bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoionization states of SO2
Authors: Wu C. Y. R. , Ng C. Y.
Published: February 2003

We report the assignments of five autoionizing states of SO2 in the 960–810 Å region. The experimental data used in the present analysis have been previously obtained by a molecular beam photoionization mass spectrometry. The observed vibrational progressions are tentatively assigned to the following Rydberg transitions: 4b2→3s, 4b2→3d, 7a1→3p, 7a1→3d, and 2b1→3p. The window resonance series previously reported [C.Y.R. Wu and D. L. Judge, J. Chem. Phys. 74, 3804 (1981)] in a photoabsorption measurement is confirmed in the photoionization efficiency curves of SO+2 and SO+.
Quenching of NO(D 2Σ+, E 2Σ+) formed by UV photodissociation of NOCl
Authors: Wilson M. W. , Rothschild M. , Muller D. F. , Rhodes C. K.
Published: February 2003

The photodissociation of NOCl at 193 nm has resulted in vibrationally excited NO which was subsequently excited to the D(v = 5) and E(v = 0) states. The resulting fluorescence at 160–180 nm has been analyzed in terms of a kinetic model. Saturation of the photodissociation was observed at laser intensities above 2 MW/cm2. The quenching rate constants of NO* by Ne, Ar, Kr, and Xe were determined to be kNe = (6.4±1.6)×10−11 cm3 s−1, kAr = (1.7±0.4)×10−10 cm3 s−1, kKr = (6.6±1.7)×10−10 cm3 s−1, and kXe = (1.0±0.2)×10−9 cm3 s−1. The quenching by NO and Cl was explained in terms of charge transfer mechanism and the corresponding rate constants were found to be: kNO = (2.7±0.6)×10−9 cm3 s−1 and kCl = (2.1±0.5)×10−9 cm3 s−1.
The use of van der Waals molecules to detect a mode selective nonradiative process in chromyl chloride
Authors: Blazy Joseph A. , Levy Donald H.
Published: February 2003

A free jet expansion was used to form van der Waals complexes of helium and chromyl chloride of the type CrO2Cl2–He(x), x = 1,2,... The vibronic bands of both the complex and the corresponding parent molecule have been excited using a tunable cw dye laser, and the fluorescence excitation spectra were recorded. The lifetimes of the complexes were measured and were found to be in the range 11–121 ps. The complexes undergo vibrational predissociation after excitation. For the van der Waals molecules we have evidence of competition between the vibrational predissociation and a nonradiative process in the CrO2Cl2 portion of the complex. The fluorescence intensity of a vibronic band of the complex relative to the corresponding band of the uncomplexed parent molecule shows that there is a mode selective nonradiative process in the 1B1 excited state of CrO2Cl2. The cross section for this nonradiative process increases with increasing excitation of the ν4 mode, the CrCl2 bend. A kinetic scheme is presented to interpret these observations, and the utility of this effect to measure vibrational predissociation rates in polyatomic molecule–rare gas van der Waals complexes is discussed.
The use of holography to investigate complex photochemical reactions
Authors: Burland D. M. , Bräuchle Chr.
Published: February 2003

The growth of a hologram can be used to follow the temporal course of a photochemical reaction. In this paper the application of this technique to reactions involving more than one photochemical step is considered. A theoretical framework is developed by which the hologram growth curves can be predicted provided one knows the appropriate kinetic equations. Three different kinetic schemes are explicitly considered: a one-step reaction, two parallel reactions, and a two-step consecutive reaction scheme. The calculations are compared with experimental results obtained for the reaction of benzophenone in polymethylmethacrylate.
Evaluation of the equilibrium constant for H2O+D2O = 2HDO by direct summation over rotational-vibrational states
Authors: Chen C. L. , Bopp P. , Wolfsberg M.
Published: February 2003

The equilibrium constant K for the gas phase self−exchange reaction H2O + D2O = 2HDO has been theoretically evaluated.(AIP)
Estimating the torsional rigidity of DNA from supercoiling data
Authors: Strogatz Steven
Published: February 2003

The torsional rigidity of DNA is estimated from measurements of the free energy of supercoiling. An earlier estimate was incompatible with values inferred from studies of DNA torsional Brownian motion; the discrepancy is resolved here by a reconsideration of DNA topology. (AIP)
Optical spectra of Pa4+ diluted in ThCl4 single crystals
Authors: Krupa J. C. , Hussonois M. , Genet M. , Guillaumont R.
Published: February 2003

Absorption and emission spectra of Pa4+ in ThCl4 were recorded at different temperatures varying from 4.2 to 300 K. The seven-crystal field states were measured experimentally and fitted to the spin-orbit and crystal field parameters resulting from D2d symmetry. The obtained parameter values (in cm−1) are F0 = 3658, ξ = 1525, B20 = −1373, B40 = 1725, B44 = −2487, B60 = −2290, and B64 = −53. Emission occuring at 4915 and 4078 cm−1 was used to determine the 2F5/2 low lying levels.
Quasiclassical trajectory treatment of the O++N2→NO++N reaction
Authors: Hopper Darrel G.
Published: February 2003

Quasiclassical trajectory calculations have been carried out as part of an overall effort to understand and predict the O+/N2 reactions. In the present work, a surrogate hypersurface for the low energy adiabatic pathway governing the reaction of ground state reactants is developed. It was found that the presence of a barrier, per se, in the reaction coordinate, produces a qualitatively correct treatment of the experimentally known features. These calculations not only properly reproduce the threshold and peaking behavior of the total cross sections, and the rate enhancement effects of reagent vibrational excitation, they also predict the behavior of the differential and doubly-differential cross sections. From these comparisons, it is presently established that the key features of the N2O+(1 4A″) potential energy surface, in terms of the calculated dynamics properties, is an effective barrier to O+(4S)+N2(X 1Σg+, v⩾0) ranging from 0.2 to 0.5 eV. The use of such a barrier, 0.25 eV, is found to yield nearly quantitative agreement with experiment. This effective barrier results from a combination of potential and dynamics effects and is shown to be composed of a barrier in the potential energy surface of about 0.2–0.3 eV and a ’’steric’’ factor which varies from approximately 0.0–0.2 eV. The vibrational enhancement effect, while significant, is found to be much less important than the translational enhancement effect. That is, near threshold, a given increment of energy added to the reagents increases the reactivity four times as much if it is placed in the translational mode than if it is placed in the vibrational mode.
Rotationally resolved photoelectron spectroscopy of n-H2, p-H2, HD, and D2
Authors: Pollard J. E. , Trevor D. J. , Reutt J. E. , Lee Y. T. , Shirley D. A.
Published: February 2003

The 584 Å photoelectron spectra of n-H2, p-H2, HD, and D2 were recorded at a resolution of 11 meV FWHM using a supersonic molecular beam source. Spectra were taken at several stagnation temperatures and pressures in order to vary the rotational population distribution in the beam with a corresponding variation in the relative intensities of the rotational transitions. Many of the Q-branch components were resolved for the first time. ΔG(v+1/2) and Bv values were measured for all observed vibrational states of H+2, HD+, and D+2 and were used to determined the ionic vibrational and rotational constants: ωe, ωexe, ωeye, ωeze, Be, and αe. The results represent a substantial improvement over previous experimental determinations and were found to be consistent with the available theoretical rotation-vibration energy levels. The measurement of the intensity distribution of photoelectrons as a function of vibrational states yielded photoionization cross sections which were in good agreement with the theoretical values calculated by O′Niel and Reinhardt.
Transport properties of monatomic carbon
Authors: Biolsi Louis , Rainwater James C. , Holland Paul M.
Published: February 2003

Transport properties of monatomic gases depend on the two-body atom–atom interaction potential. When two ground state carbon atoms interact, they can follow any of 18 potential energy curves corresponding to the C2 molecule. Accurate representations of these curves have been obtained for each of the 18 states and transport collision integrals have been calculated for each state. Those states with an attractive minimum in the potential have been represented by the Hulburt–Hirschfelder potential and the purely repulsive states have been represented by the exponential repulsive potential. The collision integrals are compared with results obtained in previous studies. The effects of the details of the potential on the resulting transport collision integrals are discussed.
Precondensation phenomena in acoustic measurements
Authors: Mehl James B. , Moldover Michael R.
Published: February 2003

Theoretical and experimental studies of the behavior of acoustic resonators whose walls are coated with a film of condensed vapor are reported. As a sound wave is reflected from the resonator walls, further condensation and evaporation will alter the thickness of the condensed film during the course of an acoustic cycle. We have modeled this effect for smooth walls and have calculated the associated specific acoustic admittance, which we refer to as βfilm. Over a wide range of conditions, the magnitude of βfilm is governed by the derivative of the film thickness with respect to pressure. Thus, for typical adsorption isotherms, the magnitude of βfilm becomes large at very low pressures and at pressures just below the saturated vapor pressure. It seems possible that acoustic techiques could be used to study adsorption in both pressure regimes. If the resonator walls are rough (e.g., machined metal), a significant quantity of vapor will condense in the recesses of the walls at pressures well below the saturated vapor pressure. The specific acoustic admittance associated with such thick films is often more than ten times larger than the specific acoustic admittance predicted by the usual Kirchoff–Helmholtz formula. If this excess wall admittance is not recognized, the resonance frequencies will appear to imply an anomalous decrease in the speed of sound (c) as the saturated vapor pressure is approached. Such a decrease in the apparent value of c of nitrogen has been reported by Younglove and McCarthy, who observed decreases as large as 1%. We demonstrate that the same inhomogeneous precondensation phenomena can be easily be seen in propane at ambient temperature. These precondensation phenomena will influence measurements of acoustic virials at low temperatures, as well as the behavior of certain acoustic thermometers. Measurements of acoustic dissipative processes are also strongly affected. We have observed an increase of reflection losses by more than a factor of 200 as the pressure of propane on an aluminum surface was increased from 90% to 99.5% of the saturated vapor pressure.
Some aspects of cluster diffusion on surfaces
Authors: Titulaer U. M. , Deutch J. M.
Published: February 2003

We consider models, based on a master equation, for the motion of bound clusters of adatoms, over a crystalline surface or along one-dimensional channels on such a surface. In particular, we outline efficient methods for determining the diffusion tensor and other quantities that characterize the motion of such clusters for long times.
Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique
Authors: Vernon M. F. , Krajnovich D. J. , Kwok H. S. , Lisy J. M. , Shen Y. R. , Lee Y. T.
Published: February 2003

Water clusters formed in a molecular beam are predissociated by tunable, pulsed, infrared radiation in the frequency range 2900–3750 cm−1. Absorption spectra of the clusters are obtained by detecting the recoiling fragments off-axis from the molecular beam as a function of laser frequency using a rotatable mass spectrometer. By carefully adjusting the expansion conditions of the molecular beam and monitoring the largest cluster observable, excessive contamination by clusters larger than the specific one of interest is avoided. It is found that the spectra of clusters containing three or more water molecules absorb over the same frequency range as the liquid. Dynamical information on the predissociation process is obtained from the measured angular and velocity distributions of the fragments. An upper limit to the excited vibrational state lifetime of ∼1 μs is observed for the results reported here. The most probable dissociation process concentrates the available excess energy into the internal motions of the fragment molecules. From adiabatic dissociation trajectories and Monte Carlo simulations it is seen that the strong coupling present in the water polymers causes extensive energy sharing among the intermolecular motions in the polymer before dissociation, consistent with the experimentally measured energy distributions. Comparison between current intermolecular potentials describing liquid water and the observed frequencies is made in the normal mode approximation. The inability of any potential to predict the gross spectral features (the number of bands and their observed frequency shift from the gas phase monomer) suggests that substantial improvement in the potential energy functions is possible, but that more accurate methods of solving the vibrational wave equation are necessary before a proper explanation of the spectral fine structure is possible.
Structures of the paraelectric and ferroelectric phases of NaD3(SeO3)2 by neutron diffraction: A vertex model for the ordered ferroelectric state
Authors: McMullan R. K. , Thomas R. , Nagle J. F.
Published: February 2003

Neutron diffraction studies have been performed on layered sodium trideuterium selenite Na(H0.06D0.94)3 (SeO3)2 in both the paraelectric and the ferroelectric phases. The crystal data are a = 10.365(2), b = 4.850(1), c = 5.792(1) Å, β = 91.16(3)°, Z = 2, space group P21/n for the paraelectric phase at 298 K; and a = 10.314(3), b = 9.663(2), c = 5.768(2) Å, β = 91.23(3), Z = 4, space group Pn for the ferroelectric phase at 173 K. An external field of 15 KV/cm was applied to the crystal at the transition temperature before the low temperature measurements. The atomic parameters of the two structures were determined by full-matrix least-squares methods. The final agreement indices are R(F2) = 0.038, Rw(F2) = 0.049 on 748 reflections for the paraelectric structure and R(F2) = 0.035, Rw(F2) = 0.044 on 1636 reflections for the ferroelectric structure. The results resolve a controversy concerning the ordered hydrogenic state in the ferroelectric phase. Local charge neutrality is found for each molecular unit NaD3(SeO3)2 rather than previously proposed charged local configurations NaD4(SeO3)21+ and NaD2(SeO3)21−. However, the ground state is not as simple as might be expected. To help in understanding the ordering we develop a phenomenological vertex or site model which also includes interactions between pairs of hydrogen bonds. This model does indeed yield the observed ground state in each layer upon suitable choice of parameters, although the mechanism for three-dimensional ordering is still unclear. Various bond lengths, bond angles, and their perturbation upon hydrogenic ordering are discussed.
The breakdown of the one-electron picture in the ligand XPES of Mo2 (O2CH)4, Mo2 (O2CCH3)4, and Cr2 (O2CCH3)4
Authors: Atha P. M. , Hillier I. H. , MacDowell A. A. , Guest M. F.
Published: February 2003

The C1s and O1s photoelectron spectra of gaseous Mo2(O2CH)4, Mo2(O2CCH3)4, and Cr2(O2CCH3)4 are reported. An intense satellite peak is associated with C1s ionization in Mo2(O2CH)4 and Mo2(O2CCH3)4, but is absent in the other spectra. These observations are interpreted using ab initio MO calculations, together with initial and final state correlation effects. The intense satellite is associated with the transition δ→Lpπ, where δ is a metal–metal bonding orbital and Lpπ is an orbital of the same symmetry localized on the ligand from which ionization has occurred.
Laser photofragmentation dynamics of an acrolein supersonic molecular beam at 193 nm
Authors: Shinohara Hisanori , Nishi Nobuyuki
Published: February 2003

A pulsed supersonic molecular beam of acrolein has been photodissociated by an ArF excimer laser light at 193 nm in an ultrahigh vacuum chamber. Time-of-flight (TOF) spectra show that the molecule dissociates to give C2H3 and CHO radicals upon one-photon excitation to a (π, π*) state. The average translational energy of the fragments is 10.1 kcal/mol. Observed isotropic angular distribution implies that acrolein molecule lives a much longer period of time than the rotation period, suggesting that the photodissociation of acrolein at 193 nm is predissociative. The TOF spectra also suggest that the molecule undergoes extensive photofragmentation into smaller fragments (e.g., C2H2) via two-photon excitation of 193 nm laser light. Moreover, emission resulting from the photofragmentation of acrolein has been investigated by incorporating a pulsed supersonic free jet as a sample source. Strong emission from the CH(A 2Δ, B 2Σ−, C 2Σ+→X 2Π) systems and weak emission from the C2 (d 3Πg→a 3Πu) Swan system have been observed. From the laser fluence dependence on the emission intensity, the generation of the CH(A 2Δ) and C2(d 3Πg) states require the absorption of two and three photons, respectively. The molecules are considered to be pumped into superexcited states from which they rapidly undergo fragmentation.
Anharmonic Raman intensities of overtones, combination and difference bands
Authors: Montero S.
Published: February 2003

The influence of anharmonicity up to the cubic force constants on the Raman tensors of binary overtone, combination, and difference bands is investigated. Formulas for the absolute differential Raman scattering cross sections of these bands are reported for all possible cases of degeneracy as a function of the invariants of the anharmonic Raman tensors. The evaluation of anharmonic Raman tensors as a function of Hoy, Mills, and Strey’s ℒ tensor, cubic force constants, and bond polarizability parameters is illustrated for the tetrahedral AB4 molecule.
Theory of electron transfer reactions. II. Exact quantum number scaling relationship for semiclassical time-dependent dynamics
Authors: DePristo Andrew E. , Sears Stephen B.
Published: February 2003

We consider the quantum number scaling properties of the exact solutions to the dynamical equations describing electron transfer between two heavy particles of arbitrary size. The only assumptions are that the Born–Oppenheimer approximation holds for the separated reactants and products, and that the relative translational motion of the heavy structured particles is classical. We derive an exact scaling relationship between the various rovibrational state transition amplitudes in the reaction. As an example of the utility of this result, we investigate the implications of the Franck–Condon approximation on the quantum number variation of electron transfer cross sections, without recourse to dynamical calculations.
Macroscopic anisotropy in plastic neopentane by Raman light scattering
Authors: Depondt Ph. , Debeau M.
Published: February 2003

Polarized (VV) and depolarized (VH) Raman scattering have been performed on the 922 cm−1 internal line of neopentane both in the liquid phase and a multidomain single crystal of the plastic phase between 250 and 210 K. Small but systematic differences between the VV and VH spectra of the plastic phase, which are absent in the liquid phase, show anisotropy effects unrevealed up to now in this phase. The origin of the effect is discussed.
Infrared–optical double resonance spectroscopy of the NH2 radical
Authors: Amano Takayoshi , Kawaguchi Kentarou , Kakimoto Masao , Saito Shuji , Hirota Eizi
Published: February 2003

Vibration-rotation transitions of NH2 in the Ã 2A1 state were observed with sub-Doppler resolution, by using a Rh 6G dye laser and a CO2/N2O laser combined with the laser magnetic resonance technique. When the dye laser pumped the Ã 2A1 (0,9,0) 220←X̃ 2B1(0,0,0) 110 transition, 39 MJ components of (0,10,0) 211←(0,9,0) 220, and 5 MJ components of (0,10,0) 111←(0,9,0) 220 in Ã were observed by sweeping the magnetic field. Four additional lines which corresponded to changes in fluorescence intensity opposite in sign to those for the transitions mentioned above, were also observed and assigned to transitions from Ã 2A1(0,9,0) to a highly excited vibrational state of X̃ (“u’’ level). The rotational quantum numbers N and J and the spin splitting of the u level were determined as well as the interaction term between the u and Ã (0,10,0) 211 states. The u level is tentatively assigned to a rotational level in X̃(2,8,0), however, the observed spin splitting does not agree with that for X̃(0,8,0) calculated by Jungen, Hallin, and Merer.
Structure of sodium cyanide by molecular beam electric resonance spectroscopy
Authors: van Vaals J. J. , Meerts W. Leo , Dymanus A.
Published: February 2003

The results of the first successful observations of the microwave spectrum of sodium cyanide are presented. Twenty rotational transitions between 9.5 and 40 GHz were used to determine the rotational constants and the effective structure of the free molecule in the ground vibrational state. The structure was found to be T-shaped and the results (in Å) are: rCN=1.169(6), rNaC=2.366(29), and rNaN=2.243(27). (AIP)
Relaxation time study of motion and phase transitions in hydrazine dinitrate N2H6(NO3)2
Authors: Harrell J. W. , Horgen Douglas A.
Published: February 2003

Proton T1 and T1ρ measurements have been made in polycrystalline N2H6(NO3)2 from 360 to 106 K. The measurements have shown the existence of at least two and possibly four different phases. Phase I, the high-temperature phase, has been characterized in terms of the identical reorientation of both –NH+3 groups and by a large-scale motion of the N2H6++ ion. In phase II, which could only be seen in combination with phase I, the –NH+3 groups reorient more rapidly than in phase I. Two additional phases may exist at the lowest temperatures; however, the motions characterizing these phases could not be determined.
Energy transfer as a continuous time random walk
Authors: Blumen A. , Zumofen G.
Published: February 2003

In this work we study the energy migration on regular lattices in the framework of a continuous time random walk (CTRW). This extends our former investigations [A. Blumen and G. Zumofen, J. Chem. Phys. 75, 892 (1981); G. Zumofen and A. Blumen, J. Chem. Phys. 76, 3713 (1982)] to the continuous time domain. Here the ingredient is the stepping time distribution function ψ(t). We derive this function from an exact formalism, for microscopic transfer rates due to multipolar and to exchange interactions. Furthermore, we study the decay law due to trapping by randomly distributed substitutional traps, starting from an exact expression. We analyze the interplay between the temporal and the pure random-walk stochastic aspects, and their respective influence on the decay law. The analysis is rendered transparent by using the cumulants of the random variables, which also offers a means to derive handy approximate expressions for the decay laws. We exemplify the findings for a square and a simple cubic lattice for CTRW mediated by dipolar interactions, as compared to random walks with constant stepping frequency.
Theoretical and experimental studies of the valence photoelectron spectrum of C2H2
Authors: Müller J. , Arneberg R. , Ågren H. , Manne R. , Malmquist P.-Å. , Svensson S. , Gelius U.
Published: February 2003

A high resolution ESCA spectrum of C2H2 was recorded using monochromatized AlKα excitation and was analyzed by means of configuration interaction and multiple configuration SCF wave functions. The role of different schemes for electron-configurational selection in the initial and final states on transition moments and energies was investigated. The spectrum shows a prominent satellite structure in the inner valence region, which is analyzed and discussed in terms of electron correlation, dissociative photoionization, interference, and vibronic coupling effects.
Analysis of the far infrared H2–He spectrum
Authors: Cohen E. Richard , Frommhold Lothar , Birnbaum George
Published: February 2003

Previous measurements of the far infrared absorption due to H2–He collisions at the temperatures of 77, 195, and 292 K are analyzed. The spectra are fitted by a semiempirical line shape representing the isotropic induced overlap component and combined anisotropic quadrupolar and overlap components. The experimental spectral moments are evaluated and compared with theory for several induced-dipole and potential models. From the isotropic contribution, the range and strength of the induced dipole is evaluated and compared with the results of ab initio calculations. Fitting parameters are obtained with physically plausible temperature dependences which allow simple and accurate representation of the spectra and of their moments at temperatures different from those of the measurements.
Vibrational relaxation of the bending modes of D2O, D2S, and H2Se gas mixtures
Authors: Miljanić Šćepan S. , Specht Eliot , Moore C. Bradley
Published: February 2003

The method of laser-excited vibrational fluorescence has been used to measure vibrational relaxation of the bending modes ν2 of H2Se and D2S in gas mixtures at 295 K. For H2Se relaxed by H2Se, H2, D2, He, and N2 rates of 30±2, 11±1, 3.4±0.2, 1.5±0.1, and 1.1±0.1 (all×10−13 cm3 molecule−1 s−1 were found). For D2S relaxed by D2S and by N2, rates are 5.5±0.6 and (0.12–0.37) (both ×10−13 cm2 molecule−1 s−1). Fluorescence from HDO (ν2) following excitation of D2O (ν2) gave a rate for vibration–vibration transfer of a bending quantum from D2O to HDO of about (1.4±0.6)×10−11 cm3 molecule−1 s−1. D2O (ν2) is relaxed to translation and rotation at approximately the same rate by HDO as by D2O.
Theory of resonances in three-dimensional chemical reactions. I. Feshbach analysis and computational techniques
Authors: Shoemaker Curtis L. , Wyatt Robert E.
Published: February 2003

An analysis of internal excitation resonances in three-dimensional, symmetric atom/diatom chemical reactions is presented. The description is based on the Feshbach projection operator theory and is formulated in terms of ‘‘natural collision coordinates’’ (NCC) and the NCC Hamiltonian appropriate for near-linear intermediates. The resonance theory is reviewed and developed using a computationally oriented matrix notation. Expressions are given for the level operator matrix, formation and decay amplitudes, and S-matrix elements. Computational techniques are emphasized. Symmetry relationships in the theory resulting from reaction symmetry are developed. Finally, resonance effects in cross sections for symmetric reactions are discussed. Numerical applications to a model reaction are presented and analyzed in the following paper.
Theory of the interaction of Frenkel excitons with local and extended perturbations in one-dimensional molecular crystals. Application of the Green’s function formalism to the energy funnel and cluster problem
Authors: Benk H. , Haken H. , Sixl H.
Published: February 2003

The Green’s function formalism is applied to calculate the perturbed Frenkel exciton states in the presence of local and extended perturbations in one-dimensional molecular crystals. Analytically exact criteria for the existence of bound and antibound exciton states are given for (1) a local perturbation, (2) for the energy funnel problem, and (3) for the cluster problem. A reduced Green’s function formalism (RGF) is presented and applied to the calculation of the effective energy funnel radii of primary guest molecules, surrounded by their own electronically induced dipolar, quadrupolar, or exponential energy funnels.
Structure of cyclohexylsilanetriol: The first x-ray crystal structure of a silanetriol
Authors: Ishida Hatsuo , Koenig Jack L. , Gardner Kenn Corwin
Published: February 2003

The structure of cyclohexylsilanetriol C6H11Si(OH)3 has been determined by single-crystal x-ray diffraction methods. The molecule crystallizes in the monoclinic system, space group C2/m, with a=7.876(3), b=6.637(6), c=15.802(11) Å, β=95.51(3)° at −60 °C, and Z=4. The intensities of 1031 independent reflections were measured using the ω-scan technique on a Syntex P3 diffractometer (monochromatic MoKα). The final R factor is 0.057, based on anisotropic thermal parameters for all atoms except hydrogens. The molecules pack in a head-to-head, tail-to-tail arrangement with the cyclohexyl groups forming a hydrophobic double sheet and the silanetriol groups forming a second, hydrophilic, double sheet. The structure has a distorted hydrogen bond network with the hydrogen on each oxygen having equal probability of hydrogen bonding to oxygens in two different molecules. Two types of hydrogen bonds exist in the hydrophilic double sheet; O(1)⋅⋅⋅O(2) intrasheet hydrogen bonds, 2.724(2)Å, and O(2)⋅⋅⋅O(2) intrasheet hydrogen bond, 2.722(3) Å.
Surface tension of a two-component liquid mixture near its critical solution point
Authors: Nagarajan N. , Webb W. W. , Widom B.
Published: February 2003

We measure the liquid–vapor surface tension of solutions of isobutyric acid and water as a function of temperature and composition in the one-liquid-phase region near the critical solution point, and compare the results with the predictions of theory. Surface waves of small amplitude and known frequency are generated by an electrostatic transducer, their wavelengths determined by diffraction of a laser beam, and the surface tensions calculated from the known dispersion law. The measured surface tensions are displayed as a function of a single scaled temperature and composition variable as suggested by theory. The experimentally determined scaling function is qualitatively of the predicted form.
Additivity of relaxation rates for the AX2 nuclear spin grouping
Authors: Werbelow Larry
Published: February 2003

General features of nuclear magnetic relaxation in the heteropolar, three-spin, AX2 grouping are considered. It is demonstrated that if spin A is relaxed rapidly compared to spins X, the measured relaxation time for spins X will be insensitive to dipolar–dipolar and dipolar–quadrupolar interference (cross-correlation) effects.(AIP)
On the nature of the bonding in Mg4 and Ca4 clusters
Authors: Pacchioni Gianfranco , Koutecký Jaroslav
Published: February 2003

The bonding in the Mg4 and Ca4 clusters is studied using a pseudopotential multireference double-excitation configuration interaction method. The results confirm the calculations of chiles et al5.(AIP)
Higher thermodynamic partial derivatives
Authors: Gilmore Robert
Published: February 2003

A systmatic method for computing thermodynamic partial derivatives of any degree is described. This algorithm contains as special cases the extensive tabulations of Shaw [Philos. Trans. R. Soc. (London) Sec. A 234, 299 (1935)]. (AIP)
A selection rule for m-dependent transitions in atom-symmetric top collisions
Authors: Davis Stephen L.
Published: February 2003

A selection rule is derived for m1=0→m2=0 transitions in atom-symmetric top collisions when the final and initial quantization axes are parallel to the initial relative velocity vector. The scattering amplitude and differential and integral cross sections for the j1k1ε10 →j2k2ε20 transition vanish unless ε1(−1)j1+k1 =ε2(−1)j2+k2 where ε is the parity of the inversion level.
Infrared multiple photon dissociation of molecular ions formed by the laser multiphoton ionization of triethylamine
Authors: Haas Y. , Reisler H. , Wittig C.
Published: February 2003

Molecular ions are prepared by laser multiphoton ionization (MPI) of triethylamine, and by adjusting the frequency of the ionizing radiation, either triethylamine+ or (C2H5)2N=CH+2 can be chosen as the dominant nascent ionic product. These ions are fragmented very efficiently via IR multiple photon dissociation, and complete dissociation of the ions produced by MPI occurs under collision-free conditions. At high IR laser fluences, the abundance of small fragments (m/e≤30) increases dramatically. The fragmentation pattern is consistent with a mechanism by which daughter ions continue to absorb IR radiation and dissociate, and fragmentation follows the low energy pathways observed with conventional mass spectroscopy.
Electron attachment to halocarbons of environmental interest: Chloroethanes
Authors: McCorkle D. L. , Szamrej I. , Christophorou L. G.
Published: February 2003

Electron attachment to the chlorofluoroethanes 1,1-C2Cl2F4, 1,2-C2Cl2F4, 1,1,1-C2Cl3F3, and 1,1,2-C2Cl3F3 was investigated in dilute mixtures with nitrogen and argon using the electron swarm method. The 1,1,1-C2Cl3F3 molecule has a very large electron attachment rate constant at thermal energy (2.8×10−7 cm3 s−1); the rate constant for this molecule decreases monotonically with increasing electron energy above thermal. The other chlorofluoroethanes investigated attach electrons less strongly and show maxima in the rate constant vs mean electron energy at ∼0.5 eV. For all four compounds, the measured rate constants are due primarily to dissociative electron attachment producing Cl−. Electron attachment cross sections were determined for these halocarbons which showed the existence of several negative ion states below ∼2 eV. Additionally, the temperature dependence of electron attachment to 1,1-C2Cl2H4 was investigated from 323–473 K. The measured rate constants and unfolded cross sections indicated electron attachment to a repulsive negative ion state from the v=0 and v=1 levels of the neutral molecule.
The shape-driven graphical unitary group approach to the electron correlation problem. Application to the ethylene molecule
Authors: Saxe Paul , Fox Douglas J. , Schaefer Henry F. , Handy Nicholas C.
Published: February 2003

A new method for the approximate solution of Schrödinger’s equation for many electron molecular systems is outlined. The new method is based on the unitary group approach (UGA) and exploits in particular the shape of loops appearing in Shavitt’s graphical representation for the UGA. The method is cast in the form of a direct CI, makes use of Siegbahn’s external space simplifications, and is suitable for very large configuration interaction (CI) wave functions. The ethylene molecule was chosen, as a prototype of unsaturated organic molecules, for the variational study of genuine many (i.e.,≳2) body correlation effects. With a double zeta plus polarization basis set, the largest CI included all valence electron single and double excitations with respect to a 703 configuration natural orbital reference function. This variational calculation, involving 1 046 758 spin- and space-adapted 1Ag configurations, was carried out on a minicomputer. Triple excitations are found to contribute 2.3% of the correlation energy and quadruple excitations 6.4%.
Mechanism and rates of conformational transitions in heterogeneous polymers
Authors: Helfand Eugene , Skolnick Jeffrey
Published: February 2003

A general expression is presented for the rate of a trans to gauche conformational transition of a bond in a polymer backbone. The polymer is composed of nonidentical atoms, i.e., centers of differing friction constants and masses. The rate is obtained from a multidimensional extension of Kramers’ steady state solution to the Fokker–Planck equation for flux over a reaction barrier of a system in a frictional medium. Langer’s formulation is used. Results are appropriate for all but extremely small friction, with simplification occurring in the high friction limit. One also determines the reaction coordinate, an examination of which gives insight into the kinetic mechanism. Explicit results are obtained for six and 32 vertex chains, and the influence of chain conformation and relative friction constants are discussed.
A generalized Franck–Condon principle for vibronic bands of diatomic molecules
Authors: Brown C. W.
Published: February 2003

The traditional Franck–Condon principle is limited in usefulness because empirical electronic transition matrix elements are not generally constant across a vibronic molecular transition band. Empirical generalizations that preserve the utility of the Franck–Condon overlap integral account for variations of the electronic matrix elements for diatomic bands in terms of transition frequency, as in a frequency-generalized Franck–Condon approximation [G. W. Robinson and R. A. Auerbach, J. Chem. Phys. 74, 2083 (1981)], or in terms of internuclear distance, as in the well-known r-centroid approximation. This paper illustrates empirically the validity of the Robinson–Auerbach method, and its relationship to the r-centroid approximation, for vibronic bands of some diatomic molecules. Most importantly, the former empirical method is derived from a gauge-invariant theory of matter-radiation interactions developed recently by Brown and Robinson [C. W. Brown and G. W. Robinson, J. Chem. Phys. (submitted)]. Both the empirical method and the gauge-invariant theory utilize continuous variability between dipole length and velocity matrix elements Rμν and Pμν/m, respectively. Using a gauge parameter ξ, the value of which is immaterial with exact molecular eigenstates, this variability is fixed in the empirical method by the ratio (im ωμνRμν/Pμν)ξ, which is unity with exact eigenstates, and in the theory by the difference ξ(im ωμνRμν−Pμν), which vanishes with exact eigenstates. The empirical form of the variability is obtained from the theory when the difference im ωμνRμν −Pμν small. The generalized Franck–Condon principle presented here has never before been successfully derived from theory.
Vibration-rotation coupling in anisotropic environments: NMR of methanes in liquid crystals
Authors: Snijders J. G. , de Lange C. A. , Burnell E. E.
Published: February 2003

It is shown that the interaction potential which describes the orientation of methane and its isotopic derivatives in a liquid–crystal environment has a simple second-order tensorial form. The dipolar couplings previously observed in the methanes arise from a vibration-rotation coupling mechanism and a rigid-molecule effect present in the nonsymmetrically substituted methanes. These effects are calculated from the methane force field. A large part of the interaction can be identified with the coupling between the anisotropic liquid–crystal electric field and the (vibrationally induced) solute anisotropic polarizability. Relative sign information is obtained on the derivatives of the methane polarizability with respect to the symmetry modes, quantities which are crucial in the determination of absolute Raman intensities.
Quantum calculation of intramultiplet mixing: Comparison with simple radial and angular mechanisms
Authors: Anderson Roger W.
Published: February 2003

Cross sections for intramultiplet mixing in the lowest 2P states of alkali atoms (K, Rb, Cs) in collisions with He atoms are calculated in body fixed coordinates. The cross sections for transitions that maintain or change the magnitude of the projection of the electronic angular momentum are compared with very simple semiclassical models for radial (R1) and angular (R2) coupling of electronic states. The angular mixing model uses a hard sphere interaction. The agreement is good for the total cross sections and for the transition probabilities for different partial waves. The total cross sections are compared with experimental and other theoretical results, and cross sections are presented for collisions of polarized 2P3/2 atoms. The quantum mechanical equations are integrated with a constant step size Magnus method, and we find uniform convergence O(h2) for small step sizes. The error rapidly increases for steps large enough to allow propagation of a channel by half of a de Broglie wavelength.
The Raman spectrum of gaseous acetic acid at 21 °C
Authors: Bertie John E. , Michaelian K. H.
Published: February 2003

The Raman spectrum of gaseous acetic acid at 21 °C is presented and assigned. It is suggested that a reassignment of the in-plane C–C–O deformation of the monomer to ∼450 cm−1 is appropriate, and that the infrared band contours between 700 and 400 cm−1 be analyzed in detail to confirm this. The Raman-active O–H stretching mode of the dimer could not be identified. The intermonomer coupling of the other intramonomer modes in the dimer is small except for the C=O stretching and C–C–O in-plane deformation modes. Two Raman-active intermonomer modes were observed for the first time, at 155 and 99 cm−1. The former is ν13(Ag), the O⋅⋅⋅O stretching mode, and allows the previously [J. Chem. Phys. 76, 886 (1982)] unobserved corresponding mode of (HCOOH)2 to be placed near 180 cm−1. Frequencies are deduced of all of the intermonomer modes, and the infrared doublet at 167/187 cm−1 is reassigned to ν42(Bu) in Fermi resonance with the combination state ν21(Bg)+ν28(Au) at ∼179 cm−1, instead of the previously assigned combination state ν29(Au)+ν21(Bg) which is now placed at 147 cm−1. The Fermi resonance explanation of the infrared doublet at 167/187 cm−1 invokes significant anharmonic interactions between in-plane and out-of-plane displacements of the hydrogen bond. It is favored by the experimental facts over the explanation that is based on coupling between the O–H and O⋅⋅⋅O stretching coordinates [J. Chem. Phys. 52, 4403 (1970)], which is not clearly compatible with the C2h symmetry of the dimer. Our assignment of the intermonomer bands of the gaseous dimer is similar to that deduced previously for matrix-isolated dimers [J. Chem. Phys. 54, 4111 (1971)] and for liquid acetic acid [J. Chem. Phys. 77, 3878 (1982)]. However, the band at 55 cm−1 in the Raman spectrum of the liquid has no analog in the spectrum of the gas, and is reassigned to an intermolecular vibration of the ‘‘liquid lattice’’. Further, our assignment differs from that for the matrix-isolated dimers in a way that is unfavorable to the interpretation of the O–H stretching band that led to the assignment of the matrix-isolated dimers. Finally, manual correction of the Raman intensities of gaseous formic and acetic acids, for frequency- and temperature-dependent factors, suggests that the vibrations below 150 cm−1 may have frequencies higher by up to 20 cm−1 than the values measured from the Raman spectra.
Difference frequency laser spectroscopy of the ν3 band of the CH3 radical
Authors: Amano Takayoshi , Bernath P. F. , Yamada C. , Endo Y. , Hirota E.
Published: February 2003

The ν3 fundamental band of the CH3 radical has been detected in absorption with a tunable difference frequency laser. Zeeman modulation is found to be inefficient, because the spin-rotation interaction is small. The molecular constants in the ν3 vibrational state have been determined with the molecular constants in the ground state fixed at the values determined from the analysis of the ν2 band. The main parameters thus obtained are the band origin ν0=3160.8212(12), B3=9.471 10(14), C3=4.701 67(15), (Cζ)3=0.345 88 (22), and q3=0.006 42(25), all in cm−1 with one standard deviation in parentheses. The transition frequencies and the molecular constants of the ν3 band may be useful in a search for interstellar CH3.
Observation of the 4s 3Σ+g state of H2
Authors: Eyler E. E. , Pipkin F. M.
Published: February 2003

A blue cw dye laser has been used to excite 14 transitions from the metastable c(2p)3Πu state to a previously unknown electronic state of H2, believed to be the (4s)3Σ+g state. The observed transitions are all Q branches and are diagonal in vibrational quantum number. Levels with v=0 and v=1 are detected by their radiative decay, but all of the v=2 levels are predissociative with lifetimes on the order of 500 ps. Approximate molecular constants are derived from the spectra and found to be similar to those of the hydrogen molecular ion. The effective quantum number is n*=3.97, in agreement with the quantum defect found for lower triplet s states.
Characteristic function of momentum density distribution
Authors: Koga Toshikatsu , Morita Mutsuo
Published: February 2003

General relations are derived between the moments 〈p1xpmypnz〉 and 〈pn〉 and the autocorrelation function B(r) based on the fact that B(r) is the characteristic function of the momentum distribution ρ(p).
Abstraction vs insertion in O(1D)+H2→OH+H
Authors: Ransome S. W. , Wright J. S.
Published: February 2003

It is shown that in the reaction O(1D)+H2→OH+H, the total reaction cross sections are almost entirely due to insertion and the contribution to the total cross section from abstraction is negligible. (AIP)
Interaction between molecular impurities trapped in rare gas crystals. II. Interpretation of the Q branch in the near infrared spectrum of hydracids
Authors: Girardet Claude , Maillard Daniel
Published: February 2003

For non-negligibly low concentrations of hydracid dopant (20≤M/R≤500) in a rare gas matrix, the near infrared spectrum exhibits, besides the well-known rovibrational structure of the monomer, a weak band in the absorption gap around the normally forbidden pure vibrational frequency of the hydracid. The intensity and the profile of this band is concentration and temperature dependent. We give here an interpretation of its structure, based on the calculations performed in the previous paper (paper I). The interactions between dopant monomers located in a wide range of positions (between a√2 and a√10, a nearest-neighbor distance) are shown to be responsible for this absorption, which appears as a distribution of Q branches corresponding to the distribution of dopants inside the crystal. The shape of the sum band and its evolution with concentration and temperature are thus explained in terms of an inhomogeneous broadening process. More particularly, the three maxima observed at 2866.5, 2869.0, and 2870.6 cm−1 for HCl trapped in argon are, respectively, connected to the absorption of second and third nearest-neighbor dopants and to the superposition of all other pair absorption in a frequency range about 1.5 cm−1.
Photovoltaic properties of Au–merocyanine–TiO2 sandwich cells. I. Dark electrical properties and transient effects
Authors: Skotheim T. , Yang J.-M. , Otvos J. , Klein M. P.
Published: February 2003

The electrical properties of thin films (200–3000 Å) of merocyanine photosensitizing dye sandwiched between a TiO2 single crystal doped n type and a thin (200 Å) Au metal layer has been studied. Dark current voltage measurements revealed that the current is space-charge limited at high current densities with an electron trapping density of ∼1017 cm−3. This was determined by using TiO2 as an electron injecting contact. Interpretation of the kinetics of rise and decay of the photocurrent suggests that the mobility of holes, the majority carriers in merocyanine, is dependent on traps, the dominant trapping level having a depth of 0.11 eV. The decay of the photocurrent is monomolecular at short times and dominated by bimolecular recombination kinetics for long times of the order of seconds. The high series resistance in the merocyanine prevents any band bending in the TiO2, as the entire built-in voltage in the junction falls across the merocyanine film. This is supported by capacitance voltage data showing a complete absence of mobile charge carriers in the junction region.