bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectron studies of resonantly enhanced multiphoton ionization of H2 via the B′ 1Σ+u and D 1Πu states
Authors: Pratt S. T. , Dehmer P. M. , Dehmer J. L.
Published: July 2002

The photoelectron spectra obtained following three photon resonant, four photon ionization of H2 via the B′ 1Σ+u, v=0–2 and via the D 1Πu, v=0, 1 resonant intermediate levels are presented. The intensity ratios of the photoelectron peaks agree qualitatively with the Franck–Condon factors calculated for ionization from the resonant intermediate levels. However, the quantitative agreement is rather poor. Alternative mechanisms for the observed non-Franck–Condon behavior are pointed out, but assessment of their relative importance requires detailed calculations.
Vacuum ultraviolet laser spectroscopy: Radiative lifetimes of interacting 2Δ states of NO
Authors: Hart D. J. , Hepburn J. W.
Published: July 2002

Interactions between the B′ 2Δ non-Rydberg state and nearby 2Δ Rydberg states of NO have been studied by vacuum ultraviolet laser-induced fluorescence spectroscopy. By using tunable, coherent radiation in the 60 000–70 000 cm−1 range, NO molecules in a supersonic jet were excited and their radiative decay was monitored by time-resolved fluorescence detection. In this way accurate, collision-free radiative lifetimes were measured for several levels of the B′ 2Δ, F 2Δ, N 2Δ, and D 2Σ+ excited states of NO. Using these lifetimes the oscillator strengths for the B′–X and F–X transitions were calculated. The radiative lifetimes for the perturbed states were quite different from the unperturbed lifetimes, and these changes are discussed in terms of the known interactions between states in this spectral region. For the unperturbed vibrational levels of the B′ 2Δ state, radiative lifetimes between 129–139 ns were measured, while for the F 2Δ state, a radiative lifetime of 30 ns was measured. For the perturbed bands of the F2Δ and B′ 2Δ states, the radiative lifetimes were accurately described by a two-state homogeneous perturbation model, but for the B′(v=7)∼N(v=0) mixed states, the lifetimes were dramatically different from those expected on the basis of two interacting states. This is caused by a third-interacting state whose identity is not known. The B′(v=8,9) states, while having unperturbed line positions, have shorter radiative lifetimes, indicating the onset of predissociation in those levels.
Second-quantized molecular time scale generalized Langevin equation theory: Boson equivalent chain
Authors: McDowell H. Keith
Published: July 2002

A second-quantized version of molecular time scale generalized Langevin equation theory is developed in an equivalent chain format for quantum boson systems. The approach allows for nonlinear Hamiltonians and strong coupling to the bath. A bath average is defined which permits reduced dynamics prescriptions to be developed. The bath average is shown to be consistent with the notion that perturbations of a primary zone should damp away at long time.
Semiclassical vibrational eigenvalues of H+3, D+3, and T+3 by the adiabatic switching method
Authors: Johnson B. R.
Published: July 2002

The adiabatic switching method is used to calculate the semiclassical vibrational eigenvalues of H+3, D+3, and T+3. The results are in good agreement with quantum calculations and are more accurate than previous semiclassical results. The calculations were facilitated by the use of hyperspherical coordinates.
A Monte Carlo simulation study of a polarizable liquid: Influence of the electrostatic induction on its thermodynamic and structural properties
Authors: Costa Cabral B. J. , Rivail J. L. , Bigot B.
Published: July 2002

An intermolecular potential function for the methyl chloride dimer which includes the electrostatic induction terms explicitly has been used in an NPT Monte Carlo statistical mechanics simulation of liquid methyl chloride at its normal boiling temperature (−23.76 °C). The nonadditive many-body induction energy is computed via an iterative procedure. It is found that the thermodynamic and structural results which are obtained with the present potential functions compare favorably with those of a previous simulation performed with effective potential functions. Modest structural changes are observed when the two simulations are compared. They mainly concern the organization around the methyl group. A detailed analysis of the electrostatic field in the liquid for both simulations shows that the mean electrostatic field is larger in the simulation with effective potential functions than with explicit induction functions. Furthermore, the induction potential functions give a more homogeneous electrostatic field within the liquid.
The optical spectra of matrix-isolated Znn (n≤6)
Authors: Schroeder W. , Wiggenhauser H. , Schrittenlacher W. , Kolb D. M.
Published: July 2002

The optical properties of small Zn clusters, especially of Zn2 and Zn3, isolated in neon have been studied over a wide photon energy range by absorption, emission, and photoelectron spectroscopy. By employing emission yield spectroscopy the optical transitions of the dimer and the trimer could be unequivocally distinguished from those of higher clusters in the matrix. For Zn2, the experimental data compare reasonably well with calculations found in the literature. However, the ground state, which is usually calculated to be nonbinding, is found to be bound. The main absorption bands of at least three more Zn clusters, tentatively assigned to Zn4–Zn6, have been derived from the concomitant growth of bands in a systematic concentration study.
State selected ion–molecule reactions by the TESICO technique. XIII. Vibrational state dependence of the cross sections in the reaction C2D+2(ν2)+H2
Authors: Honma Kenji , Tanaka Kenichiro , Koyano Inosuke
Published: July 2002

Vibrational-state selected reaction cross sections have been measured for three product channels of the reaction C2D+2(ν2)+H2, by use of the threshold electron–secondary ion coincidence (TESICO) technique. The ν2 vibrational states of the C2D+2 ion were selected up to v=2 and the collision energies were changed from 0.1 to 2.0 eV. At low collision energies up to 0.2 eV, considerable enhancement of the cross sections for the channel producing C2D2H+ was observed when the vibrational quantum number was increased successively. As the collision energy was increased, the extent of this enhancement diminished gradually and the cross section became almost independent of v at 2.0 eV. The cross section for the H/D exchange channel, on the other hand, was found to decrease with increasing vibrational quantum number at low collision energies. The latter cross section also became independent of v at high collision energies. These results have been explained in terms of the formation of an intermediate complex and the statistical decomposition of this complex to products.
Effective equation of motion for gas–solid interactions
Authors: Zeiri Yehuda
Published: July 2002

An effective equation of motion (EEM) for gas particles interacting with a solid surface is derived. The derivation is based on the equivalent harmonic chain representation (EHCR) which was proved to correctly represent the motion of the crystal atoms in processes involving gas–surface interactions. Both approaches are applied to a one-dimensional model of rare gas atom scattering from a silver surface. Comparison of the results obtained by the EHCR and EEM method show an excellent agreement. It is suggested that the EEM approach is capable of reliably describing the dynamics of large systems for which computations using the EHCR are too time consuming.
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5N spin-relaxation studies of N2 in buffer gases. Cross sections for molecular reorientation and rotational energy transfer
Authors: Jameson Cynthia J. , Jameson A. Keith , Smith Nancy C.
Published: July 2002

Nuclear spin-lattice relaxation times (T1) have been measured as a function of temperature for 15N in N2 gas and in CH4, O2, CO, Ar, HCl, CF4, Kr, and Xe. The relaxation is dominated by the spin-rotation mechanism so that empirical values of the cross sections for rotational angular momentum transfer (σJ) are obtained as a function of temperature. The values of σJ/Å2 at 300 K are 13.6±0.4 (N2–CH4), 14.9±0.4 (N2–N2), 14.7±0.6 (N2–O2), 15.0±0.9 (N2–CO), 15.9±0.8 (N2–Ar), 22.7±0.6 (N2–HCl), 30±1 (N2–CF4), 18.1±0.5 (N2–Kr), and 19.8±0.5 (N2–Xe). For almost all cases, the temperature dependence of the cross section deviates from T−1.
Theoretical A 1A″2–X 1A1 absorption and emission spectrum of ammonia
Authors: Rosmus P. , Botschwina P. , Werner H.-J. , Vaida V. , Engelking P. C. , McCarthy M. I.
Published: July 2002

Potential energy, electric dipole moment, and electronic transition moment surfaces have been calculated for the A and X states of NH3 from CASSCF and CEPA electronic wave functions. Anharmonic vibrational term values, Franck–Condon factors, and A–X radiative transition probabilities for the symmetric stretching and bending modes of NH3 and ND3 have been evaluated. The theoretical absorption spectra at room and low temperatures agree well with experimental data. The symmetric stretching mode in the A state has only small intensities in the A–X absorption spectrum. Emission rates from various initial vibronic levels of the A state are given. The ab initio electric dipole moment surfaces for the ground state of NH3 have been used to compute transition moments, which are in good agreement with experimental data.
Applications of the generator coordinate approximation to diatomic systems. II. Dunham analysis of vibration–rotation spectra
Authors: Lathouwers L. , Van Leuven P. , Deumens E. , Öhrn Y.
Published: July 2002

It is shown how a Dunham series can be derived within the generator coordinate approximation. General kernel expansions are combined with order by order angular momentum projection and generator coordinate perturbation theory. The comparison of Born–Oppenheimer and generator coordinate kernal coefficients yields a clear identification of nonadiabatic effects incorporated in the generator coordinate approximation.
Critical exponents for neighbor-avoiding walks on two-dimensional lattices
Authors: Ishinabe T.
Published: July 2002

We have reassessed several critical exponents for nearest-neighbor-avoiding walks using the exact enumerations newly extended to 21 and 25 steps for the triangular and square lattices, respectively. We correct our previous conjecture that the value of δ, an exponent characterizing the end-distance distribution, is different between two kinds of walks of neighbor- and self-avoiding chains, and confirm the hypothesis that these walks are in the same class of universality. The circular symmetry of the distribution is also confirmed for nearest-neighbor-avoiding walks.
Effective pair potentials at the McMillan–Mayer level
Authors: Guàrdia E. , Gómez-Estévez J. L. , Padró J. A.
Published: July 2002

The Adelman theory for liquid solutions is applied to obtain state-dependent solute–solute pair potentials at the McMillan–Mayer level. Generalized Langevin dynamics simulations using these effective potentials have been performed. Radial distribution functions and time correlation functions obtained from these simulations are compared with those obtained by using mean force potentials at infinite dilution and with the ones resulting from the ‘‘exact’’ molecular dynamics simulations of the complete systems.
Two-dimensional Fourier analysis of colloid crystals in dilute suspensions. I
Authors: Ito Kensaku , Ise Norio
Published: July 2002

The two-dimensional Fourier analysis was carried out for micrographs showing the distribution of polymer latex particles in suspension with the aid of a computer device. The ordered structure of the particles gave a Fourier pattern consisting of spots, whereas the completely disordered state provided no spots nor rings. The two-state structure, in which the ordered structure and disordered regions coexist, showed a pattern intermediate between the two extremes. The study suggests that the single, broad scattering peak often observed for solutions of macroions and suspensions of latex particles reflects a structural correlation between the solutes.
Theoretical state-to-state charge transfer cross sections for collisions of Ar+ (2P3/2, 2P1/2) with N2
Authors: Parlant Gérard , Gislason Eric A.
Published: July 2002

State-to-state cross sections have been calculated for collisions of Ar+(2P3/2, 2P1/2) with N2 over the relative collision energy range 1–4000 eV. The computations have been done by means of the vibronic semiclassical method recently used by Parlant and Gislason for N+2+Ar collisions. The translational motion is treated classically, and the time-dependent Schrödinger equation is solved exactly for the vibronic states of the system. The potential energy surfaces utilized are those of Archirel and Levy. The results for the total charge transfer cross sections are in fairly good agreement with experimental data over the whole energy range. An unexpected participation of the A state of N+2 at low collision energy is observed. The charge transfer cross section ratio for the two spin–orbit states is discussed in a comparison with the available experimental data. In addition, the vibrational state distributions of N+2(X;v′) show good agreement with the recent measurements of Liao et al.
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o calculation of spectroscopic properties for the HLiH− ion in the X 1Σ+g state
Authors: Senekowitsch Jörg , Rosmus Pavel
Published: July 2002

Near equilibrium three-dimensional potential energy and electric dipole moment surfaces of the bound negative ion HLiH− were calculated from highly correlated CEPA electronic wave functions. The HLiH− ion is linear with Re=1.743 Å. From the potential energy surface the anharmonic vibration–rotation term values were calculated variationally and by perturbation theory. The fundamental vibrational transitions in HLiH− are predicted to lie at ν1(J=0)=1014 cm−1, ν2(J=1)=429 cm−1, ν3(J=0)=1079 cm−1. The D0 dissociation energy relative to the LiH+H− asymptote is calculated to be 2.34 eV, the vertical electron detachment energy to be 3.10 eV. The components of the electric dipole moment surface are given analytically.
The hindrance potential and coupling of the NH3 quantum rotors in Co(NH3)6(PF6)2
Authors: Kearley Gordon J. , Blank Herma , Cockcroft Jeremy K.
Published: July 2002

The first example of transitions between almost free rotational levels of NH3 groups in the solid state is shown by the inelastic neutron scattering spectrum of Co(NH3)6(PF6)2, and can be interpreted in terms of a very weak sixfold potential. Additional satellite peaks are visible around the 0→1 rotational feature at high spectral resolution and it is shown that the temperature dependence of these satellites demonstrates that they originate from a coupling between NH3 rotors.
Infrared spectra and UHF SCF calculations of HF complexes with NO, (NO)2, and NO2
Authors: Davis Steven R. , Andrews Lester , Trindle Carl O.
Published: July 2002

HF complexes with nitric oxide and nitrogen dioxide were prepared in argon matrices and studied using IR spectroscopy and unrestricted Hartree–Fock SCF calculations. The results indicate the formation of three different complexes NO--HF, ONNO--HF, and ONO--HF, in which the hydrogen atom of HF is bound to an oxygen atom of the base in each complex. Perturbations in the N–O stretching base submolecule modes were observed in each complex and all were blue shifted with respect to the free base. From the calculations, the unpaired electron was found to be contained in a π antibonding orbital which is in the plane of the NO–HF and ONO–HF complexes.
Second-quantized molecular time scale generalized Langevin equation theory: Fermion equivalent chain
Authors: McDowell H. Keith
Published: July 2002

A second-quantized version of molecular time scale generalized Langevin equation theory is developed in an equivalent chain format for quantum fermion systems. The approach allows for nonlinear Hamiltonians and strong coupling to the bath. A bath average is defined which permits reduced dynamics prescriptions to be developed for the case of one-electron Hamiltonians. The bath average is shown to be defined such that perturbations of a primary zone damp away at long time.
Multiphoton dissociation in NO2 at 532 nm and the generation of vibrationally excited O2 and NO
Authors: Jusinski L. E. , Sharpless R. L. , Slanger T. G.
Published: July 2002

The 532 nm multiphoton dissociation of NO2 has been investigated, following the work of Matsumi et al. [Laser Chem. 1, 113 (1983)], which demonstrated that highly vibrationally excited O2 (v≤25) is a product. We have shown that O2(v) is generated in a secondary reaction, possibly through the interaction between primary O(1S) and the parent molecule. Competitive quenching experiments with N2 indicate that O(1D) is not involved in O2(v=24) production. Primary NO(v) has been detected by one- and two-photon excitation, with v≤7. Its source is probably 532 nm two-photon dissociation of NO2. The generation of O(1S) requires absorption of four 532 nm photons by NO2.
Solvent dynamical effects on electron-transfer kinetics: Influence of electronic coupling on weak-overlap exchange processes
Authors: McManis George E. , Mishra A. K. , Weaver Michael J.
Published: July 2002

A numerical integration treatment of the appropriate Kramers’ diffusion equation, involving overdamped solvent motion, is employed to estimate adiabatic barrier-crossing frequencies νos for weak-overlap electron-exchange processes featuring only outer-shell (solvent) reorganization as a function of the electronic matrix coupling element H12. Comparisons are made with estimates of νos obtained from limiting analytical expressions. The competing influence of reaction nonadiabaticity (i.e., electron tunneling) and solvent motion upon the barrier-crossing frequency is also considered as a function of H12 using a Landau–Zener treatment. The results indicate that the dominant influence of overdamped solvent motion on the preexponential factor, that yields the observed inverse correlation between the reaction rate and the solvent longitudinal relaxation time, requires reactions that feature moderate degrees of electronic coupling, around H12≳0.1 kcal mol−1, in most common polar solvents. These factors are briefly illustrated with reference to recent measurements of the solvent-dependent kinetics of cobalticinium–cobaltocene electrochemical exchange.
The production of NH(A 3Πi) through photodissociative excitation of NH3
Authors: Wu C. Y. Robert
Published: July 2002

The NH(A→X) emission produced by photodissociation of NH3 has been investigated by utilizing a line emission source in the 600–1340 Å region. The production of the NH (A 3Πi) photofragment involves a spin-forbidden transition. The fluorescence quantum yields for producing NH (A→X) fluorescence are less than 2×10−3 at wavelengths longer than 976 Å.
Nuclear motion and electric hyperpolarizabilities
Authors: Bishop David M.
Published: July 2002

Formulas are given for the vibrational components of the static and dynamic electric hyperpolarizabilities β and γ. Some previous inconsistencies in the literature are pointed out.
Theoretical investigations of small multiply charged cations. II. CNen+ (1≤n≤4)
Authors: Koch Wolfram , Frenking Gernot
Published: July 2002

Extended MCSCF calculations of the CASSCF type have been performed for the energetically lowest-lying electronic states of CNe+, CNe2+, CNe3+, and CNe4+. Whereas the mono- and tetracations exhibit essentially repulsive potential curves, the CNe2+ dication is predicted to be a kinetically stable ion. The computed barrier to dissociation for the X 1Σ+ state of CNe2+ amounts to 1.62 eV, and for the a 3Π state a potential well of 0.80 eV depth is calculated. The CNe2+ dication is therefore predicted to be experimentally observable in the gas phase. Also the CNe3+ trication is calculated to exhibit a small minimum in its X 2Σ+ state. Bonding in these unusual cations is discussed and compared to known isoelectronic species.
Stark effect of polar and unpolar dye molecules in amorphous hosts, studied via persistent spectral hole burning
Authors: Kador L. , Haarer D. , Personov R.
Published: July 2002

A simple analytical model is presented describing the shape of a persistent spectral hole in a homogeneous electric field for random orientation of the dye molecules in the host matrix. We consider the two cases that the absorbers have either one fixed value or a distribution of values of the electric dipole moment difference Δμ between the ground and excited electronic states. Comparison with experiment yields the Δμ values for chlorin (Δμ=0.214 D) and a substituted Zn-tetrabenzoporphin (∼(Δμ) =0.174 D) in poly(vinylbutyral). In the latter case the isolated dye molecule has inversion symmetry, yet there is nevertheless a dipole moment through the interaction with the polar matrix of low local symmetry.
Dynamic quadrupole echo NMR of deuterium in liquid crystalline solutions: The effect of the chemical shift
Authors: Poupko R. , Luz Z. , Vega A. J. , Zimmermann H.
Published: July 2002

The problem of calculating dynamic deuterium quadrupole echo spectra in ordered systems in which exchange takes place between noninteracting nuclei with different quadrupole interactions and chemical shifts is solved. For the solution a specific set of basic spin I=1 matrices is chosen which allows casting the solution in a form having the same dimensionality as the Bloch–McConnell equations of spin I=1/2 nuclei. The theory is applied to two dynamic systems, viz., the ring inversion of cyclohexane and the Cope rearrangement in bullvalene, both in liquid crystalline solution. It is shown that even in ordered systems the time interval between the π/2 pulses in the quadrupole echo experiment may strongly affect the shape and intensity of the spectrum, thus providing an additional experimental variable for analyzing dynamic spectra. When large chemical shifts or off-resonance pulses are involved, distorted spectra are obtained. This distortion can be removed by including π pulses in the quadrupole echo sequence which eliminate the dephasing effect of the chemical shift.
Universality of binary critical mixtures
Authors: Fast Steven J. , Yun S. S.
Published: July 2002

In this note, the quantity X(R+ξ) from two-scale factor universality is calculated for nine binary critical mixtures using heat capacity and coherence length data. The results are compared to theoretical values and are found to be in good agreement with them.
Stirring effects and bistability in the iodate–arsenous acid reaction: Premixed vs segregated flows
Authors: Hannon L. , Horsthemke W.
Published: July 2002

Using a coalescence–dispersion model of the continuous flow-stirred tank reactor (CSTR), we study the effect of premixed vs nonpremixed reactant flows on chemical bistability. The region of bistability is smaller for segregated feed streams than for a fully premixed feed stream. The transition from flow branch to thermodynamic branch is particularly sensitive to the feed stream configuration.
Resonances in molecular photoionization. I. Model calculations and analysis of general phenomena
Authors: Sobolewski A. L. , Domcke W.
Published: July 2002

Near-threshold autoionization structure in molecular photoionization is described using the projection-operator formalism of scattering theory. We address ourselves to the common situation of a number of discrete valence states interacting with the ionization continuum and the Rydberg series converging to the ionization threshold. The infinite Rydberg series are included as a whole in the treatment of the nuclear dynamics. We consider, in particular, a simplified model (single valence state and harmonic potential energy curves) which allows a very simple, fast, and numerically stable evaluation of the photoionization cross section. Model calculations are performed for a wide range of parameters (shift of potential energy curves, coupling strengths, optical transitions moments). We discuss and analyze a variety of general features of autoionization structures in total and partial photoionization cross sections.
A theoretical analysis of the Jahn–Teller effect in the photoelectron spectrum of methane
Authors: Takeshita Kouichi
Published: July 2002

An analysis of the Jahn–Teller effect in the photoelectron spectrum of methane was performed by the use of the ab initio self-consistent field and configuration interaction calculations. The molecular structures of the CH+4 ion, which have a local energy minimum, are found to be in the C2v and C3v symmetry. The vertical excitation energy is calculated to be 14.23 eV and the adiabatic ionization potentials of the CH+4 ion including zero-point vibrational energy are estimated to be 12.25 and 12.68 eV for the C2v and C3v symmetry, respectively. We calculated the normal modes of vibration and the Franck–Condon factor in the harmonic oscillator approximation, and assigned the vibrational band below 13.10 eV of the CH+4 ion.
Vibrational excitation in molecule–surface collisions. Analytic modeling vs classical trajectories
Authors: Gadzuk J. W.
Published: July 2002

The problem of translational to vibrational energy redistribution occurring in collisions between diatomic molecules and solid surfaces is considered. Attention is focused solely on a mechanism which is a consequence of a molecule–surface interaction giving rise to an intramolecular potential whose equilibrium separation is a function of distance from the surface. This ‘‘three-body’’ chemical effect is totally unrelated to mechanical excitation due to spring compression. While past work has emphasized the specific process of charge transfer/harpooning as a means for obtaining such an interaction, the mechanism is more general in the sense that it depends only upon the topology of the potential energy surface (PES) and not on what electronic properties gave rise to the topology. The T to V energy redistribution is treated both within the context of analytical models over necessarily simplified PES as well as numerically evaluated classical trajectories over more complex and realistic ones. Systematic studies are presented in which the relationship between energy conversion and PES characteristics are established. Conditions under which the analytic models provide reasonable representations of the collision are noted. I2 is the molecule of choice in this work.
ESR and ENDOR study of the guanine cation: Secondary product in 5′-dGMP
Authors: Hole Eli O. , Nelson William H. , Close David M. , Sagstuen Einar
Published: July 2002

Previous ESR studies of x-irradiated single crystals of 2′-deoxyguanosine-5′-monophosphate have indicated the presence of a radical thought to be formed by deprotonation of a primary base cation at N1. In this communication are reported some results of detailed ESR and ENDOR experiments at 10 K conflicting with the above results. One of the radicals detected exhibited two α-proton type couplings. The data analysis shows that one coupling is due to the exchangeable proton of the extra-annular NH2 group, while the other is due to the proton bonded at C8. The experimental spin densities were ρ(N10)=0.33, and ρ(C8)=0.18. The results agree reasonably well with the INDO calculated spin density distribution of a radical formed by deprotonation at N10 of a primary cation radical. The radical is stable on warming to about 200 K where it anneals rapidly.
Vibrational energy levels of methyl fluoride
Authors: Dunn Kevin M. , Boggs James E. , Pulay Peter
Published: July 2002

Energy levels up to 6000 cm−1 above the zero point energy have been calculated for methyl fluoride using an ab initio potential function adjusted to reproduce the fundamental frequencies. The calculations were made using a novel variational procedure analogous to CI methods used in electronic structure theory. The calculated energy levels agree with the available experimental spectra with an rms error of 6.2 cm−1. In particular, the calculations reproduce the complicated resonances involving the CH stretching fundamentals. Some energy levels for CD2HF are also presented.
Energy requirements for a chemical reaction. I. Halide ion transfer to antimony pentafluoride
Authors: Hershberger J. F. , McAndrew J. J. , Cross R. J. , Saunders M.
Published: July 2002

Using crossed seeded nozzle beams we have examined the energy dependence of the cross section for the reaction SbF5+RX→SbF5X−+R+, where X is a halogen and R an organic radical. By using a range of carrier gases in the two beams and by varying the nozzle temperature and the beam intersection angle, we can separately vary the relative translational energy and the vibrational temperatures of the beams. Near the threshold, vibrational energy seems to play a very important role. At energies well above threshold, the reactive cross section appears to depend largely on translational energy. We explain this by assuming that the reaction takes place on two potential energy surfaces. By choosing RX properly, the R+ product will decompose. In two cases we observe that, although vibrational energy in RX has a minor effect on the halide abstraction, it is very important in the subsequent decomposition of R+.
A general consistent model for formation and decay of rare gas excimers in the 10−2–10+5 mbar pressure range, with application to krypton
Authors: Janssens H. , Vanmarcke M. , Desoppere E. , Lenaerts J. , Bouciqué R. , Wieme W.
Published: July 2002

Using data from alpha excitation single photon counting experiments at 100–1200 mbar and from literature reports in other pressure ranges a general consistent model is proposed for the formation and decay of the rare gas excimers in the pressure range 10−2–10+5 mbar. Special attention has been paid to the study of the vibrational relaxation processes. In this model two atomic excited states (3P2,1) and six molecular excimer states (1,3Σ+g, 1,3Σ*u, 1,3Σ0u) are interconnected by a number of processes, excimer formation, atomic and molecular excitation transfer, vibrational relaxation, diffusion, resonance radiation, collision induced radiation, and excimer radiation. As a result the loss rates of the relevant atomic and molecular states of krypton are determined.
On the quenching of Na(2P) by HCl: Nonadiabatic effects
Authors: Gallo Mary M. , Yarkony David R.
Published: July 2002

The electronic structure aspects of the nonadiabatic reactive quenching process Na(2P)+HCl→NaCl+H were studied within an adiabatic states approach. Portions of the 1, 2 2A′ potential energy surfaces (PES’s) were characterized using state averaged-MCSCF/CI wave functions. Two minima on the 2 2A′ PES were found, one in the entrance channel at ΔR(NaCl)=0.89 a0, ΔR(HCl)=0.01 a0, ∠NaClH=95.4° and a secondary minimum in the interaction region at ΔR(NaCl)=0.32 a0, ΔR(HCl)=0.60 a0, ∠NaClH=90.9°. On the 1 2A′ PES a saddle point was located at ΔR(NaCl)=0.34 a0, ΔR(HCl)=0.64 a0, ∠NaClH=55.1°. Here ΔR(X)=R(X)−Re(X). The global and secondary minima on the 2 2A′ PES are stable with respect to the Na(2P)+HCl asymptote by 0.24 and 0.13 eV, respectively, while the 1 2A′ saddle point is 0.75 eV above the ground state Na(2S)+HCl asymptote. Nonadiabatic coupling matrix elements 〈Ψ(2 2A′)‖(∂/∂Rα)Ψ(1 2A′)〉 were determined in the vicinity of the minima on the 2 2A′ PES and the saddle point on the 1 2A′ PES. The region of maximum nonadiabatic coupling as measured by the Massey strength does not correspond to any of these extrema. It was found in the neighborhood of ΔR(NaCl)=0.33 a0, ΔR(HCl)=0.70 a0, ∠NaClH=100°. This region is stable by 0.10 eV relative to the Na(2P)+HCl asymptote and is characterized by close approach of the 1 2A′ and 2 2A′ PES’s.
Experiments on phase diffusion waves
Authors: Bodet J. M. , Ross J. , Vidal C.
Published: July 2002

The oscillatory Belousov–Zhabotinsky reaction is perturbed inhomogeneously by illumination with a focused laser beam for a given time interval and a quantity of heat is thus produced in a small region. The perturbation initiates a trigger wave for larger laser power. As the heat diffuses away from the initial location, the character of waves generated in succeeding cycles of the oscillatory reaction changes in a continuous manner to phase diffusion waves, predicted some years ago and observed for the first time. We measured transmission profiles with a Reticon system and calculate velocity profiles from the measurements. Phase shifts induced by the perturbation depend on the phase of the unperturbed oscillatory system at the instant of the imposition of the perturbation. For small perturbations, phase diffusion waves are induced initially. If the perturbation produces phase shifts exceeding 2π, then more than one trigger wave is generated within the first cycle of oscillation following the perturbation. A simple chemical model of oscillating reactions is used to calculate the major effects seen in the experiment.
Angular distributions of photofragments from NO2 photodissociation
Authors: Kawasaki M. , Sato H. , Fukuroda A. , Kikuchi T. , Kobayashi S. , Arikawa T.
Published: July 2002

The angular distributions of recoil of NO molecules from the photodissociation of NO2 near the dissociation threshold of 397.86 nm are presented and analyzed to obtain information about the effect of molecular rotation of parent molecules on the angular distribution. For the one-photon dissociation process, as laser wavelengths become closer to the dissociation threshold, the anisotropy of the angular distribution is reduced. When laser wavelengths become larger than the threshold, NO2 dissociates via two-photon absorption, and the photofragment angular distribution again becomes anisotropic reflecting the second photon absorption.
Molecular dynamics simulation of hydrocarbon molecules in condensed phases. II. Benzene
Authors: Anderson Jon , Ullo John J. , Yip Sidney
Published: July 2002

Molecular dynamics simulations of liquid (305 K) and solid (10 K) benzene have been carried out to investigate the vibrational properties of benzene in the condensed phase. The benzene molecule is modeled as a fully flexible system of 12 atoms with intramolecular interactions based on ab initio harmonic potentials and intermolecular interactions given by semiempirical atom–atom potentials. Vibrational frequencies are analyzed in terms of the frequency spectrum of the velocity autocorrelation function and the results are found to correlate well with optical absorption and scattering data. Single particle density fluctuations are calculated over a range of wave numbers and results are obtained that can be directly compared to the intensity distributions of inelastically scattered thermal neutrons. The different comparisons indicate that the existing potential energy function provides an essentially quantitative description of molecular vibrations of benzene.
Semiclassical perturbation theory for atom scattering from surfaces with defects
Authors: Hubbard Lynn M. , Rabitz Herschel A.
Published: July 2002

Presented here is an extension of semiclassical perturbation theory (SCP) to gas–surface scattering incorporating surface defect sites with the restriction that the defects be diffuse enough such that they have no direct interaction. The formalism is applied to a corrugated surface with atoms missing, modeling a nearly complete layer of atoms adsorbed on a metal surface. The results show the redistribution of the Bragg intensities to a continuum of momentum transfers about the former peaks.
Comparison of numerical and analytical orientation average methods in polymer light scattering
Authors: McClain W. M. , Tian Duan , Ghoul W. A.
Published: July 2002

We have calculated the Perrin matrix for elastic light scattering by two distinct numerical methods, and we present here a critical comparison. Both methods assume the dipole array model with retarded dipole–dipole interaction between subunits. However, the average over all orientations of the model is carried out differently in the two methods. The conceptually simplest method (and the easiest to program) is rotation by Cartesian matrix (CM) algebra with three-dimensional numerical integration over Euler angles. The second method is based on rotations by Wigner matrix (WM) algebra with analytic integration, and requires an infinite sum in one index which must be truncated. The two methods agree when they are pushed far enough. Both methods require substantial calculation, but the analytic method is shown to be far superior in its convergence properties. Comparing calculations of the whole Perrin matrix of scattering curves (16 curves, 21 scattering angles) in which all curves are computed to 1% accuracy, the CPU times for the numerical integration over Euler angles is about 500 times slower.
Photodissociation dynamics of water in the second absorption band. I. Rotational state distributions of OH(2Σ) and OH(2Π)
Authors: Weide K. , Schinke R.
Published: July 2002

The photodissociation of H2O and D2O in the second band (λ≳120 nm) is investigated using two-dimensional (translation and rotation) classical trajectories. The calculations include all electronic states which are involved in the dissociation dynamics, i.e., B̃ 1A1, X̃  1A1, and Ã 1B1. The nonadiabatic transitions B̃→X̃ and B̃→Ã near linearity are modeled in a very simple way, which does not yield the OH(2Σ)/OH(2Π) branching ratio. The rotational distributions for OH(2Σ) and OD(2Σ) agree qualitatively very well with the measurements. They are highly inverted and peak close to the highest accessible state. Comparing the OH(2Π) rotational distributions with recent experimental results we conclude that B̃→X̃ is probably the main dissociation pathway, although contributions from a B̃→Ã transition cannot be excluded. The OH(2Π) distribution is also highly inverted with a peak near j∼43 in excellent agreement with experiment. The majority of trajectories on all three potential energy surfaces is direct. The shape of the various rotational distributions is determined by the first step of the dissociation from the FC region up to linearity where the crossing to the X̃ or the Ã state might occur. As envisioned a long time ago the strong angular force near the FC region on the B̃ potential energy surface is responsible for the extremely high degree of rotational excitation for OH(2Σ) as well as for OH(2Π).
Theoretical studies on excited states of Ne2. II. Potential curves for states dissociating to Ne+Ne*(3s) with semiempirical spin–orbit interaction, and comparison with spectroscopic results
Authors: Grein F. , Peyerimhoff S. D.
Published: July 2002

Potential curves for low-lying excited states of Ne2 dissociating to Ne+Ne*(3s) were calculated by configuration-interaction methods using a lower threshold for configuration selection than before, leading to an estimated accuracy of ±0.2 mhartree (±0.005 eV). Semiempirical spin–orbit corrections were applied following the method of Cohen and Schneider using the same spin–orbit coupling matrix element for all R. The stable states 1u(3P2), 0−u(3P2), and 0+u(3P1) are calculated to have dissociation energies close to 1 eV, larger than previously assumed. Potential maxima and shallow minima appear to be well described, although calculated potential barriers are generally smaller than estimates based upon experiments. Comparison of the theoretical results is made with spectroscopic studies, in particular absorption from and emission to the ground state as well as absorption from the excimer states 1 1Σ+u and 1 3Σ+u.
Second-quantized molecular time scale generalized Langevin equation theory and the quantum oscillator
Authors: McDowell H. Keith
Published: July 2002

The short-time Gaussian approximation to the molecular time scale generalized Langevin equation (MTGLE) friction kernel is introduced and used to compute the time dependence of a fluctuation time correlation function. The fluctuations are shown to have two time scales, namely, the dissipation time scale and a quantum time scale given by exp[−2πkTt/ℏ]. Absorption and emission spectral functions for a quantum oscillator coupled to a bath are derived with no approximations made. The second-quantized MTGLE approach is applied to the problem of a quantum oscillator coupled linearly to a bath of quantum oscillators. The method is shown to be consistent with previous work and to provide a systematic methodology to examine more general many-body boson problems.
Transient absorption of polydiacetylene molecules
Authors: Sixl H. , Jost R. , Warta R.
Published: July 2002

During excitation with ultraviolet light, polydiacetylene crystals show a photoinduced absorption which is ascribed to a triplet excited state of the individual polymer chains. We have measured this absorption using partially and fully polymerized TS and FBS single crystals. The results of stationary and time-resolved experiments are discussed.
Microwave spectrum of the Ar⋅⋅⋅vinyl cyanide van der Waals complex
Authors: Suenram R. D. , Lovas F. J.
Published: July 2002

The microwave spectrum of the Ar⋅⋅⋅vinyl cyanide van der Waals complex has been observed using a pulsed Fourier transform microwave spectrometer. Two vibrational states have been identified. Centrifugal distortion and 14N quadrupole hyperfine analyses of the observed transitions have been performed for both states. The lower (ground) state fits an asymmetrical top Hamiltonian significantly better than the upper state. The two states are believed to arise because of a tunneling motion within the complex. The preferred structure of the complex has the Ar atom located approximately equidistant from the methylene carbon and nitrogen atoms and ∼34° out of the plane of the vinyl cyanide subunit.
Energy dependences of reactions between some atomic ions and SF6, and reevaluation of appearance potentials (SF+5/SF6) and D(SF5–F)
Authors: Richter R. , Tosi P. , Lindinger W.
Published: July 2002

The reactions of Ar+, N+, and Kr+ with SF6 have been investigated using a selected ion flow drift tube in the energy regime from thermal to a few eV relative kinetic energy of the reactants, KEcm, and the reaction of Xe+ with SF6 from 2 to 5 eV, KEcm, SF+5 is the dominant ionic product in all cases with the exception of the endoergic Xe+ reaction, where SF+3 was observed to be the product ion, the rate coefficient increasing dramatically with KEcm. The reaction involving Ar+ and N+ are fast (k∼10−9 cm3 s−1) and vary only slightly with energy. In the case of Kr+ the 2P3/2 state reacts fast (k∼6×10−10 cm3 s−1), while the 2P1/2 state is about an order of magnitude less reactive. The finding of the Kr+ (2P3/2) reaction leads to values AP (SF+5/SF6) ≤14.0 eV and D(SF5–F)=3.83±0.1 eV.
Associative ionization in collisions of K(n
d) Rydberg atoms with molecules
Authors: Kalamarides A. , Walter C. W. , Zollars B. G. , Smith K. A. , Dunning F. B.
Published: July 2002

Measurements of associative ionization in collisions of K(nd) Rydberg atoms with a variety of molecular targets are reported, demonstrating that the Rydberg electron can serve as a catalyst to promote reactions involving the Rydberg core ion.
Dependence of the triplet state properties on the orientation of metal ion perturbers in naphthalene-crown ether metal ion complexes. I. External heavy atom effect
Authors: Ghosh Sanjib , Petrin Michael , Maki August H. , Sousa Lynn R.
Published: July 2002

The lowest excited triplet state and the sublevel dynamics have been studied in 1, 5-naphtho-22-crown-6 (I), 1,8-naphtho-21-crown-6 (II), and 2, 3-naphtho-20-crown-6 (III) and their complexes with various metal ions (Na+, K+,Cs+, Tl+) using optical detection of magnetic resonance at 1.2 K in zero applied magnetic field. The results indicate that the orientation of the heavy ion perturber with respect to the naphthalene chromophore selectively influences both the sublevel radiative rates and their populating rates by intersystem crossing. The largest heavy atom effect results when the metal ion perturber is located along the out-of-plane axis originating from the center of the naphthalene chromophore (I). The selective effects on the sublevel dynamics can be explained in terms of symmetry restrictions which enter the spin–orbit matrix elements via overlap integrals between the pi electrons of naphthalene and the p orbitals of the heavy atom.
Vibrational relaxation dynamics of matrix-isolated BH2D−2
Authors: Kammen D. M. , Gosnell T. R. , Tkach R. W. , Sievers A. J.
Published: July 2002

Infrared spectroscopy, fluorescence, and incoherent saturation experiments have been performed on matrix-isolated BH2D−2. We find that the 942 cm−1 vibrational mode of this molecule in KBr is unsaturable up to laser pump intensities of 1 MW/cm2 in marked contrast with the earlier measurements on ReO−4, which give a saturation intensity of 55 W/cm2. The different behavior for the light molecule is a result of one-phonon decay to a nearby lower-lying internal vibrational mode. Because of the small moment of inertia of the molecule high frequency librational modes provide a third-order decay channel between this lowest frequency internal vibrational mode and the ground state.
Trajectory studies and sensitivity analysis of rotational energy transfer in gas–surface collisions
Authors: Smith Charles B. , Lucchese Robert R.
Published: July 2002

The stochastic trajectory method has been applied to the scattering of CO from an LiF(100) surface. At low surface temperature TS, the trajectories of the gas molecule exhibited multiple collisions with the surface. The degree of rotational and translational energy accommodation could be related to the residence time at the surface. The residence time of the molecule on the surface was in turn related to a desorption rate constant which had an Arrhenius form with an activation energy which was about one third of the interaction potential well depth. At high TS most of the trajectories exhibited only one gas–surface collision. In this scattering regime we used stochastic sensitivity analysis (SSA) to obtain first and second order sensitivity coefficients which described how the final rotational and translational energies were coupled to TS and to the initial rotational and translational energies. At low initial translational energies EiT, we found that the most important effect on the final rotational energy of increasing EiT was the increase of the accommodation of energy between the surface modes and the rotational modes of the molecule. The direct coupling of the translational to rotational modes became dominant only at higher EiT. The energy parameters found at high TS with the SSA were also found to yield the per collision rate of energy accommodation at low TS.
Observations of a torus in a model of the Belousov–Zhabotinskii reaction
Authors: Barkley Dwight , Ringland John , Turner Jack S.
Published: July 2002

The first observation of quasiperiodic oscillations in a model of the Belousov–Zhabotinskii reaction is presented and the evolution along two parameter paths of the associated torus is described. Comparison is made with experiment and the hysteresis–Hopf normal form. The model dynamics is shown to be more complex than that of the normal form. The torus is also shown to be related to two other features of the BZ reaction: (1) the transition from small amplitude to mixed-mode oscillations and (2) alternating periodic–chaotic sequences.
A simple analytical eigenvalue calculation for barrier crossing rates in the weak coupling limit
Authors: Okuyama Shoichi , Oxtoby David W.
Published: July 2002

We present an analytical eigenvalue analysis of barrier crossing dynamics in the extremely weak coupling limit. Approximate, but quite accurate eigenfunctions to a well-known model in this limit are found. The advantage of the simple eigenvalue analysis presented in this paper is twofold: First, it enables us to study the short-time dynamics as well as the long-time barrier crossing rate and clarifies how the separation of short and long time scales emerges. Secondly, it shows how much the probability distribution is skewed from equilibrium near the barrier top as a function of the height of the barrier. Consequently, the limits of validity of well-known results, including Kramers’, are shown in an intuitive manner. We recover some recent, more rigorous results that become identical to Kramers’ formula in the proper limits.