bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared and Raman Spectra of Solid Beryllium Borohydride, BeB2H8
Authors: Nibler Joseph W. , Shriver Duward F. , Cook Thomas H.
Published: February 2004

Infrared and Raman spectra of solid BeB2H8, BeB2D8, Be10B2D8, and BeB2D7H have been obtained at 20 and 180°K. These data indicate that a structural change occurs in going from the vapor to the solid and suggest the presence of the borohydride anion, BH4−, paired with an unusual hydrogen bridged cation, +BeBH4. A detailed examination of the isotopic frequency shifts supports this view and an excellent fit of the BH4− frequencies is obtained from a normal coordinate analysis. Reasonable assignments of the +BeBH4 fundamentals are given and the structure of the +BeBH4 ion is discussed.
Principle of Corresponding States in the Phase Transition of Solid Methanes
Authors: Nakamura Tuto , Miyagi Hiroshi
Published: February 2004

Quantum corrections for the orientational distribution function of tetrahedral molecules in a potential field are presented. By taking the primary correction into account and applying the resulting distribution function to the theory of phase transitions based on the Hartree approximation, we predict TC + Θ = const for the upper transition of various isotopic methanes, where TC is the transition temperature and Θ a quantum mechanical parameter dependent on the moment of inertia: kBΘ = ℏ2 / I, (ℏ2 / 3) (2 / I1 + 1 / I3), (ℏ2 / 3) (1 / I1 + 1 / I2 + 1 / I3), respectively, for spherical, symmetric, and asymmetric rotors. This prediction agrees very well with measured results. For the lower transition, we predict TC + 2Θ = const, which is rather close to a linear equation, TC + (5 / 3)Θ = const, to be expected from measured results. The concentration dependence of the upper transition temperature of mixed solids CH4–CD4 is studied, in excellent agreement with the measurements.
Vibrational Spectrum and Analysis. Silver Azide Crystals
Authors: Bryant James I. , Brooks Robert L.
Published: February 2004

The vibrational spectrum (infrared, Raman, and far infrared) of silver azide crystals has been measured over the frequency range from 40 to 4000 cm−1. A factor-group analysis was carried out for the classification and determination of selection rules of the k ≃ 0 vibrational modes of the crystals. Individual assignments are made for the modes due to lattice transitions, the multiplicity of fundamentals in the infrared and Raman, and for numerous combinations constituting fine structure in the medium infrared. Observed band structure of single-crystal spectra are strongly influenced by crystal structure orientation with respect to the incident beam. Numerical checks are provided for the assignment of essentially all combinations and indirect determinations are made of the frequencies of several modes which are neither infrared nor Raman active. Discussion is made of observed absorptions which apparently are not governed by factor group selection rules. The over-all observed spectrum is in general agreement with the reported crystal structure, D2h26—Ibam.
Dielectric Relaxation in α, ν-Dibromoalkanes
Authors: Chandra Suresh , Prakash Jai
Published: February 2004

The dielectric constant and loss of 1,3-, 1,4-, 1,5-, and 1,6-dibromoalkanes have been measured at the frequencies 1.8 mHz, 2 GHz, 4 GHz, 10 GHz, 22 GHz, and 37 GHz and at 30, 40, 50, and 60°C. The complex plots of dielectric loss against dielectric constant have been found to be skewed arcs, which are discussed in terms of (i) the Davidson–Cole representation as a result of intramolecular cooperative relaxation and (ii) superposition of two noninteracting Debye-type absorptions. The relevant thermodynamic parameters are also evaluated.
Experimental Study on the Wavelength Dependence of the Raman Scattering Cross Sections
Authors: Kato Yoshiaki , Takuma Hiroshi
Published: February 2004

The Raman scattering cross sections of the 992-cm−1 line of C6H6, the 1002-cm−1 line of C6H5CH3, the 1345-cm−1 line of C6H5NO2, the 656-cm−1 line of CS2, and the 459-cm−1 line of CCl4 were measured with the laser excitation at 4880, 5145, and 6328 Å. The standard deviations were 3.1%–3.6%. The wavelength dependences of the results show exact agreements, except the 1345-cm−1 line of C6H5NO2, with a simplified theory in which the resonant effect of only one resonant electronic level is taken into account.
Adsorption of Neon on Graphitized Carbon. I. The Heat Capacity of Adsorbed Neon between 1.5 and 6°K
Authors: Antoniou A. A. , Scaife P. H. , Peacock J. M.
Published: February 2004

The heat capacity of adsorbed neon on graphitized carbon, Spheron 6, was measured in the temperature range 1.5–30°K for two coverages, namely, 0.5 and 1.5 monolayers. The heat capacity values for both coverages show that the state of the adsorbate is liquidlike at temperatures close to the bp of the adsorbate. As the temperature is lowered, a peak in the heat capacities is observed. The temperature at which this peak is observed depends on the coverage, and is lower at the lower coverage. These peaks suggest that a transition takes place, and that this transition is a `melting' process. The observed low temperature heat capacities depend markedly on coverage, and their values are higher at the lower coverage. This dependence of the heat capacity on coverage can be explained if the localized adatoms are considered as asymmetric three-dimensional oscillators and the two-dimensional component of these oscillators (parallel to the surface) contributes the larger portion to the heat capacity. Entropies were calculated from the observed heat capacities for 0.5 monolayers and are compared with those calculated from the partition function of independent three-dimensional localized oscillators. The frequencies considered for these oscillators are reported. The observed heat capacities for the 1.5 monolayers coverage show that the state of the adsorbate at this coverage differs markedly from that of the bulk state.
An Ab Initio Study of the Zero Field Splitting Parameters of B13 Methylene
Authors: Harrison James F.
Published: February 2004

The spin–dipole contribution to the zero field splitting parameters of methylene in the B13 state has been studied as a function of geometry. At the computed equilibrium geometry of RCH = 1.05 Å and θ = 132.5° we find D = 0.71 cm−1 while E = 0.05 cm−1 (experimental= 0.69 and 0.003 cm−1, respectively). The dependence of E / D on bond angle, bond length, and percent s character in the lone-pair density is examined. Our results suggest that the spin–orbit contribution to D and E in methylene is negligible.
Fluorescence Efficiencies of Nitrogen Excited by 1–5-MeV Positive Ions
Authors: Dunn Jerry L. , Holland Redus F.
Published: February 2004

Fluorescence efficiencies for excitation of nitrogen by 1–5-MeV positive ions have been measured at pressures of 2–19 torr. Typically, N2 pressure of 3.6 torr was required to stop a beam of 4-MeV Ne+ in the 1.5-m-long collision chamber. Power output in the 3914-Å (0, 0) N2+ first negative band was measured with a photometer, and low-pressure efficiencies were calculated from the collisional deactivation rate. For Ne+, O+, N+, N2+, and O2+ ions with various initial velocities from 3.1 to 8.3 × 108 cm/sec, the low-pressure efficiencies were between 0.4% and 0.6%. 3914-Å efficiencies were, for 2.0 and 3.4 × 108 cm/sec Kr+, 0.27% and 0.35%, and for 1.38 × 109 cm/sec H+, 0.67%. Spectra of the nitrogen emission in the 3400-7800-Å range were recorded. N2+ first negative and N2 first and second positive bands were prominent, with most first negative in the υ′ = 0 vibrational sequence, and most second positive in the υ′ = 0 − 2 sequences. The spectra were corrected for collisional quenching and low-pressure efficiencies were determined relative to the 3914-Å band. For 4–5-MeV, N+, Ne+, N2+, and Kr+, total efficiencies for the second positive υ′ = 0 − 2 sequences were about 1.5 times the 3914-Å efficiencies. Efficiencies were determined for 10 first positive bands of the υ′ = 2 to 7 sequences excited by 4.75-MeV Ne+; the (2, 0) and (3, 1) band efficiencies, for example, were about one-fourth the 3914-Å efficiency of 0.52%. The nitrogen fluorescence excited by the ions has a spectral intensity distribution similar to those observed by Hartman for 850-eV electrons in air and by Mitchell for 1.5-keV x rays in N2.
31P and 1H Spin–Lattice Relaxation in Several Substituted Phenylphosphines in the Liquid State
Authors: Seymour S. J. , Jonas J.
Published: February 2004

The temperature dependences of the 31P and 1H spin–lattice relaxation times of dichlorophenylphosphine, chlorodiphenylphosphine, and triphenylphosphine have been measured by the adiabatic fast passage method. Both dipolar and spin–rotation interactions contribute to the 31P relaxation mechanism in dichlorophenylphosphine and chlorodiphenylphosphine whereas only dipolar interactions provide the mechanism for the 1H relaxation in all three compounds studied. As the high-temperature limit of the measurements was 160°C, no spin–rotation interactions were observed for the 31P relaxation in triphenylphosphine. The calculations of the approximate potential functions for the internal rotation about the C–P bond in dichlorophenylphosphine and chlorodiphenylphosphine indicate hindered rotation and thus the spin–rotation mechanism arises mainly from spin–over-all-rotation coupling. Spin–rotation constants were estimated for 31P in dichlorophenylphosphine and chlorodiphenylphosphine from relaxation data and shielding constants. In addition to relaxation measurements, the temperature dependences of densities and viscosities of dichlorophenylphosphine and chlorodiphenylphosphine have also been measured.
Crystal-Field Spectra of d3,7 Ions. VII. Cr3+ in K2NaGaF6
Authors: Ferguson J. , Guggenheim H. J. , Wood D. L.
Published: February 2004

The T2g4 level of Cr3+ in K2NaCrF6 and in K2NaGaF6:Cr3+ is strongly mixed with the Eg2 and T2g2 levels by spin–orbit coupling in the six-coordinated cubic (Oh) site. The observed band profile for absorption and fluorescence in the transitions A2g4 ↔ 4T2g in the dilute system shows remarkably well-resolved vibrational band progressions which have been analyzed in terms of a totally symmetric vibration at 568 cm−1 (556 cm−1 for the excited state) and a large number of nontotally symmetric vibrations ranging from 25–961 cm−1.
Study of the Electronic Structure of Molecules. XIII. Bond Energy Analysis for the Ethane Molecule
Authors: Clementi E. , von Niessen W.
Published: February 2004

The total energy of the C2H6 molecule has been decomposed into one-, two-, three-, and four-center energy contributions, according to a scheme previously proposed (“bond energy analysis”). This was done for the eclipsed, for the staggered configurations, and for rotational angles of 10°, 30°, and 50°. It has been found that the 4 two-center energies of the carbon atom with its four nearest neighbors are nearly equal (the C–H being 94% of C–C), that the hydrogen–hydrogen repulsion within a given methyl group is about one-tenth of the two-center C–C attraction, and that the repulsion of a carbon on one methyl group with the hydrogens on the other methyl group is about 1.5 tenths of the C–C interaction. The repulsion of one hydrogen on one methyl group with a hydrogen on the other methyl group is small and varies around 0.2 tenths of the C–C interaction. During rotation, the field within each methyl group (taken as a unit) varies in such a way as to bring about an energy variation which opposes the barrier. On the other hand, the methyl–methyl interaction more than compensates this effect, yielding a barrier of about 3.1 kcal. In greater detail we conclude that whereas the carbon–carbon interaction favors the barrier, the rearrangement within the carbon opposes the barrier but not as much as to compensate the C–C interaction, that the rearrangement of the H3 group is more important than the interaction between the two H3 groups, and that the carbon on a methyl group interacting with the H3 of the second methyl group has an interaction of such a sign as to favor the barrier, whereas the opposite is true for the interaction of a carbon atom and H3 on the same methyl group. The bond energy analysis seems to propose a model of “checks and balances” involving local energy variations much larger than the small rotational barrier (computed within good agreement of the experimental barrier); thus, the barrier is a result of heavy cancellation of large energies with opposite sign. A word of caution concerning some of the arbitrariness of the “bond energy analysis” formalism has been inserted frequently in this paper. However, the bond energy analysis on the C2H6 molecule seems to be a tool of value for explaining not only the balance of forces but also to give a detailed model of the barrier to internal rotation.
Dickinson Energy of H2+
Authors: Weinhold Frank
Published: February 2004

Dickinson's function for H2+ is recalculated for the 1sσg and 2pσu states at nuclear separations up to 20 a.u. Although inadequate near the ground-state minimum, the Dickinson function is very good for larger separations, and describes quite accurately the shallow potential minimum (De ≈ 0.015 eV, Re ≈ 12.6 a.u.) in the “repulsive” 2pσu excited state.
Raman Spectrum of Calcium Carbonate at High Pressures
Authors: Fong Mei Y. , Nicol Malcolm
Published: February 2004

Raman spectra of calcite, CaCO3 II, and CaCO3 III have been studied at various pressures as high as 40 kbar. Thirteen lines have been observed in the previously unreported spectrum of CaCO3 II and 20 lines are reported for the CaCO3 III spectrum. These spectra are compared with Raman spectra of aragonite, KNO3 III, and KNO3 IV; and previous suggestions that CaCO3 II and KNO3 III may be isostructural and that CaCO3 III and KNO3 IV also may be isostructural are shown to be incorrect. Alternative structures for CaCO3 II and CaCO3 III are briefly considered.
Study of H+NO2 in an Argon Matrix between 4 and 14°K; The Infrared Spectra of Matrix-Isolated cis- and trans-HONO
Authors: Guillory William A. , Hunter Charles E.
Published: February 2004

The matrix-isolated infrared spectra of cis- and trans-nitrous acid molecules have been obtained in argon at low temperatures by the reaction of H atoms with NO2. The spectra, which include 15N- and 18O-substituted molecules, are not complicated by the stabilization of the acid in the presence of large concentrations of NO, NO2, and H2O. All six fundamentals of the cis and three of the trans isomers have been identified, and found generally to confirm the assignments of a previous study where some uncertainty did exist. The normal coordinate calculation performed for the cis molecule predicted the average frequencies of the four 15N- and 18O-substituted species with an error of 0.60 cm−1 or 0.068%.
Properties of the Latent Roots of a Matrix: The Estimation of π-Electron Energies
Authors: McClelland B. J.
Published: February 2004

The eigenvalues λi of an Hermitian matrix A of order n satisfy the inequality ∑ i = 1n | λi | ≤ n1/2N, where N is the Frobenius norm of A. Let n and ν be, respectively, the numbers of atoms and bonds in the conjugated system of a hydrocarbon, and let E be the corresponding Hückel matrix. Then the Hückel π-electron energy is nα + εβ, where [2ν + n(n − 1)| detE |2/n]1/2 ≤ ε ≤ (2nν)1/2. Analogous bounds are obtained for π-electron energies calculated by Wheland's method. An approximation for the Hückel π-electron delocalization energy (DE) in the closed-shell ground state of a hydrocarbon is DE / β = an1/2 − n + r, where a ≈ 1.30, and r = 0 or 1, according as n is even or odd.
Structures of the Excited States of Benzil and Related Dicarbonyl Molecules
Authors: Morantz D. J. , Wright A. J. C.
Published: February 2004

Nonhindered aromatic α-dicarbonyl molecules show abnormal spectroscopic behavior when compared to other molecules containing carbonyl groups. Taking benzil as a typical example, its photoabsorption and emission spectra cannot be accounted for by the normal Jablonski scheme. The spectral data are consistent with a mechanism involving molecular reorientation. It is postulated that photoexcitation of benzil causes it to change from its normal skew configuration into one in which the dicarbonyl system becomes coplanar while it is in the excited singlet state. As a consequence photoemission (both fluorescence and phosphorescence) takes place from this configuration, resulting in a ground-state molecule with the same nuclear configuration as the excited state; relaxation then occurs to the normal configuration. Formation of a trans configuration is most likely to occur on photoexcitation, but a cis configuration cannot be ruled out. The formation of a coplanar dicarbonyl system must involve movement of the phenyl groups into positions out of the dicarbonyl plane. Additional support for this mechanism is obtained from the energetics of the various processes.
Transient Ion Cyclotron Resonance Method for Studying Ion–Molecule Collision and Charge-Transfer Rates: N2+ and CH4+
Authors: Dunbar Robert C.
Published: February 2004

A heterodyne technique of ion cyclotron resonance is described and shown to give spectra having the form of an exponentially damped sinusoidal curve. The rate of damping is related to the collision and charge-transfer rates in the ion–molecule system. The generalized ICR equations required to analyze the data are developed and solved and are shown to fit experimental spectra very closely. Results for N2+ in N2 agree well with mobility data and with ICR linewidth studies and indicate substantial probability for charge transfer. Results for CH4+ in CH4 are found to rule out any substantial charge-transfer cross section.
Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules
Authors: Ditchfield R. , Hehre W. J. , Pople J. A.
Published: February 2004

An extended basis set of atomic functions expressed as fixed linear combinations of Gaussian functions is presented for hydrogen and the first-row atoms carbon to fluorine. In this set, described as 4–31 G, each inner shell is represented by a single basis function taken as a sum of four Gaussians and each valence orbital is split into inner and outer parts described by three and one Gaussian function, respectively. The expansion coefficients and Gaussian exponents are determined by minimizing the total calculated energy of the atomic ground state. This basis set is then used in single-determinant molecular-orbital studies of a group of small polyatomic molecules. Optimization of valence-shell scaling factors shows that considerable rescaling of atomic functions occurs in molecules, the largest effects being observed for hydrogen and carbon. However, the range of optimum scale factors for each atom is small enough to allow the selection of a standard molecular set. The use of this standard basis gives theoretical equilibrium geometries in reasonable agreement with experiment.
Infrared Spectra of Divalent Metal Monothioacetylacetonates
Authors: Siimann Olavi , Fresco James
Published: February 2004

The infrared spectra of copper (II), nickel (II), zinc (II), palladium (II), cadmium (II), and lead (II) complexes of monothioacetylacetone have been recorded from 1700–300 cm−1. Assignments for in-plane vibrations were obtained by normal coordinate analyses. The carbon–oxygen stretching vibration was located near 710 cm−1. In every case metal–oxygen stretching force constants were larger than metal–sulfur constants and carbon–sulfur constants were less than carbon–oxygen constants. Systematic trends which appeared among both metal–sulfur and metal–oxygen stretching force constants were correlated with sequences observed among the carbon–donor atom force constants.
Proton Spin–Lattice Relaxation in HCl–Ar Mixtures
Authors: Leonardi-Cattolica A. M. , Prins K. O. , Waugh J. S.
Published: February 2004

Proton spin–lattice relaxation times have been measured in gaseous HCl as a function of density and in gaseous HCl–Ar mixtures as a function of temperature and composition. Values of T1 have been extracted from the experimental data on mixtures which are appropriate to pure HCl and to HCl infinitely dilute in Ar in the density regions where only binary collisions are important. The spin–rotational interaction provides the the only important relaxation mechanism. Cross sections for changes in rotational angular momentum are estimated for HCl–HCl and HCl–Ar collisions.
Temperature Dependences of Kinetic Isotope Effects
Authors: Vogel P. Christian , Stern Marvin J.
Published: February 2004

Model-reaction calculations are used to investigate the expected incidence of temperature-dependence anomalies produced by the harmonic-vibrational contributions to kinetic isotope effects. These “anomalies” are defined as deviations from a smooth-monotonic log–log plot of isotopic rate-constant ratio vs temperature. Such deviations include inflections, extrema, and crossovers (inversions in direction with respect to the infinite-temperature, classical limit). The model systems studied represent a variety of mechanisms ranging from simple bond break to simultaneous rupture or formation of four bonds. The effects on the temperature-dependence-curve shapes of off-diagonal force-constant changes, variations in potential-barrier curvature, and tunneling corrections are examined. The major emphasis is on carbon and hydrogen isotope effects although some nitrogen and oxygen effects are also considered. Out of the 476 isotopic reaction pairs investigated, approximately 25% were found to be anomalous. Several examples of corresponding deuterium and tritium isotope effects exhibiting different types of temperature-dependence anomalies were found. Situations most likely to lead to anomalous temperature behavior are discussed. It is concluded that kinetic-isotope-effect temperature-dependence anomalies should occur fairly commonly although, at least for monosubstitution with carbon and hydrogen isotopes, probably less frequently than in equilibrium isotope effects. However, the anomalous region of a temperature-dependence curve might not fall within the range of experimental accessibility. No method of detecting an anomaly from observation of a portion of the temperature-dependence curve removed from the anomalous region has been found. It is shown that the quality of data fitting with the gamma-bar approximation cannot be used as a reliable criterion of nonanomalous temperature behavior. The significance of kinetic-isotope-effect temperature-dependence anomalies to investigations of reaction mechanisms is discussed with respect to both approximation methods and model-calculation force-field-fitting procedures.
Crystal-Field Splittings of f3 Systems: Covalency Effects
Authors: Sengupta D. , Artman J. O.
Published: February 2004

Using a simple molecular-orbital method, we have determined the A40〈r4〉 and A60〈r6〉 crystal-field parameters for both the Nd3+(4f3)- and U3+(5f3)-doped CaF2 systems. We have compared these theoretical parameters to those derived experimentally from fits to the observed energy-level structures. We also have calculated these parameters using the point-charge lattice-sum model. The molecular-orbital treatment yields the better results.
Far-Infrared and Raman Spectra of Arsonium Iodide
Authors: Durig J. R. , Pate C. B. , Li Y. S.
Published: February 2004

The infrared spectrum of thin films of AsH4I has been recorded from 33 to 4000 cm−1 at − 170°C. Raman spectra of polycrystalline samples were also recorded at − 170°C. Two librations and three translations have been assigned, and seven internal fundamentals were observed. Other bands found in the midinfrared and Raman spectra are attributed to overtone and/or combination bands involving external and internal fundamentals. Static field and correlation field splittings of approximately 25 and 10 cm−1, respectively, were observed. The vibrational data are consistent with a crystal structure of D4h7-P4/nmm with D2d site symmetry for the arsonium ion. The barrier restricting arsonium ion rotation was calculated from the observed librational frequency (317 cm−1) to be 6.9 kcal/mol. The barrier is compared to those previously obtained for the phosphonium halides.
Kinematic Model for Reaction. III. Detailed Dynamics of the Reaction of Ar+ with D2
Authors: George Thomas F. , Suplinskas Raymond J.
Published: February 2004

The kinematic model for the reaction is extended to the prediction of detailed dynamical properties of reaction: product angular and velocity distributions, differential reaction cross sections, and internal energy distributions. The dynamics of nonreactive scattering are also treated. The model is applied to the Ar++D2↝ArD++D reaction for Ar+ energies of 30, 50, and 75 eV. Good agreement with experiment is obtained. The results imply that in the relative energy range corresponding to several electron volts, the chemical process is dominated by the repulsive core interactions appropriately modified by elastic intermolecular potentials; simple mechanical considerations can characterize the process on this basis. Within the framework of the model, the forward peaking or “stripping” character of the differential reaction cross section is entirely dependent upon the attractive elastic intermolecular potential between receding products; a strongly backward peaked or “rebound” differential reaction cross section is obtained when this potential is not present.
Kinematic Model for Reaction. IV. Orientation and Isotope Effect in the Ar++HD Reaction
Authors: George Thomas F. , Suplinskas Raymond J.
Published: February 2004

The kinematic model for reaction is used to evaluate the influence of molecular reorientation on the isotope effect in the reaction of Ar+ with HD. Since the centers of mass and charge do not coincide in HD, there is a torque on the molecule during the approach of the ion which enhances the possibility of collision with the hydrogen end of the molecule. Calculations were performed both with and without this effect for Ar+ lab energies in the range 10–70 eV. The results below 30 eV have no quantitative significance, but indicate that orientation could have a considerable effect. At higher energies, both calculations give quite reasonable predictions of the isotope effect; the orientation effect provides a noticable but small difference in the results. The range of relative kinetic energies for which the predicted isotope effects are within experimental error is the same range in which the kinematic model provides relatively accurate predictions of product angular and velocity distributions.
Isotopic Studies of the Proton–Hydrogen Molecule Reaction
Authors: Holliday M. G. , Muckerman J. T. , Friedman L.
Published: February 2004

The atomic-ion–molecule systems of protons or deuterons and isotopic hydrogen molecules have been the subject of an experimental study designed to provide data to be compared with recently reported classical trajectory calculations on an ab initio potential energy surface. Absolute cross sections (accurate to within an estimated error of ± 20%) for the following atomic-ion exchange reactions D++H2→HD+H+, H++D2→HD+D+, D++HD→D2+H+ have been investigated in a tandem mass spectrometer system, with carefully calibrated geometry, as a function of collision energy. Endothermic charge-transfer processes D++H2→HD++H, D++D2→D2++D, D++HD→HD++D →D2++H, H++H2→H2++H, H++D2→HD++D →D2++H have been observed, and their cross sections were determined as a function of collision energy. Energy distributions of the ionic species participating in these reactions were measured by application of appropriate retarding fields. The experimental results for atomic-ion exchange reactions [(1)–(3)] are not easily compared with theoretical cross sections because the latter were calculated above energy thresholds for endothermic charge-transfer reactions [Reactions (4)–(10). These processes were not considered in the theoretical treatment, though our results show that, where energetically possible, they indeed dominate the reactive collisions. The extent of the observed endothermic charge transfer was unexpected, but can be rationalized by postulating that very efficient translational to internal energy conversion occurs, followed by radiationless transition to a weakly bound or repulsive excited electronic state of H3+. This E′1 state has been identified by a simple Hückel calculation. Comparisons of energy distributions of product and reactant ions superficially indicate “complex formation” at relatively low collision energies and “direct reaction” at higher energies for atomic-ion exchange reactions [(1)–(3)]. The efficient transfer of kinetic to internal energy in the endothermic charge-transfer processes suggests complex formation mechanisms. This idea is further supported by isotopic abundance data. Although the energy distributions of atomic-ion exchange products above the endothermic charge-transfer threshold are consistent with a direct mechanism, it should be noted that the relative yield of atomic-ion products compared to molecular-ion products is small in this energy range. This is in no way inconsistent with trajectory studies and may indeed be present at lower energies where it would be effectively concealed. The absolute characterization of mechanism as “direct” or “complex formation” does not appear in the trajectory calculations nor is it suggested in our experiments.
Infrared Spectra of H-Bonded Systems : Anharmonicity of the H-Bond Vibrations in Cyclic Dimers
Authors: Leviel Jean-Louis , Marechal Yves
Published: February 2004

We present a theoretical simulation of the infrared spectra of the stretching vibrations of the H atom in hydrogen-bonded carboxylic acid dimers. We have refined a model previously proposed where the H-atom stretching vibration in an H-bond X–H···Y is coupled to the “hydrogen-bond vibration” X→–H→···Y← (we suppose that the H-atom vibration is harmonic with a frequency of oscillation depending on the X···Y distance), by the introduction of an anharmonic term (Morse potential) in the X→–H→···Y← motion. This model gives a value for the frequency of oscillation of the X→–H→···Y← motion in agreement with the observed value (in contrast to the previous model where the X→–H→···Y← motion was assumed to be harmonic), simulates in terms of delta functions the experimental spectrum rather well, and predicts the isotope effect completely. We conclude that the coupling of the H-atom stretching vibration with the hydrogen-bond vibration X→–H→···Y← together with the strong anharmonicity of the latter motion are characteristic features of stretching vibrations in hydrogen bonds, at least for weak and intermediate hydrogen bonds.
Electron Impact Excitation of Rare-Gas Atoms in the Distorted-Wave Approximation
Authors: Shelton W. N. , Leherissey E. S.
Published: February 2004

The distorted-wave formalism is applied to the inelastic scattering of electrons on rare gas atoms. Both the direct and exchange contributions are included. The multiparticle aspects of the problem are handled by means of the fractional parentage expansion. In particular, the case of a transition from the LS coupled ground state to a Jl coupled excited state is worked out.
Selection Rules for Three- and Four-Photon Raman Interactions
Authors: Christie J. H. , Lockwood D. J.
Published: February 2004

The dipole moment induced by a radiation field may be expanded in terms of the electric field vector. The third- and fourth-rank tensors in this expansion, β and γ, respectively, correspond to three- and four-photon Raman effects. Diagrammatic perturbation theory is used to obtain explicit quantum-mechanical expressions for the β and γ tensors. Selection rules for the symmetric γ tensor and for the nonsymmetric β and γ tensors are then calculated for the important molecular point groups. The results are compared with those for the ordinary Raman effect, and conditions necessary for the observation of nonlinear effects are discussed.
Paramagnetic Resonance Absorption and Triplet State Energy Transfer of Photoexcited β-Methylnaphthalene Molecules in Naphthalene Single Crystals
Authors: Ashford Nicholas A. , Hutchison Clyde A.
Published: February 2004

The electron paramagnetic resonance absorption spectra of the triplet state species in the four guest–host crystal systems, β-methylnaphthalene-d10 in naphthalene-d8, β-methylnaphthalene-d10 in naphthalene-h8, β-methylnaphthalene-h10 in naphthalene-d8, and β-methylnaphthalene-h10 in naphthalene-h8, have been investigated in the temperature range ∼ 5–∼ 25°K. Values of triplet state spin-Hamiltonian parameters have been measured. Rates of triplet state signal decays after cessation of illumination have been determined. The variations of triplet state signal intensities with temperature during constant continuous irradiation have been studied. The results have been interpreted in terms of a model of energy transfer processes in these crystals. Values of the parameters of the model for the cases of these systems have been given. The triplet state species which is observed in the β-methylnaphthalene-d10 in naphthalene-h8 system has been shown to be a naphthalene host molecule, whereas in the other three systems the triplet state species is a guest β-methylnaphthalene molecule.
Measurements of Lifetimes and Quenching Cross Sections of the B 3Π0u+ State of Iodine Using a Tunable Dye Laser
Authors: Sakurai K. , Capelle G. , Broida H. P.
Published: February 2004

Lifetimes and self-quenching cross sections of selected vibrational levels from υ′ = 0–25 of the B3Π0u+ state of I2 were measured from the direct decay of fluorescence excited by a pulsed, tunable dye laser. Large variations with υ′ of lifetimes and quenching cross sections were observed. Lifetimes changed by a factor of 3; for υ′ = 10 to 13, lifetimes were 1.5 μsec while for υ′ = 4 the lifetime was 0.53 μsec. This υ′ dependence is much larger than the calculated dependence of radiative lifetimes but can be explained by spontaneous predissociation through dissociative states crossing the B state. Smaller quenching cross sections were observed for the vibrational levels with longer lifetimes.
High-Pressure Adsorption: The Adsorption of Methane on Porasil at Low Temperatures and Elevated Pressures by Gas Chromatography
Authors: Hori Yoshio , Kobayashi Riki
Published: February 2004

The adsorption of methane on fused silica beads has been studied by gas chromatography from 5 to 120 atm for − 91.9 to 31.4°C. Only a few investigations of adsorption at high pressure have been reported due to the severe experimental difficulties. The “Hypothetical Perfect Gas” perturbation technique has been revised for application at high pressure to obtain the free gas volume. Two modifications in analysis are required: one for the steric effect of the perturbation gas and the second for the adsorption of the perturbation gas on the adsorbed phase. A second method of calculation based on solubility theory has been developed to correct for the solution of the perturbation gas in the adsorbed phase at high pressures. In addition to the usually measured differential or Gibbs adsorption, the gas chromatographic technique yields the absolute or total adsorption. This distinction is not observable at low pressures. A region of constant absolute adsorption in isotherms with increasing pressure was observed above the critical temperature of methane corresponding to a practically constant gas-phase fugacity. Application of limiting conditions to the measurements of Gibbs adsorption at high pressure gave the same value for the constant region of absolute adsorption isotherm, as well as the same value for the adsorbed phase density, which was evaluated from the dependence of the gas-phase volume upon the amount of absolute adsorption. This agreement substantiates the calculation method developed here.
Light Scattering from Chemically Reactive Fluids. IV. Intensity Calculations for the Eulerian Fluid with One Reaction
Authors: Knirk Dwayne L. , Salsburg Z. W.
Published: February 2004

The hydrodynamic equations for the reactive Eulerian fluid (zero transport coefficients, one chemical reaction) have been used in the thermodynamic approach to calculate in detail the spectrum of scattered light. The mathematical technique employed was the matrix eigenvalue formulation previously introduced [L. Blum and Z. W. Salsburg, J. Chem. Phys. 48, 2292 (1968)]. The method focuses on a particular matrix which is easily derived from the linearized hydrodynamic equations. The fluctuations of the set of independent variables are resolved into normal modes of relaxation. Each mode contributes one peak to the spectrum; the position and half-width of the peak are furnished directly by the eigenvalue, while the intensity is calculated from the corresponding normal mode projection matrix. Some general relationships between positions and half-widths are derived. The Rayleigh peak due primarily to chemical reaction relaxation is considered in detail. Various intensity ratios involving this peak are calculated, and simple criteria are set forth for determining whether it will be intense enough to be experimentally observed. If it is observable, the reaction rate constant can be obtained from measurements of its half-width. Two other chemical relaxation effects, dispersion of the sound speed and skewing of the Brillouin peaks, are also examined. For small scattering angles and very fast reactions, the rate constant may be extracted from measurements of the sound speed dispersion. The range of relaxation times for which experiments seem feasible is 10−4–10−11 sec.
Excited Singlet State Radiative and Nonradiative Transition Probabilities for Acetone, Acetone-d6, and Hexafluoroacetone in the Gas Phase, in Solution, and in the Neat Liquid
Authors: Halpern Arthur M. , Ware William R.
Published: February 2004

Fluorescence lifetime and fluorescence quantum yield measurements have been made on acetone and acetone-d6 in the gas phase, in solution, and in the neat liquid. The variation of the radiative and nonradiative transition probabilities with deuteration, and the effect of solvent environment are discussed. Radiative transition probabilities are compared with those calculated from the equation of Strickler and Berg. The discrepancies between the observed and calculated lifetimes are discussed in terms of vibronically induced transitions.
Excitation Energies of Chemically Activated Isobutane and Neopentane and the Correlation of Their Decomposition Rates with Radical Recombination Rates
Authors: Hase W. L. , Simons J. W.
Published: February 2004

Intermolecular comparisons of the total insertion and addition rates of singlet-state methylene radicals with several alkanes, alkenes, and alkylsilanes indicate that for most reactants the singlet-state methylene radicals carry the same fraction of any initial excess energy into their insertion or addition products. Attempts to correlate decomposition rates of chemically activated isobutane and neopentane with estimated alkyl radical recombination rates require high critical energies for decomposition, “tight” radical models, and activated complex models with free internal rotations which give thermal decomposition A factors of ∼ 1017 sec−1.
Reactions of Methyl Radicals Produced by the Pyrolysis of Azomethane or Ethane in Reflected Shock Waves
Authors: Clark T. C. , Izod T. P. J. , Kistiakowsky G. B.
Published: February 2004

A shock tube coupled to a time-of-flight mass spectrometer has been used to study the reactions of methyl radicals at temperatures much higher than before. The radicals were formed by heating mixtures containing azomethane or dimethylmercury highly diluted in neon to between 1120 and 1400°K in reflected shock waves. Detailed measurements of methane, ethane, and ethylene production have been made over the 380 μsec of observation time. The effects of adding ethane and ethylene to the reaction mixture have also been investigated. Possible mechanisms for the hydrocarbon product formation are discussed. It is concluded that, despite the low concentrations and short observation time used, only a chain mechanism describes our observations. The main reactions are CH3+CH3→C2H6, CH3+C2H6→C2H5+CH4, C2H5→C2H4+H, H+C2H6→C2H5+H2. The temperature-independent rate coefficient k1 was found to be k1 = 1.4 ± 0.6 × 10−11cm3/particle·sec at the total density 9 × 1017 particle/cm3. Numerical integrations of this chain mechanism at 1350°K are consistent with the experimental data only when the initiation reaction (2) is assigned a rate coefficient 5.9 × 10−13 cm3/particle·sec which is close to 12 times greater than that expected from the rate data given in the literature. Other rate coefficients are within 50% of the values obtained using literature data. To test these conclusions, experiments have been made on the decomposition of ethane at 1485°K. The same chain mechanism described the product formation, and as above the numerical integration required the larger value of k2.
Molecular Relaxation Processes in Triatomic Molecules. I. T–V Transition Probabilities in the CO2–He System
Authors: Thommarson Ronald L. , Berend George C. , Benson Sidney W.
Published: February 2004

A classical method is presented for calculating translational–vibrational energy exchange between a colliding atom and linear triatomic molecule. The method entails a rigorous solution of the equations of motion of the four particles interacting in two dimensions. The interaction potential is described by three independent, atom–atom, Morse-type potential functions. Computer solutions provide the probabilities of the T–V energy-transfer processes associated with the three normal vibrational modes of the triatomic molecule. The method is demonstrated on the CO2–He system. Results show good agreement with the experimental data for excitation of the bending mode and are in accord with SSH theory predictions for excitation of the longitudinal modes.
Dynamic Jahn–Teller Effects and Magnetic Anisotropies in Aqueous Solutions and Water–Ethanol Glasses of Copper(II) Solvates and Complexes with 2,2′-Dipyridine
Authors: Noack Manfred , Kokoszka Gerald F. , Gordon Gilbert
Published: February 2004

Dynamic Jahn–Teller effects have been recognized previously in solids which contain copper(II) ions in octahedral environments. In solutions, dynamic Jahn–Teller effects have now been observed in the EPR spectrum of the tris(2,2′-dipyridine) copper(II) complex. This is shown by the small temperature coefficient of the apparent tumbling correlation time, τc, which is associated with anisotropy contributions to the EPR linewidth and by the insensitivity of τc to variations of the solvent viscosity. In partially substituted complexes, such as the tetraaquo (2,2′-dipyridine) copper(II) species which has also been studied here, the dynamic Jahn–Teller effects are inhibited due to the inhomogeneous nature of the first coordination sphere. The possible importance of dynamic Jahn–Teller effects in homogeneous solvates of copper(II) is discussed. Evidence is presented to show that addition of ethanol to aqueous solutions of copper(II) nitrate results in the formation of inhomogeneous species.
Configurational Averages for Chain Molecules: Higher Moments and Related Quantitites
Authors: Flory P. J. , Abe Y.
Published: February 2004

The higher even moments 〈r2p〉0 of the end-to-end vector r of a chain molecule are formulated according to a straightforward procedure which is free of complications for large values of p. It is generally applicable also to averages of other configuration-dependent quantities, and simplifies their treatment. The condensation of self-direct matrix products derived by Nagai for reducing the complexity of computation of higher moments is achieved directly through an appropriate transformation, which is defined for such a product of any degree. Major reductions of the orders of the statistical weight matrix and associated expressions permissible for symmetric chains are achieved succinctly by similar matrix transformations. It is pointed out that further condensations can be realized through deletion of superfluous rows and columns from the generator matrices (G, G⊗G, etc.) for the moments.
Energy Transfer between N2 and Electronically Excited Inert Gas Atoms and Ions
Authors: Kassal T. T. , Fishburne E. S.
Published: February 2004

Collisions of the second kind between N2 and metastable inert gas atoms and ions have been studied in order to investigate the energy exchange mechanism. Excited inert gas atoms are created by means of an electron beam. The state of the nitrogen molecule immediately after the energy exchange is determined by examining the spectra produced by the excited nitrogen molecule. A nonthermal rotational excitation appears to accompany most of the electronic energy transfer processes. In the case of the reaction between Kr+ and N2, the rotational excitation is limited to the N2+(B 2Σu+) υ = 1 level. With the collision between a metastable argon atom and N2, the rotational excitation is limited to the υ = 0 level of the N2(C 3Πu) state. The Franck–Condon factors for the change in vibrational levels during an electronic transition are not obeyed during either of these processes.
Electronic States of Heavily Doped Molecular Crystals—Naphthalene. II. Experimental
Authors: Hong Hwei-Kwan , Robinson G. Wilse
Published: February 2004

The energy states and optical spectra of heavily doped mixed crystals are investigated. Studies are made for the following binary systems: (1) naphthalene-h8 and -d8, (2) naphthalene-h8 and -αd4, and (3) naphthalene-h8 and -βd1, corresponding to strong, medium, and weak perturbations, respectively. In addition to ordinary absorption spectra at 4°K, band-to-band transitions at both 4 and 77°K are also analyzed with emphasis on their relations to cooperative excitation and over-all density-of-states functions for mixed crystlas. It is found that the theoretical calculations presented in a previous paper agree generally with experiments except for cluster states observed in system (1) at lower guest concentrations. These features are discussed semiquantitatively. As to the intermolecular interaction parameters, it is found that experimental results compare favorably with calculations based on experimental density-of-states functions but not with those based on octopole interactions or charge-transfer interactions. Previous experimental results of Sheka and the theoretical model of Broude and Rashba are also compared with present investigations.
Statistical Mechanical Study of Hydrophobic Interaction. I. Interaction between Two Identical Nonpolar Solute Particles
Authors: Ben-Naim A.
Published: February 2004

The tendency of two nonpolar particles to adhere to each other in aqueous environment is examined within the framework of classical statistical mechanics. The system under investigation consists of N solvent molecules and two simple solute particles at fixed positions R1 and R2. The Helmholtz free energy for such a system is split into three terms: AN+2(R1, R2) = A0 + U12(R1, R2) + AHI(R1, R2). The main problem of the article is formulated in terms of the function AHI(R12). The hydrophobic interaction is defined as the indirect part of the work [AHI(R12 = ∞) − AHI(R12)] associated with the process of bringing the two solute particles from infinity to the distance R12. Three different estimates of the strength of the hydrophobic interaction for various solute–solute distances are discussed. A quantity, based on available experimental data, is suggested to serve as a simple and practical index for comparing the hydrophobic interaction in various media. Using this quantity, the unique behavior of liquid water with regard to hydrophobic interaction is established.
Electric Dipole Moment of Diatomic Molecules by Configuration Interaction. I. Closed-Shell Molecules
Authors: Green Sheldon
Published: February 2004

A scheme has been developed for selecting a manageable number of configurations (less than 200) to be used in a configuration interaction calculation to obtain the electric dipole moments of closed-shell diatomic molecules. Calculations have been performed on LiH (Re = 3.015 a.u.), CO (Re = 2.132 a.u. and R = 2.2853 a.u.), CS (Re = 2.89964 a.u.), and NaLi (R = 5.5 a.u.). A dramatic improvement over the restricted Hartree–Fock value is obtained. At Re the RHF, CI, and experimental dipole moments (in debye) are LiH: 6.00, 5.86, 5.83; CO: − 0.27, 0.12, 0.11; and CS: 1.56, 2.03, 1.97.