bluuebunny/crossref_metadata_2025 huggingface dataset:
Equilibria in Hydrogen—Tritium Mixtures. Steady States and Initial Reaction Rates at 76.7°K
Authors: Jones Wesley M.
Published: January 2005

H2, T2, and HT are brought to thermodynamic equilibrium by the tritium β particles at 299° and 192°K if precautions are taken to minimize impurities; otherwise the steady-state quotient, Q=(HT)2/(H2)(T2), tends to be higher than the equilibrium constant K. At 192°K the initial reaction rates in H2—T2 mixtures correspond to about 3000 molecules reacting per ion pair. The results can be understood in terms of the thermal ion—molecule chain reactions of Thompson and Schaeffer. If the chains are shortened by impurities, the importance of hot processes tending to make Q>K is emphasized. The hot processes may be hot atom—molecule reactions caused by hot atoms formed by the recombination of H3+ ions (chain-breaking step). At 76.7°K the behavior is quite different. Initial reaction rates correspond to only about 20 molecules reacting per ion pair. Q is in general significantly higher than K (76.7°K)=0.63 and approaches K only in the limits of zero pressure or zero tritium content. This behavior is discussed in terms of short thermal ion—molecule chains and of hot processes resulting from the products of recombination of H3+ ions. The importance of the hot processes seems to be determined by a competition between wall and volume recombination.
Anisotropies of Polarizability ofn-Alkanes
Authors: Nagai Kazuo
Published: January 2005

Anisotropies of polarizability, or optical anisotropies, of n-alkanes have been calculated by the matrix method, on the basis of the additivity principle of bond polarizabilities. The geometrical model employed is the familiar GG′-eliminated three-state [trans (θ(T)=0°), gauche (θ(G)=120°), and gauche prime (θ(G′)=−120°)] rotational—isomeric model. For this model, expressions derived involve two parameters, EG the energy of the gauche bond relative to that of the trans, and Δαe=(α1—α2)C–C −2(α1—α2)C–H the effective anisotropy of the C–C bond, where (α1—α2)C–C and (α1—α2)C–H are the bond anisotropies of the C–C and C–H bonds. Numerical results are compared with experimental data in the pure liquid and in various solvents, determined by Clément and Bothorel from measurements of depolarizations of Rayleigh scattering. Data in CCl4 are fairly well fitted with theory by using a reasonable value of EG=800 cal/mole. Data in n-pentane, n-heptane, and in the pure liquid are greater than predicted by using acceptable values of EG, the difference being much more pronounced with longer chains. This effect is ascribed to the orientational order existing among geometrically asymmetric molecules in condensed phase.
Spin-Relaxation Effects on the EPR Spectrum of Gaseous Nitrogen Atoms
Authors: Brown Robert L. , Brennen W.
Published: January 2005

Experimental evidence is presented which indicates that N atoms produced in a flow system by a microwave discharge through purified N2 can have a relaxation time T1 comparable to their residence time in the EPR magnetic field. As a result, atoms generated outside the field (and therefore unmagnetized) can arrive at the microwave cavity before reaching their equilibrium magnetization. Under such conditions, we found that addition to the discharged N2 of as little as 40-ppm O2 (which did not affect the N-atom concentration) decreased T1 and led to increases as great as sevenfold in unsaturated N-atom EPR line intensities. Interpreting the effects of O2 addition in terms of a two-level spin model for N, we estimated a value of ≃0.5×10−15 cm2 for the N–O2 spin-exchange cross section. Without added O2, power saturation of the N-atom lines was found to be governed primarily by the rate at which unsaturated atoms entered the cavity and not by collision relaxation processes. Several qualitative observations regarding the nitrogen-pink afterglow, electron production, and the effects of NO addition are also reported.
Role ofl→aπ Transitions in Spin—Orbit Coupling of Aromatic Amines: Phosphorescence of Aniline and itsN-Alkyl Derivatives
Authors: Lim E. C. , Chakrabarti S. K.
Published: January 2005

Theoretical predictions supported by experimental results are presented which indicate that l→aπ charge-transfer transitions play an important role in the spin—orbit coupling of aniline and related molecules. The results consist of: (1) correlation between lifetime and polarization of phosphorescence for a series of amines, (2) effect of steric hindrance on lifetime and polarization of phosphorescence, and (3) comparison of radiative lifetimes of the lowest triplet states of anilines with those of benzene and its alkyl derivatives.
Theoretical Investigations of Translation—Rotation Energy Transfer. II. Semiclassical Treatment of (p-H2, He) and (o-D2, He) Systems
Authors: Raff L. M.
Published: January 2005

A semiclassical analysis of translation—rotation energy transfer in (p—H2, He) and (o-D2, He) systems is reported. The Krauss—Mies potential surface has been employed to calculate 0→2 rotational excitation cross sections as a function of relative velocity and attractive well depth. For a well depth of 1.675×10−3 eV, the (p-H2, He) cross sections range from 0.54 to 1.144 Å2 at relative velocities of 4.5×105 and 8.0×105 cm/sec, respectively. The (o-D2, He) cross sections vary from 1.382 to 1.461 Å2 for relative velocities of 4.5×105 and 6.0×105 cm/sec, respectively. A maximum in the excitation cross section is observed at a relative energy of about 0.427 eV for the (p-H2, He) system and at 0.27 eV for the (o-D2, He) system. In both systems the calculated cross sections increase with increasing attractive well depth. Consideration of intermultiplet transitions in the (p-H2, He) system indicates that inclusion of such transitions is unimportant in systems of this type. Comparison with previous classical calculations employing the same potential surface indicates that the classically calculated cross sections are probably high by at least a factor of 2. Calculated cross-section ratios, however, are in good agreement with the present results. Semiquantitative agreement between classical and semiclassical results is obtained with regard to the dependence of the cross sections on attractive well depth and the variation of the excitation probability with the He attack angle. It is concluded, in general, that the extent of agreement between the models is sufficient to justify the use of classical models to treat the purely quantum phonomenon of transitions between specific energy states.
Photolysis of Nitrous Oxide at 1470 Å
Authors: Yang John Y. , Servedio Frank M.
Published: January 2005

Nitrous oxide, in the pressure range of 1–760 torr, has been photolyzed at 1470 Å. The rates of N2, O2, and NO formations are independent of the N2O pressure. The quantum yields are φN2=1.40±0.02, φO2=0.58±0.03, and φNO=0.78±0.03. A reaction scheme for the photodecomposition of nitrous oxide is given, and a quantitative correlation of the observed product yields with those expected from the proposed mechanism is demonstrated.
Adjustment of Ab Initio Potential Curves
Authors: Klein D. J. , Greenawalt E. M. , Matsen F. A.
Published: January 2005

A semiempirical method of adjusting ab initio diatomic molecule potential curves is described. The adjusted curve gives the exact result in the separated- and united-atom limits and also has correct asymptotic behavior in these limits. Different adjustment procedures are considered. At present, we favor the so-called ``pseudokinetic-energy'' adjustment procedure in which pseudokinetic energies are calculated from the virial formula. This procedure is applied to several ab initio potentials for He2 (1s2, 1s2s, 3Σu+).
Energy Calculation by the Method of Local Moments
Authors: Silverstone Harris J. , Yin Moon-Lung , Somorjai R. L.
Published: January 2005

A new method for obtaining energies without integrals, which combines the formalism of the ``method of moments'' with the spirit of the ``local-energy method,'' is proposed. This ``method of local moments'' avoids some of the convergence difficulties of the method of moments and some of the arbitrariness of the local-energy method. Advantages and disadvantages are discussed, and some features of the method are illustrated by examples. Several generalized versions of the method are also discussed.
Use of Computer Experiments to Locate the Melting Transition and Calculate the Entropy in the Solid Phase
Authors: Hoover William G. , Ree Francis H.
Published: January 2005

Modern computers can accurately simulate the behavior of idealized systems of several hundred particles, but they have trouble in studying the melting process in which small-system surface effects make the transition irreversible. It is here suggested that a thermodynamically reversible path linking the solid and fluid phases can be obtained by using a periodic ``external field'' to stabilize the solid phase at low density. The properties of the artificially stabilized solid at low density are studied theoretically, and two practical schemes are outlined for determining the melting parameters by using computer-calculated entropies.
Determining Hydrogen Diffusion in Doped Fused Silica from the Fluorescence
Authors: Weaver E. A. , Heckman R. W. , Williams E. L.
Published: January 2005

Fused silica doped with both Tb and Eu exhibits a visible fluorescent green band under ultraviolet light after a heat treatment above 700°C in a hydrogen atmosphere. The growth kinetics of this band have been studied as a function of time, temperature, and hydrogen pressure in the temperature range of 700°—1050°C, and have been found to be a hydrogen diffusion-controlled reaction. From these measurements and using tritium, diffusion coefficients have been evaluated, and in the temperature range of 850°—1040°C can be represented by the relation: D=6.5×10−5 exp(−12.5 kcal mole−1/RT)cm2sec.−1 The mechanism of the fluorescent scheme is believed to be a reduction of the Eu3+ ion to Eu2+ ion by the diffusing hydrogen, with the reduced ion being able to absorb light. This is followed by an energy transfer to the trivalent terbium ion, and then a terbium fluorescence.
Electronic Structure of Hexaquometal Ions. III. Magnetic Measurements
Authors: Carlin Richard L. , Terezakis Emanuel G.
Published: January 2005

Magnetic measurements obtained by the Gouy method are reported over a temperature range (77°—300°K) for hexahydrated trivalent ions of titanium and vanadium, and estimates of trigonal field parameters are presented. Measurements on C(NH2)3V(SO4)2·6H2O to 1.96°K on a pendulum magnetometer confirm the ground state in this compound as 3A (3T1g). The correlation of these studies with earlier spectral results is discussed. It is also shown that V(urea)6Br3 exhibits magnetic behavior similar to that of the hydrates, and that C(NH2)3Cr(SO4)2·6H2O is magnetically normal.
Vapor Pressure of Holmium
Authors: Wakefield G. F. , Daane A. H. , Spedding F. H.
Published: January 2005

The vapor pressure of holmium was measured from 10−8 to 101 torr using modifications of the Langmuir and Knudsen methods. A tube-type orifice permitted use of the Knudsen method at the higher pressures, with suitable corrections. Lowest pressures were measured using a graphite condenser surrounding a large area Langmuir sample, with the vaporized metal being trapped as the nonvolatile carbide. The vapor pressure of the solid α-holmium is given by logPtorr=(−15 137/T°K)+8.426, and the vapor pressure of the liquid by logPtorr=(−14 122/T°K)+7.849. The heat of vaporization and heat of sublimation (298°K) were 64.7±0.5 and 70.6±0.7 kcal/mole, respectively. The enthalpy change from α-solid to liquid holmium, corresponding to heats of fusion and transformation, was 4.6±0.7 kcal/mole.
Paramagnetic Relaxation of Trapped Hydrogen Atoms in Irradiated Frozen Aqueous Solutions
Authors: Zimbrick John , Kevan Larry
Published: January 2005

The paramagnetic relaxation characteristics of trapped hydrogen atoms in γ-irradiated acidic and oxyanion ices were studied by power-saturation techniques. Relaxation times were measured as a function of radiation dose, deuteration, phase, and solute. The EPR linewidth of the trapped hydrogen atom was measured under various conditions. The EPR lineshape and power-saturation response indicate that the linewidth is due to contributions from both homogeneous and inhomogeneous interactions. The changes in relaxation time with radiation dose indicate that hydrogen atoms are trapped with a uniform distribution near oxyanions in the ice and are not trapped within radiation-produced spurs. The presence of phase effects on relaxation times supports an interstitial-defect model for the hydrogen-atom trapping site and suggests that the trap potential energy well is shallower in the polycrystalline phase than in the glassy phase. In polycrystalline ices the coupling between trapped hydrogen atoms and lattice phonons is modified by the type of oxyanion.
Signs of Spin—Spin Coupling Constants between Methyl Protons and Ring Fluorine Nuclei in Fluorotoluene Derivatives. Further Evidence for a Positive Hyperfine Interaction in the C–F Bond
Authors: Blears D. J. , Danyluk S. S. , Schaefer T.
Published: January 2005

The signs of spin—spin coupling constants between the methyl protons and fluorine nuclei in ortho, meta, and para fluorotoluene derivatives have been determined by double-resonance techniques. J0F,CH3 and JpF,CH3 are positive, while JmF,CH3 is negative. This sign sequence is opposite to that of the corresponding methyl proton-ring proton couplings and is the consequence of a positive hyperfine coupling constant in the C–F bond. This result implies that double-bond character in the C–F bond entails an additional σ—π interaction overshadowing that expected by analogy with the C–H bond. Sizeable negative π contributions to J0HF and JpHF are indicated by the experimental results.
Surface Interactions of Iodine Vapor with Tungsten
Authors: McCarroll Bruce
Published: January 2005

The interactions of iodine vapor with a clean tungsten surface were studied by first adsorbing the iodine on the tungsten ribbon and then thermally desorbing the adlayer. The composition of the desorption products was determined with a time-of-flight mass spectrometer. No evidence is found for the formation of surface compounds. Only iodine atoms and, at higher coverages, iodine molecules populate the surface. Both desorptions are first order, and the most tightly bound atom state has a desorption energy of ∼80 kcal. A second, lower-energy atom state is populated at higher coverages. An estimate of the iodine molecule desorption energy gives ∼40 kcal.
Electronic Spectrum of Single-Crystal Dy2O3
Authors: Henderson James R. , Muramoto M. , Henderson T. M. , Gruber John B.
Published: January 2005

The absorption spectra of single crystals of Dy2O3 observed at 10°, 80°, and 290°K were analyzed in the 0.26–40-μ wavelength region. Over 600 transitions from all eight crystalline Stark levels of the ground 6H15/2 state to 40 excited J manifolds of the Dy3+ ion in C2 sites were assigned. The observed spectrum is assigned with the aid of a calculation of ``free-ion'' energy levels of Dy3+ between the ground state and 36 000 cm−1. The Racah parameters E1=6300, E2=31.95, E3=614.2, and ζ=−1881 cm−1, all obtained by direct diagonalization and least-squares fitting, yield an rms deviation of 83 cm−1 between 31 observed and calculated free-ion energy levels. The 6F1/2 state, and all states above 23 000 cm−1 are reported and analyzed for the first time in any crystal.
Hyperfine Structure in the Microwave Spectra of CFCl3 and CHCl3
Authors: Wolf A. A. , Williams Quitman , Weatherly T. L.
Published: January 2005

The theory for the hyperfine structure in the rotational spectrum of symmetric-top molecules containing three identical quadrupolar nuclei is discussed. Formulas and tables are given from which the quadrupole interaction energies, and the transition frequencies and intensities can be calculated for the case of nuclear spin 32. The theory is applied to the molecules CF35Cl3 and CH35Cl3 with completely satisfactory results. The bond-axis quadrupole coupling constants determined for CF35Cl3 and CH35Cl3 are −79.9±0.6 Mc/sec and −77.9±0.5 Mc/sec, respectively. Rotational constants were determined for four rotational transitions of each molecule, and the results are in agreement with centrifugal-distortion theory.
Condensed-Phase Photolysis and Radiolysis of 2-Methylbutane
Authors: Scala A. A. , Ausloos P.
Published: January 2005

The condensed-phase photolysis of i-C5H12–i-C5D12 mixtures, and CH3CD (CH3) CH2CH3 has been investigated at photon energies above and below the ionization energy of 2-methylbutane (10.32 eV), that is, at 1470 Å (8.4 eV), 1236 Å (10.0 eV), and 1048–1067 Å (11.6–11.8 eV). The electronically excited 2-methylbutane molecule undergoes essentially the same primary decomposition processes in the condensed phase as in the gas phase. However, in contrast with the gas phase, the internally excited fragments formed in these primary processes are entirely deactivated.

It is demonstrated that C5H12+ ions are produced at 1048–1067 Å and to a lesser extent at 1236 Å. A fraction of these ions transfer an H2 molecule to c-C3D6 to form CD2HCD2CD2H as a product. In the krypton and argon sensitized radiolysis at 77° and 20°K, respectively, energy transfer from the rare-gas matrix to 2-methylbutane occurs with high efficiency and all products can be accounted for by decomposition of neutral excited 2-methylbutane, formed by excitation transfer and/or neutralization of ions formed in charge-transfer reactions with rare gas ions.

In the radiolysis of pure 2-methylbutane at 77°K, ethane and propane are almost entirely formed through molecular elimination and geminate radical disproportionation processes. Addition of an electron scavenger such as CCl4 lowers the yields of these products, as well as those of the corresponding olefins (e.g., C3H6 and C2H4). A change in the neutralization mechanism of the parent ion (C5H12+) can account for the latter observation. Apparently, fragmentation of the parent ion is unimportant in the condensed phase. Butane (G∼0.1) is the only product which can tentatively be related to reaction of fragment ions (C4H8+, C4H9+). The modes of formation of products, such as the pentenes and the hydrogen in the radiolysis of pure C5H12 remain unexplained.
Investigation of Some Ce3+-Activated Phosphors
Authors: Blasse G. , Bril A.
Published: January 2005

The fluorescence of a number of new Ce3+-activated phosphors is described and discussed. Only host lattices with a sublattice consisting of trivalent lanthanide ions are used to avoid charge compensation of the Ce3+ ion. Usually the Ce3+ emission is in the near-ultraviolet region. Y3Al5O12–Ce and SrY2O4–Ce, however, show emission in the visible region with a maximum in the green. Conditions for visible Ce3+ emission are indicated, viz., large crystal-field splittings (Y3Al5O12–Ce) or a large Stokes shift (SrY2O4–Ce). In a number of cases we were able to observe all crystal-field components of the excited 5d level of Ce3+. The cubic crystal-field splitting of the 5d level varies strongly with host lattice from 7000 to 14 000 cm−1. The position of the center of the 5d levels in oxides is about 30% lower than in the free ion. For some phosphors we observed more than one emission band at room temperature. This is due to fluorescence from higher excited levels. Efficient energy transfer from Ce3+ to Cr3+ was observed in Y3Al5O12.
Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of the Free Radical NCO
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

The free radical NCO is stabilized in sufficient concentration for direct infrared and ultraviolet spectroscopic identification upon vacuum-ultraviolet photolysis of HNCO suspended in various matrix materials at 4° and at 14°K. Observations on the B(2Π)—X(2Π) electronic transition of NCO have been extended to shorter wavelengths than those previously reported. Isotopically substituted NCO has been prepared in supplementary experiments involving the vacuum-ultraviolet photolysis of CO:HN3 and Ar:HCN:N2O samples, as well as by the mercury arc photolysis of matrix-isolated samples of NO+N3CN. The three vibrational fundamentals of ground-state NCO appear at 487, 1275, and 1933 cm−1 in an Ar matrix. The values obtained for the stretching force constants suggest that the carbon—oxygen bond may be somewhat stronger than the carbon—nitrogen bond. There is an appreciable positive stretching-interaction force constant. NCO is found to photolyze when subjected to radiation of wavelength near 2537 Å, leading to the production of N+CO. Reactions occurring in the various systems investigated are discussed.
Dependence of Correlation Energy upon Bond Angle: Investigation of Interactions between Nearly Degenerate Electronic Configurations
Authors: Hayes Edward F. , Pfeiffer Gary V.
Published: January 2005

Configuration interaction of low-lying electronic states is used to investigate the molecular correlation energy as a function of bond angle. Qualitative aspects of the problem are discussed using the molecular-orbital diagrams of Walsh and Mulliken. Results of configuration-interaction calculations of BeH2 and NO2+ are reported. The possibility of double minima in the potential surfaces for AB2 molecules is considered.
Ferroelectric Moment in Guanidinium Aluminum Sulfate Hexahydrate, GASH
Authors: Schein B. J. B. , Lingafelter E. C.
Published: January 2005

Examination of the details of the crystal structure of the isomorphous compounds GASH and GCrSH has lead to the recognition of a possible mechanism for the ferroelectric reversal of polarization direction. The suggested mechanism predicts the possibility of the occurrence of ``pseudodomains,'' i.e., contiguous regions in the crystal having the same direction of polarization, but separated by ``pseudodomain walls.'' Calculation, from the structure parameters, of the magnitude of the ferroelectric dipole for the two crystals gives satisfactory agreement with the experimental values. Preliminary measurements of x-ray diffraction intensities with CuKα radiation on poled crystals of GCrSH are in accord with the proposed model.
Spectrophotometric Measurements of the Vibrational Relaxation of CO in Shock-Wave and Nozzle Expansion-Flow Environments
Authors: Russo Anthony L.
Published: January 2005

Infrared and Na line-reversal spectrophotometric methods have been employed for the investigation of the vibrational relaxation of pure CO and 5% CO+95% Ar test-gas mixtures behind normal shock waves and in quasisteady expansion flows. The shock-wave studies were conducted over a range of equilibrium shocked-gas temperatures of about 1400°—3200°K and pressures of a few atmospheres. Vibrational relaxation times obtained by these two techniques were found to agree quite well and are consistent with other available shock-wave data for both test-gas mixtures. The expansion-flow results for 5% CO+95% Ar were obtained in a shock-driven conical nozzle for a range of reservoir temperatures of about 3500°—5000°K and reservoir pressures of about 45 atm. For these experiments, the Na line-reversal and CO infrared diagnostic techniques indicated vibrational temperatures much lower than those predicted by the Landau—Teller theory using the shock-wave measured rate data. In addition, the infrared measurements indicated somewhat lower vibrational temperatures than the Na line-reversal results. In terms of vibrational relaxation rates, the expansion-flow data indicate that the de-excitation process in the nozzle proceeds about two orders of magnitude faster than anticipated on the basis of the rates measured behind shock waves. These observations are consistent with previous results obtained for N2. While a conclusive explanation of these results is not presently available, the results of recent theoretical studies are discussed which suggest that the detailed mechanism of the relaxation process may depend on the gas-dynamic environment.
Mass-Spectrometric Study of the Reaction of Atomic Hydrogen with Acetaldehyde
Authors: McKnight Charles , Niki H. , Weinstock Bernard
Published: January 2005

The reaction of atomic hydrogen with acetaldehyde has been studied with a discharge-flow system coupled to a time-of-flight mass spectrometer. The results are consistent with the mechanism Primary step: CH3CHO+H→CH3CO+H2;Secondary steps: CH3CO+H→CH2CO+H2,CH2CO+H→CH3CO*→CH3+CO,and CH3+H→ lim wallCH4.

The rate constant for the abstraction of the aldehydic hydrogen in the primary step (1) for the isotopic modification CD3CDO+D has been determined directly to be 3.2±0.5×10−14 cc molecule−1·sec−1 at 300°K. Under the conditions studied, the major reaction of the acetyl radical is its further reaction with hydrogen atoms to form ketene (6). The final carbon containing products, CO and CH4, are formed from subsequent reactions of ketene with hydrogen atoms (10). The kinetic behavior of the products, CH2CO and CH4, confirms the role of ketene as a major intermediate species in this system. Isotopic studies further confirm that methane is formed from a reaction sequence of ketene with H atoms. The above mechanism is compatible with previous studies of this system, with the exception of a recent communication by Lambert, Christie, and Linnett (Chem. Commun. 1967, 338), who suggest a primary step that yields methane and the formyl radical, CHO, rather than Reaction (1).
Excited-State Wavefunctions, Excitation Energies, and Oscillator Strengths in Selenium (p4↔p3s)
Authors: Knox Robert S. , Olechna Doris J.
Published: January 2005

Solutions of the nonrelativistic Hartree—Fock equations for the 4p35s(3S) term of the Se atom have been obtained. Wavefunctions are tabulated and results of computations of excitation energies and oscillator strengths are presented. The computed emission oscillator strengths for the 3S1→4p4(3PJ) array agree with those obtained by semiempirical methods, both being in rather sharp disagreement with available experimental values. Excitation energies are predicted to within 25%.
Effect of Internal Rotation on Angular Correlation Functions
Authors: Wallach Daniel
Published: January 2005

Fluorescence polarization, nuclear magnetic resonance, and electron spin resonance experiments on appropriately labeled proteins give information about various angular correlation functions or correlation times for the reorientation of the label. Expressions are derived relating these correlation functions and times to the rotation rate of the rigid protein and the rates of the internal rotations between the label and the protein. The effective correlation time for the label is simply a series of factors times the correlation time for the rigid protein. Each internal rotation which is much faster than the protein rotation contributes a single factor ½(3 cos2θ−1)2, where θ is the angle from the internal rotation axis of interest to the next internal rotation axis, or, for the last internal rotation, to the label axis of interest. The effect of internal rotations which are much slower than the protein rotation rate is the same as the effect of averaging over molecules with a permanent geometry corresponding to the possible orientations about the internal rotation axis.
Theoretical Analysis of the Electronic Structure and Molecular Properties of the Alkali Halides. II. Sodium Fluoride
Authors: Matcha Robert L.
Published: January 2005

Results of a recent theoretical investigation of the electronic structure of NaF within the SCF—LCAO—MO approximation are discussed, with special emphasis on molecular properties. Computed values (followed by experimental values in parenthesis) for the total energy, E, equilibrium separation, Re, spectroscopic constants, ωe, ωexe, and Be, and the dipole moment μ are E=−261.37849 a.u.,  Re=3.628 a.u. (3.639),  ωe=558.3 cm−1 (536.1),ωexe=4.387 cm−1 (3.830),  Be=0.439 cm−1 (0.437),μv=8.3365+0.0610(v+12)+0.0002(v+12)2,and μv(exptl)=8.1235+0.0644(v+12)+0.0004(v+12)2.The computed dissociation energy (DeHF=0.112 a.u.) has been coupled with correlation and relativistic energy contributions (Decorr=0.067 a.u.; Derel=−0.002 a.u.) determined from atomic data, producing a net De=0.178 a.u. as compared with the experimental value of 0.182 a.u. By combining the computed field gradient, qNa=−0.3775 a.u., with experimental values for the nuclear quadrupole coupling constant, we have determined a value of 0.0951×10−24cm2 for the sodium nuclear quadrupole moment.
Molecular Schrödinger Equation. VIII. A New Method for the Evaluation of Multidimensional Integrals
Authors: Conroy Harold
Published: January 2005

A new method, of very general applicability and very easily programmed for an electronic computer, is proposed for the numerical integration of functions of many independent variables. This new method renders obsolete, in most applications, the commonly used Monte Carlo procedure and the more recent, original method of Haselgrove. In the new scheme the sample points are distributed systematically rather than at random and the ensemble of points forms a unique, closed, symmetrical pattern, which effectively fills the space of the multidimensional integration. The paper contains an extensive statistical-analytic treatment of the error characteristics of the new method, one that enables advance quantitative estimation of upper limits of error in the integration of various types of functions. For continuous functions with bounded first derivatives, the error is shown ultimately to disappear at least as rapidly as the inverse square of the number of sample points; moreover, for runs of practical length the error limits with the new scheme are smaller—by a factor ranging from 2 to perhaps 104 or more—than those of any previous general procedure. The method employs certain rational constants which govern the arrangement of sample points. Tables of such constants, suitably optimized, which will permit the integration of functions with up to 12 independent variables, are provided along with a discussion of a method by which such constants may be obtained.
17O Nuclear Magnetic Resonance of Single Crystals of D2O Ice
Authors: Waldstein Peter , Rabideau Sherman W.
Published: January 2005

17O NMR spectra have been obtained for two orientations of a single crystal of D2O enriched to 22% in 17O. The spectra of only one orientation could be assigned. This assignment yields quadrupole coupling constants for 17O in ice as follows: | e2Qqzz/h | = 1.79±0.05 MHz, η=−1.01±0.04, where the z axis is the C2 axis of the D2O molecule The isotropic chemical shift is 612±37 ppm paramagnetic to liquid D2O.
Experimental Verification of the Theory of the Thermal-Diffusion Column
Authors: Rutherford W. M. , Kaminski K. J.
Published: January 2005

The accuracy of the Jones and Furry theory of the thermal-diffusion column was tested in an extensive series of 20Ne–22Ne separation experiments. The experiments covered a range of cold-wall to hot-wall radius ratios from 2.95 to 20 and a range of hot-wall temperatures from 108° to 815°C. Measured column transport coefficients were compared to theoretical values based on the measured transport properties of neon. The average ratio of the experimentally determined initial transport coefficient to the value calculated from theory was 0.899±0.047; the similar average ratio for the convective remixing coefficient was 1.18±0.129; and the average ratio for the diffusive remixing coefficient was 0.963±0.056.
Phosphorescence of the Charge-Transfer Triplet States of Some Molecular Complexes
Authors: Iwata Suehiro , Tanaka Jiro , Nagakura Saburo
Published: January 2005

The phosphorescence spectra of some charge-transfer complexes were studied in glassy solution at 77°K. Long-lived emission spectra which were different from the phosphorescence spectra of the constituent molecules were observed for the 1,2,4,5-tetracyanobenzene complexes with mesitylene, durene, and hexamethylbenzene. The maxima of the long-lived emission spectra were found to shift to lower frequencies as the ionization potential of the donor was decreased; for example, maxima appear at 19.8, 19.5, and 18.3 (× 103 cm−1) in the complexes with mesitylene, durene, and hexamethylbenzene, respectively. This shift is parallel to that observed for charge-transfer fluorescence spectra which exhibit a mirror-image relationship with the corresponding absorption spectra. Similar long-lived emission spectra were also observed for complexes containing pyromellitic dianhydride, tetrachlorophthalic anhydride, and phthalic anhydride as electron acceptors. A combination of theory and experiment indicates that the long-lived emission is attributable to a transition from a triplet state of charge-transfer character. This is the first observation of a ``charge-transfer triplet state.'' The lifetime of the phosphorescence due to the charge-transfer triplet state was measured. The results indicate that the observed lifetime decreases with increasing donor ability for a series of complexes with a fixed electron acceptor. The mechanism of singlet—triplet mixing in the charge-transfer complexes is discussed.
Evaluation of Orbit—Orbit Interaction in Many-Electron Atoms
Authors: Malli Gulzari
Published: January 2005

Orbit—orbit interaction has been evaluated for all the neutral atoms (in their ground states) up to radon (Z=86) using the numerical Hartree—Fock wavefunctions of Froese. Agreement between the previous calculations and that reported here is excellent wherever earlier results are available.
Dipole Moments of KF and KBr Measured by the Molecular-Beam Electric-Resonance Method
Authors: Van Wachem R. , De Leeuw F. H. , Dymanus A.
Published: January 2005

The molecular-beam electric-resonance method has been used to obtain the dipole moments for different vibrational levels of 39K19F (v=0, 1, 2, 3, 4, 5), 41K19F (v=0), 39K79Br (v=0, 1, 2), and 39K81Br (v=0, 1, 2). The absolute errors in the determined dipole moments are systematical errors of one part in 104, while the relative errors are about five parts in 106 for the dipole moments of KF and 10 parts in 106 for the dipole moments of KBr.
Nuclear Quadrupole Resonance Zeeman Study of 2,4-Dichlorophenoxyacetic Acid
Authors: Peterson G. E. , Steed N. , Bridenbaugh P. M.
Published: January 2005

The major field gradient directions and field gradient asymmetry parameters for Cl in 2,4-dichlorophenoxyacetic acid are determined. Partial double-bond characters of 0.026 and 0.044 for the para and ortho chlorine atoms are found. There is apparently some molecular distortion as the angle between the (Cl–C) para and the (Cl–C) ortho vectors is less than 120°.
Reformulation of the Representation of Transport Coefficients Using the Autocorrelation-Function Formalism and the Linear-Trajectory Approximation
Authors: Berne Bruce J. , Boon Jean-Pierre , Rice Stuart A.
Published: January 2005

The linear-transport coefficients are exactly described in terms of the ``generalized force'' autocorrelation function. For weakly coupled systems these formal expressions take simple forms equivalent to the results obtained from other approaches. In addition, the linear-trajectory method is described for the case of strongly interacting systems, and an elementary analysis of the transport coefficients at finite frequency is given (see Appendix B).
Study of the Electronic Structure of Molecules. VI. Charge-Transfer Mechanism for the NH3+HCl⇆NH4Cl Reaction
Authors: Clementi Enrico
Published: January 2005

In the NH3+HCl⇆NH4Cl reaction, analyzed via the population-analysis method, we have determined that the nitrogen atom is capable of receiving pseudo-π electrons from the hydrogens of the NH3 molecule and to transfer an equivalent amount of σ electrons to the chlorine atom. This π-electron charge donated originally by the hydrogens, then accepted by nitrogen and finally donated by nitrogen as σ charge goes to the Cl atom. The hydrogen atom of HCl donates parts of its σ electronic charge to the Cl atom. Thus, the chlorine atom accepts σ electrons from the hydrogen of HCl and σ electrons from the nitrogen. Therefore, in addition to the familiar concepts of charge ``donor'' and ``acceptor'' we can make use of the concepts of charge ``transformer'' and charge ``dispatcher.'' The efficiency of the transformer is the ratio of the accepted charges of a given symmetry and the donated charges of a different symmetry. In the NH3+HCl reaction, the nitrogen atom is a π→σ transformer with nearly unit efficiency. The reaction NH3+HC⇆NH4Cl can be summarized as the process where the H3 group (of NH3) is π donor, the N atom is σ→π transformer (σ donor and π acceptor), the H (of HCl) is a charge dispatcher (transfer the σ charge of N to the Cl atom) and σ donor, and finally, the Cl atom is a σ acceptor. During the entire process the nitrogen atom has nearly constant charge of eight electrons.
Paramagnetic Relaxation of Trapped Electrons in Irradiated Alkaline Ices
Authors: Zimbrick John , Kevan Larry
Published: January 2005

The paramagnetic relaxation characteristics of trapped electrons in γ-irradiated alkaline ices were studied by power saturation methods. The relaxation times were measured as a function of radiation dose, deuteration, phase, and temperature. Linewidths were measured under various conditions. The trapped electron EPR line is inhomogeneously broadened by nuclear hyperfine interactions; the spin-lattice relaxation mechanism is probably a cross relaxation process with O−. The change in relaxation time with radiation dose indicates that the electrons are trapped with a nonuniform spatial distribution in hydroxyl anion vacancies in radiation-produced spurs of ∼30-Å radius.
Cyanide Ion—Environmental Perturbation of Its Vibrational and Rotational Motion When Isolated in Alkali Halides
Authors: Field G. R. , Sherman W. F.
Published: January 2005

The spectrum of the cyanide ion isolated in 12 different alkali halides has been investigated as a function of pressure up to 50 kbar at 100°K. Observed frequency shifts are used to optimize frequency perturbation calculations. The general form of the potential experienced by ions isolated in alkali halides is discussed, and the particular terms dominating the CN−-ion frequency shifts are indicated. Pressure-induced band-contour changes are used together with calculations on the dependence of the energy of the system on the cyanide-ion axis orientation, to obtain a better understanding of the hindered rotational motion exhibited by this ion in many of the crystals. Appreciable displacement of near-neighbor ions is shown, and preferred CN−-ion axis orientation of <001> in NaCl-type structures and <110> in CsCl-type structures is indicated.
Hypersonic Measurements of Tertiary-Butyl Alcohol-Water Mixtures
Authors: Stone J. , Pontinen R. E.
Published: January 2005

A set of hypersonic measurements of mixtures of t-butanol-water by the method of Brillouin scattering has been completed in the temperature range 2°–45°C. The hypersonic velocity isotherms as a function of alcohol concentration exhibit a common crossover point. This occurs at a mole fraction of alcohol x2=0.03 at 6 GHz, and at x2=0.05 at 3 GHz. Considerable dispersion is observed between ultrasonic and hypersonic data. Also dispersion is observable in the hypersonic region, and increases with decreasing temperature. An attempt to explain the observed dispersion by the two-state theory of Schneider is unsuccessful.
Radiationless Transitions in Polyatomic Molecules. II. Triplet-Ground-State Transitions in Aromatic Hydrocarbons
Authors: Siebrand W.
Published: January 2005

The theory of Part I is applied to nonradiative transitions from the lowest triplet state to the ground state of aromatic hydrocarbons. A previously communicated empirical relation between triplet energy, triplet lifetime, and the relative number of hydrogen atoms per molecule is substantiated and its physical implications are discussed. It is transformed into a relation between the Franck-Condon factor of the transitions and the triplet energy. In this form it can be compared with the theoretical expressions derived in Part I. No satisfactory theoretical representation of the empirical formula could be obtained on the basis of a harmonic-oscillator description of the normal modes of the molecules. However, introduction of anharmonicity leads to excellent agreement between theory and experiment. A one-parameter formula is derived which accounts with good accuracy for the dependence of the triplet lifetime on the triplet energy and the number of carbon and hydrogen atoms in the molecule. This formula shows that the Franck-Condon factors relevant to the radiationless triplet-ground-state transition are governed by CH or CD stretching modes, which behave in this respect as completely degenerate for a given molecule. The single adjustable parameter is related to the anharmonicities of these modes in the ground and triplet state. The analysis confirms that the purely radiative triplet lifetime of most if not all aromatic hydrocarbons is close to 30 sec and that the Franck-Condon factor is the only parameter in the expression for the nonradiative triplet decay constant which varies considerably between different aromatic hydrocarbons. Finally the temperature dependence of the Franck-Condon factors is considered. A theoretical treatment indicates a very small temperature dependence below 400°K. This result seems to be borne out by an analysis of recent experiments, leading to the conclusion that the observed temperature effects are associated with bimolecular processes. A notable exception is benzene, where the triplet lifetime is temperature-dependent down to very low temperatures, possibly due to a Jahn-Teller distortion.
Free-Electron Treatment of the Barrier to Internal Rotation in Ethane
Authors: Alexander Millard H.
Published: January 2005

The cylindrical-model approach to the barrier to internal rotation in ethane first proposed by Karplus and Parr is extended using a free-electron charge distribution. A double-perturbation treatment including both a nuclear geometry and an electronic-repulsion perturbation permits us to distinguish a nuclear repulsion, a polarization, and a polarization-electronic-repulsion contribution to the barrier. The threefold part of the nuclear perturbation is solely responsible both for the nuclear-repulsion contribution (+4.7 kcal/mole) and for the polarization contribution (−3.2 kcal/mole). This last term arises from the differential polarization of the initially cylindrical electron cloud, which is accompanied by a relative increase in electronic density near the center of the eclipsed system. A result of this differential density change is a slight increase in the eclipsed electronic repulsion energy, yielding a third energy contribution (polarization-electronic-repulsion) of +1.5 kcal/mole. A discussion compares the present work to other recent treatments of the internal rotation barrier in ethane.
Temperature Dependence of JFF in 2-Fluoro-α-Chloro-α,α-Difluorotoluene and 2-Fluoro-α,α-Dichloro-α-Fluorotoluene
Authors: Jonas J. , Borowski L. , Gutowsky H. S.
Published: January 2005

The F-F coupling constants JFF between the fluorine atom at the 2 position and the fluorines in the CFCl2 and CF2Cl groups were measured and found to have an appreciable temperature dependence in 2-fluoro-α,α-dichloro-α-fluorotoluene and 2-fluoro-α-chloro-α,α-difluorotoluene. The effect of temperature on the fluorine chemical shift of the CFCl2 and CF2Cl groups was also studied in these compounds. The observed temperature dependences of JFF are consistent with the existence of several conformers differing in the rotational angle of the CFCl2 and CF2Cl groups. The relative stabilities of the rotamers depend upon the repulsive nonbonded interactions of the atoms in the CFCl2 and CF2Cl groups with the 2-F and 6-H atoms. The potential functions for rotation of the CFCl2 and CF2Cl groups were estimated by means of both the simple van der Waals repulsive potential and the modified Buckingham potential. The approximate dependence of JFF upon the dihedral angle between the C-F bond in the CFX2 group and that of the 2-fluorine atom was obtained from an analysis of the high- and low-temperature limits for JFF in several compounds, including results reported earlier for some benzotrifluorides. It is found that JFF increases sharply at F-F internuclear separations of 2.5 to 2 Å, which supports the view that a nonbonded interaction makes a major ``through-space'' contribution to coupling of the fluorines.
Pure Rotational Spectrum of Water Vapor
Authors: Hall Richard T. , Dowling Jerome M.
Published: January 2005

The pure rotational spectrum of water vapor was measured over the frequency range 5–125 cm−1 at a resolution of approximately 0.07 cm−1. A complete set of energy levels up to J=7 was derived. The ground-state rotational constants were calculated and agree well with those derived from near-infrared data. The values of the ground-state rotational constants are A0=27.8761±0.0034 cm−1, B0=14.5074±0.0090 cm−1, and C0=9.2877±0.0021 cm−1. The six quartic distortion constants were also determined along with the higher-order distortion constant associated with the a axis of rotation.
High-Frequency Linear Response of Classical Fluids to Brownian Oscillators
Authors: Berne Bruce , Frisch H. L.
Published: January 2005

A modified Langevin equation is used to investigate the possibility of a nondissipative transfer of energy from a classical oscillator driven at high frequencies to a classical fluid. It is found that such an absorption of energy is quite possible even at driving frequencies which are presently attainable. The vibrational-frequency shift is found to be simply related to the mean-square force exerted by the fluid on the oscillatory degrees of freedom.
Microwave Studies of Collision-Induced Transitions between Rotational Levels. II. Observations in H2CO, HCN, and H2CCO
Authors: Oka Takeshi
Published: January 2005

The technique of high-power microwave double resonance is applied to study collision-induced transitions between rotational levels in H2CO, HDCO, HCN, DCN, and H2CCO. The K-type doublets (or l-type doublets) of these molecules for selected J levels have been ``pumped'' by high-power microwave radiation and the decreases in the intensities of the absorption lines of K-type doublets (or l-type doublets) of other J levels have been observed. The ``preferred'' collision-induced transitions previously observed for ethylene oxide have been more strikingly confirmed. Also multiple transitions with ΔJ≥2 have been observed. An approach by the use of steady-state equations is developed and used for the analysis of the observed results. Relative values of the rate constants for various collision processes (such as the ΔJ=1 collision-induced transitions versus the ΔJ=0 collision-induced transitions or collision-induced transitions with dipole selection rules vs collision-induced transitions with quadrupole-type selection rules) have been determined. The analysis has led to the following conclusions.

(1) The collision-induced transitions follow selection rules. For the molecules studied in this paper, the dipole selection rules (ΔJ=0, ±1, parity +↔—) are dominant although not always by a very large factor [see Conclusion (3) below].

(2) The rate constants for the collision-induced transitions with ΔJ=1 are of the same order of magnitude as those with ΔJ=0, although, molecules make transitions between more widely spaced energy levels in the former case. This result is evidence which supports the idea of ``rotational resonance'' introduced by Anderson for explaining the pressure broadening of ammonia.

(3) For HCN, DCN, and H2CCO, rather large rate constants have been obtained for the ΔJ=2 transitions. This suggests that the collision-induced transitions with quadrupole-type selection rules or possibly those with even higher multipole-type selection rules also play a role in these molecules.