Ab initio characterization of linear C3Si isomers

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 X3Σ − 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 (Be) 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 X3Σ − and the lowest 1Σ+ excited state, located at 0.46 eV, resulting in complex vibrational IR-band shapes, at least, when the low- frequency bendings are excited. Key words. molecular data – catalogs 1