bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Determination of the Polarization of the Microwave Zero-Field Transitions
Authors: Kalman O. F. , El-Sayed M. A.
Published: February 2004

An optical method is described by which the polarization characteristics, and thus the symmetry assignment, of the zero-field magnetic transitions can be determined in zero field. In this method, the guest molecule being studied is dissolved in a single crystal of known structure. The oriented mixed crystal is placed inside a microwave helix in a position where the magnetic field along the helical axis is maximum, with one of the crystal axes being parallel to the helix axes. A relationship is derived which relates the changes in the phosphorescence intensity of the sample to the power of the microwave radiation that induces the magnetic transitions between the zero-field levels of the lowest triplet state. At very low temperatures, when the spin–lattice relaxation processes are negligible, and at low microwave power levels, the derived relationship gives a straight line relationship where the slope/intercept ratio is related to the decay constants and the absorption cross section, σk, of the microwave power along a certain crystal direction k. The polarization ratios σk / σl for the three different combinations of orthogonal crystal axes are determined for the different zero-field magnetic transitions. These polarization ratios are then compared with those predicted for the magnetic moments being along the different molecular magnetic principal axes and from a knowledge of the crystal structure. A detailed analysis of the distribution of the magnetic field along the helical and radial axes at different positions inside the microwave helix is given. The factors that are important in determining meaningful polarization ratios using this method are examined both theoretically and experimentally. The method is used to assign the zero-field magnetic transitions of the triplet state of 2,3-dichloroquinoxaline in durene at 1.4°K. The results are in agreement with those of the magnetophotoselection techniques.
Vibrational Spectra and Structure of Oxalyl Fluoride in the Solid and Fluid States
Authors: Durig J. R. , Brown S. C. , Hannum S. E.
Published: February 2004

The vibrational spectra of oxalyl fluoride have been examined in the solid phase and re-examined in the fluid phases. From the disappearance of three major bands upon solidification, it is concluded that there must be two isomeric forms in the vapor. The spectra have been assigned on the basis of two isomers; solid-phase frequencies were used for the trans fundamentals and bands unique to the fluid states were assigned to the cis isomer. The values observed for the fundamentals in the solid are compared to those previously reported from studies of the fluid states. The internal torsion was observed at 54 cm−1 in the vapor state, and a barrier to internal rotation of 12.4 kcal/mole has been calculated. A comparison of the infrared and Raman bands in the crystal shows that the mutual exclusion principle is operative. It is concluded from this alternate forbiddance that the molecule has a centrosymmetric structure in the crystal and that each molecule occupies a Ci site. The factor group of the crystal is believed to be either C2h or D2h with two or four molecules per primitive cell.
Vibrational Spectra of Molecular Metal Nitrate Monomers and Dimers
Authors: Smith D. , James D. W. , Devlin J. P.
Published: February 2004

The infrared spectra of the matrix-isolated vapors from hot samples of lithium, sodium, potassium, rubidium, thallium, and copper (II) nitrates are reported. The spectra are simple and clearly indicate that the dominant species in each case is the monomer of the metal nitrate, although limited decomposition could not be avoided with LiNO3. Features indicative of the dimer, (MNO3)2, were also apparent for the alkali-metal nitrates. Further, Raman bands have been detected for the ν1 modes of the isolated potassium and copper nitrates. The monomers seemingly represent the extreme of anion distortion for each case since the nitrate ion experiences the electrostatic field of a single closely associated cation. Thus, a comparison of the ν3(e) distortion splitting with that observed for cases for which the nitrate ion has been used as an environmental probe was of interest. Additional physical insight has been gained by relating the ν3(e) splittings to force constant variations in the anion, and, ultimately, to cation polarizing powers.
Internal Rotation in (CH3)2X Molecules of C2υ Symmetry–Barrier to Internal Rotation in Dimethyl Ether
Authors: Tuazon Ernesto C. , Fateley William G.
Published: February 2004

A procedure is described for calculating the periodic barrier to internal rotation of C2υ molecules with two methyl groups based on one observed torsional frequency for each of the isotopic species (CH3)2X and (CD3)2X. The method is applied to dimethyl ether using the observed gas-phase B1 torsional frequencies of (CH3)2O and (CD3)2)O. The calculated coefficients of the potential function are Veffective = 946 ± 15 cm−1 and V12′ = 30 ± 9 cm−1. The evaluation of the threefold barrier (V = 907 cm−1) for the isotopic species CH3OCD3 suggests that the CH3 and CD3 torsional levels are in resonance. Comparison of the results for the three isotopic species allows the value of V12 to be estimated as − 20 cm−1.
Thermal Decomposition of Ozone
Authors: Michael J. V.
Published: February 2004

The thermal decomposition of ozone was studied from 988–1400°K, and the rate constant for O3 + M → O2 + M was obtained. The results are compared to other studies and to a theoretical calculation (HRRKM). The results may indicate a breakdown in the Boltzmann statistically based HRRKM theory applied to ozone at temperatures above 1060°K and, therefore, point to the increasing importance of vibrational population as the rate-controlling process.
Collision Reactions of Negative Ions in Several Sulfur Compounds and in Their Mixtures with ClCN
Authors: Domenico A. di , Sharma D. K. Sen , Franklin J. L. , Dillard J. G.
Published: February 2004

The formation of the principal negative ions in COS, CS2, H2S, and CH3SH and their collision reactions in mixtures of these compounds with ClCN have been studied. A time-of-flight mass spectrometer fitted with a high pressure source was employed. By comparing ionization efficiency curves for the various resonances occurring, it has been shown that the principal reactions in the above mentioned systems involve attack of S− or HS− on ClCN to yield SCN− and CN−. The rate of formation of CN− is approximately 100 times that of SCN−. Rate constants have been determined for the various reactions.
Interactions in Lanthanide Systems. I. A Raman and Infrared Study of Aqueous Gadolinium Nitrate
Authors: Nelson D. L. , Irish D. E.
Published: February 2004

Raman spectra of aqueous gadolinium nitrate solutions, and complementary infrared spectra, have been obtained for a wide range of compositions. Detailed intensity analyses indicate that the predominant species in solutions with nitrate:gadolinium ratios less than two is Gd(NO3)2+ (β2 = 4.6 ± 0.2 at 25°C). Small concentrations of a 1:1 species are not excluded but β1 < 0.8. Higher species are significant for ratios of 3 or greater. In systems of low water content evidence is presented for a bridging, polynuclear aggregate which is fragmented by heating or addition of water or nitrate ion. Band assignments are made for the ligand. The nitrate ions in the dinitratogadolinium(III) species are not equivalent: One binds through two oxygen atoms and the other through one.
Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals
Authors: Tomkiewicz Y. , Groff R. P. , Avakian P.
Published: February 2004

The singlet–triplet (T1 ← S0) excitation spectrum for delayed fluorescence and the prompt fluorescence (S1 → S0) emission spectrum have been measured for a tetracene crystal at room temperature. The origin (0–0 transition) in the two spectra at 10 100 ± 20 and 18 680 ± 30 cm−1, respectively, imply the activation energy for singlet exciton fission, ΔE = 1520 ± 70 cm−1. Raman lines corresponding to the vibrational structure in the above spectra were detected. The fluorescence emission spectra show the need for taking reabsorption effects into account.
Rotational Relaxation in Polar Gases. III. Molecular Dynamics
Authors: Zeleznik Frank J. , Dugan John V.
Published: February 2004

A 50 molecule sample in contact with a heat bath of similar molecules was used as a model to calculate the rotational collision numbers, Zrot, for HCl and DCl at 300 and 500°K, by the method of molecular dynamics. The mean rotational energy of the sample exhibits an exponential approach to a steady state value; however, there was considerable scatter about the exponential curve. The results for Zrot generally agree with previous theoretical calculations. They are intermediate to experimental acoustic data and the earlier perturbation results.
Variable Integrals Method. II
Authors: Yoshida Zen-ichi , Kobayashi Tsunetoshi
Published: February 2004

A new type of semitheoretical formula for core resonance integrals, which includes no arbitrary adjusting molecular parameters, is derived. Using this new semitheoretical formula a modified Pariser–Parr–Pople type SCFMO method, the variable integrals method II (VI/2), is proposed, and applied to various types of molecules from ethylene, formaldehyde, to benzene derivatives, heterocyclic systems, and so on. The agreement between the calculated transition energies by the VI/2 method and the observed ones is quite satisfactory and in not a few cases more improved results have been obtained by this method than by the other semiempirical MO methods.
Measurement of the Thermal-Diffusion Factor of Dilute Neon–Xenon Mixtures with the Thermal-Diffusion Column
Authors: Rutherford W. M.
Published: February 2004

Apparatus and techniques were developed for obtaining the thermal-diffusion factor from static separation measurements in the thermal-diffusion column. Reduction of the column data does not depend on the use of a theoretically derived value of the convective remixing coefficient, Kc; however, a factor related to the ratio of experimental to theoretical values of Kc is used as a test of the consistency of the data with the theory of the column. The thermal-diffusion factor was obtained at an average temperature of 311°K for mixtures containing 1 at.% Ne, 99% Xe, and 1.3% Xe, 98.7% Ne. The results were in good agreement with the data of other investigators. The consistency test showed that the experiments were in good agreement with predictions based on a recently modified theory of the thermal-diffusion column.
Close-Coupling Technique for Chemical Exchange Reaction of the Type A+BC→AB+C. H+H2→H2+H
Authors: Diestler D. J.
Published: February 2004

A new close-coupling technique for rearrangement collisions of the form A+BC→AB+C is presented. The general theory is developed for collinear electronically adiabatic encounters. A central feature of the technique is the expression of the scattering wavefunction as a sum of two terms expressed in two symmetric coordinate systems. The first term is expressed in coordinates RAC and RBC appropriate to the arrangement A+BC prior to reaction and the second term in coordinates RAC and RAB appropriate to the arrangement AB+C after reaction. Coupled equations in the single variable RAC are obtained and integrated numerically by an initial-value technique to obtain accurate transition and reaction probabilities. The theory is applied to the exchange reaction H+H2→H2+H using the Porter–Karplus potential energy surface. Although the results cannot be compared directly with those of previous accurate quantal calculations, they are internally consistent and exhibit trends qualitatively similar to those of the previous calculations.
Quantum-Chemical Study of Some Pnicogen Monofluorides
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

A quantum-chemical investigation of the nitrogen–fluorine and phosphorus–fluorine diatomic systems is described. Molecular self-consistent-field wavefunctions near the Hartree–Fock limit were computed via the Roothaan expansion method for the X 3Σ− (ground), a 1Δ, and b 1Σ+ states of NF and for the Π2 states of NF+ and NF−. Similar wavefunctions were computed for the Σ−3 ground state of PF and for PF+(2Π) and PF−(2Π). For the neutral molecules, the experimental bond lengths were used; for the charged species, the internuclear separations of the parent (3Σ) molecules were used. In addition, a wavefunction was also obtained for PF+(2Π) at its experimental internuclear separation. Values derived for the binding and ionization energies through the use of semiempirical correlation energies are in excellent agreement with experimental data; the uncorrelated excitation energies, as expected, are somewhat different than the experimental results. The electron affinities deduced from the wavefunctions indicate that the hitherto unreported NF− and PF− should be thermodynamically stable at moderate temperatures. Dipole and quadrupole moments have also been calculated for all the species. The second ionization potential of PF has been estimated based on Koopmans' theorem.
Excitation Mechanism for the O2 Schumann–Runge System
Authors: Sharma Ramesh D. , Wray Kurt L.
Published: February 2004

The Schumann–Runge band system of O2 involving transitions between the X 3Σg− ground state and the B 3Σu− excited state has been the subject of many investigations which have shown that the radiating state is strongly coupled to the O atoms and that the population mechanism is very fast. In the present study, the emitted radiation was monitored with filter–photomultiplier combinations as a function of time behind incident shock waves in O2, O2–Ar, and O2–Ne mixtures at wavelengths centered at 2300 and 3250 Å. Initial pressures in the shock tube were 1–100 torr and the (equilibrium) temperature range was 2800–5300°K. The radiation, subsequent to a short incubation time, rose monotonically to a plateau level given for each of the two channels by I2300 = 4.4 × 10−36[exp(− 20.3 × 103 / T)](O)2 and I3250 = 1.1 × 10−36[exp(− 11.3 × 103 / T)](O)2 in watts/cubic centimeters·steradians·microns where (O) is the number of O atoms per cubic centimeter. These results are in disagreement with the results of Myers and Bartle both in apparent activation energy and absolute magnitude. In general, these comparisons verified that I∝(O)2 during the entire time history—indeed, these data for the oxygen-rich mixtures yielded a very sensitive measurement of the efficiencies of O2 and O in dissociating O2. Various other excitation mechanisms were considered, and it was shown that inverse predissociation is the only one which fits the data and that it must dominate over a very wide range of conditions.
Theoretical Electronic Transition Probabilities in Diatomic Molecules. III BeH and MgH (A 2Π–X 2Σ+) Systems
Authors: Popkie H. E.
Published: February 2004

Electronic dipole-momentum and dipole-length transition moment curves obtained from the multiconfiguration (MC) wavefunctions of Chan and Davidson are presented for the BeH and MgH (A 2Π–X 2Σ+) systems. They are used to discuss the correlation correction to the Hartree–Fock (HF) curves previously reported. The MC transition moments and vibrational wavefunctions derived from both the theoretical MC and “experimental” RKR potential-energy curves for the A 2Π and X 2Σ+ states are used to calculate band oscillator strengths. A table of band wavelengths and semitheoretical transition probabilities is presented for each system and the predicted band spectrum is briefly discussed.
Quantum-Mechanical Transition Probabilities for Atom–Atomic-Oscillator Collisions with Morse Potential Interaction
Authors: Diestler D. J. , Feuer P.
Published: February 2004

Exact quantum-mechanical transition probabilities for the collision of an atom with an atomic oscillator for the case in which the interaction has the form of a Morse potential are obtained by numerical integration of the relevant close-coupled scattering equations. These transition probabilities are compared with approximate ones calculated from distorted-wave theory over a range of parameters which have been of interest in examining the collision of helium atoms with a tungsten surface. Some information is obtained concerning the range of validity of the first-order theory, and certain suggestions that have appeared in the literature for correcting the distorted-wave results are found to be inadequate.
Classical Model for Gas–Surface Interaction
Authors: Busby M. R. , Haygood J. D. , Link C. H.
Published: February 2004

A three-dimensional classical theoretical model for the interaction of a monatomic gas impinging as a monoenergetic atomic beam on its own solid phase has been formulated and tested using the experimental data for the gaseous argon–solid argon system. The theoretical interaction is modelled as the collision of hard spheres with the inclusion of an attractive surface field energy, the only adjustable parameter in the model, and surface temperature. The theoretical results from this exceedingly simple model exhibit nearly every characteristic of the available experimental data for argon.
Hydrogen Bonds Involving Sulfur. II. The Hydrogen Sulfide–Hydrosulfide Complex
Authors: Sabin John R.
Published: February 2004

The possibility of strong hydrogen bonding of the S–H–S type is investigated in the H2S–HS− adduct, using ab initio MO LCAO SCF techniques. A variety of configurations are considered. A symmetric linear form of the adduct with a very strong hydrogen bond is found to be most stable. Some properties of this bond are discussed.
INDO Molecular Orbital Study of Hyperfine Tensors: Theory, Methodology, and Applications to CH, CH3, and Radicaloid Derivatives of Malonic Acid
Authors: Beveridge David L. , McIver James W.
Published: February 2004

The theory and methodology of valence electron self-consistant field molecular orbital calculations of electron nuclear hyperfine tensors using intermediate neglect of differential overlap (INDO) is discussed in detail. The results of calculations on CH, CH3, and radicaloid derivatives of malonic acid are presented and compared with available experimental results and other theoretical calculations.
Strongly Coupled, Oxo-Bridged Iron (III) Complexes Magnetically Perturbed Mössbauer Spectra
Authors: Reiff W. M.
Published: February 2004

The electric field gradient tensor is used to study structure, spin state, and bonding in some representative binuclear iron (III) systems. Mössbauer spectra of strong (J ≈ − 100 cm−1) exchange coupled intramolecular antiferromagnets have been determined in zero applied field and also longitudinal fields up to 26 kG. The systems studied, [Fe(salen)]2O (salen-N, N′-ethylenebissalicydeneiminate), [Fe(phen)2Cl]2-OCl2·5H2O (phen-1, 10-phenanthroline), and [FeB(H2O)]2O(ClO4)4 {B=the macrocyclic ligant 2, 13-dimethyl-3, 6, 9–12, 18-pentaaza-bicyclo[12.3.1]octadeca-1(18), 2, 12, 14, 16-pentaene)} contain five-, six-, and seven-coordinate iron (III), respectively, and show approximate axial symmetry. Signs for the principal component of the electric field gradient tensor are discussed in terms of point charge geometry and σ bonding considerations. On this basis, a cis arrangement of chlorine and oxygen is proposed for [Fe(phen)2Cl]2-OCl2·5H2O, and the nature of the large quadrupole splitting is discussed. The spin state of the individual iron (III) ions is also considered and is indicated to be 52. The absence of relaxation broadening and internal field augmentation at 4.2°K are correlated with total spin zero ground states for the binuclear complexes.
Nonrigid Molecule Effects on the Rovibronic Energy Levels and Spectra of Phosphorous Pentafluoride
Authors: Dalton Bryan J.
Published: February 2004

Although phosphorous pentafluoride is known from electron diffraction, infrared, and Raman data to have a D3h trigonal bipyramid equilibrium configuration, NMR data shows only one fluorine resonance. Although this is almost certainly due to a fast intramolecular rearrangement process occurring via a Berry pseudo rotation, the detailed mechanism (e.g., classical thermal rearrangement or quantum mechanical tunneling in low vibrational levels) is unknown. A theoretical study has been made of the effects of quantum mechanical tunneling on the rovibronic levels, i.e., treating phosphorous pentafluoride as a nonrigid molecule. The levels are shown to be split in a very characteristic manner. Simple results for the relative intensities of the resultant fine structure to the original rovibronic transitions have also been obtained. This predicted, characteristic fine structure could be searched for experimentally in order to further our understanding of the intramolecular rearrangement process occurring in phosphorous pentafluoride. A theoretical study on a suitable millimeter wave spectroscopic experiment shows that such an experiment is at present on the border line of accessibility. A new general method of treating nonrigid molecule energy levels is illustrated by this application to the specific case of phosphorous pentafluoride.
Temperature Dependence of Rotational Collision Numbers from Thermal Transpiration
Authors: Annis B. K. , Malinauskas A. P.
Published: February 2004

The temperature dependence of the rotational collision numbers for O2, N2, CO, and CO2 was investigated in the range 475–676°K by the thermal transpiration technique with the use of a novel apparatus design. In all cases the collision number was found to increase with temperature. For O2 and N2, where some comparison with theory is possible, the experimental rate of increase with temperature was found to be faster than the predicted behavior. The results for CO and CO2 are in general agreement with other transpiration measurements and with acoustic absorption results which were obtained at lower temperatures.
ESR Study of Radicals Formed by γ Irradiation of K2PdCl4 and (NH4)2PdCl4 Single Crystals
Authors: Krigas Thomas , Rogers Max T.
Published: February 2004

An X-band ESR study of γ-irradiated single crystals of K2PdCl4 and (NH4)2PdCl4 has been made at 77°K. Two radicals are observed, one of which is shown to be PdCl43− with a 4d9 configuration and dx2−y2 ground state; the complete g, A(105Pd) and A(35Cl) tensors have been reported for this species. The second radical is believed to be PdCl52−, and its ESR parameters are presented and discussed.
Raman and Infrared Spectral Studies of Anhydrous Li2CO3 and Na2CO3
Authors: Brooker M. H. , Bates John B.
Published: February 2004

The infrared and Raman spectra of anhydrous crystalline Li2CO3 and Na2CO3 were measured at 300 and at 80°K. Bands observed in the vibrational spectra of Li2CO3 were assigned according to the C2h factor group symmetry. The doublet structure observed for each of the internal modes in the spectra of Na2CO3 was interpreted in terms of an ordered arrangement of CO3= ions over two nonequivalent orientations within the primitive cell. Multiple internal reflection and polarized specular reflectance techniques were used to determine transverse optical (TO) and longitudinal optical (LO) mode frequencies in Li2CO3 and Na2CO3. It was shown from these measurements that the infrared transmission spectra of these compounds exhibit band maxima which are admixtures of LO and TO modes.
Studies in Molecular Dynamics. IX. Vacancies in Hard Sphere Crystals
Authors: Bennett C. H. , Alder B. J.
Published: February 2004

The concentration of monovacancies as well as their entropy and volume of formation have been determined in a face-centered hard sphere crystal at a series of densities. The results near the hard sphere melting density compare favorably with experiments on argon and metals. Although divacancies are shown to have an increasingly larger mobility relative to monovacancies with increasing pressure, they do not contribute significantly to diffusion because their equilibrium concentration is too low. It is shown also that two monovacancies interact significantly when separated by many lattice spacings. The free energy of association of higher vacancy clusters is found to be approximately proportional to the number of vacancy–vacancy contacts, so that compact clusters are stabilized relative to extended ones. This effect was found to be greatly enhanced for different shaped vacancy clusters in square-well particle systems, by an additional amount corresponding to the potential difference in particle–vacancy contacts.
The n-π* Absorption and Emission of Optically Active trans-β-Hydrindanone and trans-β-Thiohydrindanone
Authors: Emeis C. A. , Oosterhoff L. J.
Published: February 2004

The n-π* transitions (absorption, circular dichroism, luminescence, linear and circular polarization of luminescence) of trans-β-hydrindanone (I) and trans-β-thiohydrindanone (II) are discussed. The C2 symmetry of I and II is taken into account with the aid of expressions that are derived for nonrigid molecules having a twofold axis of symmetry. This allows the absorption of I to be split into a part due to transitions polarized along the twofold axis (z axis) and a part due to x, y-polarized vibration-induced transitions. Accurate values for the electric and magnetic transition moments then are obtained. The vibrational structure of absorption and fluorescence and the latter's low degree of circular polarization are related to nonplanarity of the carbonyl group in the (n → π*)1 state. A larger nonplanarity probably is present in the triplet state of I. Circular polarization in the fluorescence was also observed when racemic I was excited with circularly polarized light. For the absorption of II, an upper limit is found for the electric transition moment and a lower limit for the magnetic moment. These give no indication that 3d orbits play an important part in the optical activity of thioketones. The luminescence at − 196°C and the longest wavelength part of the visible absorption band do not show circular polarization. They probably are singlet–triplet transitions. There is some evidence that the thiocarbonyl group is planar in the triplet and in the excited singlet state.
Exciton Migration in Molecular Crystals
Authors: Grover M. , Silbey R.
Published: February 2004

The migration of Frenkel excitons in molecular crystals is studied theoretically, starting from the microscopic equations of motion for the exciton density. The migration process is found to be diffusionlike on a long time scale for all temperatures as long as the exciton–phonon coupling is present. If there is no exciton–phonon coupling, the migration is wavelike. A discussion of the relevant time scales for the wavelike (coherent) process and the diffusion (incoherent) process is given. Several different approximation techniques, based on the cumulant expansion, projection operator, and functional derivative methods, are shown to be mathematically equivalent as applied to this problem.
Infrared Emission of OH in the Fundamental and First Overtone Bands
Authors: Murphy Randall E.
Published: February 2004

The infrared vibration–rotation spectrum of the hydroxyl radical produced by the reaction of hydrogen atoms and ozone has been recorded. The intensity of individual lines in the fundamental sequence was found to be considerably weaker than was previously predicted. The intensity of lines in the fundamental sequence is compared with the intensity of the first overtone lines to obtain ratios of the vibrational transition probabilities. These ratios are used to remove the ambiguity of the OH dipole moment function associated with previously unknown intensities of the fundamental bands. A complete set of relative transition probabilities is given. An equilibrium flux calculation using atmospheric data is performed using the derived transition probabilities to obtain the vibrational distribution of OH at formation.
Far-Infrared and Raman Spectra of Solid Methanol and Methanol-d4
Authors: Durig J. R. , Pate C. B. , Li Y. S. , Antion D. J.
Published: February 2004

The far-infrared and Raman spectra were obtained of methanol and methanol-d4 at − 185°C, and a temperature-dependence study of the Raman spectrum was carried out. In the low-temperature α phase, splitting of the C–O stretching mode was observed in the Raman spectrum but disappeared when the sample was warmed to the high-temperature β phase. The coalescence of this band is attributed to the disorder caused by the interchange of the methyl groups above and below the plane of the chain. Four bands were observed at 350, 167, 109, and 57 cm−1 in the low-frequency infrared spectrum of methanol which shifted to 325, 161, 97, and 61 cm−1 with deuteration. One skeletal mode was observed at 196 cm−1 in the Raman effect and shifted to 180 cm−1 with deuteration. It is shown that the spectra arising from the skeletal motions can be interpreted on the basis of line-group theory in which the line-group factor group is proposed to be C2 for both phases. Also the nature of the molecular motions giving rise to the low-frequency bands is discussed in relation to the observed shift factors with deuteration. Possible assignments for the skeletal modes is also given in terms of the factor group of the C22–P21 space group, but the other suggested space group C2h2–P21/m is not consistent with the number of observed far-infrared bands.
Interactions between Chemisorbed Species: H2 and CO on (100) Tungsten
Authors: Yates John T. , Madey Theodore E.
Published: February 2004

The interaction of CO with chemisorbed β-hydrogen on the (100) plane of tungsten has been investigated using flash desorption and work function methods. CO efficiently displaces chemisorbed hydrogen from tungsten at temperatures near 300°K. This is a result of the CO-induced lowering of the activation energy for H2 desorption, with the CO chemisorbing initially on sites other than those occupied by hydrogen. At ∼ 100°K, little CO-induced displacement of chemisorbed hydrogen occurs, and the production of three weakly bound hydrogen states (designated ν-hydrogen) is observed. Each ν state exhibits a range of desorption energies. During the CO-induced surface conversion of β-hydrogen to ν-hydrogen, a decrease in work function is observed. All of this behavior is indicative of a major interaction between adsorbed CO and adsorbed hydrogen. A weakly-bound molecular H2 state (δ-hydrogen) may be populated by adsorption of H2 on top of partial CO layers on W(100) at ∼ 100°K. The sites adsorbing this molecular state of hydrogen are related to the presence of β-CO species, and are probably the same sites which could adsorb α-CO at higher CO coverages. In thermal desorption, the liberation of two discrete hydrogen binding states (β1and β2) from pure hydrogen layers on W(100) is probably a result of coverage-dependent interactions between identical adsorbed H-atom species. No chemical differences are observed in this work between hydrogen species responsible for the two β-hydrogen binding states. No catalytic production of H2CO, HCO, CH4, or C2H6 was observed in coadsorption of hydrogen and CO on W(100).
Microwave Spectrum, Vibration–Rotation Interaction, and Ring Puckering Vibration in Silacyclobutane and Silacyclobutane-1,1-d2
Authors: Pringle Wallace C.
Published: February 2004

The microwave spectrum of the molecules silacyclobutane and silacyclobutane-1,1-d2 has been observed between 8 and 55 GHz and the first four vibrational states assigned. The ground state rotational constants of the former molecule are 8815.75, 6289.00, and 4245.32 MHz. The first two inversionlike intervals of the ring puckering mode were determined to be 75.75 and 7790 MHz in the normal isotopic species; the corresponding intervals in the deuterated species are 43.06 and 4430 MHz. The effect of these frequencies on the determination of the potential energy for the ring puckering vibration was investigated. The ring configuration was shown to be significantly puckered in the ground state. The a component of the dipole moment was found to be nearly constant in the four vibrational states of the normal molecule, μa = 0.4396 D, while the out-of-plane transition moment between inversion doublets dropped rapidly as the inversion levels approached the top of the barrier.
Dipole Moments of Dimethylsiloxane Oligomers and Poly(dimethylsiloxane)
Authors: Sutton C. , Mark J. E.
Published: February 2004

Dielectric constants at 20, 30, 40, and 50°C have been determined for pure liquid dimethylsiloxane oligomers (CH3)3Si–[OSi(CH3)2]xOSi(CH3)3 having chain lengths corresponding to x = 3, 5, 7, and 9. Mean-square dipole moments 〈μ2〉, calculated from the Onsager equation, are in good agreement with predicted values based on a rotational isomeric state model with neighbor dependence and chain conformational energies obtained in an independent analysis of the random-coil dimensions of such chains. In addition, the observed temperature coefficients of 〈μ2〉 are in qualitative agreement with calculated results for the stated range of x. An experimental value of the ratio 〈μ2〉 / nm2 (where n is the number of bond dipoles, each of magnitude m) in the limit of large x is estimated from published data on the pure liquid polymer at 25°C. This tentative result is in fair agreement with theory; agreement is improved if the large specific solvent effect previously observed for this polymer is interpreted as being primarily due to the effect of the dielectric constant of the medium on the Coulombic contribution to the conformational energy.
Cascade Measurements of Thermal Transpiration for Ar, N2, CO, and the Helium Isotopes
Authors: Taylor W. L. , McConville G. T.
Published: February 2004

A new experimental technique was employed to measure the thermal transpiration effect (thermomolecular pressure difference) for Ar, N2, and CO between 77 and 97°K and for helium-3 and helium-4 between 4.2 and 7°K. A cascade device consisting of seven large tubes connected top to bottom with capillaries was partially immersed in either liquid nitrogen or liquid helium while a suitable temperature difference was applied by heating the upper ends of the tubes and capillaries. Small pressure differences were established in each of the capillaries and the cumulative effect was large enough to be accurately measured with a differential capacitance manometer. The modified Weber–Schmidt theory was used to analyze the data and represented the argon data quite well. Some difficulty, which was traced to the coefficient of the temperature gradient, was encountered in obtaining a satisfactory theoretical explanation of the results for the other gases. We concluded that either an incorrect or oversimplified treatment of the temperature jump distance probably caused the discrepancy. Until further elucidation of this term, which also contains the translational Eucken factor, is forthcoming, use of this model for obtaining rotational relaxation times from thermal transpiration measurements is probably of limited value.
Wave Propagation in Nematic Liquid Crystals
Authors: Lee James D. , Eringen A. Cemal
Published: February 2004

Basic laws of motion of micropolar continuum are presented, and the adequacy of applying micropolar theory to liquid crystals is indicated. A set of constitutive equations is derived for nematic liquid crystals. Wave propagation problems are solved, and it is shown that the theoretical analysis is in good agreement with the experimental data, which indicates the isotropy of the phase velocity of the longitudinal wave and the anisotropy of the damping coefficient. The coupling, although small, is shown to exist between longitudinal and rotational waves.
Coexistence Curves of CO2, N2O, and CClF3 in the Critical Region
Authors: Sengers J. M. H. Levelt , Straub J. , Vicentini-Missoni M.
Published: February 2004

The coexistence curves of CO2, N2O, and CClF3 are analyzed in the critical region. The curves were obtained by refractive index measurements which are virtually free of gravity effects and contain much detail near Tc. After proper weight assignment, it is established that the top of the coexistence curve is asymptotically symmetric: ρ± = ρc ± Btβ; that the exponent β is independent of the range, varies little from substance to substance, and is insensitive to impurities; and that the data are in agreement with the law of the rectilinear diameter. “Best” values for β, B, and for the slope of the diameter are presented. An analysis of earlier coexistence curves for CO2 and N2O, including a weight assignment, is presented; there is agreement between the older and newer data.
Pulse Radiolysis Studies of Acetone Solutions of Biphenyl and Anthracene: Formation of Ions and Excited Singlet State
Authors: Arai Shigeyoshi , Kira Akira , Imamura Masashi
Published: February 2004

The radiolysis of acetone solutions of biphenyl and anthracene has been studied by means of the microsecond-pulse technique. Transient spectra, as well as the effects of ion scavengers, show the presence of both positive and negative ions of biphenyl and anthracene in irradiated solutions. Assuming that molar extinction coefficients of positive and negative ions are identical, one can determine the yields of ions to be G(biphenyl++biphenyl−) = 1.1 at 0.69M, and G(anthracene++anthracene−) = 1.5 at concentrations above 5 × 10−3M. Decay kinetics of aromatic ions fit the second-order rate law, which can be ascribed to the charge neutralization reaction between the positive and negative ions; rate constants are found to be k(biphenyl++biphenyl−) = 3.9 × 1011 M−1·sec−1 and k(anthracene++anthracene−) = 2.6 × 1011 M−1·sec−1. The light emitted upon irradiation of acetone solutions of anthracene is anthracene fluorescence; a part of fluorescence is delayed. The relationship between the intensity of fluorescence and the concentration, as well as the comparison of the energy level of anthracene with that of acetone, suggests the occurrence of energy transfer from the first excited singlet state of acetone to anthracene. The rate constant of energy transfer is estimated to be 6 × 1010M−1·sec−1. The yield of excited singlet anthracene is determined to be G(1anthracene) = 0.31 at the concentration of 1.0 × 10−2M. Addition of various ion scavengers to acetone solutions of anthracene reduces the yields of both excited singlet and triplet anthracene. These results may be explained by the reactions of ion scavengers with the primary ions in spurs. Thus these reactions result in the decreases in the yields of excited acetone which may be produced by geminate recombination.
Positron Annihilation in Rare-Earth Hydrides
Authors: Chouinard M. P. , Gustafson D. R.
Published: February 2004

Analysis of the angular correlations of positron-annihilation radiation from erbium, gadolinium, holmium, and ytterbium hydrides indicates that the electronic structure of these materials is basically metallic in nature. As was previously found in the case of cerium hydride, the angular correlations were found to be broader than those from their parent metals by amounts which were consistent with the assumption that the rare-earth metal valence electrons and the electrons of the hydrogen atoms are all contributing to metallic bonding.
ESR Measurement of the Reaction between H Atoms and N2H4
Authors: Francis P. D. , Jones A. R.
Published: February 2004

An ESR atom detection method has been used to measure the rate of the reaction of H atoms with hydrazine, over the temperature interval 300–540°K. From the Arrhenius plot the specific rate constant for the reaction H+N2H4=N2H3+H2 was found to be (1.5 ± 0.3) × 1012exp[(− 1300 ± 200) / RT] in units of cubic centimeters mole−1·second−1. Although the stoichiometry of the reaction was not determined a possible reaction sequence is deduced from a mass spectrometric analysis of the products. The value of this rate constant is in good agreement with the rate constant of 1.7 × 1011cm3 mole−1·sec−1 measured by Gehring et al. over the temperature interval 251–315°K and the activation energy of 1300 ± 200 cal agrees fairly closely with the 2000 cal measured by Schiavello and Volpi.
Dipole Moment of the First Excited π* ← π State of Styrene
Authors: Parker Harriet , Lombardi John R.
Published: February 2004

The Stark effect is observed in the rotational fine structure of the 0–0 band of the lowest lying π* ← π transition of styrene. This resulted in a | Δμ | = 0.13 D from the ground state. It is shown that the smallness of the change in dipole moment is consistent with the π* ← π transitions in similar substituted benzenes studied in this laboratory.
Collision Mechanism Leading to the Formation of NO+ in O+–N2 Collisions
Authors: Leventhal J. J.
Published: February 2004

The energetics of the reaction O++N2→NO++N have been investigated in the laboratory for the kinetic-energy range 3–12 eV. The results indicate that the product NO+ ion is formed with excess internal energy. The heats of reaction obtained are consistent with formation of NO+ in a stripping-type collision process above about 4-eV incident ion energy.
Reflection and Absorption Spectra of the Higher π → π* Transitions of Solid Benzene
Authors: Brith M. , Lubart R. , Steinberger I. T.
Published: February 2004

Reflection and absorption spectra of C6H6 and C6D6 were obtained at temperatures near 4.2°K, in the wavelength region of 1700 Å < λ < 2700 Å. The samples were prepared as films on a cold window. Wellresolved spectra were obtained with both methods. The reflectance data (obtained at near normal incidence) were converted, using a combination of Kramers–Kronig and curve-fitting techniques, to yield the real and imaginary parts of the dielectric constant as well as the refractive index and the absorption coefficient. The results were in good correspondence with those obtained by direct absorption measurements. The absorption bands observed below 2200 Å belong to the electronic transitions A1g1 → 1B1u(ν̃ < 50 000 cm−1, weak system) andA1g1 → 1E1u(ν̃ > 50 000 cm−1, strong system), respectively. The possible assignments of the individual bands within each system are discussed on the basis of the present results, taking into account conclusions derived from spectra of benzene embedded in rare-gas matrices. Semiempirical calculations are carried out on the shift of the different progressions within the A1g1 → 1B1u transition in the solid.
Kinetic Energy of Ions Produced by Photoionization of HF and F2
Authors: Chupka W. A. , Berkowitz J.
Published: February 2004

Kinetic energies were measured for the positive ions produced in the ion-pair formation processes HF+hΛ→H++F−, F2+hΛ→F++F− at a number of wavelengths in the region of the thresholds for these processes. The measurements prove that D0(HF) is either 5.91 ± 0.02 or 5.87 ± 0.02 eV, depending on the value of the electron affinity of the F atom. Since the latter value for D0(HF) is in good agreement with other more precise determinations, these results support the value E.A.(F) = 3.400 eV. The kinetic energy measurements also prove that D0(F2) = 1.58 ± 0.03 eV. The measurements strongly suggest that the F+ ions from F2 are produced not only in the P23 ground state but also in P13 and/or P03 states as well. At higher photon energies, the F+ ions from F2 are also produced in the D1 state. Dissociation and predissociation processes of the molecular ions are discussed.
Detection of Iodine Atoms by an Atomic Fluorescence Technique: Application to Study of Diffusion and Wall Recombination
Authors: Brewer Leo , Tellinghuisen Joel B.
Published: February 2004

An atomic fluorescence method has been used to detect iodine atoms in concentrations lower than 1010/cm3. The heart of the apparatus is a “solar-blind” photomultiplier having practically no sensitivity to radiation of wavelengths longer than 2500 Å, but with good response in the region of the two strong iodine atomic resonance lines near 1800 Å. In combination with a small photolysis flashlamp, the system is used to study recombination of ground-state (2P3/2) iodine atoms in pure I2 vapor. At pressures below 0.2 torr the removal of atoms is seen to be predominantly a first-order diffusion-controlled process, characterized by a wall sticking probability of 0.040–0.065 and a binary diffusion cross section of 100 Å2. The reaction I+I2→I3 is found to be of minor significance in this study; a rough estimate indicates that fewer than one in 104 I–I2 collisions lead to the formation of I3.
Magnetic Circular Dichroism of Al2O3:V(III); the A23 → 3T2 No-Phonon Band and Possible A23 → 1A1 Ion Pair Transitions
Authors: Spencer J. A.
Published: February 2004

The magnetic circular dichroism and axial absorption spectra of the 6295-Å A23 → 3T2 no-phonon band in V(III)-doped corundum have been measured as a function of temperature and field under high resolution. The relatively concentrated crystal [∼ 1.5 mole% V(III)] used gave only a broad, featureless absorption. The MCD, however, clearly revealed the expected Ham effect fine structure first resolved in absorption studies of dilute samples by Scott and Sturge. Use of the nonuniform dynamic Jahn–Teller quenching model permitted direct prediction of the MCD band shape. Good agreement with both absorption and MCD data was found when component line half-widths were assumed to be ∼ 3 cm−1. In addition, sharp MCD satellite structure has been observed in the A23 → 1A1 transition. This is attributed to V(III) ion pair interactions in the corundum lattice.
Photoionization Mass Spectrometric Study of F2, HF, and DF
Authors: Berkowitz J. , Chupka W. A. , Guyon P. M. , Holloway J. H. , Spohr R.
Published: February 2004

From an analysis of the threshold region for formation of F2+ by photoionization of F2, the value 15.686 ± 0.006 eV has been deduced as the first ionization potential. The process F2+hν→F++F− begins at slightly lower energy and is traced to Landau–Zener-type crossing from certain Rydberg states to a potential curve leading to the separated ions in their ground states. The Rydberg states are those converging to the ground state of F2+, Π2. The ion-pair process is still significant at higher energy, in the vicinity of the threshold for the process F2+hν→F++F+e. Subtracting the intensity of F− from that of F+ in this energy region yields a corrected threshold of 19.01 eV, which gives D0(F2) = 1.59 ± 0.01 eV. The photoionization of HF (and DF) also gives rise to these three prominent processes, i.e., parent ionization, pair formation, and dissociative ionization. The ionization potential is found to be 16.007 ± 0.01 eV for HF (16.030 ± 0.01 eV for DF). The corrected threshold for H+ is 19.445 eV (19.513 eV for D+) which gives D0(HF) = 5.845 ± 0.01 eV. Quantitative descriptions are given for the autoionization peaks observed in both the F2 and HF spectra.
Application of the Statistical Phase-Space Theory to the Reactions of Rare-Gas Ions with Nitrogen Molecules
Authors: Fullerton D. C. , Moran T. F.
Published: February 2004

The statistical phase-space theory of chemical reactions has been applied to molecular and dissociative charge-transfer reactions of He+, Ne+, Ar+, and Kr+ with neutral N2 molecules in the 0.05–200-eV energy range. Comparison between calculated and experimental cross sections for the molecular charge-transfer channels have indicated an incomplete mixing of statistically available N2+ product ion electronic states. Cross sections computed for endoergic dissociative channels of reaction are in good agreement with experiment. Calculated product ion vibrational distributions have been compared with those inferred from product N2+ kinetic energies and with vibrational distributions obtained from spontaneous radiative transitions of excited N2+ ions produced in the respective ion–molecule reactions.
Raman Spectra for XeF2, XeF4, and XeOF4 Vapors, and Force Constant Calculations
Authors: Tsao Peter , Cobb Carlee C. , Claassen Howard H.
Published: February 2004

Raman spectra of the vapor phase have been observed for XeF2, XeF4, and XeOF4. These, together with published infrared spectra, provide vapor values for all but one of the 19 vibrational frequencies of these three molecules. Normal coordinates and force constants are determined in terms of the orbital valency force field model, including repulsions between lone-pair electrons and fluorine atoms.