bluuebunny/crossref_metadata_2025 huggingface dataset:
The adsorption and reaction of methanol on Pd(100). II. Thermal desorption and decomposition
Authors: Christmann K. , Demuth J. E.
Published: February 2003

The reaction of methanol with a clean Pd(100) surface has been studied between 77 and 300 K using a variety of techniques. High-resolution electron energy loss spectroscopy, thermal desorption spectroscopy, UV photoemission work function measurements, and low energy electron diffraction reveal a complex reaction pattern. At 77 K, photoemission, vibrational loss spectra, thermal desorption data, as well as the Δφ behavior indicate the initial formation of a methoxide species which has a maximum population around 1×1014/cm2. 80% of this methoxide species desorbs as methanol between 180 and 210 K via second-order kinetics with Edes∼11.5–12 kcal/mol. Above ∼200 K, we find that 20% of all the initially adsorbed species have not desorbed but have converted to two other more stable species. These species have CH3O stochiometries as determined from thermal desorption product ratios, but cannot be further identified. The first of these is more stable and predominantly forms (95% of total remaining species). It decomposes at ∼300 K to produce CO+H on the surface and has UPS level intensities significantly different than those observed from the methoxide. The other species occur in very small concentrations and only for higher coverages of the adsorbate. It appears in small amounts, ∼5% of these remaining species as inferred from its decomposition to gaseous CO+H2 at ∼530 K. A simple bond site model is proposed to account for the ability of the low temperature methoxide species to hydrogenate in the presence of chemisorbed hydrogen. These results are compared to those on Ni(100). The observation of this hydrogenatable form of methoxide on Pd as well as its large branching ratio into methanol provides a possible explanation for the selectivity of Pd in catalytically forming methanol from synthesis gas.
Elementary process in polymer chain motion
Authors: Mashimo Satoru , Nakamura Haruki , Chiba Akio
Published: February 2003

Two dielectric relaxation processes were found in dilute solutions of methyl methacrylate–methyl acrylate copolymers in benzene by time domain reflectometry. Two kinds of chain bonds along the same chain move independently of each other. This finding offers evidence that the elementary process in polymer chain motion is a simple bond rotation between isomeric transition states.
Fluorescence of Mg porphin in anthracene
Authors: Bohandy J. , Kim B. F.
Published: February 2003

The temperature dependence of the fluorescence of magnesium porphin in anthracene has been studied. Results indicate that the guest–host coupling in this system is an order of magnitude less than for magnesium porphin in triphenylene. (AIP)
Diffusion of interacting micelles: A general treatment at low salt concentrations
Authors: Briggs J. , Dorshow R. B. , Bunton C. A. , Nicoli D. F.
Published: February 2003

The micellar diffusivity, measured by quasielastic light scattering, is described by a simple phenomenological expression for a variety of surfactants over a range of surfactant concentrations and temperatures at low salt concentration where electrostatic interactions dominate. This universal expression contains the low order perturbations to the micellar diffusivity in the absence of interactions. The dominant correction scales with the ratio of surfactant to salt concentrations and results from repulsive electrostatic interactions, screened by the added salt ions. By fitting experimental data to this expression, we obtain the Stokes–Einstein micellar radius and a relative measure of the micellar ionization fraction.
The Raman spectra of gaseous formic acid -h2 and -d2
Authors: Bertie John E. , Michaelian Kirk H.
Published: February 2003

The Raman spectra of gaseous formic acid -h2 and -d2 at 21 °C and higher temperatures have been recorded from about 70 to 4000 cm−1. The isotope ratios of the frequencies of the intermonomer vibrations, which deform the hydrogen bonds, have allowed a convincing assignment of these vibrations. All but one of the nine low-frequency infrared and Raman bands of (HCOOH)2, and all seven of (DCOOD)2, have been assigned. It has been thought for 40 years that the symmetric hydrogen-bond stretching vibration is the cause of a strong Raman band of (HCOOH)2 near 230 cm−1, but the new evidence shows clearly that this is the one low-frequency fundamental that scatters too weakly to be detected. The spectra show bands at 1381 and 1307 cm−1 due to monomeric HCOOH which are assigned to ν4 and 2ν8, respectively, as the only feasible assignment. The Raman frequencies of the intramonomer modes of the dimer show that the intermonomer coupling is large for some modes and small for others. The Raman-active hydrogen-bonded O–H and O–D stretching modes, which are subject to a double-minimum potential, scatter very weakly; they could not be distinguished from possible overtone and combination bands in Fermi resonance with the C–H or C–D stretching modes.
Absolute rate parameters for infrared photochemistry: CF3I→CF3+I
Authors: Quack M. , Seyfang G.
Published: February 2003

IR-photolysis yields are reported for CF3I irradiated with the R14 line of the (001→0200) transition of a pulsed TEA-CO2 laser (at 1074.65 cm−1) with unstable resonator optics providing a smooth and well defined fluence profile in the far field. The reaction products (CF3+I) of the primary reaction are scavenged by reactions with added NO, Br2, or ClNO in order to reliably establish the primary yields. A data treatment valid for arbitrary, smooth spatial fluence profiles is proposed for the evaluation of true yields and rate coefficients kI(st). The influence of collisions with buffer gas molecules on the evaluation of kI(st) is investigated in experiments and by model calculations. A steady state rate coefficient for the unimolecular decomposition of CF3I under irradiation with constant intensity I is obtained to be k(st) = 10(6.2±0.3) (I/MW cm−2)s−1 valid for intensities near and above 100 MW cm−2. This is consistent with a low a priori estimate of rate coefficients from a simple theoretical model involving only easily measurable molecular properties. The physical significance of this absolute rate parameter is discussed.
The unimolecular reaction of isolated CF3CN: Energy disposal into CN product degrees of freedom
Authors: Reisler H. , Kong F. , Renlund A. M. , Wittig C.
Published: February 2003

Measurements of nascent CN rovibronic state distributions following the unimolecular reaction CF3CN→CF3+CN are reported. Excitation under collision-free conditions is provided by IR multiple photon excitation using the focused output from a CO2-TEA laser, and therefore reaction occurs from a range of energies E≠, centered at some value which is determined by the laser intensity. Nascent reaction products are detected by laser induced fluorescence (LIF), and, by exciting the Δv = 0,−1, and −2 sequences of the B 2Σ+←X 2Σ+ system, rotational distributions can be determined for v″ = 0,1, and 2 with no interference. Rotational excitation in v″ = 0–2 is the same for each v″ and can be described by a Boltzmann distribution with TR = 1200±100 K. Product translational energies are estimated by monitoring LIF intensities as a function of the delay between the onsets of the CO2 and dye laser pulses. Translational energies do not change over the range v″ = 0–4, and can be ascribed a temperature of 850±150 K. CN vibrational excitation is determined by simulating the LIF spectra, and can be described by TV = 2400±150 K based on v″ = 0–3, with v″ = 4 barely detectable. These results can be explained qualitatively using a statistically based model in which the CN vibration acts as a thermometer of parent excitation, and where parent nuclear motions, including vibrations as well as motions not influenced by potential energy, are in equilibrium at the transition state. The constancy of rotational and translational excitations with respect to v″ are seen to derive from the range of E≠ from which dissociation occurs.
A classical trajectory Monte Carlo model for the injection of electrons into gaseous argon
Authors: Kuntz P. J. , Schmidt W. F.
Published: February 2003

Using about 2.5×106 classical trajectories, we have performed a Monte Carlo calculation of the response of electrons injected from a gold cathode into gaseous argon. The fraction of electrons which reach the anode F2 was computed as a function of the applied electric field E, the density of the argon gas N, and the excess energy of the injected electrons ℰ. The dependence of F2 on E/N is in good overall agreement with experiment, and the dimensionless parameter E/(Nℰσ), where σ is the momentum transfer cross section, can be used to classify the results. A statistical model of the electron’s motion in the absence of the potential energy function predicts fairly accurately the average number of atom–electron collisions required for the fate of the electron to be decided and shows that the energy loss processes are the most important input to the theory. The results are discussed in terms of the potential energy function and are compared with earlier theoretical work.
On correlation in the first row transition metal atoms
Authors: Bauschlicher Charles W. , Walch Stephen P. , Partridge Harry
Published: February 2003

CI (SD) calculations using both SCF and MCSCF references have been performed for the first-row transition metal atoms. Basis sets as large as 84 STO’s have been used. At the highest level of calculation, good agreement with experiment is found. If relativistic effects are considered, the agreement is somewhat poorer. This aspect, as well as the trends and results, are discussed.
Molecular orbital theory of the hydrogen bond. XXIX. Water–thymine complexes
Authors: Del Bene Janet E.
Published: February 2003

A b initio SCF and SCF–CI calculations with the STO-3G basis set have been performed to investigate the structures and energies of water–thymine complexes and the intermolecular water–thymine surface in the thymine molecular plane. Three water–thymine dimers are distinguishable in the ground state. The most stable is an amide wobble dimer in the N1–H and O2 region which has a stabilization energy of approximately −9.5 kcal/mol. At 1.5 kcal/mol higher in energy is a second dimer in the O2–O4 region. In this dimer, the water molecule may move easily around the N3–H group between a wobble structure at N3–H and O2 and another at N3–H and O4. The third dimer has a stabilization energy of only −4 kcal/mol, and is an open dimer with water hydrogen bonded to O4 on the C5 side of the C4 = O group. Except for the more shallow minimum associated with this dimer, the water–thymine intermolecular surface is very similar to the water–uracil surface. Absorption of energy by the C4 = O group leads to the first excited n→π* state of thymine in which hydrogen bonds formed at O4 are broken and the water–thymine dimer at O4 dissociates. When the C2 = O group is the chromophore, hydrogen bonds at O2 are broken in the second n→π* state, but all water–thymine dimers remain bound.
Theoretical calculations for the barriers to internal rotation in the neopentyl and isobutyl radicals
Authors: Pacansky J. , Schubert W.
Published: February 2003

The barriers for internal rotation about the alpha CC bonds in the neopentyl and isobutyl radicals are computed using ab initio SCF calculations. The results indicate that although very small barriers are found for both radicals, the pyramidal distortion of the radical center dramatically changes with rotation about the alpha CC bonds.
Elasticity coefficients of nematic liquid crystals
Authors: Pardowitz Iancu , Hess Siegfried
Published: February 2003

A Ginsburg–Landau type ansatz for the Gibbs free energy is introduced which involves the alignment tensors of ranks 2 and 4 and their spatial derivatives. It is applicable to both the isotropic and nematic phases. The Frank elasticity coefficients of the nematic phase are expressed in terms of the equilibrium order parameters and phenomenological coefficients which are related to bare correlation length coefficients. The full anisotropy of the elasticity coefficients is obtained and their experimentally observed temperature dependence can be reproduced for all of the ten substances which have been analyzed.
Thermodynamics of solutions of hydrogen in palladium–manganese alloys. II. Pd to PdMn
Authors: Phutela R. C. , Kleppa O. J.
Published: February 2003

The thermodynamic properties of dilute solutions of hydrogen in alloys of palladium with up to 50 at. % manganese have been studied by a combined calorimetric-equilibrium method between 555 and 909 K. The results are compared with corresponding data for hydrogen in pure palladium and in the alloy Pd3Mn; the latter undergoes an order–disorder transformation at 750–800 K. In some cases data also were obtained for deuterium; a comparison between the properties of the two hydrogen isotopes provides approximate information on the vibrational frequency of hydrogen in the alloy. For the disordered solid solution of manganese in palladium we find little change in the vibrational frequency with alloy composition. Particular interest is attached to the ’’decomposition’’ of the excess Gibbs energy into its enthalpy and entropy ’’parts’’. Our results show that for alloys up to 25 at. % manganese increasing manganese content. The dependence of the enthalpy on temperature also becomes increasingly sharp and there is a corresponding large increase in the excess entropy of hydrogen. These changes are attributed to increased occupation by the hydrogen atoms at higher temperatures of energetically less favorable sites.
On hyperspherical mapping and harmonic expansions for potential energy surfaces
Authors: Aquilanti V. , Grossi G. , Laganà A.
Published: February 2003

It is noted that the potential energy function, because of rotational invariance can be expressed in terms of six-dimensional harmonics for J = 0 only. (AIP)
Drift tube investigation of the reactions H++D2→HD+D+ and  D++H2→HD+H+ in the relative energy range 0.04–0.3 eV
Authors: Villinger H. , Henchman M. J. , Lindinger W.
Published: February 2003

The reactions of H+ with D2 and of D+ with H2 have been studied in a helium-buffered drift experiment in the regime from near thermal up to 0.3 eV relative kinetic energies KEcm of the reactants. The rate coefficient of the first, endoergic reaction, increase with KEcm, up to 8.5×10−10 cm3 sec−1 at 0.3 eV, and extrapolates smoothly at near thermal energies into values obtained recently in a SIFT experiment (Ref. 3). The second reaction shows a rate coefficient k = 1.1×10−9 cm3 sec−1, independent of energy within the regime studied here.
Theoretical study of rotational fine structure in radiationless transitions
Authors: Henke W. E. , Selzle H. L. , Hays T. R. , Schlag E. W. , Lin S. H.
Published: February 2003

In the previous paper, it is shown that, at least for the case of formaldehyde, individually resolved rovibronic levels show a systematic dependence on J and K. Here a general theory is evolved which includes the effects of rotational energy gap, vibration–rotation coupling, and Coriolis effects on radiationless transitions. This general theory in contrast to existing pessimism, predicts a clear systematic variation of the radiationless rate for formaldehyde, in reasonable agreement with the experiment. This shows that these variations are the results of a general effect and not due to particular unsystematic resonances in this molecule. Hence, it is felt that this constitutes an interesting tiepoint between high-resolution jet measurements and a successful quantitative theory of a radiationless transition.
Nickel pair spectra in MgSiF6 ⋅ 6H2O
Authors: Rubins R. S.
Published: February 2003

Low temperature EPR measurements have been made on single crystals of nickel doped MgSiF6 ⋅ 6H2O in the frequency ranges 23–25 and 34–36 GHz. The isolated Ni2+ ion and its satellite spectra were studied both for the ΔM = 0 and ΔM = 1 transitions with the external magnetic field parallel to the pseudotrigonal axis. Certain of the satellite lines in both transitions were fitted to a pair Hamiltonian containing an isotropic exchange term JS1 ⋅ S2 and a dipolar term, the contribution of the latter being calculated from the crystallographic data. The values g = 2.24±0.01, D = −(2.082±0.002) cm−1, ‖E‖ = (0.2195±0.0010) cm−1, and J = +(0.074±0.001) cm−1 were determined for parameters of the pair Hamiltonian at 4.2 K, while the spin Hamiltonian parameters for the isolated ion at 4.2 K were g = 2.24±0.005, D = −(2.16±0.01) cm−1, and ‖E‖ = (0.198±0.002) cm−1. 77 K parameters are reported for both spectra, and there is a discussion of the possible origins of the remaining ΔM = 0 satellite lines.
Nuclear magnetic resonance spectroscopy in cholesteric liquid crystals. II. The blue phase
Authors: Shivaprakash N. C. , Prasad J. Shashidhara
Published: February 2003

We have employed the nuclear magnetic resonance technique to study the little understood ’’blue phase’’ of the cholesteric liquid crystals—cholesteryl benzoate, cholesteryl methyl carbonate, cholesteryl ethyl carbonate, and cholesteryl laurate. The NMR spectra in the ordinary cholesteric phase has both structure and width; these features are reduced in the blue phase, where they resemble isotropic phase spectra. The presence of a NMR line wider than in the isotropic state, however, indicates the presence of long range orientational order and provides data which throw some light on the possible structure of the blue phase.
14N nuclear magnetic resonance study of the rotation of acetonitrile in n-alkanes
Authors: Tiffon Bernard , Ancian Bernard
Published: February 2003

14N linewidths have been measured for acetonitrile in several n-alkane solutions at variable temperatures. Unlike previously reported results on adamantane in the same solvents, the correlation time for reorientation of the major axis of acetonitrile is linearly related to the solvent viscosity function η/T. The slope, i.e., Kivelson’s κ parameter, decreases as the size of the solvent increases. Moreover, unlike the activation for the reorientation of spherical adamantane which remains constant as the size of the solvent increases, that of acetonitrile increases.
Shape resonant features in the photoionization spectra of NO
Authors: Wallace Scott , Dill Dan , Dehmer J. L.
Published: February 2003

Calculations of core and valence level photoionization spectra of NO are presented and compared with available experimental data. A low-lying continuum shape resonance is identified in the σ photoionization channel, which is the analog of similar states found in other first-row diatomic molecules. Both partial cross sections and photoelectron angular distributions are discussed, and the effect of nuclear motion on these observables is treated.
The water dissociation reaction on clean and oxidized iron (110)
Authors: Dwyer D. J. , Kelemen S. R. , Kaldor A.
Published: February 2003

The interaction of H2O with the clean Fe(110) surface, Fe(110) surfaces with absorbed oxygen, and Fe(110) surfaces after bulk oxygen penetration were investigated using UPS. At 225 K, surface absorbed hydroxyl groups are present on all surfaces studied. On initially clean Fe(110) and surfaces with up to half monolayer of absorbed oxygen, heating the hydroxyl layer produced at 225 to 360 K causes hydrogen and water desorption and additional oxygen deposition relative to the starting surface. Beyond one-half monolayer of initial oxygen coverage, dehydroxylation proceeded exclusively via water desorption with the quantitative restoration of the initial surface composition. These results demonstrate that the (110) surface of iron is passive toward oxidation by water alone below 360 K, after the first monolayer.
Product state distributions for the C+(4P)+H2(D2) reaction from chemiluminescence spectra
Authors: Kusunoki I. , Ottinger Ch.
Published: February 2003

Optical emission resulting from low-energy (1–3 eVc.m.) impact of metastable C+(4P) ions on H2 and D2 molecules has been studied spectroscopically in the 2700–3900 Å range. The b 3Σ−–a 3Π transition of CH+ (CD+) was resolved into numerous bands. From a spectrum simulation by computer, rotational–vibrational population distributions of the excited triplet state were obtained. In contrast to previous related studies, the vibrational excitation decreases with increasing collision energy. One-parameter surprisal fits of the vibrational (and, to a lesser extent, the rotational) population distributions are found to be unsatisfactory. The reaction is discussed in terms of changes of molecular orbital occupancy, which suggest a direct interaction mechanism. This is consistent with the observed population distributions.
Chemical potential, ionization energies, and electron correlation in atoms
Authors: March N. H.
Published: February 2003

The total energy E(Z,N) of an atomic ion with nuclear charge Ze and N electrons is expanded in a Taylor series about the neutral atom energy E(Z,Z). By truncating the Taylor expansion, the chemical potential μ of the neutral atom is expressed in terms of the nth ionization potential In = E(Z,Z−n)−E(Z, Z−n+1), the most refined formula given being to fifth order, and involving up to and including I4. As an approximate test of the validity of this expression, one can then make use of the empirical relation that In∼nI1, in which case, with the electron affinity consistently taken as small, one obtains μ∼−I1/2, consistent with Mulliken’s electronegativity. The relation of the present work to that of March and Bader, which involves the potential energy of the electron correlations, is briefly discussed.
Localized atomic orbitals for atoms in molecules. III. Polyatomic molecules
Authors: Aufderheide Keith H. , Chung-Phillips Alice
Published: February 2003

Using a previously described method, localized atomic orbitals (LAOs) for atoms in molecules are constructed for the atoms C, N, O, and F in the polyatomic molecules CH4, NH3, OH2, CH3CH3, CH3NH2, CH3OH, CH3F, CH2CH2, C6H6, CO2, and CHCH. As in our prior studies, LAOs partition into sets of core, lone pair, and bonding orbitals. Ordinarily, both core and lone pair LAOs are doubly occupied and bonding is described principally as the interaction of bonding LAOs on adjacent, bonded atoms. Angles between valence LAOs on a given atom continue to vary in a manner reminiscent of trends common to simple valence shell electron pair repulsion theory. Of special interest are the systems CO2, C6H6, and CH3F: The peculiarities germane to these molecules are discussed fully in the text. Finally, certain properties (orbital populations, intra-atomic orbital angles, etc.) of groups (–CH3, –NH2, –OH, etc.) common to several systems studied show a remarkable transferability.
Intermolecular force and energy operators. III
Authors: Hirschfelder J. O. , Yang K. -H. , Johnson B. R.
Published: February 2003

Semirelativistic force and energy operators for the interaction of molecules (with moving nuclei) are derived for intermediate range separations. These operators are accurate through all of the (α4mc2 or 1/c2) fine-structural terms (but not the Lamb shift). The molecules interact by means of the internal electromagnetic fields which result from their charges, multipoles, and motions. Thus, the force on molecule a due to b is the generalized Lorentz force: QaE(i)(ra;b)+ (1/c)Ia×B(i)(ra;b), where Qa and Ia are the effective charge and current on a, while E(1)(ra;b) and B(i) (ra;b) are the internal fields of b at ra. It is shown that the interaction Hamiltonian Hab is minus the Lagrangian of the cross internal fields of a and b and can be expressed as Hab = QaQb[1/rab]− [1/c2]{Ia ⋅ Ib[1/rab]+ IaIb:[rabrab/rab3]}, where rab = ra−rb is the distance between the centers-of-mass. Both Qa and Ia are expressed in terms of the electric and magnetic multipole moments. To obtain full semirelavistic precision, the electric multipoles are expressed in terms of the Kracjik–Foldy coordinates. Thus, the electric dipole moment contains spin–orbit and purely relativistic terms. The usual nonrelativistic van der Waals energy operator corresponds to setting Ia = 0. The semirelativistic corrections are usually very small but still observable. For arrays of molecules, the interaction Hamiltonians are pairwise additive and long ranged. Therefore, the semirelativistic terms may be important in condensed media such as electrolytes or biologicals. This research is a byproduct of two previous papers on the interaction of molecules with electromagnetic fields.
Monte Carlo studies of polyelectrolyte solutions at low degrees of polymerization
Authors: Vlachy V. , Dolar D.
Published: February 2003

Monte Carlo method is applied for calculation of the osmotic coefficient for a cell model of polyelectrolyte solutions. The polyion is a rigid cylinder of finite length fixed along the axis of a cylindrical cell and the counterions are hard spheres distributed within the cell in a dielectric continuum. Only Coulombic interactions among all charges are considered. The osmotic coefficient is found to decrease with increasing degree of polymerization. The concentration dependence of the osmotic coefficient exhibits a minimum which is shifted toward lower concentrations with increasing degree of polymerization.
Effective polarizabilities of n-alkanes: Intramolecular interactions in solution and in the gas phase
Authors: Ladanyi Branka M. , Keyes Thomas
Published: February 2003

The interacting atom model (IAM) of molecular polarizabilities, used previously to describe depolarized light scattering from gas phase n-alkanes, is applied to the optical response of longer n-alkane chains. A skeletal model of n-alkanes is used. The effective polarizabilities, observed in dilute solution light scattering experiments, are modeled either by decreasing the atomic polarizabilities from their gas phase values or by the screening of intramolecular dipole induced dipole interactions. It is found that both of these effective polarizability IAM’s resemble more closely the bond additive effective polarizability than the ’bare’ IAM polarizability does. It is also found that the chain length dependence of effective mean squared anisotropic polarizabilities and depolarization ratios, predicted by the IAM and by the bond additive approximation (BAA), became more similar as the chain length increases. This suggests that the two models lead to the same asymptotic chain length dependence of molecular polarizabilities.
The three-particle distribution function of lattice gases
Authors: Johnson Elijah
Published: February 2003

A variational method for determining the three-particle distribution function of classical systems from the single-particle and pair distribution functions is used to treat one-dimensional nearest-neighbor interaction lattice gases. Apparently, no approximations were used to develop this method. Since the three-particle distribution function of finite range interaction lattice gases can be determined by using the transfer matrix method, the suitability of the variational method for determining three-particle distribution functions is examined. The results show that the variational method is successful.
Torsion and bending of nucleic acids studied by subnanosecond time-resolved fluorescence depolarization of intercalated dyes
Authors: Millar D. P. , Robbins R. J. , Zewail A. H.
Published: February 2003

Subnanosecond time-resolved fluorescence depolarization has been used to monitor the reorientation of ethidium bromide intercalated in native DNA, synthetic polynucleotide complexes, and in supercoiled plasmid DNA. The fluorescence polarization anisotropy was successfully analyzed with an elastic model of DNA dynamics, including both torsion and bending, which yielded an accurate value for the torsional rigidity of the different DNA samples. The dependence of the torsional rigidity on the base sequence, helical structure, and tertiary structure was experimentally observed. The magnitude of the polyelectrolyte contribution to the torsional rigidity of DNA was measured over a wide range of ionic strength, and compared with polyelectrolyte theories for the persistence length. We also observed a rapid initial reorientation of the intercalated ethidium which had a much smaller amplitude in RNA than in DNA.
Quantum beats in the fluorescence of jet-cooled diazabenzenes
Authors: Okajima S. , Saigusa H. , Lim E. C.
Published: February 2003

We report here the observation of intramolecular quantum beats in the fluorescence of jet-cooled pyrimidine and pyrazine, which represents only the second example of interference effects exhibited by closely-spaced singlet–triplet molecular eigenstates of polyatomic molecules. (AIP)
s-tetrazine: Coupling of the S to the S1 electronic state by two out-of-plane b3u vibrations
Authors: Innes K. K.
Published: February 2003

Large effects of vibronic coupling upon vibrational levels of the ground and first excited singlet states of s-tetraazabenzene-d0 and d2 are successfully modelled. The model is used also in discussing observed large radiationless transition probabilities and some anomalous infrared and visible transition probabilities.
Excitation of cesium atoms by electron impact
Authors: Ganas P. S.
Published: February 2003

Calculations are preented for the optical oscillator strengths, generalized oscillator strengths and integrated cross sections from threshold up to 5 keV for the electron impact excitation of cesium. The excitation studied is from the ground 65(2S) state to the four excited states 6P, 7P, 8P, and 9P (2P).
Longitudinal diffusion coefficients and test of the generalized Einstein relation for Br−–Ne, Br−–Ar, Br−–Kr, and Br−–Xe
Authors: Holleman F. B. , Pope W. M. , Eisele F. L. , Twist J. R. , Neeley G. W. , Thackston M. G. , Chelf R. D. , McDaniel E. W.
Published: February 2003

The generalized Einstein relation has been tested experimentally for Br− ions in Ne, Ar, Kr, and Xe. The Br− ion mobilities are used to calculate the diffusion coefficients of the Br− ions. (AIP)
Direct observation of collision induced transitions from N2(B 3Πg) to N2(B′ 3Σ−u)
Authors: Rotem A. , Nadler I. , Rosenwaks S.
Published: February 2003

Direct observation of collision induced transitions from N2(B 3Πg,v = 8,9) to N2(B′ 3Σ−u,v = 4,5), respectively, is reported. Following laser pumping of N2(A 3Σ+u,v = 5,6) to N2(B,v = 8,9), the wavelength and time-resolved fluorescence of both N2 (B) and N2 (B′) is monitored and the mechanism of the induced transitions is discussed.
Liquid crystals under pressure: X-ray investigation of smectic C phases
Authors: Guillon D. , Stamatoff J. , Cladis P. E.
Published: February 2003

Under pressure P, the layer spacing of a smectic C phase, which is followed immediately by a nematic phase at higher temperatures, is found to be constant. In contrast, the layer spacing of a chiral smectic C, denoted smectic C*, which transforms to a smectic A phase at higher temperatures, changes dramatically as the pressure increases from the smectic C*−smectic A transition pressure Pc. If ϑ is the tilt angle, we find ϑ∼(P−Pc)β with β∼0.5, a classical result. We postulate that these two smectic C phases are stabilized by different intermolecular forces.
A two-dimensional model for the infrared and microwave spectrum of diatomic molecules trapped in monatomic crystals
Authors: Mauricio F. , Velasco S. , Girardet C. , Galatry L.
Published: February 2003

A two-dimensional model is developed to approach the spectral properties of a diatomic polar molecule embedded in a monatomic crystal. This model introduces two rotational degrees of freedom in the limit of small amplitude oscillations. The first one describes the angular (planar) motion of the dipole moment of the molecule. The second one is connected to some collective motion of the nearest atom neighbors of this molecule (called the first shell). The remaining atoms of the crystal act as a thermal bath. This problem is treated first in a classical and then in a quantum version. The experimental data presently available (i.e., for CO molecules trapped in argon crystal) are compared to the theoretical results.
The influence of double bonds on the Raman active longitudinal acoustical model (LAM) in t
r
a
n
s-alkenes
Authors: Rabolt John F. , Twieg R. , Snyder C.
Published: February 2003

Raman measurements on a series of trans-alkenes having the double bond at various locations along the backbone have been obtained. Compared to the n-alkanes, a dramatic decrease in the intensity of LAM-1 has been observed, while that of LAM-3 and LAM-5 remains relatively unchanged. Normal coordinate calculations indicate that in the trans-alkenes there is a significant long-range coupling between longitudinal and transverse motion in LAM-1 due to the presence of the double bond which effectively diminishes its intensity. In LAM-3 and LAM-5 the longitudinal/transverse coupling is less, and much more localized about the double bond, preserving both the longitudinal character and intensity of these modes. Raman intensity variations in the –CH2– bending region have been utilized to study the lateral packing of methylene groups in the crystalline subcell, and the trans-alkenes have been found to crystallize in structures analogous to their polyalkenamer counterparts.
Infrared radio frequency double resonance spectroscopy of the 13CF4 ν3 fundamental using a tunable diode laser
Authors: Takami Michio
Published: February 2003

Pure rotational spectrum of 13CF4 was investigated in the ν3 vibrational state by infrared–radio-frequency double resonance. A frequency tunable semiconductor diode laser was used as an infrared pumping radiation source. About 100 radio-frequency transitions among the ν3 tetrahedral fine structure splittings were measured with the accuracy of a few tens of kHz. The observed spectrum showed that the ν3 state of 13CF4, in particular the R = J+1 highest Coriolis sublevel, was largely perturbed by 2ν4 which was about 15 cm−1 above ν3. Seven tensor constants were determined tentatively from the transitions measured in the R = J and J−1 sublevels.
Fluorescence studies of neptunium and plutonium hexafluoride vapors
Authors: Beitz James V. , Williams Clayton W. , Carnall W. T.
Published: February 2003

The first observation of fluorescence from gas phase, electronically excited, transuranic hexafluorides is reported. Fluorescence peaking at 1360 nm was observed from 237NpF6 gas excited at 1064 nm. The measured fluroescence lifetime was 3.53±0.01 ms, independent of NpF6 pressure. Fluourescence peaking at 2300 nm has been observed from 242PuF6 gas excited at 1064 nm. The measured fluorescence lifetime was 204±12 μs, independent of PuF6 pressure. In both cases the emitting state is assigned as a vibronic component of the first excited electronic state of the hexafluoride based on previously reported absorption spectra and energy level calculations. Fluorescence in the 1900 and 4800 nm region was observed from PuF6 gas excited at 532 nm. The lifetime of this fluorescence was 86±4. The emitting state giving rise to this shorter-lived fluorescence was not identified. Estimated fluorescence quantum yields are reported.
Mass spectrometric observation of the stable negative molecular ions HI− and H2I−
Authors: Spence David , Chupka W. A. , Stevens C. M.
Published: February 2003

Using a 100 in. radius double focusing mass spectrometer we have detected the negative molecular ions HI− and H2I− produced in a Pennig ionization discharge source. The ions are identified by an absolute precision mass measurement, and their flight time through our machine is ≊10−4 sec, indicating the ions are stable with respect to autodetachment. This observation determines the electron affinity of HI to be positive and ≳0.007 eV.
Electrical conduction of bis(phthalocyaninato)neodymium and gadolinium compressed disks
Authors: Yamana M. , Tsutsui M. , Ham J. S.
Published: February 2003

The unusual low resistivity of [Pc2Nd]−H+ reported by Kirin and Moskalev was re-examined in a hydrogen ambient. Our results reveal that the low resistivity is a consequence of oxygen adsorbed in the substance. The relationship of the low resistivity and low activation energy with the structure are discussed. (AIP)
High resolution proton NMR of dilute spins in solids
Authors: Eckman Richard
Published: February 2003

High resolution proton NMR spectrum in solids is demonstrated by isotopic dilution of protons in a deuterated solid combined with magic angle spinning. Isotropic chemical shift spectra are obtained with greater resolution then all other methods to date. (AIP)
State-to-state unimolecular reaction of t-butylhydroperoxide
Authors: Rizzo T. R. , Crim F. F.
Published: February 2003

Direct excitation of v = 6 of the OH stretching overtone vibration in tert-Butylhydroperoxide combined with time-resolved laser induced fluorescence determination of the OH fragments produces a direct measurement of the unimolecular decay rate an overtone spectrum of the OH stretching vibration as well as an excitation spectrum of the OH product fragments. This technique also holds the possibility of determining the effect of excitation site on the unimolecular decay process by exciting overtones at different locations in the molecule.
Dielectric and far infrared study of solutions in the glassy state from 100 Hz to 10 THz: Discovery and characterization of the universal γ process
Authors: Reid C. J. , Evans M. W.
Published: February 2003

The process of whole molecule libration, or torsional oscillation, of molecular dipoles evolves dynamically in supercooled solutions and glasses on an observable time scale extending from picoseconds to kiloseconds and longer. This can be measured using the dielectric loss spectrum of rigid dipolar solute molecules dissolved in glass-forming solvents such as decalin. The complete spectrum extends from below 100 Hz to THz frequencies, where the short time behavior can be detailed using the far infrared power absorption coefficient. This occurs universally and is characterized here for the first time as the γ process—the high frequency adjunct of the α and β processes discovered by Johari and co-workers. Results are presented over a broad frequency range (kHz to the far infrared, discontinuous) for the halogenated benzenes and for methylene chloride. In C6H5F/decalin there is a well defined β process, in C6H5Cl/decalin it is much less intense, and in C6H5Br/decalin it is either unresolved or vanishingly small. The multidecade loss profile of methylene chloride is reported in various glass-forming solvents. The loss shows three peaks (α, β, γ) in a total range of over 12 decades. Both the α and β processes in various glasses and supercooled solutions are associated with very high activation energies of about 100 kJ/mol. This feature appears to be specific to CH2Cl2. The high frequency (γ) part of the loss in the far infrared region may be studied in detail because of the relation between the dielectric loss and the optical power absortion coefficient. In some solvents there is a very large difference between the γ profile in the liquid at ambient temperature and the low temperature glass.
Chlorine NQR of single crystals SnCl2⋅xH2O (x = 1.5, 2): The evidence for the existence of hydrate with x = 1.5
Authors: Pirnat J. , Lužnik J. , Trontelj Z. , Kaučič V.
Published: February 2003

Single crystals of SnCl2⋅xH2O have been grown, with x = 1.5 and x = 2. The 35Cl NQR signals were observed in single crystals with x = 1.5. These crystals did not exhibit the order–disorder phase transition at 218 K which is observed in single crystals with x = 2. The angular dependence of proton NMR helped us to estimate the positions of water molecules in SnCl2⋅1.5H2O. The orientations of Sn–Cl bonds in SnCl2⋅1.5H2O were determined from the Zeeman perturbed 35Cl NQR spectra. There is good agreement between the conclusions obtained from the analysis of chlorine NQR data and x-ray diffraction data.
Concentration dependence of diffusion controlled processes among static traps
Authors: Muthukumar M.
Published: February 2003

An effective medium theory of competition effects in diffusion controlled reactions is presented. We consider a random array of static spherical traps which react with a density field of another reactant. Using the complete absorption boundary condition to describe the reaction at the surfaces of the traps, we calculate self-consistently the concentration dependent rate constant for the reaction and the diffusion constant of the density field in the steady state at all trap concentrations. The rate constant does not diverge at any physical packing fraction of the traps in contrast to the case of regular arrays of traps.
Ring closure dynamics in alkane chains
Authors: James C. , Evans G. T.
Published: February 2003

The relative motion of chain ends in a series of homogeneous polymethylene chains is investigated using Brownian dynamics. In particular, the end-to-end vector and several functionals of the end-to-end distance are probed. Analytic and numerical methods are used to determine the ring closure reaction rates in the framework of the Wilemski–Fixman theory of diffusion-controlled reactions. It is found that the N−3/2 dependence (where N is the number of bonds of the chain) of the electron exchange rate observed by Shimada and Szwarc is determined by the static properties of long Guassian chains. By contrast, the dynamic part of the rate, or autocorrelation function of the fluctuating sink functions, illustrates an N independence and shows a striking similarity to the isomerization or Kramers rate.
Neutron inelastic scattering from oriented and polycrystalline polyethylene: Observation and polarization properties of the optical phonons
Authors: Jobic H.
Published: February 2003

The neutron inelastic scattering spectra of oriented and polycrystalline polyethylene have been recorded with a beryllium filter spectrometer between 40 and 450 meV, at two different temperatures: 80 and 300 K. At low temperature we find a good agreement between the observed spectra and the calculated one-phonon distribution functions; the influence of the Debye–Waller factor is found negligible. At room temperature the multiphonon contributions are important; nevertheless, considerable structure in the frequency distributions is still visible contrary to existing calculations. The polarization of the vibrational modes is neatly evidenced, even for the CH stretching modes situated at 360 meV.
Extrapolation formulas for polymer solution properties
Authors: Muthukumar M. , Edwards S. F.
Published: February 2003

We have derived general expressions for the average size of a labeled chain and the osmotic pressure of the polymer solution as functions of polymer concentration and the strength of the excluded volume effect both varying from very low to very high. By employing a combination of path integral and field theoretic techniques to treat the correlations of the density fluctuations, we have renormalized the excluded volume interaction and the chain step length in terms of a screening length. The renormalized step length and the screening length are coupled by integral equations. In the limit of these lengths being independent of wave vectors, they are related by algebraic equations. In the region of criticality, we recover scaling laws and the known results for low and high polymer concentrations, respectively. We have also obtained the various numerical prefactors in terms of the free chain prefactor. Our development provides extrapolation formulas for the screening length, effective step length, free energy of the solution, and the average size of a chain, for intermediate concentrations and for intermediate strengths of excluded volume effect.
Quasilinearized form of the CPMET method for closed-shell molecules
Authors: Kvasnička Vladimír
Published: February 2003

A diagrammatic version of the quasilinearized (QL) form of the coupled-pair-many-electron-theory (CPMET) equations for closed-shell molecules is suggested. Using the Feynman–Goldstone diagrammatic technique, a special type of one- and two-particle effective interactions is introduced, and then the CPMET equations can be formally rewritten in a form very similar to the linear coupled-cluster approach (CCA) of Coester, Kümmel, and Čížek. The QL–CPMET facilitates the formulation of the coupled-electron-pair-approximation (CEPA) methods.
Hypervirial perturbative treatment of the hydrogen atom inside boxes with paraboloidal surfaces
Authors: Fernández Francisco M. , Castro Eduardo A.
Published: February 2003

The hypervirial perturbative method (HPM) is applied to study the behavior of the hydrogen atom within paraboloidal boxes with impenetrable walls. Numerical results obtained from an analytical closed formula are compared with those reported previously by Ley-Koo and Rubinstein from a numerical procedure.
Ultraviolet continuum spectroscopy of vibrationally excited ozone
Authors: Adler-Golden S. M. , Schweitzer E. L. , Steinfeld J. I.
Published: February 2003

A model is presented for the Hartley ultraviolet spectrum of vibrationally excited ozone based upon infrared–ultraviolet double resonance spectroscopy and previous temperature-dependent absorption measurements. The double-resonance transient arises from a 3500 cm−1 red shift of the absorption spectrum of ozone excited into the stretching vibrational states, with respect to the ground vibrational state. The double-resonance method is used to study relaxation kinetics of vibrationally excited ozone and to measure infrared energy deposition resulting from CO2 laser pumping. The energy deposition is found to scale linearly with sample pressure and with infrared fluence, except for excitation on-resonance, which is strongly saturated. The UV spectral model is also used to calculate the wavelength and temperature dependence of the O(1D) photodissociation quantum yield, which is an important component of stratospheric photochemistry.
Polarization spectroscopy as a probe of Raman optical activity
Authors: Oudar Jean-Louis , Minot Christophe , Garetz Bruce A.
Published: February 2003

Polarization-sensitive coherent antistokes Raman spectroscopy and the Raman-induced Kerr effect are considered as possible techniques for investigating Raman optical activity. Generalized nonlinear optical susceptibilities including both magnetic dipole and electric quadrupole interactions are derived semiclassically. These terms can be distinguished from electric dipole terms through their particular symmetry, and several polarization configurations are discussed which seem appropriate to the study of Raman optical activity. These might constitute a convenient alternative to the conventional technique of circular differential Raman scattering for measuring this property.
The rotational spectrum and molecular properties of a hydrogen-bonded complex formed between hydrogen cyanide and hydrogen chloride
Authors: Legon A. C. , Campbell E. J. , Flygare W. H.
Published: February 2003

The rotational spectra of four isotopic species of a weak complex formed between HCN and HCl have been detected and analyzed by using the technique of Fourier-transform microwave spectroscopy conducted in a Fabry–Perot cavity with a pulsed nozzle molecular source. The rotational constants B̃0, centrifugal distortion constants DJ, and nuclear quadrupole coupling constants χaa that result are as follows:

Interpretation of the spectroscopic constants leads to the conclusion that the atoms in the complex are colinear in the order HCN⋅⋅⋅HCl, with the weak binding through a hydrogen bond to the N atom HCN. Some quantitative details of the molecular geometry and intermolecular potential function have also been determined for the complex and are compared with those similarly obtained for other members of the series HCN⋅⋅⋅HX and the series B⋅⋅⋅HCl, where B is one of several different proton acceptors.