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22 Jun 1999

Volume 110, Issue 24, pp. 11679-12266

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The Gaussian-2 method with proper dissociation, improved accuracy, and less cost

Patton L. Fast, María Luz Sánchez, José C. Corchado, and Donald G. Truhlar

J. Chem. Phys. 110, 11679 (1999); http://dx.doi.org/10.1063/1.479112 (3 pages) | Cited 22 times

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The Gaussian-2 method (G2) is modified by deleting the empirical high-level correction and instead using empirical coefficients to extrapolate to full configuration interaction and an infinite basis set. The resulting method, called multicoefficient Gaussian-2 (MCG2) is less expensive than G2 but a factor of 1.7 more accurate for molecules composed of H and first-row atoms. © 1999 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Landau level of gaseous nitric oxide studied by two-color multiphoton ionization spectroscopy

Ken Takazawa and Haruo Abe

J. Chem. Phys. 110, 11682 (1999); http://dx.doi.org/10.1063/1.479113 (3 pages) | Cited 6 times

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Two-color multiphoton ionization spectra of gaseous nitric oxide via a single Zeeman sublevel in the A 2Σ+ (v = 1) state were measured in magnetic fields up to 10 T. The Zeeman effect on high-lying Rydberg states (n ≥ 28) and Landau levels above an ionization potential corresponding to the v = 1 vibrational level of cation were observed. Landau level spacing gradually decreased with increasing energy, reflecting the transition from the quasi-Landau level to the Landau level. The broadness of the band due to the transition to the Landau level is discussed based on ionization mechanism. © 1999 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.57.+c Magneto-optical and electro-optical spectra and effects
31.50.Df Potential energy surfaces for excited electronic states
33.80.Wz Other multiphoton processes

On the ground electronic state of MoO+: Upgrade density functional theory calculations

Ewa Broclawik, Witold Piskorz, and Katarzyna Adamska

J. Chem. Phys. 110, 11685 (1999); http://dx.doi.org/10.1063/1.479114 (3 pages)

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Density functional theory calculations for MoO+ with the new BPW91 exchange-correlation functional are reported and compared to recent experimental results regarding electronic states and bonding in the cation. In variance to the local and previous versions of nonlocal functionals, BPW91 gives proper description of the ground state of MoO+ and ionization potentials of MoO in very good agreement with the experiment. © 1999 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
02.30.Nw Fourier analysis
02.30.Uu Integral transforms
02.30.Vv Operational calculus
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The K-rotational labeling problem for eigenvectors from internal rotor calculations: Application to energy levels of acetaldehyde below the barrier

Juan Ortigoso, Isabelle Kleiner, and Jon T. Hougen

J. Chem. Phys. 110, 11688 (1999); http://dx.doi.org/10.1063/1.479115 (12 pages) | Cited 7 times

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The problem of attaching K rotational quantum number labels to computer-generated numerical eigenvectors with extensive basis set mixing is considered for the internal-rotationoverall-rotation problem in molecules with one methyl top. Quantum number labeling problems arise physically because the torsional and the rotational degrees of freedom both pass from one limiting case to another as the torsional energy moves from below the top of the internal rotation barrier to above it, i.e., the torsional degree of freedom changes from a vibration to an internal rotation, while the rotational degree of freedom moves its direction of quantization from a principal axis to an axis depending also on angular momentum generated by the methyl top rotation. Since the choice of axis system, basis set, and computational scheme all influence the eigenfunction labeling procedure, consideration is limited to a commonly used two-step matrix-diagonalization scheme and to acetaldehyde as a numerical example. Torsional labels vt = 0, 1, and 2 for eigenfunctions generated in the first diagonalization step are assigned in order of increasing eigenvalues, and rotational energy surfaces are constructed for the A and E symmetry components of these three torsional states. Projections of rotational eigenvectors over angular momentum coherent states are used to show that classical trajectories on the appropriate rotational energy surface give faithful representations of the quantum wave functions. Irregularities in the rotational energy level structure within a given torsional state can then be understood in terms of extra separatrices in the classical phase space and unusual wave function densities in the coherent state projections. Results are used to devise an automatic K labeling scheme for numerically obtained torsion-rotation levels belonging to torsional states below the top of the internal rotation barrier. © 1999 American Institute of Physics.  
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33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Quantum Monte Carlo study of the dipole moment of CO

F. Schautz and H.-J. Flad

J. Chem. Phys. 110, 11700 (1999); http://dx.doi.org/10.1063/1.479170 (8 pages) | Cited 18 times

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We have calculated the dipole moment of CO along the potential energy curve using the pure diffusion quantum Monte Carlo method. Good agreement with coupled cluster singles–doubles calculations has been obtained throughout. An accurate treatment at the equilibrium distance requires a multi-reference trial wave function for which we obtained a dipole moment in accordance with experiment. We discuss the Hellmann–Feynman theorem within the fixed-node approximation in the case of field-dependent smoothly varying nodes. It is shown that the Hellmann–Feynman theorem is applicable to this case due to vanishing boundary contributions. A comparison has been made between the finite field correlated sampling approach and a direct calculation of the expectation value for the dipole moment operator. In the present application both methods perform equally well. © 1999 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Perturbatively selected CI as an optimal source for externally corrected CCSD

G. Peris, J. Planelles, J.-P. Malrieu, and J. Paldus

J. Chem. Phys. 110, 11708 (1999); http://dx.doi.org/10.1063/1.479116 (9 pages) | Cited 13 times

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Perturbatively selected configuration interaction (PSCI) is used as a source of higher than pair clusters in the externally corrected coupled cluster method with singles and doubles (ecCCSD). This significantly decreases the dimension of the standard multireference (MR) CISD that is employed by the so-called reduced MR (RMR) CCSD method, thus enabling the use of relatively large active spaces. The performance of the proposed PSCI CCSD method is illustrated by considering the ground state potential energy curves of the HF molecule using DZP and cc-pVTZ basis sets (breaking of a single bond), and of the N2 molecule using a TZ basis set (breaking of a triple bond). It is shown that notwithstanding a large reduction in the dimension of the external source, the accuracy of the resulting ecCCSD energies is almost the same as that obtained when correcting with the full MR CISD wave function. © 1999 American Institute of Physics.
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31.15.vn Electron correlation calculations for diatomic molecules
31.15.bw Coupled-cluster theory
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.Fm Bond strengths, dissociation energies

Critical conditions for stable dipole-bound dianions

Cecilia Sarasola, Joseph E. Fowler, and Jesus M. Ugalde

J. Chem. Phys. 110, 11717 (1999); http://dx.doi.org/10.1063/1.479117 (3 pages) | Cited 11 times

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Full configuration interaction calculations for two electrons moving in the field of an electric dipole have been carried out in order to determine whether bound states with respect to detachment of one electron exist. Model dipoles are constructed by the placement of point charges q = 1, 2, 3 a.u. at varying distances. It was found that for a dipole constructed of point charges q = 3 separated by a distance of 0.8788 a.u., the energy of binding one and two electrons is equivalent. In all cases, there exist charge separation lengths for which the binding of two electrons gives a binding energy only slightly less than that of binding one electron. Escape channels were not calculated, but may provide barriers allowing the existence of dipole-bound dianions with lifetimes long enough to allow detection. © 1999 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Calculation of frequency-dependent first hyperpolarizabilities using the second-order Møller–Plesset perturbation theory

Takao Kobayashi, Kotoku Sasagane, Fumihiko Aiga, and Kizashi Yamaguchi

J. Chem. Phys. 110, 11720 (1999); http://dx.doi.org/10.1063/1.479171 (14 pages) | Cited 9 times

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We perform the first calculations of frequency-dependent first hyperpolarizabilities in the second-order Møller–Plesset perturbation theory (MP2) as analytical third derivatives of the time-averaged MP2 quasienergy with respect to electric field strengths. The calculations of frequency-dependent first hyperpolarizabilities using the quasienergy derivative (QED) method-based MP2 (QED-MP2) response theory are presented for the electro-optic Pockels effect (EOPE) [β(−ω;ω,0)] and second harmonic generation (SHG) [β(−2ω;ω,ω)] of the FH, H2O, CO, and NH3 molecules. The QED-MP2 values of the SHG first hyperpolarizabilities β∥(−2ω;ω,ω) for the H2O, CO, and NH3 molecules show good agreement with the experimental values. The QED-MP2 response theory is the simplest in ab initio methods for including dynamical electron correlation effects in dynamic response properties efficiently. © 1999 American Institute of Physics.
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31.15.xp Perturbation theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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An ab initio potential energy surface for Ne–CO

George C. McBane and Slawomir M. Cybulski

J. Chem. Phys. 110, 11734 (1999); http://dx.doi.org/10.1063/1.479118 (8 pages) | Cited 37 times

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A new ab initio two-dimensional potential energy surface for the Ne–CO interaction is described. The surface was obtained by the supermolecule method at the CCSD(T) level of theory. It is compared with several experimental data sets and with the symmetry-adapted perturbation theory (SAPT) surface of Moszynski et al. [J. Phys. Chem. A 101, 4690 (1997)]. The new surface gives modestly better predictions of experimental results that depend on close approach of Ne to CO, but does not describe the ground state geometry as well as the SAPT surface. © 1999 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.xp Perturbation theory
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
34.50.-s Scattering of atoms and molecules
31.15.bw Coupled-cluster theory

State to state Ne–CO rotationally inelastic scattering

Stiliana Antonova, Ao Lin, Antonis P. Tsakotellis, and George C. McBane

J. Chem. Phys. 110, 11742 (1999); http://dx.doi.org/10.1063/1.479119 (7 pages) | Cited 8 times

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Measurements of state-to-state integral cross sections for rotational excitation of CO by collisions with Ne are reported. The measurements were performed in crossed molecular beams with resonance enhanced multiphoton detection at collision energies of 711 and 797 cm−1. The cross sections display strong interference structure, with a propensity for odd Δj below Δj = 10. Predictions of the ab initio potential surface of Moszynski et al. [J. Phys. Chem. A 101, 4690 (1997)] and the new ab initio surface of McBane and Cybulski [J. Chem. Phys. 110, 11734 (1999), preceding paper] are compared to the data. The new surface agrees more closely with the observed interference structure, although significant disagreements remain. © 1999 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
37.20.+j Atomic and molecular beam sources and techniques
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.A- Ab initio calculations
32.80.Wr Other multiphoton processes
33.80.Wz Other multiphoton processes

Uniform semiclassical calculation of the direct part of the photodissociation cross section of water

Bruno Hüpper and Bruno Eckhardt

J. Chem. Phys. 110, 11749 (1999); http://dx.doi.org/10.1063/1.479172 (7 pages) | Cited 4 times

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The photodissociation cross section of water in the first absorption band naturally splits into two parts, a rather dominant and broad background, and a series of isolated resonances. We focus here on the semiclassical calculation of the background term. We compare various semiclassical methods of calculation, including the reflection approximation, the Wigner–Weyl series, Airy function approximations, and higher-order approximations in the time domain, and find that only the latter gives quantitative agreement. They are numerically efficient as they can be reduced to a 2-D spatial integration together with a Fourier transform. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
02.30.Nw Fourier analysis

Vibration-rotation emission spectra and combined isotopomer analyses for the coinage metal hydrides: CuH & CuD, AgH & AgD, and AuH & AuD

Jenning Y. Seto, Zulfikar Morbi, Frank Charron, Sang K. Lee, Peter F. Bernath, and Robert J. Le Roy

J. Chem. Phys. 110, 11756 (1999); http://dx.doi.org/10.1063/1.479120 (12 pages) | Cited 28 times

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High resolution infrared emission spectra have been measured for AuH and AuD and for two isotopomers of each of CuH, CuD, AgH, and AgD. The molecules were made in a carbon tube furnace (King furnace), and in spite of intense background thermal emission from the furnace (at >2000 °C), vibration–rotation emission data could be recorded. Together with high resolution measurements taken from the literature, the data for each species were treated using two types of combined-isotopomer analysis: One based on fits to empirical molecular parameters, and the other based on direct fits to the underlying potential energy functions, both of which take account of mass-dependent Born–Oppenheimer breakdown correction terms. Accurate isotopically related Dunham parameters and Born–Oppenheimer breakdown parameters are obtained for each species, as well as accurate analytic potential functions and adiabatic and nonadiabatic radial correction functions. © 1999 American Institute of Physics.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Quantum molecular dynamics calculations and experimental Raman spectra confirm the proposed structure of the odd-numbered dimeric fullerene C119

Sergei Lebedkin, Hermann Rietschel, Gary B. Adams, John B. Page, William E. Hull, Frank H. Hennrich, Hans-Jürgen Eisler, Manfred M. Kappes, and Wolfgang Krätschmer

J. Chem. Phys. 110, 11768 (1999); http://dx.doi.org/10.1063/1.479121 (11 pages) | Cited 9 times

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A first-principles quantum molecular dynamics (QMD) method and a bond polarizability model, whose parameters were optimized on the basis of C60 data, have been used to calculate theoretical Raman spectra for four possible low-energy isomers of the odd-numbered dimeric fullerene C119 produced by thermolysis of C60 oxides. Comparison of the calculated and experimentally determined spectra provides strong evidence that the structure obtained by thermolysis is indeed the thermodynamically most stable isomer with C2 symmetry, as proposed earlier on the basis of semiempirical molecular modeling and 13C-NMR spectroscopy. This isomer has the structure originally predicted for C119 on the basis of QMD simulations. © 1999 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.xv Molecular dynamics and other numerical methods

Orientation of pyrimidine in the gas phase using a strong electric field: Spectroscopy and relaxation dynamics

Karen J. Franks, Hongzhi Li, and Wei Kong

J. Chem. Phys. 110, 11779 (1999); http://dx.doi.org/10.1063/1.479169 (10 pages) | Cited 15 times

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Orientation of pyrimidine in a strong electric field was measured using resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF). The ion and fluorescence yields showed preference for perpendicular excitation relative to the orientation field, implying a perpendicular relationship between the permanent dipole and the transition dipole. Calculation results using a linear variation method reproduced the observed spectral features, overall transition intensity, and polarization preference of the excitation laser. The permanent dipole of the S1 state of pyrimidine was thereby determined to be +0.6 Debye. Measurements of polarization preferences in photoexcitation, i.e., linear dichroism, provide a direct approach for determination of transition dipole moments. A general theory of deriving directions of transition dipoles relative to permanent dipoles based on this type of measurement/calculation was also developed. In addition, we report observations of complex relaxation dynamics of pyrimidine in an electric field. At 50 kV/cm, the overall fluorescence yield was quenched to a quarter of its value under field free conditions. The spectral intensity distribution exhibited dependence on the delay time of the ionization laser in the REMPI experiment. Qualitative assignments of the REMPI spectra revealed that the loss of signal strength with delay time was primarily from levels containing high rotational angular momenta. Elimination of contributions from levels with M′ ≥ 3 in the calculation was sufficient to reproduce experimental spectra recorded with a delay time of 200 ns. These observations and interpretations agree with previous reports on photophysical properties of pyrimidine, including relaxation and quenching in a magnetic field. © 1999 American Institute of Physics.
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33.80.Wz Other multiphoton processes
33.80.Eh Autoionization, photoionization, and photodetachment
33.50.Dq Fluorescence and phosphorescence spectra
31.70.Dk Environmental and solvent effects

The photodissociation dynamics of CFBr excited into the (1A″) state

Pamela T. Knepp and Scott H. Kable

J. Chem. Phys. 110, 11789 (1999); http://dx.doi.org/10.1063/1.479122 (9 pages) | Cited 12 times

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The dynamics of the photolysis reaction, CFBr+hν→CF+Br, have been investigated for photolysis energies in the range, math = 23 500–26 000 cm−1 (λ=385–435 nm). These energies correspond to excitation into the (1A″) state of CFBr with 2500–5000 cm−1 of excess vibrational energy. Following dissociation of jet-cooled CFBr, the internal energy (Ω, Λ, J) of the nascent CF fragments (X 2Π, υ = 0) was probed by laser induced fluorescence spectroscopy. Two distinct types of product state distributions were observed. At energies above T00+3360 cm−1 the populations of the 2Π1/2 and 2Π3/2 spin–orbit states of CF were equal, while A″ lambda doublet states were preferred over A′. These populations are consistent with a direct dissociation mechanism on the state, over a barrier with a height of 3360 cm−1. The strong state mixing in the vicinity of the barrier ensures a statistical mixture of final spin–orbit states. The preference for the A″ lambda doublet states is consistent with the two lone electrons in in-plane orbitals pairing up in the final CF product, leaving one unpaired electron in an out-of-plane orbital, lying parallel to the J vector of the recoiling fragment. For excitation at energies below T00+3360 cm−1 the ground spin–orbit state of CF (2Π1/2) is preferred, while the lambda doublet populations are equal. The interpretation of these populations is that at these energies state CFBr is stable with respect to dissociation over the barrier. The molecule crosses to either the math or state where it encounters a deep attractive potential well. The subsequent slower dissociation rate allows the molecule to follow a more adiabatic pathway producing the lowest spin–orbit state of CF, and for any preference for lambda doublet states to be lost. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.-b Photon interactions with molecules

Photofragmentation spectroscopy of Al+(C2H4)

J. Chen, T.-H. Wong, P. D. Kleiber, and K.-H. Yang

J. Chem. Phys. 110, 11798 (1999); http://dx.doi.org/10.1063/1.479123 (8 pages) | Cited 17 times

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We have studied the structure and dissociation dynamics of the weakly bound bimolecular complex Al+(C2H4) by photodissociation spectroscopy in the 216–320 nm spectral region. Experimental studies are supported by ab initio electronic structure calculations of the ground and low-lying excited states of the complex. Al+ is the dominant photofragment observed throughout the absorption profile. C2H4+ charge transfer product is also observed for shorter photolysis wavelengths, λ<252 nm. The Al+–C2H4 bond dissociation energy is measured as D0 = 0.37±0.15 eV. Three molecular absorption bands are observed and assigned to the transitions (2 1A1,1 1B1,1 1B2←1 1A1) in C2v equilibrium complex geometry. The excited states are of predominantly charge-transfer character correlating with the product channel Al(3s23p)+(C2H4)+. The 2 1A1 and 1 1B2←1 1A1 absorption bands appear broad and structureless. This observation is consistent with ab initio results that suggest a pathway for rapid nonadiabatic dissociation through a 1 1B2–1 1A1 surface crossing facilitated by a stretch in the C–C bond of ethylene. In contrast the 1 1B1←1 1A1 molecular band shows significant vibrational structure. Spectroscopic analysis yields a band origin (000 = 40 042 cm−1) and corresponding vibrational mode frequencies for the 1 1B1 excited state. The observed modes have been assigned to the intermolecular Al–C2H4 stretch of a1 symmetry (ν2 = 230 cm−1), the Al–C2H4 out-of-plane wag with b1-symmetry (ν3 = 328 cm−1), and two intramolecular ethylene modes of a1 symmetry at 1264 and 1521 cm−1. The assignment for these higher frequency ethylene modes is not conclusive. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies

Basis set superposition error-counterpoise corrected potential energy surfaces. Application to hydrogen peroxide⋯X (X=F−, Cl−, Br−, Li+, Na+) complexes

Martha C. Daza, J. A. Dobado, José Molina Molina, Pedro Salvador, Miquel Duran, and José Luis Villaveces

J. Chem. Phys. 110, 11806 (1999); http://dx.doi.org/10.1063/1.479166 (8 pages) | Cited 18 times

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Møller–Plesset (MP2) and Becke-3-Lee-Yang-Parr (B3LYP) calculations have been used to compare the geometrical parameters, hydrogen-bonding properties, vibrational frequencies and relative energies for several X− and X+ hydrogen peroxide complexes. The geometries and interaction energies were corrected for the basis set superposition error (BSSE) in all the complexes (1–5), using the full counterpoise method, yielding small BSSE values for the 6-311+G(3df,2p) basis set used. The interaction energies calculated ranged from medium to strong hydrogen-bonding systems (1–3) and strong electrostatic interactions (4 and 5). The molecular interactions have been characterized using the atoms in molecules theory (AIM), and by the analysis of the vibrational frequencies. The minima on the BSSE-counterpoise corrected potential-energy surface (PES) have been determined as described by S. Simón, M. Duran, and J. J. Dannenberg, and the results were compared with the uncorrected PES. © 1999 American Institute of Physics.
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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
33.15.Bh General molecular conformation and symmetry; stereochemistry

Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogen

Toni Kiljunen, Jussi Eloranta, and Henrik Kunttu

J. Chem. Phys. 110, 11814 (1999); http://dx.doi.org/10.1063/1.479173 (9 pages) | Cited 20 times

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Ground-state potential-energy curves and distance dependent isotropic hyperfine coupling (IHC) constants for ground-state H–RG (=Ne, Ar, Kr, Xe) are obtained at CCSD(T) (coupled-cluster single double triple) and MP4(SDQ) (fourth-order Moller–Plesset single double quadruple) levels, respectively, with an augmented basis set aug-Stuttgart (RG)/aug-cc-pVQZ (H). The obtained Rm and ϵ are for NeH: 3.45 Å and −1.36 meV; ArH: 3.65 Å and −3.48 meV; KrH: 3.75 Å and −4.32 meV; XeH: 3.90 Å and −5.22 meV. The computed pair potentials are utilized in classical molecular-dynamics simulations of H–RG lattices. Along the classical trajectory, the many-body perturbation on the H atom hyperfine coupling constant is computed by pair-wise addition of the individual RG–H contributions obtained from the present quantum-chemical calculations. The computed IHC shifts are compared with electron paramagnetic resonance (EPR) spectra obtained in low-temperature matrix isolation experiments. For most cases this theoretical treatment agrees very well with the experiment and confirms the previous site assignments. However, for H–Xe, the theory would suggest stability of both interstitial Oh and substitutional sites, whereas only one site is observed in the experiment. Based on the present calculations this site can be assigned as a nearly undistorted substitutional site. © 1999 American Institute of Physics.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Pw Fine and hyperfine structure
31.15.A- Ab initio calculations
31.15.xv Molecular dynamics and other numerical methods
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
31.15.bw Coupled-cluster theory
33.35.+r Electron resonance and relaxation
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Chlorine atom formation dynamics in the dissociation of CH3CF2Cl(HCFC-142b) after UV laser photoexcitation

Richard A. Brownsword, Patricia Schmiechen, Hans-Robert Volpp, Hari P. Upadhyaya, Young Jae Jung, and Kyung-Hoon Jung

J. Chem. Phys. 110, 11823 (1999); http://dx.doi.org/10.1063/1.479124 (7 pages) | Cited 8 times

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The dynamics of chlorine atom formation after UV photoexcitation of CH3CF2Cl(HCFC-142b) in the gas phase was studied by a pulsed laser photolysis/laser-induced fluorescence (LIF) “pump-and-probe” technique at room temperature. The parent molecule was excited at the ArF excimer laser wavelength (193.3 nm) and nascent ground state Cl(2P3/2) and spin-orbit excited Cl∗(2P1/2) photofragments were detected under collision-free conditions via laser induced fluorescence in the vacuum ultraviolet spectral region. Narrow-band probe laser radiation, tunable over the wavelength range 133.5–136.4 nm, was generated via resonant third-order sum-difference frequency conversion of dye laser radiation in Krypton. Using HCl photolysis at 193.3 nm as a source of well-defined Cl(2P3/2) and Cl∗(2P1/2) concentrations, values for the total Cl atom quantum yield (ΦCl+Cl∗ = 0.90±0.17) and the [Cl∗]/[Cl] branching ratio 0.39±0.11 were determined by means of a photolytic calibration method. From the measured Cl and Cl∗ atom Doppler profiles the average relative translational energy of the fragments could be determined to be 125±25 kJ/mol. The corresponding value fT = 0.48±0.10 of the fraction of total available energy channeled into product translational energy was found to be (within experimental uncertainty) in agreement with the result fT = 0.39 of a dynamical simulation assuming a repulsive model for single C–Cl bond cleavage. Both the measured total Cl atom quantum yield and the energy disposal indicates that direct C–Cl bond cleavage is a primary fragmentation mechanism for CH3CF2Cl after photoexcitation at 193.3 nm. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.20.-w Chemical kinetics and dynamics

Radiative lifetime measurement of the a 3Σ+ metastable state of NO+ using a new type of electrostatic ion trap

R. Wester, K. G. Bhushan, N. Altstein, D. Zajfman, O. Heber, and M. L. Rappaport

J. Chem. Phys. 110, 11830 (1999); http://dx.doi.org/10.1063/1.479168 (5 pages) | Cited 9 times

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A new type of ion trap is used to measure the radiative lifetime of the NO+(a 3Σ+) metastable state. The ion trap is designed to store ion beams with an energy of a few keV and is well suited for the study of metastable states. The measured value for the radiative lifetime is τr = 760±30 ms, in good agreement with the last experimental values of Calamai and Yoshino [J. Chem. Phys. 101, 9480 (1994)], and with the theoretical value of Kuo et al. [J. Chem. Phys. 92, 4849 (1990)]. © 1999 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
37.20.+j Atomic and molecular beam sources and techniques
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Quartet and sextet states of CS−

M. Hochlaf, G. Chambaud, P. Rosmus, T. Andersen, and H. J. Werner

J. Chem. Phys. 110, 11835 (1999); http://dx.doi.org/10.1063/1.479125 (6 pages) | Cited 18 times

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The potential energy and spin–orbit functions have been calculated for several electronic states of CS and CS−. Comparison with experimental data for CS shows very good agreement, making reliable predictions possible for the CS− molecule such as the existence of long-lived metastable states. The a 4Σ−, b 4Π, and a 6Π states were found to lie energetically below the triplet or quintet states of the CS molecule. The calculated spin–orbit integrals between the electronic states suggest that the depletion of the J = 5/2 or 7/2 components in the Π states will mainly occur via weak interactions with the electron continuum wave. © 1999 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Vibrational levels and statistical analysis of the X(1Σg+) ground state of CS2

G. Brasen and W. Demtröder

J. Chem. Phys. 110, 11841 (1999); http://dx.doi.org/10.1063/1.479174 (9 pages) | Cited 8 times

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Single rovibronic levels in the perturbed 1B2(1Δu) state of CS2 molecules in a cold molecular beam were excited by ultraviolet (UV) photons from a frequency doubled single mode continuous wave (cw) dye laser. The dispersed fluorescence spectrum, detected by a liquid nitrogen (LN) cooled charge coupled device (CCD) array behind a monochromator allowed the determination of vibrational term values in the X(1Σg+) state from the (0,00,0)level up to 20 000 cm−1. Based on calculations including Fermi resonances, most of the measured vibrational bands could be assigned to several vibronic ground state level progressions. A statistical analysis of the positions of all measured levels shows for the nearest neighbor distances and the Δ3 statistics a pure Poissonian distribution. This indicates that no strong correlation between neighboring vibrational levels nor long range interactions are present and therefore no chaotic behavior could be found in contrast to the cases of NO2 and SO2. © 1999 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Tp Vibrational analysis
02.50.-r Probability theory, stochastic processes, and statistics

Photodissociation dynamics of acetylacetone: The OH product state distribution

Min-Chul Yoon, Young S. Choi, and Sang Kyu Kim

J. Chem. Phys. 110, 11850 (1999); http://dx.doi.org/10.1063/1.479126 (6 pages) | Cited 14 times

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Acetylacetone in the supersonic jet, which exists predominantly as an enolic form, is found to give rise to the OH fragment after the π–π∗ transition induced by the UV absorption. The nascent OH product state distributions are determined using a laser-induced fluorescence technique at the excitation wavelengths of 291 and 266 nm. The OH fragment is vibrationally cold, and its rotational state distribution is peaked at N = 3 or 4 at the pump wavelength of 291 or 266 nm, respectively. No fluorescence from the excited acetylacetone has been observed even in the energy region near the origin, suggesting the ultrafast nonradiative processes of the excited state. From the measured OH product state distributions, the upper bound for the dissociation energy of the acetylacetone is estimated to be 90.3 kcal/mol. The ratios of Λ-doublets and spin–orbit states of the OH fragment are also measured. A slight preference of the OH fragment in the 2Π3/2 state over the 2Π1/2 state is observed. The Π−/Π+ ratios, determined by the relative intensity ratios of Q and P (or R) lines, are found to be less than unity, suggesting the preferential cleavage of the C–OH bond on the molecular plane probably due to a relatively strong intramolecular hydrogen bonding of the enolic acetylacetone. The prior calculation reproduces the experiment quite well for the OH rotational state distribution at 291 nm, while it does not for that at 266 nm. This suggests that the transition state in the acetylacetone dissociation, at the low energy near threshold, may be completely loosely defined on the potential energy surface which does not have a barrier to recombination, and it becomes tightened as the energy increases above the reaction threshold. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.20.Hf Product distribution
33.15.Fm Bond strengths, dissociation energies
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions

Scratching the surface of the water dication

Timothy J. Van Huis, Steven S. Wesolowski, Yukio Yamaguchi, and Henry F. Schaefer

J. Chem. Phys. 110, 11856 (1999); http://dx.doi.org/10.1063/1.479127 (9 pages) | Cited 11 times

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The math 3Σg−,  1Δg, and math 1Σg+ states of the water dication, H2O2+, have been investigated using several high-level ab initio methods and a range of basis sets. With Dunning’s augmented correlation consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set at the complete active space self-consistent field second-order configuration interaction (CAS-SOCI) level, it is confirmed that the ground and first two excited states of H2O2+ are all of D∞h symmetry, in violation of Walsh’s rules for 6 valence electron AH2 systems. The singlet–triplet splitting (math 3Σg− 1Δg) is predicted to be 53.6 kcal/mol (2.32 eV, 18 700 cm−1), while the math 3Σg−math 1Σg+ separation is predicted to be 91.1 kcal/mol (3.95 eV, 31 900 cm−1). The vertical double ionization potentials (IPs) from math 1A1 H2O to the math 3B1, 1 1A1, math 1B1, and 2 1A1 states of H2O2+ are predicted within the cc-pVQZ basis to be 40.1, 41.2, 42.6, and 46.1 eV, respectively, in good agreement with recent double-charge-transfer spectroscopic results. The corresponding adiabatic double IPs are 37.0, 39.3, and 41.0 eV to the math 3Σg−,  1Δg, and math 1Σg+ states of H2O2+, respectively. The activation barrier to fragmentation of H2O2+ (math 3Σg− H2O2+→3Σ− OH++H+) at the cc-pVQZ CAS-SOCI level is predicted to be 2.1 kcal/mol (0.10 eV, 738 cm−1), and the reaction is exothermic by 126.4 kcal/mol (5.48 eV, 44 210 cm−1), providing a challenge for direct experimental detection of this elusive molecule. © 1999 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
31.15.vq Electron correlation calculations for polyatomic molecules
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

The rotational spectrum of chloryl chloride, ClClO2, in its ground vibrational state

Holger S. P. Müller, Edward A. Cohen, and Dines Christen

J. Chem. Phys. 110, 11865 (1999); http://dx.doi.org/10.1063/1.479179 (11 pages) | Cited 6 times

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Rotational spectra of the four main isotopomers of ClClO2 which together span the quantum numbers 10 ⩽ J ⩽ 77 and 0 ⩽ Ka ⩽ 34 have been studied in selected regions between 10 and 417 GHz. The in situ syntheses using reactions between FClO2 and either HCl or BCl3 are described. Rotational and centrifugal distortion constants have been derived and used for structure and harmonic force field calculations. The quadrupole coupling constants for both Cl nuclei have been determined and the molecular dipole moment has been derived from low field Stark effect measurements in the submillimeter region. The results are discussed in relationship to published results from a matrix-isolation study, from theoretical calculations, and from studies of related molecules. © 1999 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.25.+k Nuclear resonance and relaxation
33.57.+c Magneto-optical and electro-optical spectra and effects
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
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