J/ApJ/708/1452 Quadratic Fij force field in l-CH4- (Senent+, 2010)
Ab initio characterization of C-4, C4H, and C4H-.
Senent M.L., Hochlaf M.
<Astrophys. J., 708, 1452-1458 (2010)>
=2010ApJ...708.1452S 2010ApJ...708.1452S
ADC_Keywords: Atomic physics
Keywords: astrochemistry - ISM: molecules - molecular data - molecular processes
Abstract:
Using state-of-the-art theoretical methods, we investigate the stable
isomers of C-4, C4H and C4H-. Three of them are relevant for
astrophysics and astrochemistry. These computations are performed
using highly correlated ab initio methods and the aug-cc-pVXZ (X=T,Q)
basis sets. In addition to the linear isomers, we predict the
existence of several cyclic and branched forms for these molecules.
For all the molecular species of interest here, sets of spectroscopic
parameters are determined with perturbation theory, which compare
quite well with experiment. For l-C4H-(X1Σ+), the
quartic force field is computed at the coupled cluster level of
theory. This force field is derived from full nine-dimensional
potential energy surface generated close to the equilibrium geometry
of this anion. Finally, we treat the thermochemistry of the hydrogen
attachment and the electron attachment reactions that may lead to the
formation of the C4H- from either C-4 or C4H.
Description:
Electronic structure calculations have been achieved with the MOLPRO
program suite (MOLPRO version 2002). The search of stationary points
and determination of first-order spectroscopic parameters were
performed at the coupled cluster including perturbative treatment of
triple excitations ((R)CCSD(T); Knowles et al. 1993JChPh..99.5219K 1993JChPh..99.5219K)
and at the complete active space self consistent field (CASSCF;
Knowles et al. 2000JChPh.112.3106K 2000JChPh.112.3106K) levels. For these computations,
the Dunning's basis sets including diffuse functions were employed
(Dunning 1989JChPh..90.1007D 1989JChPh..90.1007D; Kendall et al. 1992JChPh..96.6796K 1992JChPh..96.6796K). The
main group of spectroscopic parameters of the l-C4H- anion has
been calculated with second-order perturbation theory applied on the
quadratic, cubic, and quartic force fields derived from a
CCSD(T)/aug-cc-pVQZ nine-dimensional potential energy surface (PES)
and the code FIT-ESPEC (Senent 2007ApJ...670.1510S 2007ApJ...670.1510S). For CASSCF
calculations, the active space was defined considering all the π
orbitals.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 20 187 *(R)CCSD(T)/aug-cc-pVTZ quadratic Fij force
field of l-CH4-
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Note on table4.dat: computation with the MOLPRO program suite (version 2002).
See Knowles et al. 1993JChPh..99.5219K 1993JChPh..99.5219K for (R)CCSD(T) treatment.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- i [-7/7] The i component of the force field
4- 5 I2 --- j [-7/7] The j component of the force field
7- 8 I2 --- k [-7/7] The k component of the force field (1)
10- 11 I2 --- l [-6/7] The l component of the force field (1)
13- 20 F8.4 --- Term Most significant term
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Note (1): When "k" and "l" are zero the force field is anharmonic quartic.
When just "l" is zero the force field is cubic and when neither
"k" and "l" are zero the force field is quartic.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 22-Feb-2012