bluuebunny/crossref_metadata_2025 huggingface dataset:
EPR of Cationic Radicals Formed by uv Irradiation of Cu2+-doped Amino Acid Crystals at 77°K: Glycine and Dimethylalanine
Authors: Tomkiewicz Y. , Fujimoto M.
Published: February 2004

After uv irradiation at 77°K, the EPR intensity of the impurity ion complexes in copper-doped glycine and dimethylalanine crystals decreased, and a new spectrum appeared at the g=2 position. This effect was attributed to a charge transfer process between divalent copper ions and the surrounding host molecules. The radicals formed as a result of this process were identified as cationic radicals, [NH2CR2CO2H]+ (R is H or CH3).
Virial Field Relationship for Molecular Charge Distributions and the Spatial Partitioning of Molecular Properties
Authors: Bader R. F. W. , Beddall P. M.
Published: February 2004

Arguments and numerical examples are presented which suggest that the distribution of electronic charge in a molecular system can be related to the total virial of all the forces exerted on each element of the charge density. Further numerical evidence is given indicating that it is possible to partition a molecular system in such a way that the same virial relationship between the average kinetic and potential energies observed for a total molecular system is found to hold for the individual fragments. This partitioning scheme is based on an observable property of the charge distribution. The proposals presented here provide a basis for the understanding and prediction of molecular charge distributions and their properties.
Determination of Intermolecular Potentials by the Inversion of Molecular Beam Scattering Data. III. High Resolution Measurements and Potentials for K–Hg and Cs–Hg
Authors: Buck U. , Kick M. , Pauly H.
Published: February 2004

High resolution differential scattering cross section measurements for K–Hg and Cs–Hg were made using the method of crossed molecular beams. Up to 10 rainbow maxima for K–Hg and up to 14 rainbow maxima for Cs–Hg were resolved. The intermolecular potentials were obtained from these data by direct inversion, employing the procedure described in Papers I and II. The shape of the reduced potentials for all three of the alkali-metal-mercury systems determined up to now by use of this inversion procedure is the same, to within the experimental errors, but it deviates significantly from that of model potentials commonly used.
van der Waals Constants and Nonadditive Triple-Dipole Force Constants for He and Ne by the Coupled Hartree-Fock Approximation
Authors: Kaneko Shobu
Published: February 2004

The dynamic polarizability and the dipole shielding factor at imaginary frequencies are calculated for He and Ne by the coupled Hartree-Fock approximation. The integrodifferential equations for the perturbed wavefunctions are solved numerically without use of the variational procedure. By using Casimir-Polder type formulas, the van der Waals constants μ and the nonadditive triple-dipole force constants ν are computed for He and Ne. Results (in atomic units) are μHeHe=1.38, μHeNe=2.71, μNeNe=5.44, νHeHeHe=1.33, νHeHeNe=2.51, νHeNeNe=4.76, and νNeNeNe=9.10.
Dissociation Energy of TiO and TiO2 Gaseous Molecules
Authors: Balducci G. , De Maria G. , Guido M. , Piacente V.
Published: February 2004

Using the Kundsen effusion-mass spectrometric technique, the reactions: TiO2(g)=TiO(g) + O(g) and TiO2(g) + Ti(g)=2TiO(g) were studied in the temperature ranges 2000°–2250°K and 2150°–2500°K. The dissociation energy of TiO(g) and TiO2(g) were derived from all gas reactions involving only titanium-oxygen species: D0 ° (TiO)=144 ± 5 and D0 ° (TiO2)=286 ± 10 kcal/mole, respectively. A comparison with the results by other authors is also reported.
Limits of the Validity of the Kinetic Theory of Hot-Atom Reactions
Authors: Malcolme-Lawes D. J.
Published: February 2004

Using a simple stochastic model the kinetic theory of hot-atom reactions is tested under conditions of high reactivity and nonconstant α values. The meaning of the derived kinetic parameters and their relation to the corresponding properties of the model are discussed. It is found that the kinetic-theory parameters are unreliable if α varies within the hot reaction region.
Lifetime Determination of the NO A Σ+2 State
Authors: Weinstock E. M. , Zare R. N. , Melton L. A.
Published: February 2004

A coincidence of the Te I emission line at 2147.25 Å with the Q1(21/2) and the QP21(21/2) absorption lines of the (1, 0) band of the NO γ system is used to perform a Hanle-effect measurement on the v′=1, N′=10 level of the NO A Σ+2 state. A linear least squares fit to the pressure-broadened data yields an intercept of 3.37 ± 0.36 G for the zero-pressure linewidth and a slope of 12.7 ± 2.4 mG/mtorr. By measuring the zero-field polarization of the resolved fluorescence lines, the ratio of the hyperfine splitting to the rotational spin splitting is estimated to be less than or equal to 1:5, and the angular momentum coupling scheme is found to conform closely to Hund's case (bβJ). An optical radio-frequency double resonance study provides further confirmation. Using g values appropriate to Hund's case (bβJ), the radiative lifetime is determined to be 178 ± 19 nsec. These results are in excellent agreement with the previous Hanle-effect measurements by German, Zare, and Crosley on the v′=1, N′=13 level.
Autoionizing and Negative Ion States of Xe and Kr below the 2P1/2 Limits
Authors: Marmet P. , Bolduc E. , Quemener J. J.
Published: February 2004

A new electron impact apparatus has been used to measure the ionization current of Xe and Kr between the 2P3/2 and 2P1/2 thresholds with a high signal to noise ratio. In both gases we have observed the contribution of several autoionizing d′ levels as well as perturbations of the ionization continuum due to negative ion states.
Effective Long Range Potential for the Scattering of Electrons by Atoms and Molecules
Authors: Huo Winifred M.
Published: February 2004

An effective potential Ṽf0 is defined such that the direct scattering amplitude is expressed by a Borntype integral. It is found that Ṽf0 consists of three types of potentials characterized by their q dependence, where q is the distance between the incident electron and the scattering center. The long range potential, Ṽf0LR, is important at large q. It is expressed as an inverse power series and expressions up to the q−6 term are obtained. The first non-Born term in Ṽf0LR is just the dipole polarization potential. The next term is proportional to q−5 and complex. The oscillatory potential, Ṽf0OS, is also expressed as an inverse power series but multiplied by eiaq. The leading term in Ṽf0OS is proportional to q−4. Because of the presence the oscillatory factor, Ṽf0OS will decrease faster than Ṽf0LR at large q. At small q, the short range potential Ṽf0SR becomes important. It is characterized by an exponential dependence on q. The symmetry properties of Ṽf0LR and Ṽf0OS are studied and compared with the selection rules recently obtained by Lassettre. For elastic scattering, a semiempirical effective potential is introduced which incorporates the leading terms in Ṽ00LR and Ṽ00OS. It is found that some recent experimental results of Bromberg can be qualitatively accounted for by this potential.
Triplet Exciton EPR and Crystal Structure of [TMPD+]2[Ni(mnt)2]−2
Authors: Hove Mufaro J. , Hoffman Brian M. , Ibers James A.
Published: February 2004

We report in this paper the results of EPR and x ray diffraction studies on the ionic-radical salt [TMPD+]2[Ni(mnt)2]−2 composed of an organic free radical cation and a diamagnetic transition metal complex ion. This crystal exhibits the triplet exciton EPR spectrum characteristic of an alternating chain of spins. Exciton creation energy is Δ E=0.240 ± 0.005 eV; triplet spin Hamiltonian parameters are | D | =215 ± 1 G and | E | =28 ± 1 G; gzz=2.0029, gyy=2.0033, gxx=2.0035, all ± 0.0005. The complex crystallizes in Ci 1- P1̄ of the triclinic system, with cell dimensions of a=9.145 (9) Å, b=11.502 (9) Å, c=7.762 (8) Å, α=98.24 (5)°, β=105.69 (2)° and γ=92.64 (4)°. The organic free radicals form very strongly alternating linear chains and we examine the extent to which EPR results for a triplet exciton system may, through knowledge of the crystal structure of the system, be related in a detailed fashion to the zeroth order picture of the spin excitation of an isolated free radical pair.
Analytical Mechanics of Chemical Reactions. VI. Rotational and Vibrational Distributions of the H + H2 Reaction in a Plane
Authors: Wu Shiou-fu , Marcus R. A.
Published: February 2004

Rotational and vibrational distributions for the exchange reaction H + H2 → H2 + H are obtained numerically for reaction in a plane and compared with the vibrationally adiabatic solutions. Evidence is obtained regarding the two adiabatic solutions for the final rotational state predicted earlier and for the disappearance of one of these at higher initial relative velocity. Good agreement between calculations based on natural collision coordinates and these based on Cartesian coordinates was found, where tested. The vibrational motion for reaction in a plane is fairly adiabatic on the average at energies of thermal interest. Connections with other properties are noted. The results support the idea of statistical adiabaticity suggested earlier in this series and thus support a derivation of activated complex theory based on this concept.
Theoretical Study of the F2 Molecule Using the Method of Optimized Valence Configurations
Authors: Das G. , Wahl Arnold C.
Published: February 2004

The method of optimized valence configurations (OVC) is used to study the potential curve for the ground state of the F2 molecule. All the important electron correlation-effects within and between various molecular shells are investigated via the multiconfiguration self consistent field (MCSCF) process. It is found that, consistent with the philosophy of the OVC method, these effects fall into two distinct categories: (1) the molecular correlation, which vanishes when the molecule dissociates into the constituent atoms, and (2) the atomic correlation, which passes asymptotically to that for the atoms. The very weak interdependence or ``coupling'' of the two correlation types results in considerable computational simplification by permitting MCSCF calculations to be performed on groups, consisting of a comparatively small number of configurations, and the evaluation of their respective contributions to the bonding interaction by a simple summation in the spirit of pair theory. Such calculations on F2 yield a potential curve which is very similar to the one derived from experiment. Our calculated values of the spectroscopic constants De, ωe, Re are, respectively, 1.67 eV, 942 cm−1, 2.67 bohr. These are in good agreement with the corresponding experimental values 1.68 eV, 932 cm−1, 2.68 bohr. General rules are given for applying this procedure to other molecular systems.
Theory of Semiclassical Transition Probabilities (S Matrix) for Inelastic and Reactive Collisions. Uniformization with Elastic Collision Trajectories
Authors: Marcus R. A.
Published: February 2004

A canonical transformation is described for uniformizing the coordinates used in Paper I of this series. For comparison with the results of Paper III, which based a uniformization on exact trajectories, the present article describes one based on elastic collision trajectories. The question of invariance of S-matrix elements with respect to semiclassical unitary transformations is also discussed.
133Cs Spin-Lattice Relaxation and Resonance in Ferroelectric CsD2AsO4 and CsH2AsO4
Authors: Blinc R. , Mali M. , Slak J. , Stepišnik J. , Žumer S.
Published: February 2004

The electric field gradient (EFG) tensor at the Cs sites in CsH2AsO4 and the 133Cs spin-lattice relaxation rate in CsD2AsO4 have been determined. The results show that the time averaged value of the EFG tensor at the Cs site in the paraelectric phase is the average of the two ferroelectric EFG tensors for opposite directions of polarization, and that the time dependence of the Cs EFG fluctuations is determined by the same dynamic process which governs the EFG fluctuations at the deuteron sites in the O–D ··· O bonds.
On a Classical Trajectory Study of Energy Transfer in Some Atom-Diatomic Molecule Systems
Authors: Thompson Donald L.
Published: February 2004

Atom-diatomic molecule energy transfer has been studied using classical trajectories. The main objective was to evaluate the effects of initial vibrational, rotational, and translational energy on energy transfer so that some understanding of the dynamical mechanism of energy transfer in these systems could be obtained. The four collision systems studied are H2+I, H2+Cl, HCl+H, and HCl+Cl. The initial states of these three-dimensional trajectories were chosen in accordance with quantum rules. The potential-energy surfaces employed in the calculation were of the semiempirical VB formalism. The H-atom exchange reaction Cl′ + HCl′′ → HCl′ + Cl′′ was shown to be a contributor in the relaxation of vibrationally excited HCl molecules.
Molecular Beam Kinetics: Four-Atom Collision Complexes in Exchange Reactions of CsCl with KCl and KI
Authors: Miller W. B. , Safron S. A. , Herschbach D. R.
Published: February 2004

Angular distributions of scattering from crossed molecular beams have been measured for CsCl+KCl and CsCl+KI and velocity distributions for the latter case. The parent beam temperatures are ∼ 1000°K, corresponding to mean collision energy of ∼ 4 kcal/mole and mean total energy of ∼ 11 kcal/mole. Both systems show ``sticky collision bumps'' at wide angles, indicating formation of collision complexes with lifetime at least comparable to a rotational period ( ≳ 10−12 sec). The cross sections for complex formation are roughly ≳ 200 Å2. The surface ionization detector used does not distinguish between products and reactants for these systems (all salts yield atomic alkali ions). However, the kinematic effect of the mass change in the CsCl + KI → CsI + KCl reaction allows the reactive and nonreactive contributions to the velocity distributions to be resolved. Reactive decay is estimated to occur in about one out of every three or four collisions in which a complex is formed. The velocity analysis also shows that the relative translational energy of the products is distinctly less than (∼ 60%) that of the reactants, and less than that for decay of comparable three-atom complexes. The data are compared with a simple statistical, transition-state theory for a four-atom complex. As a consequence of the unusually strong long-range dipole-dipole interaction, this essentially requires no molecular parameters other than the number of degrees of freedom, masses, bond strengths, and dipole moments. The statistical theory gives good agreement with the observed translational energy and angular distributions, but apparently overestimates the ratio of reactive to nonreactive decay of the complex. This may be due to geometrical isomerism. Ionic model calculations predict two stable isomeric configurations of alkali halide dimers. The more stable isomer is a cyclic, planar rhomboid; it provides a pathway for the concerted making and breaking of pairs of bonds in the exchange reaction. The less stable isomer is a linear chain; it may often dissociate nonreactively rather than rearrange to the cyclic form, especially in collisions with large impact parameters, when the centrifugal momentum is very large and thus keeps the chain ``ends'' apart.
Theory of the Interface between Immiscible Polymers. II
Authors: Helfand Eugene , Tagami Yukiko
Published: February 2004

A theory is developed to predict the interfacial properties between two immiscible polymers. A self-consistent-field approach is employed to describe the configurational statistics of polymer molecules in the interfacial region. The density profiles and surface tension are calculated, and compare well with experiments. The interfaces are found to be much broader than for ordinary liquids. Also discussed are the distribution of chain ends and block-copolymer joints in the interface, and the effects of adding moderate amounts of solvent.
Thermodynamics of Molten Salts
Authors: Grindley T. , Lind John E.
Published: February 2004

The configurational thermodynamic properties of several molten tetraalkylammonium tetraalkylborate salts have been measured and are compared with the properties of fluids composed of their isoelectronic, electrically neutral hydrocarbons. These comparisons have been made over a 40C° temperature range and a 15% variation of their volumes in an attempt to determine the contribution of the internal Coulomb field of the salt to its thermodynamic properties. The pressure of the salt is of the order of 1000–2000 bars less than that of the nonelectrolyte when they are compared at the same temperature and volume. In examining the thermodynamic equation of state, the major contribution to the decreased pressure of the salt comes from the increase of (∂U/∂V)T by the Coulomb field and only a small contribution comes from a decrease of (∂S/∂V)T. For the several salts, the entropy derivatives (∂S/∂V)T scale onto one another with the same parameters that scale the neutral hydrocarbons. This scaling indicates that the small differences of (∂S/∂V)T between salt and nonelectrolyte arise from the softness and deformability of the ions and not primarily from the ordering by the Coulomb field. The relation between (∂U/∂V)T for the salt systems containing ions of different sizes is approximately the same as that for different crystalline salts having the same type of lattice. The present stage in the development of the theory of electrolytes is shown to predict the correct sign for all the effects as a nonelectrolyte is charged up to form a molten salts as well as their relative orders of magnitude, but it considerably underestimates the absolute magnitudes of the effects.
Vibrational and Rotational Relaxation in Ammonia
Authors: Bass H. E. , Winter T. G.
Published: February 2004

Ultrasonic absorption has been measured in ammonia in the temperature range 300–773°K over the f/p range 1–100 MHz/atm. This data was analyzed to obtain vibrational and rotational relaxation times and collision numbers. The vibrational collisions numbers are unusually small and decrease only slightly with increasing temperature. The maximum in the collision number predicted by Shin's theory for polar molecules is not observed. The temperature dependence of the rotational collision numbers is in good agreement with the classical calculation of Zeleznik for polar diatomic molecules.
Triatomic Photofragment Spectra. I. Energy Partitioning in NO2 Photodissociation
Authors: Busch George E. , Wilson Kent R.
Published: February 2004

The photofragment spectrum of NO2 has been measured in the near ultraviolet at 28 810 cm−1. A molecular beam of NO2 is crossed with brief pulses of polarized laser light and measurements are made on the distributions of speed and direction of the recoiling O and NO fragments produced by photodissociation. The average translational energy of the fragments is about 60% of the available energy. There are at least two prominent peaks in the translational energy distribution. We conclude that the two peaks most likely correspond to nearly equal probability of recoil with the NO fragment in the v=0 and v=1 vibrational states. Such vibrationally excited NO fragments produced by photodissociation in polluted atmospheres could perhaps react with different rates than ground state fragments. The positions and widths of the peaks indicate that there is a significant rotational distribution. Statistical and direct models for photodissociation energy partitioning are briefly explored, and their predictions compared with the experimental measurements. A model is tentatively endorsed in which the nascent NO fragment is formed with vibrational excitation already present in the NO2 excited state. Dissociation is then assumed to occur quickly before statistical equilibration is reached. This is the first of a series of four papers on the photofragment spectra of triatomic molecules, using NO2 and NOCl as examples.
EPR of Defect Sites in Thulium Ethyl Sulfate Crystals. II. Characterization of Defect Sites
Authors: Baker D. C. , Dearman H. H.
Published: February 2004

Anomalous resonance lines in the EPR spectrum of thulium ethyl sulfate single crystals at 4.2°K were investigated at three microwave frequencies, 9, 25, and 35 GHz. It is shown that the resonance absorption occurred from Tm3+ (4f12, 3H6) ions located at a site of local symmetry of C2v or lower, rather than at the normal C3h site. The symmetry axes of the defect sites were found to lie in the mirror plane of the normal sites and to be spaced 120° apart in this plane. Two distinct types of defects having these general characteristics were found and suggestions for these structures are made. Spin-Hamiltonian parameters for each type site are reported, as are values for Tm3+ in the Y2(SO4)3· 8H2O lattice. It is shown that the ground states for both sites are of μ=0 type and consist mainly of MJ=± 6.
Relative Cross Sections for the Intramultiplet Quenching of Hg(63P2) to Hg(63P1)
Authors: Van Itallie F. J. , Doemeny L. J. , Martin R. M.
Published: February 2004

Relative intramultiplet quenching cross sections for the transition Hg(63P2)→ Hg(63P1) have been obtained for a variety of collision partners by using crossed molecular beams and monitoring the phosphorescence of Hg(63P1) from the cross beam interaction region. Energy resonance with vibrational states does not appear to be a major factor in determining the magnitude of the intramultiplet cross sections for this process. The results with He and Xe indicate that internal degrees of freedom are required for significant cross sections when the quencher lacks excited electronic states below Hg(63P2). In general the large differences in cross sections observed with molecules are best explained in terms of competitive processes, e.g., highly reactive molecules tend to have small intramultiplet cross sections. The present data are compared with total and intramultiplet cross sections for Hg(63P1) which have been obtained by optical excitation in bulb experiments.
Low-Temperature Magnetic Characteristics of Tetrahedral CoCl4 2−. I. g-Tensor Orientation in Doped [(C2H5)4N]2ZnCl4
Authors: Shankle G. E. , McElearney J. N. , Schwartz R. W. , Kampf A. R. , Carlin R. L.
Published: February 2004

Electron paramagnetic resonance measurements were made on single crystals of cobalt-doped tetraethylammonium tetrachlorozincate (II) at 4.2°K. The results show that the CoCl4 2− tetrahedra are oriented in several magnetically nonequivalent directions in the host lattice, which is isostructural with the analogous cobalt compound, tetraethylammonium tetrachlorocobaltate (II). Each tetrahedron can be characterized by an effective spin S′= 12 and by the principal g values gx ′=5.44, gy ′=4.84, and gz ′=2.34. Although the individual CoCl4 2− anions exhibit only rhombic symmetry, these ions are so oriented at 4.2°K as to maintain the tetragonal axis exhibited by the crystal at room temperature.
Angular Dependence of Electron Impact Excitation Cross Sections of O2
Authors: Trajmar S. , Williams W. , Kuppermann A.
Published: February 2004

The electron-impact excitation spectrum of O2 has been studied at 20 and 45 eV impact energies and at scattering angles ranging from 10° to 90°. The angular behavior of the differential scattering cross sections for excitation of the a 1Δg, b 1Σg +, B 3Σu − states, for the 9.97 eV (``longest'' band), and the 10.29 eV (``second'' band) transitions, for the broad feature at 6.1 eV energy-loss (previously assigned to the excitation of the A 3Σu + state), and for elastic scattering has been determined. The experimentally measured relative differential and integral cross sections for these processes have been approximately normalized to the absolute scale. The intensities of the different transitions in optical and electron-impact spectra are compared and the importance of spin-orbit coupling and exchange processes are discussed. It is found that the energy-loss feature at 6.1 eV in the electron-impact spectrum is mostly due to the excitation of the c 1Σu − state. This new assignment is supported by the angular and energy dependence of the scattering cross section (and by the intensity pattern found in various electron impact processes).
Quantum Mechanical Perturbation Expansion for the Second Virial Coefficient and the Ursell-Mayer Function
Authors: Baer S. , Ben-Shaul A.
Published: February 2004

Starting from a quantum mechanical diagrammatic expansion of the grand partition function ξ, and of the coefficients Vbl in the activity expansion of ξ, and making a term by term passage to the limit of classical nuclear motion, results in a corresponding diagrammatic expansion of the Ursell functions Ul(R1, . . ., Rl). Presently only the expansion of the Ursell-Mayer function f(R) has been explicitly examined and the terms up to second order perturbation theory, including exchange, have been evaluated. The truncated expansion gives a reasonably accurate expression of f(R) for long and medium range distances (R≥4a0) and within this range can be transformed, to the same order of accuracy, into the classical standard form f(R)=exp[ −u(R)]− 1, although in principle an exact formulation in such a form is not necessarily possible.
Determination of Thermal Transport Properties from Thermal Transpiration Measurements. II
Authors: Tao J. C. , Ganzi G. C. , Sandler S. I.
Published: February 2004

The analysis of thermomolecular pressure difference experiments to obtain information on thermal transport properties is critically examined. It is concluded that the finite difference form of the dusty-gas equation, which has been used to analyze the thermal transpiration phenomenon, is internally inconsistent. A form of the integrated dusty-gas equation developed in this paper, while more difficult to use than the finite difference equation, yields results for the Eucken factor which are in better agreement with direct measurements of this quantity than are obtained with the approximate equations. It is observed, however, that when using the integrated dusty-gas equation there is a temperature variation of the apparent capillary diameter which cannot be explained.
I-Molecule Reactions of Ethane at Low Electron Energy
Authors: Dunbar Robert C. , Shen Jacob , Olah George A.
Published: February 2004

The ion-molecule reaction chemistry of ethane has been examined by ICR spectroscopy at 13 eV and ·10−4 torr pressure. The interpretation of single- and double-resonance peak heights under these conditions is discussed quantitatively, and the double resonance spectra are used to assign relative rates to the observed reactions. The chemistry is strikingly different from that at higher electron energy. Substantial formation of C3H9+ and C4H11+ was observed, while no C2H7+ was obtained, and this result is taken to show low internal excitation of the C2H6+ reactant ion under these conditions. The observed formation of the C3H3+ ion is not in accord with the energetics of the reaction derived from electron impact studies, and the previously proposed cyclopropenyl structure is suggested for the C3H3+ ion formed in this system. The marked contrast between the positive ion-molecule reactions in ethane and diborane is discussed.
Microwave Spectrum, Structure, and Dipole Moment of Bicyclo[2.1.0]pentane
Authors: Suenram Richard D. , Harmony Marlin D.
Published: February 2004

The microwave spectra of the normal and three singly substituted 13C isotopic species of bicyclo[2.1.0]pentane have been assigned and analyzed. Using the moments of inertia derived from these spectra the following structural parameters have been obtained for the carbon skeleton: C1 – C2=C3 – C4=1.528 Å, C2 – C3=1.565 Å, C1 – C4=1.536 Å, C1 – C5=C4 – C5=1.507 Å, and the dihedral angle α=67.26°. The disagreement of these results with those of an earlier electron diffraction study has been discussed. It seems likely that a reanalysis of the electron diffraction data will lead to concurrence with the results of the present study. We have compared our structural parameters to those of other cyclic systems and have discussed the essential constancy of the average C – C distances in cyclobutyl systems and also in cyclopropyl systems. Finally, Stark effect measurements have yielded a total dipole moment of 0.27 D.
Self-Diffusion in Plastic Crystals
Authors: Tanner J. E.
Published: February 2004

Self-diffusion coefficients of cyclohexane, neopentane, hydrogen sulfide, and hydrogen chloride have been measured in the plastic crystal phase just below the melting points by pulsed-gradient, spin-echo NMR. Except for a study of solid He3 by Reich and Garwin this is the first measurement of self-diffusion in a solid substance by spin-echo NMR. For all substances D ≈ 3 × 10-9 cm2/sec, which is about four orders of magnitude lower than the diffusion coefficients in the corresponding liquids just above the melting points. These results are in good agreement with values predicted from diffusional correlation times derived from spin relaxation measurements in the solid phases.
Kinetics of Methane Oxidation
Authors: Skinner Gordon B. , Lifshitz Assa , Scheller Karl , Burcat Alexander
Published: February 2004

To supplement previous ignition delay investigations on methane-oxygen-argon mixtures, product distributions were determined for methane-oxygen-argon and methane-hydrogen-oxygen-argon mixtures that had been heated in a single-pulse shock tube. On the basis of these combined data and literature values, extensive kinetic calculations, involving numerical integration of 23 reactions, have been made. The calculations have reproduced ignition delay times or product distributions of 14 sets of experimental data for hydrogen-oxygen-argon, methane-oxygen-argon, and methane-hydrogen-oxygen-argon mixtures, and seem to be able to correlate all available data within the limits of experimental error.
Rydberg States in Cyclic Alkanes
Authors: Raymonda John W.
Published: February 2004

Vacuum-ultraviolet spectra in the range 50–78 kK are presented for cyclohexane, cyclohexane-d12, adamantane, and bicyclo[2.2.2]octane (1 kK=1000 cm−1). A sharp Rydberg series leading to an ionization potential of 9.31 eV is found in adamantane. This I.P., which differs significantly from a recent low resolution photoelectron spectroscopic (PES) value, was confirmed by high-resolution PES. The Rydberg nature of the observed transitions was confirmed by pressure effect studies. Sharp Rydberg series were also found in the cyclohexanes and I.P.'s of 9.88 eV for C6H12 and 9.91 eV for C6D12 were measured. A Rydberg series leading to an I.P. of 9.43 eV was found in bicyclo[2.2.2]octane. The I.P. was checked using high-resolution PES. A sharp transition not fitting into this series was found to be definitely a Rydberg using pressure effect and was assigned to a separate series. A weak sharply structured transition in cyclobutane is presented and assigned as a symmetry forbidden Rydberg. The orbital natures of the Rydberg excited states are discussed.
Proton, Deuteron, and Nitrogen Resonance of Dimethylformamide in Nematic Polypeptide Liquid Crystals
Authors: Samulski Edward T. , Berendsen Herman J. C.
Published: February 2004

An experimental study of proton, deuteron, and nitrogen resonance of dimethylformamide and deuterated DMF has been made in oriented nematic liquid crystals of poly-L-glutamic acid. The solvents used were various mixtures of DMF and H2O or D2O. From the proton spectra the complete order matrices were determined for each solvent system. From consistency between the solvent systems the angle HCN of the amide could be determined and was found to be 107± 1°. From the observed quadrupole splittings of all deuterium nuclei and of nitrogen in (deuterated) DMF in three solvent systems, all elements of the quadrupole coupling tensors of these nuclei were obtained. The quadrupole coupling constants and asymmetry factors found were: for the amide deuteron 197 kHz, 0.13; for the methyl deuterons trans to the amide oxygen 46 kHz, 0.19 and for those cis to the amide oxygen 64 kHz, 0.06 (averaged over methyl rotation); for the nitrogen 3.3 MHz, 0.4. Deuteron quadrupole splitting of solvent water was also observed, while proton dipole splitting of water did not occur because of too fast proton exchange.
Quantum Yield for Unimolecular Dissociation of I2 in Visible Absorption
Authors: Brewer Leo , Tellinghuisen Joel
Published: February 2004

An atomic fluorescence technique has been used to observe iodine atoms under conditions of steadystate irradiation of I2 between 5000 and 6300 Å. Photodissociation quantum yields are reported for narrowband excitation at 12 wavelengths within this range. The yield exceeds 90% at both ends of this region with a minimum of 33% near 5900 Å and a subsidiary maximum of 72% at 5460 Å. These results are further resolved into contributions from direct dissociation via the A[1u(3Π )]← X[O+g(1Σ )] and 1u(1Π )← X transitions, and a spontaneous predissociative decay, B[O+u(3Π )]→ 1u(1Π ). The rate for this predissociation fluctuates with v′ in a manner which accounts for the previously reported erratic behavior of the B-state lifetime. The total radiative decay rate varies smoothly but strongly with v′, implying that the B↔ X electronic transition moment attains a maximum for some internuclear distance in the region 3.0–3.2 Å.
Mobilities of Polyatomic Ions
Authors: Patterson P. L.
Published: February 2004

Experimental data on the mobilities of the polyatomic ions SO2F−, SO2F2−, SF5−, SF6−, F−(SF6), and SO2F2–(SO2) in an He carrier gas were compared with the predictions of the mobility theories of Langevin and of Mason and Schamp. As a consequence of the low polarizability of He and the large size of the ions, these mobilities were found to be dominated by the interaction of the ion-neutral repulsive cores rather than the conventional point-charge-induced-dipole interaction. In fact, these data were reasonably well reproduced by simply a hard-sphere collision model, completely neglecting any polarization force. Differences in the ion sizes were found to be manifested in readily measured differences in the mobilities. Experimental mobilities of SF5− and SF6− in O2, CH4, and SF6 gases were also compared with theory. These gases all have larger polarizabilities than He, and a fit of the mobilities required a 12–6–4 interaction potential with a relatively large r−6 term.
Diffusion of Hard-Spherical Macromolecules in Solution
Authors: McLaughlin E.
Published: February 2004

Recently developed theory of diffusion in a mixed dense hard-sphere fluid is applied to the case where the diffusing particles are very dissimilar in size. It is shown that at very low concentrations of macromolecules the diffusion analog of the Einstein equation for the viscosity of a suspension of hard spheres can be obtained under certain restrictive assumptions. The theory is used to discuss the dependence of the limiting value of the mutual diffusion coefficient on the size and molecular weight of the macromolecules in solution.
Tandem Chemical Laser Measurements of Vibrational Energy Distribution in the Dichloroethylene Photoelimination Reactions
Authors: Molina Mario J. , Pimentel George C.
Published: February 2004

Equal-gain temperature measurements with two laser tubes in the same optical cavity (a ``tandem'' laser) are described. In this way, rate constant ratios can be measured for vibrational transitions that do not have highest gain. The HCl laser emissions caused by photolysis of the 1, 1- and cis-1, 2-dichloroethylenes were examined in this manner. For 1, 1-dichloroethylene, k3/k2=0.85± 0.02 and k2/k1=1.08± 0.03 and for cis-1, 2-dichloroethylene, k3/k2=0.71± 0.03 and k2/k1=0.76± 0.02. The trends confirm the earlier inference that HCl vibrational excitation is more significant in the 1, 1-dichloroethylene photo-elimination, with the attendant implication that HCl vibrational excitation tends to favor, 1, 1 addition (Markovnikov addition) in the reverse reaction between HCl and monochloroacetylene.
Electric Deflection of Molecular Beams of Carbon Suboxide and Carbon Subsulfide
Authors: Dyke T. R. , Klemperer W. , Ginsberg A. P. , Falconer W. E.
Published: February 2004

The deflection behavior of molecular beams of C3O2 at 200 and 300°K and C3S2 at 300°K has been studied in inhomogeneous electric fields. Both species show net defocusing of the scattered beam with applied field. By comparison with the bent molecule NO2 whose electric dipole moment is known, upper limits of 0.15 D were placed on the electric moments of C3O2 and C3S2. These limits, coupled with extimates of the integrated absorption intensities obtained from published spectra for the ν7 vibration, permit upper limits of 0.15 rad to be placed on the bending angle. The most probable configuration is thus linear.
Excitation with Monochromatic Light of a Vibronically Broadened Molecular Band
Authors: Beswick J. A. , Lefebvre R. , Plumejeau A. M.
Published: February 2004

This paper studies the effect of a monochromatic electromagnetic field of arbitrary strength and duration on an isolated molecule presenting the energy level scheme which is the basis for current theories of radiationless processes in the so-called statistical limit: the system is assumed to possess bands of excited levels which are due to the dilution of well separated electric dipole allowed states into a dense set of forbidden states. The frequency of the light is set approximately equal to the transition frequency of one of these bands. Two models are set up, a quantized one with a n-photons one-mode field, and a semiclassical one with an oscillating electric field. They yield identical results. Two limiting cases, termed weak field and strong field can be obtained. In the weak field case, two different steps can be distinguished: first, the excitation of the dipole allowed state; second, the selective excitation of the molecular states at resonance with the field. The strong field case corresponds to a nonlinear response characterized by a damped nutation between ground and allowed states. After a long irradiation time the molecule is left in states which are distributed according to the level scheme corresponding to the ``molecule dressed with photons''. The spontaneous emission rate after the light is switched off is found not to depend on the particular form which is obtained for the initial state. This result, which is shown to hold for more general forms of the electric field in the semiclassical treatment, is a consequence of the analytical properties of the amplitudes.
Precision Spectroscopy of the N2O, 00°1–10°0 Laser Band by Frequency Mixing in an Infrared, Metal-Metal Oxide-Metal Point Contact Diode
Authors: Sokoloff D. R. , Javan A.
Published: February 2004

Using the technique of laser frequency mixing in an infrared, metal-metal oxide-metal point contact diode, the frequencies of 27 P- and R-branch lines of the N2O, 00°1–10°0 laser band are measured absolutely by comparison to the known frequencies of the P branch, 00°1–10°0 band CO2 laser transitions. In addition to providing a new set of precision secondary frequency standards in the 10-μ region, these measurements enable a determination of the rotational constants of the 00°1 and 10°0 N2O levels and a determination of the center frequency of the 00°1–10°0 band as 28 146 139 MHz to a part in 106.
Viscosity of the Binary Gaseous Mixture Helium-Nitrogen
Authors: Kestin J. , Ro S. T. , Wakeham W. A.
Published: February 2004

The paper presents new relative measurements of the viscosity of binary mixtures of helium and nitrogen, together with repeated determinations of the viscosity of the pure gases. The experiments were performed, using an oscillating disk viscometer; they were made at atmospheric pressure and in the nominal temperature range 25–700°C, the precision being one of ±0.1%. Tables of thermodynamically consistent values of the thermal conductivity of the pure gases are given. The binary diffusion coefficient for the mixture has also been computed.
Higher Derivatives in the Thermodynamics of Nonuniform Solutions. I. Basic Interface Theory
Authors: Hopper R. W. , Uhlmann D. R.
Published: February 2004

The thermodynamics of nonuniform solutions usually employs a gradient energy term in the expression for the local free energy. This arises from retaining the first nonvanishing terms of a MacLaurin expansion of the free energy in the composition and its derivatives. The nature of this expansion is discussed, and the formulation is extended to include derivatives higher than the second. General, a priori arguments suggest that a reasonable next approximation is f*=f(c) + κ1 ∇2c+κ2 (∇ c)2 + κ3∇4c+κ4(∇2c)2 + κ5∇ c · ∇3c + κ6(∇ c)2∇2c+ κ7(∇ c)4, for an isotropic solution. The results for a cubic system are also presented. The significance of the coefficients are discussed using a simple mean field pair interaction analysis. This interpretation provides physical insight into the nature of the terms and suggests that in the absence of specific knowledge about a particular situation, the derivative terms may be ordered in the following sequence of decreasing importance: κ1 ∇2c, κ3∇4c, [κ2(∇ c)2, κ5∇ c · ∇3c], [κ4(∇2 c)2, κ6(∇ c)2∇2c, κ7 (∇c)4]. The effect on the profile and interfacial tension of a flat diffuse interface of the κ3∇4c and the κ7(∇c)4 terms are determined. The pair interaction analysis indicates that the κ3∇4c term sharpens the interface profile and decreases the interface tension. When κ7 is positive, the κ7(∇c)4 term increases the interfacial tension and makes the interface more diffuse.
Binary Collision Broadening: Determination of Dispersion Forces
Authors: Hood R. J. , Reck G. P.
Published: February 2004

The width and shift of the potassium absorption line (42S1/2-52P1/2) perturbed by krypton is used to characterize excited-state interactions within the limitations of the nonresonant, adiabatic, binary collision impact approach. Calculations of width and shift using JWKB scattering phase shifts for both LJ potentials and potentials which include a dipole-quadrupole dispersion term are presented. The relationship of these calculations to thermal averages and more approximate theories is analyzed and discussed. The use of LJ potentials for excited-state interactions is shown definitely to be inconsistent with experiments. Through the use of the simple procedure developed here the contribution of the dipole-quadrupole dispersion to the interactions is estimated and shown to be completely in line with experimental results.
Theory of Intersystem Crossing in Aromatic Hydrocarbons
Authors: Lawetz V. , Orlandi G. , Siebrand W.
Published: February 2004

The electronic matrix elements governing intersystem crossing in aromatic hydrocarbons are derived and evaluated. The derivation is equivalent to Fano's treatment of resonance scattering. It is shown that the best first-order description for crossings that show simple unimolecular behavior involves molecular states that are both spin contaminated and vibronically contaminated, but can be adequately represented by an expansion to second order in pure-spin adiabatic Born-Oppenheimer states. The corresponding first- and second-order matrix elements are expanded about a nuclear equilibrium configuration and the expansions are terminated through the application of a symmetry argument. This yields five different types of matrix elements with small or vanishing cross terms; these matrix elements are associated with five experimentally distinguishable mechanisms, namely (1) direct spin-orbit coupling, (2) vibronically induced spin-orbit coupling, (3) mixed vibronic and spin-orbit coupling, (4) resonant spin-orbit coupling, and (5) vibronically induced resonant spin-orbit coupling. To distinguish these mechanisms use is made of isotope effects, spin polarization and vibrational selection. The available experimental data on singlet-to-triplet crossing in naphthalene and anthracene are analyzed in detail and compared with qualitative and quantitative theoretical predictions. It is concluded that at low temperature singlet-to-triplet crossing in naphthalene is dominated by crossing to the third-lowest triplet state via the third mechanism. At high temperature the dominant process involves either resonant crossing to the fourth-lowest triplet state via the fifth mechanism or resonant crossing to the fifth-lowest triplet state via the fourth mechanism. In an appendix spin-rotational and orbital-rotational coupling are shown to be too small to contribute measurably to these crossings.
Viscosity of the Noble Gases in the Temperature Range 25–700°C
Authors: Kestin J. , Ro S. T. , Wakeham W. A.
Published: February 2004

New relative measurements of the viscosity of xenon at a pressure P=1 atm and in the temperature range T=25–700°C are reported. The viscosity of argon has also been remeasured. A careful analysis of the long-term reproducibility of the oscillating-disk viscometer employed in the work is presented together with best estimates of the viscosity of all the noble gases. Standard reference values of the viscosity of the gases at atmospheric pressure and at zero density at 25°C are given. The data for all the monatomic gases are represented by means of a single empirical correlation.
Infrared Spectrum of AlCl3 and Al2Cl6 Isolated in Solid Argon
Authors: Lesiecki Michael L. , Shirk James S.
Published: February 2004

The infrared spectra of monomeric and dimeric aluminum chloride trapped in solid argon have been observed. For the monomer AlCl3 four infrared-active fundamentals including the symmetric stretch are observed, implying a pyramidal equilibrium structure. Other experimental data for AlCl3 are consistent with such a structure. A normal coordinate analysis suggests a Cl–Al–Cl angle near 112°. The structures of the aluminum halides are compared with observed trends in alkaline-earth dihalides.
NMR Study of ThAl2: 27Al, Dipolar Doublet, Quadrupole, and Anisotropic Shift Interactions
Authors: Torgeson D. R. , Barnes R. G. , Creel R. B.
Published: February 2004

The nuclear magnetic resonance spectra of powdered intermetallic compounds MX2 of the C32 (AlB2) structure type lend themselves to analysis and interpretation in terms of nuclear dipole doublet interaction, nuclear electric quadrupole, and anisotropic Knight shift interactions. Within the hexagonal plane of the C32 structure three Pake pairs may be formed with each of the X nearest neighbors. The observed doublets in the NMR spectra of X nuclei are of the Pake type when the magnetic moment of the N nuclear species is small. Examples are 11B in ZrB2 and TiB2 and 27Al in ThAl2. An extensive analysis of the ThAl2 NMR spectra is presented which yields values for the lowest pure quadrupole frequency νQ=230.5± 2.0 kHz and Knight shift parameters Kiso=(0.042± 0.003)% and Ksx=−(0.012± 0.003)% The nearest-neighbor distance obtained was in agreement with spacings determined by x-ray techniques.
Low Energy Electron Attachment to Ozone using Swarm Techniques
Authors: Stelman D. , Moruzzi J. L. , Phelps A. V.
Published: February 2004

The rate coefficients for the attachment of low energy electrons to ozone have been measured using the drift tube technique. The rate coefficients obtained in pure ozone at 300°K and in ozone-carbon dioxide mixtures at 200 and 300°K are consistent with a two-body attachment process which is independent of temperature. The rate coefficients measured in O3–CO2 mixtures can be expressed as (1.9± 0.4)× 10−9 (εK)1.46 cm3/sec for characteristic electron energies εK between 0.02 and 0.3 eV. This result is used to derive an energy dependent cross section for electron attachment to O3 for comparison with the electron beam data.
Thermomagnetic Torque for Nitric Oxide
Authors: Dahler John S. , Park Won-Hoon
Published: February 2004

The theory of the thermomagnetic torque due to Levi, McCourt, and Beenakker has been used to assess the relative magnitudes and field dependences of the torque contributions due to the second derivative dyad of temperature and to thermal creep. In the case of nitric oxide the latter is found to be responsible for approximately 25%−50% of the total torque.