bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron propagator calculations on linear and branched carbon cluster dianions
Authors: Zakrzewski V. G. , Ortiz J. V.
Published: July 2002

Electron propagator calculations have been performed on linear carbon cluster dianions from C2−7 to C2−10 and on branched C2−7, C2−9, and C2−11 structures which have a central, tricoordinate carbon bound to three branches with alternating long and short bonds. The more stable, branched isomer of C2−7 has a positive vertical ionization energy, but the linear form does not. While linear C2−10 is stable with respect to electron loss, it is not possible to decide from these calculations whether linear C2−8 and C2−9 have the same property. There is evidence that better calculations would obtain bound C2−8 and C2−9 species. Vertical ionization energies of all branched dianions are positive. Feynman–Dyson amplitudes for dianion ionization energies display delocalized π bonding, with the two terminal carbons of the longest branches making the largest contributions.
Local-scaling transformations and the direct determination of Kohn–Sham orbitals and potentials for beryllium
Authors: Ludeña Eduardo V. , Maldonado Jorge , López-Boada Roberto , Koga Toshikatsu , Kryachko Eugene S.
Published: July 2002

Local-scaling transformations are used in the present work to obtain accurate Kohn–Sham 1s and 2s orbitals for the beryllium atom by means of a density-constrained variation of the single-determinant kinetic energy functional. An analytic representation of these Kohn–Sham orbitals is given and the quality of the different types of orbitals generated is discussed with particular reference to their kinetic energy and momenta mean values. In addition, we determine the effective Kohn–Sham potential and analyze it in terms of its exchange-only and correlation contributions.
A scaling and mapping theory for excess electrons in simple fluids
Authors: Cao Jianshu , Berne B. J.
Published: July 2002

A simple scaling argument is proposed to understand the localization of excess electrons in simple fluids and to interpolate numerical results of path integral simulations and reference interaction site—polaron theory. A mapping is found between an impenetrable object of arbitrary geometry and a spherical hard sphere. Numerical simulations of solvated electrons in atomic and diatomic solvents are used to demonstrate the validity and applicability of these scaling and mapping schemes.
A new potential energy surface for N+O2: Is there an NOO minimum?
Authors: Walch Stephen P.
Published: July 2002

We report a new calculation of the N+O2 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of NO2 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the O1s and N1s electrons with a cc-pVQZ basis set.
A new method for calculating the rovibrational states of polyatomics with application to water dimer
Authors: Althorpe S. C. , Clary D. C.
Published: July 2002

A new method is developed for calculating the lowest few rovibrational states of polyatomic molecules, using the discrete variable representation (DVR). The method is an extension to the diagonalization-truncation procedure which has been used in most DVR calculations to date. It starts with a set of functions which approximately describe the wave function at a set of DVR points, and adds corrections to them by using variation-perturbation theory. This is done iteratively, after the manner of the recently developed iterative secular equation (ISE) method of Slee and LeRoy. This new ‘‘DVR-ISE’’ method can be successfully applied to molecules whose dynamics involve strong coupling between all degrees of freedom. To demonstrate this it is applied to (H2O)2 in calculations of the lowest few energy levels for intermolecular angular motion. Better convergence is obtained than was found possible in conventional finite basis calculations on the same system.
Infrared absorption of cis- and trans-alkali-metal peroxynitrites (MOONO, M=Li, Na, and K) in solid argon
Authors: Lo Wen-Jui , Lee Yuan-Pern , Tsai Jyh-Hsin M. , Tsai Hui-Hsu , Hamilton Tracy P. , Harrison Joseph G. , Beckman Joseph S.
Published: July 2002

Potassium nitrate (KNO3) isolated in solid argon at 13 K was irradiated with emission from an ArF excimer laser at 193 nm. Recombination of the photofragments led to formation of both cis- and trans-potassium peroxynitrites (KOONO). The cyclic conformer, cis-KOONO, absorbs at 1444.5, 952.3, 831.6, and 749.1 cm−1, whereas trans-KOONO absorbs at 1528.4, 987.4, and 602.2 cm−1. The assignments are based on observed 18O- and 15N-isotopic shifts and comparison with similar compounds, cis–cis and trans–perp HOONO. Ab initio calculations using density functional theory at a Becke3LYP level predicted similar line positions and isotopic shifts for both conformers. Photoconversion among these three isomers was achieved at various wavelengths and periods of irradiation; cis-KOONO was photolyzed readily at 308 nm, whereas trans-KOONO increased slightly in intensity initially and was eventually transformed to KNO3 on prolonged irradiation. Similar results were obtained for LiNO3 and NaNO3; cis-LiOONO and cis-NaOONO absorb at (1423.4, 1422.0), 966.2, 874.2, 792.3 cm−1 and (1437.4, 1434.6), 961.4, 840.7, (770.9, 768.7) cm−1, respectively, whereas trans-LiOONO and trans-NaOONO absorb at (1581.6, 1580.4), (998.3, 995.6), 600.4 cm−1 and (1549.3, 1540.6), (996.3, 994.1), (609.4, 607.4) cm−1, respectively; the numbers in parentheses are due to line splitting.
Pure rotational spectrum of FeCO
Authors: Kasai Yasuko , Obi Kinichi , Ohshima Yasuhiro , Endo Yasuki , Kawaguchi Kentarou
Published: July 2002

The rotational spectrum of the FeCO radical has been observed by using a Fabry–Perot type Fourier-transform microwave spectrometer combined with a pulsed discharge nozzle. The radicals have been generated by a discharge of Fe(CO)5 diluted in Ar, and subsequently cooled down to a few kelvins in a supersonic free jet. Four spectral lines observed in the 8.5–35.5 GHz region have been assigned to the transitions in the Ω=0 spin component of 56FeCO, the most abundant isotopic species, in the 3Σ− electronic ground state, and analyzed to obtain the spectroscopic constants. Transitions in the Ω=±1 spin components have not been detected due to the small population in these levels. Spectra of other four isotopic species, 54FeCO, 57FeCO, Fe13CO, and Fe13C18O, have also been observed to confirm the identification of the species, yielding the substituted coordinates of the molecule. The determined Fe–C bond length [rs(Fe–C)=1.727 Å] is about 0.1 Å shorter than that of Fe(CO)5, but the C–O bond length [rs(C–O)=1.160 Å] is almost the same as that of Fe(CO)5, which indicates stronger Fe–CO bonding than that of Fe(CO)5. We have searched for the 34 GHz transition of the radical toward several molecular clouds on various evolutionary stages by using the Nobeyama 45 m radio telescope. The signal of this radical was not detected with rms noise level of 10 mK, which gives an upper limit for the molecular column density of (2–4)×1012 cm−2.
Quantum scattering studies of the Λ doublet resolved rotational energy transfer of OH(X 2Π) in collisions with He and Ar
Authors: Esposti Alessandra Degli , Berning Andreas , Werner Hans-Joachim
Published: July 2002

Three dimensional potential energy surfaces for the collision systems OH(X 2Π)+He and OH(X 2Π)+Ar have been calculated using the coupled electron pair approximation (CEPA) and large basis sets. The asymptotically degenerate 2Πx and 2Πy states split into two states of 2A′ and 2A″ symmetry, respectively, when the C∞v symmetry is lifted by the approach of the noble gas atom. The average and half difference of the calculated points on the A″ and A′ potential energy surfaces were fitted to analytical functions, which were then vibrationally averaged. These potential energy surfaces have been used in quantum scattering calculations of cross sections for collision induced rotationally inelastic transitions. Test calculations showed that the cross sections obtained from exact close-coupling calculations (CC) and within the coupled states approximation (CS) are in close agreement for these systems, and therefore the CS approximation has been used in all further calculations. Rotational transitions with Λ doublet resolution show, within the same spin–orbit manifold and at low collision energies, a propensity to populate preferentially the e final levels in the F1(2Π3/2) state and an e/f conserving propensity in the F2(2Π1/2) state, while transitions between the two spin–orbit manifolds show a parity conserving propensity. For the v=2 vibrational level kinetic rate coefficients were calculated for a large range of temperatures. The calculated cross sections are in excellent agreement with recent measurements of Schreel, Schleipen, Epping, and ter Meulen.
Photoelectron spectroscopy of silicon–carbon cluster anions (SinC−m)
Authors: Nakajima Atsushi , Taguwa Tetsuya , Nakao Kojiro , Gomei Motoki , Kishi Reiko , Iwata Suehiro , Kaya Koji
Published: July 2002

Photoelectron spectra of SinC−m cluster anions (1≤n≤7 and 1≤m≤5) were measured at the photon energies of 3.49 eV, by using a magnetic bottle electron spectrometer. The SinC−m clusters were produced either by a laser vaporization of a silicon–carbon mixed rod or by two laser vaporizations of carbon and silicon rods in a He carrier gas. The spectra of the SinC−1 (3≤n≤7) clusters are similar to those of pure Si−n+1 clusters in the peak positions and their envelopes, which is attributed to the isovalent electronic structure of Si and C atoms as well as to the similar geometrical structure. In contrast, the similarity in the photoelectron spectra is not observed between C−m+1 and Si1C−m (2≤m≤5) clusters, which is attributed to a change in their geometry; from chain to ring. These experimental conclusions are discussed with the results of our theoretical calculations.
Ab initio potential energy surface for the HCl dimer
Authors: Tao Fu-Ming , Klemperer William
Published: July 2002

An intermolecular potential energy surface for the dimer of hydrogen chloride in the ground state is calculated at the levels of the second-order (MP2) and fourth-order (MP4) Mo/ller–Plesset approximations using a large basis set containing bond functions. The surface is characterized by the minimum energy pathway through two equivalent hydrogen-bonded structures. The hydrogen-bonded equilibrium geometry has the centers of mass distance Rm=3.78 Å and polar angles θ1=8.0° and θ2=90.0° (at MP2 level). The well depth at the hydrogen-bonded minimum is Vm=−710.9 cm−1 at MP2 and Vm=−643.9 cm−1 at MP4 level. The interchange barrier between the two equivalent minima occurs at R=3.68 Å, θ1=θ2=46.0°, with the barrier height of 58.6 cm−1 at MP2 and 45.9 cm−1 at MP4 level (with the MP2 geometries). These results are in good agreement with a new empirical potential of Elrod and Saykally. Our calculations show that the bonding in the HCl dimer is dominated by the dispersion forces, which is different from the bonding in other classical hydrogen-bonded systems such as the hydrogen fluoride dimer and the water dimer.
Theoretical studies on the conductance of polyaniline chains
Authors: Hey R. , Schreiber M.
Published: July 2002

We investigate the electrical transport properties of polyaniline chains. On the basis of available band structure data, we construct an empirical tight-binding Hamiltonian of the respective molecules. From the so-derived parameters we are able to obtain the scattering properties of the system. These scattering coefficients determine the transmission through the sample required to calculate the conductance of the chain within the Landauer–Büttiker approach.
Resonance-enhanced multiphoton electron detachment spectrum of C5−
Authors: Ohara M. , Shiromaru H. , Achiba Y. , Aoki K. , Hashimoto K. , Ikuta S.
Published: July 2002

The resonance-enhanced multiphoton electron detachment spectrum of C5− was measured. The peaks observed at 470–500 nm were assigned to be 1 photon excitation of 2Πu to the 2Πg state. The vibrational structure gives the symmetric stretching frequency of ν2=718±43 cm−1 for the excited state of C5−.
Line coupling effects in anisotropic Raman Q branches of the ν1/2ν2 Fermi dyad in CO2
Authors: Lavorel B. , Fanjoux G. , Millot G. , Bonamy L. , Emond F.
Published: July 2002

The generalized energy corrected sudden model is used to calculate the Q branch of the anisotropic coherent anti-Stokes Raman scattering spectra corresponding to the ν1 and 2ν2 transitions of the Fermi dyad of CO2. The corresponding experimental spectra have been recorded for pressures leading to a consistent overlapping between the rotational components. This leads to a new experimental evaluation of the relaxation time of the second-order tensor associated with the rotational angular momentum. The value is in excellent agreement with that already obtained from the study of the infrared absorption Q branch, the Rayleigh scattering, and the viscomagnetic effect.
Internal dynamics contributions to the CH stretching overtone spectra of gaseous monohydrogenated nitromethane NO2CHD2
Authors: Cavagnat D. , Lespade L. , Lapouge C.
Published: July 2002

The methyl CH-stretching overtone spectra of gaseous monohydrogenated nitromethane NO2CHD2 have been recorded with conventional near infrared spectroscopy in the ΔvCH=1 to 4 regions and by intracavity laser photoacoustic spectroscopy in the ΔvCH=5 and 6 regions. They all exhibit a complex structure with, at ΔvCH=1 and 2, a characteristic asymmetric top vibration–rotation profile which vanishes as vibrational energy increases. These spectra have been analyzed with a theoretical model which takes into account in the adiabatic approximation the coupling between the anharmonic CH stretch described by a Morse potential and the quasifree internal rotation of the methyl group. All the parameters of this model (the zero point energy, the CH stretch frequency, the expansion coefficients of the dipole moment function) and their variation with the internal rotation coordinate have been determined from HF/6-31G** ab initio calculations. This simple calculation, which contains no adjustable parameters, successfully describes the relative intensity and frequency of each peak within a given overtone and accounts for the variation of the dipole moment function as the vibrational energy increases. Owing to the relative localization of the wave functions within the effective potential wells, the spectral features can be assigned to particular pseudoconformers. The outer bands correspond to rovibrational transitions associated with the parallel and perpendicular conformation of the CH bond versus the molecular plane, the central band is generated by ‘‘free rotor’’ rovibrational transitions. Fermi resonance phenomena lead to no sizeable IVR until the fifth overtone. The CH/CD interbond coupling shifts the overtone spectra toward high frequency and is responsible for some additional weaker features in the high overtone spectra (Δv=5 and 6).
Spin density in first-row diatomic hydrides from the Hiller–Sucher–Feinberg identity
Authors: Rassolov Vitaly A. , Chipman Daniel M.
Published: July 2002

The delta function and Hiller–Sucher–Feinberg (HSF) operators are compared for calculation of electronic spin density at the nucleus. New methods are designed and implemented for evaluation of the difficult molecular integrals over the HSF operator. Calculations are carried out with wave functions that include spin polarization effects using Gaussian basis sets and, to estimate the complete basis set limit, with a seminumerical procedure. Results are reported for the diatomic hydrides CH, NH, and OH in their ground states. While the HSF operator gives much better total densities at the heavy atoms, the delta function and HSF operators are found to perform overall about equally well for spin densities.
On the mechanism of pinning in phase-separating polymer blends
Authors: Castellano Claudio , Glotzer Sharon C.
Published: July 2002

We reexplore the kinetics of spinodal decomposition in off-critical polymer blends through numerical simulations of the Cahn–Hilliard equation with the Flory–Huggins–De Gennes free energy functional. Even in the absence of thermal noise, the solution of the discretized equation of motion shows coarsening in the late stages of spinodal decomposition without evidence of pinning, regardless of the relative concentration of the blend components. This suggests this free energy functional is not sufficient to describe the physics responsible for pinning in real blends.
Quantum mechanical studies of photodesorption of ammonia from a metal surface: Isotope effects, final state distributions, and desorption mechanisms
Authors: Guo Hua , Seideman Tamar
Published: July 2002

The photodesorption dynamics of ammonia from a copper surface is studied quantum mechanically using empirical potential energy surfaces. The desorption is facilitated by substrate-mediated electronic excitation and subsequent de-excitation of the adsorbate, which are simulated in our model as Franck–Condon pump and dump between two electronic states. The delayed de-excitation populates metastable predesorption states which lay above the desorption limit. The slow decay of these resonances via energy transfer from an internal mode to the desorption mode results in incomplete and rather slow desorption. The desorbed molecules have significant vibrational excitation and their translational energy distributions are highly structured, due to the dominance of the predesorption mechanism. The desorption yield depends sensitively on the time delay between the excitation and de-excitation. Strong isotope effects are observed, consistent with experimental findings. The anomalously large NH3 yield relative to ND3 is attributed to its faster motion along the inversion coordinate on the excited state.
Backward Euler and other methods for simulating molecular fluids
Authors: Wu Jian , Watts Robert O.
Published: July 2002

Two implementations of the backward Euler method for simulating molecular fluids are compared with Brownian dynamics and molecular dynamics simulations of a single diatomic molecule, liquid argon, a single butane molecule, and liquid butane. By comparison with standard molecular dynamics results, backward Euler simulations give different thermodynamic properties for liquids; predict liquid structures which are too solidlike; and incorrectly represent dynamical relaxation processes. The backward Euler methods allows longer time steps to be used in simulations at the cost of an energy minimization at every time step. Even when time steps more than 20 times larger than that required for energy and momentum conservation are used, neither implementation of the backward Euler algorithm is more accurate than standard molecular dynamics calculations with the same time step. We conclude that the new methods offer no computational advantages over more usual methods for simulating molecular fluids and that they often predict incorrect results.
Three-body effects on molecular properties in the water trimer
Authors: Gregory Jonathon K. , Clary David C.
Published: July 2002

We report an application of diffusion Monte Carlo to investigate the importance of three-body forces on the properties of the water trimer. The potential energy surface used is due to Millot and Stone and is based on intermolecular perturbation theory to which three-body induction and dispersion energies are added. The effects of the three-body forces are considered by comparison with the same potential containing only pairwise water interactions. We have calculated minimum energy structures, vibrationally averaged structures, zero-point energies, rotational constants, cluster dissociation energies, and tunneling splittings, with and without the three-body forces. The values obtained for the vibrationally averaged rotational constants with the three-body potential are fairly close to the experimental values. Whereas the rotational constants are shown to have a significant dependence, the tunneling splittings are changed little by the three-body forces. Based on the calculated difference in anharmonic zero-point energies in water dimer and trimer, we predict that vibrational excitation of a stretching mode will cause predissociation in (H2O)3 but probably not in (D2O)3.
A new method for obtaining distributions of relaxation times from frequency relaxation spectra
Authors: Alvarez F. , Alegría A. , Colmenero J.
Published: July 2002

Starting from the well-known CONTIN algorithm/program [S. W. Provencher, Comput. Phys. Commun. 27, 213 (1982)] for the calculation of inverse Laplace transformations, we have developed a new method for obtaining distributions of relaxation times out of frequency relaxation spectra. The method has been tested under several different restrictive conditions, many of them harder than those of actual real experiments and has proved to be successful. Moreover, to our knowledge, it gives the best power resolution ever referenced and its ability to undergo the problem of noise seems to be better than those of other algorithms used to treat the kind of ill-conditioned problems presented here. Our program can be directly applied on the data without the need of performing any interpolation nor extrapolation, which could somehow bias the results, especially in the extrapolation case. Some practical applications of the method are shown for the analysis of the dielectric relaxation spectra of both, a bulk homopolymer polyvinyl chloride and a liquid crystalline polymer. The method is also generalized to deal with different problems where the physical mechanisms involved or the technical procedure suggest to use distributions of non-Debye processes.
A comparison of liquid–vapor coexistence in charged hard sphere and charged hard dumbbell fluids
Authors: Shelley J. C. , Patey G. N.
Published: July 2002

Simulations are used to show that fluids of charged hard spheres and charged hard dumbbells have similar liquid-vapor coexistence curves. We conclude that the condensation of ionic fluids is largely driven by the interaction of ion pairs. The relevance of this observation to current theories of ionic condensation is discussed.
Computer simulations of the linewidth of the Raman Q-branch in fluid nitrogen
Authors: Michels J. P. J. , Scheerboom M. I. M. , Schouten J. A.
Published: July 2002

By means of molecular dynamical simulations, the width of the Raman line in fluid N2 is calculated at room temperature and pressures up to the melting line. The results are compared with experimental results for the linewidth and for the dephasing time. Detailed information is given about the relaxation mechanism of the vibrational frequency. For instance, a marked influence of the vibration-rotation coupling is seen, in particular at high pressures. Moreover, the time correlation function of the frequency reveals a long time behavior at high pressures. From a comparison of the simulated change in vibrational frequency as a function of pressure with experimental data for the line shift, an estimate is made for the contribution of the so-called ‘‘attractive part’’ to that shift.
Characterization of the minimum energy paths for the ring closure reactions of C4H3 with acetylene
Authors: Walch Stephen P.
Published: July 2002

The ring closure reaction of C4H3 with acetylene to give phenyl radical is one proposed mechanism for the formation of the first aromatic ring in hydrocarbon combustion. There are two low-lying isomers of C4H3; 1-dehydro-buta-1-ene-3-yne (n-C4H3) and 2-dehydro-buta-1-ene-3-yne (iso-C4H3). It has been proposed that only n-C4H3 reacts with acetylene to give phenyl radical, and since iso-C4H3 is more stable than n-C4H3, formation of phenyl radical by this mechanism is unlikely. We report restricted Hartree–Fock (RHF) plus singles and doubles configuration interaction calculations with a Davidson’s correction (RHF+1+2+Q) using the Dunning correlation consistent polarized valence double zeta basis set (cc-pVDZ) for stationary point structures along the reaction pathway for the reactions of n-C4H3 and iso-C4H3 with acetylene. n-C4H3 plus acetylene (9.4) has a small entrance channel barrier (17.7) (all energetics in parentheses are in kcal/mol with respect to iso-C4H3 plus acetylene) and the subsequent closure steps leading to phenyl radical (−91.9) are downhill with respect to the entrance channel barrier. Iso-C4H3 plus acetylene also has an entrance channel barrier (14.9) and there is a downhill pathway to 1-dehydro-fulvene (−55.0). 1-dehydro-fulvene can rearrange to 6-dehydro-fulvene (−60.3) by a 1,3-hydrogen shift over a barrier (4.0), which is still below the entrance channel barrier, from which rearrangement to phenyl radical can occur by a downhill pathway. Thus, both n-C4H3 and iso-C4H3 can react with acetylene to give phenyl radical with small barriers.
Variational transition state theory for curve crossing processes: A uniform rate expression
Authors: Rips Ilya , Pollak Eli
Published: July 2002

A new approach is suggested for evaluation of the radiationless transition rate for the curve-crossing problem in the presence of dissipation. The rate is evaluated by using the conventional Landau–Zener theory but for a collective system–bath coordinate, which is characterized by a maximal mean-free path in the vicinity of the crossing point. Variational transition state theory (TST) is employed for determination of this quasiballistic mode. The resulting uniform rate expression bridges between the known nonadiabatic, solvent controlled and TST limits. The main effect of dissipation is the reduction of the slope difference of the potential of mean force along the quasiballistic mode compared to that along the original reaction coordinate. This results in an increase of the reaction adiabaticity. Application of the theory is illustrated for the symmetric normal crossing of two parabolic diabatic terms with Ohmic dissipation. Explicit results for the rate in the relevant physical limits are derived. The theory is also used to analyze resonant electron transfer reactions in Debye solvents.
Diffusional distortion of the free-energy gap law
Authors: Burshtein A. I.
Published: July 2002

The free-energy gap law in back electron transfer reactions is shown to be affected by encounter diffusion in photogenerated ion pairs. The ion separation quantum yield increases when initial separation of ions is large compared to the radius of the reaction layer and decreases in the opposite situation when ions are created in contact but recombine outside. The effect changes the sign with free energy when passing from the normal region of recombination to the inverted one. As a result, the top of a bell-shaped curve representing the free-energy gap law is subjected to qualitative distortion, which is stronger when diffusion is slower.
Experimental investigation of weakly bound B(2p,3s)–H2/D2 complexes through laser fluorescence excitation spectroscopy
Authors: Yang Xin , Hwang Eunsook , Alexander Millard H. , Dagdigian Paul J.
Published: July 2002

The nonbonding interaction of boron atoms, in their ground 2s22p 2P and excited 2s23s 2S states, with H2 and D2 has been investigated through laser fluorescence excitation spectroscopy in a supersonic free jet. For these isotopomeric complexes, an asymmetric, unstructured feature is observed, with maximum intensity ∼620 cm−1 to the blue of the 3s 2S–2p 2P atomic transition. The width of this feature is somewhat narrower for B–D2 than for B–H2. The fluorescence emission occurs in the same wavelength range as the boron atomic transition. These observations imply that the B(3s)–H2 interaction is repulsive in the Franck–Condon region. No evidence for chemical reaction on the excited BH2 potential energy surface was found. The observed formation of these complexes in the supersonic beam also suggests that there is a significant barrier to formation of the stable BH2 molecule from B(2p)+H2. These spectra have been interpreted with the help of ab initio calculations of the B(2p,3s)–H2 interactions and the bend–stretch energies of the complex, both reported in the preceding paper [M. H. Alexander and M. Yang, J. Chem. Phys. 103, 7956 (1995)]. From comparison with these calculations, our spectra can be assigned as electronic excitation from the lowest bend–stretch level of the B(2p)–H2/D2 complex to a repulsive region of the electronically excited potential energy surface. Spectral simulations based on the theoretical treatment of this nonbonding interaction reproduce quite well the observed spectra.
The dipole moment and magnetic hyperfine properties of the excited A 2Σ+(3sσ) Rydberg state of nitric oxide
Authors: Glendening Eric D. , Feller David , Peterson Kirk A. , McCullough E. A. , Miller R. J.
Published: July 2002

The dipole moment and magnetic hyperfine properties of the A 2Σ+ Rydberg state of nitric oxide have been evaluated at a variety of levels of theory with extended correlation consistent basis sets. Using the finite field approach to compute the dipole moment, restricted coupled cluster RCCSD(T) and complete active space-configuration interaction CAS-CI+Q methods yield values (1.09–1.12 D) that are essentially identical to experiment. In contrast, dipole moments computed as an expectation value of the dipole moment operator typically differ from experiment by 0.1–0.6 D. The rather unfavorable comparisons with experiment reported in previous theoretical studies may stem, in part, from the method chosen to evaluate the dipole moment. Magnetic hyperfine properties were evaluated using a variety of unrestricted and restricted open-shell Hartree–Fock-based methods. We estimated the full CI limiting properties by exploiting the convergence behavior of a sequence of MRCI wave functions. The isotropic component Aiso(14N) of 39±1 MHz evaluated in this fashion is in excellent accord with the experimental value of 41.4±1.7 MHz. Highly correlated UHF-based methods [e.g., CCSD(T) and QCISD(T)] yield comparable values of 40–41 MHz that are in good agreement with both experiment and the apparent full CI limit. However, for Aiso(17O), the full CI limit (−97±2 MHz) and the UHF-based results (ca.−118 MHz) differ by roughly 20 MHz. It remains unclear how to reconcile this large discrepancy.
Ab initio characterization of the low-lying vibrations of HCO (DCO) in the B̃ 2A′ state
Authors: Qi Jianxin , Bowman Joel M. , Manaa M. Riad
Published: July 2002

We report a force field for HCO in the B̃ 2A′ electronic state, based on ab initio electronic energies obtained using state-averaged multiconfiguration-self-consistent field/configuration interaction wave functions. The force field is used in rigorous calculations of 27 excited vibrational states of HCO and DCO, which are compared with experiment. A detailed analysis of the fundamentals of HCO and DCO suggests a reassignment of the experimental fundamentals of DCO is necessary.
The spin-forbidden a 4Π(ν=13–15) and b 4Σ−(ν=3)←X 2Π(ν=0) bands of nitric oxide: A new scheme for quantum state-specific high-resolution kinetic energy measurements
Authors: Drabbels Marcel , Morgan C. G. , Wodtke A. M.
Published: July 2002

A new scheme for performing high-resolution kinetic energy measurements on single quantum states of NO is described. Laser excitation of the a 4Π(ν=13–15) and b 4Σ−(ν=3)←X 2Π(ν=0) spin-forbidden bands has been used to produce NO a 4Π, either by direct excitation or after excitation to NO b 4Σ− followed by b→a emission. The sensitivity is compared to previous experiments on CO, employing the forbidden Cameron system. In the course of these experiments, three previously unknown vibronic levels of the a 4Π state were observed for which high precision molecular constants have been obtained. The derived molecular constants have been used to construct a chemically accurate RKR potential for the a 4Π state to within 0.2 eV of the dissociation limit. In addition, the electric dipole moments for the a 4Π(ν=13–14) levels have been determined. By comparing the experimental results with two ab initio calculations, the polarity of the dipole moment of the a 4Π state at equilibrium separation could be determined. A set of supplementary molecular beam laser-induced fluorescence studies on the b 4Σ−(ν=3)←X 2Π(ν=0) band were also carried out. These allowed the fluorescence lifetime of b 4Σ−(ν=3) state to be obtained under collision-free conditions and the electronic origin of the quartet manifold to be determined within 0.03 cm−1.
Determination of the long-range potential and dissociation energy of the 1 3Δg state of Na2
Authors: Ji Bing , Tsai Chin-Chun , Li Li , Whang Thou-Jen , Lyyra A. Marjatta , Wang He , Bahns John T. , Stwalley William C. , LeRoy Robert J.
Published: July 2002

The 1 3Δg state of Na2 has been studied extensively by both filtered fluorescence and ionization detection and analyzed by both Dunham-type expansion and near-dissociation expansion (NDE) models in the analysis. Our observations have covered 99.998% of the potential well depth with the outermost Rydberg–Klein–Rees (RKR) turning point at 28.02 Å. NDE analysis gives Te=28 032.468 (±0.021) cm−1, De=7162.436 (±0.021) cm−1, and Re=3.463 81 (±0.000 28) Å. Significant long-range behavior in the near dissociation levels has been observed. Fitting of the RKR turning points gives the long-range coefficients C5=1.388 (±0.031)×106 cm−1 Å5 and C6=0.4008 (±0.0046)×108 cm−1 Å6. These newly observed results show reasonable agreement with recent theoretical calculations.
A fast Fourier transform method for the quasiclassical selection of initial rovibrational states of triatomic molecules
Authors: Eaker Charles W. , Schwenke David W.
Published: July 2002

This paper describes the use of an exact fast Fourier transform method to prepare specified vibrational–rotational states of triatomic molecules. The method determines the Fourier coefficients needed to describe the coordinates and momenta of a vibrating–rotating triatomic molecule. Once the Fourier coefficients of a particular state are determined, it is possible to easily generate as many random sets of initial Cartesian coordinates and momenta as desired. All the members of each set will correspond to the particular vibrational–rotational state selected. For example, in the case of the ground vibrational state of a nonrotating water molecule, the calculated actions of 100 sets of initial conditions produced actions within 0.001ℏ of the specified quantization values and energies within 5 cm−1 of the semiclassical eigenvalue. The numerical procedure is straightforward for states in which all the fundamental frequencies are independent. However, for states for which the fundamental frequencies become commensurate (resonance states), there are additional complications. In these cases it is necessary to determine a new set of ‘‘fundamental’’ frequencies and to modify the quantization conditions. Once these adjustments are made, good results are obtained for resonance states. The major problems are in labeling the large number of Fourier coefficients and the presence of regions of chaotic motion. Results are presented for the vibrational states of H2O and HCN and the rovibrational states of H2O.
Molecular dynamics simulation of atom ejection from the (0001) surface of single crystal zirconium due to keV ion bombardment
Authors: Li Aijun , Watts Robert O.
Published: July 2002

Atom desorption from the (0001) surface of a HCP single crystal Zr induced by 2 keV Ne+, Ar+, and Xe+ ions at four incident angles is studied using molecular dynamics simulations. The atom ejection pattern for normal ion incidence has six approximately equal intense spots around a weak central spot, in agreement with the pattern observed experimentally. Few surface atoms have a high probability of being sputtered and they contribute significantly to the formation of the intense spots. The mechanism for the formation of the spots is determined primarily by the first two layers of the crystal and knock-on sputtering by primary recoil is important for all three ions. The relative importance of primary recoil knock-on ejection increases with ion mass. Other mechanisms involve momentum transfer through second layer atoms. The Lehmann–Sigmund mechanism is not applicable for the ion masses and energies used in the simulations. Similarities and differences between the HCP (0001) and FCC (111) surfaces are discussed and it is proposed that, to a certain extent, the atom ejection mechanisms described in this paper may also apply to FCC (111) surfaces under similar sputtering conditions.
Effects of geometrical disorder on hole transport in molecularly doped polymers
Authors: Young Ralph H.
Published: July 2002

The mobility of holes is compared between two molecularly doped polymer systems. The charge-transporting material in one [TAPC, 1,1-bis(di-4-tolylaminophenyl)cyclohexane] is a dimeric analog of the other (TTA, tri-4-tolylamine). The charge-transport sites are essentially identical, but their packing is different because of their pairing in TAPC. The influence of packing and geometrical (off-diagonal) disorder is investigated, and current theories and notions of the effects of such disorder are tested. At equal, low site concentrations, TAPC probably has the greater degree of geometrical disorder. As expected on this basis, the mobility is a less rapidly increasing (or more rapidly decreasing) function of electric field strength in TAPC than in TTA. Contrary to predictions of the Gaussian Disorder Model [H. Bässler, Phys. Status Solidi B 175, 15 (1993)], there is no concomitant effect on the magnitude of the mobility as extrapolated to zero field strength. Other predictions of the model, concerning the dependence of the mobility on field and temperature, are also not verified. The manner in which the field dependence in TTA varies with varying concentration is qualitatively consistent with the results of recent simulations [B. Hartenstein et al., Chem. Phys. 191, 321 (1995)], but the specific field dependence is not. A comparison of TTA at very low concentrations with a tetrameric analog leads to a proposal on the specific influence of site clustering (dimeric or tetrameric) on transport. The low-concentration data also exhibit a drift velocity that decreases with increasing field strength, nondispersive transport at low field strengths, and dispersive transport at high field strengths. The relative importance of molecular packing in general and the implications for the interpretation of transport data on other systems are discussed.
Fourier transform infrared study and ab initio calculation of ClNO complex with HCl
Authors: Sanna N. , Schriver-Mazzuoli L. , Hallou A. , de Saxce A. , Schriver A.
Published: July 2002

The molecular complex in a 1:1 ratio of nitrosyl chloride ClNO with hydrogen chloride has been characterized in argon matrices by infrared spectroscopy. Ab initio calculations using the self-consistent-field Hartree–Fock, the second order Mo/ller–Plesset, and the Becke–Lee–Yang–Paar density functional (DFT methods) were undertaken on all possible structures. Only one stable structure was found. It showed simultaneously interaction of the Cl, N, and O atoms of ClNO with the H atom of HCl. The complexation induces a mean variation of about −0.005 Å of the NO bond and about +0.005 Å of the ClN bond. The HCl bond length is calculated to lengthen by about +0.008 Å.
A simple model for conjugation lengths in long polyene chains
Authors: Kohler Bryan E. , Woehl Jörg C.
Published: July 2002

By assuming that the conjugation length of a long polyene chain may be broken into segments (for example, by twists about the single bonds) and that the energy to create such a conjugation break is independent of where it occurs, a conjugation length distribution is derived. For long chains this distribution is dominated by short fragments, in agreement with conclusions drawn from measured absorption spectra.
Can AlH5 exist?
Authors: Schreiner Peter R. , Schaefer Henry F. , Schleyer Paul von Ragué
Published: July 2002

Six candidate AlH5 structures were examined in detail using the self-consistent-field (SCF), configuration interaction including single and double excitations (CISD), and coupled cluster including single, double and perturbatively included connected triple excitations [CCSD(T)] methods in conjunction with double-ζ plus polarization (DZP), triple-ζ plus polarization (TZ2P), and augmented TZ2P(f,d) basis sets. The C4v and the D3h isomers are high in energy [72 and 84 kcal mol−1, respectively, relative to the Cs(I) structure at DZP CCSD]. Although structure Cs(I) is the global minimum, the second Cs form, where AlH5 is comprised of nearly planar alane (AlH3) and dihydrogen, is essentially equal in energy. Hence, the rotation of the hydrogen moiety is virtually free. The global Cs(I) minimum was characterized by vibrational frequency analyses at TZ2P CCSD(T). Final energies were obtained at CCSD(T) TZ2P(f,d). At room temperature, the alane–dihydrogen complex AlH5 is unstable toward dissociation by 3.1 kcal mol−1. However, at the absolute zero (0 K), the complex forms exothermically (−1.7 kcal mol−1). Hydrogen scrambling via the C2v (3) transition structure seems to be very unlikely since the activation barrier for this process is at least 24.6 kcal mol−1 higher than the dissociation energy of AlH5 into AlH3 and H2.
Dispersed fluorescence spectroscopy of excited rovibrational states in S formaldehyde
Authors: Emery Charles D. , Overway Kenneth S. , Bouwens Rychard J. , Polik William F.
Published: July 2002

Dispersed fluorescence (DF) spectroscopy is used to explore the rovibrational structure of highly excited S0 formaldehyde (H2CO). A narrowband laser excites formaldehyde molecules to a single S1 rovibronic quantum state, and the resulting fluorescence is dispersed with a monochromator. DF spectra of ten vibrational levels with excitation in ν2, the carbon–oxygen stretch, and ν4, the out-of-plane bend, have been recorded, and the effective A, B, and C rotational constants are extracted. Five of the effective A rotational constants and seven of the effective B and C rotational constants are new to the literature. The dependence of these effective rotational constants on vibrational state are both calculated and discussed with regard to both the present and previous experiments. Particular attention is given to the manner in which that the effective A rotational constant depends on increasing excitation in ν4 due to the strong A-axis ν4/ν6 Coriolis interaction. For states where v2 is less than two, quantitatively accurate values for the nonlinear dependence of the A rotational constant on quanta in ν2 and ν4 is achieved by a simultaneous consideration of the strong A-axis ν4/ν6 Coriolis interaction and the 11↔42, 11↔62, and 51↔2161 Fermi interactions.
Two-photon ionization and dissociation of ethyl iodide
Authors: Knoblauch Nils , Strobel Andreas , Fischer Ingo , Bondybey Vladimir E.
Published: July 2002

Both spin–orbit states of C2H5I+, the X̃1 2E1/2 and the X̃2 2E1/2 electronic states, are studied by one-color two-photon ionization of ethyl iodide, utilizing the zero kinetic energy pulsed field ionization (ZEKE-PFI) photoelectron technique. Compared with conventional photoelectron data the two-photon spectra exhibit a more extensive vibrational structure mainly involving the C–I stretching and the C–C–I bending modes. This additional vibrational excitation in the two-photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative Ã-state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two-color ZEKE spectra is reported.
A general model for pattern formation in electrode reactions
Authors: Flätgen G. , Krischer K.
Published: July 2002

Experiments on pattern formation in electrochemical systems show qualitative differences in comparison with phenomena observed with other chemical systems. In this paper we derive a general model from the basic transport equations which takes into account the special aspects of electrochemical systems. Stepwise introduction of three approximations considerably simplifies the equations and demonstrates the dominant role the electric potential plays for pattern formation. The simplest form of the model contains migration as the only transport mechanism, and the importance of intrinsic global coupling for the dynamic behavior of electrochemical systems becomes apparent. This simple model already reproduces the experimentally observed front behavior we recently reported [G. Flätgen and K. Krischer, Phys. Rev. E 51, 3997 (1995)].
Effects of magnetic field on the 15V 31 344.9 band of CS2 studied by sub-Doppler high-resolution spectroscopy
Authors: Katô Hajime , Doi Atsushi , Taroura Yoshikazu , Nagakura Saburo
Published: July 2002

Effects of an external magnetic field on the excitation spectrum of the 15V 31 344.9 band of the CS2 molecule are measured with sub-Doppler resolution. New lines are observed to appear near the R(2) and P(4) lines when a magnetic field is applied. These lines are observed to be composed of five components both for the π pump and for the σ pump. From a theoretical analysis, we identify the new lines as transitions to the 3A2(A1−B1)(v−;12M) levels, which become allowed by Zeeman interaction with the V 1B2(v′;03M) level that is mixed with the 3A2(B2)(v;03M) level by spin–orbit interaction. Variations of energy shifts and intensities with the magnetic field strength are explained quantitatively by this analysis. M-dependent perturbation and the quenching of fluorescence are observed. The reason why large Zeeman splittings are observed at many lines in the V system of CS2 can be attributed to the spin–orbit interaction between the V 1B2(v′;KJM) level and the 3A2(B2)(v;KJM) level combined with the rotational and/or the Zeeman interactions between 3A2(B2)(v;KJM) level and either 3A2(A1+B1)(v0;K±1JM) or 3A2(A1−B1)(v±; K±1J±1M) levels which are accidentally close in energy.
A study of the Ã 2B2–X̃ 2A1 band system of CaNH2 employing molecular beam optical Stark spectroscopy
Authors: Marr A. J. , Tanimoto M. , Goodridge D. , Steimle T. C.
Published: July 2002

The 000 Ã 2B2–X̃ 2A1 visible band system of a supersonic molecular beam sample of calcium amide, CaNH2, recorded in the presence of a variable static electric field has been studied using high resolution laser induced fluorescence spectroscopy. The determined spectroscopic parameters are (in cm−1), origin=15 464.366 9(8); A″=13.057 4(9); B″=0.300 47(5); C″=0.292 88(5); εbb″=0.001 1(3); εcc″=0.001 1(3); A′=11.448 7(2); B′=0.307 1(1); C′=0.299 2(1); εaa′=8.238(2); εbb′=0.005 2(6); εcc′=0.055 7(6); Δsk=−0.060 8(5). The rotational parameters are interpreted to give an approximate r0 structure. The large spin-rotation parameter for the Ã 2B2 state is discussed in terms of a second order spin–orbit interaction with other low-lying electronic states. Stark splitting of the PP11(1.5)+PQ12(0.5) branch feature was analyzed to produce a ground state permanent electric dipole moment, μ″, of 1.74(1) D. A comparison of μ″ with other monovalent calcium compounds is given.