bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave spectra and structures of the NNO–HCN, 15NNO–HCN, and NNO–DCN complexes
Authors: Pauley D. J. , Kukolich S. G.
Published: July 2002

A total of 60 a- and b-dipole rotational transitions were measured in the 4–18 GHz range for the NNO–HCN, 15NNO–HCN, and NNO–DCN bimolecular complexes using a pulsed-beam, Fourier transform microwave spectrometer. Spectroscopic constants (A−DK), B, C, DJ, DJK, eQqaa (N of HCN), and eQqbb (N of HCN) were obtained by fitting the observed transition frequencies with a first-order quadrupole coupling interaction Hamiltonian. The structure of the complex appears to be planar with NNO and NCH nearly parallel. It can be described with the distance Rcm between the center-of-masses of the monomer subunits, the angle θ between HCN and Rcm, and the angle φ between N2O and Rcm. A least-squares fit to the nine rotational constants to obtain the structure parameters Rcm, θ, and φ, produced three local minimia for bent structures with standard deviations of <25 MHz. A Kraitchman analysis was used to determine magnitudes of principal axes coordinates for the N of HCN, and the terminal N of NNO. The best nonlinear least-squares fit result (structure I, lowest standard deviation of the fit =7.2 MHz) produced the best match to the coordinates from the Kraitchman analysis. The spectroscopic constants B, C, and eQqaa were used in a second structural analysis to determine values for Rcm, θ, and φ. These results were compared with the above coordinates. The best least-squares fit structure parameters for the vibrationally averaged structure are Rcm =3.253(4) Å, θ=89.1(5.4)°, and φ =76.4(0.4)°. Comparisons are made with other similar weakly bound complexes.
Collisional excitation of CO2(0111) by hot hydrogen atoms: Alternating intensities in state-resolved vibrational, rotational, and translational energy transfer
Authors: Khan Farooq A. , Kreutz Thomas G. , O’Neill James A. , Wang Chen Xi , Flynn George W. , Weston Ralph E.
Published: July 2002

Time domain tunable diode laser absorption spectroscopy has been used to measure rotationally resolved transient absorption line shapes and nascent rotational populations for CO2 molecules excited into the (0111) vibrational state by collisions with translationally hot hydrogen atoms. The even rotational levels are more heavily populated than the odd levels, in agreement with propensity rules derived earlier by Alexander and Clary. The nascent populations and transient linewidths are interpreted in terms of a theoretical model that lends insight into the H–CO2 collision dynamics. The cross section for exciting (0111) is ∼0.23 times the cross section for exciting (0001), and ∼0.38 times the cross section for exciting (1000).
Nonvariational configuration interaction calculations by local scaling method
Authors: Koga Toshikatsu , Yamamoto Yoshiaki , Ludeña Eduardo V.
Published: July 2002

To first order, the Hartree–Fock one-electron density of a given state of an N-electron system is identical to the exact density. For this reason, an accurate wave function must fulfill the necessary condition of yielding a one-electron density similar to the Hartree–Fock density. For a given configuration interaction (CI) wave function with arbitrary parameters, we have used the local scaling method in order to construct a modified CI wave function which associates a one-electron density exactly the same as the Hartree–Fock density. The resultant nonvariational CI wave function is shown to have an energy comparable to that from the variational CI calculation for the ground state of the helium atom.
Time-resolved spectroscopy of 3-amino–s-tetrazine and 3-amino–6-methyl–s-tetrazine in a supersonic jet
Authors: Alfano Joseph C. , Martinez Selso J. , Levy Donald H.
Published: July 2002

Time-resolved measurements have been performed on seven vibronic levels of the S1 states of 3-amino-s-tetrazine (AT) and nine vibronic levels of 3-amino–6-methyl–s-tetrazine (AMT) ranging from 0 to 1907 cm−1 of excess vibrational energy. The resulting fluorescence lifetimes were found to range from 219 to 59 ns, and monotonically decreased with increasing excess energy. We have estimated the nonradiative rates and fluorescence quantum yields for these 16 levels by two different methods, which give reasonable agreement. These show that AT and AMT have nonradiative rates around 106–107 s−1, and very high fluorescence quantum yields, ranging from 0.07 to 0.29. This stands in contrast to s-tetrazine, which has a fluorescence lifetime of 800 ps, a nonradiative rate of 1.25×109s−1, and a fluoresence quantum yield of 0.000 94. This difference in the photophysical properties of AT and AMT relative to tetrazine is discussed in terms of the extensive work done on the photophysics and substituent effects of other azabenzenes, particularly pyridine.
Measurement of the distribution of bond angles in H2O+
Authors: Zajfman D. , Belkacem A. , Graber T. , Kanter E. P. , Mitchell R. E. , Naaman R. , Vager Z. , Zabransky B. J.
Published: July 2002

A quantitative analysis of the bending mode of H2O+ is made using the Coulomb Explosion technique. The full extent of the angular distribution is measured and is in good agreement with the previously measured bending frequency. The equilibrium value for the angle is extracted from the data with high precision and is in excellent agreement with theoretical predictions as well as spectroscopic measurements.
Microscopic free energy functional for polarization fluctuations: Generalization of Marcus–Felderhof expression
Authors: Chandra Amalendu , Bagchi Biman
Published: July 2002

A microscopic expression for the free energy functional for polarization fluctuations in a dipolar liquid in the presence of an external field is derived from the first principles by using the density functional theory. The microscopic expression is shown to reduce to the well known free energy expressions of Marcus and Felderhof in the appropriate limits. The microscopic free energy functional can be especially useful to describe those dynamical processes when intermolecular correlations are important.
Molecular monolayers of charge-transfer complexes: Protonation and aggregation studied by second harmonic generation
Authors: Xiao Xu-dong , Vogel Viola , Shen Y. R. , Marowsky G.
Published: July 2002

Second-order optical nonlinearities of molecules can be strongly affected by the environment. Protonation and aggregation of the dyes 4-amino-4′-nitrostilbene (NS) and hemicyanine (HC), are investigated by second harmonic generation from molecular monolayers floating on water. The observed second-order nonlinearity of such molecules in the form of either a pure monolayer or a monolayer diluted with stearic acid directly reflects the degree of protonation of the molecules. For NS and HC, the variation of the second-order molecular polarizability with protonation is opposite. It is demonstrated that the measured nonlinearity can be used to deduce the effective proton concentration in the surface region. The proton concentration close to a stearic acid monolayer floating on water, for example, is found to be ∼7 orders of magnitude larger than the bulk proton concentration when the latter is low. The effects of stearic acid in diluting a dye molecular monolayer on changing the environment and breaking dye aggregates are discussed.
Monte Carlo simulation of the three-dimensional dilute Widom model of microemulsions
Authors: Stauffer Dietrich , Ho J. S. , Sahimi Muhammad
Published: July 2002

Widom suggested a spin-1/2 Ising model for microemulsions. As a simple model of microemulsions in a porous medium such as sandstone, we simulate it on a randomly dilute simple-cubic lattice with sizes up to 252.3 Our results for the critical demixing temperature are somewhat similar to those of Velgakis in the square lattice.
The role of direct and substrate excitation in ultraviolet photolysis of phosgene on Pt(111)
Authors: Zhu X.-Y. , White J. M.
Published: July 2002

The photodissociation rate of phosgene (Cl2CO) adsorbed on Pt(111) has been measured as a function of photon energy at normal incidence and as a function of incident angle using p-polarized light. Compared to the gas phase, the wavelength dependence of the initial photolysis cross section on the surface is redshifted. The angular response to p-polarized light is wavelength dependent. Above 315 nm, the angular dependence correlates with calculated metal absorption. At 280 nm, the angular dependence is much too strong to be accounted for solely by substrate excitation. A combination of substrate and direct excitation is adequate. This is the first direct evidence, for monolayers on metals, that both direct and substrate excitation contribute to surface photochemistry but dominate at different wavelengths.
Hard shape potentials from rotational state-to-state inelastic cross sections: A possible route to inversion
Authors: Bosanac S. Danko , Murrell John N.
Published: July 2002

A two-parameter hard shape potential has been deduced which reproduces previously reported rotationally inelastic integral cross sections for He–HF collisions. A potential optimized to the 0→1 and 0→2 cross sections at a collision energy of 41.4 meV reproduces well other Δj=±1 and ±2 cross sections at this energy and at 81.9 meV. The potential is quite close to the 81.9 meV contour surface of a published He–HF potential. If this surface is used to define the hard shape potential then, although the Δj=±2 and Δj=±3 cross sections are improved, the Δj=±1 cross sections are approximately 50% too large.
Electron degradation and yields of initial products. VIII. Subexcitation electrons in H2 and D2 gases
Authors: Kimura Mineo , Krajcar-Bronić Ines , Inokuti Mitio
Published: July 2002

The moderation of subexcitation electrons in H2 and D2 is investigated by using the Spencer–Fano (SF) equation and the continuous-slowing-down approximation (CSDA). Cross-section data are adopted from the compilation by Buckman and Phelps [J. Chem. Phys. 82, 5001 (1985)]. Throughout, we focus on isotope effects, i.e., differences between H2 and D2, and consider electrons at energies appreciably higher than thermal energy. In summary, because vibrational and rotational excitation channels have lower thresholds in D2, subexcitation-electron behavior in D2 at energies below 0.6 eV shows different characteristics from that in H2. The moderation rate in H2 is larger than that in D2 by a factor of about 1.7. This difference is close to but not exactly the factor of 2 expected from an elementary estimate.
(2+1) resonance-enhanced multiphoton ionization–photoelectron spectroscopy of the OH radical
Authors: de Beer Esther , Koopmans M. P. , de Lange C. A. , Wang Yumin , Chupka W. A.
Published: July 2002

A (2+1) resonance-enhanced multiphoton ionization–photoelectron spectroscopy (REMPI-PES) study of the OH radical has been carried out in the two-photon energy region between 81 300 and 88 900 cm−1. Translationally and rotationally hot OH radicals are generated via photodissociation of hydrogen peroxide or formic acid. The known D 2Σ− (v′=0–2) and hitherto unobserved 3 2Σ−(v′=0) intermediate states in this region (at 81 815.8 and 87 643.7 cm−1 above the ground state) are shown to possess predominant Rydberg character. From the rotational structure in the REMPI spectrum physical parameters have been derived for these states.
The birefringence of shearing colloidal suspensions
Authors: Wagner Norman J.
Published: July 2002

An expression for the form birefringence of a shearing colloidal suspension is derived from the renormalization of Adriani and Gast [J. Chem. Phys. 91, 6282 (1990)]. Calculations based on recent predictions for the nonequilibrium microstructure of a shearing hard-sphere suspension are compared with previous measurements. The error in the predictions is in agreement with earlier comparisons of this structure against light scattering and rheological measurements.
Exponentially generated configuration interaction theory. Descriptions of excited, ionized, and electron attached states
Authors: Nakatsuji Hiroshi
Published: July 2002

A method of calculating wave functions of excited, ionized, and electron attached states on the basis of the correlated wave function for the ground state is given. This method, called excitator method, is a generalization of the SAC-CI (symmetry adapted cluster–configuration interaction) method. The excitator method is applied to the exponentially generated configuration interaction (EGCI) method previously proposed. The computational algorithm is described and test applications are performed for several lower states of the singlet, triplet, ionized, and anion states of CO and C2 at different internuclear distances. The accuracy of the proposed EGCI method is shown to be good relative to the full-CI energies for various states with different multiplicities, different numbers of electrons, different single and multi-electron processes, and different internuclear distances. Although the sizes of the present test calculations are small, these properties are important for studying dynamics and reactions involving different electronic states.
Rotational spectra of the ∑ bend states of Ar–H/DCl and the ∑ stretch of Ar–HCl
Authors: Chuang C. , Gutowsky H. S.
Published: July 2002

Rotational transitions of excited van der Waals states of Ar–H/DCl have been observed using the Balle–Flygare pulsed nozzle, Fourier transform, microwave spectrometer. Rotational constants and hyperfine interactions have been determined for the 35Cl/37Cl isotopes of both Ar–HCl and Ar–DCl in the lowest ∑ bending state. The HCl results are in good agreement with previous tunable far-infrared work [J. Chem. Phys. 89, 1268 (1988)]. For Ar–D35Cl and Ar–D37Cl, the rotational constants B and D and the quadrupole interaction χaa(Cl) were determined to be 1727.9887(1) MHz, 39.505(1) kHz, and −28.246(9) MHz, respectively, and 1686.4892(2) MHz, 39.167(4) kHz, and −22.344(10) MHz. χaa(D) for the Ar–D35Cl was found to be 132(7) kHz. Analysis of the 35Cl/37Cl isotope effects shows that the H(D) in H(D)Cl is pointed predominately away from the Ar. Measurement of the J=0→1 to J=4→5 transitions and their hyperfine structure for the ∑-stretch state of Ar–H35Cl give the rotational constants B, D, H, L, and the quadrupole interaction χaa(Cl) to be 1562.876(1) MHz, −67.2(1) kHz, −415(7) Hz, 1.6(1) Hz, and −20.774(7) MHz, respectively. The negative D centrifugal distortion constant and the large H and L constants suggest that this state is strongly perturbed by Coriolis interaction with the π bending state.
Simulation of the steric stabilization of polymer colloids by diblock copolymers
Authors: Rodrigues Klein , Mattice Wayne L.
Published: July 2002

The steric stabilization of polymer colloids by diblock copolymers is simulated on a 22×22×22 cubic lattice with periodic boundary conditions. In the systems described here, the lattice contains 20 chains, the volume fraction of polymer never exceeds 0.0376, and the number of beads in a chain never exceeds 20. The behavior is monitored by evaluation of the dimensionless ratios Mn/M0 and Mw/Mn, where M0 is the mass of an individual chain, and Mn and Mw are the number- and weight-average molecular weights of the particles in the system. By suitable variation in the pairwise interaction energies, one can cause the system to (1) establish a dynamic equilibrium, in which aggregates easily form and dissociate, (2) follow an irreversible path toward the formation of the largest possible aggregate, or (3) reach a long-lived metastable state in which the system prefers smaller aggregates than those that would exist at a true equilibrium. The metastable state arises from the steric stabilization of the dispersed state, as is shown by its characteristic response to the variation in the size of the soluble (stabilizing) block, at constant size of the insoluble block and constant interaction energies. The simulation also documents an interesting influence of the energy of the self-interaction of the insoluble block on the efficiency of the steric stabilization of the metastable state.
Stochastic model of intermode couplings in protein dynamics
Authors: Cartling Bo
Published: July 2002

For the purpose of bridging the short- and long-time regimes of protein dynamics, a stochastic description of the residual interactions beyond an extracted deterministic part of the interactions in a protein system is investigated. A protein dynamics trajectory is determined by integrating the classical equations of motion and projected onto a normal coordinate and an internal coordinate, serving as a reaction coordinate of a conformational transition. It is shown that the short-time fluctuations of the normal coordinate are well described by a Langevin equation of motion for Brownian motion, whereas the internal coordinate is a superposition of such stochastic variables. The stochastically treated interactions are underlying conformational transitions and these in turn contribute to the interactions. The stochastic description is useful for the determination of the rates of conformational transitions, which are elementary steps of the long-time conformational relaxations important to the functions of proteins.
Triple-resonance spectroscopy of the higher excited states of NO2. III. ‖Δv‖>1 autoionization and vibronic coupling
Authors: Campos Francis X. , Jiang Yanan , Grant Edward R.
Published: July 2002

Multiresonant, ionization-detected absorption spectra of autoionizing ns and nd Rydberg states converging to the (200) and (300) vibrational states of the NO+2 core show unexpectedly broad resonances for many states nominally requiring Δv=−2 and −3 vibrational transitions in the core to energetically achieve electron ejection. The resonances observed do not show evidence of significant predissociation, implying that the autoionization process is primarily vibrational. Perturbed line shapes and the presence of many resonances not clearly associated with the assigned sσ, dσ, and dπ series indicate extensive vibronic coupling with other Rydberg vibrational manifolds. A particularly broad feature at a total energy of 78 720 cm−1 appears in spectra scanned both from the (200) and (300) levels of the 3pσ state. This energy falls just below the threshold for forming NO+2 in the vibrational state (100), and the broad features that appear at this point in the higher vibrational manifolds can be identified as components of a complex resonance reflecting a coupling of the (100), (200), and (300) manifolds with the (000) continuum. We suggest that such vibronic coupling accelerates autoionization throughout the spectrum and that analysis in terms of fixed values of Δv is not possible.
Keto-enol tautomeric equilibrium of acetylacetone in trifluoromethane near the critical temperature
Authors: Akao K. , Yoshimura Y.
Published: July 2002

The keto-enol tautomeric equilibrium of acetylacetone in trifluoromethane were studied at 300±0.5 K (1 K above the critical temperature) from 130 kg m−3 to 800 kg m−3 by using FT–NMR. No anomalous behavior near the critical point has been found within the experimental error. The equilibrium constant decreases rapidly in the low density region (<200 kg m−3) and the decreasing rate reduces with increasing the density of solvent. The density dependence is interpreted by the hydrogen bonding between trifluoromethane and acetylacetone.
Order–disorder transitions in quasi-two-dimensional argon solvent clusters
Authors: Bösiger Jürg , Bombach Rolf , Leutwyler Samuel
Published: July 2002

Structures and order–disorder transitions of the rare-gas solvent clusters carbazole⋅Arn were studied for n=1–7 by molecular dynamics and Monte Carlo simulation methods. This study was motivated by the investigation of these clusters by size-specific electronic spectroscopy. Cluster structures corresponding to absolute and local energy minima were obtained by molecular-dynamics slow cooling and annealing. For n=1–3, single minimum-energy structures of Cs symmetry were found, with all n atoms on the same side of the molecular substrate. For n=4–7, the number of energetically low-lying monolayer isomers rises very rapidly with n. Orientational ordering of the adcluster by the substrate is unimportant for n≥4. The isomers for n≥4 differ by (i) rotational/translational displacements of the cluster relative to the substrate, (ii) promotion of atoms to the second solvent layer, and (iii) adsorption of atoms on the second side of the substrate. Order–disorder transitions of the monolayer solvent clusters were studied by MC methods as a function of temperature. Four different quasi-two-dimensional order–disorder transitions were found: the racemization and surface-decoupling transitions reflect the loss of cluster–substrate orientational correlation, while the cluster rigid–fluxional and melting transitions derive from the loss of intracluster bond-orientational order, and increase in bond-length fluctuations. Analogies to order–disorder phase transitions in two-dimensional rare-gas films are discussed.
Rotational analysis of the nonthermal NO(A 2Σ+, v′=0) distribution observed in the N2(A 3Σ+u, v′=0)+NO(X 2Π, v″=0) energy transfer reaction
Authors: Thomas Joseph M. , Katayama Daniel H.
Published: July 2002

A rapidly pumped discharge-flow reactor was constructed to characterize the N2(A 3Σ+u,v′)+NO(X 2Π, v″=0) energy transfer (ET) reaction. Emission spectra of the NO γ bands from the product NO A 2Σ state formed in the title reaction were collected with a 2.2 m vacuum-ultraviolet spectrograph monochromator utilizing both photographic and photoelectric techniques. The rotational structure of the γ bands resulting from the title reaction is resolved with a spectral resolution of Δλ∼0.1 Å. The product NO(A,v′) emission spectra were measured as a function of total pressure (∼0.8≤pTOTAL≤∼3.0 Torr) and initial N2(A,v′) population distribution at 298 K. The product NO(A,v′,N′) rotational distributions yield temperatures much higher than room temperature (>1600 K) and are discussed in detail. Vibrational level specific bimolecular rate constants kv′ ’s for the N2(A,4≤v′≤6)+NO reaction were measured using N2(B 3Πg–A 3Σ+u) laser-excited fluorescence detection with a fixed reaction time. The kv′ ’s are (9.5±1.0), (11.3±1.2), and (11.2±1.1)×10−11 cm3 molecule−1 s−1 for v′=4, 5, and 6, respectively. A comparison with previous measurements is presented.
Lowest energy excited singlet states of isomers of alkyl substituted hexatrienes
Authors: Buma Wybren Jan , Kohler Bryan E. , Song Kyuseok
Published: July 2002

Vibrationally resolved S0→S1 excitation spectra for the alkyl substituted linear polyenes heptatriene, octatriene, and decatriene seeded into a supersonic He expansion have been measured by resonance enhanced multiphoton ionization spectroscopy. As is the case for the parent compound hexatriene, the lowest energy excited singlet state in all of these molecules is the 2 1Ag state. The measurement of S0→S1 excitation spectra of three of the four double bond isomers of heptatriene gives a detailed picture of the dependence of the electronic structure of the 2 1Ag state on molecular conformation. The three isomers for which spectra are presented have the cis configuration at either the central or the alkyl substituted double bond, or both. For the case of the mono cis species with the cis configuration at the alkyl substituted double bond the spectra show the presence of two single bond conformers. Because of the increased number of distinguishable isomers and conformers for octatriene and decatriene we were unable to unambiguously separate the observed spectra of these molecules into contributions from single specific molecular conformations. However, the increased excitation intensity in the low frequency region relative to that in the C–C and C=C stretching region for octatriene and decatriene as compared to heptatriene suggests that vibrational relaxation is enhanced in the more complex molecules. In the case of unsubstituted hexatriene, previously reported spectra show that the 2 1Ag state has lower symmetry than does the ground state (most likely due to nonplanarity at the terminal carbon atoms). There is no evidence for an analogous distortion in the excitation spectra measured for the alkyl substituted hexatrienes.
The effects of vibrational mode, spin–orbit state, and collision energy on collision-induced dissociation and predissociation of OCS+
Authors: Yang Baorui , Chiu Yu-hui , Fu Hunghsin , Anderson Scott L.
Published: July 2002

We report the first study of the effects of mode specific vibrational excitation on collision-induced dissociation of a polyatomic cation. Resonance-enhanced multiphoton ionization was used to produce OCS+ ions with variable excitation in each of the three vibrational modes, in combination with either spin–orbit electronic state. Cross sections for fragmentation of the state-selected ions in collision with Xe and Ar atoms were measured over the collision energy range from 0.5 to 9.0 eV, using a guided ion beam tandem mass spectrometer. Both spin-allowed and spin-forbidden channels are observed for both collision partners, and the cross sections in both cases are enhanced by collision energy and all modes of vibrational excitation. Vibration is more effective than collision energy, but the effect is nonmode specific. The absolute magnitude of the dissociation cross sections and the relative vibrational effects are bigger for collisions with Xe than for Ar. The spin–orbit state of the primary ion has no effect on dissociation of ground vibrational state OCS+, but there appears to be some synergy between vibrational and spin–orbit excitation. The results are discussed in view of the electronic structure of OCS+ and possible scattering mechanisms.
Energy dependence of the reaction of CH+2 with HCl
Authors: Glosik J. , Freysinger W. , Lindinger W.
Published: July 2002

The energy dependence of the reaction of CH+2 with HCl has been investigated using a selected ion flow drift tube (SIFDT) in the center-of-mass kinetic energy (KEc.m.) range from 0.04–2 eV. The reaction rate coefficient is fast at near thermal energies (k∼1.5×10−9 cm3 s−1) but decreases dramatically with increasing KEc.m. to k<1×10−10 cm3 s−1 at 2 eV, which is quite uncommon for a thermally fast ion–molecule reaction.
A classical, simulated, microscopic Poisson process
Authors: Romiszowski Piotr , Yaris Robert
Published: July 2002

It is shown that both the full simulation and the generalized Langevin dynamics simulation π flips in a two-dimensional array of interacting benzene rings [P. Romiszowski and R. Yaris, J. Chem. Phys. XX, xxxx (1991)] satisfy Poisson statistics.
Resonance enhanced two-photon dissociation of H2 by the X→(E
F+G
K+I ) transition via intermediate B,C states
Authors: Banerjee Sima , Chakrabarti M. K. , Bhattacharyya S. S. , Saha Samir
Published: July 2002

The generalized resonance enhanced two-photon dissociation (RETPD) cross sections of H2 are calculated for linear parallel polarizations of the two photon fields. The reduced density operator formalism is used to study the wavelength and quantum number dependences for the transitions X 1Σ+g (vg=0, Jg=0–4) →vuv B 1Σ+u (C 1Πu) [vi=0,3, Ji=0(1)–3] →uv/visible [(EF+GK)1 Σ+g +I 1Πg, Ef, Jf]. By resonant absorption of the first photon an aligned population in the intermediate B(C) is created which is then dissociated by the second photon. The wavelength is so chosen that ionization from the resonant intermediate state is energetically forbidden. The contribution of the EF state to the total cross section is found to be negligible. The relative contribution of the GK and I states varies sharply with wavelength of the second photon and the resonant intermediate state. For both B and C states, dissociation through the I state is more prominent over a narrow range of wavelengths far from the dissociation threshold when the vibrational quantum number (vi) is large. For small vi the contribution of the I state is less. Due to the presence of a barrier above the dissociation threshold in the I state potential, narrow shape resonances occur. The cross sections at these shape resonances are a few orders of magnitude higher than the background. The detailed line shapes at these resonances have been presented for all the rotational quantum numbers considered for vi=0 and 3 of the B and C states.
Dissociative single and double photoionization of CH3F in the region 20–110 eV studied by mass spectrometry and the photoion–photoion coincidence method
Authors: Masuoka Toshio , Koyano Inosuke
Published: July 2002

Dissociative single and double photoionization of methyl fluoride (CH3F) has been studied in the photon energy region of 20–110 eV by use of synchrotron radiation, a time-of-flight (TOF) mass spectrometer, and the photoion–photoion coincidence (PIPICO) method. The TOF mass spectrometer facilitates relatively efficient extraction of energetic ions, which is essential for quantitative measurements. Photoion branching ratios are reported for the observed 11 singly charged ions, H+, H+2, CH+n (n=0–3), F+, CHnF+ (n=0–3). Stable CH3F2+ is not observed in all of the energy region studied in a μs time scale. The double photoionization threshold is measured to be 35.0±0.5 eV. PIPICO spectra measured at higher photon energies show the following five types of dissociation processes:(1) CH3F2+→H++CHnF+ (n=0–2), (2) H+2+CHnF+ (n=0–1), (3) H++CH+n (n=0–2), (4) H+2+CH+, (5) H++F+, with ten total dissociation channels. These processes are characteristic in regard to bond breakage involved, whether a rearrangement reaction occurs, and which atom and/or molecule is ionized, and are correlated with the electronic states of CH3F2+ calculated by the Green’s-function method [C. -M. Liegener, Chem. Phys. 151, 83 (1988)]. PIPICO branching ratios for these channels are also reported as a function of the photon energy.
Electron spin echo envelope modulation spectroscopy on orientationally disordered systems: Line shape singularities in S=1/2, I=1/2 spin systems
Authors: Reijerse E. J. , Dikanov S. A.
Published: July 2002

The electron spin echo envelope modulation of S=1/2, I=1/2 spin systems is analyzed for orientationally disordered systems. Analytical expressions are derived for the position of the combination frequencies which can be observed in primary (two-pulse) ESEEM experiments. The conditions for which line shape singularities of the basic and combination frequencies emerge are conveniently mapped in a standard graph. Using this graph it is demonstrated that for virtually all combinations of hyperfine parameters the ESEEM spectra will contain interpretable features. Especially the application of multifrequency techniques (i.e., variation of the nuclear Larmor frequency) will enable full use of the line shape singularities of the combination frequencies.
Thermal diffuse scattering from colloidal crystals
Authors: Rundquist Paul A. , Kesavamoorthy R. , Jagannathan S. , Asher Sanford A.
Published: July 2002

Measurement of the Bragg diffraction and thermal diffuse scattering from colloidal crystals consisting of aqueous suspensions of polystyrene spheres with and without strongly absorbing dye molecules show that dynamical diffraction theory is valid even for absorbing colloidal crystals. In addition, we show that thermal diffuse scattering from colloidal crystals may be described by the simple Debye model. We determine the effective penetration depth of the incident electric field for cases where the Bragg condition is satisfied.
Investigation of photoinduced molecular switching in a single monolayer by a displacement-current-measuring technique
Authors: Iwamoto Mitsumasa , Majima Yutaka , Naruse Haruhiko , Noguchi Tetsuya , Fuwa Hiromasa
Published: July 2002

The optical molecular switching in single monolayers containing azobenzene derivatives at the air water interface due to photoinduced cis-trans isomerization was detected by using a displacement-current-measuring technique. The reversible displacement current generation was found to be sustained by the alternative applications of ultraviolet light and visible light, whereas, the current generation was never initiated by the successive irradiation of ultravilolet or visible light. In order to clarify the physical mechanism relevant to the displacement current generation, the optical molecular switching in single monolayers deposited on solid substrates was also examined by the displacement-current-measuring technique using a (indium tin oxide)/monolayer/air-gap/(indium tin oxide) structure. As a result, the displacement-current generation from single monolayers deposited on the solid substrates was found to be initiated in a similar manner as that from monolayers formed on the water surface. Finally, we concluded that the technique developed here will be used for a better understanding of the relationship between the structure and function of monolayers and will also be used in future molecular electronic technologies.
Opto-thermal spectroscopy of the benzene 4←0 C–H stretch overtone
Authors: Scotoni Mario , Leonardi Cristina , Bassi Davide
Published: July 2002

The 4←0 C–H stretching overtone of benzene has been measured in a supersonic molecular beam by means of the opto-thermal technique. Several vibrational transitions contribute to the absorption spectrum in the 11 400–11 550 cm−1 region. The upper limit for the homogeneous linewidth is found ≊17 cm−1.
On the distribution of reactive barriers in disordered materials
Authors: Schellenberg P. , Friedrich J. , Daltrozzo E.
Published: July 2002

We investigated the hole-burning photoreaction of a dye complex in alcohol glass which undergoes both photochemical and photophysical transformations. By measuring separately the disappearance of the photoproduct at the respective wavelength ranges under thermal cycling conditions, we found that the photochemically transformed species recovered according to a Gaussian distribution of barrier heights, whereas the photophysically transformed species recovered in accordance with a 1/(V)1/2 distribution. It is suggested that this behavior is rather general and is intimately related to the nature of the phototransformation process.
Structure-constrained anionic polymerization in hydrogen-bonded acrylonitrile clusters
Authors: Tsukuda Tatsuya , Kondow Tamotsu
Published: July 2002

Electron attachment processes involving acrylonitrile (AN) clusters and high-Rydberg Kr atoms (Kr**) were investigated by mass spectrometry. A particular abundance of cluster fragment anions, [(AN)n−H]−, [(AN)n−H2]−, and [(AN)n−H2−HCN]− with N=3,6,9,..., was explained by formation of a trimeric core ion xolvated with stable AN trimer units as a result of anionic polymerization of three AN molecules in a ring geometry in the parent cluster.
A C≡C stretching vibration of the C6H (hexatriynyl) radical in Ar at 10 K
Authors: Doyle T. J. , Shen L. N. , Rittby C. M. L. , Graham W. R. M.
Published: July 2002

A study of the Fourier transform infrared (FTIR) spectrum of the products of the vacuum ultraviolet (VUV) photolysis of acetylene and 1,3-butadiene trapped in solid Ar has resulted in the identification of a vibration of the C6H (hexatriynyl) radical at 1953.4 cm−1. The spectra of various D and 13C isotopomers of C6H produced from isotopically substituted precursors have been observed. The complex, overlapping spectra resulting from partial 13C substitution have been fitted using a force constant adjustment calculation and support the assignment of the 1953.4 cm−1 absorption to a C≡C stretching fundamental of linear C6H. The results of an ROHF/6-31G* ab initio calculation of the vibrational frequencies for the fundamentals of linear C6H are also reported.
Low-frequency Raman spectra of guanosine and nucleotides in ordered states: Origin of the lowest-frequency mode
Authors: Urabe Hisako , Sugawara Yoko , Tsukakoshi Motowo , Kasuya Takahiro
Published: July 2002

Raman spectra of self-associates of guanosine were investigated in the 5–200 cm−1 region together with crystals of guanosine⋅2H2O, Na2⋅5′–UMP⋅7H2O, Na2⋅5′–GMP⋅7H2O, Na2⋅5′–CMP⋅8H2O, Na2⋅5′–dGMP⋅4H2O, and Na2⋅ATP⋅3H2O, to clarify the origin of the lowest Raman active mode of deoxyribonucleic nucleic acid (DNA). When the bases stack well to form a column, as in guanosine self-associates and crystals of guanosine and adenosine triphosphate (ATP), the spectral patterns are similar to that of DNA. The lowest-frequency bands are sharp and isolated from other bands. The result suggests that the origin of the lowest-frequency mode of DNA is assigned to the motion of bases stacked in a column. Guanosine has no phosphate groups, and ATP has no hydrogen bonds between bases in the crystal state. Therefore, neither hydrogen bonds between bases nor phosphate groups are necessary for the existence of this mode.
Vibrational spectroscopy of Xe+2 via pulsed field ionization
Authors: Tonkyn Russell G. , White Michael G.
Published: July 2002

Delayed, pulsed field ionization of extremely high-n Rydberg states has been used in combination with a high-resolution vacuum ultraviolet radiation source to measure the vibrationally resolved spectra of the first three bound states of Xe+2. For the ground state of the ion (A 2Σ+u), a long progression beginning at v+=56 was observed which included isotopically resolved energy levels. The spectroscopic parameters obtained from a fit of the data to anharmonic oscillator energy levels are reported. The resulting Xe2 ionization potential is somewhat higher than previously reported. Several vibrations of the first excited state (B 2Π(3/2)g) were observed near 97 000 cm−1. An absolute vibrational assignment was not possible due to an unusual alternation of intensities. Nevertheless, a lower bound on the binding energy and an estimated vibrational frequency are reported. For the C 2Π(3/2)u state, the v+=0–2 vibrational levels were observed with an intensity distribution consistent with the weakly bound nature of this state. The derived binding energy and vibrational frequency for the C 2Π(3/2)u state are reported.
Bicontinuous phase in a lattice model for surfactant mixtures
Authors: Ciach A. , Ho/ye J. S. , Stell G.
Published: July 2002

A lattice counterpart of a bicontinuous phase is found in a three-dimensional lattice model of ternary surfactant mixtures. The structure of this phase is determined and discussed. The region of stability of the new phase in the parameter space is found at zero temperature. Also determined are the boundary of stability of the disordered phase, the water–water structure factor in this phase, and the disorder line.
Zero kinetic energy electron spectroscopy of molecules: Rotational symmetry selection rules and intensities
Authors: Müller-Dethlefs Klaus
Published: July 2002

The rotationally resolved ‘‘zero kinetic energy (ZEKE)’’ photoelectron spectra for linear and planar molecules are interpreted as transitions into highly excited Rydberg states corresponding to Hund’s coupling case (d). The general case (d) is described for planar and linear molecules. The observed ZEKE transitions can be understood in terms of near-symmetry selection rules for the one-electron states involved. The proposed model consists of two steps: photon absorption leads to a state where the angular momentum of the excited electron is still coupled to the figure axis (the internuclear axis for diatomics and the highest symmetry axis for planar molecules). For planar molecules this leads to a selection rule for the projection quantum number K. The second step is the decoupling of the excited electron from the figure axis and its recoupling to the total angular momentum vector of the ion core. The decoupling process is assumed to occur adiabatically and hence with preservation of the electronic symmetry of the excited electron state. This leads to a selection rule for the total angular momentum N and explains the occurrence of only a single peak with v+2=1, N+=4, K+=3 in the ZEKE spectrum of the B̃ state of ortho-NH3 with v2=2, JB=3, KB=1. Also, analytical formulas are presented for the intensities of 1+1 and 2+1 photoionization processes including the alignment of the intermediate state.
Asymmetry of the coexistence curve in binary systems. Size effect
Authors: Damay Pierre , Leclercq Françoise
Published: July 2002

The asymmetry of the coexistence curve in binary systems is either due to a difference of size between the components or to mixed fields as seen in the liquid–vapor case. The size effect may be corrected if the proper order parameter is used. Taking advantage of the many formal possibilities of choosing the order parameter in these systems, we show that the size effect may be exactly corrected for asymmetric mean field models. Making the same type of calculation on real systems with critical indices, we found that the same type of correction is possible. In these cases, there were no mixed field effects detected (t1−α divergence of the diameter), at least in a reduced temperature range t<0.02. The details of the calculation are reported only for acetonitrile–cyclohexane system which is one of the best sets of data found in literature. A new computing method to determine the parameters of the coexistence curve is also presented. The shape of the coexistence curve, including extended scaling correction, as well as the curvature of the diameter and the critical constants Tc and xc may be obtained from a single fit; we show the interest of analyzing, in detail, the coupling between all the parameters.
Phase stability of a simple fluid model mixture
Authors: Malescio G.
Published: July 2002

The dependence on the interparticle potential of the spinodal line of a model binary mixture of simple fluids is studied making use of the hypernetted-chain equation. The behavior of the isothermal and osmotic compressibilities in the approach to the unstable region is also investigated. According to the results the mixture can exhibit a liquid–gas as well as a consolute phase transition.
Angular momentum conserving statistical method for rate constant calculations. Application to N+(3P)+H2(1Σ+g) →NH+(2Π)+H(2S)
Authors: Nyman Gunnar
Published: July 2002

A quasiclassical Monte Carlo simulation procedure for calculating bimolecular rate constants is presented and applied to the reaction N+(3P)+H2(1Σ+g) →NH+(2Π)+H(2S). Effective potential theory is used to generate a spherically symmetric potential energy surface from an ab initio based global potential energy surface due to Wilhelmsson and Nyman. A complex is formed if the reactants can reach the strong coupling region. Based on the available phase space, a microcanonical procedure conserving total angular momentum is used to determine into which channel the complex decomposes. Complex formation cross sections, branching ratios, and reaction cross sections are presented. Good agreement with previous trajectory calculations is found.
A lattice model description of amphiphilic mixtures. I. Equilibrium properties
Authors: Gunn John R. , Dawson K. A.
Published: July 2002

A three-component lattice model with unit-vector orientations at the lattice sites is presented. The model describes ternary mixtures of oil, water, and amphiphile, and in particular the microemulsion phase. The phase diagram of the model is derived using mean-field theory and simulation. It is shown that the results of Monte Carlo simulations of sufficiently large systems show remarkable agreement with experiment. In particular, the present model reproduces the mesoscopic order of the microemulsion phase. The structure of the microemulsion is understood in terms of the liquid-crystalline phases adjacent to it on the phase diagram and the nature of the phase transitions that occur between them. The behavior of the system when the ratio of oil to water is changed is investigated and the percolation threshold is described. A method for carrying out dynamical simulations is discussed.
Direct atomic-orbital-based time-dependent Hartree–Fock calculations of frequency-dependent polarizabilities
Authors: Feyereisen Martin , Nichols Jeff , Oddershede Jens , Simons Jack
Published: July 2002

We have formulated and implemented a direct atomic integral driven method for the calculation of frequency-dependent response properties at the self-consistent-field level. By avoiding the integral transformation step, as well as the storing and retrieving of atomic-orbital-based integrals, we are able to use large basis sets. The practicality of the approach is illustrated and calibrated by performing a series of calculations on cyclopropenone employing up to 232 basis orbitals. We examined the scaling of the dipole polarizability (α) with the size of the system for paranitroaniline and its dimer. Except for a small positive enhancement of the component along the molecular axis, we find little effect of size on α for this system. However, if the –NN– linkage of the dimer is replaced by a –CC– linkage, thus more effectively extending the π-orbital conjugation by making the dimer planar, we find a large, frequency-dependent increase in the polarizability relative to twice that of the monomer (factors varying from 3 to 18, depending on frequency). This makes the –CC– linked polymer a potential candidate for achieving nonlinear chain length dependence of properties that depend on α.
Microscopic simulation of a chemical instability
Authors: Mareschal M. , De Wit A.
Published: July 2002

We present a direct simulation of a reacting dilute mixture, for which the corresponding rate equations for the concentrations display a limit cycle behavior when the system is forced out of equilibrium by an external mass current. The time dependent concentrations computed in the simulation compare well with the solutions of the macroscopic rate equations. We also find agreement between the microscopic simulations results and a Langevin description for what concerns the concentration fluctuations in the system below and beyond the bifurcation point.
Measurement of static polarizabilities on C1H8 and C1D8
Authors: Heitz S. , Weidauer D. , Rosenow B. , Hese A.
Published: July 2002

Laser Stark spectroscopy has been performed on C10H8 and C10D8 molecules in a collimated, seeded supersonic beam. The Stark splittings and shifts of many rotational lines in the 810 band of the A 1B3u←X 1Ag transition of naphthalene–H8 and –D8 could be measured in a static homogeneous electric field. The determined polarizability anisotropies of the A 1B3u state of C10H8 are P′aa−Pbb=9.9(2) Å3 and P′bb−Pcc=6.4(2) Å3, whereas the X 1Ag ground state results are P″aa−P″bb=6.2(2) Å3 and P″bb−P″cc=7.2(2) Å3. The change of the average polarizability between these states was determined to ΔP=P′−P″=1.6(1) Å3. The corresponding values of C10D8 were found to be P′aa−P′bb=10.1(2) Å3, P′bb−P′cc=6.2(2) Å3, P″aa−P″bb=6.1(2) Å3, P″bb−P″cc=7.3(2) Å3 and ΔP=P′−P″=1.6(1) Å3.
A Born–Green–Yvon integral equation treatment of incompressible lattice mixtures
Authors: Lipson J. E. G.
Published: July 2002

The case of a binary incompressible lattice mixture is treated using the Born–Green–Yvon (BGY) integral equation approach with the Kirkwood superposition approximation. Analytic expressions for ΔEmix and ΔAmix are derived without invoking the random mixing approximation. The BGY predictions for ΔEmix and ΔS(nc), the noncombinatorial contribution to the entropy of mixing, are compared with those of the lattice cluster (LC) theory of Freed and co-workers for mixtures in which at least one of the two components is a polymer.