bluuebunny/crossref_metadata_2025 huggingface dataset:
Unitary approach to capillary condensation and adsorption
Authors: Philip J. R.
Published: February 2003

The capillary component of the potential Ψ, the partial specific Gibbs free energy associated with the solid–liquid interactions, is taken to depend on the liquid–vapor interface mean curvature; and the adsorptive component to depend on the normal distance of the interface from the solid. The equilibrium condition that it is a surface of constant Ψ then yields the differential equation of the interface. Simple methods of solution are developed for two-dimensional (spaces between parallel plates, wedge-shaped pores, spaces between circular cylinders) and axisymmetrical (circular tubes, spaces between spheres) configurations. Illustrative examples are given for capillary condensation of water vapor ( relative humidity 0.70–0.98) at 300 K in the space between parallel plates; in wedge-shaped pores with semiangles π/12, π/6, and π/4; and in circular tubes. We find values of ‖Ψ‖ between plates and in tubes which are, respectively, 60% and 44% greater than the values given by the Kelvin equation; and we find for wedges very much greater condensation for a given Ψ than the Kelvin equation predicts. These examples suggest, further, that the expedient of allowing for adsorption by modifying the radius of curvature in the Kelvin equation by an assumed constant film thickness is inadequate. The extension of the approach to include gravity is indicated.
Pulsed photoconductivity action spectra of β-metalfree phthalocyanine thin films
Authors: Popovic Zoran D. , Sharp James H.
Published: February 2003

Using pulsed photoconductivity techniques, transient action spectra have been recorded on vacuum sublimed β-metalfree phthalocyanine thin films in the wavelength range 360♯740 nm. Quantum efficiencies for carrier generation and carrier ranges were deduced assuming (a) range limited transport and (b) wavelength and field independent quantum efficiency. Carrier generation is shown to be a bulk phenomenon and the lowest excited singlet state is the common intermediate in the carrier generation process. Two sets of measurements have been performed, 5 and 12 weeks after sample preparation. The quantum efficiency changed from 2.5×10−4 to 10−3, probably due to an increase in the amount of absorbed oxygen.
Carbon-13 NMR of carbon monoxide. I. Pressure dependence of translational motion in β-CO
Authors: Fukushima Eiichi , Gibson A. A. V. , Scott T. A.
Published: February 2003

Activation parameters for self-diffusion of carbon monoxide molecules have been studied in the hexagonal beta phase of CO as a function of pressure and temperature. The carbon-13 nuclear transverse relaxation time T2, which is proportional to the average molecular jump rate τ−1, was measured by the Carr–Purcell Meiboom–Gill method. The activation enthalpy increases from 13 to 16 kJ/mole between 0 and 1.75 kbar and the activation volume is 44±5 cm3/mole, which corresponds to 1.5 molar volumes. The results indicate a single diffusion mechanism in this P–T range; most probably the diffusion takes place by migration of monovacancies.
Hartree–Fock electron affinity of the CN radical
Authors: Pacansky J. , Liu B.
Published: February 2003

Self-consistent-field calculations on CN(X 2Σ+) and CN−(X 1Σ+) have been performed at several internuclear separations. The estimated Hartree–Fock limit value for the adiabatic electron affinity of CN is 3.29±0.05 eV as compared with the observed value of 3.82±0.02 eV. A qualitative explanation has been proposed for the large electron affinity of CN.
Molecular calculations with the MODPOT, VRDDO, and MODPOT/VRDDO procedures. II. Cyclopentadiene, benzene, diazoles, diazines, and benzonitrile
Authors: Popkie Herbert E. , Kaufman Joyce J.
Published: February 2003

A procedure for carrying out nonempirical LCAO–MO–SCF calculations on large molecules is outlined. Use is made of an approximation for neglecting some one- and two-electron integrals proposed by Wilhite and Euwema. The differential overlap between a pair of basis functions is set to zero if the pseudo-overlap is less than the adjustable threshold. We refer to this method as variable retention of diatomic differential overlap (VRDDO). In addition, only the valence electrons may be explicitly considered. The influence of the core electrons is taken into account by using the model potential (MODPOT) Hamiltonian suggested by Bonifacic and Huzinaga. The two methods can be used together resulting in the MODPOT/VRDDO procedure. VRDDO, MODPOT, and MODPOT/VRDDO calculations are reported for cyclopentadiene, benzene, pyrazole, imidazole, pyridazine, pyrimidine, pyrazine, and benzonitrile. The accuracy of the VRDDO calculations is very good. Orbital energies and gross atomic populations differ from the reference values by only 0.001–0.002 a.u. The maximum error in the total energy is 0.0024 a.u. and in the dipole moment is 0.009 a.u. Valence electron-only calculations with the MODPOT and MODPOT/VRDDO procedures yield orbital energies and charge densities that the quite good in comparison with the ab initio calculations taking all electrons into consideration. Orbital energies and gross atomic populations differ from the reference values b by 0.001–0.011 a.u. The maximum error in the dipole moment is 0.018 a.u. For benzonitrile, the largest molecule studied, introduction of the VRDDO procedure results in a 25% saving in computer time. The MODPOT calculation is three times faster than the ab initio reference calculation, while the MODPOT/VRDDO calculation is four times faster.
Determination of potassium ion–rare gas potentials from total cross section measurements
Authors: Budenholzer F. E. , Gislason E. A. , Jorgensen A. D.
Published: February 2003

Incomplete total cross sections have been measured for K+ scattered by He, Ne, Ar, Kr, and Xe in the range EΘR=2–100 eV deg. Here E is the energy of the K+ beam, and ΘR is the nominal resolution angle of the apparatus. The cross sections have been analyzed to obtain estimates of the potentials in the region of the attractive well. The results are compared with other theoretical and experimental work on these systems.
Infrared spectra of isotopically mixed CO2 crystals
Authors: Cahill J. E.
Published: February 2003

Infrared spectra are reported for 12C16O2/13C16O2, 12C16O2/12C18O2, and 12C18O2/13C16O2 mixed crystals throughout their complete concentration ranges. The changes with concentration in both the frequencies and the line shapes are in reasonable agreement with current theories of the effects of impurities on exciton states. An apparent exception is an anomalously rapid broadening with concentration in impurities whose transition energies are larger than that of the host. Effects due to interference between guest and host spectral bands, reflection, and possibly particle shape are observed. An analysis of the frequencies of dilute impurities indicates that the ν2 vibrational exciton band has a highly asymmetric density of states with a second moment of about 30 cm−2 and a total spread of about 22 cm−1.
CNDO/S studies on the electronic structure of carbazoles. I. The parent molecule
Authors: Bigelow R. W. , Johnson G. E.
Published: February 2003

A semi-empirical molecular orbital calculation, using the CNDO/S spectral parameterization of Del Bene and Jaffe, has been carried out for carbazole. The ground state occupied orbital eigenvalues are used to provide an orbital assignment of the photoelectron spectrum of carbazole. A limited configuration interaction procedure, utilizing the lowest 60 singly excited configurations, is subsequently carried out to determine the energies of excited singlet and triplet states of carbazole. Agreement between theoretical calculations and experimental results for the lower lying electronic transitions of carbazole is such as to allow higher lying transitions to be assigned with a degree of confidence.
Orbital level splitting in octahedral symmetry and SF6 rotational spectra. I. Qualitative features of high J levels
Authors: Harter William G. , Patterson Chris W.
Published: February 2003

The interesting qualitative features of octahedral symmetry splitting of orbital levels with large angular momentum are derived using a simple quantum mechanical model. The clustering of certain octahedral group representations which has recently been observed in high resolution SF6 spectra is explained in detail. Semiquantitative formulas for splitting of the clusters are derived. An analogy with electron energy bands and Bloch waves is shown. The groundwork is laid for a quantitative theory which is given in the following article.
Orbital level splitting in octahedral symmetry and SF6 rotational spectra. II. Quantitative treatment of high J levels
Authors: Patterson Chris W. , Harter William G.
Published: February 2003

We give a quantitative analysis for the clusters of octahedral terms which appear in the high resolution rotational spectra of SF6 for large angular momentum. We derive approximate expressions for the cluster energies and the splittings within each cluster which obviate the diagonalization of the octahedral deformation potential.
A flash photolysis–resonance fluorescence study of the O+C2H2 and O+C2H3Cl reactions
Authors: Westenberg A. A. , deHaas N.
Published: February 2003

The kinetics of the reactions O+C2H2 and O+C2H3Cl have been studied at room temperature by the flash photolysis–resonance fluorescence technique. In the O+C2H2 case the measurements were complicated by a strong background chemiluminescence in the vacuum ultraviolet which had to be subtracted from the total observed photon count. The overall O+C2H2 rate constant based on the measured O decays (at 297±1°K) was 7.2±0.2×1010 cm3 mole−1⋅s−1. The chemiluminescent backgrounds were interpreted in terms of a suggested mechanism in the literature, and the O+C2H2 rate constant derived from the chemiluminescent decays was 8.2±0.2×1010. The measured overall O+C2H3Cl rate constant (much less complicated by background chemiluminescence) was 4.1±0.1×1011. Comparisons with literature data are made.
Accurate determination of H2, He, and D2 Compton profiles by high energy electron impact spectroscopy
Authors: Lee J. S.
Published: February 2003

The effective nonrelativistic Compton profiles J (q,K) of H2 and He {defined in terms of the absolute generalized oscillator strength (GOS), df (K,E)/dE, as J (q,K) = (2K3/E)[df (K,E)/dE], where q is (E−K2)/2K, with K the momentum transfer and E the energy loss} have been studied as a function of scattering angle by means of high energy electron impact spectroscopy (HEEIS) with an incident energy of 25 keV over an angular range of 3°–10°. It was found that the binary encounter limit is not reached until the x-ray incoherent scattering factor reaches its large K asymptotic limit N, the number of target electrons. At 10° , the results of the Compton profiles of He and H2 were fitted by least squares to a polynomial of the form Σmn=1{an/[1+(q/ζn)2]n+2}, which leads to analytic expressions for the one electron momentum density and its integer powered moments. The fits proved to be radically different for He and H2. The experimental values for the moments of the momentum density function were found to be in excellent agreement with the best available theoretical results. In addition, the Compton profile of D2 at 8° was measured and no significant deviations from the Compton profile for H2 were observed. The new results reported here for H2 clear up a disagreement between theory and experiment and suggest that quoted uncertainties in the previous studies were unrealistically small owing to improper analysis of systematic experimental errors.
Approximate nonperturbative model of the nonresonant half-widths for a gas of symmetric top molecules
Authors: McMahon D. R. A.
Published: February 2003

An approximate theory which neglects rotationally inelastic collisions but includes molecular reorientations is developed and applied to the problem of nonresonant half-widths. Unlike a perturbative theory, the theory gives half-widths of the correct order of magnitude although still too small by 40% or more. The relative successes of the calculation of nonresonant half-widths and the resonant half-widths for the NH3 inversion spectrum are contrasted.
Viscous liquids and the glass transition. VI. Relaxations in simple molecule glasses in the 4–77 K range
Authors: Hayler Lewis , Goldstein Martin
Published: February 2003

Previous dielectric studies from our laboratory have shown that a secondary relaxation β, usually attributed to molecular flexibility, occurs as often, with the same strength, and in the same place (0.75 Tg for 1 kHz measuring frequency) in glasses made of simple rigid molecules. We concluded that the β relaxation is a universal feature of amorphous packing. We have now extended our previous studies on molecular and fused salt glasses to the 4–77 K temperature range, and found relaxations at about 0.2–0.5 Tg in seven of 16 substances examined. These low temperature relaxations appear in some rigid molecule and in some flexible molecule glasses, but not all. We conclude flexibility is not a necessary condition for a low temperature relaxation, but feel the evidence that such relaxations are also characteristic of amorphous packing is weak. Four alcohols studied gave evidence of an additional loss peak below 4 K. We suggest this peak may be related to the well-known very low temperature anomalies common to most glasses. A general explanation of secondary relaxations in glasses in terms of the amorphous cluster model of glass structure is proposed.
Theory of thermal unimolecular reactions at low pressures. I. Solutions of the master equation
Authors: Troe J.
Published: February 2003

The master equation for a thermal unimolecular reaction in gases at low pressures is formulated. Steady-state solutions are derived in analytical form with an exponential model of collisional transition probabilities, (i) for vibrational energy transfer in molecules with variable densities of states, and (ii) for combined rotational and vibrational energy transfer in molecules with variable heights of the centrifugal barriers. Other models of transition probabilities are treated numerically. The diffusion limit of energy transfer is discussed. In all cases, the nonequilibrium populations of excited states and the weak collision efficiency factors βc are calculated.
Theory of thermal unimolecular reactions at low pressures. II. Strong collision rate constants. Applications
Authors: Troe J.
Published: February 2003

Theoretical expressions for the strong collision rate constants of thermal unimolecular reactions at low pressures k0sc are discussed. The rate constant is split up into various factors: a basic expression for a simplified harmonic oscillator model, a factor accounting for anharmonicity effects, a factor accounting for the energy dependence of the density of states, an overall rotation factor accounting for the effects of centrifugal barriers, and an internal rotation factor accounting for the barriers of hindered rotors. Simplified and easily applicable expressions for these factors are derived. The theory is applied in detail to many practical examples. The comparison with experimental results demonstrates the large importance of the weak collision effects which have been treated in part I of this article. Empirical values for the weak collision efficiencies βc are derived and compared with predicted values.
Determination of the absolute energy levels of organic molecules in the gas phase and in condensed media. I. Solution and gas phase ionization energies and electron affinities of substituted pyridine-N-oxides
Authors: Loutfy Rafik O.
Published: February 2003

The basic principle for the determination and interrelation of the absolute energy levels of organic molecules in the gas phase and condensed media are discussed. The electrochemical and gas phase data for a series of substituted pyridine-N-oxides were used to examine the validity of Born’s formula, which approximate the chemical solvation energies of ions. A linear free-energy relationship between the gas phase ionization potentials (I.P.) and the electrochemical half-wave oxidation potentials (Eox1/2) for substituted pyridine-N-oxides was found. This relationship was utilized to predict the ionization potentials of other heterocyclic amine-N-oxides whose I.P.’s have not been measured. The estimated effective ionic radius reff for pyridine-N-oxide derivatives was found to be highly dependent on the nature of the substituent and linearly related to the electrophilic substituent constant σ+. Substituted pyridine-N-oxides have moderately low ionization energies and form stable positive radical cations. Their use as hole traps when immersed in insulating fluid in contact with photoconductors will be discussed.
SCF–Xα scattered wave MO studies of the electronic structure of ferrous iron in octahedral coordination with sulfur
Authors: Tossell J. A.
Published: February 2003

SCF–Xα scattered wave calculations are presented for the FeS10−6 cluster at Fe–S distances of 2.50, 2.38, and 2.26 Å for quintet and singlet spin states and the transition state intermediate between them. These results, together with those of recent calculations on S−12, are used to interpret the x-ray and optical spectra of FeS2 (pyrite) and FeS (troilite). A crossover of the internal energies of the quintet and singlet states of FeS10−6 is predicted at R (Fe–S) =2.28 Å and the ease of spin pairing in FeS is related to its high compressibility and its large volume change upon spin pairing.
Theory of elasticity of polymer networks. The effect of local constraints on junctions
Authors: Flory P. J.
Published: February 2003

The effects of restrictions on the fluctuations of network junctions imposed by neighboring chains are treated by resort to a model in which these restrictions are represented by domains of constraint. Whereas in a phantom network devoid of such constraints the displacements of junctions from their mean positions are invariant with strain, involvements with neighbors in a real network render them dependent on the strain. The observed stress consequently is increased above predictions for the equivalent phantom network. On the plausible assumption that the dimensions of the domains are transformed linearly (affinely) by the macroscopic strain, the constraints become less restrictive in the direction of a principal extension λt with increase in λt. Hence, the relative enhancement of the stress diminishes with the strain. The characteristic departures of the observed tension (f) –extension (α) curve for elongation from the expression f∝kT (α−α−2) of previous molecular theories are qualitatively reproduced by the present theory, which also accounts for the approximate constancy of f/(α−α−2) observed in compression and the decrease of this ratio with dilution.
A transient kinetics study of the reaction of CO with chemisorbed oxygen on platinum
Authors: White J. M. , Golchet A.
Published: February 2003

Transient pressure-jump experiments are reported in which the reaction between gas phase carbon monoxide and chemisorbed oxygen on polycrystalline platinum is followed using both CO2 decay and CO titration methods. The experiments are carried out at 540 °K and low pressures below 5×10−7 torr. From the data we conclude that the reaction between chemisorbed oxygen atoms and gas phase carbon monoxide is first order in CO pressure and, at high oxygen atom coverages, zero order in the adsorbed oxygen atom concentration. These results imply that CO impinging on the platinum surface visits several sites during the course of a single encounter.
Light scattering in carbon tetrachloride: Liquid and plastic crystal phases
Authors: Djabourov M. , Lévy-Mannheim C. , Leblond J. , Papon P.
Published: February 2003

The quasielastic light scattering spectra of carbon tetrachloride have been studied from room temperature to the solidification point and in both plastic phases, allowing measurements of the hypersound velocity and damping. Thermal relaxation effects have been observed in the liquid over the whole temperature range investigated and the spectra analyzed according to Mountain’s theory. The evolution of the isothermal and adiabatic compressibilities was derived from relative intensity measurements. Their behavior is in good agreement with a classical thermodynamic description (down to a few degrees before solidification). In the solid phase our experiments bring new information to elucidate the phase diagram.
Theory of the chemical bond. IV. Long range interatomic interactions and their relationship to internal kinetic and potential energy variations
Authors: Matcha Robert L. , King Stephen C.
Published: February 2003

Implicit perturbation theory is applied to the study of long range interactions. It is shown that internal kinetic and potential energy changes effect the interaction energy in the third order.
Continuous-time-random-walk in three dimensions as a model for electron scavenging and ion recombination in liquids
Authors: Helman W. P. , Funabashi K.
Published: February 2003

Time-dependent rates of electron scavenging reactions were calculated using the model of continuous-time-random-walk (CTRW) of Montroll and Weiss for the hopping time distribution functions of an exponential form and a few nonexponential forms. The result was applied to the charge neutralization reaction using the Laplace transform technique. It was found that the rate constant in the CTRW model is smaller than the Smoluchowski transient rate, but is larger than the time-independent (asymptotic) value at the time scale which is comparable or shorter than the average jump time. The differences in the decay pattern and the survival fraction of electrons between the CTRW model and the Smoluchowski treatment are much less than those in the rate constants themselves.
Generalization of the classical theory of capillarity
Authors: Boruvka L. , Neumann A. W.
Published: February 2003

Gibbs’ concept of dividing surfaces is supplemented explicitly by the concepts of dividing lines and dividing points. The general forms of the fundamental equations for dividing surfaces and lines are established by considering the proper extensive geometric properties, in addition to area and length. The detailed description of the fluid part of a capillary system by these fundamental equations is used to obtain the general conditions of equilibrium. Proper generalizations of the Laplace equation, the Neumann relation, and the Young equation are derived.
Calculations of resonance Raman spectra of conjugated molecules
Authors: Warshel Arieh , Dauber Pnina
Published: February 2003

A method for calculations of the complete resonance Raman (RR) spectrum of large conjugated molecules is presented. The method is based on calculations of the Franck–Condon factors and on differentiation of the electronic transition moments with respect to the vibrational normal modes. This approach is more simple and practical than previous treatments which are based on the Herzberg–Teller expansion. It allows one to evaluate quantitatively the contributions of the A and B terms to the RR intensity pattern. This paper gives the detailed derivation of the calculation scheme and examines different possible approximations. The multimode nature of the RR process is considered in detail and the effect of combination levels is taken into account explicitly. It is shown that in cases of resonance with strong electronic transitions the A term is much more important than the B term. The calculations are demonstrated by the evaluation of the Raman spectra of butadiene and 1,3,5-hexatriene in the nonresonance region, and by the evaluation of the RR spectra of β-carotene, β-ionone, and all-trans retinal. A reasonable agreement is obtained between the calculated and observed relative intensities and excitation profiles. Applications of the calculations to cases of weak electronic transitions are also considered.
Self-diffusion in liquid water
Authors: Ricci F. P. , Ricci M. A. , Rocca D.
Published: February 2003

The behavior of the self-diffusion coefficient in water, along the coexistence curve for −31 °C⩽T⩽350 °C, is explained in terms of local fluctuations of free volume, energy per molecule, and ’’percentage of broken H bond’’ as derived from ir data. Our theoretical expression agrees with the experimental data, within their errors, in the overall range we considered. The transition to amorphous state is derived.
Electronic structure change at a phase transition in a polydiacetylene crystal
Authors: Iqbal Z. , Chance R. R. , Baughman R. H.
Published: February 2003

A Raman spectral study is reported for a polydiacetylene crystal with substituent group (CH2)4OCONHC6H5. At low temperatures (<100 K) or high pressures (≳1.5 kbar) a phase change occurs accompanied by changes in the electronic structure of the polymer backbone. The Raman evidence suggests that the high temperature phase is best described with a butatriene bonding sequence [-RC=C=C=CR-n] while the low temperature (or high pressure) phase is best described with an acetylene bonding sequence [-RC–C≡C–CR-n].
X-ray photoemission studies of tellurium and some of its compounds
Authors: Bahl M. K. , Watson R. L. , Irgolic K. J.
Published: February 2003

The energies of the 3p1/2,3/2, 3d3/5,5/2, 4s, and 4d3/2,5/2 photopeaks have been measured for tellurium metal and 23 of its compounds. An attempt is made to interpret chemical bonding in some of the tellurium compounds by comparing core level binding energy shifts with isomer shifts observed through Mossbauer spectroscopy. The widths of the 3p3/2 photopeaks measured relative to the 3p1/2 photopeaks are examined for broadening by electric field gradients and Coster–Kronig transitions. Variations in the spin–orbit splitting of the tellurium 4d level in its various compounds do not seem to be dependent on crystal field interactions.
Dissipative structures in one dimensional pseudo-one component systems
Authors: Hanson M. P.
Published: February 2003

A one dimensional, multicomponent, open system of chemical reactions containing a single species with finite diffusion coefficient, and subject to boundary conditions fixing all concentrations at their homogeneous steady state values is analyzed. It is shown that the steady state equations are analogous to a particle moving in a one dimensional conservative force field. All possible steady states are identified, and a number are shown graphically together with their rates of entropy production. The stability of the various steady states is determined. For a system large enough that multiple steady states are possible, only the solutions that are either everywhere larger or everywhere smaller than all others are stable, and all other solutions are unstable.
On the use of generalized x-ray scattering factors for analysis of charge density from gas-phase electron diffraction intensities
Authors: Epstein Joel , Bentley John , Stewart Robert F.
Published: February 2003

Generalized x-ray scattering factors for H2 (1Σg+) and N2 (1Σg+) are reported for [2‖2] and [3‖3] expansions. Results for O2 (3Σg−) include [2‖2], [3‖3], and [4‖4] expansions. The multipole analysis of the molecular x-ray form factor of these diatomics is a guide to a rational choice for the pseudoatom multipoles and for the radial basis functions in the Kohl–Bartell model [J. Chem. Phys. 51, 2891 (1969)]. It appears that by using more multipoles, relatively simple radial functions for the pseudoatoms are needed for a Kohl–Bartell model in the analysis of electron diffraction intensities for charge density information.
Theory of phase transitions in solid methanes. XI. Infrared and Raman spectra of the ν3 and ν4 modes in phase II of solid CH4
Authors: Kobashi Koji , Okada Kenkichi , Yamamoto Tsunenobu
Published: February 2003

The infrared and Raman spectra of the ν3 and ν4 modes of intramolecular vibration of methane in phase II have been theoretically studied on the basis of the extended James–Keenan model. Low-lying vibration–rotation states coupled through the first order Coriolis coupling are obtained. Two kinds of energy level schemes have been worked out, one for the molecules with an orientational order (D2d molecules) and the other for those without it (Oh molecules). The rotational structures (positions and intensities) of the ir spectra have been calculated, and a good agreement with experiment has been obtained, if the fundamental vibration frequencies of the ν3 and ν4 modes are put equal to 3012.1 and 1295.9 cm−1 for Oh molecules and 3007.3 and 1300.8 cm−1 for D2d molecules, respectively. Raman spectra are also treated and their rotational structures are predicted.
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o calculations using a floating basis. Periodic correlations in second row diatomic hydrides
Authors: Blustin Peter H.
Published: February 2003

Calculations have been performed on second row diatomic hydrides and cations using an adaption of the floating spherical Gaussian orbital model of A.A. Frost. Geometries are determined to about 3%. The periodic trends in ionization potentials, geometry changes on ionization, population analysis, dipole and quadrupole moments, the total potential at the hydrogen nucleus, polarizabilty and susceptibilities are described and discussed (when appropriate) in terms of changes in the localized orbital model. The results suggest that the hydrides and their cations may be divided into electrovalent and covalent groups, but that the absolute ionicity is not a definite guide to the electronic structure.
Excimer densities and destruction mechanisms in a high pressure pure mercury positive column
Authors: Mosburg Earl R. , Wilke Mark D.
Published: February 2003

A study of a pure mercury vapor dc discharge at gas densities of 0.75×1018 to 1019 cm−3 and currents of 30–100 mA has allowed us to determine the densities of the atomic 6 3P0,1,2, and 7 3S1 levels and the dimer 31u level as well as the density of free electrons. We find the density of the 31u level (which radiates the 335 nm band) to be several orders of magnitude below that needed for lasing on this transition. An analysis of the measured spacial profiles leads us to conclude that mercury trimers figure prominently into the kinetics of the system and that the destruction of these trimers is primarily by electron collisions. We also report evidence that the three-body rate for production of trimers from dimers greatly exceeds that for the formation of dimers from excited atoms. The procedures for analysis of the spacial profiles developed here constitute a new method for the semiquantitative determination of rate coefficients not otherwise accessible to measurement.
EPR of methylene. Temperature dependence in a xenon matrix
Authors: Bernheim R. A. , Chien S. H.
Published: February 2003

The EPR spectra of CH2 and CD2 were examined between 2.18 and 9.2 °K in a xenon matrix. The zero-field splitting and linewidths of the randomly oriented triplet CD2 were temperature independent below 4.2 °K which is consistent with the currently accepted model in which the trapped methylene occupies its lowest discrete tortional level in the matrix. Increasing the temperature above 4.2 °K produces a decrease in the zero-field splitting of CD2 and an increase in linewidth. The zero-field splitting for CH2 exhibited a temperature dependence between 4.2 and 2.18 °K. The variation of the zero-field splitting parameters could be described by a thermal activation energy of about 30 cm−1 for CD2 and approximately 14 cm−1 for CH2. These relative magnitudes are likely a consequence of the fact that CH2 has a larger zero-point energy than CD2 and therefore requires a smaller energy of activation to jump or tunnel to a random orientation. The temperature dependence of the homogeneous broadening of the z1 and z2 EPR spectral lines of CD2 could be described by a thermal activation energy between 36 and 42 cm−1. The mechanism for the line broadening is probably the same for the decrease in D, and the difference in experimental activation energies probably arises from uncertainties in the deconvolution of the spectral linewidth into a homogeneous and an inhomogeneous part. It was also found that methylene in a xenon matrix could be warmed to 50 °K before significant diffusion with subsequent reactive recombination takes place.
14N PNQR investigation of the effect of pressure on phase transition in malononitrile
Authors: Zussman Avigdor , Rapoport Eliezer
Published: February 2003

The 14N pure nuclear quadrupole resonance frequencies in the molecular crystal malononitrile were measured as a function of hydrostatic pressure up to 5.6 kbar. Above T=21.55°C, the second order phase transition previously studied by Zussman and Alexander was observed at high pressures. Above the transition pressure pc, each resonance line splits into two. The splittings Δν along an isotherm at 23°C were fitted to the equation Δν=B (p−pc)β and the critical exponent β was found to be close to 0.5. The variation of Tc with pressure was measured to 2 kbar and the line of transition could be described by the linear equation Tc(p) = 21.51+16.5734p. The present results for the variation of Δν along an isotherm were compared with previous results obtained along an isobar.
The monomeric character of xenon hexafluoride vapor. The mass spectroscopy of noble gas binary fluorides and xenon oxide tetrafluoride
Authors: Falconer W. E. , Vasile M. J. , Stevie F. A.
Published: February 2003

Positive ion mass spectra have been obtained for KrF2, XeF2, XeF4, XeF6, and XeOF4 using 60 or 70 V electron impact ionization and a molecular beam source designed especially for reactive fluorides. Flight time distribution measurements have been made for neutral XeF6. Both these and the mass spectrometric fragmentation pattern indicate monomeric species in the saturated vapor. Associated (dimer) molecules can be obtained by isentropic expansion of XeF6; these are detected as dimer ions at one part in 104 of the monomeric ions in the mass spectrum. Electric deflection measurements on XeF6 vaporizing from inlets at temperatures from −19 to 40 °C showed no focusing effect.
Optically detected magnetic resonance spectra of the lowest triplet states of benzophenone, 13C-benzophenone, and three 4,4′-dihalobenzophenones
Authors: Mucha John A. , Pratt David W.
Published: February 2003

We describe measurements of the complete angular dependence of the optically detected magnetic resonance (ODMR) spectra of the lowest triplet states of benzophenone, carbonyl-13C-benzophenone, 4,4′-difluorobenzophenone, 4,4′-dichlorobenzophenone, and 4,4′-dibromobenzophenone in 4,4′-dibromodiphenylether host crystals at liquid helium temperatures. The principal axes and values of D (including the absolute signs) and g are reported and used to evaluate the spin–spin and spin–orbit contributions to the fine-structure tensor of the parent molecule. It is found that the dipolar contributions to D in 3(n,π*) benzophenone are at least a factor of 2 less than recent ab initio estimates of the spin–spin contributions to D in 3A2 formaldehyde. Carbon-13 hyperdfine splittings have been observed in the ODMR spectra of 13C-benzophenone; an analysis of these yields estimates of the orbital spin densities ρ2sC(O)?0.008 and ρ2pxC(O)?0.14 and suggests that the C1–C(O) –C1′ fragment is planar. The fine-structure parameters of triplet benzophenone are strongly influenced by halogen atoms in the para ring positions. The ODMR spectra of the 4,4′-difluoro and 4,4′-dibromo derivatives also exhibit ring halogen atom hyperfine structure from which the estimate ρ2pπC4?0.10 is obtained. Taken together, the results of this investigation suggest that as much as 50% of the total spin density in the lowest triplet state of benzophenone itself resides on the aromatic rings, thereby accounting for the reduction in the dipolar contributions to D in the parent molecule and for the changes in the principal values (and directions) of D which occur in its heavy-atom substituted derivatives.
Level-anticrossing and cross-relaxation effects in oriented molecular triplet states. 3(n,π*) benzophenones in 4,4′-dibromodiphenylether
Authors: Mucha John A. , Pratt David W.
Published: February 2003

This paper reports the observation and analysis of magnetically induced changes in the phosphorescence intensities of triplet state benzophenone, carbonyl-13C-benzophenone, and three 4,4′-dihalobenzophenones in single crystals of 4,4′-dibromodiphenylether at 1.6°K. The signs, magnitudes, field positions, and widths of these changes can be interpreted in terms of two effects, anticrossings of two different electron–nuclear spin manifolds of the guest molecule and cross relaxation between the spin system of the guest and that of the host. At fields where anticrossings occur, the mixing between the spin states is strong and no hyperfine structure is observed. However, by comparing the results for the different molecules in the same host, it is shown that secular terms of the hyperfine interaction play a key role in determining the minimum spectral widths of the ’’transitions’’. At fields where cross relaxation predominates, the mixing between the spin states is weak and hyperfine and quadrupole splittings of both the guest and host can be resolved. The magnetic and optical parameters obtained by fitting the ’’spectra’’ are in excellent agreement with those determined by ODMR techniques [J. A. Mucha and D. W. Pratt J. Chem. Phys. 66, 5339 (1977), preceding paper]. Thus, experiments of this type can be utilized to provide information about the fine-structure, g, hyperfine, and quadrupole tensors of emitting paramagnetic species in the complete absence of perturbing radiofrequency or microwave fields. Moreover, the systems described herein offer considerable promise in future studies of spin relaxation mechanisms in molecular solids by optical detection methods.
Depolarized Rayleigh scattering in 10M amorphous and liquid KOH aqueous solutions
Authors: Mazzacurati V. , Nardone M. , Signorelli G.
Published: February 2003

An interpretation of the low frequency Raman scattering in all disordered systems including liquids is suggested in terms of phononlike excitations damped by anharmonicity and by structural relaxations. In principle, owing to the disorder-induced breakdown of the k vector selection rule, all of these excitations are allowed to participate to the scattering process. An ad hoc simplified model is also proposed to calculate the low frequency Raman scattering, and it is found to reproduce at least qualitatively the main features of the depolarized spectrum in amorphous solid and liquid 10M KOH water solutions at different temperatures.
Dynamic effects in the scattering of electrons by small clusters of atoms
Authors: Bartell L. S. , Raoult B. , Torchet G.
Published: February 2003

Dynamic scattering corrections were calculated for 40 kV electrons diffracted by randomly oriented fcc clusters of argon and of gold atoms ranging in size from 13 to 135 atoms. Computations were carried out according to several variants of two limiting theoretical approaches, namely, the direct summing up of atomic contributions calculated through single–single and single–double scattered waves by modifications of Glauber theory, and the extrapolation to limitingly small crystallites of conventional dynamic theory in the Blackman and Fujimoto formulations. For the small clusters studied, integrated intensities of diffraction rings (through single–double scatterings) calculated for three dimensional crystallites differ insignificantly from Glauber theory intensities calculated by projecting atomic potential energies onto a plane perpendicular to the mean direction of the incident and scattered wave vectors. The fractional dynamic correction increases with cluster size very nearly as N2/3 in both the Glauber and Blackman–Fujimoto limiting treatments. For crystalline clusters 8–20 Å in diameter, the dynamic effect calculated by summing single–double scatterings is an order of magnitude larger than that according to Blackman–Fujimoto theory. For argon clusters the dynamic effect is not serious; but according to our direct sums, dynamic corrections for 16 Å spheres of gold are surprisingly large, exceeding 25% for 111 reflections. Since the direct sums have been verified experimentally for several vapor-phase molecules, the present work indicates that, in the limit of very small scatterers, extrapolations from conventional two-beam dynamic theory may seriously underestimate the magnitude of dynamic effects.
Molecular motions in compressed liquid heavy water at low temperatures
Authors: DeFries T. , Jonas J.
Published: February 2003

The NMR deuteron spin–lattice relaxation times T1, self-diffusion coefficients D, and shear viscosities η have been measured as a function of pressure in the temperature interval −15 to 10°C. The low-pressure extreme of the measurements is Ice I, whereas Ice V represents the high-pressure boundary of the experiments. In analogy with anomalous motional behavior in compressed liquid water, the initial compression of liquid D2O in the temperature interval studied results in higher motional freedom of D2O molecules so that T1 and D dependences with pressure exhibit a maximum and shear viscosity shows a minimum. This is a result of distortion and weakening of the hydrogen bond network owing to compression. Further compression hinders molecular motions as a result of increased repulsive interactions due to higher packing. This study also enables us to test the applicability of hydrodynamic equations at the molecular level for liquid heavy water. Analysis of the relaxation and shear viscosity data show that the Debye equation fails to describe the density effects on reorientation of D2O molecules. It appears that the success of the Debye equation to describe temperature effects on reorientation of H2O and D2O molecules at 1 bar is accidental. However, the data show that the deuteron relaxation rate (1/T1)D is proportional to η/T under isochoric conditions. The fact that the slope of the (1/T1)D vs η/T plot diminishes with increasing density indicates that compression leads to diminished coupling between rotational and translational motions of water molecules. The shear viscosity and self-diffusion data show that the Stokes–Einstein equation does not represent the relationship between D and η in liquid heavy water. A brief discussion of the isotope effects on shear viscosity in liquid D2O and H2O is presented.
The potential energy curves of the X 1Σ+ and A 1Σ+ states of LiH
Authors: Stwalley William C. , Zemke Warren T. , Way Kermit R. , Li Kwong C. , Proctor Timothy R.
Published: February 2003

As an important intermediate step in a long-term project to fully understand the spectroscopy of the three lowest singlet states of LiH, (X 1Σ+, A 1Σ+, and B 1Π), we have constructed accurate hybrid potential energy curves for the X1Σ+ and A1Σ+ states to complement earlier work on the B1Π state. In each case the known Rydberg–Klein–Rees (RKR) for low vibrational levels was joined to the long-range region of the potential (represented by new C6, C8, and C10 coefficients reported herein) fixed by the accurately known dissociation limits. The joining was obtained by scaling slightly the ab initio results of Docken and Hinze in the region of interpolation. Extrapolation to smaller distance was also done using ab initio results.
Stability of the equilibrium for atomic H in solid H2
Authors: Rosen Gerald
Published: February 2003

The previously reported phenomenological rate process theory for the storage of atomic hydrogen free radicals in a tritium-impregnated crystalline molecular hydrogen solid is used to determine the dynamical stability of the constant uniform equilibrium solution. Our analysis indicates that the equilibrium is unstable (thus, unattainable experimentally) for storage temperatures in a certain range (specifically, 0.134 K≲T0≲0.80 K for 0.03% tritium by weight, 0.165 K≲T0≲0.80 K for 1.20% tritium by weight), while being absolutely stable with respect to arbitrary small-amplitude perturbations for all storage temperatures below and above this range. The theory also predicts the maximum size for a stable H/H2 sample with an appreciable concentration of trapped H and a net excess rate of volumetric heating due to the tritium decay. These theoretical results are wholly consistent with the Webeler experiments performed to date.
Infrared absorption spectra of gaseous HD. IV. Analysis of the collision-induced fundamental band of the pure gas
Authors: Reddy S. Paddi , Prasad R. D. G.
Published: February 2003

Studies of the infrared absorption spectra of the HD fundamental band in the pure gas, reported for the room temperature in Paper I of this series, have now been extended to temperatures 77 and 196 K. The spectra of the band were recorded for a number of gas densities up to 50 amagat. In addition to the usual collision-induced broad features of the infrared fundamental band of a symmetric diatomic gas, these spectra at 77 and 196 K show the dipole-allowed sharp R1(0) and R1(1) transitions owing to the individual molecules. Derived binary absorption coefficients of the collision-induced band are (1.15±0.06) ×10−35 and (1.71±0.07) ×10−35 cm6 s−1 at 77 and 196 K, respectively. An analysis of the absorption profiles of the band at 77 and 196 K and those of the band at 298 K reported in Paper I was carried out, and the characteristic half-width parameters δd and δc of the short-range overlap-induced transitions and δq (and δq′) of the long-range quadrupole-induced transitions are derived. The contributions of the overlap- and quadrupolar-interactions to the absorption intensity of the band are separated by the method of profile analysis. The magnitude parameter λ and the range ρ of the overlap-induced dipole moment for the HD–HD collision pairs are determined by obtaining the best fit of the calculated overlap part of the binary absorption coefficient as a function of temperature to the experimental values. Derived overlap parameters are λ=5.60×10−3, ρ=0.25 Å, and μ (σ) (the overlap-induced dipole moment at the Lennard–Jones intermolecular diameter σ) =3.1×10−2 ea0.
Absolute coverage determination of CO on Ni(111)
Authors: Erley W. , Besocke K. , Wagner H.
Published: February 2003

The adsorption of CO on Ni(111) has been studied using LEED and calibrated Auger measurements in order to determine the absolute amount of adsorbed CO molecules. At room temperature and CO pressures of up to 1.3×10−3 Pa a saturation coverage of ϑCO?0.28, corresponding to 5.2×1014 molecules per cm2, has been obtained. This is contrary to the commonly accepted opinion that the saturation coverage of nondissociated CO on various transition metals should always amount to about 1×1015 molecules per cm2 irrespective of the underlying substrate structure.
Molecular beam Zeeman effect and dipole moment sign of ClF
Authors: Fabricant Barbara , Muenter J. S.
Published: February 2003

Molecular beam electric resonance spectroscopy has been used to observe hyperfine, Stark, and Zeeman properties of chlorine monofluoride. The dipole moment from Zeeman data is 0.85(15), −FCl+, in agreement with the known magnitude. The sign obtained here is the opposite of earlier, less precise, Zeeman results but agrees with calculations and van der Waals molecule experiments. Hyperfine, Stark, and Zeeman properties for 35ClF and 37ClF are reported, including polarizability anisotropy, α∥−α⊥=1.32(8) Å3, molecular quadrupole moment, ϑ∥=1.54(7) ×10−26 esu⋅cm2, and the chlorine quadrupole coupling constant derivative, deQq/dR=−90(20) MHz/Å.
Stark and Zeeman properties of ozone from molecular beam spectroscopy
Authors: Mack Kenneth M. , Muenter J. S.
Published: February 2003

Stark and Stark–Zeeman transitions within single J states of ozone have been studied using molecular beam electric resonance spectroscopy. Results include dipole moment, μ; dipole moment of the first excited bending mode, μ (010); polarizability anisotropies, αaa−αbb and αaa−αcc; rotational magnetic moments, ga, gb, gc; magnetic susceptibility anisotropies, χaa−χbb and χaa−χcc; and quadrupole moment components, ϑaa, ϑbb, ϑcc. μ=0.5337(1) D, μ (010) =0.5261(1) D, αaa−αbb=2.82(1) Å3, αaa−αcc=2.63(4) Å3, gaa=2.98933(8), gbb=−0.22919(3), gcc=−0.07623(b), χaa−χbb=5.91(2) KHz/kg2, χaa −χcc=12.05(4) KHz/kg2, ϑaa=−1.4(2) ×10−26 esu⋅cm2, ϑbb=−0.7(2) ×10−26 esu⋅cm2, ϑcc=2.1(3) ×10−26 esu⋅cm2.