bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of simple potential functions for simulating liquid water
Authors: Jorgensen William L. , Chandrasekhar Jayaraman , Madura Jeffry D. , Impey Roger W. , Klein Michael L.
Published: February 2003

Classical Monte Carlo simulations have been carried out for liquid water in the NPT ensemble at 25 °C and 1 atm using six of the simpler intermolecular potential functions for the water dimer: Bernal–Fowler (BF), SPC, ST2, TIPS2, TIP3P, and TIP4P. Comparisons are made with experimental thermodynamic and structural data including the recent neutron diffraction results of Thiessen and Narten. The computed densities and potential energies are in reasonable accord with experiment except for the original BF model, which yields an 18% overestimate of the density and poor structural results. The TIPS2 and TIP4P potentials yield oxygen–oxygen partial structure functions in good agreement with the neutron diffraction results. The accord with the experimental OH and HH partial structure functions is poorer; however, the computed results for these functions are similar for all the potential functions. Consequently, the discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons are also made for self-diffusion coefficients obtained from molecular dynamics simulations. Overall, the SPC, ST2, TIPS2, and TIP4P models give reasonable structural and thermodynamic descriptions of liquid water and they should be useful in simulations of aqueous solutions. The simplicity of the SPC, TIPS2, and TIP4P functions is also attractive from a computational standpoint.
High vibrational overtone photochemistry of cyclobutene
Authors: Jasinski Joseph M. , Frisoli Joan K. , Moore C. Bradley
Published: February 2003

Direct single-photon excitation of high CH stretching overtone transitions has been used to induce the isomerization of cyclobutene to 1,3-butadiene. Values of the unimolecular isomerization rate constant k(E) have been measured as a function of energy and overtone transition by studying the pressure dependence of the photoisomerization rate constant. The values of k(E) depend on the total energy and do not show any observable dependence on the type of CH overtone transition excited. The values of k(E) are in reasonable quantitative agreement with RRKM calculations.
Determination of Slater–Condon and Trees parameters in terms of the exact effective valence shell Hamiltonian
Authors: Oleksik John J. , Freed Karl F.
Published: February 2003

The empirical approximate Slater–Condon and Trees parameters of atomic spectra and semiempirical molecular electronic structure theories are expressed in terms of the matrix elements of the exact effective valence shell Hamiltonian (ℋv) for the snpm case. The nature of the configuration and occupation dependence of the Slater–Condon and Trees parameters is thereby made explicit by their representation in terms of exact configuration and occupation independent ℋv-matrix elements. Ab initio values of the latter for oxygen and nitrogen ions are utilized to provide ab initio Slater–Condon and Trees parameters for these systems.
On the participation of domains in the high spin (5T2) ⇄ low spin (1A1) transition in dithiocyanatobis (2,2′-bi-2-thiazoline) iron (II)
Authors: Müller E. W. , Spiering H. , Gütlich P.
Published: February 2003

The hysteresis in the high spin ⇄ low spin transition of [Fe(bt)2(NCS)2] (bt=2,2′-bi-2-thiazoline) has been studied by magnetic susceptibility measurements in two different preparations and in a mechanically treated (ball mill) sample. From the measurement of two inner hysteresis loops and a comparison with Everett’s theorems for hysteresis effects, it could be established that independent domains (i.e., groups of complex molecules of like spin that can only change their state simultaneously) participate in the spin transition in the unperturbed sample. The domains were found to be no longer independent in the milled sample. This property may result from a different limitation in the size of the domains caused by lattice defects as compared to the unperturbed sample.
Emission spectra of CF3 radicals. V. Photodissociation of CF3H, CF3Cl, and CF3Br by vacuum ultraviolet
Authors: Suto Masako , Lee L. C.
Published: February 2003

The absorption cross sections of CF3H, CF3Cl, and CF3Br and the fluorescence cross sections for their photofragments are measured in the 106–155 nm region using synchrotron radiation as a light source. The threshold wavelengths for producing the CF3 UV fluorescence from photodissociation of CF3X (X=H, Cl, and Br) are 113.0, 122.2, and 132.4 nm, respectively. The threshold energy is nearly equal to the calculated sum of the CF*3 excited state energy and the dissociation energy for each molecule. The excitation spectra for the UV and visible fluorescence are different, and the threshold wavelength for the CF3 visible fluorescence is slightly longer than that for the UV fluorescence. These results strongly support previous conclusions that the upper states of the CF3 UV and visible fluorescence are different, and that the upper state energy of the UV fluorescence is higher than that of the visible one. The processes for photodissociation of CF3X into various fragments are discussed.
Kinetics of the Cl–H2 system. III. The deuterium isotope effect in Cl+H2
Authors: Miller John C. , Gordon Robert J.
Published: February 2003

The rate constant for the reaction Cl+D2 was measured over the temperature range 200–500 K, using the flash photolysis-resonance fluorescence technique. These data, together with previous measurements for Cl+H2, are compared with the isotope effect measured by Persky and Klein in a static bulb. Over the range 295–500 K, our data are in excellent agreement with their results. At lower temperatures, the Cl+D2 rate constant displays an anomalous non-Arrhenius curvature. A mechanism involving the reaction of Cl atoms with vibrationally excited D2 is proposed to explain this effect.
Effects of a partial relaxation of the crystal lattice on the calculation of the electronic structure of CrF3−6 in ‘‘isolated-cluster’’ and ‘‘shared-cluster’’ crystals
Authors: Barandiarán Z. , Pueyo L.
Published: February 2003

The electronic structure of the CrF3−6 in isolated-cluster crystals (K2NaCrF6, Rb2NaCrF6, Rb2KCrF6, and Cs2KCrF6) and in the shared-cluster system CrF3 has been calculated in terms of an open-shell Hartree–Fock–Roothaan SCF methodology which includes the corresponding cluster–lattice interactions. These interactions have been calculated with different models of the crystal lattice. First, a rigid point-charge model has been used to compute the lattice potential. Then, this lattice representation has been partially relaxed in the sense that either the values of the point charges q(Cr), q(F) or the Cr–F internuclear distance or both are allowed to change in order to be consistent with the predictions of the cluster calculation. In CrF3 the relaxation has been limited to the values of the point charges. In the isolated-cluster lattices it is extended to include the lattice value of the Cr–F distance. The results of these calculations have been analyzed with particular attention to the prediction of the equilibrium geometry and the electronic transition 10Dq. The effect of the partial lattice relaxation on these two observables turns out to be rather significative in CrF3 but uniformly small in the isolated-cluster lattices. The values of Re and 10Dq obtained in the best calculation on CrF3 are in very good agreement with the experimental observations.
A systematic density functional approach to the mean field theory of smectics
Authors: Lipkin Michael D. , Oxtoby David W.
Published: February 2003

We present a systematic density functional approach to the mean field theory of the isotropic–nematic– smectic A transition. We show that our theory is a generalization of the McMillan theory of smectics, and point out that an additional term arises in the free energy which was not present in the earlier work. Our approach provides a starting point for the investigation of chemical effects on liquid crystal phase transitions.
Laser excitation spectrum and microwave optical double resonance spectrum of the 31 band in the ã 3A2–X̃ 1A1 system of H2CS: The hyperfine structure of the ã 3A2 state
Authors: Suzuki Tetsuo , Saito Shuji , Hirota Eizi
Published: February 2003

The dye laser excitation spectrum of the 310 band in the ã 3A2 ← X̃ 1A1 transition of H2CS was observed in the region 15 280 to 15 400 cm−1 with Doppler-limited resolution. The observed spectrum was analyzed to yield precise values for the rotational constants, the centrifugal distortion constants, and the spin–spin and the spin-rotation interaction constants in the upper triplet state and for the band origin. Transitions with Ka′=4 and 5 revealed the effect of the c-type Coriolis interaction between the v3′=1 and v6′=1 states, which, when analyzed, allowed determination of the ν3−ν6 difference to be 99.341 cm−1. 15 K-type doubling transitions and two a-type R branch transitions in the ã state were observed by a microwave or radio-frequency optical double resonance technique, of which two K-doubling transitions of Ka=1 and two R branch transitions (all F3 components) were resolved into three hyperfine components. From the observed splittings the proton hyperfine coupling constants were determined to be aF=27.7(25), Tbb+Tcc=12.8(44), and Tbb−Tcc=7.89(19) MHz with one standard errors in parentheses.
Dissociation dynamics of vibrationally excited van der Waals clusters: I2XY → I2+X+Y (X, Y=He, Ne)
Authors: Schatz George C. , Buch Victoria , Ratner Mark A. , Gerber Robert B.
Published: February 2003

The dynamics of sequential dissociation processes of the type XI2(v)Y → X+I2(v′)Y → X+Y+I2(v″) (X,Y=Ne, He) are studied using classical trajectory calculations and a recently presented classical version of the time-dependent self-consistent field (TDSCF) method. The results obtained indicate the presence of significant dynamical correlation effects of the rare-gas atoms on each other despite the negligible direct interaction between them; this is in qualitative agreement with experimental findings. Good agreement is found for the rate constants and the variation with rare gas as well as the branching ratios (NeI2He → NeI2+He vs → I2He+Ne) calculated from TDSCF and from classical trajectories. Both classical trajectories and TDSCF show an essentially impulsive dissociation mechanism, in which dissociation typically follows a considerable number of vibrations, and is due to a relatively rare internal hard collision between an I atom and the rare gas. As in the three-body I2X case, this mechanism differs from that in the RRKM strong coupling model. Energy- and momentum-gap relations, based on the weak-coupling picture, are found to be relatively successful but fail to describe the dynamics quantitatively.
Dimers in jet-cooled s-tetrazine vapor: Structure and electronic spectra
Authors: Haynam Christopher A. , Brumbaugh Donald V. , Levy Donald H.
Published: February 2003

Dimers with two distinct conformations form as s-tetrazine vapor (C2N4H2) is cooled in a supersonic jet expansion. Rotationally resolved laser-induced fluorescence excitation spectra of both hydrogen and deuterium substituted dimers have been obtained with single frequency scanning dye lasers. Dimer structures were determined by a combined rotational contour generating program and nonlinear least squares fitting procedure. One dimer conformation is planar with two translationally equivalent monomer units. In this conformation one hydrogen of each ring is in close proximity to the nitrogen lone pair of the other, allowing for stabilization by weak hydrogen bonds. The center-to-center ring separation is 5.6 Ȧ. The other dimer conformation is T shaped with symmetrically inequivalent rings giving rise to two electronic transitions with different rotational band types. In this configuration, one hydrogen of the first monomer is in close proximity to the π cloud of the second monomer, and the ring centers are separated by 4.4 Ȧ. The two electronic transitions are due to two close lying electronically excited states where the electronic excitation is localized on one or the other of the two rings. Additional spectral features are attributed to dimer vibrations and larger clusters.
Two-dimensional analysis of the ring-puckering and PH inversion vibrations of 3-phospholene
Authors: Harthcock M. A. , Laane J.
Published: February 2003

The ring-puckering energy levels for 3-phospholene, CH2CH=CHCH2PH, in both the ground and excited states of the PH inversion vibration have been established from the vibrational spectra of this molecule. The availablity of such extensive data made it possible to determine a reliable two-dimensional (with the ring-puckering and the P–H inversion as the two coordinates) potential energy surface. For the calculations, the kinetic energy coefficients g44, g55, and the cross term g45 were accurately represented as functions of both coordinates. An initial approximation to the asymmetric two-dimensional potential energy surface was obtained from the one-dimensional ring-puckering function as well as from structural data from microwave spectroscopy. Symmetry constraints established which potential terms were to be utilized. Three separate computer programs were written in order to calculate the vibrational energy levels and to adjust the potential parameters. The most efficient approach utilized a product of two prediagonalized basis sets for the basis functions. Initial attempts to fit the data with a potential surface using terms up through fourth power proved unsatisfactory in fitting data for the inversion excited state. A local solution based on Van Vleck perturbation theory was thus obtained and then expanded, using the symmetry constraints, to the entire solution. The resulting potential surface, which required the use of sixth power terms, gave excellent agreement with the observed spectra. Only five variable parameters were adjusted (for the local solution) in order to fit the 20 observed frequencies. The final potential surface has a central barrier of about 5500 cm−1 for the planar configuration. The more stable endo conformation lies 785 cm−1 in energy below that of the exo form with similar puckering angle (18°).
Quantum vs classical calculation of nonlinear spectra-reduced dynamics and intramolecular entropy
Authors: Mukamel Shaul
Published: February 2003

A non-Markovian reduced equation of motion (REM) is derived for a generating function P(a,t;a′) which allows the calculation of two-time correlation functions in nonlinear systems. The form of the REM is identical for classical and quantum systems and it depends on an entropy function ln g(a), a velocity kernel W(a,a″), and a non-Markovian kernel K(a,a″,t), a being the expectation value of the dynamical variable under consideration. We give exact formal expressions for these quantities for the quantum and the classical case. In the linear (harmonic) limit the REM reduces rigorously to a non-Markovian Fokker–Planck equation. The present approach may allow a convenient and a systematic way for the calculation and the comparison of classical and quantum nonlinear spectra.
Perturbation theory of the electron correlation effects for atomic and molecular properties. VII. Complete fourth-order MBPT study of the dipole moment and dipole polarizability of H2O
Authors: Diercksen Geerd H. F. , Kellö Vladimir , Sadlej Andrzej J.
Published: February 2003

The dipole moment and dipole polarizability tensor of the water molecule are calculated by using a complete fourth-order many-body perturbation theory (MBPT) approach based on the coupled Hartree-Fock (CHF) solution for the one-electron perturbation problem. The CHF-based MBPT calculations reveal that the fourth-order correlation corrections involving triple and single substitutions in the reference HF determinant are by no means negligible. On the contrary they represent the two largest in magnitude fourth-order terms. The present study reveals that good results obtained with several approximate fourth-order MBPT schemes follow from some mutual cancellations between the neglected lower and higher-order contributions. Among these approximate MBPT approaches particular attention is given to the CHF-based MBPT treatment which involves only singly and doubly substituted states (SD-MBPT) and which provides a reasonable agreement with both the experimental data and more accurate theoretical values.
The A←X transition in Cr2: Predissociation, isotope effects, and the 1–1 sequence band
Authors: Riley S. J. , Parks E. K. , Pobo L. G. , Wexler S.
Published: February 2003

Two-color resonance-enhanced ionization spectroscopy with mass analysis is performed on beams of Cr2 produced by laser vaporization and isentropic expansion cooling. For the A←X 0–0 band near 459.6 nm an extensive rotational spectrum is observed and its intensity profile is found to have a systematic modulation with J. This modulation, and its surprisingly strong dependence on isotopic composition, are interpreted in terms of a two-step predissociation of the A state and suggest a potentially important new procedure for isotope enrichment in metal systems. An additional resonant feature is found ∼1 nm to the red of the origin band and is assigned to the 1–1 sequence band.
The reaction H2+D2⇄2HD. A long history of erroneous interpretation of shock tube results
Authors: Lifshitz Assa , Bidani Menashe , Carroll Harvey F.
Published: February 2003

An ultraclean 2 in. i.d. single pulse shock tube coupled to an atomic resonance absorption system was constructed in order to determine hydrogen atom concentration by Lyman-α absorption. The tube was baked to 300 °C and pumped down to ∼10−7 Torr. Ultrapure argon could be shock heated to ∼2500 K with no spurious H atom absorption. The system was constructed in order to study the kinetics of chemical reactions which are strongly catalyzed by H atoms, under the conditions where no such atoms are present. Specifically, the role of H atoms in the H2+D2→2HD exchange reaction was studied. Mixtures of hydrogen and deuterium diluted in argon were shock heated to 1375–1760 K; samples were then taken from the tube and analyzed mass spectrometrically for the ratio [HD]/[D2]. 1400 K was the highest temperature at which no spurious H atom absorption was observed in a shocked mixture of 1% H2–1% D2. At 1400 K, under the conditions of no absorption, no, or ≤1%HD conversion was obtained. At higher temperatures Lyman-α absorption was detected and more HD conversion was observed. A comparison between these results and results obtained previously in conventional systems suggests that the high HD conversion observed in the past was caused by hydrogen atoms generated from impurities. The existence of a molecular mechanism in the H2–D2 exchange reaction is highly doubtful.
A computer simulation of the time-dependent Ginzburg–Landau model for spinodal decomposition
Authors: Petschek R. G. , Metiu H.
Published: February 2003

In this paper we discuss the results of computer simulations of the time-dependent Ginzburg–Landau equation appropriate to the spinodal decomposition of a two-component mixture with a conserved order parameter. The results for quantities of theoretical interest, such as the probability that the concentration has a particular value in a particular cell, as well as experimentally accessible quantities such as the structure function, are presented. For reasons of computer space, the simulation was done in two dimensions. The effects of incompressible flow, which might be important in some experimental situations, were not included in these calculations.
Theory of critical micelle concentration for solutions of block copolymers
Authors: Leibler Ludwik , Orland Henri , Wheeler John C.
Published: February 2003

A simple microscopic model for micellar formation in mixtures of block copolymers and homopolymers is presented. The size, number of chains, and energy of formation of micelle are calculated. The fraction of copolymer chains aggregating into micelles is computed as a function of the overall copolymer content. A critical micelle concentration behavior is found for low copolymer contents even for weak incompatibilities of species. The similarity with an aborted phase transition is underlined.
Infrared photodissociation of hydrogen-bonded clusters: C2H4⋅HF and C2H4⋅HCl
Authors: Casassa Michael P. , Western C. M. , Celii Francis G. , Brinza D. E. , Janda K. C.
Published: February 2003

Infrared photodissociation spectra of C2H4⋅HF, C2H4⋅HC1, and C2H4⋅NO formed in molecular beams are reported. Parameters determined are absorption frequencies ω0, initial-state lifetimes τ, and transition moments 〈μ〉2: All are blue shifted relative to the 949 cm−1 monomer ν7 absorption frequency. While the frequency for C2H4⋅HF is close to that observed in an Ar matrix, the frequency for C2H4⋅HC1 is shifted 6.8 cm−1 further than that observed in a matrix. The results are discussed in terms of the bonding interaction and the photodissociation mechanism.
Diffusion of interacting Brownian particles in a fluid with fixed macroparticles
Authors: Cukier R. I.
Published: February 2003

The diffusion of interacting Brownian particles in a fluid with an added macroparticle species is discussed. The added particles are fixed on the time scale of the Brownian motion. The effective (collective) diffusion coefficient De of the Brownian particles, characterizing relaxation of Brownian number density fluctuations, is calculated to linear order in Brownian concentration. We construct the friction tensor ζ(r) describing Brownian pair interactions by considering the reflections of the fluid from the Brownian and fixed particles, and averaging over fixed particle configurations. We find that a naive expansion in fixed particle concentration na leads to divergent integrals. Introducing a diagrammatic representation, we sum to all orders in na and obtain convergent results, with ζ(r) depending on na in a nonanalytic fashion. This ζ(r) is inverted and used in a Smoluchowski equation to find De. To lowest order, we find that the modification to De from the fixed particles enters as √na. Measurement of De by quasielastic light scattering techniques should confirm this behavior.
Enhanced light reflection by dye monolayers at the air–water interface
Authors: Grüniger H. , Möbius D. , Meyer H.
Published: February 2003

The reflection of light from an air–water interface is enhanced by dye containing monolayers in the spectral region of the dye absorption. The intensity of the reflected light depends linearly on the density of chromophores in the mixed monolayer. From the measurement of both absorption and reflection spectra of a dye containing monolayer the damping constant of coherent light scattering can be estimated. The value of the reflection measurement for the investigation of adsorption processes and the control of monolayer organization is demonstrated.
On the electronic structure of the X, A, and B states of CaCl
Authors: Honjou Nobumitsu , Adams George F. , Yarkony David R.
Published: February 2003

State-averaged multiconfiguration self-consistent-field (SA-MCSCF)/configuration interaction wave functions are used to characterize the near equilibrium electronic structure of the X 2Σ+, A 2Π, and B 2Σ+ states of CaCl. Spectroscopic constants Te, ωe, and Re were determined and are in reasonable agreement with experiment although the Re are uniformly long. The dipole moments for the X, A, and B states and the electronic transition moments for the A–X, B–X, and B–A systems were determined at the CI level and are in good agreement with the available experimental data. The three states are described by a Ca+2Cl− core plus one electron in a nonbonding calcium centered orbital, which is polarized away from the Cl− ion. The present calculations are in general accord with the polarizable ion model which has been inferred from experimental analyses of these states. However, participation of the calcium 3d orbital in the A 2Π state is surprisingly limited. Calculations in which the chlorine K and L shells are replaced by effective core potentials reproduce the results of the all electron calculations quite well.
Highly excited Rydberg states of Na2: Decoupling between electronic and nuclear motion
Authors: Martin S. , Chevaleyre J. , Bordas M. Chr. , Valignat S. , Broyer M. , Cabaud B. , Hoareau A.
Published: February 2003

The excited Rydberg states of Na2 are observed for very high n values up to 70. Four series nd 1Δg, nd 1Πg, nd 1Σg+, and ns 1Σg+ are identified and their quantum defects are measured. At high n values the observed spectrum is completely modified by the decoupling between the electronic angular momentum l of the Rydberg electron and the internuclear axis (l uncoupling). A perturbation model is developed to treat this phenomenon and appears sufficient to account for the main features such as interference effects in the electric dipole transition to the Rydberg series. Finally the Na2+ ion molecular constants are deduced.
Crossover behavior of transport properties of dilute polymer solutions: Renormalization group approach. III
Authors: Oono Y.
Published: February 2003

Detailed results of the renormalization group calculation for the crossover behavior (e.g., temperature dependence) of transport properties of dilute polymer solutions are given. Universal plots are proposed which can be directly compared with experimental results without any adjustable parameter. The comparison of these plots with existing experimental results is satisfactory in some cases, but, generally, the wild scattering of existing data calls for more accurate and systematic experiments.
The photoionization of oxidized metal clusters
Authors: Dao P. D. , Peterson K. I. , Castleman A. W.
Published: February 2003

Oxidized metal clusters (NaxO and KxO for 2≤x≤4) were formed in a gas phase reaction between metal clusters and an oxidizing gas using a double expansion technique. Their appearance potentials were measured using a molecular beam-photoionization mass spectrometer system. These first photoionization data for oxidized clusters provide information on trends of ionization potentials as a function of the degree of aggregation. The ionization potentials do not differ greatly from the analogous metallic species, but in the case of the sodium tetramer the value does fall below that of the bare metal cluster. This finding is in accord with what has been observed as an influence of impurities on the work function of the bulk sodium. The results are also of interest concerning questions of octet rule violations and hypervalency.
A photoelectron spectroscopic study of ionization selectivity in resonantly enhanced multiphoton ionization of Xe and Kr
Authors: Sato Kenji , Achiba Yohji , Kimura Katsumi
Published: February 2003

Photoelectron energy and angular distribution measurements were carried out for resonant multiphoton ionization (MPI) of Xe and Kr through some Rydberg excited states under collision-free conditions. From the (3+1) resonant MPI of Xe through the 5d[2 1/2]0 J=3 Rydberg state, it has been clearly demonstrated that removal of a Rydberg electron gives rise to only the 2P3/2 ionic state. Such selectivity has also been observed for the 5d[3 1/2]0 J=3 Rydberg state of Xe and the 5s[1 1/2]0 J=1 Rydberg state of Kr. For the 6s[1 1/2]0 J=1 Rydberg state of Xe, however, both the 2P1/2 and 2P3/2 states are produced. This breakdown of the one-electron ionization picture may be due to the near resonance in the fourth-photon level. Photoelectron angular distributions obtained here for the resonant MPI of Xe and Kr show obvious deviations from the cosine square distribution, reflecting the spatial alignment of the total electronic angular momentum in the resonant Rydberg states.
On the electron affinity of Be2
Authors: Bauschlicher Charles W. , Partridge Harry
Published: February 2003

The electron affinity (EA) of Be2 is computed using a large STO basis set and extensive correlation with a large CASSCF reference. The adiabatic electron affinities are estimated to be 0.44 eV for the 2∑+g state and 0.56 eV for the 2Πu state.
A quantum calculation of multipole relaxation and transfer cross sections in collisions of Na with Xe
Authors: DeVries Paul L.
Published: February 2003

Well-established quantum mechanical methods were used to calculate multipole cross sections in sodium–xenon collisions. The cross sections were opacity analyzed to determine the relative importance of various angular momenta; the relaxation of the alignment was found to be the multipole most dependent upon low angular momenta (e.g., small impact parameter) collisions. While all the cross sections reported are found to be in satisfactory agreement with experiment, the relaxation of occupation of the j=1/2 state was found to be in excellent agreement with recent experimental results.
Mode specificity and energy dependence of the dynamics of single rovibrational levels of S1 acetaldehyde in a supersonic jet
Authors: Noble Marcus , Lee Edward K. C.
Published: February 2003

The dynamics of selected single rotational S1 levels of low lying vibrational levels near the π*←n (A″←A′) electronic origin of CH3CHO (T′00=29 771 cm−1) and CH3CDO (T′00=29 820 cm−1) have been examined. The aspects that have been studied include the effects of three low frequency vibrational modes; ν′10 (CCO deformation), ν′14 (CH out-of-plane bend), and ν′15 (CH3 torsion), the effect of rotation, the effect of deuterium substitution, and the similarity as well as any differences with the S1 dynamics of formaldehyde. The fluorescence decay times measured in the supersonic jet show (i) single exponential decay, (ii) lifetimes in the range 225–95 ns for CH3CHO and 1.52–1.02 μs for CH3CDO, (iii) ν′10 and ν′14 are effective in promoting the S1 decay, but ν′15 is not, (iv) an underlying trend of decreasing lifetimes with increasing E′vib, (v) no evidence of explicit dependence on the rotational state at low energies, and (vi) no evidence for quantum beats which would possibly be associated with strong S1–T1 coupling. The observation of a single exponential decay from a cold single rotational level is decidedly different from the recent report of dual exponential decay behavior at room temperature.
Quantitative photoexcitation and fluorescence studies of C2H2 in vacuum ultraviolet
Authors: Suto Masako , Lee L. C.
Published: February 2003

The photoabsorption and fluorescence cross sections of C2H2 were measured in the 105–155 nm region using synchrotron radiation as a light source. The quantum yield for producing the C2H* fluorescence from photodissociation of C2H2 was measured in the 106–136.5 nm (threshold) region. The absorption spectrum shows sharp Rydberg states, but the quantum yield is a smooth function of excitation wavelength. The quantum yield data were used to derive a quasidiatomic repulsive potential curve for dissociation of C2H2 into C2H*+H. The quenching of the C2H* fluorescence by C2H2, N2, and Ar was studied. The products of radiative lifetime quenching rate constant increase with increasing excitation wavelengths, varying from 10−16 cm3 at 110 nm to 5.5×10−16 cm3 at 134 nm for N2 and Ar as quenchers. The data of lifetimes, quenchings, and fluorescence spectra point to a conclusion that the upper state of the C2H* fluorescence is well bound, and the lower state is a repulsive or weak-bound state.
Rotor frequency lines in the nuclear magnetic resonance spectra of rotating solids
Authors: Vega S. , Olejniczak E. T. , Griffin R. G.
Published: February 2003

An analysis of a magic angle sample spinning experiment with a noncommuting time-dependent Hamiltonian is presented using Floquet Hamiltonian theory. The results obtained from this analysis are used to explain additional lines in multiple pulse magic angle sample spinning experiments which occur at multiples of the rotor frequency. Frequency shifts of the normal magic angle sample spinning sidebands and the intensities of the additional rotor frequency lines as a function of the resonance offset are given.
Multiproperty empirical anisotropic intermolecular potentials. II. HeSF6 and NeSF6
Authors: Pack R. T , Piper E. , Pfeffer G. A. , Toennies J. Peter
Published: February 2003

Crossed molecular beam measurements of the total differential cross sections (DCS) for the scattering of He and Ne by SF6 are reported. Using anisotropic MSV potential forms and the IOS approximation to do the scattering dynamics, we determine anisotropic intermolecular potentials by simultaneously fitting the DCS, viscosities, virial, and diffusion coefficients. Damping of the diffraction oscillations in the DCS determines the anisotropy of the minimum position rm of the HeSF6 interaction; damping of the rainbow determines the anisotropy of the well depth ε of the NeSF6 interaction. Consistency between the systems verifies the accuracy of the resulting HeSF6 and NeSF6 potentials.
ESR spectra of matrix isolated Li7 clusters
Authors: Garland D. A. , Lindsay D. M.
Published: February 2003

ESR spectra assigned to 6Li7 and 7Li7 have been produced by co-depositing atomic lithium with excess argon in a liquid helium cooled cryostat. The spectra are characterized by an isotropic g value, g0=2.00045(6) for 7Li7, and hf coupling constants a1=36.39(5) G for two equivalent 7Li nuclei plus a2=2.19(2) G for (most likely) five equivalent 7Li nuclei. Both g0 and a2 show a small temperature dependence in the range 4.1–30 K, but the mechanism for this effect remains open. As in the case of Na7 and K7, the ESR spectra may be interpreted as arising from a pentagonal bipyramidal molecule with ground state symmetry 2A″2. The average p character for Li7 is much greater than in the corresponding sodium and potassium septemers and, if a2<0, is comparable in magnitude to the hybridization of the bulk metal.
Hypersonic relaxation studies of molten zinc chloride
Authors: Knape H. E. Gunilla
Published: February 2003

Brillouin spectroscopy has been used to study the frequency and temperature dependence of sonic waves in molten ZnCl2. The hypersonic velocity has been determined for two different scattering angles, 90.1° and 140.2°, and in the temperature range 294–741 °C, where a relaxation process was revealed. The sound absorption has been studied at temperatures lower and higher than those corresponding to the absorption peak. Shear and structural relaxations were both present with the same single relaxation time within experimental uncertainty. The temperature dependence of the longitudinal relaxation time was an Arrhenius type relation.
Dynamic light scattering study of semidilute solutions of a stiff-chain polymer
Authors: Russo Paul S. , Langley Kenneth H. , Karasz Frank E.
Published: February 2003

We report results from dynamic light scattering on the translational mobility of poly-γ-benzyl-L-glutamate in semidilute solutions with N, N-dimethylformamide as solvent. Dimethylformamide is shown to be a good solvent for the virtually rodlike poly-γ-benzyl-L-glutamate molecules. The observed translational diffusion coefficient is seen to increase with concentration of polymer, in disagreement with the theory of Doi and Edwards, and also with the recent results of Zero and Pecora, who studied the poly-γ-benzyl-L-glutamate, 1,2-dichlorethane system. The increase in diffusion coefficient with concentration is attributed to a repulsive thermodynamic contribution. The magnitude of this term was estimated from a linear virial expansion and subtracted from the measured diffusion coefficient. The difference represents diffusion in the absence of thermodynamic effects and does decrease with increasing concentration, perhaps even more strongly than expected. In qualitative agreement with the dynamic structure factor predicted by Doi and Edwards, a slow decay mode was found, but not until well above the concentration of molecular overlap, suggesting delayed onset of entanglement, as found by other workers. The unexpectedly high concentrations required for entanglement may be due to minor flexural motions of the imperfectly rigid rods.
Dynamic simulation of sheared suspensions. I. General method
Authors: Bossis G. , Brady John F.
Published: February 2003

A general method is presented for simulating the dynamical behavior of a suspension of particles which interact through both hydrodynamic and nonhydrodynamic forces. In the molecular-dynamics-like simulation there are two different procedures for computing the interactions among particles: a pairwise additivity of forces and a pairwise additivity of velocities. The pairwise additivity of forces is the preferred method as it preserves the hydrodynamic lubrication forces which prevent particles from overlapping. The two methods are compared in a simulation of a monolayer of identical rigid non-Brownian spherical particles in a simple shear flow. Periodic boundary conditions are used to model an infinite suspension. Both methods predict the presence of a shear induced anisotropic local structure whose form and strength depend on the concentration of particles, the nonhydrodynamic forces, and the shear rate. Increasing the particle concentration up to near the maximum fraction that can still flow results in a transition to a layered structure in which planes of particles slide relative to one another. The anisotropic local structure and transition to a layered structure predict a non-Newtonian suspension rheology.
Surface plasmon-enhanced Raman scattering at thin silver films
Authors: Corn Robert M. , Philpott Michael R.
Published: February 2003

Raman spectra are reported for liquids and Langmuir films enhanced by the electromagnetic fields of plasmon surface polaritons at flat silver surfaces. The Kretschmann prism coupling configuration is used to excite the incident surface polariton and to couple out the Raman shifted surface wave. The spectra are interpreted with the help of a simple quantum theory and compared with previously reported grating spectra. Enhancement factors, polarization characteristics, and the feasibility of using surface polaritons to enhance the Raman spectra of adsorbates on flat electrodes in contact with aqueous electrolyte are discussed.
Differential cross sections for ionization of methane, ammonia, and water vapor by high velocity ions
Authors: Wilson W. E. , Miller J. H. , Toburen L. H. , Manson Steven T.
Published: February 2003

Cross sections, differential in the energy of secondary electrons, for ionization of methane, ammonia, and water vapor by high energy protons are presented. The results are based on a model that uses photoabsorption and ion impact ionization data to evaluate the coefficients in Bethe’s asymptotic cross section for inelastic scattering of high velocity ions. Model cross sections are compared with previously published data and new data on ionization of methane and water vapor by 3.0 and 4.2 MeV protons. The simple, analytic model should be very useful in transport calculations where differential ionization cross sections over a broad range of primary and secondary energies are needed.
Fluorescence and phosphorescence of 9-hydroxyphenalenone in solid neon and its hydrogen tunneling potential function
Authors: Bondybey V. E. , Haddon R. C. , English J. H.
Published: February 2003

Absorption and emission spectra of 9-hydroxyphenalenone in solid neon have been studied. Vibrational relaxation in the first excited singlet state is shown to be relatively slow and extensive unrelaxed fluorescence is observed. Analysis of the spectra yields information about the magnitude of the tunneling splitting in the double minimum potential both for normal (Δ″H=69 cm−1) and deuterated (Δ■D=12 cm−1) 9-hydroxyphenalenone. The upper state values are 311 and 172 cm−1, respectively. A long lived (τ∼25 ms) phosphorescence with origin near 17 350 cm−1 is also observed.
State selected charge transfer reactions in the BC++Ar⇄BC+Ar+ systems: Comparison among BC=H2, O2, and NO
Authors: Kato Tatsuhisa
Published: February 2003

The relative state selected cross sections for the low-energy charge transfer (CT) reactions in the systems H+2(X2 Σ+g,v)+Ar, Ar+(2PJ)+H2, O+2(a 4Πu,v) +Ar, Ar+(2PJ)+O2, NO+(a 3Σ+,v)+Ar, and Ar+(2PJ)+NO have been determined using the threshold electron-secondary ion coincidence (TESICO) technique. In the (H2+Ar)+ system, the cross sections for both the forward and backward reactions were found to show a characteristic internal-state dependence which can be consistently interpreted in terms of a single model based on energy defects (ΔE) and Franck–Condon (FC) factors. In contrast, in the (O2+Ar)+ and (NO+Ar)+ systems, the strong dependence of the cross sections on the selected internal states were observed only for the forward (starting from the diatomic ions) reaction, and not for the backward (starting from the Ar+ ion) reaction. The results for the forward reactions were again interpreted, at least partially, by the energy defects and FC factors between the reactant and product states. These features of the internal-state dependence of cross sections have been discussed in conjunction with the characteristics of the relevant potential energy surfaces of each system. The discrepancy between the (H2+Ar)+ system and the (O2+Ar)+ and (NO+Ar)+ systems in the behavior of the forward and backward cross sections was ascribed to the difference in the number of potential surfaces involved; in the former system only two surfaces are involved in both forward and backward  reactions  allowing  exactly  the  same  mechanism  for  both  reactions, whereas in the latter two systems, the occurrence of more than two surfaces causes different mechanisms for the forward and backward reactions. In the (O2+Ar)+ system, the doublet and quartet surfaces participate in the backward reaction, leading to two different states (X 2Πg and a 4Πu) of the O+2 product ion, while only quartet surfaces are involved in the forward reaction. In the (NO+Ar)+ system, different reaction paths arise between the [NO+(a 3Σ+)+Ar] and (Ar++NO) states due to the anisotropy in these interactions. This allows the different behavior of the forward and backward reactions, in spite of the fact that the product state of the backward reaction is predominantly NO+(a 3Σ+)+Ar. An ab initio calculation of partial potential energy surfaces for the triplet states of the (NO+Ar)+ system supported this view. From these considerations, low-energy charge transfer reactions in the (BC+Ar)+ systems have been classified into two groups according to the possible types of nonadiabatic transitions. These groups are considered to correspond respectively to the phenomenological ‘‘direct’’ and ‘‘intimate’’ reaction mechanisms.
Diatomic and triatomic scandium and diatomic manganese: A resonance Raman study
Authors: Moskovits M. , DiLella D. P. , Limm W.
Published: February 2003

Resonance and preresonance Raman spectra of Mn and Sc containing argon matrices are reported. For scandium, we assign the progressions to the diatomic and triatomic molecules. The former is found to have vibrational constants ω″e=239.9 cm−1 and ω″ex″e=0.93 cm−1. The latter is best described as an equilateral or near equilateral triangle with a symmetric stretching vibrational frequency of 248 cm−1 and a degenerate (asymmetric stretch–bend) vibrational frequency of 150 cm−1. In addition a low lying electronic state 395 cm−1 above the ground state is attributed to Sc3 based on the observation of a second progression. In Mn containing matrices one identifies three progressions with nearly equivalent vibrational spacings and assigns them to Mn2. The ground state vibrational constants of Mn2 are found to be ω″e=124.7 cm−1 and ω″ex″e=0.24 cm−1. Two more progressions resulting from transitions to states 135.7 and 196.7 cm−1 above the ground state are interpreted by assuming Mn2 to be an antiferromagnetic dimer possessing several spin states whose energy spacings are given by the Landé interval rule. With the frequencies of Mn2 and Sc2 one now has all the frequencies of the first row transition-metal diatomics. The trends across the periodic table are discussed and the properties of diatomics are compared with those of the analogous bulk metals.
Electronic excited states of CO2: An electron impact investigation
Authors: McDiarmid Ruth , Doering J. P.
Published: February 2003

The electronic excited states of CO2 were restudied by variable incident energy, variable angle electron impact spectroscopy. In this study, valence states of mixed configurations were distinguished from pure Rydberg states. Our results are incompatible with the theoretical description of CO2, in which only two valence singlet states are located.
The static dipole polarizabilities of the lithium dimer, its cation and anion
Authors: Bishop David M. , Pouchan Claude
Published: February 2003

The static dipole polarizability components (α∥, and α⊥) of Li2, Li+2, and Li−2 in their electronic ground states have been calculated using a pseudopotential treatment for the core electrons. Valence-electron correlation has been incorporated by the method of configuration interaction. Values for different bond lengths are used to obtain vibrational and thermodynamic averages. For T=300 K, we found for Li2, α∥=361 and α⊥=141 (in a.u.) and for Li+2 , α∥=63 and α⊥=57. For Li−2 , the precision of the determined values does not warrant a thermodynamic averaging and we report only one pair of values for the bond length of 5.88 bohr, namely, α∥=700 and α⊥=334. Only one experimental polarizability is known, that for the isotropic component of Li2 at T=990 K; our calculated value agrees well with this value.
Size consistency in perturbation theories
Authors: Sheppard Maurice G.
Published: February 2003

Several versions of Rayleigh–Schrödinger (RS) and Brillouin–Wigner (BW) perturbation theories are tested for size consistency using a composite system consisting of N identical noninteracting subsystems. None of the BW versions and only two implementations of RS perturbation theory pass the test. The nondegenerate Brueckner–Goldstone expansion and the quasidegenerate theory of Brandow which employs a complete model space are size consistent. The incomplete model space version of Hose and Kaldor is not generally size consistent, except under special circumstances.
Direct observation of the transition to counterion condensation
Authors: Klein James W. , Ware B. R.
Published: February 2003

Direct observation of the transition to counterion condensation is demonstrated by measurement of the electrophoretic mobility of 6, 6-ionene, a polyelectrolyte of charge spacing 8.7 Å, under conditions of varying dielectric constant. In this way, the reduced charge density parameter ξ can be varied between 0.82 and 1.85. At precisely ξ=1, we observed a drop in the electrophoretic mobility of greater than a factor of 2. Independent viscosity experiments were used to verify that the polymer does not undergo a major conformational transition under these conditions. The reduction of electrophoretic mobility, presumably the result of the reduction of charge density by counterion condensation, is substantially greater in magnitude than current theories of counterion condensation theory would predict. It is suggested that the physical basis for the departure from theory is the fact that near ξ=1, the spacing of condensed counterions predicted by counterion condensation theory is greater than the Debye screening length.
Metal-deficient iron oxide clusters formed in the gas phase
Authors: Riley S. J. , Parks E. K. , Nieman G. C. , Pobo L. G. , Wexler S.
Published: February 2003

Molecular beams of oxidized iron clusters are produced by pulsed laser evaporation of iron followed by reaction of the resulting iron clusters with O2 in a continuous flow reactor. Nonstoichiometry of the iron oxide clusters is found, the composition rapidly approaching Fe0.9O as cluster size increases. The relation of these results to the similar nonstoichiometries found in bulk FeO is discussed.