bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Thermal Energy Transfer between Free Electrons and Molecular Vibration
Authors: Hurle I. R. 
Published: January 2005

Thermally averaged probabilities for the electron de-excitation of the first vibrational level in N2 are calculated from the discrete velocity-dependent collision cross sections measured by other workers. The results are presented for the electron temperature range 1000° to 5000°K. Over this range the probability is found to have an empirical temperature dependence of the form AT—1.8 exp (T⅓), with A=1.58×10—3. The probability increases from 10—4 at 1000°K to 10—2 at 5000°K. By comparison, the corresponding experimental probabilities for the de-excitation of N2 vibration by nitrogen molecules are 10—8 at 1000°K and 3×10—4 at 5000°K. These figures imply that in some circumstances an electron concentration of only 1 in 3×106 could halve the normal nitrogen molecular relaxation time at 1000°K, and that a concentration of 1 in 6×103 could do so at 5000°K. Existing spectrum-line reversal measurements of N2 vibrational relaxation carried out in nozzle-expansion flows in the presence of small amounts of easily ionized Na and Cr atoms are reviewed in the light of these findings. It is shown that the electron concentrations in these experiments were too low to have significantly influenced the relaxation measurements.
The relative rates of degradation of electron kinetic energy to the translational, rotational, and vibrational modes of N2 are considered on the basis of the above calculations. From these considerations it is proposed that in many nonequilibrium molecular systems the kinetic electron temperature will be closely coupled to the vibrational temperature of the molecules. Some results of current expansion-flow experiments which support this proposed coupling process are briefly mentioned, and its possible importance in relation to the extent of chemical and ionization nonequilibrium in other expansion flows of shock-heated air in hypersonic nozzles and around re-entry vehicles is discussed. It is suggested that free electrons, although present perhaps in small quantities, could be important in energy-degradation processes in these systems. Other existing observations in N2 plasms which appear to support the proposed coupling mechanism are reviewed.
Guest—Host Interactions: An Examination of the Solvent-Induced Spectral Shift in a Model System
Authors: Sun Huei-Ying , Rice Stuart A. , Jortner Joshua 
Published: January 2005

In this paper we study the effect of a surrounding lattice of He atoms on the manifold of electronic states of the H2+ molecule-ion. One-center expansions of the molecular wavefunctions are employed, calculated by the Tibbs—Wannier method. The spherically averaged wavefunctions are in good agreement with the known exact solutions.
A detailed study of the environmental effect of the He lattice leads to the prediction of a blue shift of the first electronic transition, arising from a delicate balance between changes in the impurity excitation energy, Coulomb, exchange, van der Waals, and three-center interaction terms. The signs of the various energy changes are rationalized in terms of the overlap charge density. These results are compared with previous treatments of environmental spectral shifts based on continuum models.
Far-Ir Spectrum of Dimethylacetylene: Internal Rotation and Evidence for a D6h Effective Symmetry
Authors: Kopelman Raoul 
Published: January 2005

The spectrum of dimethylacetylene vapor, liquid, and solid phases has been measured in the region 50 to 450 cm—1. Therefrom, together with previous work, a unique and ``complete'' vibrational assignment is derived. Rotational fine structure seems to confirm ``free internal rotation,'' i.e., a barrier below 100 cal/mole.
Dimethylacetylene is an ethane-type molecule with practically free internal rotation. The new data strongly confirm the previous conclusion that neither D3, D3h, or D3d are appropriate symmetry groups. The selection rules are consistent with a D6h effective symmetry.
An appendix deals with the relative intensities in degenerate vibrational transitions.
Molecular Motion and the Moment Analysis of Molecular Spectra. III. Infrared Spectra
Authors: Gordon R. G. 
Published: January 2005

The shapes of infrared rotation—vibration bands are analyzed theoretically in terms of their moments. The third and fourth moments of a band are found to increase when the molecular rotation is hindered, whereas the second moment is almost unchanged by the intermolecular torques. Explicit expressions are given for the third and fourth moments of interacting almost classical rigid asymmetric rotors, in terms of functions of the intermolecular torques, the temperature, the principal moments of inertia and the polarization direction of the transition. For the special case of a diatomic molecule or a parallel transition in a linear molecule, the theory is refined to include the first-order quantum corrections, the rotation—vibration interaction, and the effects of frequency shifts. The analysis is applied to available infrared spectra of carbon monoxide in gaseous, liquid, and solid pure phases and mixtures. Values of the mean-squared torque on the CO molecule are derived from the experimental data. It is found that the rotational motion of CO is strongly hindered in the solid, liquid, and highly compressed gas.
The mean-squared torque in gaseous CO and CO–Ar mixtures increases linearly with the density until densities close to those of the liquid. Therefore the intermolecular torques between CO–CO and CO–Ar must be of very short range. Sufficient data are available so that some tests of the consistency of this interpretation may be made.
Temperature Dependence of Pure Nuclear Quadrupole Spin—Lattice Relaxation in SnI4
Authors: Daniel Alfred C. , Moulton W. G. 
Published: January 2005

The pure nuclear quadrupole spin—lattice relaxation times for 127I in SnI4 have been measured over the temperature range from 4.2° to 300°K. Measurements were performed on both the 208- and 416-Mc/sec transitions. From the solution of the rate equations the transition probabilities, W1 and W2, corresponding to Δm=±1 and Δm=±2 transitions, are evaluated using the experimentally determined relaxation times. The ratio of the two required relaxation times is found to have a rather insensitive dependence upon W2/W1 and could be determined only at temperatures below 77°K. For temperatures below about 15°K a third relaxation time was required to describe the observed relaxation curves. Since cross-relaxation or spin—diffusion effects were not observed, the determination of the spin—lattice relaxation times from the stimulated echo was found to give far more accurate results than the conventional two-pulse technique.
The theory of quadrupolar relaxation developed by Bayer and the modification given by Woessner and Gutowsky have been reformulated for nuclei with spin 53. The third time constant required to fit the low-temperature data is predicted by either theory even though the details of the theory do not agree well with experiment results. The ratio W2/W1 is found from the experimental observations to increase by a factor of about 2 as the temperature decreases from 77° to about 7°K. The results obtained from Bayer and from Woessner and Gutowsky indicate an opposite effect. However, by assuming a temperature dependence for the molecular vibrational frequencies, better agreement can be obtained between the expressions for W2/W1 and the experimentally determined values. The temperature dependence of the lifetime of the molecular torsional oscillations has not been determined in detail and remains as a second parameter of poor definition. Because of the limited information describing the molecular torsional oscillations, relatively poor agreement is obtained between the theoretical and experimental determinations of the individual W1 and W2 transitions.
Dissociation Energies of Diatomic Molecules of the Transition Elements. I. Nickel
Authors: Kant Arthur 
Published: January 2005

The Ni2 molecule has been shown to exist in the vapor phase over liquid nickel above 2000°K.
Using information derived from a combination of effusion and mass-spectrometric techniques, the dissociation energy of Ni2 has been calculated from the ratio of dimeric and monomeric nickel in equilibrium with liquid: D00(Ni) = 54.5±5 kcal.
From the accepted value of the heat of sublimation of nickel and the dissociation energy of the dimer the heat of sublimation for the process 2Ni(solid) = Ni2(gas) is, at 0°K, 146.9±7 kcal.
Raman Spectrum of Polycrystalline Methyl Bromide
Authors: Ito Mitsuo 
Published: January 2005

The Raman spectrum of polycrystalline methyl bromide has been observed at 77°K. Two Raman bands at 585 and 594 cm—1 of ν3 were characteristic of rapidly cooled samples. The band at 585 cm—1 disappeared from samples slowly cooled or subjected to warming and cooling several times. The origin of the 585-cm—1 band is discussed and ascribed to the supercooled crystal or to the amorphous solid. Only the intramolecular fundamental ν5 has been observed to split due to the crystal field.
Four lattice vibrational frequencies have been obtained and their tentative assignments are presented.
Electronic Absorption Spectra of the Gaseous 3d Transition-Metal Dichlorides
Authors: DeKock C. W. , Gruen D. M. 
Published: January 2005

Electronic absorption spectra of gaseous VCl2, CrCl2, FeCl2, CoCl2, NiCl2, and CuCl2 have been measured near 1000°C and in the range 4000–50 000 cm−1. With the exception of VCl2, extensive vibronic structure was observed in the spectra of these molecules. The spectra are characterized by low intensity (ε=10–120 liter/mole·cm) dn←dn transitions in the 4000–22 000-cm−1 region and by higher intensity (ε=2500–24 000 liter/mole·cm), transitions in the 19 000–50 000-cm−1 region.
The dn←dn transitions are reasonably well fitted by A2=±900 cm−1, A4=±100 cm−1, the two ligand-field parameters appropriate for a molecule of symmetry D∞h. The narrow band (half-width ∼120 cm−1) at 11 727 cm−1 in NiCl2 is assigned to a 1Σ(1D)←3π(3F) transition.
Internal Rotation in Completely Asymmetric Molecules. II. Interactions between Vibration and Internal Rotation
Authors: Quade C. Richard 
Published: January 2005

The theory of internal rotation for molecules with asymmetric internal rotors is extended to include the interactions of normal vibrations with the hindered internal rotation. The Sayvetz condition is derived for separation of internal rotation and vibration in zeroth order in the kinetic energy. Then the complete Hamiltonian is developed which includes the effect of the α dependence of the vibrational kinetic energy as well as those terms which are introduced through the reduction in symmetry of the vibrationally distorted molecule. An effective internal, over-all rotation Hamiltonian is isolated for the vth vibrational state by a Van Vleck transformation.
The behavior of various terms in the Hamiltonian are examined in detail in the case of molecules for which both the framework and top possess planes of symmetry. Particular attention is devoted to the use of symmetry properties in discussing the α dependent properties of the Hamiltonian. Perturbation theory is used to obtain an effective rotational Hamiltonian for the nth torsional state. It is found that the structure of some rotational transitions is sensitive to particular new terms which are introduced by vibration. The microwave spectra of CH2DCOH and CHD2COH are analyzed on a parametric basis.
Relativistic Intermolecular Forces, Moderately Long Range
Authors: Meath William J. , Hirschfelder Joseph O. 
Published: January 2005

The generalized Breit—Pauli Hamiltonian is used to give a systematic treatment of magnetic and other relativistic intermolecular energies through O(α2) (where α is the fine-structure constant) for intermolecular separations, R, sufficiently large that the charge distributions of the two molecules do not overlap, but sufficiently small that R&lt;λ/0=(αΔε)−1, where Δε is the excitation energy of the first allowed transition of one of the molecules.
The theory is discussed in general and many types of interaction energies are obtained which depend on the spin and orbital angular-momentum states of the molecules. The interaction of two nondegenerate atoms (L=0, S=0) is considered specifically. Of particular interest is an interaction-energy term which varies as α2/R4.
Formation of N2(A3Σu+) and N(2D, 2P) by Photodissociation of HN3 and N2O and Their Reactions with NO and N2O
Authors: Welge Karl H. 
Published: January 2005

The formation of NO (A 2Σ+) and NO (B 2II) in the photolysis of N2O at 1236 and 1470 Å was investigated by observing the fluorescence of the γ and β bands. The β-band fluorescence is obtained when pure N2O is photolyzed at 1236 and 1470 Å in a flow system. The β bands are observed with vibrational excitation up to v′=3. The β bands disappear with the addition of small amounts of NO, whereas the emission of rotationally hot γ bands is obtained. The γ bands are observed with vibrational excitation up to v′=2. According to the energetics, NO (A 2Σ+) and NO (B 2II) are formed at 1470 Å as well as at 1236 Å not by direct photodissociation of N2O but by secondary reactions. No fluorescence is obtained when N2O or N2O/NO mixtures are irradiated at wavelengths ≧1600 Å, i.e., within the long-wavelength absorption band of N2O. The roles of N2 (A 3Σu+), N (2D), N (2P) are evaluated and discussed.
The emission of γ bands is also obtained in the photolysis of HN3/NO mixtures at 1470 and 1236 Å. This observation is explained by the photodissociationHN3→N2(A Σu+)+NH(X 3Σ−)followed by the reaction between N2 (A 3Σu+) and NO, yielding NO (A 2Σ+). The other possibility, that O atoms which are formed by photodissociation of NO react with HN3 to form excited NO—as in the O/N2H4 atomic flame—is excluded.
Molecular Orbital Theory of Sulfur and Selenium Radicals
Authors: Chen Inan , Das T. P. 
Published: January 2005

The electronic structures of various sulfur and selenium radicals were studied by semiempirical molecular orbital theory in the form of a parameter theory. The ESR data (g values) were used to determine the actual value of the parameter α, which is the coefficient of the s orbital in the bonding hybrid of the S(Se) atom in the radical. The physical significance of α so determined was studied by investigating some quantum chemical quantities such as valence state energies Ev and bond strengths B as functions of α. As a result, a criterion for the determination of the parameter value was deduced, namely, the selection of that value of α which maximizes B2 | Ev |.
From theoretical considerations and experimental data in the literature, the relative signs of the principal values of the hyperfine-structure tensor of selenium were determined, and the magnitudes of the isotropic and anisotropic components were evaluated.
Energetic and Angular Studies of ArD+ and N2D+ Formation
Authors: Doverspike L. D. , Champion R. L. , Bailey T. L. 
Published: January 2005

The reactions Ar++D2→ArD++D and N2++D2→N2D++D have been studied with an angular ion-scattering apparatus at ion laboratory energies in the range 2–100 eV. Kinetic-energy distributions as well as angular distributions of the product ions have been determined. The experimental method consists of directing a mass-analyzed and velocity-selected ion beam into a collision chamber containing target gas at low pressure. The product ions are velocity analyzed with a 127° electrostatic velocity selector and mass analyzed in a quadrupole field radio-frequency mass filter. The product-ion analysis and detection system rotates about the center of the scattering region. It is found that the observed Q values for these reactions (where Q is the energy transformed from internal to translational) show a marked dependence on the primary-ion kinetic energy, E1. The Q values for both reactions are endothermic over the entire energy range of these experiments, being approximately zero at the lowest energies and exhibiting endothermic maxima in the region 50&lt;E1&lt;60 eV. It is shown that these maxima correspond to the formation of internally excited product ArD+ and N2D+ ions, with excitation energies approximately equal to the dissociation energies for ArD+→Ar+D+ and N2D+→N2+D+. The product-ion kinetic-energy distributions also give evidence of back scattering in the center-of-mass system. The energetic and angular features of both reactions are essentially the same, indicating that the collision mechanisms leading to the formation of both product ions do not differ significantly.
The experimental results indicate that both reactions proceed according to a ``pickup'' mechanism at moderate coilision energies. At very low collision energies the results suggest that complex formation may become important.
Diffusion of Triplet Excitons in Crystalline Anthracene
Authors: Levine Menahem , Jortner Joshua , Szöke Abraham 
Published: January 2005

In this work we present an experimental study of triplet-exciton diffusion in crystalline anthracene. Triplet-exciton lifetime was determined by the time intermittency method, while the diffusion coefficients and the components of the diffusion tensor were determined by the space intermittency technique. From the comparison of the experimental data with the results of the theoretical analysis we conclude that:
(a) The magnitude of the diffusion coefficient for triplet excitons [D=(2.0±0.5)×10−4cm2/sec] yields a strong support for the strong scattering random-walk model for triplet-exciton migration in crystalline anthracene.
(b) The diffusion tensor of triplet excitons in crystalline anthracene was found to be isotropic.
(c) The isotropy of the diffusion tensor in the ab plane can be properly accounted for in terms of the calculated intermolecular electron exchange and charge-transfer interactions.
Adsorption of Potassium on Tungsten: Measurements on Single-Crystal Planes
Authors: Schmidt L. D. , Gomer R. 
Published: January 2005

Work functions of the (110), (211), (100), and (111) regions of a thermally annealed tungsten field emitter were measured as a function of potassium coverage. Immobilely adsorbed layers yielded absolute dipole moments, permitting estimates of adsorbate charge. The results at low coverage are μ110=15.7 D, μ211=13.6 D, μ100=11.5 D, μ111=9.5 D, with μ defined as 2qd0=Δφ/2πn. At coverages θ≳0.6 there is evidence of higher layer formation and field enhancement. Work functions after thermal equilibration in combination with φ-vs-n data for immobilely adsorbed deposits yielded coverage anisotropies under equilibrium conditions. At θ̄≈0 n110/n̄=40,n211/n̄=0.35,n111/n̄&lt;0.04,n100/n̄&lt;0.01. As θ increases the anisotropies decrease, and for θ̄≳0.5 the ratios n̄→1 for all regions except 100. The corresponding differences in heats of adsorption at θ̄≈0 are less than 0.4 eV for all regions except possibly 100, with binding strongest on 110. A quantum-mechanical model is briefly sketched, and a quasistatistical treatment of alkali adsorption is outlined. It is shown that the small differences in H for substrate regions of considerably different work function and structure can result from the near cancellation of variations in explicitly electrostatic effects and exchange effects.
The φ-vs-n curves on single planes can be fitted by a simple depolarization model leading to values of the ad-complex polarizability of 26 Å on (110), 46 Å on (211), 35 Å on (100), and 29 Å on (111). It is shown that the concept of ad-complex polarizability follows naturally from the statistical model.
On the Hyperfine Structure of InH and the Theory of the Hyperfine Structure of Molecules in Hund's Case (C)
Authors: Freed Karl F. 
Published: January 2005

The hyperfine structure in the 3Π1 state of InH, which deviates strongly from the magnetic hyperfine interval rule, is explained by the electric quadrupole interaction of the In nucleus. The quadrupole coupling constant for the 3Π1 (v=0) state eQqπ is +0.1 cm−1±100%. The off-diagonal quadrupolar interaction, namely the eQ sin2θ exp (±2iφ)/r3 part, gives an F-dependent contribution to the Λ-type doubling of the 3Π1 (v=0) state, eQq′ = +0.066 cm−1(2000 Mc/sec)±50%. An upper limit to the quadrupole coupling constant of the X 1Σ+ (v=0) state is ∼|eQqx|≳0.07 cm−1±100%.
The theory of hyperfine structure in Hund's Case (c) is discussed, and the matrix elements of the hyperfine interactions are evaluated for two Case (c) coupling schemes for a diatomic molecule with two nuclear spins. The matrix elements are evaluated by the generalization of Van Vleck's method of reversed angular momenta to spherical tensor form.
Flash Desorption and Isotopic Mixing of Hydrogen and Deuterium Adsorbed on Tungsten, Iridium, and Rhodium
Authors: Mimeault V. J. , Hansen Robert S. 
Published: January 2005

Flash desorption of hydrogen from tungsten, iridium, and rhodium dosed at 100° and 300°K was investigated together with isotope mixing in coadsorbed mixtures of hydrogen and deuterium.
The desorption of hydrogen from tungsten, iridium, and rhodium dosed at 300°K proceeds by a second-order process with an activation energy of desorption well represented by ΔH=ΔH0—αn. At low surface coverages, values of 35, 24, and 18 kcal/mole, respectively, were obtained for ΔH0; the parameter α was determined from desorption curves at higher initial coverages and was found to be 28±2, 14±1, and 24±2 kcal/mole (1015 molecules/cm2)−1, respectively.
The desorption spectrum of hydrogen from these metals dosed at 100°K contains two peaks, α and β. The distribution of the isotopes in the desorbed phase formed from coadsorbing H2 and D2 indicates that the α peak is due to an atomic species in the case of iridium and rhodium and a molecular species in the case of tungsten.
Absorption Spectrum of Fluorine in the Vacuum Ultraviolet
Authors: Iczkowski Raymond P. , Margrave John L. 
Published: January 2005

The absorption spectrum of F2 has been observed in the vacuum ultraviolet region. A special windowless absorption apparatus and a Lyman discharge light source were used in combination with a one-meter normal incidence spectrograph.
A Rydberg series establishes the ionization potential of F2 as 15.7 ev. From a progression of bands at 874 A, one can deduce the dissociation energy of fluorine as 37.5±2 kcal/mole. The binding energy of F2+ is 3.3 ev. The low value of the ionization potential is consistent with the observed low value of the dissociation energy.
Paramagnetic Resonance of Bis-Cyclopentadienyl Vanadium
Authors: McConnell H. M. , Porterfield W. W. , Robertson R. E. 
Published: January 2005

The paramagnetic resonance spectrum of a benzene solution of bis-cyclopentadienyl vanadium shows a g factor equal to 2.00 and a V51 isotropic hyperfine splitting equal to 77 Mc. The small V51 hyperfine splitting demonstrates that none of the three odd electrons in this sandwich compound spends an appreciable part of its time in a 4s atomic orbital of the vanadium atom. The observed spectroscopic splitting factor shows that the orbital ground state is a singlet. This result signifies that one of the three unpaired electrons in this substance must be in an orbital of a1g symmetry, and that the other two electrons must be in orbitals of eg symmetry. This latter conclusion is in good agreement with theoretical orbital energy levels derived by a number of investigators.
The paramagnetic resonance spectrum of an air oxidation product of bis-cyclopentadienyl vanadium has been observed. The spectroscopic splitting factor is g=1.99 and the hyperfine splittings are 210 Mc. It is suggested that the oxidation product may be the neutral vanadyl sandwich, VO (C5H5)2.