bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of space-charge polarization and electrode-discharge effects
Authors: Macdonald J. Ross
Published: February 2004

A combined, general treatment of intrinsic and extrinsic conduction in a liquid or solid is presented. Positive and negative species of mobile charge of arbitary valences and mobilities are assumed present, together with homogeneous immobile charge in the extrinsic case. The general equations are specialized to a one-dimensional situation and then to that where both position-dependent static and much smaller sinusoidally time-varying components of charge, field, and current are simultaneously present. Sufficiently general boundary conditions are used that any condition from complete blocking to free discharge of positive and negative mobile carriers separately can occur at the electrodes. For the flat-band condition (zero static field; in the binary electrolyte case, coincidence of the zero charge potential and the equilibrium potential) exact equivalent circuits and an exact expression for the small-signal impedance are obtained. Relatively simple, closed-form expressions for the zero-frequency limiting values, Ci0 and Ri0, of the two frequency-dependent elements which appear in the equivalent circuit, Ci and Ri, are derived even in general cases. The dependence of the normalized quantitities CiN0 and RiN0 on detailed boundary conditions, mobility ratio, valence ratio, temperature, and impurity doping level is examined in detail, reserving examination of frequency and temperature dependence of CiN and RiN themselves for later publication. Even for complete blocking of charges of both sign, Ci0 and Ri0 are not both intensive (interface) quantities unless the electrode separation contains many Debye lengths and the mobility and valence ratios are equal. When charges of one sign are completely blocked and those of the other partially or completely free to discharge, neither Ci0 nor Ri0 is generally intensive, and Ci0 may be many orders of magnitude larger than the completely blocking, diffuse-double-layer value. The dependence of CiN0 and RiN0 on all the above parameters is quite different in the extrinsic conduction case depending upon whether the discharging species involves majority or minority carriers.
Proton NMR in nematic liquid crystalline solvents: The use of deuterium decoupling
Authors: Hewitt Richard C. , Meiboom Saul , Snyder Lawrence C.
Published: February 2004

Nuclear magnetic resonance spectra of molecules dissolved in an oriented (nematic) solvent become exceedingly complex when the solute molecules contain more than about eight magnetic nuclei. In this paper a technique for greatly simplifying the proton spectra by partial deuterium substitution is described. The deuterium is decoupled by irradiation at a frequency corresponding to a double quantum deuteron transition. Experimental details are presented, as well as results obtained on partially deuterated cyclohexane. The behavior of the spectra as a function of deuterium irradiation intensity and frequency offset is shown in a series of experimental spectra, and compared with computer simulated spectra calculated with a theory presented in a companion paper. It is shown that the spectrum behavior under frequency offset of the irradiation can be a tool in the assignment of spectrum peaks.
Theory of proton NMR with deuteron decoupling in nematic liquid crystalline solvents
Authors: Snyder Lawrence C. , Meiboom Saul
Published: February 2004

The theory required to interpret proton NMR with deuteron decoupling in liquid crystalline solvents is developed. The Bloom and Shoolery analysis of double resonance experiments, in which the spectra of a pair of nonidentical nuclei with isotropic coupling are interpreted in terms of quantization in an effective field in a rotating coordinate system, is extended to systems having anisotropic interactions such as direct dipolar and quadrupole couplings. Applications are made to model systems of one-proton-one-deuteron and two-protons-two-deuterons to facilitate interpretation of recent decoupling experiments, which are described in a companion paper, on partially deuterated cyclohexane in a nematic solvent.
Ultraviolet absorption spectra of CdCH3, ZnCH3, and TeCH3
Authors: Young P. J. , Gosavi R. K. , Connor J. , Strausz O. P. , Gunning H. E.
Published: February 2004

Ultraviolet absorption spectra were recorded for the transient radicals CdCH3, ZnCH3, and TeCH3 produced in the flash photolysis of the appropriate dimethyl metals. For CdCH3 and ZnCH3 two systems were observed and assigned to the two transitions Ã 2E← x̃2 A1 and B̃ 2E← x̃2 A1. For the TeCH3 radical only one system was observed which was assigned to the B̃← x̃ transition. The progressions in the spectra are assigned to the upper state carbon-metal stretching vibration (ν′3) and CH3 symmetric deformation vibrations (ν′2).
Dynamics of the O+-H2 reaction. I. Reactive scattering of O+(4S 3/2) at relative energies below 15 eV
Authors: Gillen Keith T. , Mahan Bruce H. , Winn John S.
Published: February 2004

Product velocity vector distributions show that the reaction O+(H2,H)OH+ and its isotopic variations proceed from ground state reactants to predominantly electronic ground state products via a direct interaction. Spectator stripping is a prominent feature at the lower relative energies of collision, but the stripping peak is lost at energies where the internal excitation of OH+ (3Σ−) makes it unstable to dissociation. Production of forward scattered electronically excited OH+, probably in the 1Δ state, is observable when the initial relative energy is high enough that OH+(3Σ−) formed by spectator stripping is unstable with respect to dissociation. At these relative energies, OH+ from HD is predominantly scattered into barycentric angles less than 90°, while the OD+ appears at approximately 90° at larger angles. The propensity for formation of OD+ at large angles can be understood in terms of general kinematic considerations which apply to collinear collisions.
Optical birefringence in the solid isotopic methanes
Authors: Ballik E. A. , Gannon D. J. , Morrison J. A.
Published: February 2004

A sensitive method of measuring optical birefringence in crystals has been developed. The technique is used to measure birefringence quantitatively in the lowest temperature phase (phase III) of the three solid phases of the isotopic methanes. For the experiments, the methanes were each condensed in a thin glass cell mounted in a cryostat, and their optical properties were examined in the temperature region from 6°K to the melting points. Gross cracking of the solids, due to contraction during cooling, was not troublesome because the area of specimen that needed to be viewed was no more than 0.035 mm2. The phases III of CD4, CHD3, and CH3D were observed to have stable birefringences of magnitudes 3.8(± 0.4) × 10−4,3.8(± 0.5) × 10−4, and 1.7(± 0.4) × 10−4, respectively. In contrast to this, the birefringence of CH4 was found to be both time and temperature dependent and is interpreted as resulting from conversion between spin species of the molecule. The birefringence of phase III of CD4 is consistent with the tetragonal structure tentatively assigned on the basis of recent x-ray and neutron diffraction studies.
Magnetic resonance and relaxation in NH4ClO4
Authors: Riehl J. W. , Wang Richard , Bernard H. W.
Published: February 2004

The proton spin-lattice relaxation, second moment, and magnetization of NH4ClO4 have been investigated between 1.5 and 100°K, using pulse NMR techniques. The system has a T1 minimum at 29°K and, below 20°K, evidences nonexponential recovery with a relatively weak temperature dependence. The second moment gradually increases from 1.3 G2 to ∞ 4 G2 at 2°K. Spin conversion is observed below 4°K. The data are interpreted with reference to the possible hindered rotor levels of the NH4+ ion.
Bounds for thermodynamic Green's functions from the application of path integral methods
Authors: Bruch Ludwig W. , Revercomb H. E.
Published: February 2004

Symanzik's inequalities for thermodynamic Green's functions are applied to correlation functions occurring in the quantum statistical mechanics of dilute gases. The application is based on the use of the constant-force Green's function. The results are compared with the results of classical path approximations. The Green's function inequality corresponding to the Feynman-Hibbs partition function inequality is derived and discussed. Applications to a model of hydrogen vapor and to the statistical mechanics of the hydrogen atom are presented.
Atomic and molecular calculations with the pseudopotential method. IX. One-valence-electron photoionization cross sections using Hellmann-like potentials
Authors: McGinn George
Published: February 2004

An l-independent Hellmann-like pseudopotential method is used to investigate the photoionization cross section for the ns-ε p transitions of the alkali atoms Na, K, Rb, and Cs for the continuum energy range 0–2.0 Ry. The results are compared to previous pseudopotential calculations, other theoretical calculations, and to observed values.
Photoionization mass spectrometric study of NO. A closer look at the threshold region
Authors: Killgoar P. C. , Leroi G. E. , Berkowitz J. , Chupka W. A.
Published: February 2004

The photoionization efficiency curve of NO+ was obtained using the argon continuum in the energy range 9.25–10.00 eV. Considerable fine structure is observed superimposed upon the vibrational steps of the NO+ ionization curve, which is attributed to vibrational autoionization. This structure has been assigned to Rydberg series converging to the excited vibrational levels of the ground NO+ ion (1Σ+).
Photodecomposition and electronic structure of lead azide
Authors: Hall Robert B. , Williams Ferd
Published: February 2004

Photodecomposition, optical absorption, and conductivity measurements were performed on thin films of lead azide in order to determine interrelation between electronic structure and chemical instability. Both pure lead azide and thallium and bismuth doped films were investigated. The azide films are prepared by chemical conversion of evaporated metallic films by the vapor of hydrazoic acid and are found to consist of 1 μm2 platelets which lie parallel to the substrate and are optically active. No effects of doping on the Fermi level are observed and we conclude that the dopants are self-compensated by native defects. The observed changes in ultraviolet and infrared absorption during thermal or photodecomposition can be attributed to the formation of azide vacancies. Thallium doping results in changes in optical properties similar to those obtained on decomposition. The initial step in photodecomposition appears to be the creation of charge-transfer excitons.
Detailed balancing approach to disordered copolymeric Ising chains
Authors: Lacombe R. H. , Simha Robert
Published: February 2004

The problem of disordered copolymeric one-dimensional Ising chains with nearest-neighbor interactions is formulated in full generality, using the principle of detailed balancing. The natural variables in this theory are a set of nearest-neighbor conditional probabilities and singlets. A set of coupled nonlinear difference equations in these variables is derived, which completely determine the state of the chain with respect to both composition and fine structure. A special but nontrivial case of the general model is treated in detail to illustrate the theory and to make possible comparisons with the work of others. The problem of the strictly alternating copolymer is readily solved by way of illustration. An efficient and accurate numerical approach, employing a Monte Carlo technique, is used to evaluate these equations for disordered chains, both random and nonrandom. Example calculations, based on data for a binary RNA, show the doublet variables to be more sensitive to differences between random and nonrandom chains than the singlets. Triplet and higher configurational probabilities can also be readily calculated. The numerical computations make it clear that our results are equivalent to ensemble average results given by Lehman and McTague who numerically evaluate integral and functional equations for the logarithm of the partition function.
Classification of configurations and the determination of interacting and noninteracting spaces in configuration interaction
Authors: McLean A. D. , Liu B.
Published: February 2004

The n-particle space of a configuration interaction (CI) calculation, spanned by configuration state functions (CSF's), is partitioned into subspaces defined, relative to a set of zeroth-order CSF's, by the type of orbital excitation and by the lowest order of the Rayleigh-Schrödinger perturbative correction contributed by the subspace. A method is given for determining CSF's spanning the ith-order subspace which contains those and only those functions that have a nonzero interaction through the Hamiltonian with some member of the (i−1)th-order subspace. These subspaces are anticipated to be of considerable use in structuring and interpreting configuration interaction wavefunctions.
Right-rotatory cholesteric liquid crystals: Derivatives of Δ8(14)-cholestanol
Authors: Beebe Leder Lewis
Published: February 2004

A new series of cholesteric liquid crystals which are derivatives of Δ8(14)-cholestanol has been synthesized. Although some of the compounds are monotropic and others enantiotropic, on the average, they are liquid crystalline about 30°C lower than the cholesteryl equivalents. Their effective pitches, as measured by the method of mixtures, are all smaller than those of the equivalent cholesteryl compounds. A note-worthy feature is that they are all strongly right handed, and from extrapolation of a plot of pitch vs number of alkyl carbons for the esters, it is expected that they will remain right handed up to C16 chain length. Heretofore, only a few individual right-handed cholesteric liquid crystals have been known.
Valence-bond study of the (H2, D2) exchange reaction mechanism
Authors: Freihaut B. , Raff L. M.
Published: February 2004

A minimal-basis VB formulation of the H4 system together with the Mulliken approximation is used to investigate the potential barrier in the (H2, D2) bimolecular exchange reaction for a ``Y''→``T''→``Y'' mechanism previously suggested by Gimarc. The results indicate that ``T'' conformation energies are 100–160 kcal/mole above that of (H2+D2) and that an exchange process occurring via such a mechanism would yield activation energies incompatible with present shock-tube data.
Nonempirical LCAO MO SCF studies of the group IIa dihalides BeF2, MgF2, and CaF2
Authors: Gole James L. , Siu Albert K. Q. , Hayes Edward F.
Published: February 2004

Nonempirical LCAO MO SCF calculations are reported for the ground, C2ν states of the Group IIa dihalides, BeF2, MgF2, and CaF2. These calculations demonstrate the importance of 3d orbitals in the bonding trends of the dihalides and, hence, in the determination of the equilibrium bond angles and the bending force constants. The calculations on BeF2 indicate that d orbitals play an important role in the bonding but do not preferentially alter the general features of the total energy curve at any bond angle. In the case of MgF2, d orbitals are found to preferentially lower the energy of the nonlinear configurations. However, for both species, the ground-state equilibrium bond angle is predicted to be 180°. Configuration interaction studies also support the fact that, in the gas phase, the linear configuration is most stable. On the basis of s(1s, 2s, 3s, 4s, 2p, and 3p orbitals on Ca) basis set calculations, it is predicted that CaF2 is linear. However, when 3d orbitals are added to the s basis set, the predicted equilibrium bond angle is 145°. This is in good agreement with the value of 141° deduced from matrix-isolation spectroscopy. The bonding in these molecules is discussed with reference to the nonempirical molecular correlation diagram.
Molecular orbital theory of the hydrogen bond. V. Hydrogen bonding through the lone pair and the pi system in HF–HCN
Authors: Del Bene Janet E. , Marchese Francis T.
Published: February 2004

Ab initio LCAOSCF calculations with a minimal STO-3G basis set have been performed on dimers HF–HCN with HCN as the proton acceptor molecule. The equilibrium dimer has a linear FH··· NCH structure which is well described by the general hybridization model for the hydrogen bond. Hydrogen bond formation through the π electron system of HCN has also been investigated. It is found that the π dimers do not correspond to equilibrium structures on the intermolecular HF–HCN potential surface.
Spectroscopic determination of ion-defect pair energies in KCl:Sm2+
Authors: Naberhuis S. L. , Sundberg M. N. , Fong F. K.
Published: February 2004

Hitherto undetermined symmetry origins of fluorescence lines occurring in the KCl:Sm2+5D0→7F5 transition region are examined in terms of lifetime measurements. From relative intensity measurements of all the dominant lines observed in the entire D0→75FJ(0≤ J ≤ 6) fluorescence spectrum and experimentally determined effective equilibrium distribution temperature of 219°K, the binding energies of the nearest-neighbor [C2ν(1,1,0)] and next-nearest-neighbor [C4ν(2,0,0)] Sm2+−K+ vacancy pairs are found to be −0.45 and −0.39 eV, respectively. At ordinary temperatures, the dominant sites, in the order of relative importance, are the C2ν(1,1,0), Cs(2,1,1), and C4ν(2,0,0) pairs. This observation is interesting in view of the predominance of the C4ν(2,0,0) site in the KCl:Sr2+ and KCl:Mn2+ systems.
Helical twisting power of a diastereomeric pair of branched-chain esters of cholesterol
Authors: Hakemi H. , Labes M. M.
Published: February 2004

The branched-chain 2-methylvaleric acid esters of cholesterol were prepared with (+), (−), and (±) configuration of the ester chain. Branching leads to monotropic smectic behavior in the pure esters; studies made by dissolving them in a compensated cholesteric or in a nematic solvent indicate that they have helical twisting powers which vary with the configuration at the asymmetric center.
Complex-valued classical trajectories for reactive tunneling in three-dimensional collisions of H and H2
Authors: Doll J. D. , George T. F. , Miller W. H.
Published: February 2004

Complex-valued classical trajectories for three-dimensional reactive collisions of H+H2 have been calculated at collision energies below the classical threshold for reaction, and from such trajectories classical S-matrix elements for the 0 → 1 rotational transition have been constructed. Comparison with available quantum mechanical results for the same system are encouraging and suggest that this semiclassical theory is capable of accurately describing reactive tunneling in a physically realistic model of a chemical reaction. Ways of simplifying the practical aspects of applying classical S-matrix theory to three-dimensional reactive systems are also described.
An EPR study of VO2+ and Cr3+ in (NH4)2SbCl5
Authors: Flowers J. M. , Hempel J. C. , Hatfield W. E. , Dearman H. H.
Published: February 2004

Single crystal X-band EPR studies of VO2+ and Cr3+ in the matrix (NH4)2SbCl5 show the impurity ions to substitute in an antimony site, a site of approximately C4v five coordinate symmetry. The vanadyl species exhibits axial symmetry with g∥=1.9478± 0.0001, g⊥=1.9793± 0.0001, A∥=0.01688± 0.00001 cm−1, A⊥=0.0062± 0.00001 cm−1, and the chromium species rhombic symmetry with gx=1.9835± 0.0002, gy=1.9839± 0.0002, gz=1.9853± 0.0001, D=0.03706± 0.00001 cm−1, E=0.00304± 0.00001 cm−1, A=0.00165± 0.00002 cm−1. Molecular orbital and ligand field calculations support the assignment of the magnetic species as VOCl42− and CrCl52−, respectively.
Matrix infrared spectra and anharmonic force field of NCO−
Authors: Smith D. Foss , Overend John , Decius J. C. , Gordon Donald J.
Published: February 2004

Cyanate ions enriched in 15N, 13C, and 18O have been prepared by direct oxidation reactions and introduced into KCl and KBr single crystals to a maximum concentration of ≈ 5 wt%. The infrared absorption spectra of the resultant cyanate ion isotopic species observed between 550 and 5000 cm−1 from 320 to 77°K have added more than 50 new vibrational features to those previously reported. 2v3 has been observed for 14N-12C16O− and 15N12C16O− in both KBr and KCl matrices, thus permitting an unambiguous determination of x33. The observed energy levels reported here have been combined with those previously reported and have been used to determine the anharmonic force field including cubic and quartic force constants in KBr, KCl, and KI matrices.
Molecular beam kinetics: The reactions of Li atoms with alkali halide molecules
Authors: Lees A. B. , Kwei G. H.
Published: February 2004

Angular distributions of alkali atoms produced in crossed-beam reactions of Li atoms and alkali halide molecules (MX where M = K or Cs) have been measured. For these systems, the reaction exoergicity and ratio (reactants-to-products) of reduced masses vary from Δ D0∼2.4 kcal/mole and μ/μ′≈ 0.1 for Li+CsI to ∼20.4 kcal/mole and 0.4 for Li+KF; thus, these and previous M+M′ X→MX+M′ reactions span complementary chemical and kinematic domains. The main features are: (1) Laboratory distributions of the product alkali atoms formed in the reactions Li+MF show only a single peak strongly resembling the M-atom distributions formed in the reactions of H atoms with MF. Least-squares analyses of the data with assumed flux-Boltzmann recoil-velocity distributions produce center-of-mass (c.m.) distributions that confirm these results. (2) Product distributions formed in the less exoergic reactions are similar to those obtained in earlier M+M′X studies and exhibit the bimodal peaking indicative of the formation of long-lived complexes. However, in contrast to the earlier studies, the ratio of collisional angular momentum L to reactant rotational angular momentum J is small, and the angular term in the c.m. distributions is nearly isotropic; the sharp laboratory peaks result instead from the c.m.→LAB transformation which provides an accummulation of intensities at LAB angles which intersect the ``edges'' of the sharp recoil-energy distribution. (3) The smaller values of L for these reactions suggest that J and J′ may no longer be negligible in comparison with L and L′; since there is a large decrease in reduced mass of the diatomic partner upon reaction, angular momentum conservation suggests that L′>L and that the exit channel centrifugal barrier will be somewhat higher than predicted by the statistical-complex model. RRKM recoil energy distributions for a ``tight'' complex at the critical configuration provide good agreement with experiment if a low-energy cutoff corresponding to a higher barrier is introduced; this implies a favoring of reactive decompositions with large L′ or the existence of an activation barrier in the exit channel. (4) For the Li+MF reactions, reaction cross sections were estimated by normalizing the wide-angle nonreactive scattering to the hard-sphere cross section; this gave crude values of ∼20 Å2 and ∼80 Å2 for KF and CsF, respectively. Comparison of observed intensities with other systems suggests that reaction cross sections for the other Li+MX reactions were roughly comparable. (5) The transition from a long-lived collision-complex mechanism to an impulsive mechanism for the Li+MF reactions results from the increased exoergicity of these reactions and agrees with the ``osculating'' complex model and crude RRKM lifetime estimates if potential wells slightly deeper than predicted by pseudopotential calculations are assumed for both systems or if a shallower well is assumed for the LiFM systems.
Vibrational relaxation of HCl with inert gas collision partners
Authors: Seery Daniel J.
Published: February 2004

The vibrational relaxation of HCl has been measured behind incident shock waves in the presence of He, Ne, Ar, and Kr over a temperature range of 800–4100°K and a pressure range of 10–400 torr. The data show a decrease in the efficiency of energy transfer with increasing reduced mass. This tendency appears to be much stronger than predicted by present theories even when the reduced mass is assumed to be that for H atom-inert gas collisions rather than HCl-inert gas.
Temperature dependence of electron attachment at low energies for polyatomic molecules
Authors: Spence D. , Schulz G. J.
Published: February 2004

The cross sections for production of negative ions by attachment of low-energy (<0.2 eV) electrons to selected polyatomic (SF6, CCl4, CFCl3, CH2Br2, CH3I, CHCl3, CF3Br, CH3Br) molecules have been determined as a function of target gas temperature in the range from 300 to 1200°K. For the case of SF6 it is found that the total cross section for negative ion production is independent of gas temperature, although it is known from the experiments of Chen and Chantry that the relative abundances of different species of negative ions produced from SF6 are strongly temperature dependent. In contrast to SF6, the total cross sections for negative ion production in some halogenated hydrocarbons are found to be strongly temperature dependent. It is found that the total cross section for negative ion production in many polyatomic molecules tends towards an absolute maximum as the gas temperature is increased.
Σ
+
7
and Π7 states of manganese hydride
Authors: Bagus Paul S. , Schaefer Henry F.
Published: February 2004

Ab initio self-consistent-field calculations have been carried out close to the Hartree-Fock limit for the high spin Σ+7 and Π7 electronic states of MnH. Five different hydrogen-centered basis sets of Slater functions are tested for H− and MnH. Predicted spectroscopic constants (with experimental values in parentheses) for the Σ+7 ground state are De=1.57 eV (2.4 ± 0.3), ωe=1549 cm−1 (1548), re=1.780 Å (1.722), and Be=5.32 cm−1 (5.68). And for the Π7 state, Te = 21 870 cm−1 (17 700), ωe=1708 cm−1, re=1.703 Å, and Be=5.88 cm−1 (6.43). The electronic structure of the two states is discussed with respect to the contributions of the different molecular orbitals to the electric dipole moment and population analysis. Although the population analysis predicts the Σ+7 state to be more ionic than the Π7 state, the dipole moments are computed to be 1.6 and 4.1 D, both +MnH−. The small dipole moment of the Σ+7 state is seen to be due to a large −MnH+ contribution from the nonbonding 8σ orbital (which is replaced by 4π in the Π7 state). The manganese atom 3d5 configuration survives essentially unchanged in both states of MnH, and it is suggested that the electronic structure of other transition metal hydrides may be quite similar, involving a single ionic bonding σ orbital.
Accurate ab initio calculation of the BeH molecule. I. The X 2Σ+ and A 2Π states
Authors: Bagus P. S. , Moser C. M. , Goethals P. , Verhaegen G.
Published: February 2004

Results of calculations using a configuration interaction LCAO-MO method are presented for the X 2Σ+ and A 2Π states of BeH. Apart from the 1s shell of Be, the correlation energy of the remaining three electrons is calculated quantitatively using an extended basis set and complete configuration interaction including all single, double and triple replacements. The calculated spectroscopic constants are in excellent agreement with available experimental data. The present calculations also predict a value of De(BeH, X 3Σ+)=2.115 eV, and dismiss the possibility of a potential maximum in the ground state potential energy curve.
Wide-line nuclear magnetic resonance study of solid methanols
Authors: Garg S. K. , Davidson D. W.
Published: February 2004

A proton magnetic resonance study of dry CH3OH and CH3OD between 1.8°K and the melting points shows rotation of the CH3 group over the complete temperature range, a well-defined decrease in line-width at the temperatures of the monoclinic to orthorhombic transformation, and absence of the narrow line found in earlier NMR studies. Inconsistencies between previous NMR results are ascribed to the effects of saturation, inadequate thermal conditioning, and the presence of water. Second moments of the monoclinic form show adjacent CH3 groups to be further apart than given by Tauer and Lipscomb's x-ray structure. Second moments of the orthorhombic form agree with dielectric results in showing large-amplitude rotatory motion. The ``second transition'' found in earlier volumetric and dielectric studies of CH3OH and CH3OD probably marks the eutectic temperature where monoclinic methanol, methanol monohydrate, and liquid phase coexist. The second moment of CD3OH is almost invariant between 4 and 155°K although there is a significant change in line shape.
Calculation of thermodynamic averages of phonon spectra for fcc Lennard-Jones harmonic crystals
Authors: Pollock E. L.
Published: February 2004

Based on moments of the frequency distribution, delta function representations for the phonon frequency distribution of an fcc Lennard-Jones harmonic crystal over a wide density range are given using the law of corresponding states. Their use and convergence is illustrated for the zero point energy and rms displacement. A comparison with a previous harmonic theory calculation is given for the specific heat of solid argon.
Model for V→ T, R relaxation: CH4 and CD4 mixtures
Authors: Zittel Paul F. , Moore C. Bradley
Published: February 2004

A laser-fluorescence technique is used to determine vibration-to-vibration energy transfer rates for relaxation of HCl (v=1) and DCl (v=1) by CH4 and CD4. The rates of subsequent vibration-to-rotation and translation relaxation of the bending vibrations of CH4 and CD4 by several collision partners are measured. These data are interpreted in terms of a model which includes rotational motion of both collision partners, as well as relative translational motion. The variation of deactivation probabilities with the mass parameter, (μ†)−1=m−1+A1(μR1)−1+A2(μR2)−1, and temperature qualitatively indicates the relative importance of rotation and translation in each deactivation process.
Compound-negative-ion resonance states and threshold-electron excitation spectra of N-heterocyclic molecules: Pyridine, pyridazine, pyrimidine, pyrazine, and sym-triazine
Authors: Pisanias M. N. , Christophorou L. G. , Carter J. G. , McCorkle D. L.
Published: February 2004

The threshold-electron excitation spectra of the N-heterocyclic molecules pyridine, pyridazine, pyrimidine, pyrazine, and sym-triazine have been studied with a newly constructed electron spectrometer. These are presented, discussed, and compared with photoabsorption and, whenever possible, with electron impact spectral data. Optically forbidden and n→ π* transitions have been observed. Two compound negative ion resonance (CNIR) states (``shape'' resonances) have been detected below the first excited electronic states of all N-heterocyclic molecules studied, except sym-triazine for which only one CNIR state has been observed. These CNIR states are discussed in terms of the effect of a perturbation introduced by the more electronegative nitrogen atom(s) in the benzene ring on the two lowest (degenerate) antibonding orbitals of benzene.
On the magnetic circular dichroism of aromatic carbonyl compounds
Authors: Dearman Henry H.
Published: February 2004

The magnetic circular dichroism of the single-ring aromatic compounds benzaldehyde, acetophenone, and phthalaldehyde and of the two-ring compounds benzophenone, anthrone, 9,10-anthraquinone, and 10-methylene anthrone is reported. In each case the molecular symmetry is so low that only B terms contribute to the magnetic ellipticity. The magnitude of the magnetic ellipticity in the nπ* absorption region is discussed in terms of vibronic and electronic intensification mechanisms. The MCD of the ππ* transition region of the single-ring compounds is discussed in terms of a model which considers magnetic field mixing of the 1Lb and 1La benzene states alone. The MCD of the two-ring compounds, other than benzophenone, reveal ππ* transitions which are not observed in either absorption or polarized phosphorescence excitation spectra.
Projected Hartree product wavefunctions. VI. Natural orbital CI expansions in nonsinglet cases
Authors: Koller R. D. , Gallup G. A.
Published: February 2004

The NSO's and NO's have been determined for some wavefunctions for Li, Be1+, B2+, C3+ 2S, and Be 3S wavefunctions containing radial correlation. It is shown how the NO's may be utilized to form rapidly converging CI expansions in general. The role of the NSO's in this problem is discussed.
Upper and lower bounds in the theory of classical fluids
Authors: Snider Neil S. , Knudson Stephen K.
Published: February 2004

We investigate a number of inequalities, rigorous and conjectured, in the theory of classical fluids. We first investigate approximate calculations, based on the Gibbs inequality, of thermodynamic functions for the Lennard-Jones fluid. If the hard sphere fluid is the reference system, such calculations are simplified when one uses a form of the Gibbs inequality which is valid for systems with the same volume, number of particles and entropy. The internal energy of the Lennard-Jones fluid at moderate and high densities is accurately calculated by the simplified procedure. The procedure does not, however, give accurate values for the pressure at high densities. We also investigate inequalities which apply to fluids for which the pair potential is purely repulsive and has a cutoff. One such (nonrigorous) inequality gives a lower bound to the Helmholtz free energy at fixed density and temperature. It therefore complements the Gibbs inequality, and it gives rise to a fairly simple and accurate procedure for calculation of pressure and internal energy.
Inner electron excitation of iodine in the gaseous and solid phase
Authors: Comes F. J. , Nielsen U. , Schwarz W. H. E.
Published: February 2004

The absorption spectra of gaseous and solid iodine have been measured in the photon energy range of 45–160 eV. The radiation of the 7.5 GeV electron synchrotron DESY was used as the light source. The intensity distribution of the 4d→ ε f continuum is discussed. A fine structure, similar in both phases, is found near the low-energy side of this continuum. This fine structure can be ascribed to transitions of 4d5/2 and 4d3/2 electrons into the lowest empty molecular orbital and into Rydberg states of the molecule. One-electron level energies and the 4d3/2, 4d5/2 ionization energies (58.95, 57.25 eV±0.2 eV) are deduced from the observed spectra. A rediscussion of the optical spectrum of the iodine molecule is given in the light of these results.
Infrared chemiluminescence and energy partitioning from the reactions of fluorine atoms with the primary carbon-hydrogen bonds of alkanes, halogenated methanes, and tetramethyl silane
Authors: Chang H. W. , Setser D. W.
Published: February 2004

The infrared emission from the HF† product of the elementary abstraction reaction between fluorine atoms and CH4, C2H6, CH3CF3, C(CH3)4, Si(CH3)4, CH3Cl, CH2Cl2, CHCl3, and CH3Br has been observed, and relative vibrational populations (v = 1, 2, 3) were determined. The experiments were conducted at 10−3–10−4 torr in a vessel with cold (77°K) walls, and for most reagents the observed populations are the initial ones of the reaction. The H2 reaction also was examined in order to compare the results from our apparatus with studies from other laboratories. The reaction of F atoms with cyclo-C6H12 was used for calibration of experimental conditions. In general more than 50% of the potential energy was partitioned to vibrational energy of HF†, and a population inversion between the v′ = 1 and 2 levels was observed for every example except CHCl3, but the populations from this reaction may have been affected by relaxation. Although a generally similar pattern for the HF† vibrational distribution was found, the relative populations did vary from one reagent to another. For example, more HF† (v = 3) was found from the CH3Cl and CH3Br reactions than from the reactions with alkanes. Rotational relaxation was partially arrested, and some qualitative differences in the HF† rotational populations from the reagents cited here were found; some much larger differences are reported in the following paper.
Infrared chemiluminescence and energy partitioning from reactions of fluorine atoms with hydrides of carbon, silicon, oxygen, sulfur, nitrogen, and phosphorus
Authors: Duewer W. H. , Setser D. W.
Published: February 2004

The HF† infrared chemiluminescence from the reactions of fluorine atoms with PH3, SiH4, H2O, H2O2, H2S, NH3, N2H4, and three additional carbon compounds, (CH3)2O, (CH3)2S, and (CH3)3N, was studied in the same way as described in the preceding paper. With the exceptions of the N2H4 reaction, a large fraction of the energy, ≳ 45%, was released as vibrational energy of the HF† product, and population inversions were frequently found. The strong chemical interaction between HF† and NH3, (CH3)3N, N2H4, and PH3 may have led to efficient vibrational relaxation for these reactions; however, the redissociation of the adducts may give mainly HF† (v = 0), and modification of the vibrational distribution may not be severe. The results can be used to establish upper limits to some uncertain bond energies: D(SiH3–H)≤ 87 kcal mole−1; D(PH2–H)≤ 78 kcal mole−1, D(NH2–H)≤ 110 kcal mole−1 and D(N2H3–H)≤ 85 kcal mole−1. Since these F atom reactions tend to populate vibrational levels up to the maximum allowed by the thermochemistry, these limits with the exception of D(H–N2H3), which has a substantial uncertainty, probably are within 5 kcal mole−1 of the actual bond energy. Although rotational relaxation was only partially arrested, a sizeable amount of HF† rotational energy was found from the (CH3)2O, (CH3)2S, PH3, and SiH4 reactions. The (CH3)2O and (CH3)2S reactions partition more rotational energy and less vibrational energy to HF† than the reactions with most other primary C–H bonds.
Production of excited OD+ in O+−D2 collisions at low relative energies (below 4 eV)
Authors: Harris H. H. , Leventhal J. J.
Published: February 2004

The energetics of OD+ ions formed in collisions of ground state O+ with room temperature D2 molecules have been studied at relative energies in the range 0.76–3.58 eV using ion beam techniques. Excited electronic states of OD+ are inaccessible below about 1.3 eV, so that product internal energy must be vibrational-rotational excitation of ground state (X 3Σ)OD+ below this energy. It was found that OD+ is formed with internal energy over the entire energy range. The spectator stripping mechanism seems to predominate over the entire energy range.
Constrained density matrix study of simple basis sets for helium
Authors: Henderson George A. , Lee Michael A.
Published: February 2004

The method of Clinton et al. for the direct determination of an idempotent density matrix subject to constraints is used to examine in detail the ability of two basis sets, each consisting of a pair of 1s functions to predict one- and two-electron properties for the helium atom. The two bases differ in that one has variationally optimized exponents. Idempotent density matrices constrained to give each of eleven different expectation values computed from the accurate Pekeris wavefunction are constructed for each basis. These constrained densities are then evaluated in terms of the accuracy of the other expectation values compared to the Pekeris values. As the basis becomes energetically optimized, one-electron properties improve, as expected for an independent-particle model, but all computed two-electron properties become less accurate. Several criteria for over-all quality of the electron densities are examined. Although the density can change significantly in specific regions while the energy changes only slightly, the energy is found to remain a prime indicator of average quality. There is evidence that the accuracy with which a free-variational density already predicts a given property may provide a prior indication of the effectiveness of that property as a constraint in a constrained-variational calculation.
Angular dependence of the β-proton isotropic hyperfine coupling constant
Authors: Adam F. C. , King Frederick W.
Published: February 2004

The angular dependence of the β-proton isotropic hyperfine coupling in alkyl or π radicals is investigated using a limited CI approach. Values of B0 and B2 for the equation Aβ=B0+B2 cos2θ are found to be 2.71 and 50.14 G, respectively. The dominant contribution is found to arise from an electron exchange mechanism. Approximate treatment of this term by a simple charge transfer model leads to an expression for the β-proton coupling constant, Aβ=413.2 {1+sgnF(θ)[1+F(θ)−2]−1/2}, where F(θ) is a simple function of the angular variable cosθ and sgn F(θ) indicates its sign. The CI study also shows that the cos4θ factor in a power series expansion of Aβ makes a negligible contribution to the hyperfine coupling.
Study of the electronic structure of molecules. XVIII. Interaction between a lithium atom and a cyano group as an example of a polytopic bond
Authors: Clementi E. , Kistenmacher H. , Popkie H.
Published: February 2004

We have reinvestigated the LiCN and LiNC molecules in the linear configurations. With very near to Hartree-Fock functions we obtain the following equilibrium distances: R(Li–C)=3.65± 0.015 a.u., R(C–N)=2.14± 0.015 a.u. for LiCN; R(Li–N)=3.35± 0.015 a.u. and R(C–N)=2.18± 0.015 a.u. for LiNC. The Hartree-Fock energy (at equilibrium) are −99.8176 a.u. for LiCN and −99.8275 a.u. for LiNC. These data are corrected using a statistical model to compute the correlation energy. The resulting atomization energy (total binding relative to dissociation into ground state atoms) is 13.48 eV for LiCN and 13.78 eV for LiNC. (These data are, therefore, confirming previous computation by Bak, Clementi, and Kortzeborn, done with smaller basis set.) With a constant value for the C–N distance, we have mapped the energy surface for a number of geometries in nonlinear conformations, following the lowest energy path leading from LiCN to LiNC: no energy barrier was found between the LiCN and the LiNC linear configuration or between the linear and nonlinear configuration (if one remains in the vicinity of the bottom of the energy surface valley). Thus by thermal excitation (of about 0.3 eV or above) the lithium orbits around the CN radical, and no preferred structural formula can be drawn (in a traditional sense). It is expected that this somewhat untraditional type of bond is somewhat common especially for high temperature species, where thermal excitation is sufficient to compensate for law (if any) barriers between isomers. We have referred to this bond as a ``polytopic bond'' to stress its equality in energy for substantially different position, relative to the remainder of the molecule.
Time resolved ESR spectroscopy. II. The behavior of H atom signals
Authors: Verma N. C. , Fessenden Richard W.
Published: February 2004

The time dependence of the ESR signals of H atoms formed in acid water by pulse radiolysis has been examined at times >2 μsec after the pulse. As in steady-state experiments, the two lines are of very similar amplitudes but with the low-field line appearing in emission. A growth of signal is observed for the first 4–10 μsec depending upon the microwave power and dose per pulse. At the higher microwave powers (>1 mW) an oscillatory decay is observed which must be caused by the transient response of the spin system. An attempt has been made to explain the over-all behavior of the ESR signals by introducing the assumption that the signal enhancement arises upon nuclear spin dependent recombination. This effect is included in the Bloch equations by a production term for Mz which is proportional to radical concentration (taken to decay by a second-order kinetic curve). The results of this calculation were very successful in fitting all details of the observed curves including the initial growth and the oscillatory behavior. An alternative assumption, that the singal enhancement occurred upon radical formation, did not lead to agreement with the observations. Because the initial growth is a direct consequence of the Bloch equations it is not necessary to invoke any chemical complications, such as a precursor of lifetime ∼ 5 μsec, to explain this phenomenon. The ESR signals of H atoms in acid were found to double upon addition of tert-butyl alcohol as an OH scavenger, and a much larger fractional increase was found in neutral, N2O saturated water. These results are taken to show that the reaction H+OH is not selective as to the spin state of the H atom and so as a result produces no signal enhancement, while the reactions H+H and H+R do lead to signal enhancement.
CNDO calculation of dipole moment derivatives and infrared intensities of formaldehyde
Authors: Bruns Roy E. , Person Willis B.
Published: February 2004

The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in-plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out-of-plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCO values from a series of X2CO molecules (and also with ∂p/∂rCS for X2CS molecules) reveals an interesting trend. An analysis of the various contributions to the calculated ∂p/∂rk values is presented, with an explanation of the calculated results for the out-of-plane bending coordinate ∂p/∂γ.
Deactivation of laser excited CH3F in CH3F–X mixtures
Authors: Weitz Eric , Flynn George
Published: February 2004

The vibrational relaxation of CH3F in mixtures of rare gases, O2, N2, H2, and D2 has been studied by means of laser induced fluorescence. The data can be interpreted qualitatively in terms of a combination of V → T/R energy transfer processes from both the ν3 and ν6 v=1 states of CH3F. V → R processes seem to be dominant for heavy collision partners while V → T processes appear to dominate for light collision partners. The quantitative agreement between theory and experiment is also considered.
Temperature effects on radiative and radiationless transitions of Gd3+ in solution
Authors: Haas Yehuda , Stein Gabriel , Würzberg Elhanan
Published: February 2004

Temperature effects on the fluorescence of Gd3+ in H2O solution are presented and discussed. The quantum yield does not approach unity near the freezing point. In the case of Gd3+, high energy vibrations of single solvent molecules do not quench the fluorescence. The results are interpreted by use of the ``junction'' mechanism involving the ion and solvation shell [Y. Haas and G. Stein, J. Phys. Chem. 76, 1093 (1972)] and by clarifying the role of the levels giving rise to a broad band in both absorption and emission in solution.
Reaction H+C2H4: Investigation into the effects of pressure, stoichiometry, and the nature of the third body species
Authors: Michael J. V. , Osborne D. T. , Suess G. N.
Published: February 2004

The detection of H atom concentrations by Lyman α photometry has been employed in a time resolved experiment to obtain the pressure dependence of the apparent bimolecular rate constant for the reaction of H atoms with C2H4 at room temperature. A computer simulation analysis has been applied to adjust the observed rate constants for H atom depletion in reactions subsequent to the initial reaction. The pressure falloff behavior at low pressures of various heat bath species He, H2, N2, Ar, Ne, Kr, and SF6 were also obtained. Experiments at high pressures of He have permitted an extrapolation to the high pressure limit of the rate constant of (16.1± 3.2) × 10−13 cc molecule−1· sec−1.