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22 Dec 1998

Volume 109, Issue 24, pp. 10539-11131

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Rotational spectrum of a salt-containing van der Waals complex: Ar–NaCl

Asao Mizoguchi, Yasuki Endo, and Yasuhiro Ohshima

J. Chem. Phys. 109, 10539 (1998); http://dx.doi.org/10.1063/1.477754 (4 pages) | Cited 11 times

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The first spectroscopic identification of a van der Waals complex containing salt, Ar–NaCl, has been reported. A cm-region rotational spectrum of the complex has been observed for the 35Cl and 37Cl isotopomers by using a Fourier-transform microwave spectrometer combined with a laser ablation nozzle source. The vibrationally averaged geometry of the complex is of the linear Ar⋯Na–Cl configuration, with the internuclear distance of R(Ar⋯Na) = 2.887 Å. An almost fully resolved hyperfine structure in low-J transitions has yielded precise nuclear quadrupole coupling constants associated with both Na and Cl nuclei, which indicate a substantial charge rearrangement in the NaCl molecule by complexation with Ar. © 1998 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Pw Fine and hyperfine structure
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Cavity size in reaction field theory

Chang-Guo Zhan and Daniel M. Chipman

J. Chem. Phys. 109, 10543 (1998); http://dx.doi.org/10.1063/1.477755 (16 pages) | Cited 31 times

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The optimum size of the cavity accommodating a solute in the reaction field theory of solvation is considered by empirical calibration of the results of electronic structure calculations against experiment. To isolate the long range electrostatic free energy contributions treated by reaction field theory from the many other short range contributions not explicitly considered, computational results are compared to experimental determinations of conformational free energy differences in polar solutes having two or more stable or metastable isomers. When the cavity shape is defined by a solute electronic isodensity contour, it is found that the best overall agreement with experiment is obtained with a cavity size corresponding to the 0.001 a.u. contour. © 1998 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
82.20.Fd Collision theories; trajectory models

Time- and frequency-resolved coherent two-dimensional IR spectroscopy: Its complementary relationship with the coherent two-dimensional Raman scattering spectroscopy

Kisam Park and Minhaeng Cho

J. Chem. Phys. 109, 10559 (1998); http://dx.doi.org/10.1063/1.477756 (11 pages) | Cited 25 times

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A theoretical description of the coherent two-dimensional IR spectroscopy is presented. Two consecutive IR pulses can be used to create two consecutive vibrational coherence states. The third off-resonant optical pulse is used to probe the two-dimensional transient grating thus created and then the scattered field is measured. The corresponding nonlinear response functions are obtained in the analytic forms by assuming that the vibrational modes are weakly anharmonic Brownian oscillators. Since one can experimentally control the two delay times as well as the two IR field frequencies, it is possible to extract vital information on the vibrational relaxation in time domain as well as the intra- and intermolecular vibrational mode couplings in frequency domain. Numerical calculations are carried out to clarify the quantitative features of the coherent 2D IR spectroscopic phenomenon. © 1998 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.Ez Rotational and vibrational energy transfer

Calibration and comparison of the Gaussian-2, complete basis set, and density functional methods for computational thermochemistry

G. A. Petersson, David K. Malick, William G. Wilson, Joseph W. Ochterski, J. A. Montgomery, and M. J. Frisch

J. Chem. Phys. 109, 10570 (1998); http://dx.doi.org/10.1063/1.477794 (10 pages) | Cited 90 times

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We have reexamined several high-accuracy Gaussian-2, complete basis set and density functional methods for computational thermochemistry (in order of increasing speed): G2, G2(MP2), CBS-Q, G2(MP2,SVP), CBS-q, CBS-4, and B3LYP/6-311+G(3df,2p). We have employed ΔfH2980 for the “extended G2 neutral test set” for this comparison. Several errors in previous studies have been corrected and experimental spin-orbit interactions have been included in all calculated atomic energies. The mean absolute deviations from experiment are 1.43, 1.76, 1.19, 1.64, 2.34, 2.66, and 3.43 kcal/mol, respectively. The maximum deviations from experiment are 10.6, 8.8, 8.1, 9.4, 11.4, 12.9, and 24.1 kcal/mol respectively. The species responsible for these maximum errors are in order: SiF4, SiF4, Cl2C�CCl2, F2C�CF2, ClF3, ClF3, and SiCl4. All seven methods have relatively large errors for bonds to halogens, but these errors are sufficiently systematic to benefit from empirical corrections. After a discussion of ill conditioning in the “bond separation reaction” implementation of isodesmic reactions, we determine “isodesmic bond additivity corrections” (BACs) for several types of bonds by least-squares fits to the heats of formation for 76 organic species with up to ten carbons and a variety of heteroatoms. The mean absolute deviations are reduced from 1.49, 1.93, 1.22, 1.53, 2.28, 3.09, and 3.45 kcal/mol to 0.55, 0.57, 0.77, 0.63, 1.03, 0.98, and 1.16 kcal/mol. The maximum errors are reduced to about 3 kcal/mol for all but the DFT method (4.2 kcal/mol). The BACs are especially useful for larger molecules with many similar bonds. For example, the CBS-Q error for Cl2C�CCl2 is reduced from 8.1 to 3.0 kcal/mol and the CBS-4 errors for benzene and naphthalene are reduced from 10.5 and 17.5 to 2.1 and 1.6 kcal/mol, respectively. © 1998 American Institute of Physics.
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82.60.-s Chemical thermodynamics
31.15.E- Density-functional theory

A quantum electrodynamical treatment of second harmonic generation through phase conjugate six-wave mixing: Polarization analysis

Ian D. Hands, Shujie Lin, Stephen R. Meech, and David L. Andrews

J. Chem. Phys. 109, 10580 (1998); http://dx.doi.org/10.1063/1.477757 (7 pages) | Cited 6 times

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The theory underlying a six-wave mixing experiment is developed using the methods of molecular quantum electrodynamics. This general theory allows the intensity of the second harmonic radiation generated by the six-wave process to be found for arbitrary arrangements of the generating laser beams. Several different polarization geometries are treated in detail, and comparison is made to experiments performed using near-resonant conditions. The agreement is good in all cases and allows detailed information pertaining to the six-wave tensor to be extracted. The information thus obtained provides evidence of a marked departure from Kleinman symmetry. © 1998 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
12.20.Ds Specific calculations
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Comparison of the performance of local, gradient-corrected, and hybrid density functional models in predicting infrared intensities

Mathew D. Halls and H. Bernhard Schlegel

J. Chem. Phys. 109, 10587 (1998); http://dx.doi.org/10.1063/1.476518 (7 pages) | Cited 52 times

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Density functional theory has been used to calculate infrared (IR) intensities for a series of molecules (HF, CO, H2O, HCN, CO2, C2H2, H2CO, NH3, C2H4, CH2F2, CH2Cl2, and CH2Br2) in an effort to evaluate relative performance of different functionals. The methods employed in this study comprise most of the popular local, gradient-corrected, and hybrid functionals, namely, S-VWN, S-PL, B-LYP, B-P86, B-PW91, B3-LYP, B3-P86, and B3-PW91. Calculations were carried out using various qualities of split valence basis sets augmented with diffuse and polarization functions, both to determine basis set dependence and to evaluate the limit performance. Computed intensities were compared with results from conventional correlated ab initio methods (MP2 and QCISD). Hybrid functionals give results in closest agreement with QCISD over the other methods surveyed. Local and gradient-corrected methods performed remarkably alike, both are comparable to MP2, and outperform Hartree–Fock. Hartree–Fock intensities can be dramatically improved by scaling, making them similar to MP2 results. © 1998 American Institute of Physics.
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33.70.Fd Absolute and relative line and band intensities
33.20.Ea Infrared spectra
31.15.E- Density-functional theory

Vibrational second hyperpolarizability of CH4−nFn molecules with n = 0–4

Olivier Quinet and Benoît Champagne

J. Chem. Phys. 109, 10594 (1998); http://dx.doi.org/10.1063/1.477758 (9 pages) | Cited 25 times

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The frequency-dependent vibrational second hyperpolarizability of CH4−nFn molecules with n = 0–4 has been computed for the most common nonlinear optical (NLO) processes by adopting the perturbation approach due to Bishop and Kirtman [J. Chem. Phys. 95, 2646 (1991)]. These calculations have been performed by using the Sadlej atomic basis set with the Hartree-Fock technique as well as with the Møller-Plesset second order perturbation theory (MP2) procedure. The inclusion of electron correlation and of the first-order mechanical and electrical anharmonicities turn out to be of quantitative importance for most quantities. In particular, it permits us to improve the agreement with the experimental data for the difference between the anisotropic dc-Kerr and mean electric-field-induced second harmonic generation (ESHG) vibrational second hyperpolarizability of CF4. With the exception of the small ESHG vibrational second hyperpolarizability the infinite optical frequency method turns out to be a satisfactory approximation for evaluating the vibrational NLO responses. © 1998 American Institute of Physics.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
31.15.xr Self-consistent-field methods
31.15.vq Electron correlation calculations for polyatomic molecules
33.57.+c Magneto-optical and electro-optical spectra and effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

One- and two-dimensional ensemble quantum computing in spin Liouville space

Z. L. Mádi, R. Brüschweiler, and R. R. Ernst

J. Chem. Phys. 109, 10603 (1998); http://dx.doi.org/10.1063/1.477759 (9 pages) | Cited 72 times

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New concepts are described for nuclear magnetic resonance (NMR) implementations of spin ensemble quantum computing in one and two dimensions. Similarities and differences between ensemble and pure state quantum computing are discussed by using a Liouville space formalism based on polarization and single transition operators. The introduction of an observer spin, that is coupled to the spins carrying the quantum bits, allows a mapping of the states of a quantum computer on a set of transitions between energy levels. This is spectroscopically favorable compared to a mapping on the energy levels themselves. Two complementary parallelization schemes for quantum computing are presented: one exploits the parallel processing feature inherent in multidimensional NMR, while the other employs mixed superposition states represented by operators in Liouville space. The spin swap operation, introduced in this paper, allows a convenient extension of quantum computing to spin systems where not all spin–spin couplings are resolved. The concepts are illustrated by implementations of logic operations and identities consisting of a sequence of basic logic gate operations. © 1998 American Institute of Physics.
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76.60.-k Nuclear magnetic resonance and relaxation
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Patterns due to quintic kinetics in a diffusion-reaction system with global interaction

Moshe Sheintuch and Olga Nekhamkina

J. Chem. Phys. 109, 10612 (1998); http://dx.doi.org/10.1063/1.477760 (8 pages)

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We study the process of pattern selection in a catalytic ribbon or disk subject to global interaction. The diffusion-reaction system, xt−Δx = f(x,y)−〈f(x,y)〉; yt = ϵ(−αx−y), with a quintic source function f(x,y) = −x(x2−1)(x2−a2)+y, qualitatively describes the behavior of catalytic or electrochemical oscillations subject to control or gas-phase mixing and the kinetics describes a system with two simultaneous or consecutive reactions. This model shows a richer class of solutions than the extensively studied one with a cubic source function (f = −x3+x+y) since f(x) = 0 is tristable and for a wide separation of time scales the system admits, without global interaction, coexistence of a stable and oscillatory states. Also the reaction-diffusion equation with a quintic source may admit one large and two small fronts and their domains of existence and stability are mapped. Under global interaction the system exhibits all the patterns unveiled with the “cubic kinetics,” along with multifront patterns and new patterns at the border of instability of the large front. © 1998 American Institute of Physics.
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82.30.-b Specific chemical reactions; reaction mechanisms
82.20.-w Chemical kinetics and dynamics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

An information-entropic study of correlated densities of the water molecule

Minhhuy Hô, Donald F. Weaver, Vedene H. Smith, Robin P. Sagar, Rodolfo O. Esquivel, and Shigeyoshi Yamamoto

J. Chem. Phys. 109, 10620 (1998); http://dx.doi.org/10.1063/1.477761 (8 pages) | Cited 15 times

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The Shannon entropy of the water molecule was calculated at different correlation levels including full configuration interaction (CI) for the D95 basis set. The results show that an analysis of both the position and momentum space entropy yields insights into the characteristics of different correlated methods from the density perspective and provides an alternative way of interpreting the wave function. Various changes in the electronic densities intrinsic to these correlation methods are also related to concepts within the information entropy framework. © 1998 American Institute of Physics.
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05.70.Ce Thermodynamic functions and equations of state
31.15.vq Electron correlation calculations for polyatomic molecules

Global analytical potential hypersurfaces for large amplitude nuclear motion and reactions in methane. I. Formulation of the potentials and adjustment of parameters to ab initio data and experimental constraints

Roberto Marquardt and Martin Quack

J. Chem. Phys. 109, 10628 (1998); http://dx.doi.org/10.1063/1.476513 (16 pages) | Cited 31 times

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Analytical representations of the global potential energy surface of XYn molecules are developed and applied to model the potential surface of methane in the electronic ground state. The generic analytical representation allows for a compact, robust, and flexible description of potentials for XYn systems irrespective of the specific nature of the atomic interactions. The functions are global in that structures near several minima of the potential hypersurface as well as saddle points and dissociation limits are well described. Clusters of atoms Yn can be represented as well by this type of function. Care is taken to implement conditions resulting from the symmetric group Sn and to construct positive definite bilinear forms of special functional forms of certain coordinates (such as bond lengths and bond angles), in order to avoid artifacts in exceptional ranges of the potential hypersurface. These special functional forms include intrinsic, symmetry allowed couplings between coordinates such as bending and stretching. We include linear potential terms in bond angle coordinates, which result in effectively quadratic potential terms for highly symmetric structures. True logical multidimensional 01-switching functions Ssw(r) of bond lengths r are used to interpolate between limiting ranges in the hypersurface. The particular form Ssw(r) ∼ exp(−(rsw/r)nsw) allows us to describe the potential as a multipole expansion representation in the limit of large r(→∞). In the application to methane, first the representations are fitted to data from high level ab initio calculations using multireference configuration interaction techniques. Additional conditions which help to improve the description of experimental data are considered during the fit. Typically, these conditions involve some parameters or parameter groups and refer to the equilibrium geometry and harmonic force field. Other constraints apply to the energies of dissociation channels. We describe the model potentials METPOT 1 to METPOT 4 in the present work. © 1998 American Institute of Physics.
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82.20.Kh Potential energy surfaces for chemical reactions
33.15.Dj Interatomic distances and angles

Calculating frequency-dependent hyperpolarizabilities using time-dependent density functional theory

S. J. A. van Gisbergen, J. G. Snijders, and E. J. Baerends

J. Chem. Phys. 109, 10644 (1998); http://dx.doi.org/10.1063/1.477762 (13 pages) | Cited 87 times

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An accurate determination of frequency-dependent molecular hyperpolarizabilities is at the same time of possible technological importance and theoretically challenging. For large molecules, Hartree–Fock theory was until recently the only available ab initio approach. However, correlation effects are usually very important for this property, which makes it desirable to have a computationally efficient approach in which those effects are (approximately) taken into account. We have recently shown that frequency-dependent hyperpolarizabilities can be efficiently obtained using time-dependent density functional theory. Here, we shall present the necessary theoretical framework and the details of our implementation in the Amsterdam Density Functional program. Special attention will be paid to the use of fit functions for the density and to numerical integration, which are typical of density functional codes. Numerical examples for He, CO, and para-nitroaniline are presented, as evidence for the correctness of the equations and the implementation. © 1998 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.E- Density-functional theory
02.60.Jh Numerical differentiation and integration

Accurate density functional calculations on frequency-dependent hyperpolarizabilities of small molecules

S. J. A. van Gisbergen, J. G. Snijders, and E. J. Baerends

J. Chem. Phys. 109, 10657 (1998); http://dx.doi.org/10.1063/1.477763 (12 pages) | Cited 73 times

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In this paper we present time-dependent density functional calculations on frequency-dependent first (β) and second (γ) hyperpolarizabilities for the set of small molecules, N2, CO2, CS2, C2H4, NH3, CO, HF, H2O, and CH4, and compare them to Hartree–Fock and correlated ab initio calculations, as well as to experimental results. Both the static hyperpolarizabilities and the frequency dispersion are studied. Three approximations to the exchange-correlation (xc) potential are used: the widely used Local Density Approximation (LDA), the Becke–Lee–Yang–Parr (BLYP) Generalized Gradient Approximation (GGA), as well as the asymptotically correct Van Leeuwen–Baerends (LB94) potential. For the functional derivatives of the xc potential the Adiabatic Local Density Approximation (ALDA) is used. We have attempted to estimate the intrinsic quality of these methods by using large basis sets, augmented with several diffuse functions, yielding good agreement with recent numerical static LDA results. Contrary to claims which have appeared in the literature on the basis of smaller studies involving basis sets of lesser quality, we find that the static LDA results for β and γ are severely overestimated, and do not improve upon the (underestimated) Hartree–Fock results. No improvement is provided by the BLYP potential which suffers from the same incorrect asymptotic behavior as the LDA potential. The results are however clearly improved upon by the LB94 potential, which leads to underestimated results, slightly improving the Hartree–Fock results. The LDA and BLYP potentials overestimate the frequency dependence as well, which is once again improved by the LB94 potential. Future improvements are expected to come from improved models for asymptotically correct exchange-correlation potentials. Apart from the LB94 potential used in this work, several other asymptotically correct potentials have recently been suggested in the literature and can also be expected to improve considerably upon the relatively poor LDA and GGA results, for both the static properties and their frequency dependence. © 1998 American Institute of Physics.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.E- Density-functional theory
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods

Size-consistent wave functions for nondynamical correlation energy: The valence active space optimized orbital coupled-cluster doubles model

Anna I. Krylov, C. David Sherrill, Edward F. C. Byrd, and Martin Head-Gordon

J. Chem. Phys. 109, 10669 (1998); http://dx.doi.org/10.1063/1.477764 (10 pages) | Cited 102 times

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The nondynamical correlation energy may be defined as the difference between full configuration interaction within the space of all valence orbitals and a single determinant of molecular orbitals (Hartree–Fock theory). In order to describe bond breaking, diradicals, and other electronic structure problems where Hartree–Fock theory fails, a reliable description of nondynamical correlation is essential as a starting point. Unfortunately, the exact calculation of nondynamical correlation energy, as defined above, involves computational complexity that grows exponentially with molecular size and is thus unfeasible beyond systems of just two or three heavy atoms. We introduce a new hierarchy of feasible approximations to the nondynamical correlation energy based on coupled-cluster theory with variationally optimized orbitals. The simplest member of this hierarchy involves connected double excitations within the variationally optimized valence active space and may be denoted as VOO-CCD, or VOD. VOO-CCD is size-consistent, has computational complexity proportional to the sixth power of molecule size, and is expected to accurately approximate the nondynamical correlation energy in such cases as single bond dissociation, diradicals, and anti-ferromagnetic coupling. We report details of our implementation of VOO-CCD and illustrate that it does indeed accurately recover the nondynamical correlation energy for challenging multireference problems such as the torsion of ethylene and chemical bond breaking. © 1998 American Institute of Physics.
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31.15.bw Coupled-cluster theory
31.15.xt Variational techniques
31.15.xr Self-consistent-field methods
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Charge transfer and fragmentation of liquid helium clusters that contain one or more neon atoms

Thomas Ruchti, Kirk Förde, Berton E. Callicoatt, Henrik Ludwigs, and Kenneth C. Janda

J. Chem. Phys. 109, 10679 (1998); http://dx.doi.org/10.1063/1.477765 (9 pages) | Cited 38 times

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An investigation of the electron impact ionization and fragmentation of helium clusters that contain Ne atoms and Nek subclusters has been performed. The charge transfer probability from He+ to Ne and the branching ratios for fragmentation of the Nek subclusters were found by analyzing the dependence of the ion signal intensities on the Ne pressure in the “pickup” region. The measured charge transfer probability from He+ to Ne ranges from 0.06±0.01 for clusters of mean original size 〈N〉 = 3300 to 0.43±0.02 for 〈N〉 = 1100. Charge transfer to a single Ne atom within the helium clusters never yields bare Ne+ ions. Instead, fragments of the type NeHen+ are produced. The charge transfer from He+ to Ne2 subclusters yields mainly Ne2+ for smaller initial cluster sizes, but NeHen+ or Ne2Hen+ fragments are more probable for larger clusters. This shows that He droplets of a few thousand atoms are able to cage Ne2 subclusters by dissipating the entire energy released by charge transfer and formation and vibrational relaxation of the Ne2+ ion. Interestingly, it was found that in these relatively small helium clusters the Ne3 and Ne4 subclusters never survive the charge transfer from He+. Fragments such as Ne2+ and Ne2Hen+ are more likely to survive than are Ne3+ and Ne4+. In general, the results presented here are qualitatively similar to those for a recent study of the ionization of Ar in helium droplets. In both cases fragmentation to the bare ion is rare, while fragmentation to the dimer ion dominates. However, the helium cluster caging effect is more efficient for Ne subclusters than for Ar subclusters. Also, there is no evidence for shell structures in the NeHen+ ion fragment distributions. © 1998 American Institute of Physics.
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36.40.Qv Stability and fragmentation of clusters
36.40.Wa Charged clusters
34.80.Gs Molecular excitation and ionization
34.70.+e Charge transfer

On the Einstein–Stern model of rotational heat capacities

Jens Peder Dahl

J. Chem. Phys. 109, 10688 (1998); http://dx.doi.org/10.1063/1.477766 (4 pages)

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The Einstein–Stern model for the rotational contribution to the heat capacity of a diatomic gas has recently been resuscitated. In this communication, we show that the apparent success of the model is illusory, because it is based on what has turned out to be an unfortunate comparison with experiment. We also take exception to the possibility of assigning any meaning to the rotational zero-point energy introduced by the model. © 1998 American Institute of Physics.
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51.30.+i Thermodynamic properties, equations of state

Hydrogenated and deuterated iron clusters: Infrared spectra and density functional calculations

Mark B. Knickelbein, Geoffrey M. Koretsky, Koblar A. Jackson, Mark R. Pederson, and Zoltan Hajnal

J. Chem. Phys. 109, 10692 (1998); http://dx.doi.org/10.1063/1.477767 (9 pages) | Cited 17 times

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Iron clusters react sequentially with hydrogen molecules to form multiply hydrogenated products. The increases in cluster ionization potential upon reaction verify that hydrogen chemisorbs dissociatively to form iron cluster–hydride complexes, FenHm. At low source temperatures, the cluster–hydride complexes take up additional hydrogen molecules which are shown to be physisorbed onto the underlying FenHm complexes to form FenHm(H2)p species. The infrared spectra of FenHm and FenDm (n = 9–20) were obtained by the photodissociation action spectroscopic method in which depletion of the FenHm(H2)p and FenDm(D2)p species was the signature of absorption. The spectra, recorded in the 885–1090 cm−1 region, consist of several overlapping bands, each approximately 20 cm−1 in width. The dissimilarity of each FenHm(H2)p spectrum with the corresponding FenDm(D2)p spectrum indicates that the carrier involves hydrogen and is not merely due to absorption by the underlying iron cluster. Density functional calculations were performed on model complexes, Fe13H14 and Fe13D14, the iron portion of which was assumed to have Th symmetry. The infrared-active vibrational frequencies involving hydrogen bending and deuterium stretching are predicted to lie within the experimental frequency range of the experiment, well removed from the skeletal modes of the underlying iron cluster. The complexity of the observed spectra as compared to simulations based on the assumed (high-symmetry) model imply that the experimentally produced complexes possess low symmetry. © 1998 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
31.15.E- Density-functional theory
33.80.Gj Diffuse spectra; predissociation, photodissociation

An ab initio study of the mono- and difluorides of krypton

Gerald J. Hoffman, Laura A. Swafford, and Robert J. Cave

J. Chem. Phys. 109, 10701 (1998); http://dx.doi.org/10.1063/1.477768 (6 pages) | Cited 2 times

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Results from ab initio calculations at the CCSD(T) level of theory are presented for krypton monofluoride (KrF), krypton monofluoride cation (KrF+), linear, ground-state krypton difluoride (KrF2), the triplet state of krypton difluoride, and the krypton–fluorine van der Waals complex (Kr–F2). These are the first calculations demonstrating that KrF is a bound molecule, in agreement with experimental observation. When corrected for basis-set superposition error, the calculated potential displays quantitative agreement with the attractive wall of the experimentally measured potential curve. Results are also presented for KrF+ and linear KrF2 which yield accurate values for their dissociation energies. The triplet state of KrF2 is found to have a minimum energy below that of separated atoms, and its structure is bent, with a small F–Kr–F bond angle (71 deg). The van der Waals complex, Kr–F2, appears to consist of an unperturbed F2 molecule attached to a krypton atom in the expected T-shaped structure. © 1998 American Institute of Physics.
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31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.bw Coupled-cluster theory

State-to-state inelastic scattering from vibrationally activated OH–H2 complexes

Jeanne M. Hossenlopp, David T. Anderson, Michael W. Todd, and Marsha I. Lester

J. Chem. Phys. 109, 10707 (1998); http://dx.doi.org/10.1063/1.477769 (12 pages) | Cited 24 times

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State-selective infrared excitation of o-H2–OH via the pure OH overtone transition has been used to induce a half-collision inelastic scattering event between the OH radical and ortho-H2 under restricted initial orientation conditions. The time evolution and final state distribution of the OH products from vibrational predissociation have been evaluated by ultraviolet probe laser-induced fluorescence measurements. The half-collision scattering takes place with ∼3350 cm−1 of energy available to the OH (v = 1)+o-H2 products, an energy that exceeds the classical barrier to reaction. The OH (v = 1) products are preferentially populated in high rotational levels with a distribution that is consistent with an energy gap law. A significant fraction of the OH fragments are promoted to the excited spin–orbit state in the predissociation process. A strong lambda-doublet propensity is also found, indicating that the OH unpaired pπ orbital is preferentially aligned perpendicular to the rotational plane of the OH products. Finally, the OH rotational and fine structure distributions are compared with those obtained in previous full collision inelastic scattering studies at energies below the threshold for reaction. © 1998 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.50.Dq Fluorescence and phosphorescence spectra

Photodissociation dynamics of trifluoroethylene at 157 nm excitation

J. J. Lin, T. C. Hsu, D. W. Hwang, Y. T. Lee, and X. Yang

J. Chem. Phys. 109, 10719 (1998); http://dx.doi.org/10.1063/1.477770 (8 pages) | Cited 9 times

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Photodissociation of trifluoroethylene (F2CCFH) at 157 nm has been investigated using photofragment translational spectroscopy. Four dissociation channels have been experimentally observed: molecular HF elimination, H atom elimination, F atom elimination, and double bond breaking. Double bond breaking is found to be the most important channel, while molecular HF elimination and H atom elimination are found to be significant. Contribution from F atom elimination is minor. Product translational energy distributions for all dissociation channels have been determined. The translational energy distributions for all four dissociation channels are peaked away from zero energy. This is quite similar to that of 1,1-difluoroethylene. Branching ratios and averaged energy partitions for all dissociation channels have also been estimated. © 1998 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.-b Photon interactions with molecules

Photoelectron spectroscopy of As−, As2−, As3−, As4−, and As5−

T. P. Lippa, S.-J. Xu, S. A. Lyapustina, J. M. Nilles, and K. H. Bowen

J. Chem. Phys. 109, 10727 (1998); http://dx.doi.org/10.1063/1.477771 (5 pages) | Cited 10 times

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The negative ion photoelectron spectra of As−, As2−, As3−, As4−, and As5− have been measured. From these, the electron affinities of As, As2, As3, As4, and As5 have been determined to be 0.814, 0.739, 1.45, <0.8, and ∼1.7 eV, respectively. In the case of As2−, the following molecular constants were also determined: re(As2−) = 2.239 Å, ωe(As2−)=293 cm−1, ωeχe(As2−)=4.9 cm−1, D0(As2−)=3.89 eV, and ΔE[2Πg(3/2)−2Πg(1/2)] = 0.256 eV. In the case of As3−, vertical detachment energy (VDE) was measured to be 1.62 eV, and for As3, ΔE(2A2−2B1) was determined to be 0.36 eV. For As4−, VDE was found to be 1.52 eV. The relatively high stability of As5− suggests that it, like P5−, may be a candidate for forming cluster-assembled, ionic crystals of stoichiometry, MAs5, where M is an alkali metal atom. Similiarities with other small cluster anions of Group V elements are also discussed. © 1998 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.60.+q Photoelectron spectra
32.80.Fb Photoionization of atoms and ions
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
32.50.+d Fluorescence, phosphorescence (including quenching)
33.80.Eh Autoionization, photoionization, and photodetachment
32.80.Gc Photodetachment of atomic negative ions

Quantum mechanical study of the CH(v = 2) overtone in 30-mode benzene

Robert E. Wyatt

J. Chem. Phys. 109, 10732 (1998); http://dx.doi.org/10.1063/1.477772 (8 pages) | Cited 14 times

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The results of large-scale quantum mechanical calculations of the CH(v = 2) 1st overtone spectrum for 30-mode benzene are reported. This overtone was chosen for investigation because of its high degree of fragmentation and resulting complexity compared to spectra for the fundamental and higher overtones. These calculations use the best available ab initio force field supplemented by higher-order terms for the CH stretch–wag interaction. The dynamical calculations were conducted in large active spaces with 12 000 or 16 000 vibrational basis functions. The recursive residue generation method was used to compute residues (intensities) and eigenvalues. From these quantities, the lineshape function, survival probabilities, and vibrograms were computed. Wherever possible, these results were compared to experimental overtone spectra and to other computational results. © 1998 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
33.70.Jg Line and band widths, shapes, and shifts
33.70.Fd Absolute and relative line and band intensities

Ultrafast multiphoton ionization dynamics and control of NaK molecules

Jan Davidsson, Tony Hansson, and Emad Mukhtar

J. Chem. Phys. 109, 10740 (1998); http://dx.doi.org/10.1063/1.477773 (14 pages) | Cited 11 times

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The multiphoton ionization dynamics of NaK molecules is investigated experimentally using one-color pump–probe femtosecond spectroscopy at 795 nm and intermediate laser field strengths (about 10 GW/cm2). Both NaK+ and Na+ ions are detected as a function of pulse separation time, pulse intensities, and strong pulse–weak pulse order. To aid in the analysis, the potential energy curves of the two lowest electronic states of NaK+ and the electronic transition dipole moment between them are calculated by the GAUSSIAN94 UCIS method. Different ionization pathways are identified by Franck-Condon analysis, and vibrational dynamics in the A 1Σ+ and 3 1Π states, as well as in the ground state, is observed. Further, the existence of a highly excited (above the adiabatic ionization limit) neutral state of NaK is proposed. By changing the strong pulse–weak pulse order of the pulses, the ionization pathways for production of both ions can be varied and thus controlled. © 1998 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Wz Other multiphoton processes
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Zero electron kinetic energy and photoelectron spectroscopy of the XeI− anion

Thomas Lenzer, Michael R. Furlanetto, Knut R. Asmis, and Daniel M. Neumark

J. Chem. Phys. 109, 10754 (1998); http://dx.doi.org/10.1063/1.477774 (13 pages) | Cited 28 times

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The XeI− anion and the corresponding neutral X1/2, I3/2, and II1/2 electronic states have been studied by means of zero electron kinetic energy (ZEKE) and photoelectron spectroscopy. The ZEKE spectra show rich and well-resolved progressions in the low-frequency vibrations of the anion and the neutral van der Waals complexes. From our spectroscopic data we construct model potentials for the anion and three neutral states, which are compared to previously obtained potential functions for this system. The intensity of the I3/2←anion transitions relative to the X1/2←anion transitions in the XeI− ZEKE spectrum is considerably lower than expected from a Franck-Condon simulation based on the model potentials. Comparison with the photoelectron spectrum of XeI− indicates this is due to a small s-wave partial cross section for photodetachment to the I3/2 state. © 1998 American Institute of Physics.
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34.80.-i Electron and positron scattering
33.60.+q Photoelectron spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Fd Absolute and relative line and band intensities

Coupling of a Jahn–Teller pseudorotation with a hindered internal rotation in an isolated molecule: 9-hydroxytriptycene

Alan Furlan, Samuel Leutwyler, and Mark J. Riley

J. Chem. Phys. 109, 10767 (1998); http://dx.doi.org/10.1063/1.477775 (14 pages) | Cited 2 times

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The irregular vibronic structure in the S1←S0 resonant two-photon ionization (R2PI) spectrum of supersonically cooled triptycene is a result of a classic E⊗e Jahn–Teller effect [A. Furlan et al., J. Chem. Phys. 96, 7306 (1992)]. This is well characterized and can be used as an effective probe of intramolecular perturbations. Here we examine the S1←S0 R2PI spectrum of 9-hydroxytriptycene and the fluorescence from various excited state vibronic levels. In this system the pseudorotation of the Jahn–Teller vibration is strongly coupled to the torsional motion of the bridgehead hydroxy group. This torsional motion results in a tunneling splitting in both the ground and excited states. The population of the upper level in the ground electronic state results in additional vibronic transitions becoming symmetry allowed in the R2PI spectrum that are forbidden in the bare triptycene molecule. The assignment of the R2PI and fluorescence spectra allows the potential energy surfaces of these vibrational modes to be accurately quantified. The full C3v vibronic point group must be used to interpret the spectra. The time scale of the internal rotation of the–OH group and the butterfly flapping of the Jahn–Teller pseudorotation are of similar magnitude. The tunneling between the nine minima on the three dimensional potential energy surface is such that the Jahn–Teller pseudorotation occurs in concert with the–OH internal rotation. The Berry phase that is acquired during this motion is discussed. The simple physical picture emerges of the angle between two of the three benzene moieties opening in three equivalent ways in the S1 electronic state. This geometry follows the position of the hydroxy group, which preferentially orients itself to point between these two rings. © 1998 American Institute of Physics.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.30.-i Corrections to electronic structure
33.80.Wz Other multiphoton processes
33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.50.Dq Fluorescence and phosphorescence spectra
31.50.Df Potential energy surfaces for excited electronic states
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
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