2,032 research outputs found

### Resonances in electron-impact electron detachment of C-2(-)

Molecular R-matrix with pseudostate calculations are reported for the electron-impact ionization cross section of the carbon dimer anion. A (1)Sigma(+)(g) g resonance is found near the detachment threshold and two further resonances, of (3)Pi(g) and (1)Pi(g) symmetry, are found near 10 eV close to the structures observed experimentally. These unusual shape resonances are a result of the competition between the repulsive Coulomb interaction and the large, attractive polarizability of C-2(-). Use of the Born approximation to allow for higher partial waves gives a total cross section close to that observed experimentally

### Electron-impact rotational excitation of symetric-top molecular ions

We present electron-impact rotational excitation calculations for polyatomic molecular ions. The theory developed in this paper is an extension of the work of RabadÃ¡n et al (RabadÃ¡n I, Sarpal B K and Tennyson J 1998 J. Phys. B: At. Mol. Opt. Phys. 31 2077) on linear molecular ions to the case of symmetric-top species. The H3+ and H3O+ ions, as well as their deuterated forms D3+ and D3O+, are used as test cases and cross sections are obtained at various levels of approximation for impact energies up to 5 eV. As in the linear case, the widely used Coulombâ€“Born (CB) approximation is found to be unreliable in two major aspects: transitions with Î”J > 1 are entirely dominated by short-range interactions and threshold effects are important at very low energies. Electron collisional selection rules are found to be consistent with the CB theory. In particular, dominant transitions are those for which Î”J â‰¤ 2 and Î”K = 0

### Continuum states of CO+

Continuum states of the CO+ cation are studied as a function of internuclear distances in the range 1.7-3.0 a(0). R-matrix wavefunctions are constructed for 1Sigma(+), (2)Pi, (2)Delta and 4Pi total symmetries by study of collisions of electrons with a CO2+ target. Complex quantum defects are obtained from above threshold energy scattering calculations, yielding resonance energy curves and corresponding electronic couplings to the CO+ continuum. Results are presented and discussed for the high-n Feshbach resonances of the CO+ spectrum converging to excited states of CO2+. These curves are responsible for the recently observed dissociative recombination of Co2+

### Asymptotic vibrational states of the H-3(+) molecular ion

Vibrational calculations for H-3(+) are performed using an accurate global ab initio potential energy surface. Fourteen bound states close to dissociation are found to have interesting long-range dynamics. These asymptotic vibrational states (AVS) are studied graphically by cuts through their wave functions and by calculating a rotational constant. These AVS, which overlap open system classical trajectories that form half-tori, should lead to an increased density of states near dissociation. Their influence on the infrared near-dissociation spectrum of H-3(+) remains to be determined

### R-matrix calculation of electron collisions with electronically excited O2 molecules

Low-energy electron collisions with O$_2$ molecules are studied using the
fixed-bond R-matrix method. In addition to the O$_2$ ${X}^3\Sigma_{g}^-$ ground
state, integrated cross sections are calculated for elecron collisions with the
${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ excited states of O$_2$ molecules. 13
target electronic states of O$_2$ are included in the model within a valence
configuration interaction representations of the target states. Elastic cross
sections for the ${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ excited states are
similar to the cross sections for the ${X}^3\Sigma_{g}^-$ ground state. As in
case of excitation from the ${X}^3\Sigma_{g}^-$ state, the O$_2^-$ $\Pi_u$
resonance makes the dominant contribution to excitation cross sections from the
${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ states. The magnitude of excitation
cross sections from the ${a}^1\Delta_{g}$ state to the ${b}^1\Sigma_{g}^+$
state is about 10 time larger than the corresponding cross sections from the
${X}^3\Sigma_{g}^-$ to the ${b}^1\Sigma_{g}^+$ state. For this
${a}^1\Delta_{g}$ $\to$ ${b}^1\Sigma_{g}^+$ transition, our cross section at
4.5 eV agrees well with the available experimental value. These results should
be important for models of plasma discharge chemistry which often requires
cross sections between the excited electronic states of O$_2$.Comment: 26 pages, 10 figure

### MARVEL: measured active rotational-vibrational energy levels

An algorithm is proposed, based principally on an earlier proposition of Flaud and co-workers [Mol. Phys. 32 (1976) 499], that inverts the information contained in uniquely assigned experimental rotational-vibrational transitions in order to obtain measured active rotational-vibrational energy levels (MARVEL). The procedure starts with collecting, critically evaluating, selecting, and compiling all available measured transitions, including assignments and uncertainties, into a single database. Then, spectroscopic networks (SN) are determined which contain all interconnecting rotational-vibrational energy levels supported by the grand database of the selected transitions. Adjustment of the uncertainties of the lines is performed next, with the help of a robust weighting strategy, until a self-consistent set of lines and uncertainties is achieved. Inversion of the transitions through a weighted least-squares-type procedure results in MARVEL energy levels and associated uncertainties. Local sensitivity coefficients could be computed for each energy level. The resulting set of MARVEL levels is called active as when new experimental measurements become available the same evaluation, adjustment, and inversion procedure should be repeated in order to obtain more dependable energy levels and uncertainties. MARVEL is tested on the example of the H-2 O-17 isotopologue of water and a list of 2736 dependable energy levels, based on 8369 transitions, has been obtained. (c) 2007 Elsevier Inc. All rights reserved

### An ab initio HCN and HNC rotational vibrationallinelist for astronomy

We present a new ab initio HCN/HNC linelist. The linelist forms themost accurate and extensive HCN/HNC data set presently in existence.The data contain rotation vibration line frequencies and line strengths,for all transitions that are not rigorously dipole forbidden, between stateswith energy less than 18 000 cm-1 and with J ? 60

### Absorption spectrum of (H2O)-O-18 in the range 12 400-14 520 cm(-1)

Fourier transform spectra recorded using (a) natural abundance water vapor, (b) (H2O)-O-18-enriched water vapor, and (c) (H2O)-O-17-enriched water vapor are analyzed. The ratio of intensities in three spectra is used to identify 927 lines due to absorption by (H2O)-O-18. Intensities and self-broadening parameters are derived for these lines. Using theoretical linelists, comparisons with previously assigned (H2O)-O-16 spectra, and automatic searches for combination differences, 747 lines are assigned. These lines belong to 14 vibrational states in the 3nu + delta and 4nu polyads. Newly determined (H2O)-O-18 vibrational band origins include 4nu(1) at 13 793.09 cm(-1), 3nu(1) + nu(3) at 13 795.40 cm(-1), 2nu(1) + 2nu(3) at 14 188.82 cm(-1), nu(1) + 3nu(3) at 14 276.34 cm(-1), and 2nu(2) + 2nu(2) + nu(3) at 13 612.71 cm(-1). These results are compared with data in HITRAN. (C) 2002 Elsevier Science (USA)

### Opacity data for HCN and HNC from a new ab initio line list

A new extensive ab initio rotation-vibration HCN/HNC line list is presented. The line list contains rotation-vibration energy levels, line frequencies, and line strengths for transitions between states with energy less than 18,000 cm-1 and with Jâ‰¤60. This line list greatly improves the quality and range of HCN/HNC data available. It is presently the most extensive and most accurate ab initio HCN/HNC line list in existence. It is hoped that this data set will be used in models of C star atmospheres and elsewhere

- â€¦