bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetothermodynamics of CuK2 (SO4)2· 6H2O. V. Fields along the α Axis. Thermodynamic Temperature without Heat Introduction below 0.5°K. The Freezing-In of Magnetic Structure in the Lambda Region
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2004

The magnetothermodynamic properties of a 3.912-cm-diam spherical single crystal of CuK2 (SO4)2· 6H2O have been measured down to 0.007°K with fields along the α magnetic axis. Forty-four of 49 adiabatic magnetizations from unknown low temperatures and zero field were shown to be isentropes. Measurements with electronic entropies below 0.08 gibbs/mole showed entropy production at low fields. The measurements were combined with available reference data above 0.5°K to determine the thermodynamic temperatures, both in and out of magnetic fields, without heat introduction below 0.5°K. The zero-field temperatures at entropies below 0.8 gibbs/mole were systematically different from those obtained previously after demagnetization with the field along the γ magnetic axis. It is concluded that an unstable magnetic structure, with an energy of about 0.003 cal/mole above that of the stable structure at 0°K, has been frozen-in. The instability develops below the lambda region where cooperative effects dominate the properties.
Vibrational Intensities in F2CO: Some Corrections
Authors: McKean D. C. , Bruns Roy E. , Person Willis B. , Segal Gerald A.
Published: February 2004

A number of errors in earlier reports of the infrared intensities of F2CO and their interpretation have been discovered and corrected in the present paper. The earlier values of ∂p/∂Si calculated using the CNDO/2 approximate quantum mechanical treatment have been corrected, and the previous results extended so that the calculated bond moments can be compared with the experimental values, similarly corrected. These results are now much more closely in agreement with chemical intuition that the earlier results implied.
Low Frequency Vibrations in Molecular Solids. XII. Low Frequency Modes and Barriers to Internal Rotation of Some Dimethyl Compounds of Elements in Group VI
Authors: Durig J. R. , Player C. M. , Bragin J. , Li Y. S.
Published: February 2004

The far infrared spectra of solid CH3OCH3, CD3OCH3, CD3OCD3, CH3SCH3, CH3SeCH3, CH3TeCH3 have been recorded between 350 and 33 cm−1. The B2 and A2 torsional frequencies have been assigned at 268 and 244, 245, and 208, 207 and 182, 247 and 210, 207 and 175, and 185 cm−1 for the above molecules at liquid nitrogen temperatures. The barriers calculated from these assignments are 3.50, 3.48, 3.39, 3.22, 2.40, and 2.27 kcal/mole, respectively. The lattice bands observed in the infrared spectra of the isotopic dimethyl ethers have been assigned to librational and translational motion on the basis of the deuteration shifts. The infrared spectra of the sulfide and selenide in the region of the lattice frequencies are similar and a tentative assignment of these bands to librational and translational motions is presented based on the expected shift factors. The infrared lattice spectrum of dimethyl telluride is also presented.
EPR Study of LiGa5O8: Cr3+
Authors: Glynn T. J. , Kelleher L. , Imbusch G. F. , Larkin D. M. , Merritt F. R. , Berggren M. J.
Published: February 2004

An EPR study has been undertaken of Cr3+ in LiGa5O8. The site symmetry is rhombic and the system can be described by the spin Hamiltonian, H=gβH·S+D [Sz2− 1 3S (S+1)]+E (Sx2− S y2), where D=0.331±0.002 cm−1, E=0.018±0.002 cm−1, and the average g value, assumed isotropic, is 1.980±0.005. The axes of the spin Hamiltonian are tilted slightly from the expected crystallographic directions. The arrangement of Li+ and Ga3+ ions in next-to-nearest neighbor positions results in a large electrostatic field of odd parity at the site of the chromium ion.
Magnetic Properties of Protactinium Tetrachloride
Authors: Hendricks M. E. , Jones E. R. , Stone J. A. , Karraker D. G.
Published: February 2004

Magnetic susceptibility of PaCl4 was measured from 3.2–296°K with a vibrating-sample magnetometer at fields up to 12 000 Oe. PaCl4 has a ferromagnetic transition at Tc=182±2° K. Below Tc the magnetization deviates markedly from Brillouin behavior and is far from saturation at 12 kOe; hysteresis is absent above 3.3°K. A high degree of covalency is suggested to explain the high Curie point; a large anisotropy energy is indicated by the lack of saturation. From 180–210°K, PaCl4 obeys the Curie—Weiss law, χ=C/(T-θ), with θ=157°K and μ eff=1.04 μ B. The measured paramagnetic properties were compared to those calculated from crystal-field theory, with and without J mixing included. The comparison indicates that J mixing is significant in PaCl4.
ESR Study of Radicals Formed by Irradiation of K2PtCl4 Single Crystals
Authors: Krigas Thomas , Rogers Max T.
Published: February 2004

Single crystals of K2PtCl4 irradiated at 77°K show two groups of ESR lines, one belonging to a radical giving rise to hyperfine interaction with two equivalent platinum nuclei and the second from a radical giving hyperfine interaction with one platinum and three chlorine nuclei. On the basis of the observed g, A (195Pt), and A (35, 37Cl) tensors, it is suggested that these species are [(PtCl4)2]3− and [PtCl3]2−, respectively, with d15 and d9 configurations. On warming to 125°K part of the dimeric radical is converted to a new species whose ESR parameters are consistent with the structure [PtCl5]2+ with a d7 configuration. The structures of these radicals are discussed.
Investigation of Energy-Transfer Mechanisms in Pyrene Crystals
Authors: Chu Nori Y. C. , Kawaoka Kenji , Kearns David R.
Published: February 2004

In this paper we have examined the fluorescence emission spectra, intensity, and decay characteristics and the excitation spectra of pure pyrene crystals and of perylene-doped pyrene crystals at temperatures down to 1.7°K. From these observations we conclude that energy transfer in pyrene crystals occurs by four different mechanisms with the following characteristics: (i) Reabsorption of emitted photons: important at high guest concentrations or with thick samples. (ii) Monomer exciton migration: Operates at all temperatures with a transfer rate constant on the order of ∼1012 sec−1. (iii) Excimer exciton migration: important only at temperatures above about 130°K, thermally activated with an apparent activation energy of 112 cm−1 and a transfer rate constant of 4×106 sec−1 at room temperature. (iv) Forster transfer from excimers to perylene guest molecules: important only with perylene concentrations greater than about 10−3 mole/mole, or at slightly lower concentrations at reduced temperatures. In addition to obtaining information about the nature of energy-transfer processes which take place in pyrene crystals, we have also examined the crystal absorption spectrum on the long-wavelength side of the first major absorption band. The low-temperature excimer excitation spectra of highly purified pyrene crystals exhibits a tail which extends almost to 425 nm and appears to overlap with the origin of the excimer emission. This tail absorption is attributed to direct excitation to the excimer state.
Microwave Spectrum, Ring-Puckering Potential Function, and Dipole Moment of 3,3-Difluoroxetane
Authors: McKown Gary L. , Beaudet Robert A.
Published: February 2004

The microwave spectrum of 3,3-difluoroxetane has been observed and assignments made of the rotational constants for the ground state and for six excited states of the ring-puckering vibration. From the rotational constant variation, intensity information, and inertial defect considerations it is concluded that the molecule is planar in the ground state with zero barrier to the ring-puckering motion. The ring-puckering potential function is given by V (X)=ν0(X4+7.0 X2). The dipole moment is directed along the a axis and has a value of 0.40±0.01 D.
Surface Thermodynamic Functions for NaCl
Authors: Chen T. S. , Alldredge G. P. , de Wette F. W. , Allen R. E.
Published: February 2004

The surface entropy and surface specific heat at constant volume, and the vibrational contributions to the surface energy and surface Helmholtz free energy have been calculated as functions of temperature for the (100) surface of NaCl. To our knowledge, these are the first calculations of surface thermodynamic functions for an ionic crystal to be based on a realistic lattice-dynamical determination of the vibrational frequencies, rather than on the use of a continuum model, Einstein model, or unrealistically simple lattice model. The main approximations in the present treatment are the harmonic approximation and the neglect of the polarizabilities of the ions (i.e., the use of a rigid-ion model). Comparison is made between the present theoretical results and the experimental results for the excess heat capacity of finely divided NaCl. At low temperatures, the present results are in good agreement with the recent data of Barkman et al. The position of the peak in the surface specific heat is in good agreement with the data of Morrison and Patterson; a discrepancy of about 40% in the height of the peak may be due to experimental uncertainties in determining specific surface areas.
Classical Path Approximation for the Boltzmann Density Matrix
Authors: Miller William H.
Published: February 2004

Using the classical-limit approximation for the quantum mechanical time evolution operator and the formal relation between time and reciprocal temperature (t=−iℏ β, β=1/kT), a ``better than classical'' approximation is obtained for the Boltzmann density matrix. The result involves classical trajectories in a potential which is the negative of the actual potential; it is seen that this effectively allows for some degree of tunneling. This new approximation gives exact quantum results in any region that the potential is quadratic and quite reasonable results for any potential, even in the limit of zero temperature.
Rutile: Normal Probability Plot Analysis and Accurate Measurement of Crystal Structure
Authors: Abrahams S. C. , Bernstein J. L.
Published: February 2004

The x-ray scattering by two different rutile crystals, within a hemisphere of reciprocal space having radius (sin θ) /λ=1.02 Å−1, was measured at 298°K with PEXRAD. The integrated intensities of 780 reflections from each crystal were determined, resulting in 136 symmetry independent Fmeas from Crystal 1 and 122 Fmeas from Crystal 2. The crystal structure was refined by the method of least squares: The agreement factor R for all Fmeas is 0.0286, and the single position parameter x(0)=0.30479±0.00010. Normal probability plot analysis shows the least squares derived standard deviations are underestimated by 33%, and the two sets of Fmeas contain an appreciable parallel bias. The lattice constants, measured at or corrected to 298°K on two different crystals, are a=4.593659±0.000019 and c=2.958682±0.000008 Å. The Ti–O distances are 1.9800±0.0009 and 1.9485±0.0005 Å. Pairs of shorter bonds define O–Ti–O angles of 81.21° and 98.79°, forming a plane normal to the two longer bonds. The resulting octahedral Ti–O bond arrangement is apically extended, as is found in all AIVB2 compounds with rutile structure: The remaining nine well-determined non-Group IV AB2 family members contain, without exception, apically compressed AB6 octahedra. Bauer and Khan's, and also Niizeki's, x-ray results on rutile are compared with the present measurements.
Optical Spectrum of Trivalent Dysprosium in Calcium Tungstate
Authors: Wortman D. E. , Sanders D.
Published: February 2004

Optical absorption and fluorescence spectra of Dy3+ in single crystals of CaWO4 have been examined. The measurements were made using 0.1 and 0.5 at.% Dy3+ in crystals at temperatures of 2, 25, and 85°K, and they were made over wavelength regions corresponding to transitions to all the 6H ground-term states. A definitive identification of all the energy levels of the ground term was not possible because of some term mixing and some mixing of the σ and π polarization measurements. Possible identifications of the energy states were obtained by comparisons made with calculated energy states, however. The calculations were made using the method of Karayianis in which an effective Hamiltonian is diagonalized in a basis of Russell—Sanders wavefunctions for the entire ground term of Dy3+. This calculation includes all the J-mixing effects of the crystal field and the effects of the spin—orbit interaction to better than second order. The parameters which give an rms deviation of 9 cm−1 between 24 experimental and calculated ground-term energy levels, in cm−1, are λ1=−333, λ2=−4.11, λ3=−0.226, B20=428, B40=−825, B60=−6.6, B44=972, B64 Re=448, and B64 Im=2.5 where the Hamiltonian used is H=Σnλn(L·S)n+ΣkmBkm+Ckm. Calculated g factors for the lowest lying energy states were found to be quite sensitive to changes in the Bkm. Hence, these data and results of earlier EPR studies are not yet able to allow definitive symmetry properties to be assigned to the ground state.
Interaction of Oxygen with Polycrystalline Tungsten. II. Corrosive Oxidation
Authors: King David A. , Madey Theodore E. , Yates John T.
Published: February 2004

The kinetics of formation of a corrosive oxide layer of apparently unlimited thickness during the interaction of oxygen with a polycrystalline tungsten filament at temperatures between 500 and 1000°K has been investigated by line-of-sight flash desorption mass spectrometry. The major desorption product from this multilayer oxide film is WO2, which desorbs over the temperature range 1000–1300°K. The rate of formation of the oxide film was shown to be directly proportional to the oxygen gas phase pressure at pressures ≲ 10−4 torr. A study of the temperature dependence of the oxidation rate revealed that the formation of the WO2-producing oxide layer proceeds through two distinct steps; these occur subsequent to the first three stages in the interaction of oxygen with W characterized in Paper I. In the final state of oxidation, the rate is shown to be independent of the thickness of the oxide film. The results are in qualitative accord with the theoretical model of Mott. Desorption of the oxide film is a zero order process, with a desorption activation energy of 420 kJ mol−1.
Analysis of the D and 17O Quadrupole Coupling Constants in Ice Ih
Authors: Gornostansky S. D. , Kern C. W.
Published: February 2004

Hydrogen bond formation in enriched heavy ice is observed experimentally to alter the D and 17O quadrupole coupling constants relative to the vapor. In this study the dependence of these coupling constant shifts on electronic structure is examined theoretically with two types of all-electron, single-determinant wavefunctions constructed from Slater-orbital basis sets for the water monomer, dimer, trimer, and pentamer. SCF computations are first performed with the various multimers constrained to a geometry based on the observed structure of ice (Ih). The sensitivity of these results to geometry and to the electron distribution is then examined with bond-orbital wavefunctions. It is concluded that the solid—vapor coupling-constant shifts can be accounted for with a representation of the crystal which includes exchange forces between bonds, direct charge transfer due to hydrogen bond formation, and elongation of the normal O–D bond. The relative importance of these contributions is discussed for both nuclei.
Senftleben Effects and the Thermomagnetic Torque for Nitric Oxide
Authors: Moraal H. , McCourt F. R.
Published: February 2004

A detailed analysis of the room temperature Senftleben effects for nitric oxide is presented. In particular, it is shown how these magnetic field effects in NO at room temperature may be treated, to a very good approximation, in terms of the theory of the Senftleben—Beenakker effects for diamagnetic gases. Using such a procedure, the collision integrals relevant to the Senftleben effects have been extracted from the experimental data available for this gas. The procedure of analysis employed yields, in addition to the collision integrals, a value of −47.4 for the effective g factor for NO, in excellent agreement with the data from other sources. From the information so determined for NO, the Senftleben effects and the related thermomagnetic torque have been calculated numerically and are found to be in good agreement with the experimental curves.
Modified Hubbard Model for Complex TCNQ Salts
Authors: Soos Zoltan G. , Klein Douglas J.
Published: February 2004

The magnetic, electric, and optical properties of the complex salts of tetracyanoquinodimethan (TCNQ) are related to a single theoretical model, the modified Hubbard Hamiltonian, for molecular crystals whose lowest electronic excitations involve electron transfers. Complex TCNQ salts correspond to less than half-filled modified Hubbard models and require explicit treatment of both spatial and spin correlations among electrons. The charge and spin excitations for less than half-filled Hubbard models are obtained near the separated molecule limit and applied to Cs2(TCNQ)3.
Matrix-Isolation Study of the Interaction of Electrons and Alkali Metal Atoms with Various Nitrogen Oxides. Infrared Spectra of the Species NO−, NO2−, and N2O2−
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

The infrared spectra which result when samples of NO2 are codeposited with the various alkali metals in an argon matrix at 4 or at 14°K are consistent with the occurrence of strong charge-transfer interaction. In addition to isolated NO2−, previously identified in this system, ion pairs of general formula Mx+NO2− are stabilized. When NO is substituted for NO2, the infrared spectrum of the initial deposit shows an absorption between 1350 and 1375 cm−1 which can be assigned to the NO− stretching fundamental of Mx+NO− ion pairs, in good agreement with the vibrational spacing recently reported for ground-state NO− in the gas phase. Weak charge-transfer interaction occurs between alkali-metal atoms and N2O in an argon matrix environment. Results of the present experiments can be explained by postulating that the upper, predominantly ionic state of the charge-transfer complex decomposes producing O−, which may diffuse through the matrix. A new absorption which appears at 1205 cm−1 has tentatively been assigned to ν4(b1) of a planar O2N=N− anion. In studies of the interaction of sodium atoms with Ar:NO:N2O mixtures, mercury-arc irradiation of the sample leads to the appearance not only of the N2O2− absorption, but also of absorptions due to isolated NO2− and to Nax+NO2−.
Rotational Diffusion of Spherical-Top Molecules in Liquids. II. Reorientation in Liquid Methane and Solutions of Methane in Liquid Noble Gases
Authors: McClung R. E. D.
Published: February 2004

Numerical calculations of reorientational correlation functions and spectral densities for spherical-top molecules in the extended rotational diffusion models are presented. The correlation functions obtained from Fourier transformation of the v3 infrared band contours for CH4 and CD4, in pure liquid form and in dilute solutions in liquid noble gases, are compared with calculated correlation functions. This comparison suggests that rotational energy transfer is much more rapid in the neat liquid methanes than in liquid noble gases, and allows an estimate of the anisotropy of the intermolecular potential experienced by the methane molecules.
Use of the CNDO Method in Spectroscopy. V. Spin—Orbit Coupling
Authors: Ellis R. L. , Squire R. , Jaffe H. H.
Published: February 2004

We report here the use of CNDO/S wavefunctions in the calculation of oscillator strengths of singlet—triplet transitions and the corresponding triplet radiative lifetimes induced by spin—orbit coupling. The starting functions for the perturbation calculations are ground and excited state functions including limited configuration interaction. Numerical calculations are carried through for formaldehyde and azulene. The importance of the calculated σ→π* states is discussed.
Kinetic Energies of Ionization Products from Collisions of Ar–Ar, He–He below 150 eV c.m. Energy
Authors: Hammond R. H. , Henis J. M. S. , Greene E. F. , Ross John
Published: February 2004

Measurements have been made of the energy spectra of ions and electrons produced in the collision of beams of neutral Ar of given energy (laboratory energy range 57–240 eV) with a gas of Ar and of neutral He (145–300 eV) with a gas of He. The energy dependence of the total cross section for ionization is consistent with previous results. The electron spectra from collisions of Ar+Ar show peaks at 0, 6, and ∼9 eV. From this we estimate that about 15% of the Ar+ ions produced come from autoionizing states of Ar. For certain ranges of initial relative energy Ar–Ar ionization occurs mostly in backscattering collisions. An analysis of the ion spectra of experiments at these initial relative energies (greater than 33 eV), made with a simple model, shows that most ions are produced by two curve crossings 12±2 eV and 22±1 eV above the ionization potential (15.8 eV).
Interpretation of Rate Constants Measured in Drift Tubes in Terms of Cross Sections
Authors: Woo S. B. , Wong S. F.
Published: February 2004

The basic equation of the rate constant of a two-body reaction, κ= ∫ vg ∫ vi fgas(vg)fion(vi)vrσ(vr)dvidvg, is used to infer the cross section from the rate constant of ion—molecule reactions measured in drift tubes as a function of E/p0, κ, vr, and σ are the rate constant, relative speed, and cross section, respectively. The Maxwellian distribution at gas temperature is used for fgas. A displaced Maxwellian, having a temperature parameter defined by the diffusion coefficients, and a displacement defined by 〈 vz〉=vd, is used for fion. vd is the drift velocity. Justifications are given. The advantage of this approach is in the interpretation of rate constants of endothermic reactions. Qualitative and quantitative examples are considered. Very good agreements with experimental results are obtained. A way for calculating the rate constant of ion—molecule reactions under thermal equilibrium conditions is proposed. Its limitations are discussed. The importance of endothermic reactions to ionospheric model calculations is emphasized.
Search for a Trapped Hole in an Irradiated Crystal of L-Alanine by the ESR Technique
Authors: Friday Estelle A. , Miyagawa Ichiro
Published: February 2004

Crystals of L-alanine, CH3CHNH3+CO2−, and also CH3CHND3+CO2−, CH3CDNH3+CO2−, and CH3CDND3+CO2− were irradiated at 80°K, and their ESR absorptions were observed at the same temperature. Most of the observations were made at 9 GHz, although some observations were made at 24 and 35 GHz. In addition to the known absorption from the trapped electron (or anion), an absorption with many peaks was detected and was attributed to the trapped hole (or cation) of L-alanine. From the hfs tensor for one of the methyl protons and other evidence, the electron hole was found to be trapped predominately at the C–C bond connecting the methyl group to the α-carbon atom. In the four crystals examined, the concentration of the cation was comparable to that of the anion.
Free Radicals in Pyrimidines: ESR of X-Irradiated Single Crystals of Barbital (5,5-Diethylbarbituric Acid)
Authors: Haak Richard , Benson Brent
Published: February 2004

X-irradiated single crystals of one polymorph of 5,5-diethylbarbituric acid show ESR spectra characteristic of a radical formed by abstraction of an ethyl group from C(5) of the pyrimidine ring. The principal values of hyperfine coupling are AA=13.2, AB=11.4, AC=10.1 G, and the principal values of the spectroscopic splitting factor are gu=2.0052, gv=2.0041, and gw=2.0023. The spin density on C(5) was determined to be approximately 0.4 with the remainder delocalized onto O(4) and O(6). All barbituric acid derivatives studied previously have formed radicals via a variety of mechanisms which also leave the major site of unpaired electron density at C(5). This is also a preferred site for other pyrimidines. The unpaired spin density on C(5) in the barbituric acid derivatives shows a large dependence on the substituent group on C(5), with values of 0.4 for ethyl, 0.5 for hydroxyl, and 0.7 for hydrogen.
Shock-Tube Studies of HF Vibrational Relaxation
Authors: Bott J. F. , Cohen N.
Published: February 2004

The vibrational relaxation of HF has been studied behind incident shock waves in the temperature range 1350–4000°K by monitoring the 2.7−μ infrared emission. Relaxation times reduced to standard pressure were obtained for mixtures containing 1%–10% HF in argon and for mixtures containing N2, He, and D2. These data were used to calculate the relaxation times of HF due to these various gases. The relaxation times can be summarized by the expressions PτHF-HF=1.02×10−2 exp(34.39/T1/3) μsec· atm, PτHF-Ar=1.62×10−3 exp(111.97/T1/3) μsec· atm, PτHF-He=1.52×10−4 exp(133.3/T1/2) μ sec· atm, and Pτ HF-D2=5.1×10−4 exp(96.6/T1/3) μsec· atm. The values of PτHF-N2 fell between those for helium and deuterium. The relaxation time of HF due to itself is compared to the predictions of several theories of V-T and V-R energy transfer, and to published experimental data for other hydrogen halides. The HF rates of this study, together with the measured rate at room temperature, suggest the possibility of an attractive potential playing a dominant role in energy transfer at low temperature.
Formation of Magnesium Ions by Charge Transfer
Authors: Rutherford J. A. , Mathis R. F. , Turner B. R. , Vroom D. A.
Published: February 2004

The charge transfer cross sections for several ions in collision with atoms of magnesium to form Mg+ have been measured in the energy range 1–500 eV. The ions O+, N+, N2+, NO+, O2+, H2O+, H3O+, N2O+, and Mg+ have been used. The results obtained are analyzed by considering the possibility of resonant or near resonant processes being responsible for the large cross sections obtained for most processes. When the possibility of resonance-type mechanisms does not exist, the cross sections are found to be considerably smaller. The effect of metastable states present in the primary ion beam on the charge transfer cross section is examined. Extrapolation of the measured cross sections to thermal energies has also been performed.
Photolyses of Propane, n-Butane, and Cyclobutane at Xe and Kr Resonance Lines
Authors: Obi K. , Akimoto H. , Ogata Y. , Tanaka I.
Published: February 2004

The photolyses of propane, n-butane and cyclobutane have been carried out at Xe and Kr resonance lines in the presence of nitric oxide. The isotopic study has been done on the photolysis of CH3CH2CD3. The relative importance of primary processes are assessed from the relative yields of the products. The relative importance of C–C and C–H bond cleavages in primary processes are briefly discussed.
Spectrum of Light Quasielastically Scattered from Tobacco Mosaic Virus
Authors: Schaefer D. W. , Benedek G. B. , Schofield P. , Bradford E.
Published: February 2004

We present measurements of the spectrum of light scattered from solutions of tobacco mosaic virus. The spectrum, which is generally not Lorentzian in shape, was measured at a series of angles ranging from 20° to 170° in solutions of 0.02% and 0.04% by weight. We have analyzed this data in terms of a theory which includes the effect on the spectrum of both rotational and anisotropic translational diffusion of rodlike molecules of length L. By calculating the angular dependence of the spectra both in tails and at the line center, it is possible to provide graphically and analytically simple means of estimating the average translational diffusion constant, D¯, and a linear combination of the rotational constant, DR, and the translational anisotropy, D∥-D⊥. We find D¯=(0.390±0.01)×10−7 cm2/sec, and −6.65 (D ∥-D⊥)+0.84DRL2= (3.10±0.30)×10−7 cm2/sec at 25°C for both tobacco mosaic virus solutions.
Approximate Differential Cross Sections at Large Scattering Angles for Simple Repulsive Potentials
Authors: Gislason E. A.
Published: February 2004

The classical deflection angle θ and the classical differential cross section I(θ) are examined in the region near θ=180° for three simple repulsive potentials: the repulsive power potential; the exponential repulsive potential; and the screened Coulomb potential. An expansion for θ valid at small impact parameters is carried through second order and compared with exact calculations of θ and I(θ). In most cases, the expansion is quite accurate in the region from θ=180° to θ=80°. Numerical formulas are given for evaluating the first two coefficients in the expansion. Interpretation of experimental cross sections using these results is discussed.
Molecular Beam Kinetics: Differential Cross Sections of the Reactions Cl+I2 and Cl+IBr
Authors: Cross J. B. , Blais N. C.
Published: February 2004

The chemical reactions Cl+I2 and Cl+IBr were studied using a crossed molecular beam apparatus. Angular and recoil velocity distributions were obtained for all reaction product molecules. In the center of mass system the forward to backward scattering ratios for the reactions Cl+IBr, Cl+I2, Cl+Br2, [N. Blais and J. Cross, J. Chem. Phys. 52, 3580 (1970)] and Cl+BrI were found to be 4, 6, 8, and 12, respectively. The recoil energy distributions were determined by the chemical bond being formed rather than the one which was broken. For ICl, 50% of the total available energy was found in internal excitation with a very broad distribution. For BrCl, 80% of the total available energy was found in internal excitation with a rather narrow distribution. We conclude that the angular distributions are consistent with those arising from short range attractive forces and that the reaction time is less than one rotational period.
Electric-Field-Induced Perturbations in the Ultraviolet Spectra of Polyatomic Molecules; the 1B2 State of Benzonitrile
Authors: Huang Kwo-Tsair , Lombardi John R.
Published: February 2004

We report the observation of an electric-field-induced perturbation in the 0–0 band of the π*←π (1B2←1A1) transition of benzonitrile (2738 Å). Strong nonlinear Stark effects are observed at fields as low as 0.5 kV/cm. Analysis of the observations allow determination of the dipole moment of the perturbing state (1.35±0.3 D), the transition moment between the mutually perturbed excited states (1.0±0.5 D) and the zero-field separation of the perturbing states (0.01±0.01 cm−1). In addition the vibronic symmetry of the perturbing state is shown to be B2. It is argued that the most likely perturbing state is the previously unobserved π*←n (1B1) state.
Vibronic Effects in Hydrogen Bonding
Authors: Anderson George R. , Lippincott Ellis R.
Published: February 2004

Vibronic states of model hydrogen (H)-bonded systems X-H···X are computed using a numerical solution to the Schrödinger equation. From the calculated energy eigenvalues, model properties are derived and compared with those experimentally observed in H-bonded systems. Numerous trends of the strong and weak H bonds are duplicated in the model systems, and some of the anomolous variances of structural and spectroscopic properties with isotopic substitution (D for H) are calculated, also. The importance of the H-atom vibrational contribution to the energy of the H bond is of particular interest in this study. The Born—Oppenheimer approximation is extended beyond solely electronic energy considerations to include the light atom (H or D) kinetic-energy terms. As the zero-point energy of a particle in a box decreases when the size of the box is enlarged, the energy of a X-H vibrator decreases when juxtaposed with an appropriate H acceptor to form the X-H···X bond. The relative importance of this vibrational-energy bonding term is found to be of the same order of magnitude as the energy derived from purely electronic interactions of the H bond: Δ E (vib)/ΔE (total)≃23%- 33 %. Although the relative importance of the net vibration energy to the H bond may vary beyond the limits found in this study, the effect is thought to be general. A name might be suggested for this part of the bond energy, the ``ν bond,'' so that no confusion need arise in referring to this effect: H bond=electronic interaction+ν bond.
Condensation of Hydrogen on Tungsten
Authors: Tamm P. W. , Schmidt L. D.
Published: February 2004

The condensation kinetics of hydrogen on the (110), (111), and (100) planes of tungsten are examined as functions of crystal temperature, coverage, and population of the various binding states. Measurements were carried out simultaneously on all three crystals in the same ultrahigh-vacuum system in order to accurately compare sticking coefficients and amounts adsorbed. There are large variations in the initial sticking coefficients s0; at 78°K these vary between 0.26 on the (111) plane to 0.07 on the (110) plane. This implies that the electronic transition involved in bond formation depends sensitively on the geometric and electronic structures of the substrates. Also s0 is observed to be almost independent of substrate temperature for all planes, showing that phonon assisted processes do not determine the energy transfer. The coverage dependence of s shows considerable variation between states. In all cases a weakly adsorbed precursor state is involved, but the kinetics of conversion to the tightly bound states are quite different for different planes and states. Models are developed to explain condensation into multiple states for sequential and simultaneous population of the states on a plane, and these are compared with the experimental results.
Correlation Studies on H3+. I. The Wavefunctions
Authors: Duben Anthony J. , Lowe John P.
Published: February 2004

Four configuration interaction calculations on the D3h H3+ molecule—ion are reported. Two Gaussian lobe basis sets are used and calculations are made with only doubly substituted configurations and also with both doubly and singly substituted configurations. The best calculation gives an energy of −1.34050 hartree at a fixed internuclear distance of 1.6406 bohr. The wavefunctions are analyzed in terms of natural orbitals and compared with each other and with some wavefunctions from the literature.
Exact Solution of the Mean Spherical Model for Fluids of Hard Spheres with Permanent Electric Dipole Moments
Authors: Wertheim M. S.
Published: February 2004

The mean spherical model is solved in closed form for a fluid of hard spheres with permanent electric dipole moments. Both the pair distribution function g(12) and the direct correlation function c(12) consist of a spherically symmetric term and two other terms with different dependences on the orientations of the two dipole moments. The spherically symmetric part is the solution of the Percus-Yevick equation for hard spheres. The angle-dependent terms satisfy two coupled integral equations, which can be decoupled by appropriate changes of the dependent variables. The solutions are expressed in terms of the solution of the Percus-Yevick equation for hard spheres for both positive and negative densities. The effect on g(12) of the finite size of the sample is calculated for the case of a sphere. The correction term in g(12) is found to be of order 1/𝒱, where 𝒱 is the volume of the sample. It is a function not only of the relative distance vector of the two molecules, but also of their positions in the sample. The contribution to the polarization is, nevertheless, constant throughout the sample, in agreement with classical electrostatics. The dielectric constant ε, calculated by Kirkwood's formula, is obtained in closed form. It is a function of a single variable which does not contain the hard sphere diameter.
Electronic Spectroscopy of Maleimide and Its Isoelectronic Molecules. I. Maleimide and N-Alkylmaleimides
Authors: Seliskar Carl J. , McGlynn Sean P.
Published: February 2004

The electronic absorption spectra of maleimide and two N-alkylmaleimides are presented. Molecular-orbital classifications of four electronic transitions with energies 〈 6.5 eV are made for maleimide. Vibrational structure appearing in two of the transitions in the N-alkylmaleimides in the vapor phase is interpreted and assignments of the active vibrational modes discussed. A series of hot bands derived from the 2000-Å band of N-methylmaleimide is analyzed and employed in the association of the corresponding active ground- and excited-state vibrational modes. The vacuum-ultraviolet vapor absorption spectrum of N-methylmaleimide is presented. Phosphorescence emissions from maleimides in glassy media at 77°K suggest that the T1 states of these molecules are Γ n π*3.
Calculated Properties of Metal Aggregates. II. Silver and Palladium
Authors: Baetzold Roger C.
Published: February 2004

Extended Hückel and CNDO calculations have been made for Ag and Pd aggregates. Bond energy, ionization potential (I.P.), and electron affinity (E.A.) are reported for these particles up to 30 atoms in size. Linear chains are the most stable geometric form of small Ag aggregates, but a transition above 30 atoms is expected at which fcc is more stable. The three-dimensional symmetric geometry is the most stable form of small Pd aggregates. The I.P. and E.A. in both types of geometry converge to a common value at 20 atoms in Ag and at 4 atoms in Pd. These converged values depend upon aggregate geometry, but do approach the work function of bulk metal. Palladium particles are found to have ≈ 0.35 d-band hole per atom, which is close to values reported for bulk metal.
On a Modified Rayleigh—Schrödinger Perturbation Expansion
Authors: Rubinstejn Francoise , Yaris Robert
Published: February 2004

It is shown that a modified Rayleigh—Schrödinger perturbation series is invariant to arbitrary non-physical changes in the choice of the unperturbed Hamiltonian and the perturbation while the standard Rayleigh—Schrödinger series is not. As an example of the use of the modified expansion and to demonstrate its improved convergence properties, a very limited basis-set modified double-perturbation calculation of the polarizability of H2 is presented, with the results being compared with both a standard double-perturbation calculation and the geometric approximation calculated using the same basis set.
Crystal-Field Splitting of Ho3+ and Tm3+ J Levels in Hydrated Chloride Salts
Authors: Stöhr Joachim , Olsen David N. , Gruber John B.
Published: February 2004

The crystal-field splitting of Ho3+ in HoCl3· 6H2O was calculated for the ground-state 5I8 and 10 excited J levels and compared to the observed splitting. In order to carry out the crystal-field splitting calculation, a systematic procedure was developed to obtain crystal-field parameters from a knowledge of the polarization of observed optical transitions. The crystal-field parameters for HoCl3· 6H2O resulting from a fit of 10 J levels with 84 Stark components are as follows: A20=108, A22=195, A2−2=−340, A40=−63, A42=−200, A4−2=275, A44=220, A4−4=220, A60=−4.5, A62=−117, A6−2=50, A64=240, A6−4=−80, A66=260, A6−6= −200. All parameters are in units of cm−1. By means of a least squares fit, the crystal-field parameters determined from an analysis of the holmium spectrum were used to determine the 15 crystal-field splitting parameters for Tm3+ in TmCl3· 6H2O. The crystal-field parameters for both crystals were found to agree in sign and to be close in magnitude. The calculated crystal-field splitting of J levels for both ions Ho3+ and Tm3+ agrees very well with the observed splitting. The calculated crystal-field wavefunctions for Tm3+ in TmCl3· 6 H2O were used to explain the magnetic properties of this particular salt.
Electronic Absorption Spectrum of MnO4− in the Far-Red Region
Authors: Johnson L. W. , Hughes E. , McGlynn S. P.
Published: February 2004

Polarized absorption spectra of single crystals of LiClO4· 3H2O/LiMnO4· 3H2O and Ba(ClO4)2· 3H2O/Ba(MnO4)2· 3H2O have been measured at 4.2°K in the region λ>5800 Å. The transition whose ⊥ components possess zero-phonon origins at 13774 cm−1 in the lithium salt and at 14247 cm−1 in the barium salt is unequivocally identified as an electric-dipole forbidden T11←A11 transition of the parent tetrahedral point group. In the C3v site symmetry of the lithium salt the ⊥ component of this transition is shown to be electric-dipole allowed; in the C3 site symmetry of the barium salt the crystallographic site-splitting of the ⊥ and ‖ components is 152 cm−1, and both component transitions are shown to be electric-dipole allowed. It is deduced that both the far-red transition and the 5200-Å absorption band of permangante ion arise dominantly from e↔ t1 or e↔ t2 single-configurational excitations. A discussion of the extensive phonon coupling and the anomalous Franck—Condon pattern of this transition is also provided.
Kinetic Theory of Thermal Transpiration and Mechanocaloric Effect. I
Authors: Loyalka S. K.
Published: February 2004

A general kinetic theory analysis of the cross phenomena of thermal transpiration and the mechanocaloric effect is presented. The Onsager reciprocal relations are verified and the mass flux and the heat flux are expressed in terms of the stationary values of appropriate variational functionals. These considerations are valid for the linearized Boltzmann equation with general forms of the boundary conditions and a capillary of arbitrary shape. It is felt that some of the work reported here should be of general interest in that similar considerations could be used for a study of other cross effects. Some explicit numerical results are given for the case of parallel plates by using the BGK model and assuming diffuse reflection at the surface.
Distribution Function Theory of Nematic Liquid Crystals
Authors: Wulf Alejandro
Published: February 2004

The method of distribution functions—governed by Kirkwood integral equations—is applied to anisotropic fluids of the nematic type. It is shown how to obtain the self-consistent-field theory of Maier and Saupe (assuming their anisotropic dispersion force) with the help of some approximations. When the repulsive forces are included an additional term is present in lnρ(1)(θ)[ρ(1)(θ) ≡ orientational distribution function]; estimating this term we conclude that the repulsive force cannot be neglected if l/d〉2 (l and d=molecular length and diameter) and the molecules are not too flexible. Also, the first few terms of Onsager's virial expansion for the free energy are derived.
Paramagnetic Mössbauer Spectra of Some Rhombic Fe3+ Materials: Correlation with ESR
Authors: Lang G. , Aasa R. , Garbett K. , Williams R. J. P.
Published: February 2004

A number of magnetically dilute Fe3+ compounds of EDTA have been examined by ESR and Mössbauer spectroscopy. At low temperature complicated magnetic hyperfine structure is seen in the Mössbauer spectra, and this is considerably sharpened by application of spin decoupling fields of order 100 G. Mössbauer measurements are in good agreement with calculated spectra based on crystal field splittings derived from the ESR spectra. Measurements made on frozen solutions indicate that the crystal field splittings are solvent dependent.
Rare Gas Scattering from LiF. III. Multilobular Structure for Neon
Authors: Keefe D. R. O' , Palmer R. L. , Smith Joe N.
Published: February 2004

Additional data to that previously reported for the scattering of Ne from the (001) surface of LiF are presented and compared with the results of a recent theoretical analysis. The data presented include details of the in-plane scattering for the case in which the plane of incidence intersects the surface in the 〈 110 〉 azimuth as well as a detailed examination of the out-of-plane scattering for the case in which the plane of incidence lies along both the 〈 010 〉 and 〈 110 〉 aximuthal directions. Measurements are made as a function of angle of incidence, beam temperature, and surface temperature. A complex multilobate structure is observed and, in those instances in which a direct comparison with the theory is available, very good agreement is obtained.
Normal Coordinate Analysis and Intensity Calculations for 1A′ and 1A″ Electronic States of Propynal
Authors: Williams Denis R.
Published: February 2004

A normal coordinate analysis using a quadratic force field is carried out for the ground and first-excited singlet electronic states of the molecules HC≡C·CHO, DC≡C·CHO, HC≡C·DCO. Three force constant matrix elements are transferred from ground to excited states. The normal coordinates enable the intensities of a number of transitions to be calculated and favorably compared to those observed. The agreement between calculated and observed frequencies is excellent for all isotopes. Semiempirical SCF MO theory (CNDO/2) is used to correlate the changes of geometry and electronic structure on excitation as well as to account for the remaining observed electronic bands of propynal.
Electric, Magnetic, and Spectral Properties of H3+ Ground State Calculated from Single-Center Wavefunctions
Authors: Kawaoka Kenji , Borkman Raymond F.
Published: February 2004

Single-center wavefunctions, employing up to 100 configuration-interaction terms, are used to compute electric, magnetic, and spectral properties of the A1′1 electronic ground state of equilateral triangular H3+. The best values for several computed properties are: electronic energy, E=−1.3405 hartree; equilibrium internuclear distance, R=1.65 bohr; electric quadrupole moment, Θzz= −1.2540 B; and Larmor contribution to the mean diamagnetic susceptibility, χ¯L=−3.2693×10−6 cgs·emu. Expectation values for the squared electronic coordinate operators 〈 x12〉, 〈 y12〉, 〈 z12〉, and 〈 r12〉 are also given. The derivative of the electric quadrupole moment with respect to symmetric motion of the nuclei was calculated to be ∂ Θzz/∂ R=−2.5531 B/Å, while the derivative of the electric dipole moment (center-of-mass origin) with respect to molecular bending was calculated to be ∂ μx/∂ φ=−0.0193 D/deg. These latter results permit prediction of the strengths of the quadrupole-allowed A1′ and dipole-allowed E′ vibrational fundamentals in the infrared spectrum. Finally, using excited-state wavefunctions and oscillator strengths reported previously, we have calculated the components of the electric dipole polarizability for the A1′1 state, αxx=αyy=0.4879 Å3, αzz=0.2567 Å3, α¯=0.4109 Å3.
Absorption Spectrum of Borazine in the Vacuum Ultraviolet
Authors: Kaldor Andrew
Published: February 2004

The absorption spectrum of both vapor-phase and matrix-isolated borazine has been investigated in the 2000–1500-Å region. Three electronic transitions have been observed. The strongest absorption, with a maximum at 1650 Å, is assigned to the allowed E′1−A1′1 transition. Two weaker absorptions, with forbidden origins at 1975 and 1889 Å, are assigned to the forbidden transitions A2′1−A1′1 and A1′1−A1′1, respectively. The A2′1−A1′1 transition is made vibronically allowed by one quantum change in the ν16 and ν17 e′ vibrations. The vibration making allowed the A1′1−A1′1 transition could not be determined.
Ab initio potential surface for H4+
Authors: Poshusta R. D. , Zetik D. F.
Published: February 2004

A portion of the potential surface of H4+ was calculated with several wavefunctions based on valence bond configuration interaction. Polarization and ionized structures were considered. The calculated potential surface shows a long range attraction between H2 and H2+ which becomes strong at short distances. Calculations were made on a potential hypersurface containing a favorable reaction coordinate for the reaction H2+ H2+→ H3++H. Simple wavefunctions without polarization show no long range attraction between H3+ and H; when polarization is included a long range attraction is found. Calculations with ionized structures and polarization suggest that H4+ is stable with a binding energy Do=0.85 kcal/mole. Failure to detect H4+ is attributed to the absence of a mechanism to produce this ion under experimental conditions.