bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-of-Flight Determinations of Electron Diffusion Coefficients and Electron Drift Velocities in Ethylene, Water Vapor, and in Hydrogen
Authors: Hurst G. S. , Parks J. E.
Published: January 2005

The time-of-flight method for the determination of electron diffusion coefficients D and drift velocities w of electrons in gases has been improved in two essential ways. First, an accurate method of measuring all fluctuation in the time-of-flight distribution, except that due to the diffusion process itself, has been developed. Second, a data analysis procedure has been worked out in which the effects of instrumental fluctuations are removed and accurate values of the parameters D and w are found from a generalized least-squares procedure making use of a digital computer. Distortions in the electron time-of-flight distributions arising out of electron losses during detector dead times were calculated by assuming that single-electron detection follows Poisson statistics. This assumption was examined experimentally and was not found to be in error. Application of the improved method has been made to ethylene, ethylene—water vapor mixtures, and hydrogen over the range of E/P from 0.01 to 1.0 V cm−1·torr−1. Independent measurements of the quantities D and w were made; the ratios D/w were compared with theory in the region of thermal electron energies. The ratio of the momentum transfer cross sections for H2O compared to ethylene was essentially the same whether use was made of D(E/P) or w(E/P) data in the region of thermal energies. In the cases of ethylene and ethylene—water vapor mixtures, it was found that the value of D/w for thermal electrons was 12% higher than the theoretical value.
Helium Molecular Radiation in the Positive Column of a dc Discharge
Authors: Hurt W. B. , Collins C. B.
Published: January 2005

Helium atoms in the 23P level are shown to significantly contribute to the formation of excited helium molecules in the positive column of a dc discharge.
Conductivity and Crystal Phase Change in Phthalocyanines
Authors: Harrison S. E. , Ludewig K. H.
Published: January 2005

The crystal phase transition in phthalocyanines is shown to have no influence on the electrical conductivity; the intrinsic conductivities are identical. The changes in intermolecular overlap are too small to be discerned. The stronger propensity of the α phase to absorb oxygen is the source of the apparently higher conductivity of the α phase.
Simultaneous Donor Quenching and Acceptor Sensitization in Phosphorescence Studies of Triplet Energy Transfer: The Biacetyl—Benzil System
Authors: Richtol H. H. , Belorit Arlene
Published: January 2005

The simultaneous measurement of donor quenching and acceptor sensitization of a triplet-energy-transfer system as studied by phosphorescence techniques is presented. The quenching constant (KQ = 900±90 liter mole−1) is found to be different than the sensitization constant (KS = 390±40 liter mole−1). A general mechanism is proposed which accounts for these results, and also for cases where KS = KQ. Arguments are presented for the reevaluation of the triplet energies of benzil and anisil, and the newly appraised values are ET (benzil) = 19 000 cm−1 and ET (anisil) = 19 300 cm−1.
Time-Dependent Ising-Model Description of Binary Liquid Mixtures
Authors: Heims Steve P.
Published: January 2005

Phase transitions are not only characterized by singularities in thermodynamic derivatives, but also by peculiarities in the time-dependent behavior of the system. By employing a time-dependent generalization of the Ising model and a master equation, the relaxation of a local deviation from equilibrium for a system near its critical temperature is described. Approximate solution of the equations yield results in agreement with recent optical experiments, in which the decay of concentration fluctuations in critical mixtures of liquids is measured; results are also consistent with NMR measurements in antiferromagnets. If the equations are solved more accurately, however, it is found that the decay of a local displacement from equilibrium concentration in the critical region is in general not describable by a single exponential.
Ionization Potential of the CH2 Free Radical by Mass Spectrometry
Authors: Foner S. N. , Hudson R. L.
Published: January 2005

Mass-spectrometric studies of the methylene free radical, produced by short-duration pulsed electrical discharges in methane, give for the ionization potential the value I (CH2) = 10.33±0.1 eV, in good agreement with the spectroscopically determined value I (CH2) = 10.396 eV, thereby removing the large discrepancy that had previously existed between electron-impact and the optical spectroscopic measurements of the ionization potential. The absence of resolved structure in the CH2 ionization curve indicates that the energy separation between the ground states of the two known modifications of CH2, the linear form in the 3Σg− state and the bent form in the 1A1 state, is small but the information is insufficient to establish which is the true ground state of the molecule. In the course of the work, the ionization potential of the methyl radical was remeasured with the result I (CH3) = 9.86 eV, in excellent agreement with the spectroscopically known value I (CH3) = 9.843 eV.
Electric Dipole Moment of the Lowest Singlet π* State of Propynal
Authors: Freeman D. E. , Lombardi J. R. , Klemperer W.
Published: January 2005

Stark-effect measurements of the 0–0 band of the 3820-Å transition (1A″←1A′) have been made. Analysis of the pP subbands with K″ = 9, 10, and 11 yields a value μa′ = 0.7±0.2 D. The other component of the dipole moment, μb′, of the upper state is not determined. The relatively complex spectrum produced in the Stark effect is readily simulated by computed spectra. The techniques used appear to be applicable to complex spectra.
Effect of Pressure on the Melting Points of the Sodium Halides
Authors: Pistorius Carl W. F. T.
Published: January 2005

The melting curves of the sodium halides have been determined to 40 kbar. The present curves for NaCl and NaF are in agreement with Clark's corrected curves to 17 kbar, but the agreement for the other sodium halides is less good. There are no triple points on the melting curves to 40 kbar and it is concluded that the transitions found previously in NaF and NaCl near ∼20 kbar, if real, are metastable and shear induced.
EPR in Selenium
Authors: Sampath P. I.
Published: January 2005

EPR studies at X-band frequencies have been carried out between 300° and 77°K on amorphous and crystalline selenium. Dominating the spectra of the amorphous material were a large number of paramagnetic centers ∼1019/cc which contribute to an unusually broad and inhomogeneous line of width, ΔHp p∼3Kg and g=2.3 to 2.8±0.01. The linewidths and g values were very sensitive to heat treatments. This broad line is attributed to electrons at chain ends in a highly disordered region of the solid. A different species was also present in much lower concentrations ∼1013/cc, as observed by a sharp resonance with peak-to-peak linewidth, ΔHp p∼6 G and g=2.0039±0.0006, which is close to the g value of 2.0023 for a free electron. Heat treatments altered the magnitude of the signal in an erratic manner and up to ∼1016/cc spins were observed with no changes in ΔHp p or g value. The identification is rather uncertain. Theoretical considerations of the g value and linewidth favor a center associated with an impurity (i.e., oxygen) at the end of the selenium chain but have shown that a chain end interacting with a neighboring chain cannot be ruled out. Experimental results tending to minimize the role of oxygen were that no conclusive differences were observed when samples were heat treated in air or vacuum or prepared by evaporation, and the appearance of a virtually identical resonance when single crystals of hexagonal selenium were damaged (mechanically and by electron bombardment).

No resonances were found in pure ``as grown'' monoclinic or hexagonal selenium. This result was unexpected for the latter material, and chemisorption of oxygen on the surface is thought to be the explanation.
Shape of Emission Bands of Fluorescent Complex Molecules
Authors: Voorhof H. , Pollak H.
Published: January 2005

The shape of emission bands is determined by the vibrational-energy distribution of the luminescence centers and by the form of the potential curves. A new potential is introduced, permitting us to establish the intensity distribution within a band as a function of frequency and temperature. The calculations are based on a semiclassical approximation of the Franck—Condon factors and are worked out with the aid of the Mehler formula. The obtained expression is in close agreement with the experimental results.
Absorption and Emission Spectra of Anthracene Dimers
Authors: Chandross Edwin A. , Ferguson J. , McRae E. G.
Published: January 2005

The preparation of two types of anthracene dimer is described and their absorption and fluorescence spectra are reported. The basic spectral features of each dimer, together with a consideration of the method of formation, enable us to assign a geometry to each pair. One dimer, prepared by photolytic dissociation of dianthracene, has a symmetrical sandwich configuration. The geometry of the other dimer, prepared in solution at low temperatures, is deduced from an analysis of the vibronic structure of its first absorption band (1A1g→1B2u transition of a single molecule) using the theory of vibronic coupling in dimers. The two molecules have a configuration related to that of the two molecules in the unit cell of the crystal; one in which the short in-plane axes make an angle of 55 deg with each other while the long axes are parallel. The resonance splittings of the 1B2u and 1B3u states in each dimer are deduced from the spectra and the results are discussed in relation to the theories of the energy levels of dimers. The fluorescence of the sandwich dimer is of the excimer type while the fluorescence from the other dimer is excited dimer emission with a vibrational intensity distribution different from that in the corresponding monomer spectrum.
Microwave Spectrum, Quadrupole Coupling Constants, and Dipole Moment of Carbamyl Fluoride
Authors: Rigden John S. , Jackson Robert H.
Published: January 2005

The microwave spectrum of carbamyl fluoride, H214N12COF, has been studied. The rotational constants are A = 11 304.39 Mc/sec, B = 11 176.14 Mc/sec, and C = 5616.06 Mc/sec. The quadrupole coupling constants have been determined from the splittings of low-J transitions. These are eQqm = −4.05 Mc/sec and η=−0.165. Two components of the dipole moment were determined and are μa = 3.33 D and μb = 2.31 D. No excited-state spectrum was observed.
Minimization of the Width as an Alternative to the Conventional Variation Method
Authors: Goodisman Jerry
Published: January 2005

The choice of param eters in a trial function to minimize the width Q2 (Q2 = 〈H2〉 − 〈H〉2 for a normalized wavefunction) is an alternative procedure to the usual minimization of 〈H〉 for generation of approximations to the true wavefunction. The minimization of the width is related to solving the eigenvalue equation by making the local energy HΦ/Φ as constant as possible, and other arguments can be put forth which suggest that this procedure should yield a wavefunction closer to the exact than that given by the usual variational method. For the ground state of H2 near its equilibrium internuclear distance, we choose the parameters ci in Φ = ΣiciΦi to (a) minimize the width and (b) minimize the energy. The expectation values from the function obtained by (a) are almost always worse than those from (b). Modifications of procedure (a) designed to improve the wavefunction in a specific region of configuration space were also attempted, without encouraging results.
Natural, Brueckner, and SCF Orbitals for Alternant Systems
Authors: Koutecký Jaroslav
Published: January 2005

It is shown that natural orbitals, Brueckner orbitals, and SCF orbitals have pairing properties for alternant systems, where alternant systems are defined as systems with polyelectronic Hamiltonians fulfilling a certain commutation relation with the pairing operator. For an alternant system, the sum of the occupation numbers for two paired natural orbitals is equal to 1. The eigenvectors of the spinless density operator and of the resultant spin-density operator have properties similar to the properties of corresponding quantities in the one-electron approximation. This is shown to be partly true even for the density operator of the second order. The conditions sufficient and necessary for the existence of alternant properties for a group of electrons in a molecule are formulated. A concept of contraction of an operator is introduced, which allows unique formulation of the density operators, Hartree—Fock effective Hamiltonians and other quantities in second quantization formalism.
Molecular Properties Which Depend on the Square of the Electronic Coordinates; H2 and NNO
Authors: McLean A. D. , Yoshimine M.
Published: January 2005

Relationships betwen the diamagnetic susceptibility, diamagnetic anisotropy, rotational magnetic moment, molecular quadrupole moment, and computed expectation values of 〈r2〉, 〈p2〉, 〈z2〉 for linear closed-shell molecules are given. A promising way of obtaining molecular quadrupole moments by combining theory and experiment is pointed out. Applications are made to H2 and N2O. New results are that the sign of the rotational g factor for N2O is negative and the diamagnetic anisotropy of this molecule is −13×10−5 a.u.
Geometry of Molecules. III. F2O, Li2O, FOH, LiOH
Authors: Buenker Robert J. , Peyerimhoff Sigrid D.
Published: January 2005

LC (Hartree—Fock) AO MO SCF calculations have been carried out for F2O, Li2O, FOH, and LiOH. Correlation diagrams showing the variation of orbital energies with internuclear angle have been constructed and demonstrated to be the theoretical counterparts to previous empirical correlation diagrams given by Mulliken and Walsh. Consideration of mathematical inequalities arising from the Hartree—Fock equations emphasizes the geometry-determining nature of the orbital-energy sum; at the same time such an investigation relates the fact that the sum of orbital energies does not have a minimum for the equilibrium linear configurations of Li2O and LiOH to the highly ionic character of these systems.
On the Excitation Spectrum of Polystyrene in the Vacuum Ultraviolet
Authors: Leibowitz M. , Weinreb A.
Published: January 2005

The over-all fluorescence yield of polystyrene has been investigated as a function of excitation wavelength in the region 2850–584 Å. Polystyrene dissolved in cyclohexane and solid samples of polystyrene after various modes of treatment (machining, pressure, polishing, etc.) as well as thin films were investigated. In all cases a strong dependence of the quantum yield on excitation wavelength has been found. The behavior of polystyrene in solution is basically different from that of the solid plastic. For the solid two types of behavior have been found, depending on the preparation of the sample. The results indicate the decisive influence of the state of aggregation on the luminescent behavior for excitation of the higher electronic levels.
Isotope Effects in the 77°K γ Irradiation of Ice
Authors: Siegel Seymour , Rennick Robert
Published: January 2005

The radiation yields of H2, D2, and HD obtained by the 77°K γ irradiation of solute-free mixed H2O and D2O ice mixtures have been determined by use of mass spectroscopy. The total gas yields have been determined, too, both by use of a calibrated mass spectrometer and by manometric methods. Significant isotope effects were observed over a wide range of the isotopic compositions studied (i.e., the deuterium content varied from ∼0.016% to 99.8%). The separation factor αG=(H/D)gas(H/D)icevaried from about 70 for the high D content ice to about 1.0 for natural isotopic abundance ice. At (H/D)ice=1.0, αG is 1.7. Values of αG were obtained for 99.80% D2O over a temperature range of 4.2° to 196°K. The separation factor was found to be inversely proportional to temperature. The results of this study are compared with those in a previously published EPR study of stabilized H and D atoms after irradiation at 4.2°K. The observed effects are discussed briefly in terms of several models of selective energy absorption.
Study of Inelastic Collisions by Drifting Ions
Authors: Kaneko Y. , Megill L. R. , Hasted J. B.
Published: January 2005

A series of experiments has been performed in which a mass-analyzed ion beam is injected into a drift tube containing gas. The ions drift through the tube under the action of a uniform electric field and they undergo inelastic processes. The product ions are mass analyzed upon exit. The drift velocity and the ratio of the primary and secondary ion currents are measured as a function of the electric field and the gas pressure in the drift tube. From these data the cross section of the process is calculated. The effect of the lateral diffusion in the drift tube is discussed theoretically.

Cross sections are determined in the energy range from 0.06 to 10 eV for the processes, Ne++Ar→Ne+Ar+,Ar++Ne→Ar+Ne+,O++N2→O+N2+,O++O2→O+O2+.Because of the nature of the ion source used these processes are supposed to be conducted largely by the ions in their excited states. It is shown that the cross sections of the former two processes agree well with predictions based on the theory of Rapp and Francis if appropriate combinations of excited states are assumed. At the high-energy end, the cross sections of the latter two processes agree well with the results of the beam experiment of Stebbings et al. At the low-energy end, the cross section of the last process agrees well with experimental result of Fehsenfeld et al. at room temperature. A remarkable minimum is found in the last process.
Theory of Relaxation Phenomena in Polymers. I. Rotational Motion of Side Elements around the Backbone
Authors: Work R. N. , Fujita S.
Published: January 2005

Dielectric relaxation in polymers is investigated by means of an extension of Glauber's dynamical theory of the Ising model. The theory is applied to a linear chain of rotators with arbitrary interactions between neighbors, and the frequency dependence of the complex electric susceptibility is found to be simply expressed in terms of the Fourier—Laplace transform of a correlation function. The latter is related to the extent of correlated motion of nearby segments. If the correlation function contains a time dependence of the form (1/τ1) exp(—t/τ1), where τ1 is the time constant for the establishment of the equilibrium correlation function, then both the effective dielectric relaxation time and the effective dipole moment of the dipolar rotators are frequency dependent. A time dependence of this form may introduce asymmetry or even a bimodal structure into the dielectric loss spectrum. The temperature dependence of the spectrum is discussed within the framework of the theory, and application is made to mechanical-relaxation phenomena. The direction of continuing efforts to extend the theory to other modes of internal motion is indicated.
Semiempirical Molecular Orbital Calculations. III. The Resonance Integral in the Wolfsberg—Helmholz Method
Authors: Carroll D. G. , McGlynn S. P.
Published: January 2005

The approximation for the resonance integral in the Mulliken—Wolfsberg—Helmholz semiempirical MO method Hij=½k(Hii+Hjj)Sij is examined. It is shown that the electronic energy is better represented by k=(2—| Sij |) than by a constant k=1.75. Some support for k=(2—| Sij |) is obtained by comparison with the Hartree—Fock Hamiltonian matrix elements in B2 and BH. Bond lengths calculated using either value of k have little or no physical significance. It is shown that with k=1.75 the calculated bond lengths decrease rapidly as the π contribution to the bonding increases.
Nuclear Magnetic Double Resonance with an Incoherent Radio-Frequency Field
Authors: Ernst R. R.
Published: January 2005

The decoupling of heteronuclear spin systems by means of a strong irradiation of rf magnetic random noise is explored theoretically and experimentally. It is shown that it is feasible to eliminate simultaneously all splittings due to one or more nuclear species. Double resonance with random noise is of particular advantage if the resonance frequencies of the nuclei causing the splittings cover a wide spectral range and if, at the same time, the couplings are relatively weak. In the case of a narrow spectral range and strong couplings, double resonance with a coherently frequency-modulated rf field can give comparable decoupling effects. Double resonance with random noise has a strong similarity to the effects of chemical exchange and relaxation.
Mass-Spectrometric Study of Ions at Near-Atmospheric Pressure. III. The Alpha Radiolysis of Methane
Authors: Haynes R. M. , Kebarle P.
Published: January 2005

The ion—molecule reactions occurring in the alpha-particle radiolysis of methane have been studied in a mass spectrometer under near-conventional radiolysis conditions (1–160 torr pressure and a few milliseconds ion reaction time). Comparison of the observed high intensities of CH5+ and C2H5+ at 1 torr with spectra obtained previously with conventional microsecond reaction times shows that the reactions of CH5+ and C2H5+ with methane are very slow (k<10−15 cc molecule−1·sec−1). At higher pressures CnH+2n−1, CnH+2n+1, and CnH+2n+3 are observed with n≦6. The addition of trace concentrations of normal and deuterated hydrocarbons helps to elucidate some of the reactions involved. The ions observed in the presence of traces of deuterated alkanes present a complete confirmation of reactions proposed earlier by Ausloos whose work was based on neutral product studies in α-radiolyzed methane and deuterated alkanes. The present work with additives shows that impurities at concentrations of 1 ppm affect the course of the ionic reactions in the radiolysis of methane at near-atmospheric pressures. The origin of the ions observed in the present work in ``pure'' methane at pressures above 10 torr is therefore uncertain. These ions are probably largely due to impurities.
X- and γ-Ray-Induced Radiolytic Isomerization of Solutions of Stilbene
Authors: Fischer Ernst , Lehmann H. P. , Stein Gabriel
Published: January 2005

X-ray and γ-ray irradiation of benzene solutions of cis- or trans-stilbene causes interconversion towards a stationary cis→trans mixture. The yield of interconversion is smaller for cis→trans than for trans→cis. Both yields increase with stilbene concentration up to a limiting G(trans→cis) of about 2.5 at 0.1M, which corresponds to G(excited stilbene) of about 5. At low stilbene concentrations the yield is lowered by oxygen and by anthracene and enhanced by naphthalene, triphenylene, phenanthrene, and diphenyl. Diacetyl and p-terphenyl preferentially enhance the trans→cis conversion. The results are explained on the basis of primary excitation of solvent benzene which forms excited stilbene by energy transfer, as in photosensitized isomerization. Direct excitation and possibly charge recombination may account for the primary solvent excitation. Enhancement by additives is due to energy transfer from excited benzene to form eventually triplet additive, which, owing to its much longer lifetime, has a greatly improved chance to transfer its energy to stilbene, at lower concentrations of the latter. A detailed study was made of the change of G(isomerization) with the concentration of stilbene (5×10−5 to 10−1M) and of naphthalene (0–7.8M). For 0.1M trans-stilbene, G(formation of excited stilbene) is about 5 in benzene and about 6 in molten naphthalene. Cyclohexene, used as a specific scavenger of triplet benzene, retards the isomerization by about one-third, while nitrous oxide, used as an electron scavenger, has no effect. Isomerization yields in toluene are higher than in benzene, while those in methylcyclohexane are much lower. Addition of naphthalene strongly increases the isomerization yields in both solvents, just as in benzene. No significant temperature dependence was found. X rays at 200 kV have only about 60% of the efficiency of 60Co gamma rays.
Electron Spin Resonance of Fe(CN)5NO3− and Fe(CN)5NOH2−
Authors: van Voorst J. D. W. , Hemmerich P.
Published: January 2005

It has been shown by means of ESR in aqueous, nonaqueous, and aprotic solution as well as in irradiated single crystals in the temperature range of 77°—300°K, that two paramagnetic species are obtained by reduction of pentacyanonitrosoferrate(II) which are in a protonation—deprotonation equilibrium. In support of the ESR data, electronic spectra have been investigated and pKa values have been determined by acidimetry and spectrophotometry. The spin density was calculated from ESR data of nFe(CN)5NO3− for n=56, 57 isotopes and found to be consistent with the lowest antibonding orbital being mainly π*NO.
Single-Center Calculations on the Lowest-Lying Πu and Πg Excited States of H2
Authors: Hoyland James R.
Published: January 2005

Single-center wavefunctions are constructed for the lowest-lying singlet and triplet Πu(1sσ2pπ) and Πg(1sσ3dπ) excited states of the hydrogen molecule using a basis set of integral Slater-type orbitals centered at the molecular midpoint. It is found that the convergence is more rapid than for a corresponding single-center calculation on the ground state. The error in the binding energy is about 0.065 eV for the Πu states and 0.033 eV for the Πg states if a 19-term configuration-interaction wavefunction is used for the description of each.
Temperature Dependence of the Total Intensity of Difference-Band Systems: The 10-μ Band System of CO2
Authors: Malkmus W. , Ludwig C. B. , Ferriso C. C.
Published: January 2005

The temperature dependence of the total intensity of difference-band systems is discussed and a general expression is given in the harmonic-oscillator approximation for difference transitions between two nondegenerate vibrations. The results are compared with experimental measurements of the sum of the total intensities of the (ν3—ν1) and (ν3−2ν2) difference bands of CO2 (the 10-μ band system). New data are presented at temperatures higher than previously investigated (up to 2300°K). In the temperature range studied, the main contribution to the temperature dependence comes from the Boltzmann term.
Distinction between Intermediates Produced in Main and Side Electrodic Reactions
Authors: Damjanovic A. , Genshaw M. A. , Bockris J. O'M.
Published: January 2005

A diagnostic criterion was developed to distinguish between an intermediate formed in an over-all reaction path and a product in a parallel electrochemical reaction. It utilizes the method of the rotating-disk electrode with a concentric ring, first proposed by Frumkin and Nekrassov. From the dependence of currents at the disk and at the ring electrode on the rate of disk rotation, individual rates of parallel reactions can be obtained.
Gas-Phase Electron Resonance Spectra of Fluorine and Chlorine Atoms in Their Ground (P322) and Excited (2P½) Electronic States
Authors: Carrington Alan , Levy Donald H. , Miller Terry A.
Published: January 2005

The gas-phase electron resonance spectra of fluorine and chlorine atoms in their ground (P322) and excited (2P½) states are described. Fluorine atoms are formed by passing CF4 through a microwave discharge; the P322 spectrum shows six strong lines and five weaker lines, three of the latter being previously unreported and arising from ΔMF=0 transitions. Two lines of the 2P½ spectrum are detected and their intensity relative to that of the ground-state spectrum indicates a non-Boltzmann distribution between the P322 and 2P½ states.

Chlorine atoms are formed by passing CF3Cl or CF3Cl/Cl2 mixtures through a microwave discharge. In addition to the intense 35Cl and 37Cl P322 spectra, four weak lines arising from excited 35Cl 2P½ atoms are detected. The intensities of these lines also indicate a non-Boltzmann distribution between the ground and excited states.
ESR Absorption Spectra of Two Phosphorous Defect Centers in Irradiated Single-Crystal Calcite
Authors: Serway R. A. , Marshall S. A.
Published: January 2005

Two paramagnetic defect centers associated with phosphorous impurities and corresponding to S=½ and I=½ have been observed in irradiated single-crystal calcite. One center, which is produced by γ irradiation, has an ESR absorption spectrum which consists of six doublets at 77°K and below, each exhibiting orthorhombic symmetry with spin-Hamiltonian parameters given by gxx=2.0072, gyy=2.0033, gzz=2.0122, Axx=52.53 Mc/sec, Ayy=56.16 Mc/sec, and Azz=52.21 Mc/sec, where the relation between the x, y, z coordinates and those of calcite is discussed. As the temperature is raised, the lines of this spectrum are observed to broaden and at about 150°K the spectrum collapses into one doublet pattern which exhibits symmetry about the calcite (111) direction suggesting that the coordinates of the defect center undergo some form of motion whose mean z axis is parallel to the calcite (111) direction. This behavior is attributed to thermally induced reorientations of the defect between six magnetically inequivalent sites. The activation energy for this reorientation is estimated to be 0.10 eV from low-temperature line-broadening data. An electron—nucleus double-resonance absorption spectrum observed at 4.2°K has demonstrated the doublet to be associated with 31P. It is concluded that the center giving rise to this ESR spectrum is the PO42− molecule—ion.

The second defect center is produced by neutron irradiation and has an ESR absorption spectrum consisting of a doublet pattern which exhibits symmetry about the calcite (111) direction. This center is stable up to about 300°K and at 77°K has spin-Hamiltonian parameters given by g∥=2.00165, g⊥=2.00162, A∥=2293.2 Mc/sec, A⊥=1789.6 Mc/sec, and gnβn/gβ=−0.000608. This spectrum is identified with the PO32− molecule—ion which is believed to occur as a substitution for the carbonate ion.
Isotopic Thermal-Diffusion Factor for Krypton
Authors: Paul R. , Watson W. W.
Published: January 2005

The isotopic thermal-diffusion factor α0 for krypton has been determined over a temperature range of 242° to 643°K. An artificial mixture of krypton isotopes containing about 14% 82Kr and 10% 86Kr was utilized in this study in conjunction with a 10-tube swing separator, α0 being obtained from the concentration changes in these two isotopes only. A least-squares fitting procedure yields potential parameters α=16.1±0.6, and ε/k=244°±13°K for the exponential-six potential model. Further least-squares fitting with viscosity data gives rm=3.88±0.02 Å. Satisfactory agreements have been obtained, between experimental data and values calculated according to the present potential, for coefficients of diffusion and thermal conductivity. The calculated values for second virial coefficient from this potential, however, shows rather poor agreement with the experimental values.
Paramagnetic Relaxation of ClO2 in Solution
Authors: Adams J. Q.
Published: January 2005

The paramagnetic relaxation of ClO2 in dilute solution was studied as a function of temperature, viscosity, and solvent system. In paraffin solutions, where the ClO2—solvent interaction is apparently small, the ClO2 electron paramagnetic resonance linewidth is linearly proportional to temperature but essentially unaffected by even a hundredfold increase in solution viscosity. This unusual behavior can be rationalized quantitatively by the Brown, Gutowsky, and Shimomura random-jump spin—rotation interaction mechanism. In hydrogen-bonding or electron-donating solvents, where the ClO2—solvent interaction is known to be large, the linewidth is inversely proportional to solution viscosity in agreement with the Hubbard rotational-diffusion spin—rotation interaction mechanism.
Relaxation of Oscillators in a Gas
Authors: Rand S.
Published: January 2005

The relaxation of harmonic oscillators in a gas has been studied. Hard collisions between the oscillator and external gas particles are treated simultaneously with dissipative effects which result from many weak collisions, and the time-dependent osciliator occupation numbers are thereby obtained. The dissipative effects are treated by perturbation theory, whereas the description of a hard collision goes beyond the range of perturbation theory, although the motion of the gas particle during the collision is treated classically. In order to include these effects simultaneously, a quantum-mechanical analog of the Fokker—Planck equation is used. The relationship of the two interaction mechanisms is discussed for the case of a Coulomb interaction between the oscillator and the gas particle. A method for extending the technique, to a system more complicated than an oscillator, is proposed.
Configuration Interaction in Two- and Three-Electron Atoms
Authors: Brown Robert T. , Fontana Peter R.
Published: January 2005

The ground states of the first four members of the helium isoelectronic series and the 22S and 22P states of lithium are calculated using a configuration-interaction expansion in a complete denumerable set of single-particle functions, with one adjustable scale parameter. The best energies for the two-electron systems, obtained with 120-term expansions, are E(H−) = −0.52748, E(He) = −2.90335, E(Li+) = −7.27945, and E(Be+ +) = −13.65504, in units of e2/a0. The energies for all but He are lower than any heretofore obtained with a configuration-interaction approach. The dependence of energy on scale factor is found to be very pronounced, in contrast to the corresponding behavior for wavefunctions which contain the interparticle coordinates explicitly. The best energies for the lithium states, obtained with 208-term expansions, are E(22S) = −7.47369 and E(22P) = −7.40366. The 22S energy is not as good as has been obtained with either expansions in terms of interparticle coordinates or configuration interaction with many nonlinear parameters. The 22P energy is of approximately the same accuracy but is lower than any previously published.
Thermal Diffusion in Some Binary Mixtures of the Hydrogen Isotopes
Authors: Grew K. E. , Humphreys A. E.
Published: January 2005

Thermal-diffusion measurements have been made by the two-bulb method for the mixtures H2—HD, H2—HT, H2—D2, HD—D2, and D2—DT. With one bulb always at 293°K, the temperature of the other was varied between 14° and 195°K and the separation factor was determined. For H2—HT, the upper limit was 770°K. Values of the thermal-diffusion factor αT in the temperature range 200°—300°K, where it is nearly independent of temperature, are given for all the mixtures (Table I), and compared with measurements by other workers. The values show large discrepancies. Below 200°K, αT decreases with decreasing temperature as expected theoretically and eventually becomes negative at very low temperatures. The absolute magnitude of αT for any mixture in the region where it is negative is very much greater than that predicted unless quantal considerations are invoked.
Potential Function for the Inversion Process of Ammonia
Authors: Moccia R. , Randaccio L.
Published: January 2005

The process of inversion of ammonia has been considered as described by two totally symmetric internal coordinates.

The potential function has been chosen by theoretical considerations and the values of the parameters which appear in it have been fixed by minimizing the differences between the calculated eigenvalues of the vibrational problem and the known values of the observed frequencies. Two versions of the vibrational problem have been considered; a simplified one (monodimensional), where only the bond angles are allowed to change, and a complete two-dimensional one where the bond lengths were also allowed to change.

The potential functions so obtained give a fairly good agreement between calculated and observed frequencies. The two-dimensional potential function has the minimum at a bond length of 1.878 a.u. and at a bond angle of 105°36′ and gives a value of 0.00905 a.u. as the potential barrier to inversion. The bond length for the minimum of energy at the planar configuration is 1.837 a.u.

This potential function and the resulting eigenfunctions of the vibrational Hamiltonian have been employed to calculate some spectroscopic constants, such as the quadratic and cubic force constants related to two totally symmetric coordinates, and the differences between the rotational constants of the odd and the even levels. The agreement with the available experimental data is satisfactory. Results of the above calculations are also given for ND3.
Mass Spectrometry of Ions in Glow Discharges: Application to H2—D2 Exchange Reactions
Authors: Dawson P. H. , Tickner A. W.
Published: January 2005

The negative glow of the dc glow discharge was used to study H2—D2 exchange by an ionic chain reaction. The ions present were observed directly by mass spectrometry. The chain carrier was H3+ and the chain length about 15 at 0.3 torr. The inhibition by added rare gases was examined and detailed comparisons are made with radiolysis experiments. Qualitatively the agreement is excellent. Several possible inhibition mechanisms are considered.
On the Evaluation of Two-Center Overlap and Coulomb Integrals with Noninteger-n Slater-Type Orbitals
Authors: Silverstone Harris J.
Published: January 2005

Some formulas are developed which facilitate computation of two-center overlap and Coulomb integrals with noninteger principal-quantum-number (n) Slater-type orbitals by the Fourier-transform convolution technique. A conceptually simple, closed-form analytical expression for the overlap and Coulomb integrals with integer-n Slater-type orbitals is also given.
Born—Oppenheimer Approximation and the Calculation of Infrared Intensities
Authors: Cohan Norah V. , Hameka Hendrik F.
Published: January 2005

In evaluating transition moments it is customary to transform from the momentum representation to the dipole representation by making use of the commutator relations between the Hamiltonian and the particle coordinates. In the present paper we show that in the case of infrared, vibrational transitions it makes quite a difference whether we introduce the Born—Oppenheimer approximation before or after this transformation. In the first case the transition moment depends on the nuclear contribution to the molecular dipole moment and in the second case on the total dipole moment of the molecule. In order to dissolve this discrepancy we calculated the first-order correction to the Born—Oppenheimer approximation. We introduced this correction in the transition moment calculations and we found that the correction terms bring the two different results into agreement with each other. It was found that the correction is quite small in the case where the Born—Oppenheimer approximation is introduced after the momentum—dipole transformation and that the correction is considerable in the case where the Born—Oppenheimer approximation is introduced before the transformation. We conclude that the correct expression for the transition moment contains the derivative of the molecular dipole moment with respect to the normal coordinates of the modes of vibration, in agreement with the expressions that are customarily used.
Time-Dependent Behavior of Activated Molecules. High-Pressure Unimolecular Rate Constant and Mass Spectra
Authors: Mies F. H. , Krauss M.
Published: January 2005

A quantum-mechanical theory of the unimolecular decay of metastable or activated molecules is developed using Fano's treatment of resonance scattering. A resonance state is synonymous with the so-called activated molecule in unimolecular kinetics, and a set of widths is associated with each state which is a measure of the coupling to the various dissociation continuum channels (each channel designates an ``activated complex''). If the widths are small compared to the spacings between those neighboring states which are coupled to the same continua, then an ensemble of molecules prepared in a given activated state will decay exponentially in time, as a radiating or autoionizing excited atomic state does. However, unimolecular decay is fundamentally a problem in ``overlapping'' resonance widths, and is best considered using Fano's theory, which incorporates proper treatment of the overlap. This paper is particularly concerned with the implications of overlapping widths on the high-pressure rate constant, and on mass spectra.

There are two effects of overlapping which are most striking. First, the time decay of an ensemble of metastable molecules is no longer a pure exponential, but for the special cases considered is represented by a sum of exponential, oscillatory, and/or linear terms; this can affect the interpretation of mass spectra. Second, the high-pressure rate constant is related to the initial rate of decay of a canonical ensemble of activated molecules, and proper consideration of overlap imposes an upper bound on the rate of dissociation without any artificially imposed restrictions on the widths. This bound yields the ``universal rate constant,'' kT/h times a transmission coefficient which is a function of the widths and spacings of the activated molecules, and has an upper limit of 1.
Spectra of Praseodymium in Yttrium Gallium Garnet and in Yttrium Aluminum Garnet
Authors: Hooge F. N.
Published: January 2005

The absorption and fluorescence spectra of Pr3+ in YGaG and in YAlG were measured at temperatures between 16°K and room temperature. Crystal-field calculations, using a cubic field with A40=−350 cm−1 and A60=90 cm−1, gave a reasonable fit with the experimentally found energy levels. Some manifolds overlap due to the large crystal-field splitting. The centers of gravity found by fitting the calculated manifolds to the experimental data are close to and well in line with the centers for Pr3+ in LaCl3 and LaBr3.
Far-Infrared Spectra of Mercuric Halides and Their Dioxane Complexes
Authors: Mikawa Yukio , Jakobsen R. J. , Brasch J. W.
Published: January 2005

The far-infrared spectra (600–60 cm−1) of HgCl2, HgBr2, HgI2 (red), and their one-to-one p-dioxane complexes (in the solid state) were investigated. All of the observed spectra, except those of HgI2, were assigned on the base of the symmetry properties of the crystals. High-pressure effects were investigated for the anti-symmetric stretching vibration of HgCl2 and its dioxane complex. The frequency shifts of all of the compounds in the various states, from the gaseous state through the dioxane complex under high pressure, were elucidated in terms of the distance between the mercury atom and its nearest neighbors.
Thermodynamic Properties of Rubidium—Graphite Lamellar Compounds
Authors: Salzano F. J. , Aronson S.
Published: January 2005

Phase equilibria in the rubidium—graphite system were studied by means of the Knudsen effusion method in conjunction with a tracer technique. A new compound, C10Rb, analogous to the compound C10Cs, was observed. Vapor-pressure measurements were made in the various two-phase regions in the rubidium—graphite system at temperatures from 350° to 750°C. Thermodynamic properties were calculated from the data and are compared to the corresponding values in the cesium—graphite system.
P—R Separations and Coriolis Constants for Symmetric-Top Molecules: Force Constants for NF3, PF3, and AsF3
Authors: Hoskins L. C.
Published: January 2005

Based on the method of Edgell and Moynihan for computing the Coriolis constants of the degenerate vibrations of symmetric-top molecules from gas-phase infrared band envelopes, an equation was developed which relates the P—R branch separation to the zeta for the case of a narrow Q branch. A computer program was written for the solution of this equation and was used to determine the Coriolis constants for the v4 vibrations of NF3, PF3, AsF3, and NH3 using the previously determined P—R separations. Significant deviation between the calculated and observed value of ζ4 for NH3 was found, indicating a breakdown in the method of Edgell and Moynihan for light molecules whose rotational structure has been smoothed by an infrared-inert broadening gas. The zetas for the Group V trihalides, together with the zeta sum rules and the vibrational frequencies, were used to determine general harmonic force constants for the E-species vibrations. Equations were also developed which permit approximate zetas to be calculated from the P—R separations of the perpendicular bands.
Survey of Negative-Ion—Molecule Reactions in O2, CO2, H2O, CO, and Mixtures of These Gases at High Pressures
Authors: Moruzzi J. L. , Phelps A. V.
Published: January 2005

The negative-ion species produced in O2 and some gases containing oxygen have been surveyed for various pressure and E/p conditions using an rf mass spectrometer coupled to an electron drift tube operating at pressures up to 5 torr. The gases studied include O2, CO2, H2O, and CO as well as the mixtures CO2–O2, H2O–O2, CO–O2 at moderate and high E/p. When CO2 is present, O2− and O− are converted to CO4− and CO3−, respectively. The rate coefficients for these reactions at 300°K are approximately 1.3×10−29 and 8×10−29 cm6/sec, respectively. When H2O is present, complex ions such as (H2O)n·O2−, (H2O)n·O− and (H2O)n·OH− are formed with n≤5. In CO–O2 and H2–O2 mixtures, ion destruction, consistent with associative detachment of O−, has been observed to proceed with rate coefficients of about 10−9 cm3 sec−1.
Conductivity and Polarization Phenomena in Phenanthrene Crystals
Authors: Arndt R. A. , Damask A. C.
Published: January 2005

Dark conductivity and photoconductivity perpendicular to the a—b plane in phenanthrene single crystals were investigated. The dark conductivity shows anomalous behavior in the region of 72°C, the same temperature at which an anomaly in the heat capacity appears. An Arrhenius plot of equilibrium resistivity yields an activation energy of 1.5 eV below 72°C and 1.1 eV above 72°C. When a crystal is cooled from above 72°C in an electric field, a polarization charge is detected which is shown to be a volume rather than a surface phenomenon. When a crystal is illuminated and heated above 72°C in an electric field, it becomes permanently polarized. Electrical-conductivity measurements show that there can be photo-carrier motion in addition to the polarization current. No anomalous behavior was found in x-ray, thermal-expansion, or dielectric measurements.
Second-Order Interactions between Polar Molecules
Authors: van der Avoird A. , Hofelich F.
Published: January 2005

The interaction energy between polar molecules is calculated up to second-order perturbation contributions. The essential result is that the dipole—induced-dipole energy calculated by quantum theory differs considerably from the corresponding classical expression. This is confirmed by a variational calculation.
Volume Viscosity in Liquid Argon at High Pressures
Authors: Naugle D. G. , Lunsford J. H. , Singer J. R.
Published: January 2005

The volume viscosity in liquid argon has been calculated from ultrasonic attenuation measurements at temperatures between 85° and 145°K with pressures up to 157 kg/cm2. Measurements taken at densities from 1.06 to 1.42 g/cm3 result in values of 2.3 to 0.8 for the ratio of volume to shear viscosity. These values are compared with theoretical predictions of other investigators. It appears that the volume viscosity increases with increasing density whereas the ratio of volume-to-shear viscosity decreases. The ultrasonic attenuation rapidly increases as the temperature approaches the critical temperature. This increase in attenuation is a consequence of the change in the density and compressibility of the medium. Thus no new mechanism of dissipation is required within about 7°K below the critical temperature.
Instability of a Linear Spin Array: Application to Würster's Blue Perchlorate
Authors: Chesnut D. B.
Published: January 2005

A linear array of coupled spins is shown under appropriate conditions to be unstable with respect to alternation of the lattice parameter much like the Peierls instability of a one-dimensional metallic lattice. A second-order phase transition occurs, below which transition temperature the magnetic susceptibility decreases to zero. The model is discussed with respect to the analogous physical system of solid Würster's blue perchlorate (N,N dimethyl paraphenylenediamine perchlorate) where qualitative agreement is observed.