Ab initio characterization of linear C₃Si isomers

¹ Universidad Andrés Bello, Departamento de Química, Facultad de Ecología y Recursos Naturales, Santiago, Chile e-mail: n.inostroza@uandresbello.edu
² Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle (MSME FRE 3160 CNRS), Champs sur Marne, 77454 Marne-la-Vallée, Cedex 2, France e-mail: hochlaf@univ-mlv.fr
³ Instituto de Estructura de la Materia, C.S.I.C, Departamento de Astrofísica Molecular e Infrarroja, Serrano 121 Madrid 28006, Spain e-mail: senent@damir.iem.csic.es
⁴ Universidad de Chile, Departamento de Ciencia de los Materiales, Facultad de Ciencias Físicas y Matemáticas, Beauchef 850, Santiago, Chile e-mail: jletelie@ing.uchile.cl

Received: 11 February 2008
Accepted: 21 March 2008

Abstract

Aims. This paper presents an ab initio characterization of linear isomers of C₃Si, which are suitable species for astrophysical detection in carbon-rich sources.

Methods. By the help of multiconfigurational calculations, two linear minima are characterized, namely l-SiCCC and l-CSiCC, whose relative energy is 3.3 eV, and their electronic ground states have symmetry, and their electronic spectra present a high density of electronic states at low energy. Anharmonic spectroscopic parameters are predicted for both isomers and for different isotopomers using second order perturbation theory and force fields derived form 6D-potential energy surfaces.

Results. The fundamental frequencies of the IR active bendings are predicted to lie around 434 cm^-1 and 169 cm^-1 for l-SiCCC. The rotational constants (B_e) are computed to be 2753.16 MHz for l-SiCCC and 3205.37 MHz for l-CSiCC. For l-SiCCC, a relatively large spin-spin constant (λ = -0.605 cm^-1) arises from the interaction between the ground and the lowest excited state, located at 0.46 eV, resulting in complex vibrational IR-band shapes, at least, when the low- frequency bendings are excited.