This correlation suggests that the diffusion mechanism for all three ions is the same and that self-diffusion in MgO takes place via the same process.
Rate and Pressure Effects in Polymers and Other Glass-Forming Substances
Authors: Bueche F.
Published: January 2005

A simplified normal coordinate computation for the thermal vibrations of molecules in a liquid has been carried out. From the result, the size distribution of voids or holes in the liquid is computed, and this distribution is then used to compute the diffusion constant. The result for low temperatures is a modified Doolittle equation. An analog to the WLF rate-process equation is also obtained. It is shown that the concept of free volume arises quite naturally in this formalism. Thermal expansion and compressibility constants are also calculated. A treatment of the rate of thermal contraction at low temperatures leads to a precise meaning for the glass temperature in terms of the parameters of the molecular system. The effects of applied pressure on glass temperature and rate processes are derived. Results of the theory are compared with experiment and, in general, are found to be fairly satisfactory.
Studies of the Shapes of Ionization-Efficiency Curves of Multiply Charged Monatomic Ions. I. Instrumentation and Relative Electronic-Transition Probabilities for Krypton and Xenon Ions
Authors: Kiser Robert W.
Published: January 2005

The determination of threshold ionization potentials for multiple ionization processes in krypton and xenon is shown to depend upon the threshold law assumed for these processes. Support has been obtained for the kth power rule for k-fold ionization by electron impact. Ionization potentials have been obtained for multiple ionization in these gases. It was found that the output electron current of the magnetic electron multiplier, obtained for the multiply charged positive ions, depends strongly upon the charge of the ion impinging upon the ion cathode of the multiplier.
Matrix Formulation of Copolymerization Statistics
Authors: Peller Leonard
Published: January 2005

The molecular distribution statistics of a binary linear copolymer are developed by the application of matrix methods appropriate to the treatment of the statistical thermodynamics of one-dimensional systems. Through the definition of a matrix of sequential probabilities, the character of the copolymerization, the various average degrees of polymerization, and the relative probabilities of certain kinds of sequences can be readily obtained. The results are applied to a number of ``most probable'' copolymerizations: For example systems in thermodynamic equilibrium and radical copolymerizations in the steady-state approximation. The question of stereoregularity in the latter case is also examined. Some generalizations of the approach are discussed.
Open-Shell Calculations of Hyperfine Splitting for the Ground State of Li-Like Ions
Authors: Kerwin J. , Burke E. A.
Published: January 2005

The hyperfine splitting of the ground state of lithium is calculated using analytic open-shell wavefunctions. The difference in the experimental and calculated value for the Li7 nucleus by this method is 36.468 Mc/sec as compared to a difference of 57.011 Mc/sec using Hartree-Fock wavefunctions.

The nuclear-spin-independent contribution to the hyperfine splitting is computed for the Li-like ions He— to Ne7+ using both open- and closed-shell wavefunctions, and the results are discussed with reference to contributions from the orbital and core electrons.
Metallic Cohesion and Vibration Spectrum of Copper
Authors: Dayal B. , Tripathi B. B.
Published: January 2005

A new method of setting up a secular determinant for copper has been described in which the ion—ion force constants are not based on hypothetical force models but have been derived from known expressions appearing in the theory of metallic cohesion. Numerical calculations have been made for copper. The Coulomb coupling coefficient has been taken from Kellermann's work on sodium chloride, while the contribution of the ion—ion exchange has been calculated from Fuchs' force constants. The single elastic constant due to the remaining terms of the interaction has been calculated, and has been used to find an expression for the electronic coupling coefficient on the lines of Bhatia's work. There is good agreement between the calculated frequencies for the longitudinal 110 branch and the experimental ones observed in neutron scattering. The calculated θ-T curve is found to be about 6%—7% higher than the experimental curve. This is due to the fact that the repulsive force constant of Fuchs is definitely an overestimate and gives higher value of C44. If this constant is calculated from observed value of (C11–C12) and C44, the calculated curve will almost coincide with the experimental one without spoiling the agreement with the results of neutron scattering.
d-Orbital Involvement in BrCl and ICl
Authors: Whitehead M. A.
Published: January 2005

An attempt is made to solve for the s-hybridization s and ionic character i of the halogens in BrCl and ICl from NQR data. It is shown that ignoring d hybridization gives untenable estimates of s and i. A tentative estimation of the d character is made.
Self-Diffusion in Liquid Tin
Authors: Ma C. H. , Swalin R. A.
Published: January 2005

Self-diffusion in liquid tin has been measured by the capillary-reservoir technique covering a temperature range of over 700°C. Considerable deviation of the data from linearity on a log D versus 1/T plot was found which is of the general type predicted on the basis of a fluctuation theory proposed by one of the authors. The curvature is believed to be significant in view of the effort which was made to minimize the problem of convection at the high temperatures. The low-temperature data are found to be in agreement with the results obtained by Careri et al. which were obtained by a somewhat different experimental technique.
Spectroscopy in Liquid-Rare-Gas Solvents. Infrared Spectra of CH4 in Argon and of HCl in Xenon
Authors: Kwok Joel , Robinson G. Wilse
Published: January 2005

A low-temperature cell employing barium fluoride windows and indium metal gaskets has been built and is being used for the study of rotational, vibrational, and electronic motions of molecules in liquid rare gases. The ν3 fundamental of CH4 in liquid argon shows a single, relatively sharp Q branch. The P and R branches are probably present but apparently are lost in the wings of the Q branch. The infrared spectrum near 3.5 μ of HCl in liquid xenon shows well-resolved P, Q, and R branches, but the individual rotational lines are not resolved. The O branch is not resolved from the tail of the P branch, but there is some indication of the S branch on the high-frequency side of the spectrum. The Q branch is shifted 36 cm—1 to the low-frequency side of its gas-phase position. The appearance of O, Q, and S branches is expected because of the presence of an induced dipole moment through the polarizability of the solvent. The agreement between the observed spectrum and that anticipated on the basis of nearly free rotation gives good evidence for the existence of quantized rotational motions of HCl in liquid xenon.
Electron Paramagnetic Resonance Spectra of Copper Complexes
Authors: Gersmann H. R. , Swalen J. D.
Published: January 2005

The electron paramagnetic resonance spectra of a number of copper complexes and of vanadyl acetylacetonate were measured in solution and in the vitreous state. By a judicious choice of various mixtures of solvents, good glasses could be obtained at low temperature, which exhibited spectra with very sharp lines. In a number of cases a complete analysis of the spectrum was possible. We were then able to calculate the magnetic parameters and some properties of the wave functions by assuming either D4h or D2h symmetry. It appears that the vitreous state is well suited for a study of ligand interaction. A hyperfine splitting due to the magnetic moment of nitrogen ligand atoms could often be observed in the vitreous state when it could not be observed in the liquid state. Relaxation of ligands is qualitatively discussed.
Second Virial Coefficient of Polyelectrolytes. I
Authors: Ise Norio
Published: January 2005

The second virial coefficient of polyelectrolytes at the limit of zero polymer concentration was studied using an interionic interaction theory based on a spherical model for macro-ions. A formulation of the polyelectrolyte—polyelectrolyte interaction parameter β22 is presented. A simple relation for the Donnan equilibrium, which was originally found with a rod-like model, and which is related to the simple electrolyte—polyelectrolyte interaction parameter β23 is discussed. It is shown, for poly(sodium phosphate)—sodium bromide—water system, that the second virial coefficient, which is given as a function of β23 and β22, can be described satisfactorily with two adjustable parameters, the dimension of macro-ions R and its polymer concentration dependence ∂R/∂n2. From the observed value of second virial coefficient, ∂R/∂n2 is found to be positive at the limit of zero polymer concentration, in contrast to the negative values of the derivative at higher concentrations. The polymer concentration dependence of the osmotic effect is shown to be consistent with a positive value for ∂R/∂n2.
On the Theory of Energy Exchange in Liquids by Isolated Binary Encounters
Authors: Herzfeld Karl F.
Published: January 2005

Litovitz and Herzfeld have given reasons for the belief that the exchange of internal vibrational and of external energy in Kneser liquids is determined by isolated binary encounters. Fixman and Zwanzig have raised objections against their calculations, Fixman by introducing Brownian motion type forces, Zwanzig by emphasizing the interference between subsequent events. The present paper tries to show that these objections are not justified in most cases.
Low-Frequency Fundamentals of Some Metal Carbonyls
Authors: McDowell Robin S. , Jones Llewellyn H.
Published: January 2005

The carbon-metal-carbon bending fundamentals of several metal carbonyls have been determined by the analysis of their combinations with the carbonyl stretching frequencies near 5 μ and by direct observation in the far infrared (60–120 cm—1). The following vapor-phase frequencies were obtained (in cm—1): Fe(CO)5: 104 (A2″), 114 and ∼68 (E′), 95 (E″); Ni(CO)4: 74 (F2), 68 (E); Cr(CO)6: 98 (F1u), 90 (F2g); Mo(CO)6: 81 (F1u), 81 (F2g); W(CO)6: 81 (F1u), 83 (F2g).
Rare-Gas Molecule-Ion Formation by Mass Spectrometry. Kinetics of Ar2+, Ne2+, and He2+ Formation by Second- and Third-Order Processes
Authors: Dahler J. S. , Franklin J. L. , Munson M. S. B. , Field F. H.
Published: January 2005

The ions Ar2+, Ne2+, and He2+ are formed in a mass spectrometer operated at high pressures (up to 300 μ) by the bimolecular excited atom reaction R*+R=R2++e, and Ar2+ and Ne2+ are formed by the termolecular ion-molecule reaction R++2R=R2++R. In helium, while He2+ is formed by a third-order process, there is doubt that an ionic reaction is involved.

Ratios of the rates (cross-sections) for excitation leading to R2+ formation and ionization are found to be 5.5×10—2, 1.0×10—2, and 6.4×10—2 for argon, neon, and helium. The measurements were made at nominal electron voltages (EV) of 15, 20, and 22 v, respectively, which correspond to maximum excitation. Values of 1.4×10—2 and 0.45×10—2 were also obtained at EV=70 v for argon and neon.

The experiments yield only the product of the bimolecular rate constant and the lifetime of the R* reactant atom (krτu), and the values of this product obtained at EV=15, 20, and 22 v are for argon, neon, and helium 3.6×10—16, 11.6×10—16, and 0.58×10—16 cc/molecule. At EV=70 v values of 2.7×10—16 and 1.1×10—16 cc molecule are obtained for argon and neon. Speculations are given concerning the magnitude of the lifetimes of R*, and it is concluded that values of about 10—8 sec must be considered as possible. The corresponding cross sections for the reaction forming R2+ lie in the range 1000–10 000×10—16 cm2.

The rate constants for the formation of Ar2+ and Ne2+ by the three-body process are, respectively, 2.1×10—28 and 2.0×10—29 cc2/molecule2sec. It is recognized that values as large as these are in disagreement with values inferred from pulsed-discharge ion-drift velocity experiments. A possible mode of reconciliation is suggested; namely, at sufficiently high pressures collisional decomposition of R2+ ions formed by the termolecular process occur in the drift-velocity experiments.
Ionizing Collisions of Metastable Helium Atoms in Gases
Authors: Sholette W. P. , Muschlitz E. E.
Published: January 2005

Ionization cross sections for collisions of metastable 23S and 21S He atoms in Ar, Kr, Xe, H2, O2, N2, and CO have been measured using a thermal-energy atomic beam in which a fraction of the helium atoms are excited by electron bombardment. Ions produced in these gases by inelastic collisions were detected at a metal electrode, and unscattered or elastically scattered metastable atoms were detected by observing the electrons they ejected from metal surfaces. Within the experimental error of the measurements, the cross sections for the triplet and singlet states of helium were the same in all cases except that of H2. For the rare gases, the results indicated that the size of the struck particle is the primary factor in determining the cross section for ionization, rather than the energy excess. In the case of the diatomic molecules an additional consideration, that of the number and type of ionization processes possible, was also found to be important.
Thermodynamic Functions at Liquid—Vapor Transition Range of the van der Waals, the Berthelot, and the Dieterici Equations of State
Authors: Ree Francis H.
Published: January 2005

The vapor pressure, the volumes of liquid and vapor at the liquid—vapor phase equilibrium, the heat of vaporization, the internal energy, and the entropy changes at the phase transition are obtained with the use of the van der Waals, the Berthelot, and the Dieterici equations of state by imposing the condition that the work done in an isothermal reversible cyclic process is zero. The results show that: (1) The vapor pressures obtained by using the van der Waals equation agree closely with the experimental data for Ar, Kr, and Xe from the triple point to the critical point, and there is an inflection point when the logarithms of the pressures are plotted against the reciprocal absolute temperatures as observed in saturated hydrocarbons; (2) Berthelot's equation of state describes fairly well the existing data of liquid and vapor densities at the liquid—vapor phase equilibrium for Ar, Kr, Xe, N2, O2, CO, and CH4; (3) none of these equations describes properly the heat of vaporization of inert gases. Formulas for the above thermodynamic quantities are given as a function of temperature by fitting the numerical results to a certain set of equations.
Structure of Water and Hydrophobic Bonding in Proteins. II. Model for the Thermodynamic Properties of Aqueous Solutions of Hydrocarbons
Authors: Némethy George , Scheraga Harold A.
Published: January 2005

The model proposed in the preceding paper for the theoretical derivation of the thermodynamic parameters of liquid water is extended to a treatment of the structure and the thermodynamic behavior of aqueous solutions of hydrocarbons. It is shown that the net intermolecular interaction energies of the solute with non-hydrogen-bonded water molecules differ from the interaction energies with the water molecules participating in the formation of hydrogen-bonded clusters. The differences are reflected in a change of the coordination number of the hydrogen-bonded water molecules near the solute. As a result, the amount of hydrogen bonding of the water in the immediate neighborhood of the solute is increased over its average value in pure water. The hydrogen-bonded clusters extend around part of the solute molecule, resulting in the formation of an incomplete cage. Equations are derived, expressing the mole fractions of molecular species of water having various numbers of hydrogen bonds within the first layer next to the solute. The partition function derived earlier for liquid water is modified in order to describe the water in this first layer. It is used to compute the contribution of the structural changes of water in this layer to the total free energy of solution. The contribution of the solute to the free energy is estimated in terms of changes in molecular configuration and van der Waals interactions when the solute is transferred from a nonpolar environment into water. The number of water molecules in the first layer surrounding the hydrocarbon, and the magnitude of the various intermolecular interaction energies, are introduced as variable parameters; their values used in the computations are shown to be of physically reasonable magnitude. The standard free energies, enthalpies, and entropies of solution are calculated for the normal saturated aliphatic hydrocarbons containing 1 to 8 carbon atoms, and for benzene and several of its homologs within the temperature range from 0° to 70°C. Observed values available for the same quantities in the literature are summarized and analyzed. The calculated thermodynamic parameters are shown to be in good agreement with the limited number of experimental data. The model also explains the unusually high heat capacity of the solutions discussed; the values calculated are in fair agreement with the available experimental data. The use of the term ``increased ice-likeness'' for the characterization of the changes occurring in the formation of aqueous solutions of nonpolar substances is shown to be justified on the basis of the model. The volume changes of solution are derived semiquantitatively, and an estimate of the volume change is given. Possible extensions of the method to other classes of nonpolar solutes are indicated.
Suggestion for the j Dependence of Some of the Results of Jaffe and Co-workers
Authors: Englman Robert
Published: January 2005

The limitation on the validity of the impact theory formula has the consequence that the shift in the vibration-rotation transition (1–0, 2–0 bands, P and R branches) lines of HCl due to the pressure of noble gases is j dependent. For high j there is a constant limit shift. For the light noble gases agreement with the data may be reached by taking into account a repulsive potential due to overlap.
Higher-Order Rotation-Vibration Energies of Polyatomic Molecules. VI
Authors: Grenier-Besson Marie-Louise , Amat Gilbert , Nielsen Harald H.
Published: January 2005

When resonance between vibration frequencies of polyatomic molecules sets in, the contact-transformation method proposed by Shaffer, Nielsen, and Thomas is not directly applicable. It has been shown by Nielsen that a contact transformation method may still be used to advantage when computing rotation-vibration energies to a second order of approximation, the transformation function being, however, a modified one. This problem is treated here when the question of the computation of the rotation-vibration energies is extended to a fourth order of approximation.
Lifetime of the Lowest Excited Level of N2
Authors: Carleton N. P. , Oldenberg O.
Published: January 2005

We have measured the probability of transition of the forbidden Vegard—Kaplan system (A3Σ—X1Σ) in N2, working from the definition of this probability as the ratio of number of photons emitted per second to number of excited molecules, both measured in the same discharge. We measure the absolute intensity of the 0,6 Vegard—Kaplan band as emitted from the discharge. Under identical conditions we find the population of molecules in the A3Σ level by measuring the strength of absorption of the 1,0 first positive band. By calculation we relate the observed loss (which is a sum of absorption by all rotational levels) to the absolute population of the excited level, in terms of the probability of transition of the first positive system. Our measurements of absorption and emission give a value of (1.6±0.4) × 106 for the ratio of the transition probability of the first positive system to that of the Vegard—Kaplan system. From recent shock-tube measurements of the former transition probability we obtain a value of 2.0(±0.9) sec for the lifetime of the A3Σ state of N2.
High-Temperature Evaporation and Thermodynamic Properties of Zirconium Diboride
Authors: Leitnaker James M. , Bowman Melvin G. , Gilles Paul W.
Published: January 2005

Vapor pressures of zirconium over zirconium diboride have been measured by the Knudsen technique over the temperature range 2150° to 2475°K. A new type of apparatus was constructed and used successfully in the study.

Zirconium diboride was determined to evaporate congruently at a composition of ZrB1.906(+0.025 or —0.010) by heating solid pressed plugs of both zirconium-rich and boron-rich material to constant composition at 2400°C to 2500°C. The over-all reaction is ZrB1.906(s)=Zr(g)+1.906 B(g)Three series of measurements were made using tungsten crucibles and different orifice sizes. Second-law and third-law treatments of the data did not agree. Thermodynamic calculations were made which indicated that water vapor at low background pressures would produce volatile oxides of both zirconium and boron. This reaction was investigated by adding water vapor to the system and the increased transport of zirconium was clearly demonstrated. Accordingly, each pressure measurement was corrected by a factor β, constant for each series, related to the background pressure.

From the corrected pressures, values of ΔH0o for the reaction were computed by the third-law treatment. From the three series a vaporization coefficient of 0.025±0.010 was computed, leading to an equilibrium ΔH0o of 458.3±6.5 kcal/mole for reaction 1, or a partial pressure of Zr over ZrB1.906 of 2.38×10—10 atm±20% at 2000°K. The variance between this and an expected value of 477.4 kcal/mole is presumed to be related, at least in part, to discrepancies in the heat of vaporization of zirconium.

The results verify the prediction that the Zr–B system exhibits a congruently evaporating phase and suggest that the congruently evaporating composition in many high-temperature systems will occur at nonstoichiometric compositions.
Fluorescence Spectrum and the Energy Levels of the Sm2+ Ion
Authors: Dieke G. H. , Sarup R.
Published: January 2005

Sm2+ which occurs as impurity in very small concentrations in LaCl3 has a very distinctive fluorescence spectrum which resembles in all details that of Eu3+. Excitation is through the very strong continuous absorption to 4f55d in the visible. The energy is transferred to the stable states 5D0 and 5D1 of the 4f6 configuration separated by 1330 cm—1 from which emission to the components of the ground multiplet 7F is observed. The fact that in all cases the spatial degeneracy is completely removed shows that the field around the Sm2+ ion has low symmetry even though the La3+ ion which it replaces is in an hexagonal field.
ESR Linewidths in Dilute Hexaaquomanganese(II) Solutions at 9.4 and 24 kMc
Authors: Nolle A. W. , Morgan L. O.
Published: January 2005

The electron spin resonance linewidth for Mn(H2O)6++ in aqueous solution is examined in the temperature range 15° to 90°C, at frequencies of 9.4 and 24 kMc. The results are interpreted on the assumption that the linewidth is a measure of the spin-lattice relaxation rate. As expected from previous NMR measurements of proton nuclear relaxation in such solutions, the linewidth decreases with increasing temperature, and is smaller at 24 kMc than at 9.4 kMc. The ESR results are approximately in agreement with the NMR results if the electronic relaxation time is assumed to follow a Bloembergen equation with the correlation time behaving with temperature according to an activation energy of 2.5 kcal/mole.
Electron-Molecule and Electron-Atom Collision Cross Sections from a Cyclotron Resonance Study of Flame Gases
Authors: Bulewicz E. M.
Published: January 2005

Low-pressure (6–40 mm Hg) acetylene-oxygen flames, diluted with various proportions of nitrogen and the rare gases, were investigated. The temperature range covered was 1600–2400°K. At 2200°K, the following results were obtained for the collision cross sections: undiluted, near-stoichiometric C2H2–O2 flame gases, 40 A2; nitrogen 30 A2, decreasing with temperature; helium, 27 A2, decreasing with temperature; argon, 7 A2; neon, 5 A2; water, about 80 A2; carbon dioxide about 37 A2. These values are up to three-fold larger than the cross sections for collisions with electrons reported for systems other than flame gases.
Experimental Oscillator Strength of the Violet System of CN
Authors: Bennett R. G. , Dalby F. W.
Published: January 2005

The radiative mean lifetime of the upper electronic state (B2Σ) of the violet system of CN has been measured to be (8.5±1.)10—8 sec, corresponding to an oscillator strength f=(2.7±0.3)10—2. These results include contributions, of undetermined weights, from the (0, 0) through (4, 4) vibrational transitions.
Compression and Phase Transitions of Solid HCl, HBr, SiH4, and SF6
Authors: Stewart John W.
Published: January 2005

Isothermal PV curves for solid HCl, HBr, SiH4, and SF6 have been determined by the direct piston displacement method up to pressures of 20 000 kg/cm2 at various temperatures between 50° and 190°K. Relative volume changes (and in some cases molar volumes) and compressibilities have been calculated for each substance. Phase transitions have been observed as discontinuities in the piston motion. First-order transitions have been observed in solid HCl, SiH4, and SF6. Phase diagrams are included. The expected second-order transition in solid HBr was not noted, probably because of impurities in the samples. The approximate volume changes accompanying the observed transitions have been determined. Their consistency with other data has been checked by means of the Clausius-Clapeyron equation.
Molecular Conformation in Oriented Fibers
Authors: Tobolsky A. V. , Gupta V. D.
Published: January 2005

A molecular model for an oriented fiber is presented. Using the mathematical method of the Markoff chain, values for the percent crystallinity, sequence length in amorphous and crystalline regions, and expressions for the dimensions of the molecular chains are presented in terms of two probability parameters.
Elementary Derivation of the Dielectric Constant of an Imperfect Gas
Authors: Kaufman Allan N. , Watson Kenneth M.
Published: January 2005

A general formula for the ``second Clausius-Mossotti coefficient'' is obtained from elementary considerations of statistical mechanics.
Intensities of Vibrational and Rotational Spectra of Charged Diatomic Molecules
Authors: Ellison Frank O.
Published: January 2005

It is shown that there exists a contribution to the transition moment (and hence to the spectral intensity) associated with pure rotational and with vibration-rotational transitions which is proportional to the net charge residing on the molecule and to the difference in masses of the nuclei. Hence, molecule-ions such as HD+ and (Cl35Cl37)+ should absorb and emit dipole radiation with significant intensity in the vibrational and rotational spectral regions.
Sound Dispersion in Ethane-Ethylene Mixtures and in Halo-Ethane Gases
Authors: Valley L. M. , Legvold Sam
Published: January 2005

Sound dispersion is examined in ethane-ethylene mixtures, in three halo-ethane gases, and in a C2H6–CH3CHF2 mixture—all at room temperature. Double dispersion is observed whenever ethane is present and single dispersion for all other gases. The relaxation times and collision lifetimes are reported along with some discussion on the effectiveness of ethane-ethane versus ethane-ethylene collisions. For the halo-ethane gases the exchange mode used should be the lowest mode of ``regular'' vibration, not the mode of hindered rotation. The free flow of energy that occurs between modes of vibration in the same molecule does not occur between the modes of vibration of two different molecules (C2H6–CH3CHF2) while in collision.
Magnetic Susceptibilities of Crystalline Stable Free Radicals in the 77–293°K Temperature Range
Authors: Duffy William
Published: January 2005

The powder susceptibilities of crystalline stable free radical samples of picryl-n-amino carbazyl, Wurster's blue, DPPH and 1,3-bisdiphenylene-2-phenyl allyl have been measured as a function of temperature from 77–293°K. All exhibit negative paramagnetic Curie points with values in the range —51° to —6°K. For Wurster's blue, the Néel temperature is found to be 186°K.
Infrared Spectra of Ammonia Suspended in Solid Nitrogen
Authors: Pimentel George C. , Bulanin Mikhail O. , Van Thiel Mathias
Published: January 2005

Matrix isolation studies of the infrared spectra of ammonia suspended in solid nitrogen at 20°K are presented. Variation of the mole ratio of nitrogen to ammonia shows that monomeric NH3 in solid nitrogen absorbs at 3440, 3332, 1620–1632, 1143, and 970 cm—1. A large enhancement of ν3, 3440 cm—1, occurs relative to ν1, 3332 cm—1, just as observed for the pure solid. The totally symmetric vibrations ν1 and ν2 are relatively sharp (half-widths are 1 and 1.5 cm—1, respectively). The umbrella mode ν2 shows no evidence of inversion nor of free rotation. The band at 1143 cm—1 is ascribed to ν2 in combination with librational movement about the B axes. The constraints to movement within the nitrogen matrix cage seem to be larger than those reported for inert-gas matrices.

Some results on the hydrogen bonding in dimeric and polymeric ammonia are reported. The dimer absorbs at 3404, 1004.5, 987 cm—1 and possibly as well at 3313, 3246 and 3237 cm—1.
Influence of Ion Size upon the Intensity of Eu3+ Fluorescence in the Tungstates
Authors: Van Uitert L. G. , Soden R. R.
Published: January 2005

The emission intensities of the rare-earth ions in inorganic compounds are sensitive to changes in structural parameters, the charge type of the cations, and rare-earth concentration. Comparisons of the fluorescence of Eu3+ in a number of related tungstates show that under long-wave ultraviolet excitation comparable series (M2+ tungstates or M0.5+M0.53+ tungstates with a fixed Eu3+ content) show a logarithmic dependence of emission intensity upon the average volume of the ions in the structure.
Rotational Energy Levels of a Linear Triatomic Molecule in a 2Π Electronic State
Authors: Hougen Jon T.
Published: January 2005

Expressions are derived for the rotational energy levels of a linear triatomic molecule in a 2Π electronic state which take into account a spin orbit interaction and a vibronic Renner interaction. The results are valid when both interactions are small compared to the bending vibrational frequency. The similarities and differences between the expressions obtained and the corresponding expressions for diatomic molecules are discussed.
Electron Spin Resonance of Tetraphenylpyrryl Radical
Authors: Blinder S. M. , Peller M. L. , Lord N. W. , Aamodt L. C. , Ivanchukov N. S.
Published: January 2005

The free radical 2,3,4,5-tetraphenylpyrryl in dilute, oxygen-free solution gives an electron spin resonance rich in hyperfine structure. The principal features of the spectrum are seven peaks in a binomial intensity distribution. These are attributed to approximately equal isotropic hyperfine interactions with the six ortho and para protons of the 2- and 5-phenyl groups. A molecular-orbital computation of spin densities in the pyrryl ring is qualitatively consistent with this result. The radical concentration may be enhanced by ultraviolet radiation but subsequently decays toward its original value with second-order kinetics. It is postulated that: (i) the radical dimerizes spontaneously until an equilibrium between radical and dimer is established; (ii) the dimer may undergo photodissociation back to the radical.
Effect of Temperature on the Structure of Gaseous Molecules. Molecular Structure of PCl3 at 300° and 505°K
Authors: Hedberg Kenneth , Iwasaki Machio
Published: January 2005

The molecular structure of PCl3 has been studied by electron diffraction from the vapor at nozzle temperatures of 300° and 505°K. Both the size of the molecule and the displacement of the atoms during molecular vibration are found to be significantly greater at the higher temperature: The P–Cl and Cl···Cl distances are longer by 0.3 and 0.4%, respectively, and the rms amplitudes associated with these distances are greater by a striking 19 and 31%. Both the increased size of the molecule and increased amplitudes are in very good agreement with prediction from simple theory. The results at 300° and 505°K, respectively, are rP-Cl=2.039±0.0014 A and 2.045±0.0016 A; rCl···Cl=3.130±0.0026 A and 3.142±0.0038 A; <Cl–P–Cl=100.27±0.09° and 100.40±0.16°; lP-Cl=0.0501±0.0013 A and 0.0594±0.0017 A; lCl···Cl=0.0834±0.0023 A and 0.1097±0.0035 A. The interatomic distances given are ra values obtained from the third cycle of least-squares refinement of intensity curves and differ from the equilibrium values re by small amounts; the lij values differ similarly from the le values. The estimated standard errors include standard deviations derived from the least-squares procedure, estimates of correlation among the data, uncertainty in the constants of the experiment, and uncertainty in the factors employed in the data reduction.
Use of Projection Operators in Perturbation Theory
Authors: Gray B. F.
Published: January 2005

By the use of projection operators a series of approximations to the perturbed problem is generated, the first of which turns out to be the second-order Brillouin-Wigner theory. This connection is used to show that the latter is in certain cases either an upper or a lower bound to the correct energy.
Vacuum Ultraviolet Photochemistry. III. Primary Processes in the Vacuum Ultraviolet Photolysis of Water and Ammonia
Authors: McNesby J. R. , Tanaka Ikuzo , Okabe H.
Published: January 2005

Water and ammonia have each been photolyzed in the absence and presence of C2D4 which served to scavenge H atoms. Wavelengths used were: for ammonia, 1849 and 1236 A; for water, 1236 A. Under conditions where H atoms are efficiently scavenged by C2D4, the production of H2 signifies a primary photochemical process giving molecular H2 directly. It is found that at 1849 A, ammonia decomposes almost entirely to H+NH2. At 1236 A, two primary processes are observed. (a)NH3→H2+NH,(b)NH3→H+NH2.Process (a) is about ⅙ as probable as process (b). At 1236 A, the photolysis of water proceeds via two primary processes. (c)H2O→H+OH,(d)H2O→H2+O.The probability of process (c) being three times that of process (d). It is suggested that primary process (d) constitutes a reasonable photochemical mechanism for hydrogen formation in the earth's upper atmosphere.
Interaction of 0.2- to 4.0-ev Electron Beams with Cleaved MgO
Authors: Cook C. J. , Fredericks W. J.
Published: January 2005

An attempt was made to determine the absorption coefficient δa for electrons incident on MgO and irradiated MgO for the impacting energy range, 0.2 ev through the conduction band (about 7.3 ev). It was found that electron trapping was so severe that the crystals would not thermally discharge at temperatures below 350°C. Consequently, the charged crystals were neutralized by a less satisfactory technique, high energy electron bombardment. δa was reproducible only at energies less than 4 ev. Sharp slope changes were observed at about 1.80 and 3.00 ev. These ``lines'' correspond to luminescence spectra obtained for catalytic recombination of N on MgO. Since slow electrons have been observed to interact predominantly with crystal defects, the data support the suggestion that defects can play a dominant role in catalytic reactions.
Negative Atomic Ions. II
Authors: Edie J. W. , Rohrlich F.
Published: January 2005

Electron affinities of negative atomic ions were obtained in a previous paper [H. R. Johnson and F. Rohrlich, J. Chem. Phys. 30, 1608 (1959)] by isoelectronic extrapolation using a four-term approximation formula. Recently, Edlén [B. Edlén, J. Chem. Phys. 33, 98 (1960)] simplified this procedure, using only three terms and improved experimental input data. The theoretical justification of this procedure lies in the assumption that these formulas are the beginning terms of a perturbation series which is at least semiconvergent. Therefore, a four-term formula should give better results than a three-term formula. It is shown here that the experiments indicate that this is not likely to be the case, thereby raising strong doubts about the justification of this method.

An alternative method is therefore suggested. Here, the regularity pattern of the ionization potentials as a function of Z (fixed degree of ionization) is extrapolated. This is therefore an extrapolation of the results of a ``horizontal analysis.'' The method requires one experimental affinity for each p shell as long as sufficiently precise data on ionization potentials of highly ionized atoms (fourth and higher spectrum) are not available. The results agree within experimental error, except for the most recent value of C— which is about 10% too low.
VCl4 Vapor Spectrum and Jahn-Teller Splitting
Authors: Blankenship Floyd A. , Belford R. Linn
Published: January 2005

The absorption spectrum of VCl4 vapor from 400 to 23 000 cm—1 was determined. A system of bands with maximum absorption coefficient at 9000 cm—1 is attributed to ligand field splitting of the 2D ground term of the free V (V) ion. The three-component structure of this band is attributed to Jahn-Teller splitting of the excited state. Simple calculations of the expected splitting are offered in support of this assignment.
Strong Field Stark Effect
Authors: Howe John A. , Flygare W. H.
Published: January 2005

The energy levels of a rigid asymmetric rotor containing one or more quadrupolar nuclei and subject to an electric field are discussed for the case in which the Stark effect energies are larger than those arising from quadrupole coupling effects.

The theory is applied to quantitative Stark effect measurements on COCl235 and CH2CCl235. The dipole moments determined by this method are 1.17 and 1.34D, respectively.