bluuebunny/crossref_metadata_2025 huggingface dataset:
Far from equilibrium phase transitions in competitive adsorption: Dimension and closure approximation
Authors: Córdoba A. , Lemos M. C.
Published: July 2002

Competitive adsorption of two species on a square lattice is considered, starting from a master equation. A doublet closure approximation is applied to obtain the kinetic equations; a Monte Carlo simulation is also performed. Unlike the results for a linear chain, multistability results, and thus there are far from equilibrium phase transitions. In this problem, the importance of the dimension of the system and the way the spatial correlations are treated in the approximation used is made clear.
Kinetics for the quenching and relaxation of boron oxide
Authors: Hinchen J. J.
Published: July 2002

Laser induced fluorescence studies are described in this paper for the kinetics of BO(A 2Π) quenching, vibrational and rotational relaxation, and for the radiative lifetime of the A 2Π state. Measured electronic quenching rates with several gases are presented. The rates are reasonably slow with He, Ar, N2, N2O, and CF4, as the collisional partners. The gases O2, F2, NO, and NO2 show a very fast quenching of the A 2Π state, probably as a consequence of chemical reaction with BO along with collisional energy transfer. Vibrational relaxation is generally slow compared to quenching except with CF4 where the collisional partner has a vibrational structure in near resonance with that of BO(A 2Π). Rotational relaxation in BO(A) by He, NO, O2, CF4, and SF6 was found to be fast, as would be expected in a molecule with closely spaced energy levels. The effects on the BO spectra of vibrational transfer with CF4 are shown. Quenching rates for BO(A 2Π) v′=0 and 2 measured over a series of helium pressure extrapolate to values of 1.75 and 1.37 μs for the radiative lifetimes of the v′=0 and 2 levels.
On the multipolar character of some 2S+1L
J transitions in Nd2Mg3(NO3)12⋅24H2O: An optical study and semiempirical crystal field analysis
Authors: Görller-Walrand C. , Fluyt L. , D’Olieslager J. , Gos M. P. , Hendrickx I.
Published: July 2002

The multipolar character of transitions in lanthanide double nitrates is stressed, thereby demonstrating the effect of small deviations from an icosahedral symmetry on the fluorescence and absorption properties. Polarized absorption spectra of Nd3+ in Nd2Mg3(NO3)12⋅24H2O have been recorded between 11 600 and 28 900 cm−1 at 77 and at 4.2 K. Supplementary data were obtained by fluorescence measurements. The energy level scheme was obtained by diagonalizing a Hamiltonian describing the free ion parameters including two and three body configuration interactions, as well as the crystal field operator. Calculations were performed using the complete basis of 364‖αSLJM〉 kets of the 4f3 configuration of Nd3+. A set of free ion and crystal field parameters have been calculated with an rms deviation of 35 cm−1 with respect to 41 experimentally determined levels. The composition of the wave functions has further been checked by a calculation of the intensities for both magnetic and induced electric dipole transitions. This last mechanism, described by the Judd–Ofelt theory, introduces a set of phenomenological Bλkq parameters. The calculations of the dipole strength were done in order to underline the multipolar character of the crystal field lines of some 2S+1LJ multiplets in the visible region of the spectrum as was also noticed on the base of the selection rules. This work gives the first intensity calculation on lanthanides in double nitrates. These compounds are involved in many ionophoric complexes of lanthanides [J.-C. G. Bünzli, Handbook Phys. Chem. Rare Earths 9, 321 (1987)].
High resolution Fourier transform emission spectrum of the (2) 3Πg–A 3Πu transition of the B2 molecule
Authors: Brazier C. R. , Carrick Patrick G.
Published: July 2002

The (2) 3Πg–A 3Πu system of B2 has been characterized for the first time. A full rotational analysis of the 0–0, 0–1, 1–0, and 1–3 bands has been performed. The molecular parameters are compared with recent high level theoretical calculations and show good agreement. An extensive perturbation of the upper (2) 3Πg state by the (1) 3Πg state was observed. This was most clearly evident for v=0 of the (2) 3Πg state for the 10B11B isotopomer, which is split into two components by the interaction with v=7 of (1) 3Πg. The perturbation interaction exhibited a significant rotational dependence, which was interpreted as arising from a change in the Franck–Condon factors as the rotational contribution to the potential changed. A weak local perturbation was observed in v=1 of the A 3Πu state from a crossing with v=2 of the a 5Σ−u state.
Photodissociation dynamics of a hydrogen molecule via superexcited states as studied through the angular-momentum population of an excited hydrogen atom
Authors: Terazawa Norihisa , Kouchi Noriyuki , Ukai Masatoshi , Kameta Kosei , Hatano Yoshihiko , Ito Kenji
Published: July 2002

Photodissociation dynamics of a hydrogen molecule via vibrationally excited superexcited states has been studied through the angular-momentum population of an excited hydrogen atom with the principal quantum number 3. The population shows a strong dependence on the incident photon wavelength in the longer wavelength region and a weak dependence in the shorter wavelength region. The population seems to converge to the equal partition as the incident photon wavelength becomes shorter. It is shown that the Rosen–Zener-type transition between the three states, not two states, at a large internuclear distance plays an important role in the dissociation dynamics. A close multilevel problem should be remarked even for a simple system such as a hydrogen molecule.
Quantum dynamical studies for photodissociation of H2O2 at 248 and 266 nm
Authors: Cai Zheng T. , Zhang Dong H. , Zhang John Z. H.
Published: July 2002

A new quantum mechanical study on UV photodissociation of H2O2 at 248 and 266 nm using a 2D fit to the Schinke–Staemmler’s (SS) potential energy surface (PES) [Chem. Phys. Lett. 145, 486 (1988)] is reported. The rotational distributions of the product OH on both the Ã and B̃ surfaces are found to be considerably hotter than those obtained in a previous quantum study [J. Chem. Phys. 98, 6276 (1993)] using an empirical PES with a very weak dependence on the torsional angle φ. The new calculation shows that the rotation distributions in both the Ã and B̃ states are Gaussianlike with a maximum at j=8 on the Ã surface and at j=9 on the B̃ surface at 248 nm. Similar distributions are found at 266 nm, but with the maximum shifting lower by approximately one quanta in both the Ã and B̃ states. The dissociation preferentially produces OH rotations with a high j1∼j2 correlation. These conclusions are in excellent agreement with the classical calculation of Schinke–Staemmler at 193 nm photolysis. Although the j distribution (rotation of OH) is similar on both surfaces, the j12(j↘12=j↘1+j↘2) distribution, which reflects the vector correlation of j↘1 and j↘2, is quite different on two surfaces. Our calculation shows that the Ã surface gives rise to more bending excitation than the B̃ surface, reflected by a hotter j12 distribution on the Ã surface. The Ã and B̃ state branching ratio of H2O2 is also evaluated at 248 and 266 nm photolysis.
A theoretical description of the b 3Π→a 3Σ+ transition of NO+
Authors: Hutter Stephan J. , Hess Bernd A. , Marian Christel M. , Samzow Reinhard
Published: July 2002

Using multireference configuration interaction methods, the potential energy curves of the ground and several low-lying excited states of the NO+ ion were calculated. We obtain spectroscopic parameters in good agreement with existing experimental data. In order to establish a one-to-one correspondence between the experimentally known term energies of the recently detected b 3Π→a 3Σ+ transition [Huber and Vervloet, J. Mol. Spectrosc. 146, 188 (1991)] and ab initio data, it is necessary to include explicitly spin–orbit and rotational coupling. Spin–orbit matrix elements were evaluated using the microscopic Breit–Pauli Hamiltonian. The off-diagonal coupling matrix elements 〈b 3Π‖HSO‖a 3Σ+〉 and 〈b 3Π‖L‖a 3Σ+〉 are found to depend strongly on the internuclear separation. The calculated vibrationally averaged fine structure parameter of the b 3Π state for v=0 (67.21 cm−1) is found to be in very good agreement with the value determined experimentally (69.699 cm−1).
Electron propagator theory of ZnCH3, Zn(CH3)2, and related ions
Authors: Zakrzewski V. G. , Ortiz J. V.
Published: July 2002

Electron propagator calculations on electron affinities of ZnCH+3 and ionization energies of ZnCH−3 provide ZnCH3 excitation energies. Excited states involving promotion of an electron from one Zn-centered hybrid to another, as well as Zn–C bond to Zn-centered hybrid charge-transfer states, are obtained. The lowest excited state, which is of the former type with an unpaired electron in a Zn-centered, p-like hybrid orbital, lies 2.98 eV above the ground state, in close agreement with spectroscopic results. A charge-transfer state, where two electrons reside in a Zn-centered, s-like hybrid orbital and an unpaired electron is described by a Zn–C bond orbital, is 4.48 eV above the ground state. Additional excited states also have been calculated. Vertical ionization energies of ZnCH−3, as well as the vertical ionization energy and several vertical electron affinities of ZnCH+3, have been determined. ZnCH3’s adiabatic ionization energy, 7.06 eV, and adiabatic electron affinity, 0.95 eV, have been inferred from additional calculations. Vertical ionization energies of Zn(CH3)2 are calculated with similar techniques and are in excellent agreement with photoelectron spectrum results. Bond energies for the dissociation of one or both methyl groups have been determined as well.
Dynamics of the reaction of O(3P) atoms with acetylene
Authors: Huang X. , Xing G. , Bersohn R.
Published: July 2002

The first step in the reaction of O(3P) with HCCH is the formation of a complex, HCCHO which lives at least as long as a rotational period. The complex has two channels of dissociation, HCCO+H or 3B1CH2+CO. To find out more about this reaction the H and CO products were probed by laser-induced fluorescence. Earlier determinations that the branching ratio between the two channels is 1.4 are confirmed but it is shown that with DCCD the ratio is 0.9. This is explained by assuming that the 1,2 migration is hindered more severely by the deuteration than is the hydrogen atom dissociation. The average H atom translational energy agrees with the value of 13 kcal/mol found in Lee’s molecular beam study. The CO product of this very exothermic reaction is rotationally and vibrationally cold. The absence of rotational excitation implies a collinear transition state which is possible if the 1,2 H atom shift forms a ketene transiently in the 3B1 state.
Dielectric properties and infrared spectra of liquid water: Influence of the dynamic cross correlations
Authors: Martí J. , Guàrdia E. , Padró J. A.
Published: July 2002

Molecular dynamics simulation is applied to the study of the infrared spectra associated to translational, librational, and vibrational motions as well as to dielectric relaxation of liquid water. Flexible simple point charge (SPC) potentials are used in the simulations. Both dielectric and infrared spectra are calculated and compared with available experimental data. The effects of the dynamic cross correlations are analyzed by comparing the results for the time correlation functions of collective and individual properties.
Formation of anomalous odd-numbered carbon cluster ions in the gas-phase coalescence reactions of fullerenes
Authors: Zhu Lei , Wang Shenyi , Li Yufen
Published: July 2002

We report the observation of efficient coalescence reactions of fullerenes in the negative ion channel by laser desorption ionization of chemical adduct compounds of C60. Not only the even-numbered daughter fullerenes by successive C2 losses or captures appeared, but also odd-numbered carbon cluster anions C−N (51≤N≤65) were detected in the chemical-fusion processes. The results suggest that the anomaly is originated from the special reaction activity of nascent C60 produced by laser-induced dissociation of adduct compound molecules, and thereby provide a new way to open fullerene cages.
Collisional deactivation of the isoelectronic 15N+2 A 2Πui (v=3) and CO+ A 2Πi (v=3 and 4) levels by helium atoms
Authors: Dentamaro Anthony V. , Katayama Daniel H.
Published: July 2002

An optical–optical double resonance (OODR) technique is used to selectively populate rotational levels of the 15N+2 A 2Πui (v=3) state and monitor collision induced electronic transitions (CIET) to the X 2Σ+g (v=6 and 7) vibronic manifolds. The branching ratio from the A (v=3) state to the X (v=6 and 7) levels is determined experimentally and used in a phenomenological model based on past results. This ratio is used to determine the state specific collisional quenching rates from observed double exponential decay curves of the A (v=3) level. Similar results are obtained for CIET from the CO+ A 2Π (v=4) level to the X 2Σ+ (v=12 and 13) levels. In this case, the branching ratio from the A (v=4) level to the X (v=12 and 13) levels is not as accurate as for the 15N+2 case, but the result agrees with the empirical model, and state specific quenching rates are also determined from double exponential decay curves. In addition, the deactivation rate is determined for the CO+ A (v=3) level from its observed single exponential laser induced fluorescence curves. These new data for quenching of the CO+ A (v=3 and 4) states continues the trend of increasing quenching cross sections with increasing vibrational quantum number observed in previously published values for the A (v=0, 1, and 2) levels. A comparison is also made between rotational relaxation within the A (v=4) state and the abovementioned electronic deactivation in CO+. These results show that CIET in CO+ compares favorably to analogous experiments with its isoelectronic partners N+2 and CN, including energy gap and Franck–Condon factor dependencies. The collider in all cases is helium.
Fourier path integral Monte Carlo method for the calculation of the microcanonical density of states
Authors: Freeman David L. , Doll J. D.
Published: July 2002

Using a Hubbard–Stratonovich transformation coupled with Fourier path integral methods, expressions are derived for the numerical evaluation of the microcanonical density of states for quantum particles obeying Boltzmann statistics. A numerical algorithm is suggested to evaluate the quantum density of states and illustrated on a one-dimensional model system.
Infrared intensities of liquids. XVII. Infrared refractive indices from 8000 to 350 cm−1, absolute integrated absorption intensities, transition moments, and dipole moment derivatives of methan-d3-ol and methanol-d4 at 25 °C
Authors: Bertie John E. , Zhang Shuliang L.
Published: July 2002

This paper reports absolute infrared absorption intensities of liquids methan-d3-ol (CD3OH) and methanol-d4 (CD3OD) at 25 °C between 8000 and 350 cm−1. Measurements were made by multiple attenuated total reflection spectroscopy with the CIRCLE cell, and by transmission spectroscopy with transmission cells fitted with calcium fluoride windows. In both cases, the spectra were converted to infrared real and imaginary refractive index spectra. The refractive indices obtained by these two methods agreed excellently and were combined to yield an imaginary refractive index spectrum k(ν̃) between 7244 and 350 cm−1 for CD3OH and between 5585 and 350 cm−1 for CD3OD. The imaginary refractive index spectrum was arbitrarily set to zero from 8000 to 7244 cm−1 (CD3OH) or 5585 cm−1 (CD3OD), where k is always less than 4×10−6, in order that the real refractive index can be calculated below 8000 cm−1 by Kramers–Krönig transformation. The results are reported as graphs and tables of the refractive indices between 8000 and 350 cm−1, from which all other infrared properties of the two liquids can be calculated. The estimated accuracy, not precision, of the imaginary refractive index is ±3%, except for ±10%, where k is less than 4×10−5. The estimated accuracy of the real refractive index is better than ±0.5%.

In order to obtain molecular information from the measurements, the spectra of the imaginary polarizability multiplied by wave number ν̃αm″ were calculated under the assumption of the Lorentz local field. The area under these ν̃αm″ spectra was separated into the integrated intensities of different vibrations. The magnitudes of the transition moments were calculated from the integrated intensities, and the double harmonic approximation was used to calculate the magnitudes of the dipole moment derivatives of the liquid-state molecules with respect to the normal coordinates. Dipole moment derivatives with respect to internal coordinates were calculated under the simplest approximations, the validity of which is demonstrated by the experimental data in many cases. The consistency of the dipole moment derivatives with respect to internal coordinates obtained for different isotopomers is shown through their relative rotational corrections. Results are presented for the O–H, O–D, C–H, and C–D stretches; the C–O–H in-plane bending; and the D–C–O–H and D–C–O–D torsion vibrations.
Equilibrium geometry of isocyanomethylene (HCNC) and comparison to the troublesome isomer cyanomethylene (HCCN)
Authors: Kellogg Charles B. , Galbraith John Morrison , Fowler Joseph E. , Schaefer Henry F.
Published: July 2002

Inspired by the recent experimental study of the radical anions HCCN− and HCNC− and by earlier examinations of HCCN, the equilibrium geometry of the HCNC molecule has been investigated using both self-consistent field (SCF) and configuration interaction methods including single and double excitations (CISD). The largest basis set used was a triple-ζ plus double polarization with diffuse functions and higher angular momentum functions appended to each atom [TZ2P(f,d)+diff]. Using this basis, the H–C–N equilibrium angle is predicted to be 128.5° at the CISD level of theory. Additionally, the zero point vibrational energy (ZPVE) corrected energy separation of the bent and linear conformations was predicted to be 10.1 kcal mol−1 at the CISD level of theory with the largest basis set employed. The barrier to linearity is 7.7 kcal mol−1 at the CCSD level of theory and 6.9 kcal mol−1 at the CCSD(T) level of theory, employing the CISD optimized geometries with a basis that was comprised of triple-ζ plus double polarization with higher angular momentum functions appended to each atom [TZ2P(f,d)]. These results were compared to those obtained in previous ab initio investigations of HCCN, which has been dubbed a quasilinear molecule by the most recent experimental investigators. HCNC is predicted to lie 22.2 kcal mol−1 above HCCN at the CISD level of theory, with a the TZ2P(f,d) basis. The differences between the two isomers are discussed and HCNC is predicted to be a definitively bent molecule, rather than quasilinear.
Cluster experiments in radio frequency Paul traps: Collisional relaxation and dissociation
Authors: Parks J. H. , Pollack S. , Hill W.
Published: July 2002

This paper presents techniques to store, manipulate, and detect cluster ions in an rf Paul trap as an approach to study the physics and chemical physics of clusters. The trap has been designed to be the primary experimental environment in the sense that experimental manipulation and ion detection are performed in situ within the trap. Specific design considerations for the trap and rf electronics relevant to metal cluster experiments are discussed. We present the application of these techniques to measurements of trapped C+60 in order to estimate their limitations for studying metal cluster ions. This paper demonstrates the capability to nondestructively detect small variations in the number of trapped C+60 ions with an ion noise level of ≊100 ions limited by thermal current fluctuations. Trapped ion lifetimes of τion≳30 min are measured following the relaxation of C+60 translational energy to ≊300 K. Measurements of the collisional dissociation of trapped C+60 ions at rates <100 s−1 by He at ∼10−6 Torr have been performed and the products detected in situ by the mass distribution of the C+n products. Several possibilities for metal cluster experiments in rf Paul traps are discussed.
The photochemical identification of two chemisorption states for molecular oxygen on TiO2(110)
Authors: Lu Guangquan , Linsebigler Amy , Yates John T.
Published: July 2002

We report the first experimental observation of two chemisorption states for molecular oxygen on a TiO2(110) surface containing anion vacancy sites. The first molecular species can be photoactivated to oxidize coadsorbed CO to CO2 (α channel) and undergoes slow photodesorption. The second molecular oxygen species only undergoes fast photodesorption (β channel). Conversion from α-O2, to β-O2 occurs upon heating the surface to above 200 K.
Relativistic ab initio model potential calculations including spin–orbit effects through the Wood–Boring Hamiltonian
Authors: Seijo Luis
Published: July 2002

Presented in this paper, is a practical implementation of the use of the Wood–Boring Hamiltonian [Phys. Rev. B 18, 2701 (1978)] in atomic and molecular ab initio core model potential calculations (AIMP), as a means to include spin–orbit relativistic effects, in addition to the mass-velocity and Darwin operators, which were already included in the spin-free version of the relativistic AIMP method. Calculations on the neutral and singly ionized atoms of the halogen elements and sixth-row p-elements Tl–Rn are presented, as well as on the one or two lowest lying states of the diatomic molecules HX, HX+, (X=F, Cl, Br, I, At) TlH, PbH, BiH, and PoH. The calculated spin–orbit splittings and bonding properties show a stable, good quality, of the size of what can be expected from an effective potential method.
High-pressure Raman study of liquid and crystalline CH3F up to 12 GPa
Authors: Wu Y. H. , Shimizu H.
Published: July 2002

High-pressure Raman spectra of liquid and crystalline CH3F were measured up to 12 GPa at 300 K in a gasketed diamond-anvil cell. Two solid phases have been found; the transition pressures of liquid to solid phase I and phase I to phase II were determined to be 2.75 and 3.63 GPa, respectively. Among these, the solid phase I is an orientationally disordered (plastic) phase, while the solid phases II is an orientationally ordered phase. The frequency of CF stretching ν3(A1) vibration shows a large red shift with a slope dν/dP of about −2.6 cm−1/GPa in the liquid phase, and it splits into the TO and LO modes in the two solid phases. The Fermi resonances between the same symmetry vibrations of ν1(A1) and 2ν5(A1), and of ν4(E) and 2ν5(E) have been observed and their behaviors have been analyzed by the Fermi resonance theory. The pressure dependence of the CH stretching mode is compared with those of the other fluorinated methanes CH2F2, CHF2Cl, and CHF3.
Conditional variation in the kinetic parameters of rare gas halide excimers
Authors: Datsyuk V. V.
Published: July 2002

In accordance with the theory of vibrational relaxation, a rare gas halide (RgX) excimer or similar electronically excited molecule cannot be characterized by one universal set of kinetic parameters. Both the quenching rate constants and the effective radiative lifetimes are discovered to depend on the internal energy of generated molecules and gaseous-mixture composition. It is emphasized that different values of a kinetic parameter have to be used under steady-state and pulse conditions.
Fermi resonances and local modes in pyramidal XH3 molecules: An application to arsine (AsH3) overtone spectra
Authors: Lukka Tuomas , Kauppi Esa , Halonen Lauri
Published: July 2002

A simple vibrational Hamiltonian expressed in terms of curvilinear internal coordinates has been used to model both stretching and bending vibrations in pyramidal XH3 molecules. The pure stretching part is expressed as harmonically coupled anharmonic oscillators and the pure bending part as harmonically coupled harmonic oscillators. The stretching and the bending modes are coupled with each other by Fermi resonance terms which contain contributions both from the kinetic and potential energy part of the full vibrational Hamiltonian. Only resonance couplings are included. The Hamiltonian matrices are symmetry factorized by employing symmetrized basis functions which consist of products of stretching oscillator and valence angle bending oscillator functions. This model is applied to observed vibrational term value data of arsine (AsH3). The least squares method is used to optimize potential energy parameters. The results obtained are in good agreement with ab initio calculations. All observed arsine overtone and combination bands have been assigned.
Oxidation of GaAs(110) with NO2: A molecular beam study
Authors: Bahr C. C. , vom Felde A. , Buratto S. K. , Cardillo Mark J.
Published: July 2002

We describe time-resolved modulated molecular beam measurements of the adsorption of NO2 on the GaAs(110) surface. These measurements provide a quantitative description of the gas–surface interaction; thermal NO2 has a nearly unity sticking probability, dissociating to form NO (which quickly desorbs) and a surface oxide of ∼1/3 ML saturation coverage. The NO2 dissociation probability is strongly controlled by the defect density, the oxygen coverage, and the surface temperature. We have characterized the competition between the processes leading to oxygen deposition, i.e., desorption and diffusion of NO 2 to reactive defects. The barrier energies Ediff=6±2 kcal/mol and Edes=9±2 kcal/mol provide an interesting example of the transition from defect-dominated surface chemistry, typical of low Miller index metal surfaces to defect- insensitive diffusion-limited chemistry, which we argue is generic to corrugated semiconductor surfaces.
Theoretical investigations of proton transfer reactions in a hydrogen bonded complex of cytosine with water
Authors: Sobolewski Andrzej L. , Adamowicz Ludwik
Published: July 2002

The potential energy functions of the electronic ground as well as the lowest ππ* and nπ* excited singlet states of the most stable hydrogen bonded complex of cytosine with water was theoretically investigated along the proton transfer (PT) reaction coordinate. The full geometry optimization was performed along the PT reaction path. In the geometry optimization, the Hartree–Fock method and the configuration interaction scheme with single excitations was used. The energy calculations at the optimized geometries were performed with the complete-active-space self-consistent-field (CASSCF) method and with second-order perturbation theory, employing the CASSCF wave function as the reference state (CASPT2), as well as with the Moller–Plesset second-order theory (MP2) for the ground state. It was found that the cytosine:water complex is stable in the amino-oxo form against the PT reaction which leads to the imino-oxo tautomeric form on the ground as well as on the excited PE surfaces. An efficient nonradiative decay channel of electronically excited cytosine resulting from nonadiabatic interactions between the ground and excited singlet states along the reaction coordinate leading to the prefulvenic form was identified. It is argued that both the above mentioned effects under the normal conditions (neutral aqueous solution, room temperature) are responsible for remarkable stability of cytosine in its ‘‘native’’ amino-oxo form against any damage that may result from exposure to UV radiation.
Absolute total cross sections for the ion–molecule reaction O+(4S
o)+H2O
Authors: Li X.- , Huang Y.-L. , Flesch G. D. , Ng C. Y.
Published: July 2002

Absolute total cross sections for H2O+ and OH+ formed by the O+(4So)+H2O reaction have been measured in the center-of-mass collision energy (Ec.m.) range of ≊0.1–60 eV. The cross sections for H2O+ are greater than those reported previously. The structure observed in the cross section curve for OH+ suggests that the OH++OH channel is produced at Ec.m.≊0.1–5.0 eV via a long-lived complex mechanism, while the OH++O+H channel is formed at Ec.m.≊5–60 eV by a short range charge transfer-predissociation pathway.
Pressure-induced d–π charge transfer in one-dimensional phthalocyanine conductors, NiPc(AsF6)0.5 and CoPc(AsF6)0.5
Authors: Hiejima Toshihiro , Yakushi Kyuya
Published: July 2002

Pressure dependence of optical absorption spectra were measured for (phthalocyaninato)-nickel hexafluoroarsenate, NiPc(AsF6)0.5 and (phthalocyaninato)-cobalt hexafluororarsenate, CoPc(AsF6)0.5. We found a charge transfer from the central metal ion to the macrocycle at 0.5 GPa in NiPc(AsF6)0.5 and 1.1 GPa in CoPc(AsF6)0.5. According to the electron-filling process in the π-conduction band, a metal–insulator transition and an evolution of the energy gap was observed in NiPc(AsF6)0.5. On the other hand, nonmetallic CoPc(AsF6)0.5 showed a continuous change.
Photophysics and dynamics of the lowest excited singlet state in long substituted polyenes with implications to the very long-chain limit
Authors: Andersson Per Ola , Gillbro Tomas
Published: July 2002

In this paper we explore the intramolecular relaxation processes within two long carotenoids, namely decapreno-β-carotene (M15) and dodecapreno-β-carotene (M19) with 15 and 19 conjugated double bonds (N), respectively. Amplified 200 fs pulses at 590 nm were used to excite the optically allowed S0→S2 (1 1Ag→1 1Bu) transition of the two carotenoids. The excited state dynamics were probed by continuum light between 400–890 nm in solvents with different polarizabilities. The transient absorption spectra consist of a bleaching region, due to loss of ground state absorption, and of an excited state absorption region at longer wavelengths, due to the S1→Sn transition. The Sn state was assigned to an n 1Bu state. The overall wavelength dependence of the measured kinetics could be well described by introducing three decay time constants. One reflects the S1 lifetime (τ1) and was determined to 1.1 and 0.5 ps for M15 and M19, respectively. A second lifetime, between 5 and 15 ps, was attributed to vibrational cooling in the ground state. A third decay time was in the subpicosecond range, and was ascribed to the vibrational redistribution and relaxation of the S1 potential surface after being populated by the subpicosecond S2–S1 internal conversion. No significant change of the decay constants was observed for M15 embedded in a 77 K matrix. This shows that the relaxation rates are only influenced by intramolecular processes.

The S2 lifetime was shorter than the pulse duration and was estimated to be in the order of 100 fs. The S0→S2 transition of M15 in the liquid phase exhibits a 0.39 anisotropy at short times, while the S1→Sn transition has an initial value of only 0.31. This corresponds to an angle of 23° between the transition dipoles. The measured S1 rate constants were analyzed, together with decay constants of shorter carotenes, in terms of the energy gap law. When going from the shortest (N=5) to the longest (N=19) polyene, τ1 decreases about 6000 times, i.e., from 3 ns to 0.5 ps. By using an empirical form of the energy gap law the 0–0 transition of S1(2 1Ag)→S0 was estimated to be located at 11 300 and 10 200±1 000 cm−1 for M15 and M19, respectively. By fitting the excitation energies of all carotenes in the series (3≤N≤19) with a truncated two or three term expansion of a power series in 1/N the long-chain limit values were extrapolated to be 11 000 and 3 500 cm−1 for the 1 1Bu and 2 1Ag state, respectively. The implication of these limit values on the electronic structure of polyacetylene are discussed.
Local density functional studies of electronic structure of Be135
Authors: Tang Shaoping , Freeman A. J. , Ross R. B. , Kern C. W.
Published: July 2002

Results of extensive studies of metallic beryllium modeled with 135 atoms are reported using a first-principles total energy molecular cluster approach based on the local density approximation. Binding energy, ionization potential, charge density, Mulliken populations, density of states and atomic forces are calculated. The results show that the ground state of Be135 is of a″ symmetry. The binding energy is 77.5 kcal/mol which is very close to the binding energy of bulk Be (75.3 kcal/mol). Comparison with earlier results from Hartree-Fock calculations shows significant differences in the calculated binding energy, ionization potential, and Mulliken populations.
Collision-induced scattering in CO2 gas
Authors: Teboul Victor , Le Duff Yves , Bancewicz Tadeusz
Published: July 2002

Carbon-dioxide gas rototranslational scattering has been measured at 294.5 K in the frequency range 10–1000 cm−1 at 23 amagat. The depolarization ratio of scattered intensities in the frequency range 10–1000 cm−1 is recorded. The theoretical and experimental spectra in the frequency range 10–470 cm−1 are compared. The anisotropic double differential cross section for scattered light is calculated theoretically considering first- and second-order dipole-induced dipole, first-order dipole–induced octopole, and first-order dipole–dipole–quadrupole light scattering mechanisms as well as their cross contributions.
Detachment and charge transfer for collisions of negative ions with ozone
Authors: Fedchak J. A. , Peko B. L. , Champion R. L.
Published: July 2002

Cross sections for electron detachment and charge transfer have been measured for collisions of O−, S−, and halogen anions with neutral ozone for laboratory collision energies ranging from 3 to 500 eV. Both electron detachment and charge transfer are found to be large over the entire range of collision energies for O− and S−+O3 whereas the cross sections for the halogen anions colliding with O3 exhibit threshold behaviors characteristic of endothermic scattering processes.
Variance reduced simulations of stochastic differential equations
Authors: Melchior Martin , Öttinger Hans Christian
Published: July 2002

Stochastic simulations are made more efficient by variance reduction techniques. Our construction of variance reduced simulations is based on importance sampling, and it requires approximate information about the simulated process. Results for Hookean dumbbells with hydrodynamic interaction are presented, where variances are reduced by up to two orders of magnitude.
Theoretical analysis of conjugated polymers with a degenerate ground state: Type-I and type-II soliton charge storage states in poly(1,6-heptadiyne) and derivatives
Authors: Lögdlund M. , Brédas J. L.
Published: July 2002

We report a theoretical study of the molecular and electronic structure of polymers with a degenerate ground state based on poly(1,6-heptadiyne). Quantum-chemical calculations are performed by means of the semiempirical Austin Model 1 and intermediate neglect of differential overlap/configuration interaction methods as well as the nonempirical valence effective Hamiltonian technique. In the case of poly(1,6-heptadiyne) itself and poly(dipropargyl-hexylamine), we first examine the torsion potential along the backbone; we then investigate the doping-induced electronic and geometric modifications. We also consider the self-doped n-type system, poly(dipropargylhexylmethylammonium). The charge-storage states induced upon doping are discussed in terms of the formation of solitons, which belong to two different types and have characteristics at variance with respect to those in trans-polyacetylene.
Transient grating excitation of interfacial acoustics: Treatment of multilayer structures
Authors: Gracewski S. M. , Miller R. J. Dwayne
Published: July 2002

Observation of acoustics generated by a surface restricted transient optical grating can be used as a sensitive probe of interface structure that can influence near-surface chemical interactions. In this paper, a theoretical analysis is presented detailing the interface acoustic waves generated by this optical grating technique for a structure consisting of a liquid/solid interface with an interposed thin solid layer. In the absence of the layer, the predicted response consists of contributions from both the Stonely and the Leaky–Rayleigh wave interface modes, consistent with experimental observations. Thin intermediate layers, those with thickness much smaller than the grating period, were found to have little influence on the acoustic response indicating that the spatial sensitivity of this technique is not sufficient for probing the short range order in liquids in contact with surfaces. However, the addition of a layer with thickness on the order of the grating spacing affects the dominate period of the response as expected from the dispersion relation for the liquid/solid/solid structure. For these thick layers, bulk waves propagating across the layer thickness also initially contribute to the response.
A new method for the recognition and size characterization of a knot in a ring molecule placed upon a lattice
Authors: Fawcett A. H. , Mee R. A. W. , McBride F. V.
Published: July 2002

We show how a knot in a ring located upon a lattice may be characterized by two different measures of the perimeter length and by the mean square radius of gyration. This characterization is performed after the knot in a well-extended form has been reduced in size by a process that involves bead elimination and bead movement, movements being governed alternately by two criteria, the need to reduce the total length of the perimeter (or at least not to increase it) and the need to move a bead closer to the center of gravity of the object, so that elimination may subsequently take place. During contractions the beads must occupy different sites upon the lattice and bonds between pairs of beads are not permitted to pass through each other, so their topology is maintained. For the first few knots of the knot table the number of bonds, Nb (or the number of beads) is useful in discriminating, though unique values are found only for the 31 and 41 knots. The mean number of bonds within a contracted knot is a good measure of the crossing number, as also are the second and third measures of knot size, the mean perimeter length, and the radius of gyration. None of these measures are capable of readily distinguishing between different knots with the same number of crossings. Compacted knots themselves have a number of configurations upon the lattice that have interesting properties.
Ab initio study of a CO monolayer adsorbed on the (101̄0) surface of ZnO
Authors: Jaffe John E. , Hess Anthony C.
Published: July 2002

Periodic Hartree–Fock total energy calculations on two-dimensionally periodic slabs have been used to predict the equilibrium geometry of a monolayer of carbon monoxide molecules adsorbed on the nonpolar (101̄0) surface of ZnO. Two physisorbed (or weakly chemisorbed) minimum energy configurations are found. In one the CO molecules adsorb with their oxygen atoms coordinated to surface Zn atoms, while in the other the carbon atoms are coordinated to surface Zn atoms. The two calculated minima are very close in energy. In the second geometry, the C–Zn ‘‘bond’’ and the C–O bond make angles of 32.5° and 39.5° with the surface normal, and the intramolecular bond shortens slightly from its free value in reasonable agreement with experimental results. No binding of CO to the surface oxygen atoms is predicted. Surface-related changes in the vibrational frequencies for the adsorbed molecules agree reasonably well with infrared spectroscopic data, and the ‘‘carbon-down’’ binding energy of the molecule with the surface is in good agreement with thermal desorption data (though electron correlation effects have to be included in the calculation to obtain acceptable results for low surface coverage).
Charge transport in lithium phthalocyanine
Authors: Dumm M. , Lunkenheimer P. , Loidl A. , Assmann B. , Homborg H. , Fulde P.
Published: July 2002

The ac electrical properties of monoclinic lithium phthalocyanine (LiPc) and of the iodinated compound LiPcI have been investigated in the frequency and temperature regimes 20 Hz≤ν≤1 GHz and 1.5 K≤T≤300 K, respectively. Both compounds are semiconductors with dielectric constants ε∞≊6 (LiPc) and 20 (LiPcI). Up to room temperature tunneling of charge carriers is the dominant conduction process in both compounds, yielding intrinsic dc conductivities σdc≊5.3×10−4 Ω−1 cm−1 (LiPc) and 0.2 Ω−1 cm−1 (LiPcI). The frequency and temperature dependence of the complex ac conductivity suggests polarons as the dominant species of charge carriers. The higher conductivity of the iodinated compound can be attributed to an enhanced mobility of the polaronic charge carriers which is most probably due to a better overlap of the π orbitals along the stacking direction of the molecules.
Entropic elasticity of end adsorbed polymer chains: The spectrin network of red blood cells as C*-gel
Authors: Everaers Ralf , Graham Ian S. , Zuckermann Martin J. , Sackmann Erich
Published: July 2002

We use Monte Carlo methods to investigate the end-to-end distance distribution and entropic elasticity of self-avoiding walks in a three-dimensional half-space with both ends adsorbed on the limiting surface. The obtained distributions are well described by the Redner–des Cloizeaux (RdC) ansatz q(x)=Cxθ exp(−(Kx)t), x being the rescaled length. Using the recent solution of the junction affine model for networks of RdC springs we apply the results to the cytoskeleton of the red blood cell (RBC), a two-dimensional network of spectrin molecules which is attached to the inner surface of the erythrocyte membrane. The shear moduli predicted for a noninteracting surface are in close agreement with simulation results by Boal for a bead–spring model of the spectrin network. Moreover, we calculate stress–strain relations for finite deformations. In particular for a network which is fully adsorbed on the bilayer we find a strongly nonlinear elastic response. Our results suggest that the elastic properties of RBCs cannot be obtained within the usual Gaussian models and depend sensitively on the degree of adsorption of the spectrin network.
Theory of sticking: The effect of lateral interactions
Authors: Kreuzer H. J.
Published: July 2002

A generalization of the kinetic lattice gas model is used to study the coverage and temperature dependence of the sticking coefficient due to intrinsic and extrinsic precursors and in the presence of lateral interactions.
A note on large correlation-consistent Gaussian basis sets
Authors: Wilson S. , Moncrieff D.
Published: July 2002

The larger correlation-consistent basis sets have evolved to a size where they might be expected to display a flexibility which facilitates their transfer between different atoms and different molecular environments with little loss in accuracy. This hypothesis is tested for three isoelectronic, first-row diatomic molecules, N2, CO, and BF.
Activated barrier crossing dynamics in slow, viscous liquids
Authors: Biswas Ranjit , Bagchi Biman
Published: July 2002

Experimental studies of reaction rates in slow, viscous liquids have often led to results at variance with conventional theoretical approaches. Here we present a self-consistent microscopic calculation of the rate which uses for the first time, the mode coupling theory (MCT) to obtain the frequency dependent friction. When this microscopic expression for the friction is used to obtain the barrier crossing rate from the Grote–Hynes (G–H) formula, the following results are found. At intermediate viscosities, the calculated rate exhibits a fractional viscosity dependence with parameter values in agreement with the experimental results. For example, we find an exponent equal to 0.8 when the barrier frequency (ωb) is equal to 2×1013 s−1, whereas the earlier calculations obtained an unrealistic value (close to 0.1) for this value of the barrier frequency. At very high viscosities we find an inverse logarithmic dependence of the rate on viscosity. This prediction can be tested against experiments.
Defect diffusion, excess intensity, and quasielastic light scattering of supercooled molecular liquids
Authors: Wang C. H. , Fischer E. W.
Published: July 2002

A microscopic theory based upon the model of molecular defect volume fluctuations is developed to provide an interpretation of the ultraslow mode and excess static light scattering intensity observed in supercooled glass-forming liquids. By including the defect volume as a variable in the set of slow variables comprising of the number density and momentum density, it is shown that in an one component viscoelastic fluid, a diffusive mode associated with the fluctuations of defect volume is present, in addition to the usual q independent structural relaxation mode associated with density fluctuations. Fluctuations of defect volume arise from the configurational rearrangement of molecules. A two fluid model previously proposed for interpreting the anomalous quasielastic light scattering results in an one component fluid follows naturally from the present model.
A self-consistent field study of the wetting transition in binary polymer blends
Authors: Genzer Jan , Composto Russell J.
Published: July 2002

A self-consistent field approach is used to investigate the partial to complete wetting transition for an A:B polymer blend at coexistence where polymers A and B have equal numbers of segments, N. The surface free energy, Fs, is modeled using the quadratic form suggested by Schmidt and Binder [J. Phys. II (France) 46, 1631 (1985)], namely, Fs=−μφ1−0.5gφ12, where μ and g are the surface equivalents of the bulk chemical potential and interaction energy, respectively, and φ1 is the surface volume fraction of the surface preferred component (A). For selected values of g and the bulk volume fraction of A, φ∞, the volume fraction profile and A surface excess, z*, are calculated as a function of increasing μ. The first and second order wetting transitions are indicated by a discontinuity and divergence, respectively, of z* and φ1. In our simulations, at high values of φ∞ only first order transitions are detected for both N=100 and N=1000. However, both first and second order wetting transitions are observed for low values of φ∞ depending on the value of g. The latter results contrast with those of Carmesin and Noolandi [Macromolecules 22, 1689 (1989)], who found that only first order wetting transitions are possible polymer mixtures. However, our results are in agreement with recent Monte Carlo simulations carried out by Wang and Binder [J. Chem. Phys. 94, 8537 (1991)] and Pereira and Wang [J. Chem. Phys. 104, 5294 (1996)].
Diode laser measurements of CD3 quantum yields and internal energy for the dissociation of dimethyl sulfoxide-d6
Authors: Rudolph R. N. , North Simon W. , Hall Gregory E. , Sears Trevor J.
Published: July 2002

Infrared diode laser absorption spectroscopy has been used to measure the CD3 radical photoproducts formed in the 193 and 222 nm photodissociation of dimethyl sulfoxide-d6. Quantum yields of CD3 have been determined to be 1.4±0.1 at 193 nm and 1.2±0.2 at 222 nm, compared to 2.0 for acetone-d6 at 193 nm. An analysis of transient waveforms reflecting the vibrational relaxation and radical recombination kinetics also yields an estimate of the nascent CD3 vibrational energy content by determining the fraction of total CD3 initially produced in the vibrationless state. The nascent CD3 population in the vibrational ground state decreases in order for the following photodissociation systems: CD3I at 248 nm, DMSO-d6 at 193 and 222 nm and acetone-d6 at 193 nm. The DMSO results are in good agreement with recent photofragment translational spectroscopy results and support a stepwise mechanism for the dissociation of DMSO at both wavelengths.