bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of Thallous Chloride in Single Crystals of KCl by a Novel Spectrophotometric Method
Authors: Reisfeld Renata , Glasner Abraham , Honigbaum Alexander
Published: January 2005

A novel attachment to the Beckman DU spectrophotometer is described, by means of which the diffusion profile of some heavy-metal ions in alkali halides may be recorded.

The diffusion of Tl+ ions in KCl in the temperature range 270°-400°C was measured. It is concluded that the activation energy for the diffusion of Tl+ varies with temperature, parallel to that of the self-diffusion of K+ ions, calculated from conductivity measurements. The diffusion constants of the Tl+, at any temperature, are several orders higher, as the associated vacancies of the divalent impurities present are also involved in the diffusion process.
Experimental Oscillator Strengths of CO and CO+
Authors: Schwenker R. P.
Published: January 2005

The radiative lifetimes of the B 2Σ state of CO+ and the b 3Σ state of CO have been measured to be (1.01±0.05) 10−7 and (8.6±0.9) 10−8 sec, respectively. The oscillator strengths of the first negative system of CO+ and third positive system of CO, calculated from these lifetimes, are (7.9±0.7) 10−3 and (8.9±1.5) 10−3, respectively.
Irradiation Damage in Type I Diamond
Authors: Dyer H. B. , Preez L. du
Published: January 2005

In addition to the GRI and uv bands induced in all diamond by 0.78-MeV electron irradiation, another optical absorption feature, which we have named the ND1 band, is found in all Type I diamonds. A single EPR line appears to be associated with the ND1 band.

It is suggested that the ND1 center arises from the combination of a defect product—probably an interstitial—and nitrogen in platelet form. Certain observations can only be explained by assuming that the ND1 centers are not distributed randomly through the crystal, but occur in clusters.

The ND1 center acts as an acceptor, the center (probably a vacancy) responsible for the GRI and uv band as a donor. In the ionized state, GRI is optically inactive; ND1 is optically active. Electron transfer by thermal excitation results in the bleaching of GRI and enhancement of ND1. Illumination with light in the ND1 band causes electron transfer in the reverse direction, restoring band strengths to their former condition. A model is proposed which defines the energies within the forbidden gap of the ground and excited states of GRI and ND1.
Deep Impurity States in Molecular Crystals: The Optical Excitation of a Substitutional Argon Atom in Crystalline Neon
Authors: Webber Stephen , Rice Stuart A. , Jortner Joshua
Published: January 2005

The calculation of the first electronic transition of an argon-atom impurity in a neon lattice is carried out in the Heitler—London scheme. The energy of this transition is taken to be the energy of the argon atomic transition, plus the correction to the SCF 4s orbital energy due to the presence of the crystal. The modification to the SCF 4s orbital is accomplished by the addition of charge-transfer functions on neighboring neon atoms. It is shown that the choice of the SCF atomic function is a very bad starting point for these systems.

A general method for choosing basis functions for bound systems is presented. It is shown that for many cases a suitably chosen ``model Hamiltonian'' may be appropriate to a more complex system, and the case of a dielectrically screened hydrogenic ``model Hamiltonian'' is worked out for Ar–Ne.
Significant-Structure Theory of Binary Mixtures. II
Authors: Ma Shao-mu , Eyring Henry
Published: January 2005

The significant-structure theory has been successfully applied to the three binary systems involving carbon tetrachloride, benzene, and cyclohexane. In the first paper, the system carbon tetrachloride—cyclohexane was discussed. In this paper the other two systems, carbon tetrachloride—benzene and cyclohexane—benzene, are considered. The excess properties have been calculated on mixing at constant pressure as well as on mixing at constant volume. By taking account of the fact that the parameters in our theory are concentration dependent, a partition function for mixtures can be formulated in a similar way to those for single liquids.
Significant-Structure Theory and Cell Theory for Two-Dimensional Liquids of Hard Disks
Authors: Wang Yun-liang , Ree Taikyue , Ree Teresa S. , Eyring Henry
Published: January 2005

The significant-structure theory of liquids is applied to describe a two-dimensional liquid of hard disks. The results are in quite good agreement with the molecular-dynamics calculations. However, the virial expansion of the equation of state is in only fair agreement with the machine calculations. Cell theory is also applied to the two-dimensional liquid; it is found that although the agreement with the molecular-dynamics data is poor in the liquid range, the cell theory shows good agreement in the solid region.
Concentration Depolarization of the Phosphorescence Emission
Authors: Chaudhuri N. K. , El-Sayed M. A.
Published: January 2005

The degree of polarization (P) of the phosphorescence for several organic molecules is studied as a function of concentration (C) in the 10−4−10−1M range in rigid medium. For all of the molecules examined, P remains unchanged until C reaches 10−2M; then P starts declining. The decline of P is shown to arise neither from the decrease in solvent rigidity nor from crystallization of the molecules studied. Two possibilities that might explain the decline of P are discussed: (a) the formation of a charge-transfer complex that perturbs the direction of the emitting oscillator and (b) T—T energy transfer. The degree of polarization of some of the compounds studied does not change during the phosphorescence decay, a result that might favor the first possibility. The sensitivity of the value of the slope of the P–C curve to the phosphorescence lifetime provides evidence in support of the T—T energy-transfer mechanism. At concentrations below 10−2M, nonradiative S–S transfer seems to be either absent or relatively inefficient in depolarizing the phosphorescence emission in the systems studied. External heavy-atom effects on the degree of polarization of the phosphorescence of aromatic hydrocarbons are found to be much greater when caused by haloaromatics than by ethyl iodide. This observation might be due to either a larger association constant or stronger spin—orbit perturbation for the former compounds than for the latter.
Benzene d-6-Sensitized Photoisomerization of Butene-2 at Low Pressures by Long-Path Infrared Spectroscopy
Authors: Sigal Paul
Published: January 2005

The benzene d-6-sensitized trans-cis photoisomerization of butene-2 has been studied by means of long-path infrared spectroscopy. Relative quantum yields at pressures less than 1 mm were determined. Mechanisms for energy transfer in benzene d-6 consistent with the data are presented.
Vibrational Energy Transfer in Gases. Atom—Diatomic Molecule Collisions
Authors: Alterman Elliott B. , Wilson David J.
Published: January 2005

The interconversion of molecular vibrational energy and translational energy is studied; the equations of motion describing collinear collisions of a Morse diatomic molecule with a Lennard-Jones 6–12 atom are integrated numerically. The effects of initial relative translational energy and initial vibrational energy are determined, and vibrational relaxation times are calculated by a Monte Carlo method at three different temperatures and with two different translational energy distributions.
Association of Aromatic Hydrocarbon Negative Ions with Alkali Ions. A Spectroscopic Investigation
Authors: Buschow K. H. J. , Dieleman J. , Hoijtink G. J.
Published: January 2005

From measurements of the electrical conductances of solutions of alkali—aromatic hydrocarbon salts in 2-methyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane, information has been gathered about the conditions under which the hydrocarbon negative ions are ``free'' or associated with the alkali counter ion. Guided by this knowledge, a study has been made of the influence of association on the electronic spectra of some negative ions in the polyacene and polyphenyl series.
Ion-Beam Excitation Effects on the Single Charge Transfer between Argon and Nitrogen
Authors: Amme Robert C. , Hayden Howard C.
Published: January 2005

Single charge-transfer cross sections for N2+ in argon and Ar+ in molecular nitrogen and argon have been measured as functions of ion energy and of ion-source electron energy. Ion energies studied were in the range of 50 to 1000 eV. The ion-source electron energy was varied from 16 to 24 eV for the N2+ ions, and 16 to 40 eV for Ar+. For the Ar++N2 case, the cross section appeared to be nonresonant and was insensitive to ionizing electron energy. The slightly endothermic charge transfer for the N2++Ar case also appeared to be nonresonant, but was measurably influenced by ion-source electron energy. This result is attributed to the presence of long-lived excited states of N2+ reported earlier. Evidence is presented to show that the (N2+)* ions exhibit near-resonant behavior in charge transfer with argon atoms. This suggests that the effect is due to an increased population of vibrational states v=1, 2 at higher electron energies.
Inorganic Radicals Trapped in Glasses at Room Temperature. I. Iodine Atoms and I2— in Boric Acid Glass
Authors: Zaliouk-Gitter Adina , Treinin Avner
Published: January 2005

The photochemistry of I— in boric acid glass has been investigated. The primary production of iodine atoms and electrons can be followed by observing their absorption spectra. Under suitable conditions these species show marked stability in the glass at room temperature. Subsequent dark reactions lead to the formation of I2—. Further information about this radical is derived from studying the effect of 185-mμ and x-ray irradiations on I2 doped glass; I2— is probably formed by the attachment of electrons to I2 molecules. The photolysis of I3— has also been investigated. I3— appears to have an intense absorption centered at ∼190 mμ, which involves a CTTS type of excitation. The role of cage effect on the radiation-induced processes is discussed.
Thermal Expansion of Some Vanadium Carbides
Authors: Storms E. K. , Kempter C. P.
Published: January 2005

The thermal expansion characteristics of cubic VC0.89, cubic VC0.73, and hexagonal V2C were determined between room temperature and ∼600°C by the Debye—Scherrer technique using gold as an internal standard. For the range 25° to 600°C, the average linear thermal expansion coefficients are ᾱ=7.20,ᾱ=7.68, and ᾱa=6.50 and ᾱc=10.96 (all ×10−6/C°), respectively. For randomly oriented V2C, ᾱ was calculated to be about 8×10−6/C° for the same temperature range.
Thermal Decomposition of Fluoroform in a Single-Pulse Shock Tube. I
Authors: Tschuikow-Roux E. , Marte J. E.
Published: January 2005

The thermal decomposition of CF3H has been studied between 1200° and 1600°K behind reflected shock waves in a single-pulse shock tube. The principal reaction products are found to be tetrafluoroethylene and hydrogen fluoride. This fact, coupled with thermochemical considerations, suggests that the primary process in the pyrolysis of fluoroform is CF3H→CF2+HF. The observed activation energy, Eobs=63 kcal/mole, is lower than the heat of the reaction which is 75 kcal/mole if a ``reasonable'' value for the heat of formation of the CF2 biradical, ΔHf°(CF2)=−24 kcal/mole, is used. The reasons for this are discussed, and it is suggested that under present reaction conditions, the unimolecular decomposition may be in the falloff region.
Time Lag in Multistate Kinetics: Nucleation
Authors: Andres R. P. , Boudart M.
Published: January 2005

The time lag before establishment of a kinetic steady state is calculated for a linear multistate process in which there are only nearest-neighbor transitions. This time is discussed with regard to general nonequilibrium behavior and the effect of this time lag in the rapid nucleation of a condensed phase in a gas is explored.
Collisional-Radiative Recombination of He2+ into Dissociative States
Authors: Robertson W. W.
Published: January 2005

Spectroscopic investigation of a flowing helium afterglow revealed the presence of strong 10 830-Å atomic helium emission corresponding to the 23P→23S transition, which could be quenched by the application of a weak microwave field to the afterglow. An examination of the axial variation and pressure dependence of the concentration of 23P atoms established that it resulted primarily from the ion—electron recombination of He2+, rather than He+, at the higher pressures examined. An extension of the theory of collisional-radiative recombination of molecular ions to include dissociating states is postulated to explain these observations.
Rotational Isomerism and Microwave Spectroscopy. III. The Microwave Spectrum of 3-Fluoropropene
Authors: Hirota Eizi
Published: January 2005

The 3-fluoropropene molecule has been confirmed by microwave spectroscopy to exist in two rotational isomers, cis and gauche. Rotational constants in the ground vibrational state are A = 17236.638, B = 6002.915, C = 4579.827 Mc/sec for the cis and A = 27720.349, B = 4263.628, C = 4131.984 Mc/sec for the gauche form. Rotational transitions are also assigned for isotopic species, eight of the cis and nine of the gauche form. By using Costain's method the molecular structure is determined separately for the two isomers. The dipole moment and its components along the principal axes of inertia are μa=0.742±0.008, μb=1.601±0.011, μtotal=1.765±0.014 D for the cis and μa=1.595±0.006, μb=0.908±0.012, μc=0.623±0.014, μtotal=1.939±0.015 D for the gauche form. Through the temperature dependence of the intensity ratio the cis form is found more stable than the gauche form by 166±67 cal/mole.

The energies of the first and the second excited states of the C–C torsion are determined by the relative intensity measurement to be 169.6±4.2 cm−1 and 322.2±9.9 cm−1 for the cis and 84.6±2.8 cm−1 and 185±25 cm−1 for the gauche form. Some of the spectra in the excited states of the gauche form are doublets due to the tunnel effect through the trans barrier. Using these data a potential function for the rotation around the C–C single bond is discussed. A correlation is pointed out between the potential function and the binding states of carbon atoms forming the rotation axis.
Proper Accounting of Conformations of a Polymer Near a Surface
Authors: DiMarzio Edmund A.
Published: January 2005

It is well known that in free space the conformations of a freely jointed chain (n-mer) can be generated with proper equal a priori probabilities by means of a particle performing an n-step random walk. However, near a boundary the method of a random walk with reflecting barriers weights too heavily those paths that touch the boundary r times by a factor (w)r where w is greater than 1. The essence of a proper accounting is to place a completely absorbing site just beyond the boundary and to count only those chains that do not terminate on the absorbing site. For example, in the limit of large n where the diffusion equation becomes valid, the proper boundary condition is that of complete absorption at the boundary (concentration equals zero) rather than complete reflection (gradient of concentration equals zero) as has been assumed previously. In considering the problem of a polymer confined to a finite length strip of a one-dimensional lattice one ends up considering nonstochastic submatrices of the matrix of transition probabilities. Characteristic polymer dimensions near a surface are found to be larger than they would be away from the surface. The diffusion equation is then generalized so that it describes a polymer chain with self-excluded volume. Energy effects are also discussed.
Far-Ultraviolet Photolysis of Nitric Oxide
Authors: Leiga Algird G. , Taylor H. Austin
Published: January 2005

Nitric oxide has been photolyzed in the region 1550–1650 Å using a hydrogen discharge and at 1470 and 1236 Å using xenon and krypton discharges, respectively. The products at all wavelengths are N2 and NO2. At 1470 Å small amounts of N2O are produced. The quantum yield of N2 increases over the nitric oxide pressure range 5–900 mm from ∼0.2–0.5 and also with added inert gas. Quantum yields of NO2 production and of NO decomposition increase in a similar manner, and the wavelength has no profound effect. Since 1236-Å light ionizes NO, it is concluded that the recombination of NO+ and an electron leads to an excited molecule which decomposes, as it does at 1600 and at 1470 Å, into N and O atoms. These react with excess NO producing N2 and NO2.
Constrained-Variation Method in Molecular Quantum Mechanics. Application to Lithium Hydride
Authors: Rasiel Yecheskel , Whitman Donald R.
Published: January 2005

A general method is developed for calculating wavefunctions by minimizing the energy subject to the constraints of theoretically or experimentally known moments. The method is applied to a valence-bond type configuration-interaction wavefunction for LiH. An extremely small sacrifice in energy results when the wavefunction is constrained to fit the experimental dipole moment exactly. The expectation values of other physical properties are calculated both for the free-variation function and the constrained-variation function with the constrained-variation function yielding improved predictions for the diamagnetic shielding, diamagnetic susceptibility, and electric field gradient at the lithium nucleus. In addition, it exhibits better gauge invariance of the total susceptibility as well as improved adherence to the Hellmann—Feynman condition. New predictions of other properties which have not been determined experimentally are also calculated, including the electric quadrupole moment.
Method of Finding Symmetry Coordinates of Complex Molecules
Authors: Slansky Richard C.
Published: January 2005

A systematic method of finding a complete set of symmetry coordinates for complex molecules is derived from group theory. Utilizing a group-vibration approach, the symmetry coordinates of the molecule are constructed from the symmetry coordinates of the chemical radicals composing the molecule. The method minimizes computational labor by exploiting the symmetry of the radicals. To apply the final equation, one only needs to know the character table of the molecular symmetry group and the irreducible representations of the chemical radicals' symmetry groups. Neopentane serves as an example.
Spectrophotometric Determination of the Rate of Dissociation of Tetrafluorohydrazine Behind a Shock Wave
Authors: Brown Lawrence M. , Darwent Basil deB.
Published: January 2005

The rate of dissociation of tetrafluorohydrazine in N2 and Ar was determined at temperatures between 344° and 410°K and total pressures between 0.6 and 6.0 atm. The reaction was carried out by shock heating the gas mixtures in a shock tube. The progress of the reaction behind the incident shock wave was followed by a time-resolved spectrophotometric technique. The absorption coefficient of NF2 at λ2602 Å was determined experimentally between 350° and 571°K and found to be 537±10 liter/mole·cm. The kinetics data indicated that the dissociation in 99% N2 was quasiunimolecular throughout the experimental pressure range, attaining its first-order limit at a total pressure not far above 6 atm and its second-order region below 0.6 atm. The observed pressure for the region of transition from first- to second-order kinetics was reasonably consistent with the transition pressure obtained from classical theory on the basis of the estimated value (2×1015 sec−1) of the pre-exponential factor for the limiting high-pressure first-order specific rate. At approximately 2 atm the observed specific rate for the nitrogen mixture was given by k2(N2)=1014.98±0.42exp[(−19.4±0.7 kcal/mole)/RT]sec−1between 344° and 407°K. The indicated uncertainties are the standard deviations of the associated values.
Calculated Elastic Scattering Cross Sections for the Li+–He System
Authors: Weber G. G. , Bernstein R. B.
Published: January 2005

Calculations of the energy dependence of the total (and differential) elastic scattering cross sections for the Li+–He system have been carried out for a number of assumed interaction potentials taken from the literature. All of these are known to yield fairly good fits to existing mobility data, sensitive primarily to the long-range (r−4) term in the potential. The present results show that the total quantum cross sections (as well as the angular distributions) are also quite sensitive to the potential at short range (e.g., r<4 Å), even at low collision energies (E<1 eV). In particular, the behavior of the extrema in the energy dependence of the total cross sections offers a means of discrimination among the potentials.
Studies of Hydrogen-Bonded Systems. II. Tunneling and Tautomeric Equilibria in the N–H···N Hydrogen Bond of the Guanine—Cytosine Base Pair
Authors: Rein Robert , Harris Frank E.
Published: January 2005

Potential curves are obtained for the protonic motion within the N–H···N hydrogen bond in a charge-transfer excited state, and in ground states of the cation and anion of the guanine—cytosine base pair, using approximate SCF wavefunctions obtained by the authors in an earlier study. For these states and the ground state, estimates are made of the tunneling rate and equilibrium between the two proton positions of minimum energy.
Organic Ions in the Gas Phase. XV. Decomposition of n-Alkanes under Electron Impact
Authors: Meyerson Seymour
Published: January 2005

Ionic decomposition reactions of n-alkanes under electron impact have been explored by studying the mass spectra of multiply deuterated undecanes and dodecanes and of octane-1-d. Label retentions in fragment ions in 70-V spectra were supplemented by voltage dependence measurements and by metastable peaks. Alkanes appear to break down mainly by initial nonselective cleavage of carbon—carbon bonds, followed by further stepwise decomposition of the primary products, with intervening energy-releasing rearrangements to give a characteristic product distribution.
On the Validity of the Lorentz—Lorenz Equation Near the Critical Point
Authors: Larsen Sigurd Yves , Mountain Raymond D. , Zwanzig Robert
Published: January 2005

Corrections to the Lorentz—Lorenz equation for the refractive index of a fluid, due to long-range density fluctuations, have been evaluated near the critical point, using Yvon's statistical-mechanical theory of the refractive index, together with the Ornstein—Zernicke asymptotic form of the two-particle correlation function. For argon, with experimentally reasonable values for the numerical parameters, the correction is smaller than one part in 104.
Ignition Delays of a Hydrogen—Oxygen—Argon Mixture at Relatively Low Temperatures
Authors: Skinner Gordon B. , Ringrose Gordon H.
Published: January 2005

The ignition of a gas mixture containing 8 mole %H2 and 2 mole %O2 in argon was studied in a shock tube at 960°—1080°K. The observed ignition delays were longer than would be expected by extrapolation of data obtained by other workers at higher temperatures. The rapid increase in induction time with decreasing temperature can be accounted for quantitatively by an ignition mechanism involving HO2 radicals.
Interaction between Chlorophyll a and Vitamin K1 in Monomolecular Films
Authors: Gaines G. L. , Tweet A. G. , Bellamy W. D.
Published: January 2005

As part of a continuing study of monolayers containing molecules involved in photosynthesis, we have examined mixed films containing chlorophyll a and vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone). This quinone quenches the fluorescence of chlorophyll, both in monolayers highly diluted with oleyl alcohol and in those composed solely of pigment and vitamin K1. Mixed chlorophyll—vitamin K1 monolayers show deviations from ideal behavior, but the excess free energy of mixing, estimated from the pressure-area characteristics, is small (∼0.1 kcal/mole). Fluorescence measurements on diluted films can be interpreted in terms of collisional quenching. In concentrated films, where the lifetime of the excited state is greatly reduced and energy migration among pigment molecules is rapid, only qualitative interpretation is possible. Under these conditions, the effectiveness of each vitamin K1 molecule in quenching excitations which arrive on neighboring chlorophyll molecules appears to be reduced, but sharing of energy among pigment molecules leads to an efficient reduction in fluorescence yield.
Vacuum-Ultraviolet Photolysis of Ethane at High Temperature
Authors: Hampson R. F. , McNesby J. R.
Published: January 2005

The rates of production of HD in the photolysis of C2H6+C2D6 at 1470 and 1236 Å at temperatures sufficiently high to eliminate internal scavenging have been used as a measure of the relative importance of molecular elimination and atomic elimination processes. This, together with complete product analysis including isotopic determinations, gives the following relative weights for the primary processes 1470 Å1236 ÅC2H6*→H2+C2H4†1.001.00C2H6*→2H+C2H40.150.88C2H6*→CH4+CH20.020.50.The probability of dissociation of C2H4† into H2 and C2H2 increases relative to collisional stabilization by a factor of about 2 when the energy of the exciting photon is increased from 1470 to 1236 Å.
Explanation of Some Differences in the Correlation Energies of CH4, Ne, and NH4+
Authors: McKoy Vincent
Published: January 2005

The most recent nonempirical value for the correlation energy of CH4, Ecorr(CH4), is −0.344 a.u. Prior to this, Ecorr of the isoelectronic systems Ne and CH4 had been assumed equal (−0.393 a.u.). This paper gives a simple explanation of 50% of this difference, that is, from electrostatics the four protons in CH4 smeared over a sphere (spherical model) and only six at the center exert a smaller potential than all 10 at the center do in neon. This leads to a much larger effective nuclear charge for the orbitals in Ne. The Z dependence of Ecorr of Ne-like ions then sets |Ecorr(CH4)| at 0.025 a.u. less than |Ecorr(Ne)|. This approach will be useful in relating molecular Ecorr's to the correlation energy of related and better-understood atomic systems and in locating molecular Hartree—Fock limits. Two other results in this paper are (a) Ecorr(NH4+) given as −0.330 a.u. is too low and should be at least 0.344 a.u., that is, Ecorr(CH4). This suggests a better choice for the proton affinity of NH3. (b) |Ecorr(SiH4)| will be about 0.08 a.u. less than |Ecorr(argon)|.
Radiolysis of Hexafluoroethane
Authors: Kevan Larry , Hamlet Peter
Published: January 2005

The radiolysis of C2F6 at 3-atm pressure has been examined. The products and 100 eV yields are CF4 (1.6), cyclo-C3F6 (0.30), C3F8 (0.21), C4H10 (0.14), and C2F2 (0.03). Good material balance is obtained; the F/C ratio in the products is 3.0. Experiments using radical scavengers indicate that 50% of the CF4 comes from radical reactions and 50% from nonradical reactions, that C3F8 and C4H10 are entirely formed by radical reactions, and that C2F2 and cyclo-C3F6 are probably formed by ionic reactions. In Ar–C2F6 mixtures energy transfer, thought to be charge transfer, is observed and ionic production of C3F8 is seen. C2F6 is about one-fifth as sensitive to radiation decomposition as is C2H6. It is concluded that excited molecule decompositions, particularly those giving molecular fluorine, are relatively unimportant in the radiolysis of perfluoroalkanes.
On Semiclassical Scattering
Authors: Barker J. A. , Johnson C. H. J.
Published: January 2005

The behavior of the quantum-mechanical phase shifts for scattering by a potential well is examined in the classical limit. The phase shifts tend to zero in the classical limit for all cases in which the corresponding classical trajectory does not pass through the well. This disproves by counterexample the result of Curtiss and Powers which indicated that there should be a contribution to the phase shifts even in the classical limit from classically inaccessible but energetically possible regions between two inner classical turning points. The error in the latter result appears to arise from the neglect of bound states of positive energy which exist in the classical limit (and only in that limit).
Effect of Three Turning Points on Semiclassical Scattering
Authors: Curtiss C. F.
Published: January 2005

When three turning points occur in the effective potential, the region between the two inner turning points is associated with classically bound trajectories or quantum-mechanically metastable states. The effect of this portion of the effective potential-energy curve on the semiclassical phase shifts and transport cross sections is discussed.
Causes of l-Type Doubling in the 3p(E″) Rydberg State of Ammonia
Authors: Child Mark S. , Strauss Herbert L.
Published: January 2005

Expressions are developed for the rotational levels of an electronically degenerate planar XY3 molecule. It is shown that there can be strong l-type doubling only in levels with no vibrational angular momentum and that this doubling has two main causes, namely, a rotational—electronic interaction and a rotational—Jahn—Teller interaction. The l-type doubling of other levels is largely quenched by vibronic coupling.

Estimates of the observed l-type doubling in the 3p(E″) state of ammonia indicate that the two above contributions act in opposite senses. A mechanism which accounts for the variation of the observed l-type doubling with vibronic state is suggested.
Atomic-Beam Scattering Studies on the Li–Hg System: Quantum Effects and Velocity Dependence of the Cross Sections
Authors: Groblicki Peter J. , Bernstein Richard B.
Published: January 2005

Measurements of the velocity dependence of the angular intensity distribution of 6Li and 7Li beams scattered by a crossed Hg beam are reported. The Li beams were velocity selected, the Hg beam Maxwellian. Angular intensity distributions were measured at various relative velocities (vr) from 700–1200 m/sec, relative total cross sections (q) from vr=300 to 1350 m/sec. The differential cross sections show expected quantum interferences. Scattering patterns for 6Li— and 7Li–Hg are found to be identical at the same de Broglie wavelength. The over-all angular dependence of the scattering at low angles follows the θ−7/3 relationship characteristic of an r−6 long-range potential. Extrema in the total cross sections q(vr) were also observed. The experimental data were analyzed in terms of a Lennard-Jones (12, 6) potential, but it was not possible to determine a unique set of potential parameters. Comparison of observed and calculated results has yielded three nearly equivalent sets of σ, ε lying within the ranges 2.5≤σ≤3.5 Å, 480°≤ε/k≤1000°K.
Entropy and Related Thermodynamic Properties of Carbon Suboxide
Authors: McDougall Lee A. , Kilpatrick John E.
Published: January 2005

The heat capacity, the temperature of fusion (160.962°±0.002°K), the heat of fusion (1290.9±0.4 cal/mole), the vapor pressures, the heat of vaporization, and the entropy of the ideal gas at 1 atm, 230°K 62.12±0.15 cal/deg·mole) have been determined for carbon suboxide. The known structure and the six known fundamental vibrations lead to a calculated entropy of 54.33 cal/deg·mole, exclusive of the unknown seventh fundamental. The unobserved, doubly degenerate bending mode must have a frequency of about 61.6±2.6 cm−1.
Determination of the Excitation Functions for Formation of Metastable States of Some Rare Gases and Diatomic Molecules by Electron Impact
Authors: Olmsted John , Newton Amos S. , Street K.
Published: January 2005

An apparatus for the determination of the excitation functions for formation of metastable states by impact of electrons of precisely defined energies in the energy range from threshold to the ionization potential is described. Results are given for Ne, Ar, Kr, H2, N2, and CO. Two sharp resonances are observed in each of the rare-gas excitation functions, which correspond to excitation with electron exchange of the first two excited configurations of these atoms. For diatomic molecules, no such resonances are observed, except in nitrogen, where there is a resonance process with an onset energy of 11.8 eV. A partial explanation for the shapes of the excitation functions is offered, based on the location and character of the various excited triplet states of the molecules studied.
On the High-Temperature Electrical Conductivity of Alumina
Authors: Peters D. W. , Feinstein Lester , Peltzer Christian
Published: January 2005

The electrical conductivity of single-crystal Al2O3 and chromium-doped Al2O3 was measured in the temperature range of 1000°—1600°C. The measurements were made with the sample in air and in helium. The effects of the atmosphere on the measurements are discussed in detail.
Electron Energy for H2+ in the Ground State
Authors: Wind H.
Published: January 2005

The 1sσg state of the hydrogen molecular ion is investigated. The result is given as a table in which the electronic energy for a two-Coulomb center is given in seven decimal places for values of internuclear separation R up to 20 in steps of 0.05 a.u.
``Improved'' Free-Volume Theory of Liquids. V. Worm Model Calculations for the 12–6 Potential
Authors: Chung Harold S. , Dahler John S.
Published: January 2005

The worm or super-cell model has been used to estimate the equilibrium properties of a fluid whose molecules interact according to the Lennard-Jones 12–6 potential. The integral equation for the radial part of the cell-cluster distribution function has been solved by an iterative method. Values of the configurational energy, configurational entropy, and of the compressibility factor are tabulated for a wide range of temperatures and densities. The results are compared with those of other theoretical studies. The calculated values of pressure, internal energy, and entropy agree remarkably well with the available experimental data.
Cross Sections and Intramolecular Isotope Effects in AB—HD Ion—Molecule Reactions
Authors: Moran T. F. , Friedman L.
Published: January 2005

Isotopic ion—molecule reactions producing ABH+ and ABD+ ions (AB=N2, CO, O2, and CO2) when AB—HD mixtures are subjected to electron bombardment in the mass-spectrometer ion source have been studied as a function of reactant ion velocity. Good agreement between the experimental and theoretical cross sections for secondary ion formation is obtained when both AB+—HD and HD+—AB interactions are taken as possible reaction paths. Ionization-efficiency curves of the secondary ion products furnish supporting evidence for the assumed reaction mechanisms. Identification of reactant ions by ionization-efficiency curves is not sufficient to establish the thermochemistry of the ion—molecule reaction; distributions of vibronic states produced by electron impact are also required. The vibrational population of excited reactant ions formed in the electron impact process has been estimated from the squares of the overlap integrals of respective ground and excited ionized states. Data taken from published photoionization experiments were used to estimate the distribution of electronic excitation in the N2+, CO+, and O2+ reactant ions. This data served to better define the reactant ion species in the above ion—molecule interactions and aided in the analysis of energy transfer processes and intramolecular isotope effects in these reactions. Intramolecular isotope effects showed an increase in the ratio of ABH+/ABD+ with increasing reactant ion velocity. The isotope effects are described in terms of a unimolecular decomposition of the collision complex and ion or atom transfer mechanisms. The isotope effects indicate that atom transfer mechanisms are favored both in reactions of ions with high kinetic energy and in strongly exothermic reactions of relatively slow ions.
Focused Laser-Beam Experiment and the Oscillator Strength of the Swan System
Authors: Jeunehomme M. , Schwenker R. P.
Published: January 2005

The beam from a Q-spoiled ruby laser is focused on a graphite block maintained under vacuum. The C2 Swan system is produced and the fluorescence decay time is interpreted as the lifetime of the A 3IIg state of C2. The lifetimes of four different vibronic levels of that state are measured. The variation of the electronic part of the transition moment over the nuclear coordinates is deduced from the spread of the lifetime values. The oscillator strength f(0, 0) for the Swan system is calculated to be (4.33±0.12) 10−3.
Classical and Quantal Scattering. I. The Classical Action
Authors: Smith Felix T.
Published: January 2005

Classical scattering is based on the action A = S − S0, where S is the action over the actual trajectory and S0 is over the equivalent without interaction. For two-body spherical potential scattering A = Δ(L, E) − LΘ, where Θ is the deflection angle and Δ is the classical phase, the classical limit of 2ℏδl (E). A new, rapidly convergent integral expression is given for Δ (L, E). From this is derived a convergent expansion in 1/E valid for fixed L≠O, and an equivalent form in 1/L valid for fixed E. The lowest term in 1/L agrees with Massey and Mohr, and higher terms are evaluated.
Systematics of Mössbauer Isomer Shifts of Organo-Tin Compounds
Authors: Herber R. H. , Stöckler H. A. , Reichle W. T.
Published: January 2005

The Mössbauer spectra of 49 organo-tin compounds have been studied at liquid-nitrogen absorber temperatures, using a ceramic 119SnO2m source at room temperature with a parabolic motion spectrometer. The linear relationship between isomer shift and ligand electronegativity suggested by Goldanskii for compounds of the type SnX4 has been extended to organo-tin compounds with mixed ligands. On the basis of the observed isomer-shift range, the percentage of ionic character in organo-tin compounds is estimated as lying within an interval of ±5% of a mean value of ∼15%. Binuclear tin compounds of the type R3Sn—SnR3 show no resolvable quadrupole splitting. In aryl-tin compounds, para and meta substitution has little or no effect on the s character of the carbon—tin bond. The ratio ρ of the quadrupole splitting to the isomer shift (with respect to SnO2) has a value larger than 2.10 for compounds in which the Sn atom is sp3d hybridized or in which there is significant departure from tetrahedral symmetry, while ρ values in the range 0 to 1.8 are associated with tetrahedral (sp3 hybridized) tin atoms.
Theory of Rydberg Terms of the Nitrogen Molecule
Authors: Duncan A. B. F.
Published: January 2005

A simplified model is developed for calculation of Rydberg terms and is applied to the three lowest terms of the Worley—Jenkins series in molecular nitrogen. Motion of the excited electron is described by an effective Hamiltonian with interaction terms defined by the core electrons. One-electron energies are obtained relative to a fixed core energy, and the computed terms agree qualitatively with experimental values. The core is described by a minimal set of atomic functions centered at the midpoint of the internuclear axis chosen so that the essential features of charge distribution from the bonding molecular orbitals are reproduced. Rigid requirements of orthogonality between Rydberg and core orbital functions and between Rydberg functions are imposed. Penetration of the Rydberg electron into the core is relatively large and accounts for the major part of δ in the Rydberg formula. It is found that the experimental terms for n=4, 5 are well described by a sum of penetration energy and of the corresponding hydrogenic term, with δ=0.
Infrared Absorption by Peroxy-Nitrogen Trioxide Free Radical in the Gas Phase
Authors: Guillory William A. , Johnston Harold S.
Published: January 2005

In the course of studying the low-pressure thermal oxidation of nitric oxide by oxygen, a new absorption band occurring on the shoulder of the P branch of nitric oxide at 1840 cm−1 was observed. The new absorption band was shown to be first order with respect to both nitric oxide and oxygen. The variation of this absorption band with time indicated that it was probably due to the free-radical intermediate present in this system, and was assigned to peroxy-nitrogen trioxide. The structural assignment OONO, rather than the symmetrical nitrate radical is based on the absorption frequency and by a comparison with frequencies expected for OONO and symmetrical NO3. By assuming a value for the absorption coefficient of OONO, which is presumably formed by the rapid reversible reaction O2+NO⇌OONO, thermodynamic data concerning OONO and the equilibrium constant were estimated.
Numerical Study of the Three-Body Ion—Ion Recombination Rate
Authors: Feibelman Peter J.
Published: January 2005

The three-body ion—ion recombination rate is studied at low density, using the Monte Carlo calculational method. Good agreement with experiment is obtained using Brueckner's recently proposed model which includes the effect of ``dissociative collisions.'' Agreement of earlier theory with experiment is shown to be largely fortuitous.
Rates of Decomposition of Light and Deuterated Alkyl Radicals. 2-Hexyl and 2-Hexyl-d12, and 2-Octyl and 2-Octyl-d16
Authors: Pearson M. J. , Rabinovitch B. S. , Whitten G. Z.
Published: January 2005

The rates of decomposition of chemically activated 2-hexyl-d12 and 2-octyl-d16 radicals have been measured relative to their corresponding light radicals by an internal comparison method. The intermolecular secondary isotope effects so determined for these nonequilibrium systems were the high-pressure values and ranged from 4.6 for 2-hexyl at 300°K to 12.1 for 2-octyl at 195°K.

Application of the quantum statistical Marcus—Rice theory to appropriate vibrational models leads to theoretical rate constants for the light and heavy species. The resulting calculated isotope effects are in reasonable agreement with those measured. The effect of energy upon the theoretical magnitudes of the isotope effect has been examined by making a comparative study of the alkyl radicals, ethyl through 2-octyl, by varying the assumed ambient temperature over the range 100° to 1000°K. The accuracy of enumeration of vibrational energy densities for these large molecules was explicitly tested.
Molecular Distributions at Equilibrium. III. Ring—Chain Equilibrium in the Dimethylsilthians
Authors: Moedritzer Kurt , Van Wazer John R. , Dungan Claude H.
Published: January 2005

By heating mixtures of cyclic dimethylsilthians with either dichlorodimethylsilane, dimethoxydimethylsilane, or dimethylmercaptodimethylsilane, liquids are formed which are shown to be mixtures of molecules by proton nuclear magnetic resonance. The equilibria resulting from exchange on the dimethylsilicon moiety of bridging sulfur atoms with either chlorine atoms, methoxyl, or methylmercapto groups is shifted strongly towards the ring compounds. At equilibrium, two sizes of rings are seen, with the trimer predominating over the dimer. The appropriate equilibrium constants giving the distribution of chains and of rings and relating the chain distribution to the ring distribution are presented.
Vacuum-Ultraviolet Photolysis of Ethane in Liquid-Nitrogen Solution
Authors: Pirog J. A. , McNesby J. R.
Published: January 2005

The photolysis of C2H6 in liquid nitrogen was studied at 1470 Å. It was found that the excited ethylene so produced, whose alternative paths are collisional deactivation and decomposition to acetylene plus hydrogen, was entirely deactivated by nitrogen with the acetylene quantum yield falling to zero at very low conversion: C2H6*→C2H4†+H2,C2H4†+M→C2H4+M.The excited ethane formed in the primary process is not deactivated by 1012 collisions per second with nitrogen. Excited ethylene formed by photolysis of ethylene at 1470 Å is not quenched by the nitrogen but is partially quenched by 0.001 mole fraction NO. Thus, electronically excited ethylene is partially deactivated by collisions at a rate of 109 sec−1. No positive evidence for reaction of CH3CH with N2 was obtained.
Triplet—Triplet Absorption in Sensitized Solvent Decomposition: An EPR Study
Authors: Siegel Seymour , Eisenthal Kenneth
Published: January 2005

The decay of the steady-state electron paramagnetic resonance (EPR) signal from naphthalene triplet-state molecules in ether and other glasses under continuous near-ultraviolet irradiation at 77°K has been examined in some detail. It has been shown that free radicals are produced by sensitized solvent decomposition at a rate proportional to the rate of the disappearance of the triplet-state EPR signal. Also, it has been demonstrated that the latter decay process has a first-order dependence upon naphthalene concentration and that it exhibits a dependence upon excitation intensity, which is consistent with a stepwise two-photon absorption mechanism.

The experimental results are discussed in terms of a model that involves the resonant transfer of energy from a highly excited triplet state of naphthalene to the solvent. Excitation of the excited triplet state takes place via the absorption of a photon by a naphthalene molecule in its lowest triplet state. The free radicals are produced by the decomposition of the sensitized solvent molecule. It is believed that the naphthalene molecule is not destroyed in this process but that the EPR signal decay arises from a radical—molecule interaction which effectively shortens the lifetime of the triplet state.
Photoreactive State of Acridine in Solution
Authors: Kellmann Arlette , Dubois Jean T.
Published: January 2005

The technique of energy transfer has been used in an attempt to establish the photoreactive state of acridine in solution. It is shown that the lowest-lying triplet of acridine, the ππ* triplet, is not the reactive species and that the reaction originates, at least in part, through the nπ* triplet. In the course of this work, the transfer of triplet-state energy from biacetyl to acridine, phenazine, anthracene, 1,2-benzanthracene, pyrene, 1,2-benzpyrene and 3,4-benzpyrene has been studied by an intensity method.
Absorption Spectra of Three Catacondensed Hydrocarbons in Compressed Plastic Media
Authors: Offen Henry W.
Published: January 2005

The electronic spectra of the catacondensed hydrocarbons phenanthrene, 1,2-benzanthracene, and chrysene in the plastic media lucite, polystyrene, cellulose acetate, and polyvinyl acetate reveal a red shift with increasing pressure. The magnitude of the spectral displacement ranges from 200–900 cm−1 at 27 kbar for the various electronic transitions. The red shift may be interpreted by the Bayliss model for solvent shifts and the assumption that the solute cavity radius varies inversely with the pressure. An unusual pressure dependence of the La band shape of 1,2-benzanthracene is observed and may arise from overlapping electronic transitions.
Statistical—Mechanical Treatment of Multistranded Polynucleotide Molecules
Authors: Litan Adiel , Lifson Shneior
Published: January 2005

The partition function and molecular averages of polynucleotide double-chain molecules are derived both for perfect matching, by direct application of the method of sequence-generating functions, and for imperfect matching, by an extension of that method. A proof of the validity of this extension is given by the method of steepest descents. Results are in agreement with those derived by combinatorial methods. The resemblance of the double strand with imperfect matching to a one-dimensional two-component system is pointed out. Extension of the theory for the treatment of triple helices is briefly discussed.
Double-Quantum External Photoelectric Effect in Organic Crystals
Authors: Pope Martin , Kallmann Hartmut , Giachino Joseph
Published: January 2005

Illumination of anthracene, tetracene, and perylene single crystals with strongly absorbed light of energy several electron volts smaller than the reported threshold for electron emission, produces electron emission at a rate proportional to the square of the light intensity, indicating the occurrence of a biphotonic process. Evidence is presented in the case of anthracene indicating that a singlet exciton—exciton interaction is involved. The efficiency of photoemission in anthracene is 10−25 I0, where I0 is the intensity of 3650-Å light. The escape depth of the electrons is estimated as equal to or greater than 40 Å.