bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of Carbon Monoxide/Methane Mixtures in Shock Waves
Authors: Dean A. M. , Kistiakowsky G. B.
Published: February 2004

CO/O2/Ar mixtures with mole fractions of 4%/2%/94% and containing 180 or 500 ppm CH4 were investigated in incident shock waves at about 5×1017 particles/cc total concentration. The reaction was followed by measuring infrared emissions from CO2 and CO for about 1500-μsec particle time over the temperature range 1750–2575°K. The rate of CO2 production initially increased exponentially and then became constant after several percent conversion. The observed [CO2]–time profiles were compared to those calculated by numerical integration on an IBM 360/65 computer. It was possible to quantitatively describe the observations in terms of a mechanism with the following main reactions (rate constants are in units of cc molecule−1·sec−1): CO+O2=CO2+O; k1 = 2.0 × 10−11exp(− 60 000 / RT), OH+CO=CO2+H; k4 = 1.9 × 10−12exp(− 1030 / RT), H+O2=OH+O; k6 = 4.2 × 10−10exp(− 16 800 / RT), CH4+M=CH3+H+M; k7 = 2.7 × 10−6exp(− 103 000 / RT), O+CH4=CH3+OH; k9 = 2.6 × 10−10exp(− 7950 / RT), O2+CH3=CH2O+OH; k12 = 5 × 10−11exp(− 10 000 / RT), O+CH3=CH2O+H; k13 = 1 × 10−10, O+CH2O=H+CO+OH; k16 = 1 × 10−10, in addition to several relatively unimportant reactions involving chain carriers and O2 with CH4 and trace impurities H2 and H2O. Values of k4 and k6 were taken from the literature; others were determined by finding the best fit of the calculated [CO2]–time profiles to the experimental ones. Consequently, some change of the individual rate parameter values is possible without losing reasonable agreement with experiments. However, a substantial disagreement between the above values of k7 and k12 and literature values is attributed to the earlier workers' use of only the induction period data. Methane was found to be more effective than either H2 or H2O in promoting the branching chain oxidation of CO. Extending these observations, it is pointed out that extremely small concentrations of organic compounds can strongly influence many features of the CO/O2 system.
Effect of Organic Impurities on the Observed Activation Energy of CO2 Dissociation
Authors: Clark T. C. , Dean A. M. , Kistiakowsky G. B.
Published: February 2004

Earlier data on the rate of CO2 dissociation in shock waves [T. C. Clark, S. H. Garnett, and G. B. Kistiakowsky, J. Chem. Phys. 51, 2885 (1969)] is reinterpreted assuming that small amounts of organic impurity were present. It is shown that the data are consistent with an activation energy for the dissociation as high as 100 kcal/mole, a significantly higher value than that previously reported. The kinetic implications of this finding are discussed.
Rydberg Terms of the CH3 Radical
Authors: Barnard Jonathan , Duncan A. B. F.
Published: February 2004

Spectroscopic terms are calculated for two of the three observed Rydberg series in CH3. One-center SCF functions of CH3+, determined by Joshi are used for the core orbitals. The molecular geometry of CH3+ is assumed to be unchanged for the Rydberg states. The calculated terms are in good agreement with experimentally observed terms but suggest a possible reinterpretation of the latter.
Counting Theorem for the Generating Function of Self-Avoiding Walks
Authors: Chay Teresa Ree
Published: February 2004

A generating function Gn(α, β, γ) is defined to contain the information which gives the number of self-avoiding walks which reach the point (I, J, K) after n jumps. Hence, the generating function yields the distribution function and the mean-square end-to-end distance of self-avoiding walks. One way of obtaining Gn is by direct computer enumeration. However, this method becomes exceedingly expensive beyond a certain value of n. In this paper we formulate a recursion relation for the generating function in terms of a restricted subclass of configurations. Since only small numbers of these configurations contribute to Gn for given n, the formulation enables one to obtain Gn for very large n with considerably less computer time.
Diffusion Coefficients for CO2–CH4
Authors: Weissman Stanley , DuBro G. A.
Published: February 2004

Mutual diffusion coefficients for the CO2–CH4 system were measured from 293 to 370°K. These measurements extend the temperature range of the previously measured values by about 75°K. The experimental values of the diffusion coefficient are in excellent agreement with values derived from the composition dependence of the viscosity of CO2–CH4 mixtures provided the quantity A12* which appears in the relation between the two transport properties is evaluated using experimental quantities.
Pseudopotential Calculation of the Electrical Properties of Liquid Metals
Authors: Gupta H. C. , Tripathi B. B.
Published: February 2004

A modified form of Harrison's model pseudopotential has been used to calculate the electrical resistivity and the thermoelectric power of liquid metals, viz., lithium, sodium, potassium, and aluminum. The results are found to be in very good agreement with the experimental values.
Enskog Theory for a Rigid Disk Fluid
Authors: Gass David M.
Published: February 2004

The Enskog theory for a dense fluid of rigid disks is developed. The collisional contribution, which dominates in liquids, is derived and added to the kinetic term, which describes a dilute gas. Expressions for shear and bulk viscosity and for thermal conductivity are obtained. The initial correlations are evaluated via the autocorrelation function approach, and the exponentially decaying functions which result are related to the Enskog theory.
Microwave Spectrum, Structure, and Dipole Moment of Difluorophosphine Borane
Authors: Pasinski John P. , Kuczkowski Robert L.
Published: February 2004

The structure of difluorophosphine borane (HF2P–BH3) has been determined from the microwave spectra of six isotopic species. The expected staggered conformation and Cs symmetry have been confirmed. The structural parameters are: d(PH) = 1.409 ± 0.004 Å; d(PF) = 1.552 ± 0.006 Å; d(PB) = 1.832 ± 0.009 Å; d(BHa) = 1.226 ± 0.005 Å; d(BHs) = 1.200 ± 0.007 Å; ∠HaBHa = 112.7 ± 0.5°; ∠HaBHs = 115.9 ± 0.4°; ∠FPF = 100.0 ± 0.5°; ∠FPH = 98.62 ± 0.25°; ∠BPF = 117.7 ± 0.3°. Two angles (PBHs = 109.9 ± 0.3°; PBHa = 99.89 ± 0.26°) indicate a tilt of the borane group away from the fluorine atoms. The value of the dipole moment obtained from Stark splittings is 2.504 ± 0.030 D. A range for the barrier to internal rotation is estimated as 3600–4500 cal/mole. The change in structural parameters of HF2PBH3 compared to similar compounds, the stability of HF2PBH3 towards dissociation, and the tilted borane group are discussed.
Effect of Thermal Energy on Ionization Efficiency Curves of Fragment Ions
Authors: Chupka W. A.
Published: February 2004

The effect of thermal energy on the shape of photoionization-efficiency curves is analyzed. Several methods for determining thresholds for dethermalized ionization-efficiency curves are presented. The assumptions and approximations used are explicitly stated for each method. The effect of thermal energy on the photoionization-efficiency curves of some alkanes is analyzed and the results are in fair agreement with the hypothesis that thermal energy is fully effective in the dissociation of the parent ions.
Virtual Orbitals in Hartree–Fock Theory. II
Authors: Huzinaga Sigeru , Arnau Catalina
Published: February 2004

The nature of virtual orbitals in the Hartree–Fock theory is discussed. A practical proposal is made to obtain meaningful virtual orbitals in the molecular calculations at the level of Pariser–Parr–Pople-type and all-valence-electron-type approximations. It is achieved by adding appropriate operators to the original Hartree–Fock operator.
Rayleigh–Raman Depolarization of Laser Light Scattered by Gases
Authors: Rowell R. L. , Aval G. M. , Barrett J. J.
Published: February 2004

The polarization of the fine structure of the Rayleigh line for light scattered by simple gas molecules is examined. New and simple relations are reported between the depolarization factor of the total line (including rotational Raman lines) and the depolarization factor of the unshifted central component. A new high-resolution apparatus for light scattering measurements in gases with photon-counting electronics and a high-power argon-ion laser light source is described. New measurements of the depolarization factor of the total line are reported for H2, N2, O2, CO2, CO, and N2O. High-resolution measurements of the depolarization factor of the central component are also reported for these gases and a critical comparison is made between experiment and classical light scattering theory. In the case of H2 a comparison with recent quantum mechanical calculations is also included.
ESR, 1H, and 2D Studies of the Radical Anion of 1,3,5-Triphenylbenzene
Authors: van Broekhoven J. A. M. , Hendriks B. M. P. , de Boer E.
Published: February 2004

MO calculations predict that the monoanion of 1,3,5-triphenylbenzene (Tpb) is in an orbitally degenerate ground state. Nevertheless, the ESR spectrum in liquid NH3 is well resolved; the derivative linewidth is equal to 0.06 Oe only. The g value and the electronic relaxation times T1 and T2 were comparable in magnitude to those of orbitally nondegenerate radicals. It is suggested that twisting of the phenyl rings out of the plane of the molecule, which may lift the orbital degeneracy, is the principal reason of this behavior. 1H and 2D NMR experiments were performed on a reduced sample of Tpb, containing both normal and perdeutero-Tpb. From the Fermi contact shifts signs and magnitudes of all hyperfine splitting constants have been determined, and they agreed very well with the ESR splitting constants. From the proton linewidths the electronic and dipolar correlation times were inferred. Quadrupole coupling constants for all deuterium nuclei were calculated from the 2D linewidths.
On the Validity of the P–R Separation Method in the Presence of l-Type Resonance
Authors: Masri F. N. , Blass W. E.
Published: February 2004

A resonance calculation computer program has been applied to a quantitative investigation of the effects of strong l-type resonances on the envelopes of degenerate (E) infrared bands of symmetric tops. The immediate object of these calculations has been to establish whether l-type resonance is likely to be a serious source of error in the P–R separation method of determining η constants. Attention has been directed mainly to bands where (C − Cη − B) is close to zero so that the mutually perturbing levels are nearly degenerate. The effect of assuming l-type doubling constants, q, much larger than those observed has been examined. All of our calculations suggest that uncertainties in the P–R separation method arising from this source are small and comparable to those deriving from other known sources, such as the neglect of α constants in the method. An explanation for these results in terms of line by line shifts is advanced.
On Observing “New” States in Small Molecules
Authors: Gelbart William M. , Jortner Joshua
Published: February 2004

In this paper we consider the general problem of a discrete state interacting with a continuum which is bounded below in energy. We investigate the optical properties of the new state which splits off below the threshold and determine its energy and oscillator strength in terms of the transition moments of the zero-order states and the matrix elements of the level shift operator. We study in particular the case of predissociation in diatomic molecules and provide numerical estimates and experimental criteria for the observation of this new effect. Finally, we discuss certain more general situations in which this phenomenon is expected to arise and suggest appropriate extensions of the present, semiempirical, treatment.
Optical and Magnetic Studies of Tripositive Thulium in Hydrated Chloride Crystals
Authors: Olsen D. N. , Gruber J. B.
Published: February 2004

The optical absorption spectra of single crystal TmCl3·6H2O and Tm3+ in YCl3·6H2O have been investigated between 2500 and 8000 Å at 4.2 and 77°K. The spectra were studied as a function of magnetic field strength and as a function of crystal orientation relative to the magnetic field. Both optical and EPR data indicate a nearly accidental degeneracy in the ground state of tripositive thulium in the hydrated chloride salts. The magnetic moment is found to be perpendicular to the twofold axis of symmetry and the zero field splitting is found to be 1.12 cm−1. The observed splitting factor is 14.00 ± 0.05 LU.
Theory of Molecular Reorientation in Liquids: Magnetic Spin Resonance Line Shapes
Authors: Sillescu Hans
Published: February 2004

The Debye model of rotational Brownian motion and the rotational random jump model have been extended to allow for time fluctuations of the rotational diffusion constant and the jump rate constant, respectively. The treatment is applicable to experimental situations which are conventionally described in terms of a distribution of correlation times and to systems where molecular reorientation is complicated, e.g., by rapid chemical exchange processes. Correlation functions for spin relaxation are discussed in some detail and are compared with the corresponding correlation functions for dielectric relaxation. In particular, the ESR (or NMR) line shape is given for a simple example of very slow reorientation where the rotational correlation time is comparable with the spin relaxation time. In this case, the Debye model and the jump model yield different line shapes, and further changes occur if environmental fluctuations are considered. Details are given for fluctuations described by an Uhlenbeck–Ornstein process.
Intensities of Optical Transitions in Imperfect Molecular Crystals. I. Moments
Authors: Fox David
Published: February 2004

Expressions are developed for the moments of dipole-strength densities of optical spectra in imperfect molecular crystals. These expressions are invariant to the unitary transformation from the diagonal representation of the Hamiltonian to the representation in which the statistical description of the disordering is available; it is therefore not necessary to have information about the eigenstates or the eigenvalue spectrum. The relationship to Green's functions is discussed. The method is applied to some model Hamiltonians.
Infrared Lasers Resulting from Giant Pulse Laser Excitation of Alkali Metal Molecules
Authors: Sorokin P. P. , Lankard J. R.
Published: February 2004

Infrared laser action is observed to occur in vapors of K, Rb, and Cs photoexcited by various giant pulse laser beams. The mechanism of excitation involves two-photon absorption by the molecular species followed by dissociation into various excited atomic states. In the case of cesium, anomalously long infrared laser pulses are obtained when helium buffer gas is present. A collisional mechanism is invoked to explain this phenomenon. Self-focusing of a ruby laser beam is also observed to occur in cesium–helium vapor under certain conditions.
Classical Trajectory Analysis of the Reaction F+H2→HF+H
Authors: Jaffe Richard L. , Anderson James B.
Published: February 2004

A classical trajectory analysis has been made for the reaction F+H2→HF+H using a semiempirical potential energy surface. The reaction cross sections, energy distributions among reaction products, and angular distributions of products were determined as functions of initial relative velocity for low-lying rotation–vibration states of H2 from Monte Carlo averages over a large number of trajectories. The modified London–Eyring–Polanyi–Sato surface used is characterized by a 1.68 kcal barrier in the entry valley with a net drop of 31.3 kcal to the exit valley occurring with F approaching H2. The reaction cross sections for H2 with υ = 0, J = 1 increased with relative velocity from a threshold value at a translational energy of 2.1 kcal to ∼ 6 Å2 at 14 kcal. Rotational energy had little effect on the cross sections. For υ = 1, J = 1 the translational energy threshold was slightly lower and the upper limit to cross sections was ∼ 8 Å2. The HF product was found to be strongly excited vibrationally with an average of ∼ 60% of the reaction energy released to vibrational excitation. Reaction rate constants determined by integrating the cross sections for thermal distributions of reactants were fitted to an Arrhenius rate expression k = A exp(− Ea / RT) with A = 1014.1cm3mole−1·sec−1 and Ea = 2.72 kcal. The results are in qualitative agreement with existing measurements of over-all reaction rates and with product energy distributions determined in measurements of infrared chemiluminescence. Results from a limited number of trajectories for the reaction F+D2→DF+F are also presented.
Triplet State EPR of 1,5-Naphthyridine
Authors: Vincent James S.
Published: February 2004

Paramagnetic resonance experiments of the triplet state of 1,5-naphthyridine in mixed crystals of durene and perdeuterated durene at 80°K are reported. The fine structure observed at 35 GHZ is described by the spin Hamiltonian, H = βH·g·S + D(Sz2 − 2 / 3) + E(Sx2 − Sy2), in which S = 1, D / hc = + 0.1030 ± 0.0008 cm−1, E / hc = − 0.0167 ± 0.0007 cm−1, and gxx = 2.0043 ± 0.0005, gyy = 2.0032 ± 0.0008, gzz = 2.0018 ± 0.0006. The sign of D is determined by the analysis of weak satellites in the hyperfine structure with the magnetic field along the X axis. The spin densities determined from the anisotropic hyperfine interaction along the three molecular axes are ρn ≈ 0.113, ρ2 ≈ 0.101, ρ3 ≈ 0.051, ρ4 ≈ 0.227, ρ9 ≈ 0.009.
Stability Conditions for the Solutions of the Hartree–Fock Equations for Atomic and Molecular Systems. IV. A Study of Doublet Stability for Odd Linear Polyenic Radicals
Authors: Paldus J. , Čížek J.
Published: February 2004

The doublet stability conditions for the restricted Hartree–Fock (HF) solutions of the simple open-shell case (i.e., one electron in addition to the closed shell) are applied to the π-electronic models of the odd linear polyenic radicals, using the Pariser–Parr–Pople-type semiempirical Hamiltonian. It is found that symmetry-adapted restricted HF solutions for linear polyenes with (4ν − 1) carbon atoms are always doublet stable while those with (4ν − 1) carbon atoms may be unstable for large enough coupling constants (i.e., the ratio of two-electronic part of the Hamiltonian to the one-electronic part). In fact the HF solutions for the latter systems are generally doublet unstable already for the currently used values of the semiempirical parameters or a very small lowering of the absolute value of the resonance integral β (i.e., ∼0.1 − 0.3 eV) is sufficient to yield instability for any (4ν − 1) type polyene. The instability, in fact, occurs already for the allyl radical, which is studied in a considerable detail. The doublet stability of the solutions for the (4ν + 1) type polyenes is explained on the basis of symmetry properties of corresponding Kekulé structures. The symmetry-nonadapted restricted HF solutions are calculated for illustration of their properties and possible multiplicities.
Vacancy-Limited Electron Transport in Rare-Gas Solids
Authors: Druger S. D.
Published: February 2004

An expression is obtained for the mobility of conduction-band electrons in rare-gas solids when both vacancy scattering and phonon scattering are effective. Deformation potential constants are obtained by a fit to experimental data. It is shown that large concentrations of vacancies which would result from the lowering of the vacancy formation energy by nonpairwise interatomic interactions might significantly affect the electronic mobility near the triple point of the solid.
Compton Profile of NH4Cl
Authors: Inkinen O. , Halonen V. , Merisalo M. , Manninen S.
Published: February 2004

The Compton profile of MoKα x rays scattered from polycrystalline NH4Cl has been measured and compared with theoretical profiles based on the superpositions (a) N+4H+Cl and (b) NH4++Cl−. The molecular-orbital wavefunctions of Moccia were used for NH4+, and the electrons in N, H, Cl, and Cl− were described by free-atom wavefunctions. The experimental results were significantly different from the profile based on the model (a) and gave good agreement with the profile obtained from the superposition (b).
Vibronic Structure in the Fluorescence Lifetimes and Quantum Yields of Aniline Vapor
Authors: Von Weyssenhoff Hanns , Kraus Frances
Published: February 2004

Aniline vapor has a well-resolved vibronic absorption spectrum in the region of the first excited singlet transition. By means of high-resolution phase fluorimetry we have determined the spectrum of fluorescence lifetimes and quantum yields over the region from 300 to 275 nm with a bandwidth of 2.7 Å. The emission spectrum was not resolved. Relative values of quantum yields at different wavelengths were measured directly while absolute values were estimated from literature data. Quantum yields fluctuate between 0.3 and 0.6 and the reciprocal lifetime, 1 / τ, varies in the range (1.3 to 2.3) × 108 sec−1. 1 / τ shows sharply pointed minima whereas the quantum yields have maxima at the wavelengths of all major absorption peaks. The calculated intersystems crossing rate constants kisc have minimum values at these wavelengths. These features are interpreted in terms of symmetry selection rules for spin–orbit and vibronic coupling.
Supersonic Molecular Beams of Alkali Dimers
Authors: Gordon R. J. , Lee Y. T. , Herschbach D. R.
Published: February 2004

Intense alkali beams containing up to 30% mole fraction of K2, Rb2, or Cs2 have been generated from a supersonic nozzle expansion, with oven temperatures up to ∼ 900°K (corresponding to alkali vapor pressures up to ∼ 350 torr) and nozzle temperatures ∼ 50–300°K higher. The total beam intensity obtained reached ∼ 5 × 1017 particles sec−1·sr−1. An inhomogeneous deflecting magnet was used to separate the dimer and atom components of the beam, and the variation of dimer concentration with oven pressure and nozzle temperature were studied for a variety of nozzle sizes (throat diameters 0.04–0.15 mm). The velocity distributions of the atom and dimer components were also measured and found to be quite similar; the peaks occur at velocities up to 70% higher than the most probable atom velocity in the oven, and the widths are very narrow, corresponding to random translational temperatures as low as ∼ 30°K, and Mach numbers up to ∼ 15. A simple one-dimensional theory of dimerization which takes into account vibrational relaxation and heat of condensation is found to be consistent with the data. It is shown that the observed velocity distributions and the variation of the dimer yield with pressure and nozzle diameter imply that most of the heat of condensation does not contribute to the beam acceleration but goes into vibrational excitation of the dimer molecules. A nominal value of ∼ 3 × 10−30 cm6 sec−1 at ∼ 600°K is obtained for the recombination rate constant for Cs+Cs+Cs→Cs2+Cs. A reduced variable plot is provided which enables the theory to be applied to nozzle expansions of any substance for which the chemical recombination is governed by three-body collisions.
Glory Scattering in Molecular Collisions. II. Formal Expressions for the Total Inelastic Cross Section
Authors: Biolsi Louis
Published: February 2004

Formal expressions for the differential and total inelastic scattering cross section when two rigid diatomic molecules with orbital and nuclear spin angular momenta collide are obtained. An extended distorted wave treatment is used to simplify the results. The nondegeneracy averaged and degeneracy averaged cases are compared.
Dipole Moment in the B21 State of p-Chlorofluorobenzene
Authors: Janiak Martin J. , Hartford Allen , Lombardi John R.
Published: February 2004

The Stark effect is observed in the rotational fine structure of the 0–0 band of the lowest lying π* ← π state of p-chlorofluorobenzene. The results are μ′ = 1.35 ± 0.10 D or 0.70 ± 0.10 D compared with 0.99 D in the ground state. Using previous correlation between structure and dipole moment, evidence is presented which gives an indication that the larger value of μ′ is more likely.
High-Temperature Heat Contents and Related Thermodynamic Functions of Seven Trifluorides of the Rare Earths: Y, La, Pr, Nd, Gd, Ho, and Lu
Authors: Spedding F. H. , Henderson D. C.
Published: February 2004

The high-temperature heat contents of high-purity YF3, LaF3, PrF3, NdF3, GdF3, HoF3, and LuF3 were measured from 100–1600°C. The heat capacity, heats of transition, heats of fusion, and related thermodynamic functions were calculated. The smoothed values of H°T − H°298, Cp, S°T − S°298, and − (F°T − H°298) / T are tabulated at 100° intervals. A comparison of the values for the transition temperature, melting points, and lattice parameters of the higher-purity fluorides of this work with those of less pure fluorides indicated that a reduction in oxygen content does not affect these properties.
Some Further Comments on the SCF Theory of the Excluded Volume Effect in Polymers
Authors: Yamakawa Hiromi
Published: February 2004

The self-consistent field approach to the excluded volume problem in a polymer chain is studied and discussed from the elementary point of view of statistical mechanics. First, true successive approximations to the self-consistent potential are derived from the corrected variation principle equation of Reiss. Second, the relationship between our basic self-consistent field equation previously derived and those derived by other routes, e.g., the Edwards equation and the Whittington hierarchy, is shown explicitly. Third, a uniform-expansion approximation is made in the potential of Edwards, and then a fifth-power-type equation for the expansion factor is obtained. A comparison of the result with those obtained previously and by Edwards provides an understanding of the effect of the uniform-expansion approximation.
Gaseous Phosphorus Compounds. IV. Thermodynamic Study of Gallium Monophosphide with a Mass Spectrometer and Dissociation Energy of Aluminum Diphosphide
Authors: Gingerich Karl A. , Piacente Vincenzo
Published: February 2004

Gaseous equilibria involving the GaP molecule have been studied by means of the Knudsen-effusion technique in combination with mass spectrometric analysis of the vapor phase. In order to obtain the desired phosphorus and gallium partial pressures of comparable magnitude, mixtures of gallium and either WP or Th3P4 which were evaporated from a graphite Knudsen cell were employed. From the experimentally determined partial pressures the equilibrium constants and the enthalpies of the reactions Ga(g)+0.5 P2(g)=GaP(g), Ga(g)+0.5 P4(g)=GaP(g)+0.5 P2(g), 0.5 Ga2(g)+0.5 P2(g)=GaP(g), and GaAg(g)+0.5 P2(g)=GaP(g)+0.5 Ag2(g) have been determined. These reaction enthalpies have been combined with appropriate literature data to yield the dissociation energy, D0° = 54.0 ± 3.0 kcal mol−1, the heat of sublimation, ΔHs,298° = 111.2 ± 5.0 kcal mol−1, and the heat of formation ΔHf,298° = 90.3 ± 4.1 kcal mol−1, of gaseous gallium monophosphide. The molecule AlP2 has been observed over the congruently vaporizing AlP(s). The enthalphy of the reaction AlP2(g)=Al(g)+P2(g) was obtained as ΔH0° = 33 ± 5 kcal mol−1. From this value the heat of atomization of AlP2, D0° = 149 ± 6 kcal mol−1, was calculated.
Transfer-State Population in Liquid Scintillators
Authors: Levin E. , Furst M. , Kallmann H.
Published: February 2004

A parameter, ne, which represents the number of primary excited solvent molecules from which energy can be transferred to the scintillator, may be determined by studying fluorescence under high-energy and ultraviolet excitations. The temperature variation of ne was measured over a range of 200°C and was found to be considerable for high-energy excitation. This variation is attributed to changes in intermolecular coupling. Following ideas of Magee and Platzman, we assume the (bulk modulus)1/3 as a measure of this coupling. The experimental results show good agreement with the theory. Study of different solutes reveals that ne is made up of two factors only one of which is temperature dependent.
Kinetic Equations for Orientational and Shear Relaxation and Depolarized Light Scattering in Liquids
Authors: Andersen Hans C. , Pecora R.
Published: February 2004

The application of Mori's theory of fluctuations to the calculation of depolarized light scattering spectra of liquids is described. Two sets of kinetic equations are derived. The first is capable of describing the shear wave doublet observed by Fabelinskii and co-workers and Stegeman and Stoicheff and reduces to the theory of Leontovich when the antisymmetric part of the stress tensor is ignored. The second set describes the doublet as well as the broad background observed in several laboratories and reduces to the theory of Volterra in the limit where antisymmetric stress is ignored. The angular dependence of the spectrum predicted by the first set of equations is compared with the experimental results of Stegeman and Stoicheff for aniline and quinoline. Good agreement is obtained for quinoline at all angles and for aniline at all but the highest scattering angle at which doublet structure was observed. Our results indicate that the relaxation of the antisymmetric part of the stress tensor may be important for discussing viscoelastic relaxation in aniline.
Ion–Molecule Reactions in the Radiolysis of Ethane
Authors: Ausloos P. , Rebbert R. E. , Sieck L. Wayne
Published: February 2004

The reactions of ions generated in ethane irradiated with gamma rays have been studied by analyzing the neutral products formed in reactions with ethane and with other molecules. In experiments in the presence of added (C2D5)2CDCD3, for example, it is shown that the following reactions take place: C2H5++C2H6→(C4H11+)*→sec-C4H9++H2; sec-C4H9++(C2D5)2CDCD3→n-C4H9D+C6D13+. The intermediate (C4H11+)* ion can be stabilized by collisions and will then undergo an undetermined reaction (neutralization or proton transfer) to give n-C4H10 as a product. The over-all rate constant for reaction of the ethyl ion with ethane is shown to be ≤ 10−10 cm3/molecule·sec. Similarly, it is demonstrated that the reaction C2H3++C2H6→C4H9+ leads predominantly to the formation of t-butyl ions under these conditions: C4H9++(C2D5)2CDCD3→(CH3)3CD+C6D13+. Supplementary experiments performed in a photoionization mass spectrometer demonstrate that ethylene ions undergo a “resonance H2− transfer” reaction with ethane: C2H4++C2D6→C2D4++C2H4D2, with a rate constant of 1.1 × 10−10 cm3/molecule·sec. Similarly, the ethane parent ion reacts with ethylene: C2H6++C2D4→C2H4++C2H2D4.
Correlated and Hartree–Fock Wavefunctions for the 1s2s 3S State of Helium
Authors: Carlton Terry S.
Published: February 2004

Energies are calculated variationally using an antisymmetrized orbital product times the correlation function g = [1 + λr12 + μ(r2 − r1)2]m (m = 12or 1). Energy errors are 0.00013 a.u. when m = 12 and 0.00030 a.u. when m = 1. Values of λ and μ are considerably smaller than in the case of the ground state. The Hartree–Fock energy is found to be − 2.17425 a.u. Various expectation values are reported for all wavefunctions.
Dissociation Energy of Diatomic Cerium and Predicted Stability of Gaseous Intermetallic Cerium Compounds
Authors: Gingerich K. A. , Finkbeiner H. C.
Published: February 2004

The Knudsen-cell mass spectrometric method has been used to study gaseous equilibria over the Au–Ce–CeS–BN–C system. The third-law enthalpies, ΔH0°, in kcal mole−1, of the reactions: (1) 0.5 Ce2(g)+0.5Au2(g)=CeAu(g) (2) Ce2(g)+Au(g)=CeAu(g)+Ce(g) and (3) Ce2(g)=2 Ce(g), were found to be 24.7 ± 0.14, 23.0 ± 0.16 and 58.0 ± 1.5, respectively. The corresponding second-law value for Reaction (3) is 53.4 ± 10. The reaction enthalpies for Reactions (1) and (2) were combined with the literature value for D0°(Au2) and the value of D0°(CeAu) obtained in the present investigation to yield the dissociation energy of diatomic cerium. The selected value for the dissociation energy of Ce2 is D0° = 57 ± 4 or D298° = 58 ± 4 kcal mol−1. Using the latter value and the literature value for the standard heat of sublimation of cerium, ΔHυ,298° = 101 ± 1 kcal mol−1, the standard heat of formation, ΔHf,298°, of diatomic cerium has been calculated as 144 ± 6 kcal mol−1. The stability of selected gaseous intermetallic cerium compounds has been predicted on the basis of the Pauling model of a polar bond and the experimental value for the dissociation energy of diatomic cerium. A reassessment of the dissociation energies, D0°, of LaAu, CeAu, PrAu, and NdAu [J. Chem. Phys. 52, 2956, (1970)] resulted in the values of 79.5 ± 5, 77.0 ± 3.5, 72.0 ± 5 and 70.6 ± 5 kcal mol−1, respectively.
Application of the Statistical Phase-Space Theory to the Reaction K+HCl→KCl+H and to Inelastic Scattering
Authors: Truhlar Donald G.
Published: February 2004

The statistical phase-space theory of Light, Pechukas, and Nikitin is applied to the endothermic reaction K+HCl→KCl+H. The results are compared to molecular beam experiments. The probability of reaction as a function of impact parameter is in fair agreement with that obtained by Moursund et al., but the phase-space theory predicts too high a reaction cross section. Further, the calculations suggest that their determination of the maximum impact parameter leading to each excited vibrational state of the product should not be trusted. The phase-space calculations, combined with an estimate of rotationally inelastic grazing collisions, predict a high ratio (2–10) of rotationally inelastic collisions to reactive collisions; the effect of these nonreactive collisions on the optical model analysis of reactive scattering is not known. Because we assumed threshold for reaction of less than 1 kcal/mole, our results are not quantitatively comparable to those of Odiorne and Brooks. Nevertheless our full calculations are in essential agreement with the ideas about angular momentum disposal which Moursund et al. and Odiorne and Brooks used to provide interpretations of their data. Many detailed properties of the reactions are predicted; these can be compared with future beam experiments. The direction and magnitude of the quantitative deviation from the experimental results is a useful guide to understanding the chemical dynamics of this collision system since the statistical phase-space theory indicates what the results would be in the limiting case that all degrees of freedom of the interacting system are coupled in the most efficient possible way.
Variational Wavefunctions and Energies for L = 2 and L = 3 States of Two-Electron Atoms
Authors: Brown Robert T. , Cortez Jose-Luis M.
Published: February 2004

Variational wavefunctions and energies have been obtained for the n1D, n3D, n1F, and n3F (through n = 8) levels of the helium isoelectronic sequence through Z = 16. The trial functions are configuration–interaction expansions in members of a denumerably complete basis set (Sturmian functions), with 39 terms used for the D states and 18 terms used for the F states. Differences between calculated and observed D state energies of He and Li+ range from 0.000001 to 0.00005 a.u.
C2 and C2− Spectra Produced by the X Irradiation of Acetylene in Rare-Gas Matrices
Authors: Frosch R. P.
Published: February 2004

The absorption and emission spectra induced by the x irradiation of acetylene trapped in Ar, Kr, and Xe matrices have been studied in the visible region. Two transitions of diatomic carbon dominate the spectrum. The B 2Σu+ ↔ X 2Σg+ transition of C2−, first identified in a matrix by Milligan and Jacox, is present in all three solvents in both emission and absorption. The A 3Πg → X′ 3Πu Swan-band system of C2 is present in emission only, and then only in Ar and Kr matrices. This result is consistent with the gas-phase ordering of states, which places the X′ 3Πu state of neutral C2 610 cm−1 above the ground state. Spectroscopic constants have been obtained by making a least-squares fit of the data. Although the deviations from the gas-phase ωe's are 1%–2% in the ground state of C2− and in the upper state of the C2 Swan system, there can be no doubt of the assignment. The ωe's of the upper C2− state and the lower state of the Swan system differ from the gas-phase values by only 1–2 cm−1. Experiments with carbon-13 enriched acetylene confirmed the vibrational assignments. The emission spectra of both molecules are particularly interesting. Emission was observed from the υ′ = 4, υ′ = 2, and υ′ = 1 levels of C2 indicating that the vibrational lifetime is as long as or longer than the radiative lifetime of the A 3Πg state. The vibrational quantum numbers of the emitting levels were found to depend on the isotopic species involved, but the same vibronic levels emitted in both Ar and Kr matrices indicating that the relaxation process is strongly dependent on the spacing of the vibrational levels but is relatively independent of the phonon structure of the surrounding medium. Vibrational relaxation was also found to be slow in the B 2Σu+ state of C2−. Emission was observed from both the υ′ = 1 and υ′ = 0 levels of this molecule in all three rare gases. The paths of electronic and vibrational excitation and relaxation in both C2 and C2− are discussed qualitatively.
Molecular-Orbital Theory for Infinite Systems: Regular Polymer Chains
Authors: O'Shea Seamus , Santry D. P.
Published: February 2004

A CNDO (complete neglect of differential overlap) molecular theory for infinite polymers has been developed and applied to two simple examples. It is found that the simplications of the SCF (self-consistent field) polymer equation under the CNDO approximation are sufficient to bring complex biological polymers within the reach of theoretical methods. Problems arising from the convergence of the SCF method of infinite systems are discussed.
Dimerization of 9, 10-Diazaphenanthrene
Authors: de Vries Reilingh D. N. , Rettschnick R. P. H. , Hoytink G. J.
Published: February 2004

The fluorescence and fluorescence excitation spectra of the dimer of 9, 10-diazaphenanthrene are given with the relative degrees of polarization of the bands. The stabilization enthalpy of the dimer is 3.6 kcal mole−1, and the association constant K = 9.1 × 10−2exp(1800 / T) for 100°K ≤ T ≤ 130°K.
Temperature Dependence of the Rate Constant for the Reaction O2(1Δg)+O3→2O2+O
Authors: Findlay F. D. , Snelling D. R.
Published: February 2004

A rate constant for the reaction O2(1Δg)+O3→2O2+O of 4.5 × 10−11exp(− 5620 / RT)cm3molecule−1·sec−1 over the temperature range 283–321°K has been obtained. The rate of the reverse reaction, calculated from the equilibrium constant, is 8.7 × 10−37exp(− 3340 / RT)cm6molecule−2·sec−1.
γ
Radiolysis of Liquids at High Pressures. X. The Reaction H+OH− and the Partial Molal Volume of the Hydrated Electron
Authors: Hentz Robert R. , Brazier David W.
Published: February 2004

G( H 2 ) is independent of pressure over the range 0–6.2 kbar in γ radiolysis of the following deaerated aqueous solutions at 23°C: (a) solutions with 0.001 M or 0.1 M hydroxide, isopropanol at concentrations in the range 9 × 10−4 M to 0.1 M, and nitrate at one-fiftieth of the isopropanol concentration; (b) solutions with 0.01 M formate, 0.001 M nitrate, and 0.01 M or 0.1 M hydroxide; (c) near-neutral solutions with 0.01 M formate and 0.01 M or 0.002 M benzyl alcohol. From pressure independence of G(H2) for such solutions and the established pressure independence of the primary yields of water radiolysis, it follows that activation volumes for the reactions of H with hydroxide, isopropanol, formate, and benzyl alcohol are equal. Consequently, ΔV1‡ = − 5.9 ml mole−1 is obtained for Reaction [1], H+OH−→H2O+eaq−. Combination of ΔV1‡ with the previously determined ΔV‡ = − 14.2 ml mole−1 for the back reaction gives ΔV for Reaction [1]. From ΔV, with a previous estimate of V̄(H) in the range 5.9–10.3 ml mole−1, the absolute partial molal volume of eaq− (based on a value of − 5.4 ml mole−1 for H+) is estimated to be in the range − 1.7–2.7 ml mole−1. With an estimated electrostriction contribution of − 3 ml mole−1, the electron cavity volume is in the range 1–6 ml mole−1. In effect, such estimates of the electron cavity volume and V̄(eaq−) are obtained from the pressure dependence of an equilibrium constant.
Absorption Intensities of the Lattice Modes of Crystalline HCl and HBr
Authors: Carlson R. E. , Friedrich H. B.
Published: February 2004

The absolute absorption intensities of the infrared active lattice modes of crystalline HCl and HBr have been measured. Assignments based on the experimental intensities indicate that all of the fundamental lattice modes lie below 350 cm−1. A dipolar coupling model was used to calculate the expected intensities. A comparison of observed intensities with calculated intensities gives evidence that the molecular dipole moments of crystalline HCl and HBr are less than their gas-phase values.
Carbon-13 Relaxation Time Measurements in Formic Acid
Authors: Alger Terry D. , Collins Scott W. , Grant David M.
Published: February 2004

The variations in carbon-13 nuclear magnetization with time have been determined for formic acid under proton-coupled and proton-decoupled conditions by the adiabatic rapid passage technique. The time-dependent variations for proton-coupled carbon-13 magnetization are nonexponential, while the nonequilibrium, proton-decoupled carbon-13 magnetization follows an exponential relationship. By applying the theoretical equations to the experimental results, spin–lattice relaxation times for the spin-decoupled case were calculated for both the formyl proton and carbon-13 nuclei as well as for the internuclear process. It is demonstrated that the carbon-13 relaxation process is dominated by the mutual relaxation of formyl protons and carbonyl carbons through the intramolecular dipole–dipole mechanism. Various means of extracting relaxation data with and without spin-decoupling equipment are discussed for the four-line two-spin system.
Attractive Nature of the Rotational Barrier in Acetaldehyde
Authors: Davidson Robert B. , Allen Leland C.
Published: February 2004

The barrier to internal rotation in acetaldehyde is investigated using LC (Hartree–Fock) AO MO–SCF calculations. The calculated barrier is in good agreement with experiment. For the first time, a threefold barrier is shown to be dominated by attractive interactions. The factors which give rise to this finding are discussed, as are its experimental consequences.
Solvation Number of the Electron in Liquid Ammonia. A Nitrogen Magnetic Relaxation Study
Authors: Pinkowitz R. A. , Swift T. J.
Published: February 2004

The high resolution proton magnetic resonance spectrum of a dilute solution of potassium in liquid ammonia shows a large contribution to the line shape from 14N spin–lattice relaxation through magnetic dipolar interaction with unpaired electrons. The predominant 14N-electron interaction occurs through Fermi contact. From total line shape analyses of the proton spectra recorded at 60 MHz and 100 MHz values were obtained for both τ(e−), the average lifetime of a given 14N in a given electron–ammonia complex, and for N, the average solvation number of the electron. The lifetime varies from approximately 1–2 × 10−12 sec over the concentration and temperature range studied. The solvation number ranges from approximately 20 to 40. These results are most consistent with the lattice vacancy model of the solvated electron.
Infrared Spectra and Structure of Matrix Isolated Thallous Halides
Authors: Brom J. M. , Franzen H. F.
Published: February 2004

The infrared absorption spectra of the vapor species over thallous fluoride, chloride, bromide, and iodide have been observed in the frequency range 33–4000 cm−1 using the matrix isolation technique. In addition to the absorption frequencies of the TlX monomers, the spectra of the Tl2F2 and Tl2Cl2 dimers have been observed. The absorption bands assigned to the dimer species are consistent with a proposed X–Tl–Tl–X dimer structure. A comparison of the observed to the calculated entropy of Tl2F2 and Tl2Cl2 lends support to the spectral assignments. A qualitative discussion of the bonding for the dimer species is included, to show that the proposed linear symmetrical structure for the Tl2X2 molecules is in agreement with several predictions based upon the qualitative bonding theory.
Zeeman Effect in Porphyrins: Zero-Field Splitting of the Excited Electronic States
Authors: Sutherland J. C. , Axelrod Daniel , Klein M. P.
Published: February 2004

Recent experimental studies have reported anomalous and contradictory results for the absorption of left and right circularly polarized light (LCPL and RCPL) by zinc and magnesium coproporphyrins in the presence of a magnetic field: for both compounds, the absorption bands for right and left circularly polarized light have distinctly different shapes at room temperature; at 77°K unexplained shoulders appear in the absorption spectra for both polarizations for the magnesium but not for the zinc compound; the value of the angular momentum of the lowest energy excited state computed from the separation of the peaks of the LCPL and RCPL absorption bands differs from the value obtained from magnetic circular dichroism (MCD) experiments by nearly 50%; no shape anomalies were observed in the MCD spectra. We derive a general solution for the mixing of two states by a magnetic field and show that all of the anomalous experimental data are explained if (a) the presumably degenerate pair of excited states are split in zero field by an energy comparable to the Zeeman energy but less than the spectral bandwidths, and also (b) the overlapping transitions have unequal intensities. Our results show that MCD should give better estimates of excited state angular momenta while the direct measurement of LCPL and RCPL is superior in detecting nondegeneracy.
Calculations of the Ground and Excited State Energies of NO2
Authors: Fink William H.
Published: February 2004

Calculations of fifteen different states of nitrogen dioxide in the ground state equilibrium geometry are reported. Nine of these are SCF calculations; the remainder are roots of a configuration interaction calculation performed using the SCF orbitals calculated for the ground state as an expansion set. The configuration interaction was performed within the A1 irreducible representation in order specifically to locate the first excited state of the same symmetry species as the ground state. A 3s-like atomic orbital was included in the basis set in order to more adequately represent molecular orbitals tending toward Rydberg levels. The SCF energy for the ground state was calculated to be − 203.907 a.u. The configuration interaction calculated yielded an energy of − 203.949 a.u. for the ground state. Probable assignments of the electronic transitions involved in the spectrum of nitrogen dioxide are discussed.
Investigation of the A11 Excited States of Water
Authors: Bishop David M. , Wu Ay-ju A.
Published: February 2004

The first six A11 excited states of water are investigated within the framework of the single-center method. Energies, wavefunctions, and electronic densities are found using a basis set which consists of 29 Slater-type orbits (with noninteger principal quantum numbers). For each state the orbital parameters (n's and ζ's) are carefully optimized. The ordering of the states and the major contributing configuration of each state is in agreement with experiment. Particular emphasis is placed on the electronic rearrangement that occurs during excitation, and this is explicitly brought out by the contour maps of the electronic density.
Electron Nuclear Double Resonance of Photoexcited Anthracene Molecules in Their Lowest Triplet State in Phenazine Single Crystals
Authors: Clarke Richard H. , Hutchison Clyde A.
Published: February 2004

The electron paramagnetic resonance and proton electron nuclear double resonance spectra of anthracene molecules in their lowest energy photoexcited states in a single crystal of phenazine have been studied. The values of the fine structure parameters and of the components of the proton electron hyperfine interaction tensors, in the fine structure principal axis system, have been determined and tabulated. The values of spin densities and of anisotropic and isotropic proton hyperfine interactions per unit spin density on the adjacent carbon, which best describe the experimental results, have been determined, discussed, and compared with similar values for other systems.