bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the K—LL Auger Spectra of N2, O2, CO, NO, H2O, and CO2
Authors: Moddeman W. E. , Carlson Thomas A. , Krause Manfred O. , Pullen B. P. , Bull W. E. , Schweitzer G. K.
Published: February 2004

A double-focusing electrostatic electron spectrometer has been used to measure the K—LL Auger spectra resulting from electron impact for each of the elements in the gaseous molecules N2, O2, CO, NO, H2O, and CO2. An energy resolution of 0.09% full width half-maximum was normally employed. A method for analyzing these complex spectra is described. It involves the identification of normal and satellite lines. The former are defined as arising from single electron ionization from the K shell without additional excitation followed by an Auger process in which one electron fills the vacancy while a second goes into the continuum, and where all the other electrons remain in their same orbitals. Satellite lines result when extra excitation occurs either in the initial formation of the K vacancy or in the subsequent Auger process. To aid in the identification of these satellite lines, auxiliary experiments have been performed such as the study of discrete energy losses in photoionization due to electron shake-up, and the comparison of Auger spectra produced by monoenergetic x rays. As a consequence of the analyses of the Auger spectra, information has been obtained on (1) the nature of initial excitation processes such as the transition of a K electron into excited discrete states and monopole excitation and (2) the identification of the energy and nature of the ground and excited states of the doubly charged molecular ions. The second ionization potential was obtained for each of the molecules, and in one case, N2, the third ionization potential was estimated. Finally, a brief discussion is made of the possible use of high resolution electron spectroscopy in molecular as well as elemental analysis.
Effect of Gravity near a Critical Point in Binary Mixtures
Authors: Mistura Luciano
Published: February 2004

The effect of gravity is calculated near a critical point in binary fluid mixtures including azeotropic critical points. It is shown that a gravity field produces density gradients very similar to those it produces in a pure substance. For small deviations the density is a linear function of the height with a slope which diverges like t- γ. The available experimental evidence supports this prediction.
Geminal Localization in the Separated-Pair π-Electronic Model of Benzene
Authors: Paldus J. , Čížek J. , Sengupta S.
Published: February 2004

A problem of the geminal ``localization'' in the separated-pair π-electronic model of benzene is studied for a wide range of a coupling constant using the Pariser—Parr—Pople-type Hamiltonian. The general form of the ``localized geminals'' leading to the separated-pair wavefunction of the C3h symmetry is found as a function of two free parameters. These geminals are used in the separated-pair model calculation, showing that the previously used localization corresponding to the equivalent orbitals (i.e., the localized Hartree—Fock orbitals) is not the best one from the separated-pair model viewpoint, except for vanishingly small coupling constants. The optimization is also carried out after the projection of the single antisymmetrized product of geminals function onto the totally symmetric subspace of the D6h point group. Finally, the general implications of the ``symmetry dilemma'' are briefly discussed for both independent-particle and separated-pair models.
Solution of the Delta Function Model for Heliumlike Ions
Authors: Rosenthal Carey M.
Published: February 2004

A one-dimensional Fredholm integral equation is derived for the ground state solution of the delta-function model for two-electron heliumlike ions. This equation is solved numerically; the perturbation series is developed through E(20) and compared with the solution of the integral equation. The series is further analyzed in terms of the singularity which determines its radius of convergence.
Redfield—Langevin Equation for Nuclear Spin Relaxation
Authors: Albers J. , Deutch J. M.
Published: February 2004

We present a derivation of a Langevin-type equation for the operator Gα α′(t)=exp (−iHt)|α′〉〈α |exp(–iHt), where |α 〉 and |α′〉 are eigenstates of the subsystem Hamiltonian and H is the full Hamiltonian for subsystem plus bath. For the case in which we consider a spin system weakly coupled to a thermal bath (lattice), the equation of motion is of the form of the Redfield equation with a fluctuating term. This equation may be used to derive the standard Redfield equation for the spin density matrix as well as Bloch equations with fluctuating terms for the components of the magnetization for individual systems in the nonequilibrium ensemble. The latter presents a first principles derivation of the magnetic analog of hydrodynamic fluctuation theory. A calculation of several of the correlation functions which may be constructed from the theory is presented.
Reactions between N2+ and N2
Authors: Maier William B.
Published: February 2004

Apparent cross sections for the reactions N2++N2→N++N+N2, N2++N2→N3++N, have been measured for laboratory kinetic energies E of N2+ between 1 and 45 eV. The primary ions are produced by electron bombardment and mass analyzed prior to reaction. The bombarding electron energy is varied from 19 to 90 eV, and the effects of excited, long-lived states of N2+ on the reactions are studied. Both reactions proceed when N2+ is in long-lived excited states and when N2+ is in the X 2Σg+ and/or A 2Πu states. When E≲15 eV, Reaction (1) proceeds primarily from long-lived states of N2+ about 8.5±1.5 eV above the ground state. There may be several long-lived excited N2+ states involved in the production of N+ and N3+ at low E, and some or all of these states may be involved in long-lived emissions which have been previously observed. A survey of the available information on N2+ suggests that detailed comparisons with theory will be seriously hampered by uncertainties in the production and lifetimes of the various states of N2+.
Pressure Broadening Measurement of the ν 2 [qR − (0,0)] Transition of 15NH3 by a CO2 Laser
Authors: Shimizu Tadao , Shimizu Fumiko O. , Turner R. , Oka Takeshi
Published: February 2004

The near coincidence of the P(16) line of the CO2 laser in 10.6 μm and the ν 2 [qR − (0,0)] line of 15NH3 was used to measure the pressure broadening and the absolute absorption coefficient of the latter transition. The pressure broadening parameter was determined to be Δνp=13.3±1.2 MHz/torr, and the transition dipole moment of the ν2 vibrational transition was determined to be 0.239 D.
Pure Thermal Diffusion. II. Experimental Thermal Diffusion Factors and Mutual Diffusion Coefficients for CCl4–C6H12
Authors: Anderson Terry G. , Horne Frederick H.
Published: February 2004

An improved phenomenological theory for pure thermal diffusion [J. Chem. Phys. 53, 2321, (1970)] has been used in conjunction with a laser wavefront shearing interferometer and a sample cell free of unwanted convection to measure thermal diffusion factors α1 and mutual diffusion coefficients D for the CCl4–C6H12 system between 20 and 35°C. The results, in mole fraction x1 of CCl4 and Celsius temperature T, are: α 1=− 1.831+0.18 1 x1+0.0104 (T−25)−0.0008x1 (T−25), with a calculated standard error in α1 of 0.019, and 105D (cm2 sec−1)= 1.481−0.187x1+0.0244 (T-25)+0.0024x1 (T−25), with a calculated standard error in 105D of 0.035 cm2 sec−1.
Theory of n to π* Transitions
Authors: Harris Robert A. , Falicov L. M.
Published: February 2004

The Pariser—Parr—Popple (PPP) theory of conjugated systems is extended to take into account non-bonding orbitals. We show that the n→π* transition gives rise to a Franck—Condon overlap analog of a Fermi π-electron system. A model calculation for pyridine is presented.
Triplet State of Benzaldehyde
Authors: Koyanagi Motohiko , Goodman Lionel
Published: February 2004

The phosphorescence spectra of benzaldehyde-h6, −1d1, −4d1, −3, 5d2 and −d6 have been studied optically in close packed matrices (acetophenone and methyl benzoate) and relaxed matrices (methylcyclohexane and perfluoro-n-hexane) at 4.2°K. All the spectra were sharp and could be analyzed vibrationally. In the close packed matrices, of the 11 possible out-of-plane (a″) fundamentals, nine are observed in Herzberg—Teller borrowing of intensity. The strongest modes are the aldehyde-H wag, the CHO torsion and CHO wag, and their intensities were found to be stronger than those of any totally symmetrical bands including the origin band. 2 and 3 quanta of aldehyde-H-wag and CHO-torsional modes are found with intensity alternation. In addition to this intensity alternation, the lack of long sequences of any nontotally symmetric mode and the analysis of the Franck—Condon envelope show that the triplet benzaldehyde does not deviate far from the ground state geometry. We conclude it is coplanar or nearly so. Deuteration effects on the vibronic intensities are remarkable. The long lifetime, ∼4×10−2sec at 4.2°K, supports a planar geometry for the triplet. The large change of lifetime and spectral intensity on substitution of the aldehyde hydrogen by deuterium shows that the aldehyde H plays an important role in the vibronic interaction. In the relaxed matrices most of the out-of-plane fundamentals are too inactive to be identified in the phosphorescence. The only out-of-plane mode clearly identified is the fundamental CHO-torsional mode and its overtone. Higher overtones are not found. Most of the intensity is in the 0–0 band and the ν (C=O) progression which is longer than in the close packed matrices. Also active are in-plane modes such as δ(Φ-CHO), ν(Φ-CHO), ν1, ν9a, and ν8a. The short lifetime in the relaxed matrices (fully 20 times shorter than in the close packed matrices), ∼2×10−3sec at 1.68°K, without appreciable deuteration effect establishes that the triplet benzaldehyde is highly nonplanar with the aldehyde group twisted out of plane. We conclude from the lifetime that the twist angle exceeds 60°. The vapor phosphorescence resembles the relaxed matrix phosphorescence, but with still reduced lifetime. We conclude that in the free molecule the aldehyde group in the benzaldehyde triplet is also strongly out of plane.
Model for Neutralization and Scavenging of Charges in Irradiated Dielectric Liquids. II Electron Scavenging under γ Radiolysis
Authors: Mozumder A.
Published: February 2004

Yield of a scavenging reaction in competition with charge neutralization is calculated in the diffusion model for the isolated ion-pair case and also for multiple ion-pair cases. Following an earlier lead by Hummel, this yield is shown as a Laplace transform of the survival probability against neutralization in absence of scavenger. The Laplace transform itself is evaluated numerically using the earlier work of the present author for the isolated ion-pair case and the results of the accompanying paper for the multiple ion-pair cases. Experimental results of Schuler et al. for electron scavenging in γ radiolysis of cyclohexane solutions are compared with the present calculations for the isolated ion pair and also for the entire track. For the latter a probability function for energy deposition derived from our previous work has been used. It is concluded that the square-root law at low scavenger concentrations is a general result of the classical diffusion theory, independent of the size and shape of the entity being scavenged and indeed independent of the mode of generation of charges. This law is, in fact, not limited to charge scavenging only. A discussion is made of other related experiments, such as of mobility (Schmidt and Allen) and of time dependence of negative-ion yield (Thomas), and it is concluded that a single set of diffusion and rate constants can consistently explain all the experimental results.
Classical S Matrix for Linear Reactive Collisions of H+Cl2
Authors: Rankin C. C. , Miller William H.
Published: February 2004

Classical trajectories are computed for linear H+Cl2 collisions and used to construct the classical limit of the S matrix for reactive and nonreactive transitions between individual quantum states. An interesting feature of this system is that both ``direct'' and ``complex'' mechanisms participate in the collision dynamics. The two mechanisms contribute additively to individual S-matrix elements, and within a ``random phase approximation'' for the complex contribution it is seen that they also contribute additively to the transition probability. The complex contribution to a transition probability is strictly classical, but interference structure may be prominent in the direct contribution. Comparison is made with quantum calculations for the same potential and the agreement is rather poor, even at a fairly coarse level. The reason for this disagreement is not completely clear, but it may be connected with the fact that complex formation is prominent.
Interaction of Oxygen with Polycrystalline Tungsten. I. Sticking Probabilities and Desorption Spectra
Authors: King David A. , Madey Theodore E. , Yates John T.
Published: February 2004

The interaction of oxygen with a polycrystalline W filament has been studied in the temperature range 300–1200°K and for exposures between 10−7 and 1 torr·sec. Both sticking probabilities and desorption spectra have been measured. After low exposures (〈2×10−6 torr·sec) the adsorbate is all desorbed as O atoms with first order kinetics. With higher exposures, oxygen is removed as oxides: WO, WO2, WO3, W2O6. The desorption spectra for each of these species are complex, and nine distinct and reproducible oxide states are identified. Saturation coverages in each of these states are independent of adsorption temperature in the range 300–1200°K. At a total coverage of 8.5×1014 O2 molecules cm−2, 2.2×1014 O2 molecules cm−2 are desorbed as oxides; after exposures 〉 10−2 torr·sec at 300°K, the total uptake rises to 15×1014 O2 molecules cm−2. At temperatures between 500 and 1000°K and exposure up to 1 torr·sec, a multilayer oxide film is formed of unlimited thickness. The desorption product from this oxide film is predominantly WO2, which desorbs in the region of 1200°K. The kinetics of adsorption and desorption are evaluated and discussed.
Cation Motion in Anionic Fields of the Polyelectrolytic Salts of Ethylenemethacrylic Copolymers
Authors: Tsatsas Andreas T. , Reed Janice W. , Risen William M.
Published: February 2004

The far-infrared spectra of the Li+, Na+, K+, Cs+ salts and acid forms of polyelectrolytic ethylene-methacrylic acid copolymers have been examined in the 800–33-cm−1 region at ambient and low temperatures. A broad band, which shifts to lower frequency as the cation mass is increased, is attributed to cation motion in anionic fields, and the appearance of a low frequency band, whose intensity is related to the cation properties, is assigned to perturbed skeletal motions of a neighboring polymer segment. Models are proposed and analyzed for the vibrational modes involving ion motion. The vibrational force constants for aggregate distortion, as calculated from the observed ion-motion frequencies, are in agreement with such constants computed here employing an ion-multipole potential energy function which does not use these experimental data. The spectral and theoretical results are considered in terms of the molecular interactions of importance in polyelectrolytes and in the physical properties of these materials.
Polarizability of Molecules in Excited Electronic States
Authors: Eisenthal K. B. , Rieckhoff K. E.
Published: February 2004

In an earlier paper we reported the first measurement of the optical anisotropy of a molecule in an excited electronic state by the method of induced birefringence. In the present paper details are presented for the application of this method to the determination of the differences in the components of the polarizability tensors between an excited electronic and ground state. Experimentally we studied naphthalene-d8 in EPA at 77°K from 4200 to 6300 Å. Our measurement of the dispersion of the polarizability near the triplet—triplet absorption provides evidence for the existence of a previously suspected weak triplet state approximately 18 000 cm−1 above the lowest-lying triplet state.
Formaldehyde Molecule in a Gaussian Basis: Electronic Density
Authors: Dunning Thom. H. , Winter Nicholas W.
Published: February 2004

Plots of the total molecular density and of the orbital densities of the six valence (canonical) molecular orbitals of formaldehyde in its ground state are presented and discussed. The relative spatial extent of the σ and π orbitals is examined in some detail and it is concluded that there is not a pronounced difference in the σ and π charge distributions.
Rayleigh-Wing Scattering by Aromatic Liquids
Authors: Zamir E. , Gershon N. D. , Ben-Reuven A.
Published: February 2004

Measurements are reported of the intensities of the diffuse line and background components of the depolarized light scattered from six aromatic liquids (nitrobenzene, quinoline, bromobenzene, and the three nitrotoluenes), and their variation with temperature. Intensity of the diffuse line in nitrobenzene and its temperature dependence, together with half-width measurements, are compatible with the suggestion that it originates from orientational relaxation by tumbling of mostly uncorrelated molecules. In quinoline a more appreciable orientational correlation between neighboring molecules apparently exists. The background component of these liquids increases with temperature in a manner suggestive of fluctuations from momentary orientational equilibrium.
ESR Study of a Carboxyl Radical Trapped in a Single Crystal of Maleic Acid Irradiated at 77°K
Authors: Eda Bunzo , Iwasaki Machio
Published: February 2004

The ESR evidence for the carboxyl radical, the existence of which is often assumed in organic solution chemistry as a reaction intermediate, has been obtained in a single crystal of maleic acid-d2 (DOOC–CH=CH–COOD) irradiated at 77°K in the dark. The radical HH\/C=C/\O=CC–O·\//OD···O has been found to be formed by the removal of the deuteron attached to the side oxygen atom. The g tensor has been determined to be (2.0261, 2.0061, 2.0035). The unpaired electron of the radical occupies the in-plane p orbitals of the carboxyl oxygen atoms, forming a σ electron radical. The carboxyl radical is believed to be produced from the positive primary by transferring the acidic proton to the neighboring molecule. It has been also found that the carboxyl radical fragments into the vinyl-type radical HH\/C=C·/O=C\OD These results indicate that R·radicals often found in irradiated carboxylic acids (RCOOH) originate from the positive primary via the carboxyl radical (RCOO·).
Free Energy in the Presence of Constraint Surfaces
Authors: Stillinger Frank H. , Cotter Martha A.
Published: February 2004

We have examined the influence of rigid boundaries on the free energy and distribution functions for classical single-component molecular assemblies. By means of boundary position variation, new formulas are derived for the flat boundary tension in both two and three dimensions. In the case of circular or spherical internal boundaries that are relevant to ``scaled particle'' theory, we prove that the associated cavity work is free of contributions varying logarithmically with the radius, in the large size limit. A similar result has been obtained for a ``droplet'' constrained to circular or spherical shape by an impenetrable boundary. The scaling theory of critical correlations has been used to analyze the behavior of the boundary tension in the critical region.
Effect of Pressure on the Electronic Structure of Complexes of Ferrous Iron with Substituted Phenanthrolines
Authors: Bargeron C. B. , Drickamer H. G.
Published: February 2004

The effect of pressure to 180 kbar has been studied on the spin state of ferrous iron in complexes and with substituted phenanthrolines. The tris complexes are low spin at 1 atm and partially convert to high spin at high pressure. The bis complexes with isothiocyanate and chloride are high spin at 1 atm. With increasing pressure they convert partially to low spin. At sufficiently high pressure the conversion tends to level and, in some cases, a reverse trend sets in. At a given pressure the amount of low spin present correlates very well with the low spin isomer shift, which, in turn, can be related to the electronic structure of the ligand and the size of the ligand field Δ. A correlation between conversion and low spin quadrupole splitting indicates that local distortion is also a factor in the change of spin state. Three compounds were studied where steric effects are prominent. The effect of pressure on their spin state is discussed in some detail.
Molecular Multipole Moments Determined from Viscosity and Second Virial Coefficients
Authors: Datta K. K. , Singh Y.
Published: February 2004

The quadrupole moment of CO2 molecule and the octopole moment of CH4 molecule have been estimated from the temperature dependence of second virial coefficients. The central potential employed was the Kihara model for which the force constants were derived from the temperature dependence of dilute gas viscosity on the assumption that the multipole moments had no measurable effect on the viscosity. The values of the moments obtained are very reasonable. The shape parameter of the CO2 molecule has been calculated and discussed.
Molecular Motions in CCl4: Light Scattering and Infrared Absorption
Authors: Bucaro J. A. , Litovitz T. A.
Published: February 2004

The depolarized Rayleigh spectrum of liquid carbon tetrachloride is compared with the experimental dielectric and far-infrared absorption spectra of Garg et al. It is argued that the high frequency part of the infrared spectrum is due to binary collisions as is the corresponding region of the light scattering spectrum. It is shown that the difference in the spectra is connected with correlations between successive collisions.
Ozone Ultraviolet Photolysis. III. Disposition of Vibrational Energy
Authors: Baiamonte Vernon D. , Hartshorn Lynne G. , Bair Edward J.
Published: February 2004

Absorption by the Schumann—Runge B3Σu−←X3Σg− system of O2 was measured in order to identify the products of the O(1D)+O3 reaction. These products are found to be O3+O(1D)→ 2O(3P)+O2, O3+O(1D)→2O2† with k2a′≳10k2a′ ′. The O2† product is observed in states v′ ′≤ 30 and is apparently formed in all levels up to the dissociation limit. The formation and disappearance of vibrationally excited O2† are correlated with measurements of changes in ozone absorbance that are usually attributed to vibrational excitation. Under marginally isothermal and nonisothermal conditions ozone is excited to a nonequilibrium energy distribution, probably by vibration→vibration energy transfer from O2†. The rates of all processes having an activation energy are enhanced by this excitation.
Studies of the Vaporization Mechanism of Ice Single Crystals
Authors: Davy J. Gordon , Somorjai G. A.
Published: February 2004

The kinetics of the vacuum sublimation of ice single crystals has been investigated by a vacuum microbalance technique in the temperature range −90 to −40°C. The vaporization coefficient αv ≡ (observed vaporization rate) ÷ (theoretical maximum rate) and the activation enthalpy of sublimation, Δ Hs*, vary markedly with temperature in this range. At temperatures below about −85°C, α v=1 and Δ Hs* equals the thermodynamic enthalpy of sublimation Δ Hs°. Between about −85 and −60°C, αv decreases slowly with increasing temperature, Δ Hs*≲ΔHs°. Between about −60 and −40°C, αv decreases progressively more rapidly with increasing temperature and Δ Hs* decreases to a high-temperature limiting value of ≃ 12 Δ Hs°. The effects of various experimental parameters such as crystal orientation, doping with impurities and adsorbed gases on the ice vaporization kinetics have also been investigated. Neither grain boundaries nor crystal orientation has a measurable effect on the rate. Ice doped with monovalent impurities was found to vaporize at steady-state rates that were uniformly lower over the entire temperature range of the study. Also, NH3 (gas) and HF (gas), present in the ambient at pressures ∼10−3–10−2 torr, reduce and increase, respectively, the ice vaporization rate. The experimental results, along with previously reported physical—chemical properties of ice are used to arrive at a vaporization mechanism: Ice at equilibrium with the vapor has a surface population of a highly mobile species assumed to be water molecules hydrogen bonded to only one nearest neighbor. These energetic molecules are the source of the vapor flux leaving the surface. At sufficiently low temperatures, vacuum vaporization does not occur rapidly enough to alter this equilibrium surface population. Sublimation at higher temperatures, however, depletes the population to a progressively greater extent with increasing temperature. Thus the rate-limiting step in vaporization, which is the desorption of the mobile water molecules at low temperatures, changes to their formation at high temperatures.
Growth of High-Purity and Doped Alkaline Earth Oxides: I. MgO and CaO
Authors: Abraham M. M. , Butler C. T. , Chen Y.
Published: February 2004

A new variation of the carbon arc-fusion technique is reported which makes possible the growth of large, high-purity MgO and CaO single crystals which are free of microbubbles. A technique has also been developed for impurity doping. We have successfully doped MgO with Na, D, Ce, Eu, Gd, Dy, and Yb; and CaO with Li, Na, Ce, and Nd. The presence of these dopants has been ascertained by chemical analyses, optical, or EPR measurements. EPR signals showed minimal effects from strains in these crystals.
Development of the Bond-Charge Model for Vibrating Diatomic Molecules
Authors: Simons Gary , Parr Robert G.
Published: February 2004

The bond-charge model of a vibrating diatomic molecule previously described by Borkman, Simons, and Parr [J. Chem. Phys. 49, 1055 (1968); 50, 58 (1969)] is embedded in an exact theory of molecular vibrations near equilibrium, and shown to be a natural first approximation to the exact description. The model, based upon the Fues potential, W=W0+W1/R+W2/R2, is made exact by letting the quantities W1 and W2 depend on R: W1=W1(R), W2=W2(R), with the electronic potential energy and kinetic energy, respectively, still having the forms 2W0+W1/R and −W0+W2/R2. It is shown that, with no loss of accuracy, one may take W1′(Re)=W2′(Re)=0, which establishes the previous parameterization of W1 and W2 in terms of a bond charge q. A potential function of the form W=W0+W1R+W2R2+W3(R−Re)3R2+··· is generated from a ``multipole expansion'' of the electronic potential energy, and a model is given which includes interactions between atomic dipoles at the nuclei and bond charges. The atomic dipoles are related to the number of valence electrons of an atom, accounting for the periodic-table column dependence of force constant relations recently pointed out by Calder and Ruedenberg. The model is shown to possess the properties (∂W/∂q)R−Re=0   and   (dq/dR)R−Re=0, in accord with recent studies on the nature of charge densities and bond orders.
Adsorption of a Chain Polymer between Two Plates
Authors: DiMarzio E. A. , Rubin R. J.
Published: February 2004

A lattice model of adsorption of an isolated chain polymer between two plates is investigated using a matrix formalism and a grand canonical ensemble (GCE) formalism. The matrix formalism is particularly convenient for calculating the polymer segment density as a function of the distance from one of the plates for different fixed plate separations. The GCE formalism can be used to calculate the fraction of loops (sequences of polymer segments whose ends are in contact with one plate and whose intermediate segments lie between the two plates), bridges (sequences of polymer segments whose ends are in contact with different plates and whose intermediate segments lie between the two plates), and trains (sequences of polymer segments which are wholly in contact with one plate or the other). All of the foregoing quantities have been calculated in the limit of infinite molecular weight as a function of the distance of separation between the plates and the energy of adsorption of a polymer segment on a plate. The self-excluded volume of the polymer chain is ignored. In addition the average sizes of loops, bridges, and trains, and the effective force of attraction between the plates is calculated.
High-Resolution Measurements of 35Cl and D Quadrupole Coupling in CH2DCl and CD3Cl
Authors: Kukolich Stephen G.
Published: February 2004

Hyperfine structure on J=1→ 0 transitions in CH2D35Cl and CD335Cl was observed with a molecular-beam maser spectrometer. Splittings arising from deuteron quadrupole coupling were completely resolved for some transitions and partially resolved in others. The 35Cl quadrupole coupling along the C–Cl bond direction was eqzzQ=74 687.3± 0.5 kHz for CH2DCl and eqzzQ=74 573.1± 0.5 kHz for CD3Cl. This is a difference of 0.15% for the 35Cl quadrupole coupling in the C–Cl bond direction. The average deuterium quadrupole coupling strength was eqzzQ=170.8± 6.0 kHz. Calculation of hyperfine structure due to four quadrupole nuclei, three of which are equivalent, is discussed.
Mass Spectrometric Study of the Vaporization of Cuprous Chloride and the Dissociation Energy of Cu3Cl3, Cu4Cl4, and Cu5Cl5
Authors: Guido M. , Balducci G. , Gigli G. , Spoliti M.
Published: February 2004

The vapor phase in equilibrium with cuprous chloride has been studied using the Knudsen effusion-mass spectrometric technique. The polymeric species Cu3Cl3, Cu4Cl4, and Cu5Cl5 were observed, the first two in comparable amounts. Partial pressures and heats of vaporization for each species were measured: 3 CuCl(s)→Cu3Cl3(g),   Δ H640o=33.7± 0.8 kcal/mole, 4 CuCl(s)→Cu4Cl4(g),   Δ H650o=34.6± 0.7 kcal/mole, 5 CuCl(s)→Cu5Cl5(g),   Δ H665o=41± 1 kcal/mole. The atomization energies for these molecules calculated on the basis of the Rittner ionic model are compared with the experimental values.
Oxidation of Methyl Radicals Studied in Reflected Shock Waves using the Time-of-Flight Mass Spectrometer
Authors: Clark T. C. , Izod T. P. J. , Matsuda S.
Published: February 2004

The oxidation of methyl radicals has been investigated using a shock tube coupled to a time-of-flight mass spectrometer between 1100 and 1400°K. The effect of varying the temperature and oxygen concentration is reported. Formaldehyde was observed as a product of the oxidation reaction. For a 10-fold excess of O2 at 1350°K the concentration—time profiles for the following principal species: CH3, C2H6, C2H4, CH4, CH2O, H2O, and CO have been obtained over the reaction time scale of 350 μsec. Numerical integration calculations have been performed using a mechanism and rate data compounded from two earlier studies in this laboratory to describe the present methyl radical oxidation data. Good agreement between all the experimental and calculated profiles is obtained, with the inclusion of one additional reaction in the integrated mechanism, O+C2H4→CH3+H+CO, with a rate coefficient k13=8.3× 10−12 cc/particle·sec at 1350°K as quoted in the literature, and if the following reactions: CH3+O2→CH2O+OH, CH3+O→CH2O+H, take on the rate values k5=3.3× 10−14 cc/particle·sec and k6=4.2× 10−11 cc/particle·sec at 1350°K which are factors of 2 greater than in the earlier studies.
Average Structures of t-Butyl Chloride and 9D-t-Butyl Chloride Determined by Gas-Phase Electron Diffraction
Authors: Hilderbrandt R. L. , Wieser J. D.
Published: February 2004

The structure of t-butyl chloride has been determined by electron diffraction. The results obtained are in good agreement with the previous structure determination by Momany, Bonham, and Druelinger. This structure is shown to be consistent with the microwave rotational constants determined by Lide and Jen in spite of the fact that the rg distance for the C–Cl bond (1.828±0.005 Å) is quite different from the rs microwave distance (1.803±0.002 Å). The remaining structural parameters were determined to be C–C (1.528 Å), C–H (1.102 Å), ∠ ClCC (107.3o), ∠ CCH(110.8o), ∠CCC (111.6o), and ∠ HCH (108.1o). A simultaneous investigation of the structure of the deuterated species suggests slight secondary isotope effects on the C–C (ΔC–C=0.0010±0.0007-Å) and C–Cl (ΔC–Cl=0.0010±0.0015-Å) distances. Observed mean amplitudes of vibration are found to be consistent with values calculated from the harmonic force field of Hüttner and Zeil.
Cross sections for the production of CO(a′ 3Σ+, d 3Δi, and e 3Σ− → a 3Π) fluorescence through photodissociation of CO2
Authors: Judge D. L. , Lee L. C.
Published: February 2004

Cross sections for the production of CO(a′ 3Σ+, d 3Δi, and e 3Σ− → a 3Π) fluorescence through photodissociation of CO2 have been measured from 764 to 923 Å using a line emission source. The CO fluorescence spectra produced in the photodissociation are presented and identified. The cross sections for the production of fluorescence from various vibrational levels of CO* using incident photons of 901 and 923 Å are also presented.
Time-of-flight determination of lifetimes of N2+(A 2Πu)-the Meinel band system
Authors: Peterson James R. , Moseley John T.
Published: February 2004

Radiative lifetimes of N2+(A 2Πu ) have been determined for vibrational levels v′=1−8. They decrease monotonically from 13.9± 1.0 μ sec for ν′=1 to 7.3 ± 0.5 μ sec for v′=8. A time-of-flight method was used to overcome collisional and diffusion effects that have affected most other measurements.
Electronic structure of unstable intermediates. I. The electronic structure of some linear triatomic molecules containing boron
Authors: Thomson Colin
Published: February 2004

Ab initio LCAO-MO-SCF wavefunctions, approaching Hartree-Fock accuracy have been carried out for the linear molecules, BCN, BNC, BCC, CBC, BBC, and BCB. The optimimum bond lengths for the ground state of these molecules were computed. BNC, BCC, and BCB are predicted to be more stable than their isomers, and in the case of BCC, the ground state configuration is consistent with the results of ESR measurements.
Theory of diamagnetism of neutral molecules
Authors: Weisenthal L. , Graaf A. M. de
Published: February 2004

A new theory of the diamagnetism of neutral molecules has been developed. The theory shines light on the significance of the role played by the gauge of the potentials describing external fields. Starting out with a Lagrangian formalism and by expanding the charge and current densities in multipole series about a configurational coordinate, a molecular Hamiltonian has been derived which is completely free of these potentials, but instead contains the fields explicitly. This has the important advantage that the diamagnetic susceptibility, obtained from this Hamiltonian, does not depend on the vector potential. Therefore, the question of which gauge to choose in order to obtain the best value of the susceptibility when only approximate wavefunctions and eigenvalues are available for computation, has become immaterial. Using simple symmetry arguments it has been shown that if the molecule is subjected to a uniform magnetic field, the natural origin of the electronic coordinates is the center of nuclear charge.
Experimental and theoretical studies of the fundamental bands of sulfur dioxide
Authors: Corice R. J. , Fox K. , Tejwani G. D. T.
Published: February 2004

The infrared-active vibration-rotation fundamentals of 32S16O2 have been measured with moderately high spectral resolution. Quantum number assignments have been made for spectral lines by comparison with theoretically computed line positions and intensities, which include the effects of centrifugal distortion. The following values for the band centers have been determined: ν1° = 1151.65 ± 0.10 cm−1, ν2°=517.75± 0.10 cm−1, and ν3°=1362.00± 0.10 cm−1.
Crossed beams chemistry: Reactions of Ba, Sr, Ca, and Mg with Cl2 and Br2
Authors: Lin Shen-Maw , Mims Charles A. , Herm Ronald R.
Published: February 2004

Reactions of Ba, Sr, Ca, and Mg with Cl2 and Br2 have been studied in a crossed beam apparatus employing an electron bombardment ionizer-mass filter detector. Product center-of-mass (c.m.) recoil energy and angle distributions have been fit to the measured monohalide product (MX) laboratory (LAB) angular distributions by averaging the c.m.→LAB transformations over the measured (nonthermal) beam speed distributions. These experiments give no indications of a dihalide product (MX2) and indicate that the formation of MX2 (by a two-body radiative association) cannot account for more than a small fraction (<∼5%) of the reactive collisions. All eight reactions favor forward product scattering (i.e., MX scattered in the direction defined by the incident M) with relatively low recoil energies (∼10%–20% of the reaction exoergicity). For reaction with either halogen molecule, the fraction of the product scattered into the forward c.m. hemisphere increases in the sequence: Mg, Ca, Sr, Ba. Similarities and differences between the results of the present study and features of the reactions of alkali atoms are discussed.
Structural dependence of birefringence in the chalcopyrite structure. Refinement of the structural parameters of ZnGeP2 and ZnSiAs2
Authors: Lind M. D. , Grant R. W.
Published: February 2004

We have found that, as a consequence of the experimentally observed geometrical regularity of the BC4 tetrahedra in AIIBIVC2V crystals with the chalcopyrite structure, the birefringence of the crystals depends on the anisotropic polarizability of the A–C bonds only. This has allowed us to predict the birefringence of several AIIBIVC2V crystals for which reliable experimentally determined values are not available. To provide additional crystal structure data, as required for the predictions, we have refined the structural parameters of ZnGeP2 and ZnSiAs2 by the method of least squares with counter measured single crystal x-ray diffraction data; the positional parameters (estimated standard errors in parentheses) are xP=0.25816 (0.00044) and xAs=0.26575 (0.00012). Final values of the conventional agreement index R were 0.029 and 0.022 for ZnGeP2 and ZnSiAs2, respectively. The GeP4 and SiAs4 tetrahedra are regular within experimental error. Experimentally determined bond distances are: Zn–P, 2.375  (0.002)  Å;  Ge–P, 2.324  (0.002)  Å;  Zn–As, 2.454  (0.001)  Å;  and  Si–As, 2.352  (0.001)  Å.
Pressure dependence of proton spin-lattice relaxation in liquid hydrocarbons
Authors: Brooks A. A. , Stejskal E. O. , Weiss V. W.
Published: February 2004

The pressure dependence of the proton spin-lattice relaxation time T1 in ten liquid hydrocarbons at room temperature (28°C) is reported. The ten compounds were (a) bicyclohexyl, (b) dicyclohexyl methane, (c) 1,3-dicyclohexyl propane, (d) 1,4-dicyclohexyl butane, (e) 1,9-dicyclohexyl nonane, (f) 1,1-dicyclohexyl ethane, (g) 1,2-dicyclohexyl propane, (h) 1,3-dicyclohexyl butane, (i) 1,3-dicyclohexyl-2-methyl propane, and (j) phenyl cyclohexyl. The maximum pressure attained was 3000 kg cm−2. Three compounds (a), (b), and (d) froze before this limit was reached. Three others (c), (e), and (h) gave evidence of higher order phase transitions. Three of the compounds (f), (g), and (i) showed T1 minima, all around 0.017 sec. The resonant frequency was 20.00 MHz. The volume of activation Δ V‡ for the molecular correlation time τc is estimated for each compound. Δ V‡ is nearly the same for (b), (c), (d), and (e). It is slightly lower for (a) and (j) and slightly higher for the rest. The significance of this and the value of τc at one atmosphere is discussed. It is felt that the reorientation of the cyclohexyl rings dominates the relaxation procsss.
Electronic structure and dynamics of tunable laser excited p-benzoquinone (-h4 and -d4) in the gas phase
Authors: Brus L. E. , McDonald J. R.
Published: February 2004

Time-resolved emission from low pressure p-benzoquinone-h4 (and -d4) is observed following single vibronic excitation of the 1B1g and 3Au states with a tunable dye laser. Evidence is presented showing that 1B1g levels undergo an intermediate strong coupling with vibronic levels of lower excited electronic states. These hybrid states, which have collision-free emissive liftimes of 7–15 μsec, are collisisonally relaxed at a near gas kinetic rate, with at least partial conversion to the vibrationally equilibrated 3Au state. A simple three level relaxation model is investigated and deemed to be inadequate. The 3Au phosphorescence liftime is 28.4 μsec (37.6 μsec for benzoquinone-d4,) independent of pressure for added argon and nitrogen and benzoquinone, itself. Comparison of the 3Au phosphorescence lifetime with Ag1→Au3 f number indicates that the 3Au lifetime is controlled by a unimolecular process other than Au3→Ag1 phosphorescence. We prospose that the unimolecular process competing with the Au3→Ag1 phosphorescence could be the symmetry and spin allowed Au3→B1g3 fluorescence that would occur in the infrared. This process is compared to the other possible deactivating route, a spin-orbit-vibronic induced radiationless transition into the 1Ag ground state. 3Au molecules are mildly deactivated by O2 and C2H2, and deactivated at near the gas kinetic rate by NO.
Microwave spectrum, dipole moment, quadrupole coupling constants, and conformation of cyanocyclobutane
Authors: Fong Mei Y. , Harmony Marlin D.
Published: February 2004

The microwave spectrum of cyanocyclobutane has been observed in the ground and first four excited vibrational states. The spectrum consisted of a- and c-type R- and Q-branch transitions. 14N quadrupole coupling constants were determined to be χaa= −3.663± 0.005 MHz, χbb= 2.086± 0.006 MHz and χcc= 1.577± 0.006 MHz. Electric dipole moment measurements led to μa= 4.00 ± 0.003 D and μc= 0.95± 0.02 D (μb = 0 by symmetry). All of the data are in accord in specifying the equatorial conformation for the puckered-ring system. Data from the excited states of the ring-puckering motion are in accord with a recently proposed potential function.
Re-examination of the vibrational analysis of the 2738 Å system of benzonitrile
Authors: Tan Han Tin , Thistlethwaite P. J.
Published: February 2004

The 2738 Å system of benzonitrile has been re-examined at a dispersion sufficient to distinguish the different band types. A number of modifications to the earlier analysis have been made.
Gas phase recombination of hydrogen and deuterium atoms
Authors: Trainor Daniel W. , Ham David O. , Kaufman Frederick
Published: February 2004

Rate constants for the reaction H+H+M → H2 + M, with M = H2, He, and Ar were measured over the temperature range 77–298°K. Hydrogen atoms were produced by thermal dissociation and absolute atom concentrations were measured through use of a self-balancing, isothermal catalytic probe detector. The specific rate constants were 8.1 ± 0.4 × 10−33, 7.0 ± 0.4 × 10−33, and 9.2 ± 0.6 × 10−33 cm6 molecules−2 · sec−1 at 298°K for M = H2, He, and Ar, respectively; these values rising to 18.5 ± 2.2 × 10−33, 12.0 ± 1.5 × 10−33, and 27.4 ± 4.6 × 10−33 cm6 molecules−2 · sec−1 at 77°K. For the equivalent deuterium atom process with D2 as the third body, the rate constants are 6.1 ± 0.3 × 10−33 cm6 molecules−2 · sec−1 at 298°K and 15.1 ± 1.0 × 10−33 cm6 molecules−2 · sec−1 at 77°K. These values are compared with previous experimental measurements and with recent theoretical calculations.
Statistical theories of chemical reactions. Distributions in the transition region
Authors: Anderson James B.
Published: February 2004

The distribution of states in the transition region is considered for chemical reactions occurring with reactants in thermal equilibrium. It is argued that when products are absent the distribution in the transition region is identical to an equilibrium distribution except that states originating from products are missing. The phenomenon is illustrated with classical trajectory calculations for three collinear systems with widely different potential energy surfaces: (a) intersecting rectangular channels of different elevation, (b) a smooth curve of parabolic cross section, and (c) a surface for the endothermic reaction H2+I → H + HI. For purely classical reactants in an equilibrium distribution a ``bobsled noneffect'' is found. The use of a conversion coefficient ξ in place of the usual transmission coefficient κ in transition state theory is shown to correct for the nonequilibrium distribution in the transition region. The equivalence of the combined phase space/trajectory method and the conventional trajectory method is demonstrated for the three examples.
Molecular dynamics studies of the properties of small clusters of argon atoms
Authors: McGinty David J.
Published: February 2004

Molecular dynamics calculations have been performed on clusters of 15, 30, 45, 60, 80, and 100 argon atoms at temperatures of up to 75°K. Values of the independent-cluster thermodynamic functions are presented and compared with those obtained from the microcrystal model. This comparison indicates good agreement for values of the Gibbs free energy of formation. The transition from solidlike to fluidlike diffusion in the cluster occurs gradually; no semblance of a phase transition is noted. The radial variation of density in the clusters have maxima and minima reminiscent of those in the radial distribution function for bulk liquids. The temperature dependence of that function indicates that clusters expand quite rapidly as the temperature is increased. The radial distribution of potential energy indicates that there is no region inside the clusters where the environment resembles that in the bulk phases; the properties of the clusters are dominated by the ``surface region'' in which nearly all the atoms exist.
Effective charge tensors of atoms in a molecule and electric dipole shielding of nuclei
Authors: Sambe Hideo
Published: February 2004

Exact formulas are derived for the electric shielding tensors of nuclei in a molecule bathed in a static, uniform, electric field. It is shown that the derived relations hold also in the coupled Hartree-Fock approximation. The resulting equations should provide useful checks on the accuracy of the first-order induced electron density, a quantity required for the calculation of the electric dipole polarizability tensor. A tensor quantity, which is a function of the electric dipole moment and its derivatives with respect to the internal coordinates, is proposed as an effective charge of an atom in a molecule.
Zeeman effect of nuclear quadrupole resonance in 1-chloro-2,4-dinitrobenzene
Authors: Vijaya M. S. , Ramakrishna J.
Published: February 2004

The Zeeman effect of NQR was studied in 1-chloro-2,4-dinitrobenzene. A low value of the asymmetry parameter (0.10) was obtained. Four physically inequivalent field gradients were located and their orientations in the crystallographic abc system were determined using symmetry considerations. From these data the orientations of the molecules in the unit cell were determined. The results agree well with the two-dimensional x-ray structural data. The bond characters of the C–Cl bond were calculated, and the values compare well with those generally obtained for C–Cl bonds in chlorine derivatives of benzene.
Cross sections for production of the CO(A 1Π−X 1Σ) Fourth Positive band system and O(3S) by photodissociation of CO2
Authors: Gentieu E. P. , Mentall J. E.
Published: February 2004

Excitation cross sections were measured for producing CO(A 1Π) by photodissociation of CO2 from threshold to 635 Å· Above 685 Å the CO(A 1Π) cross section is of the order 1 × 10−12 cm2 and exhibits considerable structure while below 685 Å the CO(A 1Π) cross section rapidly drops to a nearly constant value of [sine wave] 3 × 10−20 cm2. The structure below 790 Å correlates with predissociation from known Rydberg states of CO2 demonstrating the competition between preionization and predissociation. An upper limit of 6% of the CO(A 1Π) cross section was inferred for producing O(3S). Although not directly observed, evidence was obtained that the production of CO(A 1Π) is accompanied by production of O(1D) and O(1S) at incident photon wavelengths less than 800 and 700 Å, respectively. The CO(A 1Π−X1Σ) vibrational intensity distribution was obtained with 7 Å resolution for 16.69 eV photon impact and is similar to a 20 eV electron impact produced distribution.