bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopy, dynamics, and chaos of the CS2 molecule: Fourier transform and phase-space analysis
Authors: Pique J. P. , Joyeux M. , Manners J. , Sitja G.
Published: July 2002

In this paper we analyze the vibrational spectra of the Σ+g ground state of CS2, the experimental results of which have been described in a forth coming paper. We show that, up to 12 000 cm−1, CS2 can be described by a system of two degrees of freedom strongly coupled by a 1:2 type Fermi resonance. The corresponding vibrational spectra are refitted with the aid of only seven parameters. Analysis of the spectra by the statistical Fourier transform technique reveals stroboscopic effects between the symmetric stretching mode and the bending mode. The distinction between the ‘‘stroboscopic hole’’ due to these effects and the ‘‘correlation hole’’ due to nonintegrable terms in the Hamiltonian is discussed in detail. The study of the topology of the phase space of CS2 in the regular and chaotic cases is carried out in the basis described by a vibrational angular momentum which includes the Fermi resonance. We show the analogy between the localization of the wave packets of the eigenstates and the trajectories. We also show the destabilization of the trajectories due to a term in the Hamiltonian which couples neighboring polyads and which is a second Fermi resonance. We show that only two resonances are enough to induce a chaotic situation.
Rydberg states of NO in a magnetic field: Multichannel quantum defect approach of the linear Zeeman effect
Authors: Raoult Maurice , Guizard Stéphane , Gauyacq Dolores
Published: July 2002

The linear Zeeman effect for the nf and np Rydberg states of NO has been analyzed in the intermediate energy region (n=7 and n=15). This analysis is based on a multichannel quantum defect treatment (MQDT), including the magnetic interaction, as proposed by Monteiro and Taylor [T. S. Monteiro and K. T. Taylor, J. Phys. B: At. Mol. Phys. 22, L191 (1989)]. The nonpenetrating nf states exhibit almost no channel mixing, but they are significantly perturbed by the Zeeman interaction within each rotational channel in a moderate field of 1 T. An excellent agreement has been found between the experimental results obtained in a 1 T magnetic field and the calculations, showing in particular the first manifestation of the Paschen–Back effect in a molecule. The penetrating np states of NO exhibit channel interaction, but, on the other hand, they are less perturbed by a 1 T magnetic field than the nf states are. Theoretical predictions have been made for a larger field strength of 5 T in the case of the 7p and 15p states.
Small-angle neutron scattering from microemulsions near the disorder line in water/formamide–octane-CiEj systems
Authors: Schubert K.-V. , Strey R.
Published: July 2002

Small-angle neutron scattering measurements were performed on symmetric microemulsions containing equal volume fractions of water/formamide, n-octane, and a sufficient amount of n-alkyl polyglycol ether (CiEj). By changing the surfactant chain length in the order C8E3, C6E2, and C4E1 in pure water, as well as for given C8E3 and C6E2 by increasing the relative amount of formamide in the water/formamide mixture, the amphiphilic strength (the amphiphilicity) is reduced. We observe that the characteristic scattering peak becomes weaker and its position moves into q=0 showing that the microstructure becomes disordered. However, a q−2 and a q−4 behavior for large q in film and bulk contrast, respectively, is still observed indicating the persistence of internal interfaces. As the microstructure is further weakened, a disorder line is passed at which the behavior of the real space correlation function changes from a damped oscillatory behavior to a monotonically decreasing one. We determine that this line has been passed from fits to the bulk scattering intensity. Simultaneously, the film scattering intensities show a transition from correlated to uncorrelated films as the disorder line is passed. Closely related to the weakening of the microstructure is the occurence of a nonwetting→wetting transition in the vicinity of a Lifshitz line. Roughly speaking, microemulsions, that do show a scattering peak do not wet the water–oil interface. As predicted by Landau–Ginzburg theories, the wetting transition occurs on the microemulsion side of the disorder line. As the amphiphilicity is even further reduced, a tricritical point is reached with the interesting observation that substantial local structure still persists.
Dipped adcluster model for chemisorptions and catalytic reactions on a metal surface: Image force correction and applications to Pd–O2 adclusters
Authors: Nakatsuji Hiroshi , Nakai Hiromi , Fukunishi Yoshifumi
Published: July 2002

Electrostatic term in the dipped adcluster model proposed previously is estimated by the method of image force. This is superior to the previous one which overestimates the electrostatic correction. The refined method is applied to the Pd–O2 adcluster dipped onto a free electron bath of the solid metal, the same system as reported previously. In addition to the highest spin coupling, the paired spin coupling is also applied. The former leads to a one-electron transfer and the latter a partial number (0.25) of electron transfer from a bulk metal into an adcluster. The geometry and the vibrational frequencies of the admolecule are not much affected by the electrostatic term, though the heat of adsorption is.
A
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o correlated valence shell effective Hamiltonian method for atomic and molecular systems
Authors: Banerjee Ajit
Published: July 2002

A new method for correlated electronic structure calculations that makes explicit reference to valence electrons only is presented for atomic and molecular processes in which the core electrons remain inert. The method is based on constructing a valence Hamiltonian that includes a one-electron effective potential for the core–valence interactions. It exactly reproduces all properties (wave functions, energies, etc.) of an all electron calculation with frozen core wave functions with same bases. It has no adjustable parameters, and no restrictions on the choice of basis sets. It yields considerable savings of computer time and space over the corresponding all electron calculations. Self-consistent field (SCF) and complete active space multiconfiguration self-consistent field (CAS-MCSCF) test calculations on ground states of F, F−, and S are presented.
Isotope and impurity effects on the glass transition and crystallization of pressure-amorphized hexagonal and cubic ice
Authors: Johari G. P. , Hallbrucker Andreas , Mayer Erwin
Published: July 2002

Amorphous solid D2O from hexagonal and cubic ices and H2O from (HF, NH3, and NH4F) doped hexagonal ice have been prepared by Whalley’s method, and their thermal behavior has been investigated by differential scanning calorimetry from 103 to 250 K. For a heating rate of 30 K min−1 , the temperature of the onset of the reversible glass■liquid transition, Tg, is raised by about 4 K when H2O is substituted by D2O. Doping with NH3 and NH4F causes little change in Tg but with HF Tg becomes undetectable. The increase in heat capacity at Tg is reduced by about a factor of 3 on deuteration but marginal changes occur on doping with NH3 or NH4F. The increase in Tg on deuteration is ≊4 times of that observed for the amorphous forms made from the vapor and the liquid, and more than twice of that expected from isoviscous or isorelaxational states, assuming that the functional form of the molecular reorientation rates with temperature is unaffected by isotopic substitution. NH3 and NH4F as dopants, which generally increase the reorientation rate of water molecules in hexagonal and cubic ices, have no detectable effect on the calorimetric relaxation rate of the pressure-amorphized forms, thus indicating that the increase in the concentration of Bjerrum defects for these two dopants does not alter Tg. All these observations suggest that the structure of pressure-amorphized solids is topologically different from that of the amorphous forms made from the vapor and the liquid.
Development, justification, and use of a projection operator in path integral calculations in continuous space
Authors: Hall Randall W. , Prince Melissa R.
Published: July 2002

A projection operator, similar to one previously used by us for problems with a finite set of basis functions, is suggested for use with continuous basis sets. This projection operator requires knowledge of the nodes of the density matrix at all temperatures. We show that a class of nodes, determined from the noninteracting density matrix and present at high temperatures in the interacting system are preserved to first order in the interaction at low temperatures. While we cannot show that the nodes are present at intermediate temperatures, we suspect they do exist and, as a test of this conjecture, we perform a calculation of two electrons confined in a harmonic well, using the projection operator. We find that accurate results are obtained at a range of temperatures, suggesting that our conjecture is indeed correct. We find that the error limits determined using the projection operator are 1–2 times smaller than those obtained with straightforward Monte Carlo integration (corresponding to a reduction in time of 1–4 in obtaining a desired level of accuracy).
Coherent anti-Stokes Raman spectroscopy of shock-compressed liquid carbon monoxide
Authors: Moore D. S. , Schmidt S. C. , Shaw M. S. , Johnson J. D.
Published: July 2002

Vibrational spectra of liquid carbon monoxide shock compressed to several high pressure/high temperature states were recorded using single-pulse multiplex coherent anti-Stokes Raman scattering. Vibrational frequencies, third-order suceptibility ratios, and linewidths are reported for the fundamental and first excited-state transition. The observed vibrational frequency shift with shock pressure was substantially less than that observed previously in nitrogen, implying a significant difference in the details of their inter- and intramolecular potentials. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these shock pressures, and the vibrational temperatures obtained are comparable to calculated equation-of-state temperatures. The measured linewidths suggest that the vibrational dephasing time decreased to ∼2 ps at our highest pressure shock state.
Local-scaling density-functional theory for excited states
Authors: Koga Toshikatsu
Published: July 2002

The local-scaling density-functional method enables us to determine the ground-state electron density directly and variationally through the generation of a parent wave function of a given density. A generalization of the method to excited states is developed by the use of a configuration-interaction-type reference wave function. From a given density which approximates the nth-state density, all the mth-state wave functions (m≤n) are generated in such a manner that they satisfy the wave function and Hamiltonian orthogonalities. The nth-state electron density is determined so as to minimize the Hamiltonian expectation value over the generated nth-state wave function. An illustrative application is presented for the 2 1S state of the helium atom, and simple electron-density functions which compare well with the near-exact density are reported.
Anomalous band shifts in the 14 μm infrared absorption spectra of rare gas–BF3 complexes
Authors: Lee Gang-Ho , Matsuo Yukari , Takami Michio , Matsumoto Yoshiyasu
Published: July 2002

High resolution infrared absorption spectra of rare gas (Rg)–BF3 van der Waals complexes are studied in the 14 μm region near the ν2 band of BF3 monomer. Spectroscopic constants are determined for the 20Ne–11BF3, Ar–10,11BF3, 82–84,86Kr–11BF3, and 84Kr–10BF3 complexes. The observed redshifts from the monomer band origin correlate linearly with the rare gas polarizabilities. These shifts are about three times as large as those measured previously near the monomer ν3 band. This mode dependence of the shifts cannot be reproduced in a consistent manner with the instantaneous vibrational dipole–induced dipole interaction model, and indicates much greater enhancement of bonding energy by the excitation of ν2 vibration. The band shifts are discussed on the basis of electrostatic interaction between rare gas atom and point charges on BF3. The anomalous band shifts for the ν2 band are successfully accounted for by the interaction of vibrational dipole moment with the static induced dipole moment on the rare gas atom, which is parallel to the direction of vibrational motion. The isotope shifts observed for the Kr–BF3 complexes and the band shifts due to the modification of force field by vdW bonding are discussed with a linear triatomic molecular model.
Very low temperature helium pressure broadening of DCl in a collisionally cooled cell
Authors: Willey Daniel R. , Choong Vi-En , De Lucia Frank C.
Published: July 2002

Very low temperature pressure broadening parameters and cross sections for the J=0–1 rotational transition of DCl broadened by helium are presented. Data was taken using a collisionally cooled cell and measured cross sections range from 10.76 Å2 at 4.21 K to 8.10 Å2 at 1.85 K. This compares with a 300 K cross section of 9.36 Å2. Predictions from two currently available anisotropic He–DCl potentials do not reproduce accurately the experimental results. Modifications were made to one of these potentials to reproduce more accurately both the observed low temperature and 300 K pressure broadening cross sections. The resulting modified potential has a well depth De=32.7 cm−1 at a separation Re=3.46 Å in the linear He–Cl–D configuration.
Improved methods for path integral Monte Carlo integration in fermionic systems
Authors: Newman William H. , Kuki Atsuo
Published: July 2002

We generalize the discretized Feynman path integral expansion by replacing the path through pure states with a path through idempotent density matrices. The transformed expression converges to the ordinary path integral, but is computationally more flexible than the ordinary form. By introducing a particular choice of these idempotent density matrices, based on rotational averaging around the two-particle center of mass, we greatly reduce the sign problem for systems of two fermions in three dimensions. In the ordinary path integral Monte Carlo approach, low temperature simulation of fermions is inefficient as the integral decays exponentially faster than the integrand (and its variance) as the temperature decreases. The new rotationally averaged algorithm dramatically retards this relative decay. Fermionic simulations of the model system of Kestner and Sinanoglu, and of the harmonic oscillator, demonstrate this improvement, as integrals calculated at temperatures much lower than the singlet–triplet splitting display negligible decay of the desired averages relative to the partition function of the modified path ensemble.
Classical trajectory study of the decomposition of HCOH⋅+ on a symmetry-invariant potential-energy surface
Authors: Ma Ngai Ling , Radom Leo , Collins Michael A.
Published: July 2002

The unimolecular decomposition of HCOH⋅+ (and its deuterated analogs) to HCO+ and H⋅ has been studied using classical trajectories on a symmetry-invariant reaction path potential. The potential is based on an intrinsic reaction path of an ab initio Hartree–Fock surface. A group-theoretical procedure is applied to ensure that both hydrogens of HCOH⋅+ are treated equivalently. Classical trajectories on this surface show a nonequivalent distribution of products, the bias of which is mass dependent, despite rapid energy redistribution. The reaction mechanism and the role of energy redistribution are described, and a new interpretation of experimental data is proposed.
Path-integral molecular-dynamics calculation of the conduction-band energy minimum V of excess electrons in fluid argon
Authors: Lopez-Castillo J.-M. , Frongillo Y. , Plenkiewicz B. , Jay-Gerin J.-P.
Published: July 2002

Using path-integral molecular-dynamics simulations, we calculate the conduction-band energy minimum V0 (relative to vacuum) of an excess electron injected in fluid argon over a range of densities (n) from the gas phase to the liquid near the triple point. An accurate pseudopotential is employed to represent the electron–argon interaction. Special attention is paid to the convergence on the number of beads of the isomorphic electron polymer chain, the simulation-box size, and the question of ergodicity. The calculated V0(n) values are in very good agreement with experimental data. As a result of the very extended character of the excess electron state at all fluid densities considered, the precise value of V0 is shown to be only weakly sensitive to the degree of disorder and the coordination number of the fluid. Relaxation effects are also found to be negligible. These results account for the success of the mean-field approximation afforded by the Wigner-Seitz V0(n) calculations for the heavy rare-gas fluids. Finally, we find that screening of the long-range polarization tail plays a crucial role in the delicate balance between the attractive and repulsive electron–fluid interactions, which is responsible for the appearance of the minimum of V0(n).
Optical model calculation of the total Penning ionization cross sections for He(2 1P)–Ar, Kr, and Xe
Authors: Morishima Yasumasa , Ukai Masatoshi , Kouchi Noriyuki , Hatano Yoshihiko
Published: July 2002

Quantum mechanical calculation of the total Penning ionization cross sections for He(2 1P) –Ar, Kr, and Xe collisions has been made in the region of the collisional energy from 0.1 meV to 1 eV with an optical complex potential approach for an electronic transition. The real part of an optical potential at long range is expressed in an explicit dispersion form and that in a repulsive region is expressed in a shielded Coulomb form. We have determined a repulsive potential by an excellent fit with our experimental cross sections. The imaginary part of the optical potential at long range is expressed by a dipole–dipole autoionization width, and at a small interatomic distance an electron exchange width is also considered to account an exponentially dispersive increase of the autoionization width. Good agreement between the present calculation and the experimental data has been obtained both in the energy dependence and in the absolute cross section values. The real part of the optical potential for He(2 1P) –Ar, Kr, or Xe is analogous to that for He(2 1S) –Ar, Kr, or Xe, respectively. It has been found that the width for the electron exchange effectively increases the total Penning ionization cross section, particularly in the case of He(2 1P) –Xe.
The 2 1A
g state of isolated c
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s-1,3,5,7-octatetraene: Two-color resonance enhanced two-photon ionization studies
Authors: Buma Wybren Jan , Kohler Bryan E. , Shaler Thomas A.
Published: July 2002

Vibrationally resolved 1 1Ag→2 1Ag excitation spectra and decay times for cis,trans-1,3,5,7-octatetraene seeded in a supersonic He expansion have been measured by two-color resonance enhanced two-photon ionization spectroscopy. The excitation energy of the 1 1Ag→2 1Ag 0–0 band (29 035 cm−1 ) is ∼6500 cm−1 lower than the 35 484 cm−1 excitation energy of the 1 1Ag→1 1Bu 0–0 band. The intensity pattern of the vibronic development of this spectrum is qualitatively similar to the pattern observed previously in solid state experiments. However, a detailed analysis of the vibrational structure reveals that the electronic structure of the 2 1Ag state is more susceptible to external perturbation than previously suspected. The decay times measured for vibronic levels in the 2 1Ag state decrease with increasing vibrational energy, most dramatically for vibrational energies 1200 cm−1 and higher. This indicates the increasing importance of a nonradiative decay channel which is most reasonably associated, at least in part, with cis-trans isomerization in the 2 1Ag state.
A classical mechanical analysis of molecular motions. Resonances in transition-state spectra of FH−2, FDH−, and FD−2
Authors: Hahn Ohyeon , Taylor Howard S.
Published: July 2002

A classical method of analysis is used to assign the various peaks in the transition-state spectra of FH−2, FDH−, and FD−2 to two series of resonances. Each series is ‘‘assigned’’ to a different periodic orbit whose motion is that of the nuclei in the resonances. The assignment is based on the parallels between periodic orbit properties and the experimental spectra upon isotope substitution. Relative to previous periodic orbit analysis and exact calculations, not only are new resonances found but it is shown that their role in the dynamics was not fully appreciated for one series and somewhat different than previously believed for the other series. Classical mechanics is here used, not to compute cross sections or spectra but to locate the effective potentials that, when quantized, yield the observed quantum states. Variants of the analysis method are discussed for systems other than FH−2 where the simplest version of the method is adequate.
Rate constants for CN reactions with hydrocarbons and the product HCN vibrational populations: Examples of heavy–light–heavy abstraction reactions
Authors: Copeland Leon R. , Mohammad Fida , Zahedi Mansour , Volman David H. , Jackson William M.
Published: July 2002

The rate constants for the reactions of CN radicals with methane, ethane, propane, cyclo-propane, isobutane, and neopentane have been measured over a temperature range from 275 to 455 K. Laser photolysis was used to produce the radicals and time delayed laser induced fluorescence was used to follow the radical concentration as a function of time. The temperature dependence of the observed rate constants could be fitted with a three-parameter Arrhenius plot. The activation energies that were observed were all small and in some cases they were negative. Time resolved ir emission was used to follow the formation of the HCN(0n2) and HCN(0n′1) product emission. The time dependence of the relative emission intensities, as well as computer modeling of the decay curves, suggest that vibrational population inversion occurs for all of the hydrocarbons studied except methane and cyclopropane. These observations are discussed in terms of the current theories for these type of reactions.
Quasiparticle exciton representation of frequency dispersed optical nonlinearities of conjugated polyenes
Authors: Wang Hong Xiang , Mukamel Shaul
Published: July 2002

The frequency dispersion of χ(3) of conjugated polyenes is calculated using equations of motion which provide an anharmonic (exciton) oscillator picture. Quantum confinement of the relative electron–hole motion is shown to play an important role in determining the magnitude of χ(3). The nature of the two-photon resonance observed in two-photon absorption and third harmonic generation is discussed, and the electroabsorption spectrum is calculated for a broad range of polyene sizes with up to 160 double bonds.
Oxidation of small carbon cluster ions by O2: Effects of structure on the reaction mechanism
Authors: Sowa Marianne B. , Anderson Scott L.
Published: July 2002

We report cross sections for reaction of mass-selected carbon cluster ions (Cn+, n=2–14) with O2 over a collision energy range of 0.1–10 eV. The results give insight into the oxidation mechanism and how it is affected by the isomeric structure of the reactant cluster ion. Small clusters, which are linear, react with no activation barrier, producing primarily CnO+ at low energies. Larger clusters, which are monocyclic, have activation barriers for reaction, and the product distribution is quite different. Reactions were also studied under multiple collision conditions, and addition of up to two O atoms is observed. Possible reaction mechanisms are discussed and comparison is made with the thermal kinetics results of McElvany and co-workers [J. Chem Phys. 86, 715 (1987)].
Operator expansions for multidimensional problems: New developments and applications
Authors: Schwartz Steven D.
Published: July 2002

In this paper we report a new method for resummation of operator expansions of the evolution operator. These resummation techniques are applied to the Feynman propagator and then to the derivation of an effective Schrödinger equation for general system–bath problems. This paper presents a significant advance over work previously reported by us [J. Chem. Phys. 96, 5952 (1992)], and it provides a highly accurate way to calculate quantum mechanical data for many dimensional systems. We then apply this new analytic resummation technique to the calculation of flux–flux correlation functions for two, three, and four dimensional problems in order to study the range of applicability of the approach. For moderate frequencies and coupling strengths, not only is the resummed operator calculational method essentially exact, it also requires a fraction of the computer time that the exact calculation consumes. For truly many dimensional problems this approach should provide the first accurate quantum mechanics of rate processes.
Series integration of the diaphragm cell transport equation when the diffusion coefficient is a function of concentration
Authors: Cain Judith B. , Baird James K.
Published: July 2002

In the case of the diaphragm cell transport equation where the interdiffusion coefficient is a function of concentration, we have derived an integral of the form, t=B0+BL ln(Δc)+B1(Δc)+B2(Δc)2+..., where t is the time and Δc is the concentration difference across the frit. The coefficient, B0, is a constant of integration, while the coefficients, BL,B1,B2,..., depend in general upon the cell constant, the compartment volumes, and the interdiffusion coefficient and various of its concentration derivatives evaluated at the mean concentration for the cell. Explicit formulas for BL,B1,B2,... are given.
A mean field theory for fluids of multipolar particles in contact with a polarizable wall
Authors: Bérard D. R. , Patey G. N.
Published: July 2002

Fluids of multipolar particles in contact with a semi-infinite polarizable hard wall are considered. A mean field theory which reduces the many-body electrostatic wall–solvent interactions to an effective pair potential is described. The effective potential can be employed in conjunction with the reference hypernetted-chain approximation, or some other integral equation theory, to obtain a self-consistent solution for the wall–solvent correlation function and hence the solvent structure at the interface. Explicit results are given for dipolar hard sphere fluids in contact with walls having dielectric constants ranging from 1 to ∞. For this system, it is shown that contributions to the wall–solvent potential from images of other particles are very important and act strongly against the direct ‘‘self-image’’ interaction.
Spin–orbit perturbations between the A(2)1Σ+ and b(1)3Π states of NaK
Authors: Sun Hongqiao , Huennekens John
Published: July 2002

We have studied spin–orbit perturbations between the A(2) 1Σ+ and b(1) 3Π0 states of the NaK molecule by accurately measuring the energies of mutually perturbing levels, and by measuring ratios of A(2) 1Σ+ → X(1) 1Σ+ and b(1) 3Π0 → a(1) 3Σ+ emission intensities, for five perturbed pairs. This allows two partially independent determinations of each perturbation matrix element ‖〈1 3Π0(v′t, J′)‖Ĥso‖21Σ+(v′s,J′)〉‖. From these matrix elements, and calculated vibrational overlap integrals 〈v′t‖v′s〉, the electronic part of the perturbation matrix element, Hel≡‖〈1 3Π0(v′t, J′)‖Ĥso‖2 1Σ+(v′s, J′)〉‖/‖〈v′t‖v′s〉‖, was obtained. Our results for Hel from the two methods are consistent, and independent of vibrational and rotational quantum numbers, as expected. The determined best value for Hel is (15.64±0.39) cm−1.
Ab initio investigation of the vibronic structure of the 3p 2Π (Rydberg) state of HCO and DCO
Authors: Perić M. , Peyerimhoff Sigrid D.
Published: July 2002

The results of an ab initio investigation of the vibronic structure of the 3p 2Π (Rydberg) state of HCO and DCO are presented. The potential curves obtained by large-scale configuration interaction (CI) calculations are employed. The theoretical results confirm a recent experimental analysis of the Renner–Teller effect in this state.
Spectroscopic characterization of the hydrogen bonded OC–HI in supersonic jets
Authors: Wang Z. , Lucchese R. R. , Bevan J. W. , Suckley A. P. , Rego C. A. , Legon A. C.
Published: July 2002

The hydrogen bond OC–HI has been characterized using high resolution microwave and infrared spectroscopies in supersonic seeded molecular jets. Ground state molecular parameters of the 16O12C–HI and 16O13C–HI isotopic species determined by the pulsed-nozzle Fourier transform microwave supersonic jet technique include: for 16O12C–HI, B0 (MHz)=900.9522(1), DJ (kHz)=2.519(1), CN (kHz)=0.94(18), χ(MHz)=−1346.238(13), χJ (kHz)=−8.27(31). The corresponding values for 16O13C–HI are 882.5997(2), 2.404(2), 0.87(19), −1349.481(17), and −7.76(28). This analysis is consistent only with a linear equilibrium dimer structure in which the proton is bound to the carbon atom of carbon monoxide. Other derived dimer parameters include: r(C–I)=4.271(2) Å, αav=24.8°, kσ(N m−1)=1.713. Infrared diode laser investigations provide a band origin frequency ν0 of 2148.549 040(29) cm−1 for the ν2 C≡O stretching fundamental vibration. This corresponds to a blue shift of 5.277 28(37) cm−1 relative to free monomer CO. Excited state molecular constants B2=898.2728(33) MHz. and DJ(2)=2.614(24) kHz are also determined. Line profiles are consistent with an excited state lifetime ≥0.54 ns.
Magnetic relaxation of xenon-131 dissolved in benzene. A study by molecular dynamics and Monte Carlo simulations
Authors: Luhmer M. , van Belle D. , Reisse J. , Odelius M. , Kowalewski J. , Laaksonen A.
Published: July 2002

Molecular dynamics and Monte Carlo simulations were carried out for xenon atoms dissolved in liquid benzene in order to study the quadrupolar relaxation mechanism of the xenon-131 nucleus. We confirm that a proper description of the relaxation is obtained by taking into account the quadrupole moment of benzene molecules. In contrast to the Xe–water system, the cross-correlation contribution to the electric field gradient (experienced by the Xe nucleus) is negligible in benzene, and the time correlation function of the total electric field gradient shows a relatively smooth decay. Several molecular motions take part in this decay, but not with the same efficiency. The major contribution can be attributed to the rotation of the benzene molecules around their C2 axes. The adequacy of the Sternheimer model for quadrupolar interactions is confirmed with ab initio calculations. Some methodological aspects of simulations are also discussed, such as the use of a termination function to treat the electrostatic interactions and the effect of the xenon interaction parameters on the simulated relaxation rate.
The real-time intramolecular electronic excitation transfer dynamics of 9′,9-bifluorene and 2′,2-binaphthyl in solution
Authors: Zhu F. , Galli C. , Hochstrasser R. M.
Published: July 2002

The dynamical behavior of intramolecular electronic excitation transfer in 9,9′-bifluorene and 2,2′-binaphthyl has been investigated in various solvents using a heterodyned and background-subtracted femtosecond polarization technique. It has been found that the excitation transfer between fluorenyl moieties occurs on a time scale of around 300 fs in hexane, but evidently slows down to around 970 fs in CCl4, and there appears little observable variation in transfer dynamics when the solvent is changed through the hexane–decane–hexadecane series. It has also been found that excitation transfer between naphthyl moieties in CCl4 undergoes damped oscillations which have an apparent period of 1.2±0.1 ps and a damping time constant of 180±20 fs. While there is no clear sign of any oscillation in hexane, the transfer dynamics decays only slightly faster. All the phenomena observed can be neatly categorized, within the simple phenomenological Bloch theory, as either over- or underdamped motion relevant to the ratio of the exciton splitting to the pure dephasing rate. However, it is the thorough analysis of all the secular elements of the Redfield relaxation matrix that pinpoints the role of correlated fluctuations in the excitation transfer, and provides a quantitative relation of the pure dephasing between the excited local states to that between the excited and ground states. The equivalency of the pure dephasing rate between the two local states to the population transfer rate between the two delocalized states also prompts us to propose that a local libration of solvent CCl4 could play a key role in underdamping the excitation transfer coherence.
Lifetime measurements on ArH and ArD
Authors: Wunderlich C. , Betz V. , Bruckmeier R. , Figger H.
Published: July 2002

We present results of lifetime measurements of rotational substates of the E 2Π state in the Rydberg molecules 40ArH and 40ArD. We find reasonable agreement between our result and theoretical predictions in the case of ArH. However, for ArD we obtain a distinctively longer lifetime than for the lighter isotopic molecule, ArH, which is not unusual for hydrides but is not accounted for by theory. In addition, different lifetimes measured for the Q and R,P-branch, respectively, emitting levels of the E 2Π state in ArD, give interesting insight into the interaction between excited Rydberg states of this molecule. The dependence of the lifetime of levels emitting the Q-branch on the rotational quantum number N for N≳19 is also investigated. Furthermore, the lifetime of the state(s) responsible for the continuous emission in the ultraviolet (UV) region was measured at discrete wavelengths for each of the molecules 40ArH and 40ArD. Our results, together with theoretical predictions, clearly favor the assignment of the UV continuum to two electronic states, namely B 2Π and E 2Π.
Rotational diffusion kinetics of polar solutes in hexamethylphosphoramide–water systems
Authors: Krishnamurthy M. , Khan Kishore Kumar , Doraiswamy S.
Published: July 2002

The rotational reorientation times (τr) of three kinds of dyes—cresyl violet (a monocation), nile red (neutral but polar), and resorufin (a monoanion) were measured in a series of binary mixtures of hexamethylphosphoramide (HMPA)–water at 298 K using the picosecond fluorescence depolarization spectroscopy. A hook-type profile of τr vs η was observed for all three dyes. The contribution due to the dielectric friction is minimal and is irrelevant in explaining the rotational dynamics of nile red. The dielectric friction correction is modest for cresyl violet and resorufin. The solvation effects in the binary mixture are dominant for understanding the rotational dynamics of cresyl violet. The microscopic structure features of the binary mixture are brought out by the study of resorufin.
Formation of Ar+(4p) by He(2 3S)+Ar+(2P3/2) excitation transfer and He++Ar(3P2) charge transfer in the helium flowing afterglow
Authors: Tsuji Masaharu , Kaneko Nobuo , Furusawa Makoto , Muraoka Toshihiko , Nishimura Yukio
Published: July 2002

Arii lines have been observed by addition of Ar into the He flowing afterglow. The effect of ion collection in the He afterglow and the energetics lead us to conclude that the He(2 3S)+Ar+(3p5 2P3/2ο) excitation transfer gives the ten Ar+(4p 4P5/2,3/2,1/2ο,4p 4D7/2,5/2,3/2,1/2ο, 4p 2D5/2,3/2ο,4p 2P1/2ο) levels in the 19.22–19.80 eV range, while the He++Ar(4s 3P2ο) charge transfer populates the three Ar+(4p 2P3/2ο,4p 4S3/2ο, 4p 2S1/2ο) levels in the 19.87–19.97 eV range. The relative rate constants for excitation of individual Ar+(4p) ions have been measured. The favored exit channel is the 4p 4P3/2ο level in the former reaction, and the 4p 2P3/2ο level in the latter reaction. Since these channels are 0.5–0.6 eV below the entrance channels, attractive entrance potentials are probably important for both reactions.
The initial slope of the transient birefringence of rigid macromolecules under the action of a reversing electric pulse of arbitrary field strength
Authors: Matsumoto Mitsuhiro
Published: July 2002

A solution is presented for the rotational diffusion equation of rigid macromolecules in solution under the action of a reversing electric pulse. The distribution function is expanded into a functional series composed of products tiPj of the power of time (ti) and Legendre polynomial (Pj). The coefficients of the series are then easily obtained up to a higher order of time from the simple recursion formulas. The initial slope of normalized reversing birefringence at an arbitrary field strength is simply expressed by two averages of the first order Legendre polynomial and the second order Legendre polynomial, <P1≳ and <P2≳, initial slope=2Θβ2/γ (1−<P2≳)/<P2≳−6Θβ/γ <P1≳/<P2≳. Furthermore, the initial slope for pure permanent dipole orientation (γ=0) is found to be independent of the electric field. That is, initial slope=−12Θ. On the other hand, the initial slope obtained by neglecting the Brownian motion at high fields is larger by 6Θ. For example, it is equal to −6Θ for pure permanent dipole orientation. This discrepancy is also discussed.
Experimental and theoretical study of the reaction of HO− with NO
Authors: Van Doren Jane M. , Viggiano A. A. , Morris Robert A. , Miller Amy E. Stevens , Miller Thomas M. , Paulson John F. , Deakyne Carol A. , Michels H. H. , Montgomery J. A.
Published: July 2002

Hydroxide ion (HO−) reacts with nitric oxide by slow reactive electron detachment with a rate coefficient ∼4×10−12 cm3 s−1 at 298 K. The detachment process is presumably associative detachment forming nitrous acid and an electron. Observations, data analysis, and alternative explanations for these observations are discussed. The associative detachment reaction was also investigated theoretically through calculations of the geometries, relative energies, and normal-mode vibrational frequencies of the relevant species HO−, HO, NO, cis- and trans-HONO, and cis- and trans-HONO−. These calculations indicate that in the ion HONO−, the cis conformer is more stable, while in the neutral HONO, the trans conformer is more stable. The HO–NO bond in HONO, which is formed in this reaction, is much stronger than the HO−–NO bond in HONO− with an energy of 198.7±1.8 kJ mol−1 for cis-HONO [J. Phys. Chem. Ref. Data 14, 1 (1985)] and 52.2±5 kJ mol−1 for cis-HONO− at 0 K. HONO− is bound with respect to HONO. The adiabatic electron detachment energy resulting from detachment from cis-HONO− forming the same conformer of the neutral molecule cis-HONO is 0.29±0.05 eV. The HO–NO equilibrium bond distance in HONO− is considerably longer than that in HONO, with values of 1.750 and 1.640 Å for trans- and cis-HONO−, respectively, and 1.429 and 1.392 Å for trans- and cis-HONO, respectively. These geometric and energetic characteristics of HONO− and HONO are combined with calculations of relative energies of these species at nonequilibrium/distorted HO–NO bond lengths to give a qualitative picture of the potential energy curves for these species along the reaction coordinate. While no significant energy barrier to autodetachment of HONO− is present, the Franck–Condon wave function overlap for autodetachment is small and is likely the reason for the observed inefficiency. The maximum calculated rate constant for associative detachment is 4×10−12 cm3 s−1, in good agreement with the observed value.
A generalized valence bond representation of complete-active-space self-consistent-field (CASSCF) wave functions
Authors: Murphy Robert B. , Messmer Richard P.
Published: July 2002

A novel generalized valence bond wave function expressed in terms of local nonorthogonal orbitals is shown to attain nearly all of the correlation energy of a corresponding complete-active-space self-consistent-field (CASSCF) wave function. This new wave function allows for the local orbitals to variationally respond to different spin couplings. The result is a very compact description of correlation effects contained in complex CASSCF expansions. The CASSCF expansion is also shown to contain a description of resonance among nonorthogonal valence bond structures.
Many-body calculations of the core excitation spectra of CO and NiCO: Disappearance of the giant shake-up satellite
Authors: Ohno M. , Decleva P.
Published: July 2002

The carbon and oxygen 1s core excitation spectra of free CO and NiCO are calculated by ab initio 1h1p/1h1p and 2h2p/2h2p configuration interaction (CI) method using an extended basis set. We employed the ground state as well as core–hole relaxed orbitals. For free CO, we obtain a reasonably good description of the electron energy loss spectroscopy (EELS) spectra. The present interpretation of the spectra agrees with others. For NiCO, we obtain a reasonably good description of the near edge x-ray absorption fine structure (NEXAFS) spectra of the CO/Ni(100) system and that of the electron energy loss spectroscopy (EELS) spectra of the gas phase Ni(CO)4 . We show the existence of the Rydberg-derived additional excited states in the NEXAFS spectra of the chemisorbed molecule and give an interpretation of these states. The disappearance of the giant shake-up satellite in the NEXAFS spectra of the adsorbate is explained in terms of the hindrance of the cooperative core–hole screening mechanism in the π* resonantly excited state. The core–hole screening mechanism in the σ* resonantly excited state is also investigated.
Inclusion–exclusion calculation of the dipole–dipole energy of hexagonal ice and of cubic ice
Authors: Huckaby Dale A. , Pitiş Radu , Kincaid Robert H. , Hamilton Chris
Published: July 2002

The principle of inclusion and exclusion is adapted to derive an expansion for properties of disordered hydrogen-bonded systems. A dendritic approximation to this expansion is used to calculate the dipole–dipole energy of hexagonal ice and of cubic ice. The calculated difference in dipole–dipole energy of these open forms of ice favors the hexagonal one in stability and accounts for most of the experimental energy difference.
On the nonlinear behavior of dielectric relaxation in alternating fields. II. Analytic expressions of the nonlinear susceptibilities
Authors: Déjardin Jean-Louis , Debiais Georges , Ouadjou Abdesselam
Published: July 2002

Starting from the rotational diffusion equation of Smoluchowski, the ensemble average of the first Legendre polynomial appropriate to dielectric relaxation is calculated. The corresponding response is given up to the third order in the applied electric field by considering a constant field on which is superimposed an alternating field. Moreover, the polar molecules are assumed to be anisotropically polarizable. Thus, we obtain three harmonic components of the electric susceptibility where nonlinear coupling effects appear between the unidirectional field and the alternating field together with permanent and induced dipole moments. Dispersion plots are presented for some values of the parameter P which measures the ratio between induced and permanent moments. Also, for some values of this parameter P, the variations of phase angles with frequency are considered and it is shown how they are interesting in the treatment of experimental data by application of Kramers–Kronig relations.
Examination of several exchange-correlation energy functionals by accurate self-consistent atomic calculations
Authors: Zhu Tianhai , Lee Chengteh , Yang Weitao
Published: July 2002

Several local and nonlocal exchange-correlation functionals are tested through accurate Kohn–Sham self-consistent calculations for six nobel gas atoms and three isoelectronic series (with two, four, and ten electrons and atomic numbers up to 20). The calculated exchange, correlation, and total energies have been compared with those from accurate Hartree–Fock calculations and accurate estimates of correlation energies available recently. Improvements over local-density approximation are found for all the tested nonlocal exchange-correlation functionals. In particular, nonlocal correlation energy functionals are shown to perform significantly better than the local approximations when both are used in conjunction with the nonlocal Becke’s exchange energy functional. However, in most cases, all the functionals fail to predict the correct trends of exchange and correlation energies as the atomic charge increases.
Spectra of isotopic ice mixtures
Authors: Wojcik M. J. , Buch V. , Devlin J. P.
Published: July 2002

Studies of vibrational spectra of ice I and amorphous ice in the stretching mode frequency range were extended to include (a) the observed effect of a full range of isotopic dilution on the infrared spectra and (b) computational modeling of the observed influence of each dilution step on the properties of vibrationally excited states and on infrared and Raman spectra. The quantum-mechanical computational scheme included effects of frequency lowering due to hydrogen bonding, and of intra- and intermolecular coupling between bonds. The H2O/D2O mixtures can be viewed as a collection of clusters of one X2O isotopomer embedded in a matrix of the other isotopomer. The properties of the vibrationally excited states and of the spectra are determined by complex interplay between the size distribution of the embedded clusters, and the inter- and intramolecular coupling. Vibrational excitations are delocalized over large portions of the embedded clusters. In the limit of a pure crystalline isotopomer, the excitations are delocalized over the entire system and thus proton disorder alone is insufficient to induce localization. The excitations in pure amorphous ice show more pronounced localization effects at the band edges. Throughout the entire composition range, the vibrations of molecules in the low frequency regime retain symmetric stretch character, and the vibrations in the high frequency regime retain antisymmetric stretch character. The perpendicularly polarized Raman spectrum peaks in the region of the latter states. The parallel-polarized Raman spectrum peaks in the low frequency end of the band where the states are globally symmetric, i.e., the contributions of excitations of all bonds to a state are of the same sign. The infrared spectrum extends over the entire band and follows roughly the density of states.
Path integral description of polymers using fractional Brownian walks
Authors: Cherayil Binny J. , Biswas Parbati
Published: July 2002

The statistical properties of fractional Brownian walks are used to construct a path integral representation of the conformations of polymers with different degrees of bond correlation. We specifically derive an expression for the distribution function of the chains’ end-to-end distance, and evaluate it by several independent methods, including direct evaluation of the discrete limit of the path integral, decomposition into normal modes, and solution of a partial differential equation. The distribution function is found to be Gaussian in the spatial coordinates of the monomer positions, as in the random walk description of the chain, but the contour variables, which specify the location of the monomer along the chain backbone, now depend on an index h, the degree of correlation of the fractional Brownian walk. The special case of h=1/2 corresponds to the random walk. In constructing the normal mode picture of the chain, we conjecture the existence of a theorem regarding the zeros of the Bessel function.
Far-infrared laser vibration–rotation–tunneling spectroscopy of the propane–water complex: Torsional dynamics of the hydrogen bond.
Authors: Steyert David W. , Elrod Matthew J. , Saykally Richard J.
Published: July 2002

The far-infrared laser vibration–rotation–tunneling (FIR-VRT) spectrum of the propane–water complex has been measured in the range 18–22 cm−1. A C-type VRT band has been assigned with a band origin of 19.6 cm−1. The data support the ‘‘kite-shaped’’ structure determined from microwave spectroscopy in the accompanying paper, and indicate that the observed VRT band corresponds to torsional motion of the free water proton about the hydrogen bond. This motion is impeded by a barrier that is less than 5 cm−1. We describe our modification of the supersonic slit-jet source designed to permit Stark effects to be measured, and have used second-order Stark shifts to help assign the perpendicular transition observed.