bluuebunny/crossref_metadata_2025 huggingface dataset:
The potential surface of NCNO
Authors: Björkman Cecilia , Bagus Paul S.
Published: February 2003

Ab initio configuration interaction (CI) calculations, including all single and double excitations from a two-configuration reference state, have been performed for the ground state potential energy surface for the reaction NCNO⇄CN+NO. A comparison is made with previous CI results obtained with single configuration RHF and UHF reference states. It is established that the reference, or zeroth order wave function, must have the correct spin symmetry properties, i.e., it must be an eigenfunction of S2, as well as the correct behavior at the dissociation limit in order to give meaningful CI results. This conclusion should apply, equally well, for the choice of zeroth order wave function for other methods of obtaining accurate correlated molecular wave functions. Finally, the value of the dissociation energy is discussed.
The self-consistent electron pairs method for multiconfiguration reference state functions
Authors: Werner Hans-Joachim , Reinsch Ernst-Albrecht
Published: February 2003

An efficient direct CI method which includes all singly and doubly substituted configurations with respect to an arbitrary multiconfiguration (MCSCF) reference function is described. The configurations are generated by subsequently applying spin-coupled two-particle annihilation and creation operators to the complete MCSCF function. This considerably reduces the size of the n-electron basis and the computational effort as compared to previous multireference CI treatments, in which the configurations are defined with respect to the individual reference configurations. The formalism of the method is very similar to the closed-shell ’’self-consistent electron pairs’’ (SCEP) method of Meyer. The vector Hc is obtained in terms of simple matrix operations involving coefficient and integral matrices. A full transformation of the two-electron integrals is not required. Test calculations with large basis sets have been performed for the 3B1 and 1A1 states of CH2 (ΔE = 9.5 kcal/mol) and for the CH2(3B1) +H2→CH3+H reaction barrier (ΔE = 10.7 kcal/mol). As a preliminary test for the accuracy of the results obtained with contracted wave functions of the above type the potential energy and dipole moment functions of the OH X 2Π and A 2Σ+ states have been calculated. For the 2Π state re and ωe deviate by less than 10−3 Å and 1 cm−1, respectively, from the experimental data. For the 2Σ+ state the agreement is somewhat less good, which is probably due to basis set defects. Around the equilibrium distance the calculated dipole moment functions are in very close agreement with those previously obtained from PNO– CEPA functions.
Effect of direct, and indirect, exhange interactions on geometries and relative stabilities of H2O and H2S dimers in bifurcated, cyclic, and linear configurations
Authors: Hensbergen Bart van , Block Ruud , Jansen Laurens
Published: February 2003

An analysis is made of interaction energies for two molecules of H2O, and H2S, in three different dimer configurations: bifurcated (B), cyclic (C), and linear (L), on the basis of a method previously used to interpret hydrogen bonding in the linear dimers (HF)2 and (H2O)2, and in the molecular complex HF ⋅ H2O. In the method, an analogy is assumed between the phenomenon of indirect exchange (’’super-exchange’’) between two paramagnetic (3d-) cations via a diamagnetic anion in ionic solids and weak bonding (≊1 kcal/mol) in molecular complexes. First-order exchange perturbation theory and an ’’effective-electron’’ description of the systems are employed. For (H2O)2, the model predicts the linear dimer as most stable, in agreement with large-scale ab initio calculations. Experimental evidence indeed shows the linear dimer to be the stable one. For (H2S)2 in the gas phase, no experimental results are available. For this dimer, the most stable configuration depends sensitively on the ab initio distance between the two sulfur atoms. The bifurcated form is found to be slightly repulsive.
Molecular aggregates in cryogenic solutions
Authors: Schauer M. W. , Lee J. , Bernstein E. R.
Published: February 2003

Spectra of pyrazine, benzene, and osmium tetroxide have been obtained in cryogenic solutions. Data indicate that mixtures (∼ 10 ppm solute in solvent) deposited at low temperatures (∼ 100 K) yield clusters of solute molecules. The size of these clusters are estimated from light scattering data to be of the order of 103 Å. In particular, molecular aggregates appear in pyrazine/C3H8, benzene/NF3, CF4, OsO4/C3H8, NF3 but not in benzene/C3H8. The major factor governing the appearance of aggregates at low temperature is solubility. Upon warming these solutions to ∼150 K only solution spectra are observed; subsequent equilibrium cooling, of course, yields only precipitate.
Lattice vibrations of crystalline imidazole and 15N and D substituted analogs
Authors: Majoube M. , Vergoten G.
Published: February 2003

Raman spectra of single crystals and polycrystals of imidazole and 15N and D substituted analogs have been measured. All the active Raman bands have been observed, at 100 K, and their isotopic shifts are discussed with a view to defining unambiguously the corresponding rotational or translational modes for several bands. More detailed assignments have also been deduced from normal coordinate calculations.
Dissociative electron attachment reactions of transition metal carbonyls and their apparent influence on the thermalization of electrons by CO2
Authors: George Patricia M. , Beauchamp J. L.
Published: February 2003

Dissociative electron attachment rates are measured for the transition metal carbonyls V(CO)6, Cr(CO)6, Fe(CO)5, Ni(CO)4, Mo(CO)6, and W(CO)6. Rates are measured as a function of the pressure of CO2 added to relax epithermal electrons. Derived thermal rate constants for the formation of M(CO)−n−1 from M(CO)n are 0.6, 3.0, 2.0, 2.0, 1.3, and 1.2×10−7 cm3 molecule−1 s−1, respectively. The differences in these rate constants may be attributed to the different stabilities of the molecular anion with regard to dissociation versus autodetachment. The measured rate of thermalization of electrons by CO2 varies with the metal carbonyl used and depends on the variation of the dissociative electron capture cross section with electron energy. Each system is thus tightly coupled in that the electron energy distribution is determined not only by collisional processes involving CO2 but varies as well with the energy dependent depletion of the distribution by reactant species.
Vibrational relaxation of highly excited diatomics. I. Method, analysis, and application to HCl(v≤7)+CO2 and N2O
Authors: Berquist B. M. , Bozzelli J. W. , Dzelzkalns L. S. , Piper L. G. , Kaufman F.
Published: February 2003

The infrared chemiluminescence method of Smith and co-workers is adapted to fast flow reactor conditions where a sensitive infrared detector views the vibrationally excited products of various generating reactions through a circularly variable filter in the absence or presence of added quencher molecules. The initial v distributions are found to be totally unrelaxed vibrationally but thermalized rotationally. This allows the experimental measurement of vibrational relaxation rates of high v levels hitherto inaccessible. The modified Stern–Volmer method of analysis is described in detail. Its reference process is the rapid pumping rate constant <5×103 s−1 out of the field of view. HCl+ is generated by any one of four H atom reactions (with Cl2, ICl, ClNO, or SOCl2) or two Cl atom reactions (with HI or HBr), and its quenching rates by CO2 or N2O are measured. Quenching probabilities from about 5×10−3 to 0.5 per gas-kinetic collisions for v = 1 to 7 are found for both gases. The results are compared with the limited published data. Detailed discussion is deferred until the following paper which presents data for 18 additional quenchers.
Photochemical isomerization in solution. Photophysics of diphenyl butadiene
Authors: Velsko Stephan P. , Fleming Graham R.
Published: February 2003

We have examined the radiative and nonradiative decay rates of diphenyl butadiene in hydrocarbon and polar solvents as a function of temperature and pressure. We demonstrate that the radiative rate constant has a small dependence on solvent polarizability, in contrast to what is observed for diphenylhexatriene. We make an explicit separation of the internal molecular barrier to isomerization and the barrier due to frictional forces in the solvent. The energy of the internal barrier to isomerization is less than the activation energy observed in solution, and depends on the polarizability and polarity of the solvent. In contrast to diphenylhexatriene, it decreases, in more polar solvents. We compare the viscosity dependence of the barrier crossing process with Kramers’ theory, the recent kinetic theory result of Skinner and Wolynes [J. Chem. Phys. 69, 2143 (1978)], and the free volume theory of Gegiou, Muzkat, and Fischer, [J. Amer. Chem. Soc. 90, 12 (1968)]. Our data clearly show that the isomerization process is in the intermediate friction limit and we obtain experimental values for the parameters of the three theories. Over the viscosity region studied, Kramers’ and Skinner and Wolynes’ equations coincide exactly and do not reproduce the functional dependence of the radiationless rate pre-exponential factor as well as the free volume theory. We speculate that it may be necessary to consider the frequency dependence of medium viscosity.
Production of atomic nitrogen emission by electron-impact dissociative excitation of nitrogen molecules
Authors: Filippelli Albert R. , Sharpton Francis A. , Lin Chun C. , Murphy R. E.
Published: February 2003

Absolute optical emission cross sections for some 15 transitions in atomic nitrogen, produced by electron impact on nitrogen molecules, have been measured for incident electron energies ranging from threshold to 300 eV. The excitation functions show a broad maximum at about 85 eV and a shoulderlike structure near 35 eV. The threshold energy was found to be quite close to the energy defect of the dissociation process. Near threshold energy, an important mechanism for producing excited nitrogen atoms is beleived to be dissociative excitation through partly bound Rydberg states of N2 that are associated with the N+2 (D 2Πg) ionized state and have the appropriate dissociation limit. At energies above 50 eV, formation of N+2 in excited electronic states by simultaneous ionization and excitation with subsequent dissociation becomes a more important mechanism.
The reaction of Li with O2 in the presence of He or Ar
Authors: Kramer S. D. , Lehmann B. E. , Hurst G. S. , Payne M. G. , Young J. P.
Published: February 2003

The reaction of Li with O2 in the presence of He or Ar was studied at a temperature near 150 °C for inert gas pressures between 29 and 1500 Torr. In both cases, the rate of loss of free Li atoms was linear with O2 partial pressure between approximately 0.003 and 1.3 Torr, but had a more complex dependence on inert gas pressure. In He, the reaction probably proceeded by means of the energy transfer mechanism where the dominant intermediate was LiO2*. The results in Ar are consistent with a reaction occurring through both the energy transfer mechanism in which LiO2* plays an important role and the bound intermediate complex mechanism where LiAr is the primary intermediate.
Exact factorization relations, consistency conditions, and the reduction to the ES approximation for the T-matrix
Authors: Beard L. H. , Kouri D. J. , Hoffman D. K.
Published: February 2003

In this paper, we derive explicit expressions for exact factorizations for both inelastic and reactive scattering. The expressions enable us to reanalyze the ES factorization and obtain new insight into its optimum structure. In the first instance, we are able to give a rigorous basis to the scheme of factoring T-matrices in terms of input T-matrix elements with the same initial relative kinetic energy and show this is not a correction to the ES, but rather results directly from it. We also show that the optimum reference T-matrices in the ES factorization are not on-shell, but rather half-off-shell. This suggests new corrections to currently extant versions of the ES factorization. Finally, novel exact factorization of T-matrices for one potential in terms of those for another potential are given, as well as expressions for obtaining the exact T-matrix elements from approximate ones.
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o study of the harmonic force field and vibrational frequencies of thionylimide: Basis set and electron correlation effects
Authors: Raghavachari Krishnan
Published: February 2003

Basis set and electron correlation effects on the geometry and harmonic force field of thionylimide (HNSO) are investigated in detail. d functions on S are essential in describing the bonding in this compound. The calculated Hartree–Fock vibrational frequencies are about 15% too high. Inclusion of electron correlation at the second and third order Moller–Plesset perturbation levels (MP2 and MP3) gives vibrational frequencies within 5% of experiment. A careful analysis of the force constants reveals that the experimentally derived force fields need some revision.
Correlation diagrams for rigid and nonrigid five-body and XY5 six-body systems
Authors: Ezra Gregory S. , Berry R. Stephen
Published: February 2003

Correlation diagrams are constructed to connect the rotation–vibration energy levels of idealized limiting models for penta–atomic molecules. One limit is the completely nonrigid homonuclear five-body cluster. The method of plethysms is applied to classify the states of the nonrigid limit.Several rigid limits are considered: trigonal bipyramidal, tetrahedral, square pyramidal, pentagonal planar, and regular linear chain molecules. The tetrahedral and square pyramidal examples are generalized to allow the atom in the unique central position to differ from the rest giving (four+one)-body systems. A rigid/nonrigid energy level correlation diagram is also constructed for an XY5 molecule having trigonal bipyramidal point symmetry in the rigid limit. The steps are outlined that will be necessary for applying these diagrams to the interpretation of real molecular spectra.
Thermal resistance between the electronic spin system of CuK2(SO4)2⋅6H2O (powder) and 4He I
I below 1.8 K to magnetic fields of 15 kG
Authors: Fisher R. A. , Brodale G. E.
Published: February 2003

Thermal resistance measurements were made on randomly oriented small crystals of high purity CuK2(SO4)2⋅6H2O [CPS] in contact with 4He ii. Three magnetothermodynamic methods are described for measuring the thermal resistance. The data have the temperature independence and approximate field dependence expected from a rate determining spatial phonon bottleneck. Various heat exchange mechanisms for the CPS–4He ii system are described, and the limitations of the standard phonon bottleneck model are discussed.
Analytic and numerical surface dynamics of the triangular lattice
Authors: Hoover William G. , Ladd Anthony J. C. , Friesen Donna , Moran Bill
Published: February 2003

The high-frequency surface waves discovered by Allen, Alldredge, and de Wette, in numerical studies of three-dimensional fcc crystals, have two-dimensional analogs. Analytic solutions of the equations of motion for two-dimensional close-packed lattices reveal a high-frequency surface-mode branch linking together the high-frequency and low-frequency bulk-mode bands. The dispersion relation for this branch is used to estimate the surface entropy. The estimate agrees well with Carman and Huckaby’s recent cell-cluster calculation. Both the dispersion-relation and cell-cluster surface entropy estimates lie slightly below an accurate value we obtain here by extrapolating small-crystal entropies to the thermodynamic limit.
Theory for surface structure of dilute electrolyte solutions
Authors: Nichols Albert L. , Pratt Lawrence R.
Published: February 2003

A theory is developed for the salt concentration profile and ion–ion correlations near surfaces of dilute electrolyte solutions. We use the RPA to study the primitive surface model previously employed by Onsager and Samaras, and others. In this model the chief technical complication is the correct treatment of image forces. We invent an exact rearrangement of the mathematical formulation of the problem which makes especially transparent the special case solutions (infinite dielectric constant mismatch) previously found by Onsager and Samaras, and by Buff and Stillinger. We then show that our reformulation allows an analytical solution for arbitrary dielectric constant mismatch between the two phases, subject to the other assumptions adopted by these previous workers. These remaining assumptions affect the internal self-consistency of the results. We indicate a systematic perturbative procedure which will be of practical use in improving the self-consistency of the solutions. Finally, we discuss the questions of whether the primitive surface model studied is sufficiently general to yield generally correct surface behavior for limiting small salt concentrations, and whether limiting laws independent of short ranged correlations exist for surface thermodynamic properties. Our results strongly suggest that both answers are no.
The role of diffusion in the binding of carbon monoxide to protoheme in high-viscosity solvents
Authors: Peak David
Published: February 2003

Studies of the flash photolysis of heme-bearing proteins have often assessed the role of ligand diffusion in very approximate ways and a disagreement about the importance of ligand diffusion exists in the literature as a result. This paper provides a somewhat more sytematic analysis of diffusional effects than has been given previously for the simple case of ligand–protoheme binding. The model developed here is fit to the available data for the ligand CO in glycerol–water solvents. The fit suggests that diffusional motions become important for the kinetics of this system for temperatures below 270 K and that these motions are strongly correlated when the reactants are close through interactions with the solvent.
Energy and tangential momentum accommodation coefficients on gas covered tungsten
Authors: Shields F. Douglas
Published: February 2003

The sum of the energy (EAC) and tangential momentum (TMAC) accommodation coefficients has been measured acoustically for Ne on W exposed to the following adsorbates: CO, CO2, O2, N2, H2O, and D2; for He on W with O2 and D2 as adsorbates; and for each of these adsorbates on itself on W. An effort has been made to infer separate values of EAC and TMAC from the measured values of their sum. Good agreement is obtained with EAC values obtained from thermal conductivity cell measurements if TMAC is assumed to have a value of 0.75 for He and Ne on all the gas covered surfaces, and a value of 1.0 for all the adsorbates except D2 on itself on W. The acoustical method which was used has the capability of determining AC values under gas dynamic conditions where the surface and the gas are at essentially the same temperature. For CO2, since the acoustical measurments were made at frequencies far above the vibrational relaxation frequency, the EAC value obtained is for the translational and rotational energy only. The measurements in D2 reveal rotational relaxation.
Hyperfine structure in electronic spectra of NH+, PH+, and SH+ resolved by laser-ion beam spectroscopy
Authors: Edwards C. P. , Maclean C. S. , Sarre P. J.
Published: February 2003

Nuclear hyperfine structure has been resolved in electronic spectra of NH+, PH+, and SH+, using a laser-ion beam technique. The transitions are detected indirectly by monitoring the production of fragment ions N+, P+, or S+ which arise from predissociation of the excited electronic state. (AIP)
Variable wave vector second harmonic generation in phenanthrene
Authors: Johnson Carey K. , Small Gerald J.
Published: February 2003

Second harmonic generation is observed in phenanthrene crystals. The experimental set is used allowed the simultaneous detection of two proton excitation (TPE) and second harmonic generation. (SHG). (AIP)
Self-trapping of CO2 001 emission: A theoretical and experimental investigation
Authors: Huddleston R. K. , Fujimoto Gordon T. , Weitz Eric
Published: February 2003

Experimental results for self-trapping of CO2 0001 emission are presented along with a simple method for calculating self-trapping at low pressures. Very significant self-trapping is observed at pressures as low as 0.050 mm Torr. Calculations and experimental results are compared with possible reasons for the observed deviations discussed. (AIP)
The orientation and symmetry of adsorbed cyclopropane on Ru(001) measured by off specular high resolution electron energy loss spectroscopy and angular resolved photoelectron spectroscopy
Authors: Hoffmann F. M. , Felter T. E. , Weinberg W. H.
Published: February 2003

In order to determine the orientation and symmetry of cyclopropane adsorbed at 95 K on Ru(001) at and below saturation surface coverage, we have combined in situ high resolution electron energy loss spectroscopy (EELS) and angular resolved UV-photoelectron spectroscopy (ARUPS). Both the vibrational and the photoelectron spectra show that the molecule adsorbs associatively with neither an opening of the carbon ring nor an abstraction of hydrogen atoms from the ring. The dipole activity of the ring modes ν10(1010 cm−1) and ν11 (880 cm−1) in EELS and the polar angular distribution in photoemission of the 1a2\, 3a1′, and 1e\ molecular orbitals suggest Cs (σv) symmetry of the admolecule. This type of reduced symmetry can result from an orientation of the molecule in which one C–C bond, but not the entire carbon ring, is parallel to the surface. Both the orientation and the symmetry of the admolecule are discussed in relation to a tentative bonding picture assuming a weak interaction between the delocalized ’’external’’ σCC orbital (mainly 3e′) of the molecule and the metal surface.
Solution of the spin Hamiltonian with orthorhombic hf and g tensors (I = S = 1/2). II. Application to PO4−4 and Tl2+ centers in anisotropic matrices
Authors: Kawazoe H. , Hosono H. , Nishii J. , Kanazawa T.
Published: February 2003

A theory developed previously has been used in the analysis of ESR spectra of PO4−4 and T12+ in anisotropic matrices, which enables one to analyze ESR spectra characterized by spin Hamiltonian ℋ = βH ⋅ g ⋅ S+S ⋅ A ⋅ I, where I = S = 1/2, g and A are of orthorhombic symmetry and no limitations are imposed on the relative magnitude of the hyperfine (hf) interaction. The comparison of ESR parameters for PO4−4 obtained by the newly developed treatment with those by the first- or second-order high-field approximation showed that the new theory gave better results than the high-field approximation for the centers with a moderate hf interaction. The ESR parameters of T12+ in polycrystalline sodium metaphosphate were successfully determined from the powder pattern. This is the extreme case characterized by a dominant and anisotropic hf interaction.
Traveling-wave sub-Doppler excited molecule energy transfer spectroscopy
Authors: Iqbal Khalid , Lieb S. G. , Bevan J. W.
Published: February 2003

A general formulation of traveling-wave sub-Doppler excited molecule energy transfer spectroscopy is presented. The line profile analysis is applied to that determined experimentally for the R(22) ν3 HCN transition. Pn the noise equivalent power of the detector is demonstrated to be ⩽10−12 W. Finally, the technique is applied to resolve the KsR(7) ν1 transition head in NH3.
The collisional de-excitation of Hg(6 3P) by HgBr(X 2Σ), Br(4 2P), and Br2(X 1Σ): Evidence for ion-pair formation in the entrance channel
Authors: Helvajian H. , Wittig C.
Published: February 2003

Measurements are reported wherein Hg(6 3P0) is de-excited by collisions with HgBr(X 2Σ), Br(4 2P), and Br2(X 1Σ). In the cases of HgBr(X 2Σ) and Br(4 2P), quenching rate coefficients are larger than hard-sphere collision rate coefficients, and are consistent with ion-pair formation via the harpoon mechanism. Because of the radical–radical nature of the interaction, long-range attractive forces can draw the nuclei toward the region of coupling with the ion-pair surface, thereby catalyzing ion-pair formation. The ion-pair thus produced correlates with HgBr(B 2Σ), and provides a direct pathway for channeling metastable Hg(6 3P0) excitation into HgBr(B 2Σ), the upper state of the HgBr(B→X) laser. Quenching of Hg(6 3P0) by Br2(X 1Σ) is an order of magnitude less efficient than the above processes, and reasons for this are discussed.
Dirac states for unit position and momentum: Phase consistency of their angular momentum representations
Authors: Snider R. F.
Published: February 2003

It is shown that the position and momentum directional representations of angular momentum states must satisfy Σλs〈r̂‖λs〉〈λs‖p̂〉 = Σλs(i)λYλs(r̂)Yλs(p̂)*. This imposes phase constraints on the relation between 〈r̂‖λs〉, 〈p̂‖λs〉, Yλs(r̂), and Yλs(p̂). In the accompanying paper, it is shown that this resolves a problem in the centrifugal sudden approximation of molecular collision theory.
ESR study of the librations of O2 defects in NaClO3 and KClO4 single crystals
Authors: Bjerre Nis
Published: February 2003

The ESR spectra of O2 defects in UV-irradiated single crystals of NaClO3 and KClO4 were measured at 9 and 35 GHz in the temperature range 2.7–23 K. The O2 defect in NaClO3 has a g-tensor close to that of the free molecule and exhibits well-resolved 16O2–18O2 isotope shifts. Model calculations reproducing these shifts reveal that the discrepancy between the spin Hamiltonians of the trapped and the free molecule mainly results from the angular librations of the trapped molecule. The marked temperature dependence of the spin Hamiltonian of an O2 defect in KClO4 is accounted for in terms of fast transitions between the librational states.
ESR investigation of MoN and Mo atoms in neon, argon, and krypton matrices: Utilization of a hollow cathode ion sputter source for ESR matrix experiments
Authors: Knight Lon B. , Steadman Jhobe
Published: February 2003

A hollow cathode ion sputter source has been coupled to an ESR matrix isolation apparatus for the generation and study of metallic nitrides and other radical species. The ESR results for MoN are consistent with a 4Σ ground electronic state assignment, although unusual temperature effects indicate the possibility of very low lying excited states. A detailed analysis of the metallic hfs of 95MoN and 97MoN observed in neon, argon, and krypton matrices was conducted. The results for 95MoN in a neon matrix at 4 K are: g⊥ = 1.969(1), A⊥(95Mo) = 506.3(6) MHz, and A∥ (95Mo) = 480(8) MHz, Aiso = 498(3) MHz and Adip = −9(3) MHz. Based on these findings, the electronic structure of MoN was compared to the isoelectronic radical NbO and to VO. Mo atoms were generated by both thermal and ion sputter methods. The ESR parameters for the ground state of 95Mo (7S3) in argon at 10 K are: g = 2.000(1) and A = 237(1) MHz.
Surface vibrational spectroscopy with angle-dependent electron energy loss spectroscopy: Acetylene chemisorption on Pd(111)
Authors: Gates J. A. , Kesmodel L. L.
Published: February 2003

High resolution electron energy loss measurements and LEED observations for normal and deuterated acetylene chemisorbed on Pd(111) are reported. Analysis of specular and off-specular energy loss data permits classification of the vibrational modes in terms of long-range dipole and short-range impact scattering mechansims. Impact scattering intensities are found to be relatively strong for some modes and comparable in strength to intensities of dipole-excited modes. The vibrational data indicates that chemisorbed acetylene is strongly rehybridized (∼sp2.5), in approximate agreement with earlier photoemission work. Comparsion is made to vibrational assignments for C2H2 chemisorbed on Ni(111) and Pt(111), as well as relevant model compounds. A surface bonding geometry is proposed, which involves acetylene coordination at threefold sites on the Pd surface in the (√3×√3)R30° structure.
Time resolved resonance Raman scattering of transient radicals: The p-aminophenoxyl radical
Authors: Tripathi G. N. R. , Schuler Robert H.
Published: February 2003

p-aminophenoxyl radical exhibits a resonance enhanced Raman band at 1647 cm−1. Radicals were produced in aqueous solutions at concentrations of the order of 10−5 M by pulse radiolysis and observed by time resolved Raman methods.
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o determination of the rate constant for H+H2CO →H2+HCO
Authors: Harding Lawrence B. , Schatz George C.
Published: February 2003

The results of an ab initio determination of the rate of constant for H+H2CO are presented. (AIP)
Infrared photoacoustic spectroscopy of conducting polymers. II. P-doped polyacetylene
Authors: Yaniger Stuart I. , Riseman Stephen M. , Frigo Timothy , Eyring Edward M.
Published: February 2003

The Fourier transform infrared spectrum of polyacetylene (CH)x lightly doped with iodine is presented and compared with the spectrum of heavily n-doped (CH)x. A model of charge-transfer in doped (CH)x is proposed involving soliton and radical ion states at low and high dopant concentrations, respectively.
Average electron densities of first-row atoms studies with a two-parameter charge density function
Authors: Ray Naba K. , Tandon Harmesh C.
Published: February 2003

The two-parameters statistical model of Gazquez and Parr1 is used to estimate the ’’average electron density’’ of first row atoms and ions. (AIP).
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o calculation of infrared intensities for hydrogen peroxide
Authors: Rogers Jerry D. , Hillman John J.
Published: February 2003

Infrared intensities are predicted for the fundamental vibrations of H2O2 using atomic polar tensors obtained from ab initio quantum mechanical calculations employing a 4-31G basis set. The theoretical atomic polar tensors for H2O2 are compared to theoretical atomic polar tensors reported for H2O and for CH3OH, and the absolute intensities calculated quantum mechanically for H2O2 are compared to the previously reported intensities for H2O2 obtained by transferring a hydrogen atomic polar tensor to H2O2 from H2O and from CH3OH. These comparisons enable estimates to be made for the infrared intensities of H2O2 as follows: A1 = 14.5 km mol−1, A2 = 0.91 km mol−1, A3 = 0.058 km mol−1, A4 = 123 km mol−1, A5 = 46.2 km mol−1, and A6 = 101 km mol−1. Charge, charge flux, and overlap contributions to the dipole moment derivatives are computed for H2O2 and compared with those reported for H2O and CH3OH.
On the Z−1 and N−1/3 expansions of Hartree–Fock atomic energies
Authors: Tal Yoram , Bartolotti Libero J.
Published: February 2003

Numerical Hartree–Fock (HF) calculations for all atoms and ions in the range 2⩽N⩽86 and N⩽Z⩽N+20 were performed and analyzed in terms of the Z−1 perturbation series. Using the theoretical values of the leading expansion coefficient ε0(N), we obtain ε1(N), ε2(N), and εk(N), k⩾3, by a least squares fitting of the HF results. It is found that the difference E−(ε0Z2+ ε1Z+ε2) is, in general, not governed by ε3Z−1 but by a higher order term involving εk(N) above. The value of k increase from k=3 for N=2 to k=8 for 60⩽N⩽86. Next, we study the N-dependence of the expansion coefficients εn(N), 0⩽n⩽2, and of the total energies E(Z,N) by means of an N−1/3 power series expansion. It is noted that the extension of these functions over the set of nonintegral values of N is not unique, and consequently their N−1/3 expansions are, in part, model-dependent. We use our numerical data to extract the model-independent part of y≡E/Z7/3q1/3, q≡N/Z, which may be expressed in terms of the universal expansion y = F00(q)+ F10(q)N−1/3+F20(q)N−2/3+⋅⋅⋅. The functions Fn0(q) are computed and displayed for n⩽2.
Correlated states in finite polyenes: Exact PPP results
Authors: Ducasse I. R. , Miller T. E. , Soos Z. G.
Published: February 2003

Valence bond (VB) diagrams provide a convenient basis for correlated states in systems with one valence state per site. The exact Pariser–Parr–Pople (PPP) solution, including all configuration interactions, is presented for octatetraene (OT), a cyanine dye, and various cyclic systems. We demonstrate rapid computer generation of symmetry adapted VB basis functions, of transformation coefficients due to electron transfer, and of iterative solutions of sparse matrices for any choice of spin-independent intersite interactions. The 2 1Ag state of OT is correctly placed for standard Ohno parameters. The π-electron bond orders and charges of correlated states are contrasted to Hückel and approximate PPP solutions. The length dependence of the strong 1 1Ag→1 1Bu transition is found for even chains and rings of up to N = 8 sites. Extrapolations as N−1 yield a limiting PPP gap around 3 eV, or about 1 eV above the absorption maximum in polyacetylene, the nominally infinite polyene. The role of correlations in narrow-band organic solids and the extension of VB methods to larger systems are discussed.
Thermal transpiration and mechanocaloric effect. IV. Flow of a polyatomic gas in a cylindrical tube
Authors: Loyalka S. K. , Storvick T. S. , Lo S. S.
Published: February 2003

The phenomenological coefficients for mass and energy flows due to axial pressure and to temperature gradients on long capillary tubes containing a polyatomic gas at all degrees of rarefaction are reported. The Hansen and Morse polyatomic gas model of the linearized Wang Chang and Uhlenbeck equation was used together with Maxwell’s diffuse scattering boundary conditions. The results are consistent with previous results obtained for flow between parallel plates. Experimental isothermal flow data are nearly quantitatively represented by the theory in the transition flow regime (Knudsen number ∼ 1). Experimental thermal transpiration effect ratios (Δp/p0)/(ΔT/T0) are also quantitatively represented for simple gases, argon, air, and carbon dioxide. Thermal transpiration measurements on sulfur dioxide correlate as the other gases but the transpiration effect ratio is not quantitatively given by the theory due to inadequacy of the Hansen–Morse model and the continuum theory for strongly polar gases.
An exact expression for the average value of the population governed by the stochastic Verhulst equation
Authors: Morita Akio
Published: February 2003

The stochastic Verhulst equation with a white noise term is treated in the region of the discrete eigenvalues, in order to calculate the average value of the population as a function of time, which is expressed analytically in a finite series with an arbitrary initial value of the population. Various graphs are produced from the result so obtained.
Molecular motions in lipid bilayers. III. Lateral and transverse diffusion in bilayers
Authors: Pace R. J. , Chan Sunney I.
Published: February 2003

Models are proposed for lateral self-diffusion of lipid species in bilayers and transmembrane diffusion of small permeants. The rate determining step for lateral diffusion is assumed to be separation of two neighboring head groups by one chain diameter, allowing in-plane displacement of the adjacent test molecule head group. Expressions for the activation energy and frequency factors of diffusion are derived from an earlier treatment of chain motion in polymers. The model predicts the magnitudes of the lateral diffusion coefficients for fluid phase one and two chains species, within a factor of ∼2, and suggests a time scale for lateral diffusion of ∼10−8 s. Transverse diffusion of small molecules is presumed to occur by hopping between kinks formed on three neighboring chains in a quasihexagonal lattice. The experimentally inferred diffusion coefficients for O2 in Lα phase lipids are consistent with this mechanism, assuming the single chain bond rotation rates deduced in part II from application of the crankshaft model to NMR relaxation data, or those derived independently from molecular dynamics simulations of polyethylene chains.
Low temperature magnetic susceptibility of the expanded metal compounds Li(NH3)4, Li(ND3)4, and Li(CH3NH2)4
Authors: Stacy Angelica M. , Johnson David C. , Sienko M. J.
Published: February 2003

The magnetic susceptibility has been measured by a static Faraday method over the range 4.2–300 K on the series of compounds made by dissolving lithium in NH3, ND3, and CH3NH2. Previously reported results on Li(NH3)4 are confirmed: temperature-independent paramagnetism above the melting point 89 K, somewhat smaller TIP in the solid phase I in the range 82–89 K, Curie–Weiss paramagnetism in the solid phase II from 82 K down to about 25 K, and antiferromagnetism below 25 K. Replacement of the protium by deuterium makes little change except that it completely wipes out the solid phase I behavior, i.e., Li(ND3)4 goes directly from TIP in the liquid to Curie–Weiss paramagnetism below the melting point of 89 K. The residual electronic susceptibility of Li(ND3)4 in the solid state at 89 K, after correction for core diamagnetism, is +56×10−6 emu per mol. The magnetic behavior of Li(CH3NH2)4 is quite different. The susceptibility decreases with decreasing temperature, shows a large drop at the melting point 155 K, and remains flat in the solid. The residual electronic susceptibility of Li(CH3NH2)4 in the solid state at 155 K after correction for core diamagnetism is −9.4×10−6 emu per mol. A model is proposed to account for the observed susceptibilities in which Li(NH3)4 goes from a good metal with a lithium conduction band to a bad metal as the temperature is lowered and Li(CH3NH2)4 tends from a spin-paired semiconducting state to one with isolated, localized electrons.
The analysis of the torsional structures of the CH3(D3) asymmetric stretching vibrations of gaseous toluene
Authors: Kanesaka Isao , Satozaki Yoshiko , Kawai Kiyoyasu
Published: February 2003

The torsional structures of the asymmetric stretchings of the methyl group of toluene are analyzed on the basis of the C2v symmetry. The torsional structures observed in the IR spectrum of gaseous toluene-h3 are explained by use of the twofold and sixfold potentials in the first excited state of the CH3 asymmetric stretchings. The fundamentals analyzed are 2996.3 cm−1 for the B2 mode and 2981.8 cm−1 for the B1 mode. The Raman bands observed here at 2989 and 3012 cm−1 are assigned to the fundamentals of the A1 and A2 modes, respectively. The torsional structures of the CD3 asymmetric stretchings are explained satisfactorily by use of the potential constants obtained in the CH3 system.
Direct spectroscopic evidence for a new, low-lying electronic triplet state in SO2 at 4.2 K
Authors: Snow Judith Bannon , Hovde David C. , Colson Steven D.
Published: February 2003

The phosphorescence emission and excitation spectra of crystalline SO2 at 4.2 K exhibit an anomalous energy gap of 83 cm−1 between their respective origins. The phosphorescence excitation, whose sharp origin occurs at 26 387 cm−1, involves a transition between the 1A1 ground state and the excited 3B1 state. However, our data indicate that the phosphorescence emission originates from a second triplet state, which lies 83 cm−1 lower in energy. A very weak absorption at 26 304 cm−1 is observed in the phosphorescence excitation spectrum, which exactly coincides with the observed phosphorescence emission origin. Site-selection experiments eliminate the possibility that the observed emission is due to defect sites in the crystal, and confirm the existence of the previously unreported low-lying triplet state. Phosphorescence lifetime data and the observed time-resolved emission spectra are consistent with this finding.
Adiabatic rapid passage within a Doppler-broadened line: A technique for level lifetime measurements
Authors: Comaskey B. , Shoemaker R. L.
Published: February 2003

Adiabatic rapid passage (ARP) experiments have been done in which the ARP frequency sweep covers only a fraction of a Doppler-broadened linewidth. The population inversion thus produced is monitored by suddenly shifting the laser back into resonance with the excited molecules and then observing the size of the optical nutation signal they produce. By employing a variable time delay before the sudden shift is made, the relaxation of the population difference and hence, the level lifetimes can be determined. The technique was demonstrated using a CO2 laser and transitions in N14H3 and N15H3, with the frequency sweep and shift being done by varying the molecular transition frequency via the Stark effect. The results, which are in good agreement with those found by delayed optical nutation measurements, are presented and their physical interpretation is discussed.
Reaction kinetics of a high pressure helium fast discharge afterglow
Authors: Stevefelt J. , Pouvesle J. M. , Bouchoule A.
Published: February 2003

This work reports the study of elementary processes which govern the relaxation of the afterglow of a 3 kA 7 ns duration discharge in helium at atmospheric pressure. Populations of the dominant energy storing species were monitored as functions of time through measurements of the emission asnd absorption of radiation from the plasma. The atomic helium spectral lines, radiated during the discharge pulse, were found to rapidly transform into molecular helium bands in the visible and far ultraviolet (600–1000 Å) regions during the afterglow. The observed features of this He2 radiation were consistent with a collisional-radiative scheme of electronic recombination of molecular He2+ ions, the concentration of which was inferred from Hβ line broadening. A significant fraction of the He+2 recombination events were found to result in helium atoms in the metastable 2 3S state, and the time dependence of this dissociation process correlated with that of He2 populations characterized by quantum number n = 4. The concentration of 2 3S atoms was comparable to the electron density, ranging from 1014 to 1015 cm−3. The concentration of molecular a 3Σ+u metastables was found to be one order of magnitude lower, suggesting a collisional coupling to the radiating A 1Σ+u state. From the data rate coefficients have been extracted for the processes of electron–ion recombination, ionizing collisions between atomic metastables, and superelastic electron–metastable collisions.
Polarization model study of isotope effects in the gas phase hydronium–hydroxide neutralization reaction
Authors: Stillinger Frank H. , Weber Thomas A.
Published: February 2003

Using the polarization model to represent all interactions present, classical dynamical trajectories have been numerically generated for reactive collisions between hydronium and hydroxide ions. The four isotopic variants have been examined that are possible with reactants H3O+, D3O+, OH−, and OD−; 100 trajectories were created for each case. The results show a marked tendency for energy released by the neutralization to be concentrated on that water molecule whose oxygen originated in the hydroxide anion. Significant isotope effects appear in the various product distributions, the primary determinant of which is the mass of the transferred hydrogenic particle. These effects appear to stem from differences between the respective lifetimes of the reaction complexes.
Conformational change of protein sodium dodecylsulfate complexes in solution: A study of dynamic light scattering
Authors: Tanner R. E. , Herpigny B. , Chen S.-H. , Rha C. K.
Published: February 2003

The binding of an ionic detergent [sodium dodecyl sulfate (SDS)] to two proteins [bovine serum albumin (BSA) and ovalbumin (OA)] has been studied by dynamic light scattering to determine the changes of the hydrodynamic size and shape of the proteins as a function of binding. This study has been correlated to a previous viscosity study (Ref. 1) in which the increase in the effective hydrodynamic radius of the detergent–protein complex as the gram ratio of detergent to protein increases has been interpreted as the unfolding of the protein as a direct result of the disruption of the intramolecular hydrophobic associations in the proteins by the SDS molecules. At the maximum binding, the BSA–SDS complex exhibits a hydrodynamic radius of 72 Å while the effective size of the native BSA is 27 Å. The OA–SDS complex has an effective hydrodynamic radius of 64 Å at the maximum binding while that of native OA is 22 Å. The dynamic light scattering experiments allow us to detect the presence of two different size species in the solution, the SDS micelles and the unfolded proteins combined with SDS. However, the shape of the protein–SDS complex at maximum binding cannot be definitely determined from the present measurements alone.
Optical spectra, energy levels, and crystal-field analysis of tripositive rare earth ions in Y2O3. I. Kramers ions in C2 sites
Authors: Chang N. C. , Gruber John B. , Leavitt Richard P. , Morrison Clyde A.
Published: February 2003

Optical absorption and fluorescence spectra of the Kramers ions Ce3+, Sm3+, Dy3+, and Yb3+ in the C2 sites of Y2O3 are reported. A crystal-field analysis of these data and previously reported data for Nd3+ and Er3+ is performed that is based on a Hamiltonian of C2 point-group symmetry, including J-mixing effects. A best-fit analysis is performed for the ions Nd3+, Sm3+, Dy3+, and Er3+; resulting rms deviations between calculated and experimental levels range from 5.1 to 7.9 cm−1. Results of this analysis are used to obtain a smoothed set of crystal-field parameters for the entire lanthanide series; these smoothed parameters are used to predict the energy levels of Ce3+, Yb3+, and Gd3+ in Y2O3. Predictions for Ce3+ and Yb3+ are compared with experimental data.
Lipid-mediated interactions between intrinsic molecules in bilayer membranes
Authors: Tessier-Lavigne M. , Boothroyd A. , Zuckermann M. J. , Pink D. A.
Published: February 2003

The effect of intrinsic molecules (impurities) dissolved in phospholipid bilayers on their lipid enviroment and the related lipid-mediated interactions between such molecules are examined in terms of a ten-state model for lipid chain configurations and interchain interactions. The numerical parameters used in the calculations were previously obtained by fitting to experimental data. Numerical results are presented for the case when the impurity is a cholesterol molecule, a protein, or a vacancy and when the lipid bilayer is either in the gel or fluid (liquids crystal) phase. The calculations indicate that proteins fluidize their lipid environment when the bilayer is in the gel phase. The resulting lipid-mediated interaction is shown to be short range and to have a different behavior below and above the main gel–fluid phase transition. The relation to previous theories is discussed in the final section.
Effect of molecular shape on the dielectric relaxation in the glassy phase of rigid polar molecules–c
i
s-decalin mixtures
Authors: Agarwal C. B. , Mansingh A.
Published: February 2003

The effect of molecular shape on the α and β relaxations in the glassy phase of rigid polar molecules bromobenzene (planar), n-butyl chloride (linear), and t-butyl chloride (nearly spherical) in cis-decalin mixtures has been studied by measuring the dielectric parameters in the frequency range 0.1 to 100 kHz and over the temperatures from 77 to 300 K. The α-relaxation peaks are pronounced in all three systems, but the β-relaxation peaks are different. β peaks are almost absent in n-butyl chloride, while in bromobenzene they are of lower magnitude than the α peaks in agreement with the earlier reported results. However, in t-butyl chloride, the β peaks appear to be of higher magnitude than the α peaks. The present studies support the model proposed by Johari that in the amorphous phase above Tg the dielectric behavior is governed by the cooperative rearrangement of molecules, while in the glassy phase below Tg the β-relaxation process arises from the hindered rotation of polar molecules encaged in the glassy matrix. The static dielectric constant has been estimated in the amorphous phase from the temperature variation of ε′ at a fixed frequency. The dipole moments have also been evaluated from the static dielectric constant in the amorphous phase as well as in the normal liquid.