bluuebunny/crossref_metadata_2025 huggingface dataset:
A detailed study of a forced chemical oscillator: Arnol’d tongues and bifurcation sets
Authors: Vance William , Ross John
Published: July 2002

We investigate in detail the dynamics of a time-periodically forced chemical oscillator in the parameter plane of forcing amplitude and forcing period. In particular, we present computed bifurcation sets for two typical cases of a forced, autonomously oscillating continuous stirred tank reactor system. The total mass flow rate  j is used as the forcing variable by varying it sinusoidally in time about the autonomous system’s value. We find a wide variety of new nonlinear phenomena, including a global bifurcation structure—the skeletal bifurcation structure—that is common to the two cases presented and to other forced oscillator systems. The skeletal bifurcation structure is periodic along the forcing period axis and is mainly composed of the boundaries of Arnol’d tongues, which terminate at finite forcing amplitudes. In one of the cases studied, the invariant torus is destroyed between two critical curves and cascades of period doubling occur within the Arnol’d tongues; we relate this destruction of the torus to the discontinuous bifurcation that destroys the limit cycle in the autonomous system as j is varied.
A classical path approach to reactive scattering. II. Apparatus for three-dimensional applications
Authors: Billing G. D. , Muckerman J. T.
Published: July 2002

We describe the apparatus necessary for the application of a previously reported classical path method to three-dimensional reactive collisions. The case of D+H2 is used as an example.
On the origin of the competition between photofragmentation and photodetachment in hydrated electron clusters, (H2O)−n
Authors: Posey Lynmarie A. , Campagnola Paul J. , Johnson Mark A. , Lee Gang Ho , Eaton Joseph G. , Bowen Kit H.
Published: July 2002

Photoexcitation of size-selected hydrated electron clusters, (H2O)−n , in the near IR results in a competition between photofragmentation and electron photodetachment. To investigate the origin of this competition, the decay probability into ionic fragments for the n=25 cluster was measured as a function of photon energy from 0.91≤hν≤3.49 eV. The photofragmentation probability increases rapidly with decreasing excitation energy in the general vicinity of the vertical detachment energy of this cluster (1.4 eV) determined via photoelectron spectroscopy. This result suggests that fragmentation accompanies photoexcitation of the excess electron with near zero kinetic energy. Thus, photofragmentation appears to proceed through an optically prepared intermediate similar to that reached in electron scattering from neutral clusters, which displays an enhanced dissociative attachment pathway with near zero kinetic energy electrons.
Potential energy surfaces for water dynamics: Reaction coordinates, transition states, and normal mode analyses
Authors: Tanaka Hideki , Ohmine Iwao
Published: July 2002

Dynamics of water binding structure reorganization is investigated by analyzing the potential energy surfaces involved. The water structures in a trajectory are quenched to their local minima, called the inherent structures. The reaction coordinates, which connect the inherent structures successively visited by the system, are determined. It is found that the energy barrier heights, the transition state energies, along the reaction coordinates are mostly distributed in the range of 0.2–6 kcal/mol. The classification of inherent structures is made to groups of ‘‘overall-inherent structures’’; successive inherent structures are most often not so geometrically distinct. It is found that transitions between the overall-inherent structures, involving large collective motions, occur in the subpicosecond time scale. Individual molecular motions in these collective motions are stongly correlated, not yielding large transition energies. The transition state energy sometimes reaches up to 20 kcal/mol, when the system goes through the ridge between deep minima, yielding ballistic dynamical behavior. Temperature dependence of the collective motions is also investigated.
Dependence of NO rotational photoionization propensity rules on electron kinetic energy
Authors: Song Xinbei , Sekreta Ellen , Reilly James P. , Rudolph H. , McKoy V.
Published: July 2002

In order to study the effect of photoelectron kinetic energy on rotational photoionization propensity rules, rotationally resolved laser photoelectron spectra were measured for excitation of specific rovibronic levels in the D 2Σ+ (3pσ) Rydberg state of NO and their subsequent ionization by radiation at several wavelengths. The measured and calculated ion rotational branching ratios both show a significant dependence on photoelectron energy. Comparison between experimental data and theoretical calculations suggests that a strong ΔN=0 peak in the spectra is caused by an interaction between particular vibronic levels of the A 2Σ+ (v=4) and D 2Σ+ (v=0) Rydberg states.
Rotational spectra of Ar2–DCl and Ar3–DCl, and a pseudotriatomic force field for Ar2–H/DX
Authors: Klots T. D. , Gutowsky H. S.
Published: July 2002

Microwave rotational transitions have been observed for Ar2–D35Cl and Ar3–D35Cl/37Cl. The Cl and D hyperfine interactions have been analyzed and rotational constants determined. The structures of the clusters are similar to those reported earlier for Ar2–HF/Cl and Ar3–HF/Cl. Ar2–D35Cl is a T-shaped asymmetric top with the DCl along the C2v axis. The A, B, and C rotational constants are 1735.0958(5), 1651.6749(8), and 840.5459(1) MHz, respectively. The four independent centrifugal distortion constants, τaaaa, τbbbb, τaabb, and τabab, are −0.1171(3), −0.0763(2), 0.037 64, and −0.060 88 MHz. The 35Cl quadrupole interaction is anisotropic and slightly Jdependent, with a χaa of −38.184 0(7) and (1/(6)1/2)(χbb−χcc) of −1.3380 MHz for the 101→202 transition. χaa(D) was found to be 111.4 kHz. Ar3–DCl is a symmetric top with the DCl along the C3v axis. B0, DJ, DJK, χaa(35Cl), and χaa (D) for Ar3–D35Cl are 840.2264 MHz, 2.268 and 1.921 kHz, and −39.717(3) and 0.128(4) MHz, respectively. Analysis of the change in B0 with 35Cl/37Cl substitution shows conclusively that the DCl is oriented with the D end closest to the argons. A pseudotriatomic, bent XY2 model is used with the centrifugal distortion constants of Ar2–H/DF and –H/DCl to predict force constants, vibrational frequencies, and inertial defects of the four clusters. The predicted Ar–Ar stretching frequency of 21.8 to 23.0 cm−1 in the clusters compares favorably with the 25.7 cm−1 experimental value reported for free Ar2.
Rotationally inelastic collisions of a molecule in a 1Δ electronic state: NH(a 1Δ)
Authors: Sauder Deborah G. , Patel-Misra Dipti , Dagdigian Paul J.
Published: July 2002

The general theory for inelastic scattering of molecules 1Δ electronic states is outlined and applied to the specific case of 1Δ states arising from a π2 electron occupancy, e.g., NH(a 1Δ). Integral cross sections for rotational transitions out of the lowest rotational level (J=2) of NH(a 1Δ) v=0 are reported for several targets. A pulsed beam of rotationally cold NH(a 1Δ) was produced by 193 nm photolysis of a dilute mixture of hydrazoic acid in nitrogen seed gas at the tip of a nozzle. The target beam was also prepared as a pulsed supersonic beam. The final rotational state distribution was measured in the collision zone by laser fluorescence excitation. The state-to-state cross sections were found to decrease significantly with increasing final rotational quantum number J′. The magnitude of the J=2→J′=3 cross sections were compared for the different targets. Isotopic scrambling in NH(a 1Δ)–D2 collisions was also searched for but not observed.
T
2 can be greater than 2T1
Authors: Sevian H. M. , Skinner J. L.
Published: July 2002

We consider a quantum–mechanical two-level system under the influence of both diagonal and off-diagonal stochastic perturbations, and focus on the decay times T1 and T2, which refer to the relaxation to equilibrium of the populations and relative phase of the two levels, respectively. From both theoretical and experimental viewpoints one traditionally expects that T2≤2T1. On the other hand, from a fourth-order cumulant expansion calculation of the asymptotic time dependence of the density matrix elements, Budimir and Skinner [J. Stat. Phys. 49, 1029 (1987)] showed that, in fact, in some instances T2>2T1. In this paper we solve the stochastic model numerically, which leads to the exact time dependence of the density matrix at all times. We find that the analytic prediction that T2>2T1 is not only correct, but also meaningful, in the sense that the density matrix elements decay exponentially after only a short transient time.
Strong energy dependence of collisional vibrational relaxation between 2500 and 5400 cm−1 in T1 pyrazine
Authors: Bevilacqua Thomas J. , Andrews B. Kim , Stout Joe E. , Weisman R. Bruce
Published: July 2002

Collisional vibrational relaxation of T1 pyrazine by He and SF6 has been measured for excess vibrational energies ranging from 2500 to 5400 cm−1. Energized pyrazine vapor is formed through intersystem crossing from the optically prepared 8a1 level of S1. Triplet–triplet transient absorption is then used to monitor the T1 decay kinetics under various collisional conditions. Based on the known variation of T1 pyrazine’s nonradiative decay rate with vibrational energy, the vibrational energy content is obtained as a function of collisional history. The results show a factor of ten increase in average energy lost per gas kinetic collision as the vibrational energy content of the pyrazine increases from ∼2500 cm−1 to 5000 cm−1. The energy loss per collision seems relatively constant above 5000 cm−1. This dependence is more complex than had been found from studies of other polyatomics at higher energies. It also appears that vibrational energy loss from electronically excited organic molecules at high vibrational energies may be similar to that from ground state species.
Vacuum ultraviolet photochemistry of CHFCl2 and CHFBr2: Absorption spectra and CHF(Ã 1A″) radical formation
Authors: Ibuki Toshio , Hiraya Atsunari , Shobatake Kosuke , Matsumi Yutaka , Kawasaki Masahiro
Published: July 2002

Photoabsorption and fluorescence excitation spectra of CHFCl2 and CHFBr2 were measured in the wavelength region 106–200 nm using synchrotron radiation as a light source. The Rydberg excitations of the outer shell orbitals are discussed. The He(i) photoelectron spectrum of CHFBr2 was first measured. Diffuse emission band of CHF(Ã 1A″→X̃ 1A′) was observed in the 350–700 nm region, in which the 2n0 (n=0–4) vibrational progression and 201 transition were identified. The CClF(Ã 1A″) radical was produced together with CHF(Ã 1A″) in the photodecomposition of CHFCl2. The radiative lifetimes of the Ã 1A″ states of CHF and CClF were determined to be 2.57±0.16 μs and 644±15 ns, respectively. In the photolysis of CHFCl2 fluorescence starts at 155 nm and shows a maximum quantum yield Φ=0.22 at 107.5 nm, while the CHFBr2 excitation gives a maximum of Φ=0.016 at 117.5 nm.
Pressure induced amorphization of ice Ih
Authors: Tse John S. , Klein Michael L.
Published: July 2002

The amorphization of crystalline ice Ih under the application of external pressure as a function of temperature is examined with constant-pressure molecular dynamics calculations. The results show the existence of a crystalline→amorphous phase boundary which follows the extrapolation of the normal melting line to low temperature.
D+H2(v=1, J=1): Rovibronic state to rovibronic state reaction dynamics
Authors: Kliner Dahv A. V. , Zare Richard N.
Published: July 2002

We have studied the D+H2(v=1, J=1)→HD(v′,J′)+H reaction at ∼1.0 eV center-of-mass collision energy. The H2 is prepared in (v=1, J=1) by stimulated Raman pumping and the HD(v′=1, J′) rotational distribution is measured by (2+1) resonance-enhanced multiphoton ionization. Vibrational excitation of the H2 reagent results in substantial rotational excitation of the HD(v′=1) product, the fraction of the available energy appearing as product rotation increasing from gR=0.17 for the D+H2(v=0, J thermal) ‘‘unpumped’’ reaction to gR=0.34 for the D+H2(v=1, J=1) ‘‘pumped’’ reaction. We estimate that the reaction cross section into HD(v′=1) is at least 4 times larger for the pumped than the unpumped reaction.
Photoion anisotropy in dissociative photoionization of CF3I
Authors: Powis Ivan , Dutuit Odile , Richard-Viard Martine , Guyon Paul Marie
Published: July 2002

Dissociative photoionization of CF3I is studied in the region of the CF3I+ A state (13–15 eV). We observe a pronounced anisotropy of the I+ fragment ions in the time of flight coincidence spectra obtained at 14.24 and 15.0 eV photon energy, but having the same 13.3 eV parent ion internal energy. It is the result of a strong alignment in the photoionization process at these energies, probably related to a specific autoionization process. A new and lower value of 13.40±0.05 eV is measured for the appearance potential of the CF2I+ fragment.
Influence of fractal geometry on geminate escape probability, mean recombination time, and homogeneous reaction rate
Authors: Mozumder A.
Published: July 2002

The effects of fractal geometry on the geminate escape probability, the mean recombination time, and the homogeneous reaction rate have been evaluated for both neutral and ionic recombinations. Following López-Quintella et al. [J. Chem. Phys. 88, 7478 (1988)] the fractal geometry effect is exhibited through a position-dependent diffusion coefficient. In general, the mean recombination time increases with the mean free path, even more significantly when the latter is comparable with the reaction radius or greater. The escape probability increases with the mean free path for nearly diffusion-controlled reactions but decreases with it for reactions that are governed by energy-loss considerations. The homogeneous ionic recombination rate decreases with the mean free path, in approximate agreement with the Monte Carlo results of Tachiya [J. Chem. Phys. 87, 4108 (1987)] if the scale parameter is taken to be 3.7 times the mean free path.
Dynamics of classical systems based on the principle of stationary action
Authors: Banerjee Ajit , Adams Noah P.
Published: July 2002

Dynamics of classical systems often involve finding a path of evolution of the system between chosen initial and final configurations such as reactant and product states. We develop a method for calculating the dynamics of such classical systems posed as boundary value (configurations) problems. This method is based on recasting the principle of stationary action into a computationally tractable form which can be applied to a wide variety of boundary problems. We demonstrate that a path of minimum action does not always exist except for a short enough path. However, saddle points of the action can reveal interesting dynamical pathways. We give examples from particle mechanics and applications to reaction mechanisms for the H+H2→H2+H reaction.
Correlation diagrams for accurate adiabatic channel potentials of atom+linear molecule reaction systems
Authors: Nikitin E. E. , Troe J.
Published: July 2002

Correlation diagrams for adiabatic channels between free atoms and linear molecules (both in nondegenerate electronic states) and the corresponding reaction complexes are constructed. The accurate calculation of adiabatic channel potential curves is discussed. The magnitude of Coriolis coupling terms is illustrated.
Potential energy curves of the ground, excited, and ionized states of Ar2 studied by the symmetry adapted cluster-configuration interaction theory
Authors: Mizukami Yoshihiro , Nakatsuji Hiroshi
Published: July 2002

Symmetry adapted cluster-configuration interaction theory is applied to the calculation of potential energy curves for the ground, excited, and ionized states of Ar2. The excited states studied here dissociate into Ar(3p6)+Ar(3p54s1) and Ar(3p6)+Ar(3p54p1). Spin–orbit coupling is included by a semiempirical method. The present results, especially for the 4s Rydberg states, compare very well with the experimental results of absorption and emission spectra. Some new assignments of the observed spectra are given, particularly for excitations from bound excited states of Ar2.
Selectively breaking the O–H bond in HOD
Authors: Vander Wal R. L. , Scott J. L. , Crim F. F.
Published: July 2002

Vibrationally mediated photodissociation of HOD, in which one photon excites an O–H stretching vibration and another photon dissociates the vibrationally excited molecule, preferentially breaks the O–H bond for some photolysis wavelengths. Excitation of the third O–H stretching overtone (4νOH ) of HOD followed by photolysis with a 239.5 or 266 nm photon produces at least 15 times more OD than OH product, as determined by laser induced fluorescence detection of both species. Dissociation of HOD(4νOH ) with a 218.5 nm photon produces comparable amounts of OH and OD fragments. This large selectivity and strong dependence on the wavelength of the photolysis photon is consistent with qualitative models of vibrationally mediated photodissociation and with recent calculations.
Photodissociation dynamics of formaldehyde: H2 rotational distributions and product quantum state correlations
Authors: Butenhoff Thomas J. , Carleton Karen L. , Moore C. Bradley
Published: July 2002

The alignment and rotational state populations of ortho and para H2 (v=1) and H2 (v=3) produced from formaldehyde photolysis near the threshold for dissociation are measured with Doppler-resolved laser-induced fluorescence spectroscopy in the vacuum ultraviolet (VUV). A single rovibronic level of the first excited singlet state of H2 CO in a molecular jet is excited by a pulsed UV laser and the H2 is probed under collisionless conditions with VUV generated by third harmonic generation in Kr or Xe. The rotation of the excited H2 CO during the 10−7–10−8 s before dissociation does not completely wash out the alignment: e.g., photolysis on the 2141 rR0(0)e H2 CO line produces H2 (v=3,J=2) with A(2)0=−0.31±0.06. The ortho and para H2 rotational distributions lie on a single smooth curve peaked at J≊3. The H2 CO(S1 ) vibrational state has little influence on the JH2 distributions, but there is evidence that photolysis of higher rotational states of H2 CO(S1 ) results in warmer JH2 distributions. The Doppler profiles enable the measurement of the H2 (v,J) average velocities. Conservation of energy and linear momentum permit the corresponding CO J state to be calculated. H2 formed in high vibrational states is correlated with CO formed in low rotational states. A three-parameter, semiclassical model which combines an impulsive force with the momenta of zero-point vibrations of the parent near or at the transition state geometry reproduces all of the general features of the H2 (v,J) and CO(v,J) distributions from H2 CO photolysis near the barrier to dissociation.
Nonlocal integral-equation approximations. I. The zeroth order (hydrostatic) approximation with applications
Authors: Zhou Yaoqi , Stell George
Published: July 2002

A formally exact nonlocal density-functional expansion procedure for direct correlation functions developed earlier by Stell for a homogeneous system, and extended by Blum and Stell, Sullivan and Stell, and ourselves to various inhomogeneous systems, is used here to derive nonlocal integral-equation approximations. Two of the simplest of these approximations (zeroth order), which we shall characterize here as the hydrostatic Percus–Yevick (HPY) approximation and the hydrostatic hypernetted-chain (HHNC) approximation, respectively, are shown to be capable of accounting for wetting transitions on the basis of general theoretical considerations. Before turning to such transitions, we investigate in this first paper of a series the case of homogeneous hard-sphere fluids and hard spheres near a hard wall as well as the case of hard spheres inside a slit pore. Numerical results show that the HHNC approximation is better than the HNC approximation for both the homogeneous and inhomogeneous systems considered here while the HPY approximation appears to overcorrect the PY approximation.
On the concept and distribution of reactive sites in dissociative chemisorption
Authors: Kara Abdelkader , DePristo Andrew E.
Published: July 2002

We present results of classical stochastic molecular dynamics simulations of dissociative chemisorption in two different model systems, H2 /Ni(100) and N2 /W(110). Based upon the separation of time scales between dissociation and translations and rotations, we determine: (1) the location of the dissociation within the unit cell of the surface and (2) the orientation of the molecule at the time of dissociation. The two systems displayed opposite and unusual behavior with the former exhibiting site selectivity even though S0 ≊0.8 and the latter exhibiting nonsite selectivity for S0 ≊0.13. This behavior is explained in terms of the characteristics of the molecule–surface and atom–surface interaction potentials and the general strength of adsorbate-surface vs surface–surface bonds.
Individual cross sections for 1D2 sublevels (M
L=0, ±1, ±2) in the alignment-dependent process: Ca(4p2 1D2)+Rg→Ca(3d4p 1F3)+Rg as a function of rare gas
Authors: Robinson Ruth L. , Kovalenko Laurie J. , Smith Christopher J. , Leone Stephen R.
Published: July 2002

The Ca(4p2 1D2) state is prepared in a two-step excitation with linearly polarized lasers. Two different angular wave functions are selected, 𝒴2,0 or (𝒴2,−1−𝒴2,1)/, by using parallel or perpendicular laser polarizations, respectively. Subsequent collision with a rare gas atom (He, Ne, Ar, Kr, or Xe) populates the near-resonant Ca(3d4p 1F3) state. The dependence of the collisional energy transfer process is measured as a function of the alignment of the initial 1D2 state wave function with respect to the average relative velocity vector. The laser-selected 𝒴2,0 and (𝒴2,−1−𝒴2,1)/ angular wave functions display dramatically different alignment dependences, which are understood by an analysis of the rotation properties of these wave functions. The relative contributions to the cross section of the individual 1D2 sublevels, ML=0, ±1, and ±2, are extracted, and these vary considerably depending on the rare gas. For He, the ML=±2 sublevel (asymptotic Δ molecular state) contributes the most to the total cross section, while for all the other rare gases, the ML=0, ±1 sublevels (asymptotic Σ and Π molecular states, respectively) are more important. The contribution of the ML=0 sublevel increases smoothly with increasing mass of the rare gas collision partner, becoming the largest contributor for Xe.
The potential energy and dipole moment surfaces of NF2 and O−3 by complete active space self-consistent field
Authors: Peterson Kirk A. , Mayrhofer Rudolph C. , Woods R. Claude
Published: July 2002

Three-dimensional potential energy and dipole moment surfaces have been calculated for the 25 electron radicals NF2 and O−3 in their 2B1 ground electronic states by the complete active space self-consistent field (CASSCF) method with basis sets of 87 (NF2) and 99 (O−3) contracted Gaussian-type orbitals. Spectroscopic constants have been calculated from the analytical potential energy functions for each species, and the results for NF2 are compared to the available experimental data. Predictions of the rotational and rotational–vibrational spectra of O−3 have been made by comparison to the NF2 results. Vibrational band origins have been calculated by perturbation theory and also variationally in a basis of distributed Gaussian functions. Rotationless dipole moment matrix elements and vibrational band intensities have been determined from the CASSCF dipole moment functions. The fundamental vibrational band origins and intensities of O−3 are predicted to be 979 cm−1/0.87 cm−2 atm−1 (ν1), 565 cm−1/17.8 cm−2 atm−1 (ν2), and 739 cm−1/2620 cm−2 atm−1 (ν3). Smaller basis set calculations of the first three excited electronic states of O−3 have also been carried out, and the results are compared to previous photodissociation experiments.
Frequency-dependent polarizabilities and van der Waals coefficients of half-open-shell systems in the time-dependent coupled Hartree–Fock approximation
Authors: Hettema Hinne , Wormer Paul E. S.
Published: July 2002

In this paper we present a derivation of time-dependent coupled Hartree–Fock (TDCHF) theory for the case of half-open shells. With this method frequency-dependent polarizabilities are calculated for the hydrogen and nitrogen atom, as well as for the diatomics CN, NH, and OH+. van der Waals coefficients of the half-open-shell systems with the H atom and the H2 molecule are computed. Other dispersion coefficients for dimers consisting of these monomers are available upon request.
Variational theories for localized states of an excess electron in fluids
Authors: Shaw Michael R. , Thirumalai D.
Published: July 2002

Variational theories for the behavior of an excess electron in fluids are presented. It is shown that one can develop a class of variational theories starting from the exact partition function using different levels of approximations. In particular the density functional theory, the RISM (reference interaction site model)–polaron theory, and a new variational theory are shown to arise from an identical starting point. The discussion of the general variational theories are given for the optimal localized state of an excess electron in fluids. The usefulness of the new approximate theory developed here is established by applying it to the study of the localized state of an electron in supercritical helium. The results obtained are in very good agreement with the recent path integral Monte Carlo simulations. Finally the limitation of the variational theories are pointed out.
Time correlation functions for finite systems using second-quantized molecular time scale generalized Langevin equation theory: Effect of rotating wave approximation
Authors: McDowell H. Keith
Published: July 2002

Second-quantized molecular time scale generalized Langevin equation (MTGLE) theory is applied to the computation of time correlation functions for a finite system and shown to be convergent as a function of temperature and nonlinear coupling parameter. The system chosen is a simple nonlinear or quartic oscillator in which the rotating wave approximation has been made. The effect of this approximation in the context of an MTGLE approach to computing dipole spectra is explored. As a consequence of these computations, a new pathology of the MTGLE approach is uncovered; namely, coupling frequencies ω4cn can become negative. A procedure for dealing with this problem is demonstrated and shown to work successfully.
Laser multiphoton ionization and photoelectron spectroscopy of Co(CO)3NO and Fe(CO)5
Authors: Niles Stanley , Prinslow Douglas A. , Wight Charles A. , Armentrout P. B.
Published: July 2002

Laser multiphoton dissociation-resonance-enhanced multiphoton ionization (MPD-REMPI) and time-of-flight photoelectron spectra (TOF-PES) of Co(CO)3NO and Fe(CO)5 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Co+ and Fe+. Transitions observed in the MPD-REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF-PES spectra. The multiphoton dissociation process produces metal atoms in a broad distribution of states, ranging in energies up to 33 000 cm−1 for Co, and 32 000 cm−1 for Fe. The most intense REMPI lines are associated with low-lying electronic states (<8500 cm−1 for Fe and Co). By tuning the laser to appropriate wavelengths, neutral metal atoms in selected electronic states may be ionized. At most laser wavelengths, the atomic metal ions are formed in a distribution of states, only some of which are consistent with preservation of the core configuration of the Rydberg intermediate in the ionization step. An exception appears for ionization of Co atoms via 4d Rydberg intermediate states.
Rydberg state absorption spectroscopy of Br(CH2)nI (n=1–3)
Authors: Penner Abraham , Amirav Aviv
Published: July 2002

The absorption spectra of jet-cooled bromoiodomethane (CH2BrI), 1,2-bromoiodoethane (Br(CH2)2I) and 1,3-bromoiodopropane (Br(CH2)3I) were measured in the spectral range 1600–2100 Å, and were compared with the corresponding monohalide absorption spectra. A pronounced broadening of the halogen nonbonding→Rydberg transition was observed in CH2BrI and in Br(CH2)2I whereas the transition width was considerably smaller in Br(CH2)3I. These results are rationalized in terms of a mixing of the halogen Rydberg states and the C–X (X=Br,I) antibonding state. The photochemical implications of these spectra are discussed in connection with a possible Rydberg state selective photochemistry.
Spectral diffusion and thermal recovery of spectral holes burnt into a phthalocyanine doped Shpol’skiĭ̌ system
Authors: Zollfrank J. , Friedrich J.
Published: July 2002

We measured thermally irreversible line broadening features of photochemical holes burnt into a phthalocyanine doped Shpol’skiǐ crystal. The broadening, as obtained from temperature cycling hole burning experiments is significant, indicating that irreversible structural changes do occur in Shpol’skiǐ matrices. Different sites show a different behavior. As far as line broadening is concerned, the observed features are similar to glasses. The thermal recovery curve of the holes, however, differs very much from glasses. It can be fitted by a bimodal Gaussian distribution. This bimodal distribution is interpreted in terms of two categories of photoproduct states, which the phthalocyanine molecule can possibly occupy: In category one, the two inner protons are neighbors in category two, they are diagonal.
Molecular dynamics study of propane using two simple potential models
Authors: Vega Carlos , Lago Santiago
Published: July 2002

Two empirical potential models for propane are presented. The potential parameters were chosen to fit the experimental second virial coefficient and the bubble densities of propane. With the obtained parameters, the agreement between molecular dynamics simulation results for pressure, internal energy, and experimental values of these properties is good. We also present simulated results for the properties of a reference anisotropic system defined within the WCA spirit. Rapid convergence of the perturbation scheme is clearly shown; giving the computed values of A1 and A2. These values can be useful to test the different approximations contained in a perturbation theory recently proposed for these types of potentials. In addition, we also evaluate from the simulations, the estimated value of the self-diffusion coefficient of propane.
Estimates of relativistic contributions to molecular properties
Authors: Kellö Vladimir , Sadlej Andrzej J.
Published: July 2002

A simple method for the estimation of the relativistic contribution to atomic and molecular properties is proposed. The method assumes that the dominant portion of relativistic contribution to different properties is accounted for by the Cowan–Griffin operator. In contrast to recently investigated variational relativistic and quasirelativistic approaches, the present method is based virtually on the triple-perturbation theory approach and can be easily executed in the framework of the finite-field perturbation schemes. The method proposed in this paper is applied to the evaluation of the relativistic contribution to electric properties of hydrogen halides. This contribution turns out to be completely negligible in the case of HCl. For the HI molecule, the relativistic correction to its dipole moment becomes almost as important as the electron correlation effects. A similar result is also obtained in the case of the dipole moment of AgH. Different possible applications of the present method are discussed. The major advantage of the proposed perturbation approach is a very simple computational structure which permits the calculation of relativistic corrections from any available nonrelativistic wave function.
Quantum defect theory for asymmetric tops: Application to the Rydberg spectrum of H2O
Authors: Child M. S. , Jungen Ch.
Published: July 2002

The multichannel quantum defect theory of rotational–electronic channel interactions and spectroscopic absorption intensities for rigid asymmetric tops is described. The symmetry selection rules are given in terms of the overall rotational–electronic parity and the even or odd character of K+a=Ka−λ. The angular momentum recoupling from Hund’s case (b) to (d) is shown to be accompanied by increasingly strong propensity rules K+a=‖K″a−λ″‖ and ‖N+−J″‖≤l″, which explain the simplicity of the rotationally resolved photoionization spectra of H2O and D2O without recourse to any predissociation mechanism. The main features of this spectrum are well reproduced, and ionization limits of 101 772(2) and 101 920(5) cm−1 are derived for H2O and D2O.
Prediction of the spectrum for excitation of the van der Waals modes in ArHCN
Authors: Clary D. C. , Dateo C. E. , Stoecklin T.
Published: July 2002

A calculation of the spectrum for the excitation of the van der Waals modes in ArHCN is reported. The coupled electron pair approximation is used to compute an ab initio potential energy surface for the interaction of Ar with rigid HCN. The rovibrational bound states for the complex are calculated using a variational coupled-basis set method in which a self-consistent field approach is used to optimize simultaneously the basis sets for both the intermolecular bending and stretching motions in the van der Waals molecule. The calculations are compared with experimental results, including a measurement of the infrared spectrum of ArHCN in the region of the CH stretching vibration. The calculations predict that several bending modes with frequencies less than 20 cm−1 should have excitation intensities large enough to be observed. These low frequency bending modes arise from the small rotational constant of the HCN molecule and are not due to special features of the Ar–HCN potential energy surface.
Hard sphere cavity in a Lennard-Jones liquid
Authors: Stecki J. , Toxvaerd S.
Published: July 2002

A Lennard-Jones (6-12)liquid containing a single, immobile hard sphere cavity is studied by molecular dynamics simulation. The cavity radii range from infinity (hard wall) to 0.5σ. Number densities, Irving–Kirkwood normal pressure, force, and self-energy are reported. The particle number density extrapolated up to the cavity wall, as well as statistics of empty space around the cavity are used to extract the chemical potential of the cavity and other quantities as functions of cavity radius at constant temperature and far-away pressure (density) of the solvent. Extrapolation from macroscopic down to molecular cavity sizes greater than σ is discussed.
Artificial resonance procedure for the determination of quantum mechanical rate constants in the tunneling regime
Authors: Lefebvre R. , Moiseyev N.
Published: July 2002

The quantum mechanical thermal rate constant associated with a bimolecular reactive collision is given by Miller [J. Chem. Phys. 61, 1823 (1974)] as the Boltzmann average of the reactive flux operator F 𝒫, F being the flux operator and 𝒫 a projection operator selecting reactants to products wave functions. We show with the help of the complex rotation method that at low enough temperatures, when tunneling is the dominant mechanism, this rate can also be obtained from a set of artificial resonances produced by box quantization. This device creates two wells, one in the reactant region, one in the product region and the resonances are associated with irreversible decay from one well to the other. Illustrative one-dimensional examples are given.
Theoretical study of polarizabilities and hyperpolarizabilities of Ne, HF, F−, and OH−
Authors: Chong Delano P. , Langhoff Stephen R.
Published: July 2002

Theoretical calculations are presented for the polarizability parameters through the fourth power of an applied static electric field for Ne and HF and through the second power in the field for the negative ions F− and OH−. Large Gaussian basis sets are employed and electron correlation is incorporated using the modified coupled pair functional (MCPF) method and for Ne and HF using coupled-cluster single- and double-excitation (CCSD) methods with two approaches of including the effect of triple excitations. The MCPF method is found to perform well in relation to the more rigorous CCSD method. Our theoretical values for Ne are in good accord with the recent experimental value of Shelton, as well as with recent theoretical studies. Our best results for the first and second hyperpolarizability of HF are in slightly better agreement with experiment than previous theoretical studies, but still show a very large disparity.
Quantum Monte Carlo calculations with model potentials: Quadratic accuracy
Authors: Yoshida Takashi , Iguchi Kaoru
Published: July 2002

A quantum Monte Carlo method simulating the Green’s function to quadratic accuracy is combined with ab initio core model potentials. The ionization potential of the calcium atom and the electron affinity of the bromine atom are estimated from the valence energies. The results are in quite good agreement with the corresponding experimental values.
Geometries and energies of GeHn and GeH+n (n=1–4)
Authors: Das Kalyan K. , Balasubramanian K.
Published: July 2002

Complete active space MCSCF (multiconfiguration self-consistent field) (CASSCF) followed by second-order configuration interaction (SOCI) and multireference singles and doubles CI (MRSDCI) are carried out on the ground states of GeHn and GeH+n (n=1–4). The equilibrium geometries of these species, adiabatic ionization potentials, and stepwise bond energies [De(Hn−1Ge–H) and De(Hn−1Ge+–H)] are calculated. The ground sate of GeH+4 is a Jahn–Teller distorted 2A1(C2v) state with a GeH+2⋅H2 complex structure. The adiabatic ionization potentials (IPS) of GeHn exhibit even–odd alternation. GeH4 is the most stable among the neutral GeHn species while GeH+3 is the most stable of the GeH+n.
Experimental and theoretical total state-selected and state-to-state absolute cross sections. II. The Ar+(2P3/2,1/2)+H2 reaction
Authors: Liao C. -L. , Xu R. , Nourbakhsh S. , Flesch G. D. , Baer M. , Ng C. Y.
Published: July 2002

Total state-selected and state-to-state absolute cross sections for the reactions Ar+(2P3/2,1/2)+H2(X,v=0)→Ar (1S0)+H+2(X̃,v′) [reaction (1)], ArH++H [reaction (2)], and H++H+Ar [reaction (3)] have been measured in the center-of-mass collision energy Ec.m. range of 0.24–19.1 eV. Absolute spin–orbit state transition total cross sections (σ3/2→1/2,σ1/2→3/2) for the collisions of Ar+(2P3/2,1/2) with H2 at Ec.m.=1.2–19.1 eV have been obtained.

The measured state-selected cross sections for reaction (1) [σ3/2,1/2(H+2)] reveal that at Ec.m.≤5 eV, σ1/2(H+2) is greater than σ3/2(H+2), while the reverse is observed at Ec.m.≥7 eV. The total state-to-state absolute cross sections for reaction (1) (σ3/2,1/2→v′) show unambiguously that in the Ec.m. range of 0.16–3.9 eV the dominant product channel formed in the reaction of Ar+(2P1/2)+H2(X,v=0) is H+2(X̃,v′=2)+Ar. These observations support the conclusion that at low Ec.m. the outcome of charge transfer collisions is governed mostly by the close energy resonance effect. However, at sufficiently high Ec.m.(>6 eV) the charge transfer of Ar+(2P3/2)+H2 is favored compared to that of Ar+(2P1/2)+H2.

The relative values measured for X1/2→v′[≡σ1/2→v′/σ1/2 (H+2)] are in good accord with those predicted from calculations using the state-to-state cross sections for the H+2(X̃,v′=0–4)+Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X3/2→v′[≡σ3/2→v′/σ3/2 (H+2)] and those predicted using the microscopic reversibility argument are also in fair agreement. The spin–orbit effect for the cross section of reaction (2) [σ3/2,1/2(ArH+)] is significantly less than that for reaction (1). Both σ3/2(ArH+) and σ1/2(ArH+) decrease rapidly as Ec.m. is increased, and become essentially identical at Ec.m. ≊3.8 eV. The cross sections for reaction (3) observed in the Ec.m. range of 2.5–12 eV are ≤3% of σ3/2,1/2(H+2).

The onset for the formation of H+ by reaction (3) is consistent with the thermochemical threshold. The values for σ3/2→1/2 and σ1/2→3/2 observed here are nearly a factor of 2 greater than those measured by the energy loss spectroscopic method. However, the kinetic energy dependencies for σ3/2→1/2 and σ1/2→3/2 are in accord with the previous measurements. Theoretical cross sections for the charge transfer and spin–orbit state transition reactions are calculated at Ec.m.=19.3 eV using the nonreactive infinite-order sudden approximation for comparison with experimental values.
Electronic states of Cu+4, Ag+4, and Au+4: Interpretation of the optical spectra of Cu+4
Authors: Balasubramanian K. , Das K. K.
Published: July 2002

Complete active space multiconfiguration self-consistent field followed by single-reference and multi-reference CI calculations which included up to 1.1 million configurations are carried out on Cu+4, Ag+4, and Au+4. The ground states of all three ions are found to be X 2B1u states with equilibrium geometries of rhombus. We compute the atomization energies of Cu+4, Ag+4, and Au+4 as 6.2, 5.2, and 7.3 eV, respectively, in agreement, with the experimental prediction for AE(Cu+4) < 6.8 eV by Jarrold and Creegan. Calculations of excited states reveal a low-lying 2B2u excited state (Te ∼ 6000–7000cm−1) for all three M+4. For Cu+4 we also studied the excited 2Ag, 2B1g, and 2B2g states. Our calculations show that the optical spectra of Cu+4 observed by Jarrold and Creegan in the 690 nm region are due to the (Cud → s)2B1g–X2B1u transition while one of the unassigned bands in the 420–490 nm region is due to the 2Ag–X2B1u transition of Cu+4 which is predominantly a valence transition. Our calculations support the complex vibronic structure of the 690 nm system.
Structure of hard-particle fluids near a hard wall. IV. y
w(z,θ) for homonuclear hard diatomics
Authors: Labík S. , Malijevský A. , Smith W. R.
Published: July 2002

Homonuclear hard diatomics in the vicinity of a hard wall have been studied using Monte Carlo simulations. During the simulations the cavity distribution functions for parallel and perpendicular orientations with respect to the wall and their Legendre expansion coefficients were calculated. It is demonstrated that the Legendre expansion is rapidly convergent and only several coefficients are required to describe the wall-diatomic correlation function within the simulation error. In addition, two simple methods for theoretical prediction of the cavity distribution function at small distances are compared with the simulation data. These approaches require as input quantities only thermodynamic data for the bulk homogeneous fluid. Both methods yield good accuracy for the cavity correlation function at the specific orientations indicated and for the first two Legendre coefficients, but fail to accurately describe higher Legendre coefficients.
The effect of parent rotational state on fragment anisotropy and application to formaldehyde
Authors: Butenhoff Thomas J. , Carleton Karen L. , van Zee Roger D. , Moore C. Bradley
Published: July 2002

A quantum mechanical model for the fragment anisotropy parameter in the limit of a long dissociation lifetime with respect to parent rotation is derived. For excitation with light plane polarized along the Z axis, the anisotropy parameter can be expressed as β=A〈P2(cos θ′t)〉 +B〈sin2 θt cos 2φ′t〉, where A and B are functions of the excitation branch employed and the rotational level of the excited parent, and (θt,φ′t) are the Euler angles of the final fragment recoil direction in the molecular frame, where the z axis is along the parent excitation transition dipole moment. For low J values, classically derived expressions for the anisotropy parameter of fragments produced from the photodissociation of a Boltzmann distribution of rotating parent molecules are shown to not be valid for H2 fragments produced from the photodissociation of H2CO excited to single rovibronic levels. This formula is applied to the measured anisotropies of the H2 (v=1,J=0) fragments produced from the fragmentation of H2CO excited to several different rotational levels of the 2141 band in S1.
Structure and energetics of the lowest 1A1 and 1B1 states of dichlorocarbene
Authors: Kim Seung-Joon , Hamilton Tracy P. , Schaefer Henry F.
Published: July 2002

A recent (1989) partial structural analysis of spectroscopic measurements by Choe, Tanner, and Harmony led to the conclusion that the first excited electronic state (1B1 state) of CCl2 has a longer bond distance than does the 1A1 ground state. This is consistent with typical Franck–Condon pictures of diatomic potential curves and with experimental results for the analogous CF2 system. However, the earlier (1985) theoretical study of Nguyen, Kerins, Hegarty, and Fitzpatrick came to the qualitatively opposite conclusion, predicting the 1B1 bond distance to be shorter by 0.044 Å, which agrees with the 1989 analysis of rotationally resolved spectra by Clouthier and Karolczak. In this research high level ab initio quantum mechanical methods are used to clarify this question. The most reliable values predicted here for the CCl2 bond distances are r0=1.713 Å (1A1) and r0=1.657 Å (1B1). Large basis sets and high levels of electron correlation are required for excellent agreement with experiment in both structures and energies. The differences between CF2 and CCl2 in the behavior of the C–X bond length upon excitation is discussed. It is also argued that most closed shell carbenes are not two configuration problems.
Calculations of H2O microwave line broadening in collisions with He atoms: Sensitivity to potential energy surfaces
Authors: Green Sheldon , DeFrees D. J. , McLean A. D.
Published: July 2002

Broadening parameters for three microwave lines of water at 22.2, 183.3, and 380.2 GHz, in a bath of helium atoms, are calculated using accurate molecular scattering S matrices obtained from two theoretical potentials presented by Palma et al., J. Chem. Phys. 89, 1401 (1988). For the 22 GHz line results are in substantial agreement with values presented in that work, indicating the accuracy of approximate methods used there. The present work improves the potential energy surfaces, computed from perturbation theory (MP4) and variational interacting correlated fragments (ICF1) wave funcitons, by correcting them for basis set superposition error (BSSE), and recomputes the line broadening using a different procedure for fitting computed energy points. In addition, the entire set of calculations are repeated with a quite different basis set for orbital expansion to establish the reliability of the potential energy surface. We show that adjustments for superposition error are essential, and that broadening cross sections computed from the new surfaces are changed 10%–30% from the old, significantly improving agreement with experiment. The MP4 BSSE adjusted surface appears to be the most accurate, giving room temperature broadenings of 8.9, 11.8, and 10.0 Å2 compared with experimental determinations of 12.2±1.2, 11.9, and 11.2 Å2 for the 22, 183, and 380 GHz lines, respectively. Thus, computed line to line variation is larger than observed. The ICF1 BSSE adjusted results for pressure broadening cross section parallel those from the MP4 BSSE calculations but are about 10% smaller. We believe our computed results are stable with respect to basis set for orbital expansion and that the scattering calculations are accurate. Any theoretical inadequacy has been pinpointed to too few points on the potential energy surface resulting in an inadequate description of the angle dependence. It is not clear whether the present discrepancy between computation and experiment stems from this or from errors in the experimental values, although we show some indication that additional information on the surface might decrease the computed broadenings, worsening agreement with experiment.