bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-lived states in atom–surface collisions: Reciprocal lattice vector poles
Authors: Bosanac S. , Micha David A.
Published: February 2003

The resonance energies of long-lived states in elastic scattering of atoms by solid surfaces are related to the trajectories of poles of the scattering matrix in the planes of the complex components of the reciprocal vector G. Resonance trajectories, similar to Regge-pole trajectories, are discussed for scattering of He by LiF(001) at fixed angle and varying wavelength. This approach gives insight into the ordering of resonances. A construction is described in the plane of the G vector components to identify possible resonance energies and to discuss their high-energy behavior.
Analytic continuation in exchange perturbation theory
Authors: Jeziorski Bogumil/ , Schwalm William A. , Szalewicz Krzysztof
Published: February 2003

It has been shown that the divergence or pathologically slow convergence of perturbation expansions involving a weak or none symmetry forcing (Murrell–Show–Musher–Amos, symmetrized polarization or polarization expansions) can be circumvented by using a simple analytic continuation procedure. When applied to the interaction of a hydrogen atom with a proton this procedure provides accurate values of the exchange energy from the knowledge of the polarization series alone. When the ungerade symmetry is forced the symmetrized polarization series is shown to converge to a spurious, unphysical interaction energy. The true interaction energy can only be recovered by the analytic continuation procedure. This procedure provides us also with the information about location of singularities of the analytic functions defined by the perturbation series. Such information turns out to be sufficient for an understanding of peculiar convergence properties of the perturbation expansions and their Padé approximants.
Extensions of a method for evaluating higher-order semiclassical phase integrals
Authors: Pajunen Petri
Published: February 2003

Two new versions of a quadrature procedure for evaluating semiclassical phase integrals of the form ∮ dr f(r)/[E−U(r)]k+1/2 for integer k≳0 and any smooth potential U(r) are derived and tested. The first of these can be employed if there is only one classical turning point in the integration range and the other when the two turning points defining the integration range coalesce. Combined with earlier versions of the method this paper provides the means of evaluating all contour integrals associated with diagonal properties of bound states of one-dimensional potentials.
Energy curves and moments for PbHe and PbXe
Authors: Basch Harold , Julienne P. S. , Krauss M. , Rosenkrantz M. E.
Published: February 2003

Collision induced absorption at either the pump or Stokes wavelength could reduce the efficiency of Raman scattering of XeCl pump radiation in Pb vapor. Calculation of the collision induced absorption requires a knowledge of the different energy curves between the ground and upper states and the transition moment as a function of the internuclear distance. These curves were obtained in a first-order configuration interaction calculation of the PbHe, PbHe+, PbXe, and PbXe+ valence states. The atomic cores of Pb and Xe were replaced by relativistic effective core potentials so as to make the calculations tractable. The van der Waals interaction was also estimated by a variational perturbation calculation. These results were transformed to an Ω representation using an empirically determined spin–orbit operator. Using these theoretical data we estimate the collision induced absorption cross sections to be 10−23 and 10−21 cm2 per atmosphere of Xe for the first and second Stokes lines in the case of a 308.0 nm pump. Cross sections for He will be about an order of magnitude smaller due to the smaller transition moments. The energy defect for the pump wavelength is estimated to be so large that no significant absorption is expected for either PbXe or PbHe collision partners. There are also no calculated curve crossings at an energy lower than 0.25 eV, which indicates a very small probability for deactivation of Pb(3P2) by rare gas collision.
Relations between the pondered mean SCF and Slater’s orbital energies in open-shell configurations of isoelectronic atoms and ions
Authors: Pujol L. , Francois A.
Published: February 2003

Relationships between SCF and Slater’s orbital energies are established in the open-shell configurations (1s)2(2s)2(2p)n of atoms or ions. The relationships are used to evaluate ionization potentials with possible applications in molecular calculations where effective Hamiltonian matrix elements are related to Slater’s orbital energies.
The influence of a rare-gas matrix on the electronic levels of isolated atoms
Authors: Forstmann Frank , Ossicini Stefano
Published: February 2003

A pseudopotential model is suggested for the calculation of the matrix perturbation on the spectra of isolated atoms. The calculated shifts of the ground state and of the excited state have different signs. The energy of the outer electron of the isolated atom is lowered in the substitutional site. A blue shift for the P←S absorption lines of the right magnitude is calculated for Cu, Ag, and Au atoms on substitutional sites in Ar, Kr, and Xe matrices.
Sideband intensities in NMR spectra of samples spinning at the magic angle
Authors: Herzfeld Judith , Berger Alan E.
Published: February 2003

General integral and series expressions are derived for the intensities of sidebands observed in the magic angle spectra of inhomogeneously broadened I=1/2 systems. The expressions are evaluated for a wide range of shift parameters and the results used to construct graphical and numerical methods for extracting the principal values of chemical shift tensors from the intensities of just a few sidebands. The methods are illustrated by application to 31P spectra of barium diethyl phosphate. The results agree well with previous single crystal measurements.
Emission spectra and radiative lifetimes of the Cameron bands of CO trapped in solid rare gas matrices
Authors: Fournier J. , Mohammed Hassan H. , Deson J. , Vermeil C. , Schamps J.
Published: February 2003

The emission spectrum of the Cameron bands (a 3Π→X1 Σ+) of CO molecules trapped in solid Ne, Ar, and Kr has been studied using Xe resonance lamp excitation (λ=147 nm). The lifetime of the a 3Π state has been measured in solid Ne and found to be 90 msec. The decay time of this state is exponential within the range of experimental errors. The lifetime has been calculated assuming spin–orbit mixing between 1Σ+ and 3Π0 states, and found to be 94 msec for J=0. The lifetime values in Ar and Kr matrices are found to be 7.2 and <1 msec, respectively; this is consistent with the matrix shifts in solid Ne, Ar, and Kr, which for the 0–0 bands have been found to be −305, −946, and −2812 cm−1, respectively.
Spin–rotation and hyperfine parameters for the (001) excited vibrational state of NO2 from infrared–radiofrequency double resonance
Authors: Allegrini M. , McKellar A. R. W. , Pinson P. , Brown J. M.
Published: February 2003

Magnetic–dipole spin–rotation transitions within the ground and v3=1 excited vibrational states of 14N16O2 have been observed by the technique of infrared–radiofrequency double resonance, utilizing near coincidences between CO laser lines and NO2 ν3 band transitions around 6.2 μm. The ground state data contribute to the extensive body of microwave, EPR, and double resonance measurements now available for NO2. The excited state data are the first high resolution measurements within this state, and they are used here to determine a set of spin–rotation and hyperfine interaction parameters for NO2 in the v3=1 state.
Pressure dependence of the absolute rate constant for the reaction OH+C2H2 from 228 to 413 K
Authors: Michael J. V. , Nava D. F. , Borkowski R. P. , Payne W. A. , Stief L. J.
Published: February 2003

The pressure dependence of absolute rate constants for the reaction of OH +C2H2→ products has been examined at five temperatures ranging from 228 to 413 K. The experimental technique which was used is flash photolysis–resonance fluorescence (FP–RF). OH was produced by water photolysis and hydroxyl resonance fluorescent photons were measured by multiscaling techniques. The results indicate that the low pressure bimolecular rate constant is ∼4×10−13 cm3 molecule−1 s−1 over the temperature range studied. A substantial increase in the bimolecular rate constant with an increase in pressure was observed at all temperatures except 228 K. This indicates the importance of initial adduct formation and subsequent stablization. The high pressure results are well represented by the Arrhenius expression (kbi)∞=(6.8.3±1.19)×10−12 exp(−646±47/T) cm3 molecule−1 s−1. The present results are compared to previous investigations and are theoretically discussed. The implications of these results on modeling of terrestrial and planetary atmospheres and also in combustion chemistry are discussed.
Oxygen-17 NMR and EPR studies of water exchange from the first coordination sphere of gadolinium(III) aquoion and gadolinium(III) propylenediaminetetra-acetate
Authors: Southwood-Jones Rosalind V. , Earl William L. , Newman Kenneth E. , Merbach André E.
Published: February 2003

The 17O NMR relaxation times, T1 and T2, for water in aqueous solutions of Gd(ClO4)3 and GdPDTA− and the EPR linewidths for the same complexes have been measured. These data are analyzed in terms of the Solomon-Bloembergen-Morgan equations for relaxation of a nucleus near a paramagnetic ion and McLachlan’s theory for average EPR relaxation times. The analysis results in a consistent set of physical parameters for the electron relaxation as well as kinetic constants for the water exchange from the complexes. The rate constant for water exchange at 298 K from the Gd(III) aquoion is 10.6×108 s−1 and for the remaining waters in the GdPDTA− complex is 3.3×108 s−1. These rates are higher than the previously published lower limits for water exchange from lanthanide aquoions. A comparison of these results with the rates of formation of other gadolinium complexes leads to the conclusion that the rate of water departure is not the rate limiting step in lanthanide complexation reactions with polydentate ligands.
Extension of the matrix theory of circular dichroism for unordered polypeptides
Authors: Rabenold David A.
Published: February 2003

A Green operator technique used within a susceptibility framework is employed to present a unified theory for the circular dichroism of unordered polypeptides. The theory includes ground state wave function corrections. Two limiting cases of the formulation are the matrix theory of CD and a generalization of the rotational strength expressions derived by Tinoco [Adv. Chem. Phys. 4, 113 (1962)].
ESR studies on cation-radicals of simple olefins and dienes produced in γ-irradiated frozen solutions of trichlorofluoromethane
Authors: Shida Tadamasa , Egawa Yoshikazu , Kubodera Hideo , Kato Tatsuhisa
Published: February 2003

Cation radicals of butene-1, trans and cis butene-2, isobutene, tetramethylethylene, cyclopentene, cyclohexene, butadiene, 1,3-pentadiene, cyclopentadiene, 1,3- and 1,4-cyclohexadienes have been produced mostly for the first time in γ-irradiated frozen matrix of trichlorofluoromethane at 77 K. Well resolved ESR spectra at 77 K or at 130–155 K permit the determination of proton hyperfine coupling constants. Large hyperfine coupling constants of methylene and methyl protons adjacent to π electron systems indicate an extensive hyperconjugation in the cations. The following photoisomerizations are found: butene-1+→butene-2+, cyclopentene+→1,3-pentadiene+, 1,4-cyclohexadiene+→ 1,3-cyclohexadiene+, 1,3-cyclohexadiene+→1,3,5-hexatriene+. The nonplanar cations of cyclopentene and 1,3-cyclohexadiene undergo puckering motion in a limitedly warmed matrix. In the warmed matrix, where diffusions of the cation radicals toward unreacted hydrocarbon molecules proceed slowly, proton transfer reactions are induced. Decisive evidence for the formation of dimer cations is not obtained under the conditions studied.
Simultaneous measurement of rotational and translational relaxation by sub-Doppler optical–optical double resonance spectroscopy: BaO(A 1Σ+)–Ar and BaO(A1Σ+)–CO2
Authors: Gottscho Richard A. , Field Robert W. , Bacis Roger , Silvers Stuart J.
Published: February 2003

Sub-Doppler optical–optical double resonance (OODR) spectroscopy is used to correlate BaO(A1Σ+) rotational and translational relaxation induced by collisions with Ar or CO2 in a 0.3–2 Torr Ba+CO2+Ar flame. A selected rovibronic BaO A 1Σ+←X 1Σ+ transition is pumped by the first of two frequency stabilized, 1 MHz bandwidth, cw dye lasers. Collision-induced level-to-level processes in the A 1Σ+ state are monitored with the second laser by excitation of C 1Σ+←A1Σ+ probe transitions and detection of C 1Σ+→X 1Σ+ ultraviolet fluorescence. The dependence of J-changing collision rates on the initial A 1Σ+ (v=1) rotational level, Jo, is monitored by independent preparation of Jo=0 and Jo=15. For Ar, ‖ΔJ‖=1–20 collision rates are found to be independent of Jo and well represented by the power law, where ΔEr is the change in BaO (A 1Σ+) rotational energy in cm−1; ε=ΔEr for Jo<J and ε=0 for Jo≳J. For BaO∼CO2 collisions a single power law is inadequate to represent Jo=0 and Jo=15 data: Total BaO–Ar J-changing collision cross sections are: 60±15 Å2 for Jo=15 and 40±10 Å2 for Jo=0. For BaO–CO2, total J-changing collision cross sections are: 230±40 Å2 for Jo=15 and 50±20 Å2 for Jo=0. ΔJ≠ 0 OODR line shapes, broadened by velocity changing collisions, sample the center of mass (cm) scattering angle (ψ) distribution. For ΔJ=±1 transitions, the cm scattering angle distribution is characterized by <cosψ≳=0.81±0.05 or <ψ≳=36°±5° for BaO–Ar and <cosψ≳=0.989±0.01 or <ψ≳=8.5°±36° for BaO∼CO2 collisions. Significantly smaller angle scattering by CO2 (vs Ar) is manifested by a dramatic line narrowing upon additon of excess CO2, at constant Ar partial pressure. A small monotonic increase in <ψ≳ with ‖ΔJ‖ is found, which confirms the expectation that small angle scattering and concomitant small changes in J result from long-range collisions, whereas wide angle cm scattering with large ΔJ results from the short range part of the intermolecular potential.
Brillouin scattering in superheated water
Authors: Hareng M. , Leblond J.
Published: February 2003

We report high frequency sound velocity measurements in superheated water in the temperature range from 100 to 220 °C at atmosphere pressure at 5 GHz. These results, obtained by Brillouin scattering, are in reasonable agreement with available data given by ultrasonic techniques, and the superheated water can be considered at 5 GHz as a nonrelaxing liquid up to 220 °C.The isothermal compressibility βT as deduced from the hypersound velocity v was fitted to a critical expression of the type βT=β0εx, with x=−0.97 and ε=(T*−T)/T*. T*≃588 K(315 °C) seems to be the limit temperature of stability of the liquid phase.
Studies of molecular reorientation, translation, and vibrational relaxation of liquid 1,2,4-trichlorobenzene by depolarized Rayleigh and Raman spectroscopy
Authors: Cavanaugh David B. , Wang C. H.
Published: February 2003

The depolarized Rayleigh and Raman scattering spectra of 1,2,4-trichlorobenzene (TCB) in CCl4 have been measured as a function of concentration at several tempertures in high resolution. The depolarized Rayleigh spectra were obtained using a Fabry–Perot interferometer and the high resolution Raman spectra were obtained using a tandem spectrometer consisting of a Fabry–Perot interferometer and a double grating monochromator. The central dip due to shear wave coupling to reorientational motion is observed in the depolarized Rayleigh spectrum. The Rayleigh relaxation times τRay obtained for TCB depend on the TCB concentration. The concentration dependence of the Rayleigh times indicates the importance of orientational pair correlation in TCB. The single particle orientational relaxation times τs were obtained by extrapolating from τRay data to infinite dilution. The activation energy for molecular reorientation which is found to be affected by pair correlation decreases with decreasing concentration, with most rapid decrease occuring at low concentration. The spectral linewidth of the 677 cm−1 band shows a weak concentration dependence, thus suggesting that the vibrational effect of the 677 cm−1 band in neat TCB can be interpreted in terms of single particle dynamics. Further studies show that the vibrational linewidth is due to the intramolecular interaction.
X-ray photoelectron spectroscopy of phthalocyanine compounds
Authors: Ouedraogo G. V. , Benlian D. , Porte L.
Published: February 2003

X-ray photoelectron spectra arising from carbon 1s, nitrogen 1s, and iron 2p and 3s levels of metal-free phthalocyanine (H2Pc), iron (II) phthalocyanine [Fe (II) Pc], and several derivatives of ironphthalocyanine (FePcL), where L=Cl, NO and FePcL2, where L=imidazole, 3-chloropyridine, 3-picoline) are presented. Measurements on C1s and N1s levels are similar to those published in the literature, using the C1s main peak as an internal calibrant. Fe3s spectra show multiplet splitting for FePc and FePcL compounds while for FePcL2 there is no observable multiplet splitting. Satellite structure adjacent to the Fe2p1/2, 2p3/2 lines for FePcL2 compounds and to the N1s photolines for all compounds studied are observed. The main conclusions on the electron configuration of iron in the phthalocyanine compounds are presented and are used to discuss some unsolved charge transfer and spin state problems.
Molecular and relative segmental order in the nematic and smectic C phases: A nuclear magnetic resonance study
Authors: Bos Philip J. , Shetty Anil , Doane J. W. , Neubert Mary E.
Published: February 2003

Order parameters expressing the molecular orientational order as well as the time average conformation of the molecule are measured, some for the first time, in the nematic, N, and smectic C, Sc, phases. Deuterium spectral splittings from the compounds 4-n-octyl-d17-oxybenzoic acid-d1 (80BA-d18) and 4-n-heptyl-d15-oxybenzoic acid-d1 (70BA-d16) are interpreted in terms of parameters which are time averages of spherical harmonic functions of order 2. There are three parameters measured for each deuterated molecular segment which describe its orientational order relative to one particular segment of the molecule. The time average conformation of the molecule is therefore described in terms of the relative order of the individual segments and hence these conformation parameters. These parameters show that the wagging motion of the hydrocarbon chain is not cylindrically symmetric. In addition, the conformation parameters are shown to be temperature independent within experimental error. The temperature dependences of the observed spectral splittings are governed instead by that of three molecular order parameters describing the orientational order of the molecule as a whole. Two molecular order parameters are measured in the nematic phase which give the degree of order of the molecular long axis and the anisotropy in that order, respectively. The onset of a third molecular order parameter is observed at the N–Sc phase transition. The data appear to be consistent with a molecular model which is, on the time average, rigid and exhibits a hindered rotation about its long axis in both the N and Sc phases.
Exciton scattering and the dephasing of ESR and optical absorption lines: The 1,2,4,5-tetrachlorobenzene triplet exciton problem
Authors: Wieting R. D. , Fayer M. D.
Published: February 2003

The relationship between exciton scattering induced dephasing of the ESR and the optical transitions of triplet exciton bands is examined by properly including exchange in the line shape formalism. First, a simple heuristic model demonstrates that while the optical dephasing time can be associated with the exciton scattering rate, the ESR dephasing time is more closely associated with the distribution of final states in the scattering process. The full exchange problem is then examined and a formal solution is obtained for the low power steady state ESR spectrum. Application to the 1,2,4,5-tetrachlorobenzene triplet exciton system shows that the exciton ESR spectrum with its associated 1 μsec dephasing time can be reproduced using a 20 psec exciton scattering rate obtained from the optical dephasing time. Exciton scattering occurs to a small region of k space (∼5% of the band) surrounding the initial k state. These results resolve the apparent conflict between the optical and ESR spectra in this system and indicate that exciton transport, while not strictly coherent, is nonetheess predominantly wavelike in character.
Crystal-field analysis of triply ionized rare earth ions in lanthanum trifluoride. II. Intensity calculations
Authors: Leavitt R. P. , Morrison C. A.
Published: February 2003

Implementation of the Judd–Ofelt theory of induced electric dipole transitions is considered for rare-earth ions in LaF3. Parameters in the theory are derived a priori. Calculations of the multiplet-to-multiplet line strengths, lifetimes, branching ratios, and line-to-line squared matrix elements are performed between all the energy levels considered for the triply ionized lanthanides Ce3+ through Yb3+. Magnetic dipole calculations are also performed. The g factors for all the lanthanides with an odd number of f electrons are given. Calculated Judd–Ofelt intensity parameters and radiative lifetimes compare reasonably well with experiment.
Kinetic energy dependence of the branching ratios of the reaction of N+ ions with O2
Authors: Howorka F. , Dotan I. , Fehsenfeld F. C. , Albritton D. L.
Published: February 2003

The kinetic energy dependence of the branching ratios of the reaction of N+ with O2 has been determined in the collision energy range from 0.06 to 1.8 eV using a selected-ion flow-drift tube. At energies near thermal, the branching ratios were found to be the following percentages: O2+ 51±4, NO+ 43±4, and O+ 6±4, in good agreement with the results of some of the earlier thermal-energy studies. At relative kinetic energies above about 0.1 eV, the O+2 channel increases and eventually becomes dominant, at the expense of the NO+ channel. At the highest energy investigated in the present study, the branching ratios obtained are 79%, 19%, and 2%, respectively, and join rather smoothly with crossed-beam data extending to higher energies. The O+ channel remains a minor channel over the energy range studied here. These energy-dependent branching ratios are in striking contrast to the total rate constant for this reaction, which is virtually energy-independent for energies below 1 eV.
Calculation of the rate constant for the reaction of atomic hydrogen with molecular oxygen to form the free radical HO2
Authors: Blint Richard J.
Published: February 2003

A temperature dependent rate constant for the H+O2+M→HO2+M* recombination reaction has been calculated using classical dynamics and the kinetic theory of gases. A complete potential energy surface for the interaction of H with O2 has been calculated previously. This potential energy surface was used in conjunction with classical dynamics to calculate the equilibrium constant for the production of HO2* from the reaction H+O2?HO2* where HO2* indicates the HO2 molecule with excess internal energy. The kinetic theory of gases is used to determine the quenching rate, HO2*+M→HO2+M*, by a third body collision. A collision efficiency factor, dependent on the amount of excess energy in HO2*, is included in the calculation. The results indicate that the lifetime of the HO2* species is not the dominant factor in determining the temperature dependence of the rate constant. Rather the efficiency of the third-body in removing the excess energy determines the temperature dependence of the rate constant. Argon is the representative third body used in these calculations.
An improved and extended examination of the adiabatic distorted-wave infinite-order sudden approximation (ADWIOSA)
Authors: Bieniek Ronald J.
Published: February 2003

Eno and Balint-Kurti recently presented an adiabatic distorted-wave formulation of the infinite-order sudden approximation (ADWIOSA) that has a number of appealing qualities for calculating vibrot excitations and de-excitations in atom–diatom collisions. The numerical values they determined for a limited number of He+H2 (nj)→He+H2 (n′j′) cross sections compared favorably to close-coupled results. However, they employed spectroscopic diatomic eigenenergies while the exact calculations were based on harmonic eigenenergies. This paper reports extended ADWIOSA cross sections for (0j)→(1j′), (1j)→(2j′), and (0j)→(2j′) transitions using harmonic eigenenergies, and also gives corrected versions of ADWIOSA formulas. The small change in eigenenergy lowers cross sections to 1/2–1/4 their previous values. The comparison to exact results is then not quite as favorable, which is generally due to limitations in the basic sudden approximation rather than the distorted-wave technique. The extended analysis also reveals clear trends in the sudden approximation. For fixed total energy, the ratio of a sudden approximation cross section and the corresponding exact value is an increasing function of the energy separation between initial and final vibrot states, and is a decreasing function of j0 (the typical diatomic rotational quantum number parameterizing the sudden approximation). Although satisfactory cross sections were often obtained for Δn=1 transitions, very inaccurate values were produced for Δn=2 transitions—probably because the ADWIOSA is only a first-order perturbation technique. Finally, it is shown that the properties of the ADWIOSA that result from choosing harmonic oscillators as the diatomic wave functions not only produce analytic expressions for potentials and coupling elements, but also yield an approximate, useful relationship between (n1, j)→(n1±1, j′) and (n2, j)→(n2±1, j′) transitions for the same collisional kinetic energies: σ(n1, j→n1±1, j′)/σ(n2, j→n2±1, j′) ? [minimum(n1,n1±1)+1]/[minimum(n2,n2±1)+1].
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o calculation of the zero-field splitting parameters of the 3A′′ state of formaldehyde
Authors: Davidson Ernest R. , Ellenbogen James C. , Langhoff Stephen R.
Published: February 2003

The spin dipole–dipole and spin–orbit contributions to the zero-field splitting of the 3A″ state of formaldehyde have been evaluated at the excited state experimental geometry. Ab initio CI wave functions were generated from a Dunning double zeta plus polarization basis set using 3A″ rhf orbitals. Twelve states of each symmetry were used to evaluate the second-order spin–orbit effect. The resulting values of D and E were 0.19 and 0.03 cm−1 with the principal magnetic axes rotated 36° from the CO bond. The values of α and β relative to the inertial axes were calculated to be 0.03 and 0.01 cm−1 compared to the experimental values of 0.05±0.01 and 0.02±0.02 cm−1.
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o configuration interaction study of the Rydberg states of O2. II. Calculations on the 3Σg−, 3Σu−, 3Πg, 1Πg, and 1Σg+ symmetries
Authors: Saxon Roberta P. , Liu B.
Published: February 2003

Using the computational procedure established in the previous paper, configuration interaction calculations have been performed for the 3Σg−, 3Σu−, 3Πg, 1Πg, and 1Σg+ symmetries of O2. The lowest diabatic Rydberg state for each symmetry is presented. Vibrational energy levels of the 1Πg Rydberg state are given. The extent of Rydberg–valence interaction is discussed and the 3Σu− state is compared with a previous calculation.
Factorization of the direct correlation function. I. Basic results
Authors: Wertheim M. S.
Published: February 2003

We examine the possibility of applying the factorization technique to the Ornstein–Zernike equation in closed form for systems of molecular fluids in D-dimensional space. We find a coordinate space transform which puts the equation in pseudo-one-dimensional form by reducing the convolution term to one involving parallel vectors. The resulting factorization equations greatly resemble the one-dimensional ones, but contain the additional variables which are present for D≳1. The inverse transform is constructed and shown to exhibit a characteristic difference between odd and even dimensionality. For odd D a geometric interpretation can be given for all transforms, while even D requires an additional Hilbert transform. Expansion of the transforms in harmonics is carried out for D=2 and 3 to obtain the radial transforms. For D=3 agreement with known results is obtained. The transformation under a shift in the choice of molecular origin is considered. The transformation to the pseudo-one-dimensional form is invariant. The factorization itself depends on a certain surface associated with each molecular species. It is invariant if each surface is kept fixed with respect to the molecule rather than the shifted molecular origin. Distortion or displacement of the surface leads to a different factorization.
On the rotational motion of the ammonium ion in the CsCl-type phase of NH4Br: Results from quasielastic neutron scattering
Authors: Lechner R. E. , Badurek G. , Dianoux A. J. , Hervet H. , Volino F.
Published: February 2003

The rotational motion of the ammonium ion in polycrystalline NH4Br has been investigated by quasielastic incoherent neutron scattering at 12 different temperatures between 297 and 409 K. The measured spectra were corrected for multiple scattering and compared to the C4-rotational jump model. The elastic incoherent structure factor was determined experimentally within the range 0.15⩽Q⩽1.72 Å−1 of elastic wave vector transfer. It yields a N-H bond length of 1.028±0.005 Å. The rotational jump rate was found to follow an Arrhenius law, 1 τC4[s−1] ±0.16)×1013 exp{(−1623±16)/T[K]}, with an activation energy of Ea=13.49±0.13 kJ/mole. Within the studied temperature interval the mean square hydrogen vibration amplitude can be described by the expression 〈u2〉 [Å2−]±1.6)×10−4 T[K] −(16.4±6)×10−2.
Application of classical electromagnetic theory to an understanding of molecular vibrational energy transfer into metal surfaces
Authors: Brus L. E.
Published: February 2003

The quantitative results and qualitative understanding of the classical electromagnetic theory of energy transfer between an infrared dipole and a metal surface are explored. There are two limiting regimes: (1) a short range behavior where the rates decrease as D−3, and a long range behavior where rates decrease exponentially with D. For the analyzed surfaces, these regimes essentially represent transfer to bulk excitations and to surface plasmons, respectively. In the D−3 region, the normalized rates and energy transfer quantum yields can be extremely large as compared with electronic energy transfer in the visible and ultraviolet. A 1000 cm−1, perpendicularly oriented dipole 4000 Å from a Sn surface has a 69% energy transfer quantum yield. Extrapolation to molecules actually ’’on’’ metal surfaces suggests 10−9–10−11 sec lifetimes. Energy transfer to plasmons is explored for plasmons of varying lifetimes and electric field dependences.
Comment on the structure of a simple liquid solvent near a n-butane solute molecule
Authors: Pratt Lawrence R. , Rosenberg Robert O. , Berne Bruce J. , Chandler David
Published: February 2003

The distribution of solvent molecules aroung two different conformations of an n-butane solut molecule is discussed. Monte Carlo calculations are presented for distributions of solvent molecules around the exterior methyl and interior methylene groups of the n-butane molecule. The sampling is increased several gold from previous attempt,1 to obtain better statistics. (AIP)
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o effective valence Hamiltonian description of electron correlation for the neutral and ion valence states of transition metal atoms
Authors: Lee Yoon S. , Sun Hosung , Sheppard Maurice G. , Freed Karl F.
Published: February 2003

Results of second order ab initio effective valence shell. Hamiltonian calculations are reported, where all the valence states of Ti through Ti t+4 are computed simultaneously. The correlation energies of higher lying 4S23dn, 4S3dn+1 and 3dn+2 states and the ground state of Ti are reported. (AIP)
A semiempirical valence bond π-electron theory related to the method of diatomics-in-molecules
Authors: Roach Alan C. , Gimzewski Edmund
Published: February 2003

Following an approach related to the diatomics-in-molecules method, a valence bond semiempirical model is developed for the treatment of low-lying states of neutral conjugated hydrocarbons. Using only empirical data on the ground state and the lowest triplet state of ethylene, encouragingly accurate estimates of enthalpies of atomization, excitation energies, and equilibrium bond lengths are obtained for a selection of species in singlet, doublet, and triplet electronic states.
Describing and removing the arbitrariness in the construction of general SCF coupling operators
Authors: Morikawa Tetsuo
Published: February 2003

A general method is described which unifies a set of eigenvalue equations into one eigenvalue problem. During the formulation of this method, the arbitrariness involved in the general SCF theory is fully realized in terms of numerical parameters concerning the occupied ‖ i≳ and ‖ j≳ and virtual ‖u≳ and ‖υ≳ orbitals. The parameters are λji(=1−λij) which are necessary for constraining orthonormality among the occupied orbitals; avi(≠0) and bji(≠0, j≠i) for converting the magnitude and the direction of gradient vectors on the energy surface; and quite arbitrary matrix elements Rii and Ruv for the SCF operator. The appropriate setting of these parameters is discussed from the practical computational point of view.
Relativistic self-consistent-field methods for molecules. II. A single-determinant Dirac–Fock self-consistent-field method for closed-shell polyatomic molecules
Authors: Aoyama T. , Yamakawa H. , Matsuoka O.
Published: February 2003

The single-determinant Dirac–Fock self-consistent-field method is applied to closed-shell polyatomic molecules and numerical calculations are performed on H2, LiH, Li2, HF, F2, and H2CO. The Gaussian-type functions are employed to express the molecular spinors. Nonrelativistic calculations are also made using the equation of the nonrelativistic limit of the Dirac–Fock equation.
Consequences of extending 1-matrix energy functionals from pure–state representable to all ensemble representable 1 matrices
Authors: Valone Steven M.
Published: February 2003

Levy’s 1-matrix energy functional (Ref. 4) is modified and extended to include all ensemble–representable l-matrices in its domain. This constitutes both a generalization and a simplification of earlier observations by Gilbert. The generalization negates some criticisms of the Donnelly–Parr analysis of a 1-matrix energy functional (Ref. 3) since it was assumed to be defined only for pure-state representable 1-matrices. Further study of this analysis suggests that the taking of arbitrary variations in the 1-matrix at a certain point in their study may result in an invalid Euler equation for the 1-matrix energy functional, although this does not alter the main results of that work. The redefinition of Levy’s functional to accommodate the larger domain allows direct application of Harriman’s analysis of the geometry of density matrices in finite dimensional situations. A decomposition of the equivalent of the Vee expectation value into two terms, one with explicit and another with implicit occupation number dependence, illustrates the role of N-representability. The Vee expectation value is approximated by means of the Schwartz inequality.
Accurate method for high pressure PVT measurements and results for argon for T=−20 to +35 °C and p in the range 200–480 MPa
Authors: Morris Edwin C. , Wylie Russell G.
Published: February 2003

An accurate method for determining the PVT properties of highly compressed gases is described. It is independent of other high pressure fluid data. Novel features are largely responsible for its relatively high accuracy. Some results obtained for argon give the density ρ(T, p) and hence the compressibility factor Z (T, p) with an uncertainty of 0.05%. They are presented graphically and in the form of fitted equations from which derivatives and thermodynamic quantities can easily be calculated. The results are compared with those of other experimenters who have worked in the present region.
EPR investigations of Gd3+ in single crystals and powders of the zircon–structure orthophosphates YPO4, ScPO4, and LuPO4
Authors: Rappaz M. , Boatner L. A. , Abraham M. M.
Published: February 2003

The tetragonal xenotime (YPO4) and monoclinic monazite (CePO4) orthophosphates are known to be chemically and physically stable in geological environments and are also radiation resistant. For these reasons, materials of this type are currently candidates for the primary containment of radioactive actinide solid wastes. Single crystals of the tetragonal orthophosphates YPO4, ScPO4, and LuPO4 doped with Gd3+ were grown by slowly cooling a Pb2P2O7 flux. Finely divided (<0.1 μ), rare-earth-doped powders of these materials were also prepared using a technique of precipitation in molten urea. Electron paramagnetic resonance investigations have shown that the Gd3+ impurities occupy identical substitutional sites in both single crystal and powder specimens of the tetragonal-symmetry orthophosphates. These results provide a basis for future investigations of the effects of heavy-particle radiation damage in the lanthanide orthophosphates.
Locking of cw dye laser emission onto the wavelength of molecular fluorescence by intracavity gain: Example I2
Authors: Truesdell K. A. , Keller R. A. , Zalewski E. F.
Published: February 2003

A cw dye laser can be locked onto wavelengths corresponding to iodine (I2) fluorescence when the fluorescing samples are placed inside the dye laser cavity. The sensitivity of the dye laser to intracavity gains is analogous to its well-known sensitivity to intracavity losses. Gains as low as 0.0001 were detected. In particular, the 5145 Å emission of an Ar+ laser was used to excite I2 molecules inside of a tunable dye laser cavity to the v′=43, J′=12 and/or 16 level (s) of the B 3Π0u+ ground electronic state. The dye laser was then progressively tuned to stimulate emission to the v′′=10–15,J′′=11, 13 and or 15, 17 levels of the X1 Σ0g+ ground electronic state. The efficiency of the dye laser assisted I2 laser was 1–2 orders of magnitude higher than for the Ar+ pumped cw I2 laser. The locking of the dye laser to the I2 fluorescence frequencies was found to be a function of the specific vibrational and rotational quantum numbers. When the dye laser is operated above threshold, spatial hole burning severely limits the fraction of the laser power locked onto I2 fluorescence wavelengths.
Brillouin scattering in polymethyl methacrylate from 4 to 300 K: Temperature dependence of the Grüneisen constant and thermal properties
Authors: Kato E.
Published: February 2003

Measurements of Brillouin scattering and thermal expansion of amorphous polymethyl methacrylate (PMMA) have been carried out between about 4 and 300 K. Temperature dependence of the ratio of the anti-Stokes to Stokes intensities is measured between about 2 and 15 K. This agrees with the result calculated from the quantum theory of Brillouin scattering based on the Debye theory. The lattice Grüneisen constant γL is calculated from the above two measurements, Brillouin scattering and thermal expansion. Below about 100 K, this seems to agree with the results calculated from cell theory by Curro and independently by Simha et al. Above this temperature, there is a small deviation from the theoretical result. The thermodynamic Grüneisen constant γT is also calculated by using the bulk modulus calculated from the sound velocity obtained from Brillouin scattering. At low temperature, γT seems to coincide with γL. Using the ratio γT to γL, the intermolecular specific heat Cv (inter)is obtained. The temperature dependence of Cv(inter) agrees with the calculated one from the Debye specific heat theory. Using the results of the sound velocity and Cv(inter), the temperature dependence of the thermal conductivity is obtained, and compared with the experimental result. These nearly agree with each other.
The fluorescence excitation spectrum of free base phthalocyanine cooled in a supersonic free jet
Authors: Fitch Pamela S. H. , Haynam Christopher A. , Levy Donald H.
Published: February 2003

The fluorescence excitation spectrum of free base phthalocyanine was observed in a supersonic free jet. The spectrum was very intense, and the cooling provided by the supersonic expansion produced a very well-resolved spectrum showing extensive vibrational structure. This is the first time that vibrational structure has been resolved in the electronic spectrum of the isolated molecule. The separation between the origins of the first two excited singlet states was similar to that observed in the static gas, but in the cold spectrum both origins were at several hundred cm−1 higher energy than the band maxima observed in the static gas. The region near the origin of the first singlet was clean and well-resolved, while that near the origin of the second singlet was congested due to mixing with excited vibrational levels of the first singlet. No van der Waals molecules were observed.
Scattering of magnetically selected O(3P) atoms: Characterization of the low lying states of the heavy rare gas oxides
Authors: Aquilanti V. , Luzzatti E. , Pirani F. , Volpi G. G.
Published: February 2003

Measurements of absolute integral elastic cross sections for scattering of O(3P) atoms, magnetically selected in their sublevels mj=0, are reported at three collision energies in the thermal range for each of the target gases Ar, Kr, and Xe. Anisotropy effects, as measured by differences between cross sections with and without magnetic selection, are negligible for Ar, but of the order of a few percent for Kr and Xe: they show up in the glory structure of cross sections. These data and the dependence on velocity of cross sections without magnetic selection, suggest that in the regions of the very shallow van der Walals wells of KrO and XeO, Π-type electrostatic interactions are stronger than Σ ones.
On the phase transition in s
y
m-triazine-mean field theory
Authors: Raich J. C. , Bernstein E. R.
Published: February 2003

A Landau mean field description of the nearly second order phase transition in sym-triazine crystals at ∼200 K is presented. A model Hamiltonian is generated which consists of the appropriate symmetry elastic constant terms, molecular rotational energy, and rotation–translation coupling terms (to second order in both strains and rotations). Due to the symmetry of the crystal in the high (R3̄c) and low (C2/c) temperature phases, third order terms in the rotational order parameter are nonvanishing; the transition is thereby a first order one (although only weakly so). This Hamiltonian is then converted to a free energy by addition of an entropy term calculated for an orientation distribution (about the z axis) based on pocket state functions. The Landau mean field model is developed by choosing a set of order parameters Ry (molecular rotation about the y axis) and strains e5 and (e1-e2). The free energy expression is used to calculate relations between order parameters by setting ∂F/∂Ry=∂F/e5=∂F/∂e7=0. Coupling terms including bilinear products of eρ’s and Ry are employed in this development. Renormalized temperature dependent elastic constants are derived. e5(T) is solved for and found to be in good agreement with observed temperature dependences. Librational frequencies are determined from (∂2H/∂RiRj)ep=Iω2iδij. It is found that in the low temperature phase Δω=‖ωy−ωx∝α e5 in lowest order. Observed power laws for frequencies, splittings and strains with respect to ε≡(T−Tc/T) are discussed in light of these new results. The role of third order terms in (Rx, Ry) is considered and found to be an important factor in apparent deviation from mean field exponents.
Surface-induced ordering of a liquid crystal in the isotropic phase. II. 4-methoxybenzylidene-4′-n-butylaniline (MBBA)
Authors: Tarczon John C. , Miyano K.
Published: February 2003

The boundary order parameter of the liquid crystal 4-methoxybenzylidene-4′-n-butylaniline (MBBA) in the isotropic phase has been deduced for several surface treatments by measuring the surface-induced pretransitional birefringence. Results for the silane surface coupling agent, methyl-3-aminopropyltrimethoxy-silane (MAP) were particularly interesting, indicating a negative surface order parameter. An analytic expression for the temperature-dependent birefringence is derived from Landau’s expanison in the order parameter. This expression shows that the value of the boundary order parameter determines the absolute minimum isotroic phase temperature.
Mobilities and longitudinal diffusion coefficients for Na+ ions in Kr and Xe
Authors: Thackston M. G. , Sanchez M. S. , Neeley G. W. , Pope W. M. , Eisele F. L. , Gatland I. R. , McDaniel E. W.
Published: February 2003

The mobilities (K) and longitudinal diffusion coefficients (DL) of Na+ ions in Kr and Xe gases have been measured near 300°K and at gas pressures about 0.400 Torr.
Enthalpy difference of rotational isomers in liquid butane and pentane from infrared spectra
Authors: Colombo Lucia , Zerbi Guiseppe
Published: February 2003

In the course of a study of the absolute infrared absorption intensities of the fundamentals of liquid normal alkanes at different temperatures, the authors derived the enthalpy difference between the conformational isomers of liquid butane and pentane.(AIP)
Search for tunnel states in solid nitromethane
Authors: Lushington K. J. , Morrison J. A.
Published: February 2003

The heat capacity of nitromethane was measured in the temperature range 0.12°<T<4°K. The temperature dependence of the heat capacity is given in Fig 1. This helps to further characterize states in CH3NO2.(AIP)
The influence of crystal structure and chemical composition on the energy transfer processes in uranates
Authors: Krol D. M. , Ros J. P. M. , Roos A.
Published: February 2003

The luminescence properties of several uranates are reported. The compounds that have been investigated are Y6UO12, Li4UO5, Li2UO4, and MgUO4, all of which contain distorted uranate octahedra. Emission and excitation spectra and the quantum efficiency of the luminescence were measured at 4.2 K. Furthermore, the temperature dependence of the luminescence was investigated. The results show that the excitation energy migrates through the lattice and that the luminescence occurs from uranate centers near defects. These centers act as traps for the migrating excitation energy. The quantum efficiency of the luminescence varies strongly within this series of compounds. This is ascribed to a variation in the concentratio ratio of traps and killers (U5+ ions). When the energy migration process is described with a diffusion model, the diffusion coefficient appears to be ≳5×10−8 cm2 s−1. Finally, some more specific results are presented for Y6UO12, Li4UO5, and Li2UO4.