Ab initio ro-vibronic spectroscopy of SiCCl ($\tilde{X}^2\Pi$X̃2Π)

Abstract

The full dimensional potential energy surfaces of the (2)A' and (2)A'' electronic components of X̃(2)Π SiCCl have been computed using the explicitly correlated coupled cluster method, UCCSD(T)-F12b, combined with a composite approach taking into account basis set incompleteness, core-valence correlation, scalar relativity, and higher order excitations. The spin-orbit and dipole moment surfaces have also been computed ab initio. The ro-vibronic energy levels and absorption spectrum at 5 K have been determined from variational calculations. The influence of each correction on the fundamental frequencies is discussed. An assignment is proposed for bands observed in the LIF experiment of Smith et al. [J. Chem. Phys. 117, 6446 (2002)]. The overall agreement between the experimental and calculated ro-vibronic levels is better than 7 cm(-1) which is comparable with the 10-20 cm(-1) resolution of the emission spectrum.

Simulation of the Ã2Σ+–X̃2Π absorption and emission spectra of the SiCCl radical

“…The intensities being much more sensitive to the convergence of the final states than the energies, theà 2 + vibrational states and theX 2 vibronic states have been calculated using a larger number of functions than in our previous work (see Ref. [9]). For K ≥ 1, the Renner-Teller interaction was explicitly taken into account by solving the coupled X 2 A /X 2 A problem as described in Ref.…”

“…In order to keep the accuracy obtained for the rovibronic states of the ground electronic state [9], the same coordinates and grid settings have been used: valence bond-length and bond-angle coordinates were chosen. The above the lowest vibronic state forX 2 and up to 3500 cm −1 forà 2 + , and for 0 ≤ K ≤ 3.…”

“…The experimental values from Smith et al [6] are given in italic. rovibronic states ofX 2 have also been recomputed using the composite analytical PES [9] in order to calculate the transition dipole moments. The EVEREST code uses a discrete variable representation (DVR) approach and the exact kinetic energy operator in internal coordinates, taking into account most of the couplings between the angular momenta of the molecule (i.e.…”

“…Such emission spectra produced by laser excitations are of particular interest as they reflect the complex IR spectroscopy of Renner-Teller systems in which spin-orbit coupling often combines with non-adiabatic Renner-Teller interactions [3,[6][7][8]. Ab initio calculations can be the suitable tools to have a complete pattern of the rovibronic states of such degenerate electronic states in triatomic molecules and are often an important complement of such measurements [9][10][11]. In this domain, only few theoretical studies exist on the emission spectra of Renner-Teller systems since the difficulty resides **in knowing the population distribution of the initial states [12].…”

“…For this purpose, the rovibrational energy levels of thẽ A 2 + excited state of SiCCl must be accurately determined together with the transition dipole moments. The rovibronic states of the electronic ground state have already been obtained in a previous work [9], where the full dimensional potential energy surfaces (PESs) of the 2 A and 2 A electronic components of theX 2 state have been computed using an explicitly correlated coupled cluster method combined with a composite approach. The spin-orbit couplings have also been computed ab initio and the rovibronic energy levels have been obtained from variational calculations using the EVEREST code.…”