bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-consistent field theories of the polymer excluded volume problem. III. A self-consistent solution
Authors: Gillis H. P. , Freed Karl F.
Published: February 2003

We summarize the self-consistent field (SCF) approach of the excluded volume problem developed in two earlier articles. We emphasize that this approach leads to a hierarchy of SCF theories and that it resolves apparent conceptual conflicts between earlier SCF theories developed by Edwards and Reiss. We present an approximate solution to the simplest member of that hierarchy, and we demonstrate self-consistency for the dominant part of the solution. From that solution we show the asymptotic dependence of the mean square end separation vector on chain length to be 〈R2〉 ∼ L6/(d+2) for 1?d<4 (in d dimensions). Corrections to this asymptotic dependence, explicitly derived for d=2,3, demonstrate the crossover from the 6/5 law to the unperturbed (〈R2〉 ∼ L) behavior for finite chain lengths and for sufficiently weak excluded volume.
Dipolar nuclear spin relaxation of 19F in multispin systems. Application to 19F labeled proteins
Authors: Hull William E. , Sykes Brian D.
Published: February 2003

A theoretical description of 19F–1H dipolar nuclear spin relaxation in multispin systems is presented which serves to explain the relaxation behavior of 19F in fluorine-labeled proteins when the protons are not irradiated. The complete solution of the two-spin 1H–19F spin–lattice relaxation is discussed for the various experimental pulse techniques commonly employed in Fourier transform NMR. Recovery curves following a single 90° pulse applied to 19F in spin systems containing several protons are simulated by using a digital computer to calculate the time development of the complete set of differential equations for z-magnetizations. Steady-state experiments such as progressive saturation were also examined. The simulated 19F relaxation curves for two-spin and several-spin systems (when the protons are not irradiated) are compared to the behavior expected if the relaxation followed an ’’ideal’’ single exponential with T1 given by the standard ’’unlike’’ spins formula. These calculations were performed for various values of the correlation time τc for isotropic tumbling, and significant deviation from the ’’ideal’’ T1 behavior was observed, especially for slow tumbling times where ω0τc ≳ 1. This deviation was less in systems of several spins, and a generalized model for the spin system of a fluorine-labeled protein was developed which showed that for large spin systems the dipolar relaxation behavior of 19F will in fact exhibit the ’’ideal’’ T1 behavior whether or not the protons are irradiated. The effect of the over-all molecular tumbling as well as internal motions on T1 and the nuclear Overhauser enhancement (NOE) is discussed. Finally, a spin temperature argument is described which complements the more formal theoretical treatment and also explains all of the experimental observations that have been made on the protein fluorotyrosine alkaline phosphatase from E. coli. The treatment presented here can also be applied to other problems where dilute spins (e.g., 13C, 31P, 15N) interact with abundant spins.
A kinetic study of the mercury sensitized luminescence of H2O and NH3
Authors: Harker Alan B. , Burton C. S.
Published: February 2003

The transient species formed from the reactions of H2O and NH3 with excited Hg(6 3P0) atoms were studied by phase-sensitive modulation spectroscopy. In the Hg/NH3 system, the (Hg⋅NH3) * exciplex was observed in emission, and its lifetime was found to be 1.7±0.1×10−6 sec; the third body stabilized reaction of NH3 with Hg(6 3P0) was found to proceed with a rate constant of k5b=2.2±0.2×10−31 (cm6/molecule2 sec) for M=N2. In the Hg/H2O system the (Hg⋅H2O) * exciplex was observed in emission and its lifetime found to be ? 3.3×10−8 sec; and the quenching of Hg(6 3P0) by water was found to have a rate constant of k4a + k4b[M] =9.4±0.5×10−15 (cm3/molecule sec) when M=1 atmosphere of N2. In the Hg/H2O system the OH radical was observed both in emission and absorption, and HgH was observed in absorption. Both of these species were shown to be formed by the nonradiative dissociation of the (Hg⋅H2O) * exciplex.
Angular correlations in linear copolymers from the compositional dependence of their dipole moments. III. Experimental: Poly(4-chlorostyrene, 4-methylstyrene) copolymers
Authors: Corrado L. C. , Work R. N.
Published: February 2003

The complex dielectric constants ε*=ε′−jε″ of members of a set of ten poly(4-chlorostyrene, 4-methylstyrene) copolymers, P(4CS,4MS), that spans the whole composition range and includes the homopolymers P4CS and P4MS, have been measured at temperatures ranging from about 450 °K downwardly to their glass transition temperatures at about 390 °K. The compositional dependence of the effective dipole moment per structural unit μ2e, as determined from these measurements is analyzed by methods developed in Papers I and II of this series, but as modified for applications to copolymers having nearly random ordering of sequences of chemical types of structural units. The analysis presupposes knowledge of the compositional dependence of the condtional probabilities Pαβ that a structural unit of type β immediately follows one of type α, where α,β=0,1. The analysis is done with the help of a series expansion of the compositional dependence of μ2e, the terms of which are linearly independent functions of composition with constant coefficients. The coefficients are linear combinations of products μαμβηαβks, where ηαβks is twice the average cosine of the angle between the dipole moments μα and μβ of a pair of structural units, lying in the same chain and separated by k intervening units that are arranged in a sequence of chemical types as designated by the index s. The first few coefficients of the expansion are evaluated for P(4CS,4MS) copolymers and are used as a basis of both qualitative and quantitative discussions of the magnitudes and the nature of those localized angular correlations that contribute to μ2e. Possibilities are considered for obtaining more detailed analyses, either by choosing appropriate copolymer systems that meet certain requirements, or by using specified additional information from independent sources.
Nuclear quadrupole coupling constants in liquids. Raman line shapes and 2D spin–lattice relaxation in CDCl3 and CDBr3
Authors: Wright David A. , Rogers Max T.
Published: February 2003

Deuterium quadrupole coupling constants have been obtained for two symmetric-top molecules in the liquid phase by combining NMR relaxation data with Raman line-shape analysis of bands of A1 symmetry. The Raman lines have been corrected for vibrational and instrumental broadening by comparing the polarized and depolarized components of a single line. More than one A1 line has been studied for each molecule. The previously uncertain deuterium quadrupole coupling constant for CDBr3 has been determined in this work to be 177±5 kHz and deuterium coupling constants in CDX3 molecules are discussed. The procedure described here provides a different method for obtaining nuclear quadrupole coupling constants in the liquid phase.
Heats of reaction of trapped intermediates in γ-irradiated organic glasses and relaxation processes in unirradiated glasses measured by low temperature differential thermal analysis
Authors: Hager Stanley L. , Willard John E.
Published: February 2003

Differential thermal analysis (DTA) has been used to determine the following: (1) the heat of photobleaching of trapped electrons in γ-irradiated 3-methylpentane (3MP) glass as a function of γ dose; (2) the heats of combination of radicals and of ions in γ-irradiated 3MP and methyltetrahydrofuran (MTHF) glasses; (3) the glass transition temperatures and the rates of enthalpy loss during 77 K annealing of 3MP-h14, 3MP-d14, 3-ethylpentane, and MTHF; (4) the effect of cooling rate and annealing time on crystallization of n-hexane in 3MP cooled to 77 K. The ΔH of neutralization of photobleached electrons in γ-irradiated 3MP at 72 K is ∼−150 kcal mole−1 at low dose, implying an upper limit of 80 kcal mole−1 for the solvation energy of the combining charges, and decreases to ∼80 kcal mole−1 for a dose of 1.2×1020 eV g−1 implying an increasing ratio of reaction with radicals to reaction with cations as the dose is increased. When γ-irradiated MTHF is warmed from 77 K, a large fraction of the trapped electrons appear to react with radicals to form carbanions, which then react with cations, the total ΔH being ∼80 kcal mole−1. The ΔH of ion pair solvation is estimated to be −120 to −150 kcal mole−1. The decrease in the enthalpy of the matrix due to relaxation during annealing in 3MP at 77 K parallels the decrease in the decay rate of trapped electrons for similar samples. Seemingly anomolous effects of sample size and shape on trapped electron decay rates in 3MP glass as a function of time of annealing at 77 K can now be rationalized in terms of the restrictions on viscous flow in different types of sample tubes.
Direct correlation function: Hard sphere fluid
Authors: Henderson Douglas , Grundke E. W.
Published: February 2003

The direct correlation function c (r) and in particular the ’’tail’’ of the direct correlation function d (r) are calculated for hard spheres from reliable expressions for the radial distribution function of the hard sphere fluid. This permits a direct examination of the Percus–Yevick (PY) approximation d (r) =0. It is found that the PY approximation is very poor over-all but fairly reasonable in the most important region r ? σ. Finally a simple but relable parametrization of d (r) for hard spheres is proposed.
A theory of the hard sphere solid
Authors: Barker J. A.
Published: February 2003

A ’’self-consistent field’’ theory based on the Bethe approximation and previously shown to reproduce the exact partition function for one-dimensional hard spheres at all densities and to give good results for classical harmonic and nearly harmonic crystals is applied to the three-dimensional hard-sphere system. Solutions of the resulting equations which are approximately valid at high densities are obtained. There are two possible solutions, one of which gives values for the entropy and one-particle distribution function in good agreement with results for the hard-sphere solid derived from computer simulations. The other solution may be associated with the fluid phase.
Exact quantum, quasiclassical, and semiclassical reaction probabilities for the collinear F+H2 → FH+H reaction
Authors: Schatz George C. , Bowman Joel M. , Kuppermann Aron
Published: February 2003

Exact quantum, quasiclassical, and semiclassical reaction probabilities and rate constants for the collinear reaction F+H2 → FH+H are presented and compared. The exact quantum results indicate a large degree of population inversion of the FH product with PR02 and PR03 being the dominant reaction probabilities. The energy dependence of these two probabilities at low translational energies are quite different. PR02 shows an effective threshold of 0.005 eV which can largely be interpreted as resulting from tunneling through a vibrationally adiabatic barrier. PR03 has a much larger effective threshold (0.045 eV) apparently resulting from dynamical effects. Quasiclassical probabilities for the collinear F+H2 reaction were calculated by both the forward (initial conditions chosen for reagent F+H2) and reverse (initial conditions for product H+FH) trajectory methods. The results of both calculations correctly indicate that PR03 and PR02 should be the dominant reaction probabilities. However, the threshold behavior of the quasiclassical forward PR03 disagrees strongly with the corresponding exact quantum threshold energy dependence. By contrast, there is good agreement between the reversed trajectory results and the exact quantum ones. The uniform semiclassical results also agree well with the corresponding exact quantum ones indicating that the quasiclassical reverse and the semiclassical methods are preferable to the quasiclassical forward method for this reaction. The important differences between the threshold behavior of the exact quantum and quasiclassical forward reaction probabilities are manifested in the corresponding rate constants primarily as large differences in their activation energies. Additional exact quantum results at higher total energies indicate that threshold effects are no longer important for reactions with vibrationally excited H2. Resonances play an important role in certain reaction probabilities primarily at higher relative translational energies.
Correlations between reaction exothermicity and product energy partitioning in atom–molecule reactions
Authors: Sanders William A.
Published: February 2003

A procedure is suggested for analyzing graphically the results of energy-partitioning measurements in atom–molecule reactions. For a series of reactions of the type F+HR, there appears to be a linear correlation between the exothermicity of the reaction and the percent of the available energy deposited into HF vibrations. The absolute amount of vibrational excitation is observed to be surprisingly constant for a wide variety of stable reactants RH.
Autoionization in diatomics: Measured line shape parameters and predicted photoelectron spectra for some autoionizing states of the hydrogen halides
Authors: Terwilliger D. Thomas , Smith Allan L.
Published: February 2003

Using a Hopfield continuum source and a computer-controlled data acquisition system, we have measured relative absorption cross sections for HCl, DCl, HBr, DBr, and HI at 0.2 Å resolution from 1000 to 700 Å, a region dominated by autoionizing Rydberg states converging to the A 2Σ+ state of the HX+ ion. In order to analyze the shapes of autoionizing vibrational bands, we applied Fano’s theory of line shapes to homogeneous autoionization in diatomics, and found that the line shape parameters q, Γ, and ρ2 are independent of rotational quantum number but may depend upon the vibrational quantum number of the autoionizing state. Calculations of this vibrational dependence in HCl shows it to be most pronounced at high v. For progression I in HCl and DCl (n*=2.795) and in HBr and DBr (n*=2.748), we fit computer-generated vibronic band contours to experimental absorption cross sections to obtain q, Γ, and ρ2 which we then used to predict the photoelectron spectra of these autoionizing states. The autoionization lifetime h//Γ in HCl and DCl is 1.1×10−14 sec; in HBr and DBr it is 9.5×10−15 sec. The measured autoionization widths of bands in the next member of the Rydberg series obey the scaling rule Γ∝n*−3. We attribute an additional broadening of levels with v′?3 in progression I of HBr as the onset of predissociation, and estimate the relative rates of predissociation and autoionization. A vibrational reassignment of progression II in HCl and DCl gives n*=2.310 for these states. We saw only a single broad peak (with n*=2.78) in the absorption spectrum of HI.
Molecular spectroscopy of organometallic compounds: Organotin(IV) tropolonates
Authors: Rein Alan J. , Herber Rolfe H.
Published: February 2003

The infrared, Raman, and 119Sn Mössbauer spectra of seven organotin tropolonates (R2SnT2), (C6H5)SnT3, and bis tropolonatotin(IV) dichloride have been examined in detail. The diorganotin(IV) compounds have a six-coordinate structure with the two organic ligands occupying either cis (R=CH3, C6H5, and C6H5CH2) or trans (R=C2H5, n-C3H7, n-C4H9) positions. Owing to the asymmetric nature of the tropolone ligand, none of these structures have a center of symmetry in the solid state and both the symmetric and asymmetric Sn–C stretching vibrations are Raman active. The temperature dependence of the recoil-free fraction for the diorganotin(IV) tropolonates has been determined over the temperature range 78?T<∼140 K and can be correlated with the Raman data in the lattice mode region to yield a self-consistent assignment of the intermolecular, intra-unit-cell vibration in the solids and a value of the effective vibrating molecular mass. From the latter data it is inferred that these complexes are monomeric in the solid state with (relatively) weak intermolecular bonding forces between adjacent molecules. The tropolone ligand can thus be envisioned as acting as an anisobidentate moiety with both oxygen atoms bonded to a single metal center. The temperature dependence at the 119Sn isomer shift with respect to BaSnO3 and of the quadrupole hyperfine interaction for these compounds is also reported.
Low-energy electron diffraction studies of molecular crystals: The surface structures of vapor-grown ice and naphthalene
Authors: Firment L. E. , Somorjai G. A.
Published: February 2003

Low-energy electron-diffraction patterns have been obtained from ice and naphthalene crystal surfaces vapor grown on the (111) face of platinum at low temperatures. The surfaces of both molecular crystals were well ordered, and can be identified as a hexagonal plane of ice and the (001) face of naphthalene.
Single rotational level excitation of CO(e 3Σ−) by atomic sulfur radiation
Authors: Slanger Tom G. , Black Graham
Published: February 2003

Direct poplulation of the v = 4, J = K = 27 level of the e 3Σ− state of 12CO has been accomplished by absorption of the 1483.039 Å SI line. Perturbations of this level by the nearby A 1Π state make this particular e 3Σ− ← X 1Σ+ transition strong. Resonance of the SI line with the e 3Σ− − X 1Σ+ transition is destroyed by substitution of 13CO for 12CO, but 13CO has a very strong resonance, with a different SI line, in the A 1Π ← X 1Σ+ system. The behavior of the observed emission intensities as a function of varying the CO and inert gas pressures indicates that collisionally induced cross-relaxation processes between the A 1Π and e 3Σ− states are extremely rapid, their frequencies being greater than gas kinetic collision frequency in the case of CO.
Isotope effects in solutions of hydrogen and deuterium in niobium
Authors: Steward S. A.
Published: February 2003

Hydrogen and deuterium equilibrium pressures in the region of single-phase solid solutions (α phase) with niobium were collected. These measurements were within the temperature and composition ranges of 535 to 773 K and 0.02 to 0.20 hydrogen atomic fraction. Good partial molar enthalpy and entropy values were calculated from these data. A ground-state hydrogen vibration frequency of 1800±50 K (3.8×1013 Hz) was derived by assuming a harmonic oscillator model. Finally, the results are compared with those obtained for the Group VB metals by other authors.
Nonrelativistic configuration interaction calculations for the ground state of the vanadium atom
Authors: Munch David , Davidson Ernest R.
Published: February 2003

A new scheme for constructing L2, Lz, S2, Sz eigenfunctions within the Hartree–Fock interacting subspace has been used to generate a first-order configuration-interaction wavefunction for the ground 4F state of the vanadium atom in the nonrelativistic approximation. The basis set consisted of 62 Slater-type orbitals, with l up to 5, transformed to Hartree–Fock orbitals in the ’’occupied’’ subspace and to pseudonatural orbitals in the ’’virtual’’ subspace. Approximately 70% of the correlation energy was recovered with 500 configurations (1023 terms formed from 31 496 Slater determinants). The charge density, momentum density, x-ray scattering factor, and Compton profile were computed from both the CI and SCF wavefunctions.
ESR study of the photolysis of n-butyl iodide: Secondary photolysis and structure of the n-butyl radical
Authors: Adrian Frank J. , Bowers Vernon A. , Cochran Edward L.
Published: February 2003

The photolysis of n-butyl iodide in argon at 4 °K has been studied as a function of photon energy and photolysis time, using electron spin resonance (ESR) spectroscopy to detect the free radical products. Photolysis at 2790 Å gives only the n-butyl radical, but photolysis at 2460 Å yields hydrogen atoms and some methyl radicals in addition to n-butyl. The n-butyl yield is approximately proportional to photolysis time for photolysis at 2460 Å, but the H atom and CH3 yields have a stronger than linear dependence on photolysis time suggesting that these species are produced by secondary photolysis of the n-butyl radical. The magnetic constants of n-butyl, determined from its ESR spectrum, are: g1=2.0029, g2=2.0030, g3=2.0025; A(α)1 = −29, A(α)2 = −18, A(α)3 = −21 Oe; and A(β1)0 = 46.5, A(β2)0 = 21.3 Oe. Axis 1 is parallel to the CαCβ bond. Axis 3 is perpendicular to the α-CH2 plane and lies approximately in the plane determined by the CαCβ bond and β-CH bond of the β-proton having the 46.5 Oe isotropic hyperfine splitting constant. The magnetic constant data also indicates that the α-CH2 group has considerable freedom for torsional oscillation about this equilibrium position.
Chemiionization involving rare gas metastable atoms
Authors: West W. P. , Cook T. B. , Dunning F. B. , Rundel R. D. , Stebbings R. F.
Published: February 2003

Crossed beams studies of chemiionization in thermal energy collisions of helium, neon, argon, and krypton metastable atoms with ground state atoms and molecules (Ar, Kr, Xe, N2, H2, O2, NO, CO, CO2, and N2O) are described. Branching ratios are presented and in some cases absolute total ion production cross sections have been measured.
Molecular structure of di-π-cyclopentadienylcobalt, (C5H5)2Co, by gaseous electron diffraction
Authors: Hedberg Anne Katherine , Hedberg Lise , Hedberg Kenneth
Published: February 2003

Gaseous cobaltocene (CoCp2) has been investigated by electron diffraction at a nozzle-tip temperature of about 120 °C. As expected, the molecule has the sandwichlike structure previously found for ferrocene (FeCp2) and nickelocene (NiCp2). The data show that any distortion from D5h or D5d molecular symmetry arising from the degenerate electronic ground state (Jahn–Teller effect) is small. Accordingly, the structure was refined in terms of three types of symmetric models: one with an eclipsed conformation of the rings (D5h), one with a staggered conformation (D5d), and one with freely rotating rings. The best agreement was obtained with the freely rotating ring models. However, the differences are small and it is clear that if large-amplitude torsional motion of the rings had been included in the D5h and D5d models, the agreement from them would have been about equally good. Based on the assumption that the equilibrium conformation of CoCp2 can be approximated by one of these very symmetric models, we conclude that the barrier to internal rotation is low enough to permit large-amplitude torsional motion and that the minimum energy conformation of the rings cannot be distinguished. The conclusion concerning the hindering potential is made somewhat uncertain by the unknown effect of Jahn–Teller distortion. The values of the important distances (ra), angles, and rms amplitudes of frame vibrations (l) with 2σ error estimates are r (Co–C) =2.113 Å (0.003), r (C–C) =1.430 Å (0.003), r (C–H) =1.095 Å (0.016) &C5,H (the angle between the plane of the C5 ring and the C–H bonds) = 3.7° (3.3), l (Co–C) =0.082 Å (0.004), l (C–C) =0.056 Å (0.003), l (C–H) =0.088 Å (0.015), l (Co...H) =0.137 Å (0.029). The metal–carbon bond length in CoCp2 is about 0.05 Å longer than in FeCp2 and about 0.08 Å shorter than in NiCp2. The weakening of the bonding to the rings as the atomic number of the metal atom increases is a dramatic consequence of the antibonding effects of e1g orbitals involving the metal atoms and the rings: These orbitals are empty in FeCp2, and singly and doubly occupied in CoCp2 and NiCp2. The apparent potential hindering internal rotation of the rings is greatest in FeCp2 and least in NiCp2.
Configuration interaction wavefunctions for 3S excited states of helium
Authors: Birss F. W. , Senn P.
Published: February 2003

The method of configuration interaction is used to determine accurate upper bounds of the 23S to 233S states of helium by minimization of the eigenvalues corresponding to one state or a group of states without concern as to the fate of other eigenvalues. The relative importance of radial and angular correlation in triplet state is discussed.
Variational principles which are functionals of electron density
Authors: Nakatsuji Hiroshi , Parr Robert G.
Published: February 2003

The Ritz variational principle, ordinarily written as a functional of the ground-state wavefunction, is rewritten in such a way that only one-electron functions are included as variables. Three different such variational formulas are derived explicitly based on the formula given by Hohen Kohn. They constitute variational expressions of the integrated Hellmann–Feynman theorem, integral Hellmann–Feynman theorem, and virial theorem. These variational formulas are exact within the Born–Oppenheimer approximation, and when applied, they give the same results as does the conventional Ritz variational principle. However, they still have the defect that they require knowledge of the correct density function associated with a suitably chosen reference potential. Some applications are given for one-electron systems. A new formula for the kinetic energy plus electron–electron repulsion energy is obtained from the integrated Hellmann–Feynman theorem.
Decay mechanisms of CH3 in 3-methylpentane and 3MP-d14 glasses at 77 °K as indicated by methane yields
Authors: Neiss M. A. , Sprague E. D. , Willard J. E.
Published: February 2003

The isotopic methane yields from γ irradiation of 3-methylpentane, 3MP–1%CH3I, 3MP-d14–1%CH3I, and 3MP-d14–1%CD3I glasses confirm recent evidence from decay kinetics that thermal CH3 radicals can abstract H from C–H bonds in hydrocarbon glasses at 77°K (plausibly by tunneling) and show that similar abstraction does not occur from C–D bonds. Also, in 3MP-d14 the CH3 (formed by the CH3I+e− → CH3+I− process) does not decay by radical combination processes (CH3+CH3 or CH3+C6D13), implying that decay is by geminate recombination with the I− partner. In the γ irradiation of 3MP-d14–1%CH3I irradiated at 77°K, G (CH3D) from hot abstraction by CH3 is 0.7; thermal CH3 and CD3 radicals are able to abstract H from low concentrations of C–H bond isotopic impurities; and the yields of scavengeable electrons and of radicals are substantially different than in 3MP-h14.
Laser pumped magnetophotoselection in triplet dyes
Authors: Yamashita Mikio , Ikeda Hidenori , Kashiwagi Hiroshi
Published: February 2003

Some observations have been made on the Δm=±2 and Δm=±1 ESR spectra in rhodamine (type R), fluorescein (type F), and acridine (type A) dyes, important laser active media, during laser excitation at 77 K. The results have revealed that the spectra and the lifetimes of the dyes in the T1 states in ethanol are affected significantly by the chromophoric structure. The root-mean-square value of zero-field splitting parameters (ZFSP), D*, and the triplet-state lifetime, τT, increase in the order type R < type A < type F and type F < type R < type A, respectively. By the method of magnetophotoselection, the Δm=±1 absorption lines of acridine orange and fluorescein disodium salt dyes are assigned to three directions along the molecular axes. Furthermore, the ZFSP values and the polarization results show that the π-electron distribution is most strongly polarized along the long axis of the chromophore in the case of type F dyes.
Dissociative excitation of H2 by electron impact: Translational spectroscopy of long lived high Rydberg fragment atoms
Authors: Schiavone James A. , Smyth Kermit C. , Freund Robert S.
Published: February 2003

Electron impact excitation of H2 leads to three distinguishable groups of high Rydberg fragment atoms. High Rydberg molecules are also detected. The measurements consist of (1) excitation functions and (2) time of flight distributions which are transformed to fragment translational energy distributions. For high Rydberg fragments from molecular high Rydberg states converging to the repulsive wall of the H+2 ground state, the measured and calculated kinetic energy distributions agree, in accordance with the prediction of the core ion model of high Rydberg dissociation. The remaining high Rydberg fragments result from dissociation of states of H2 with both electrons excited to low principal quantum numbers rather than from dissociation of molecular high Rydberg states.
A Raman spectral study of amorphous solid water
Authors: Venkatesh C. G. , Rice Stuart A. , Bates John B.
Published: February 2003

Raman spectra of amorphous solid H2O, [H2O(as)], D2O(as), and 12% H2O in D2O(as) were measured over a temperature range from 30 to 120 °K. The spectra of H2O(as) resemble those of liquid water more than they do those of ice lc or ice lh. The spectra suggest that the water molecules are located in two or three types of distinguishable environments depending on the details of the assignment. No structural changes were observed between 30 and 120 °K, but at ∼160 °K the amorphous samples transformed rapidly and irreversibly to ice lc.
Evidence for predissociation in the C 2Σ+ state of NS
Authors: Chiu Chi-Lian , Silvers Stuart J.
Published: February 2003

In a series of emission, absorption, and fluorescence experiments on the C 2Σ+ state of NS it is shown that the intensities of bands originating from v′=1 and 2 levels are less (relative to v′=0 band intensities) than is expected on the basis of Franck–Condon factors. This weakening is attributed to predissociation and an upper limit of 45 380 cm−1 is obtained for De, the ground state dissociation energy. Correlations of NS states with those of NO are made and possible mechanisms of predissociation discussed.
Translational excitation of the molecular beam reaction K+HCl→KCl+H
Authors: Pruett J. Gary , Grabiner Frederick R. , Brooks Philip R.
Published: February 2003

The translational energy dependence of the reaction K+HCl→KCl+H has been studied in crossed beams in the c.m. energy range 2.1–12.1 kcal/mole (0.09–0.53 eV). Beams of HCl were generated at different translational energies by hydrodynamic expansion of various H2/HCl mixtures and the laboratory energy of the HCl was measured by time-of-flight techniques. Angular distributions of the product were measured and integrated for each energy and the total reactive cross section was found to increase monotonically with energy. The functional form of the energy dependence is well approximated by the traditional line-of-centers relation. Although the cross section increases with energy, translational excitation is not as effective as vibrational excitation and modest extrapolation of the data suggests that still larger amounts of translational energy will be similarly ineffective. The cross section might be expected to depend upon the number of states which are accessible to the products. But this number grows rapidly as the reagent energy is increased and the influence upon the cross section of this large statistical effect can obscure any subtle dynamic effects due to the nature of the potential surface. In order to remove this statistical bias, it is convenient to express the results in terms of the average state-to-state transition rate ?, the experimental rate constant divided by the density of possible product states. Even though the detailed product state distribution is not known, the density of possible product states can be calculated from the conservation laws and molecular properties of the asymptotic products. The state-to-state transition rate so obtained is found to decay exponentially with the square root of the energy in excess of the thermodynmic threshold: ?=A exp[−β (E′)1/2]. An extrapolation to energies higher than those studied predicts an eventual decrease in the reaction cross section.
Vaporization reactions in the ytterbium–fluorine system
Authors: Biefeld Robert M. , Eick Harry A.
Published: February 2003

The vaporization and sublimation reactions for the ytterbium fluoride system have been investigated by mass loss, x-ray powder diffraction, elemental analysis, and mass spectrometry. When YbF2.00 is heated in vacuum, it decomposes to give a metal rich vapor and a metal deficient residue until the composition YbF2.40(4) is reached. The following equilibrium reactions were established: YbF2.40(s,l) = (0.60)YbF2(g) + (0.40)YbF3(g), Reaction (a); and YbF3.00(s,l) = (0.05)YbF2.40(s,l) + (0.95)YbF3(g) + (0.03) F (g), Reaction (b). % A target collection Knudsen effusion method was used to determine vapor pressures for the above reactions. From the slope–intercept data the following enthalpy and entropy changes with associated standard deviations were derived at the median temperatures: For Reaction (a), ΔH°1597 = (96.9±1.1) kcal mol−1 and ΔS°1597 = (36.83±0.67 %cal mol−1⋅K−1; for Reaction (b), ΔH°1568 = (91.19±0.41) kcal mol−1 and ΔS°1568 = (37.28±0.26) cal mole−1⋅K−1. Estimated and reported thermodynamic functions were employed to reduce the thermodynamic values to 298 K. The reduced values are as follows: For reaction (a), ΔH°298 = (110.7±2.3) kcal mol−1 and ΔS°298 = (50.8±2.2) cal mol−1⋅K−1; for Reaction (b), ΔH°298 = (111.1±1.3) kcal mol−1 and ΔS°298 = (56.2±1.5) cal mol−1⋅K−1. By use of the third-law procedure, the following ΔH°298 values were derived: for (a), (109.8±2.4) kcal mol−1; for (b), (107.0±3.0) kcal mol−1. The enthalpies and entropies for the hypothetical congruent sublimation reactions of YbF2(s) and YbF3(s) are derived and compared with those of the alkaline earth difluorides and other selected lanthanide fluoride systems.
Sound velocity and the equation of state of N2 to 22 kbar
Authors: Mills R. L. , Liebenberg D. H. , Bronson J. C.
Published: February 2003

The velocity of sound and the relative volume of N2 were measured simultaneously in a piston–cylinder apparatus along five isotherms from 247 to 321 K at pressures up to 22 kbar. The data were combined to yield a consistent equation of state from which accurate thermodynamic variables can be derived.
Subpicosecond relaxation of localized electrons in liquid ammonia
Authors: Huppert D. , Struve W. S. , Rentzepis P. M. , Jortner Joshua
Published: February 2003

We report the results of an experimental study of the optical bleaching of the absorption spectrum of the solvated electron in dilute Na–NH3 and Na–ND3(2×10−4 M) solutions by a single 1.06 μ psec pulse (pulse duration 6 psec, pulse energy 30 mJ). The absorption spectrum of the solvated electron was monitored in the spectral range 1100–850 nm with the time resolution 20–3.3 psec. The line broadening of the solvated electron optical band originates from homogeneous broadening effects. The relaxation time of the excited state of the solvated electron was determined to be τ?2×10−13 sec. This ultrashort relaxation time favors relaxation between bound states of the solvated electron center.
Thermodynamic study of gaseous sodium-phosphorus-oxygen ternary molecules by high temperature mass spectrometry
Authors: Gingerich K. A. , Miller F.
Published: February 2003

The equilibrium gaseous species over a condensed sodium tripolyphosphate melt were investigated by the high temperature mass spectrometric technique in the temperature range 1270–1567 K. Third law enthalpies and, where possible, second law enthalpies were measured for the following gas phase reactions involving the gaseous ternary species, NaPO or NaOP, monomeric sodium metaphosphite, NaPO2, and sodium metaphosphate, NaPO3: NaPO(g) =Na(g) + PO(g), NaOP(g) =Na(g) + PO(g), NaPO2(g) =Na(g) + PO2(g), and 2NaPO2(g) =NaPO3(g) + NaOP(g). The resulting enthalpies of reaction, ΔH°0 (in kJ), are given as 267.8±25, 281.4±25, 333.2±12, and 39.5±35, respectively. The atomization energies, ΔH°a,0, and standard heats of formation, ΔH°f,298, for the gaseous molecules NaPO, NaOP, NaPO2, and NaPO3 were derived from these reaction enthalpies in conjunction with appropriate literature data as follows: 861±30 and −176±30; 874±30 and −191±30; 1419±20 and −492±20; and 1925±45 and −753±45 kJ mol−1, respectively. The atomization energies of the ternary molecules have been discussed in terms of the bond additivity postulate.
Infrared spectra of monomeric gallium trihalides in solid argon
Authors: Pong Richard G. S. , Stachnik Robert A. , Shirk Amy E. , Shirk James S.
Published: February 2003

We have observed the infrared spectra of GaCl3, GaBr3, and GaI3 in solid argon. Some absorptions due to the dimers are also reported. Isotopic shifts were partially resolved in several cases. The observed spectra are all consistent with a planar D3h structure for each of these molecules.
Relation between inverse emission and absorption rates for multiphonon transitions
Authors: Struck C. W. , Fonger W. H.
Published: February 2003

The relation between inverse emission and absorption rates for multiphonon transitions is investigated through detailed balancing and also through specific quantum-mechanical models of these transitions. The forced absorption rate is much smaller than the forced emission rate, not equal as in the case of radiative transitions. Because the process corresponding to spontaneous multiphonon emission at T=0 °K does not persist undiminished at higher temperatures, the separation of multiphonon emission into spontaneous and forced components is physically imprecise.
Molecular models of the smectic-C phase and magnetic resonance experiments
Authors: Wulf A.
Published: February 2003

In recent molecular models of the smectic-C phase the tilt angle χ is related to a characteristic biaxial order parameter μc; χ=const. ×μc, for small χ. We derive the effective nuclear spin Hamiltonian taking into account the orientational order parameter μc, and apply this Hamiltonian to a consideration of published nuclear magnetic resonance experiments. The order parameter μc may be defined as the Z, Y component of the order matrix 〈ν3ν2+ν2ν3〉, where ν3 and ν2 denote the directions of the long molecular axis and a given transverse axis, respectively, Z is the preferred orientation of ν3 (i.e., ? is the nematic director), and the plane ZY is the tilting plane. It is expected that μc may reach values of order 10−1. Experimentally, the orientational order in the smectic-C phase of terephtal bis(butylaniline) (TBBA) has been investigated by Luz, Hewitt, and Meiboom, using the technique of deuterium magnetic resonance. It is shown here that the outward movement of the edges of the spectra, which should occur for small sample rotations, is smaller than 1% of the maximum quadrupole splitting, if μc≲10−1. The accuracy of the experiment is not sufficient to detect this effect. On the other hand, some peculiar features of the experimental spectra, not explained by the uniaxial model, are pointed out and interpreted qualitatively in terms of μc. Such features are also present in proton resonance spectra of neat TBBA and DHAB (diheptyloxyazoxybenzene) obtained by Luz and Meiboom. We conclude that more experiments and more detailed numerical studies of the spectra, including the effect of the order parameter μc, are required to determine whether the biaxial picture of the smectic-C phase is valid.
Average and directional Compton profiles for the N2, O2, and CH2O molecules. I. Effect of electron correlation
Authors: Tawil R. A. , Langhoff Stephen R.
Published: February 2003

The average Compton profile, and the Compton profiles along directions parallel to the bonds and perpendicular to the plane of each of the N2, O2, and CH2O molecules, were calculated at two levels of approximation. The uncorrelated charge densities were obtained from wavefunctions calculated at the self-consistent-field (SCF) level and correlation was introduced by means of configuration interaction (CI). The CI wavefunctions were constructed by accepting all single excitations plus a selected set of double excitations from an initial reference list of configuration accouting for 40%–50% of the correlation energy for each of the molecules. Double-zeta and double-zeta-plus-polarization quality bases constructed from Gaussian-lobe functions were used to generate these wavefunctions. The effect of electron–electron correlation on the charge density and its anisotropies was studied by a comparison of the various profiles at the two levels. It is found that this interaction, similar to its effect in atomic systems, tends to broaden the SCF profiles and this tendency is attributed to the increased antibonding character in the momentum charge distribution introduced via CI. The effect is most pronounced on the profiles along directions parallel to bonds, least perpendicular to the plane of the molecule and intermediate for the average, and is found to be most dominant in the momentum regions affected by bonding. It is also found that the inclusion of electron-correlation uniformly brings the theoretical results into better agreement with the experimental measurements when the latter are available. These results are analyzed in detail and an attempt is made to explain them.
Chemi-ionization and secondary ion reactions in molecular hydrogen and its isotopes on impact of metastable helium atoms
Authors: Specht L. T. , Foster K. D. , Muschlitz E. E.
Published: February 2003

Relative cross sections for the following reactions are reported:             in which X2 is (a) H2, (b) D2, and (c) HD. The isotope effect in the production of HeH+ and HeD+ in Reaction (2c) was determined and relative measurements were made of the kinetic energy of the ion product in Reaction (1). The cross section for the secondary reaction     was also determined as a function of the relative kinetic energy of the reactants. This energy-dependent cross section was determined for H2+ formed both by helium metastable atom collisions and by electron impact. The cross section for H+2 formed by metastable helium was found to be greater than for H+2 formed by electron impact. This may be evidence for an additional reaction producing H+3 involving highly excited Rydberg states of H2 as reactants.
Rotational correlation times for [Co(en)3]3+ in water
Authors: Craighead K. L. , Jones P. , Bryant R. G.
Published: February 2003

The rotational correlation time for tris(ethylenediamine)cobalt(III) ion in water has been measured by three nuclear magnetic resonance methods. At 25 °C the rotational correlation time is between 30 and 35 psec. From the change in the correlation time on ion pair formation with phosphate ion it is concluded that the partners in the ion pair rotate as a unit in water.
Dissociation of CH4 and CD4 by electron impact: Production of metastable and high-Rydberg hydrogen and carbon fragments
Authors: Finn T. G. , Carnahan B. L. , Wells W. C. , Zipf E. C.
Published: February 2003

The production of hydrogen and carbon atoms in metastable and high-lying Rydberg states due to electron-impact dissociation of CH4 and CD4 has been investigated for incident electron energies from threshold to 300 eV. Onset energies for the production of metastable hydrogen atoms were observed at electron impact energies of 22.0±0.5, 25.5±0.6, 36.7±0.6, and 66±3 eV, and at 26.6±0.6 eV for the production of metastable carbon atoms. Most of the excited H fragments appear to have been formed initially in high-lying Rydberg states with the metastable H(2S) state populated principally by cascade. The differential cross section, (dσ/dΩ)90°, for the dissociative excitation of H atoms to metastable and high-lying Rydberg states reached a maximum value of approximately 1×10−19 cm2/sr at 100 eV. At the same energy, the metastable carbon differential cross section is 2×10−20 cm2/sr.
Mass spectrometric determination of the ionization potential and dissociation energy of LiD
Authors: Ihle H. R. , Wu C. H.
Published: February 2003

The ionization potential of LiD was determined as I.P.(LiD) =7.7±0.1 eV, from which a binding energy D°0(Lid+) =0.14±0.1 eV results. From measurements of the gas equilibrium Li2(g)+D2(g) ?2LiD(g) over dilute solutions of deuterium in liquid lithium a value for the dissociation energy D00(LiD) =2.49±0.04 eV was obtained.
Photodissociation and photodetachment of molecular negative ions. II. Ions formed in oxygen
Authors: Cosby P. C. , Bennett R. A. , Peterson J. R. , Moseley J. T.
Published: February 2003

Total photodestruction cross sections for O−2, O−3, and O−4 ions have been measured over a photon energy range of 1.93–2.71 eV using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The O−2 ion is found to photodetach at these photon energies with a cross section which varies from 1.2 to 2.2×10−18 cm2. The O−3 ion photodissociates to form O− over this energy range with a cross section which varies from 0.1 to 7.3×10−18 cm2 and exhibits structure indicative of the vibrational levels of a predissociating excited state. Structure is also observed in the O−4 photodestruction cross section which varies from 1.0 to 2.2×10−18 cm2, and in the O−2 photodetachment cross section.
Vibration–translation energy transfer in anharmonic diatomic molecules. I. A comparative evaluation of the semiclassical approximation
Authors: McKenzie Robert L.
Published: February 2003

The semiclassical approximation (quantum oscillator, classical path) is applied to anharmonic diatomic oscillators in excited initial states. Multistate numerical solutions giving the vibrational transition probabilities for collinear collisions with an inert atom are compared with equivalent, exact qunatum-mechanical calculations. Several symmetrization methods are shown to correlate accurately the predictions of both theories for all initial states, transitions, and molecular types tested, but only if coupling of the oscillator motion and the classical trajectory of the incident particle is considered. In anharmonic heteronuclear molecules, the customary semiclassical method of computing the classical trajectory independently leads to transition probabilities with anomalous low-energy resonances. Proper accounting of the effects of oscillator compression and recoil on the incident particle trajectory removes the anomalies and restores the applicability of the semiclassical approximation.
Dominance of dipole coupling over isotope shift effects for internal crystal modes: ν3 of KNO3 (III)
Authors: Devlin J. Paul , Frech Roger
Published: February 2003

The occurrence of well-separated and sharp transverse and longitudinal optic mode Raman features for the nitrate asymmetric stretching mode of KNO3 (III) presents an exceptional opportunity to observe the effect of isotopic dilution on the dynamics of a crystal mode based on an intensely infrared active internal mode. It has been found that for most of the range of isotopic dilution with 15N, which is known to cause an ∼32 cm−1 isotope shift for isolated NO—3 units, the KNO3 (III) Raman spectrum for backscattering along the trigonal axis contains only two relatively sharp (TO and LO) features, as observed for the 14N sample, but displaced in a regular manner towards the pure 15N sample values. The sharpness of the Raman features relative to the ν3 features observed for the orientationally disordered KNO3 (I), suggests that the spectra can be discussed as though the k?0 selection rule is operating, even though translational symmetry is clearly destroyed by isotopic mixing. It has also been shown that the atr ν3 infrared band of a 50:50 isotopic mixture behaves as though based on a single resonant mode. The results can be interpreted by assuming that dipole forces cause the nitrate units to vibrate with an ’’average’’ resonant frequency, a result that may have interpretive value in the analysis of vibrational spectra of disordered systems.
Stark spectroscopy with the CO laser: The dipole moment of H2CO in the v2=2 state
Authors: Johns J. W. C. , McKellar A. R. W.
Published: February 2003

Some transitions of the 2ν2←ν2 hot band of H2CO near 5.8 μm have been observed by the laser Stark technique using a 20 cm long intracavity absorption cell with about 4 mtorr total pressure at room temperature. The detection of this weak hot band (partial pressure in the v2=1 state ?8×10−7 torr) illustrates the high sensitivity of intracavity laser absorption spectroscipy. From the measured resonant fields of the transitions, the dipole moment of H2CO in the v2=2 state has been determined. The use of phase sensitive detection at twice the Stark modulation frequency is illustrated; this 2f detection effectively measures the strength of the transient nutation signal in the absorbing gas, and in some cases results in a better signal to noise ratio than does conventional 1f detection.