Rotational (de)-excitation of C5 by collision with He at low temperature

An appropriate estimation of the abundance of the observed C-5 radical in the interstellar medium requires accurate radiative and collisional rate coefficients. We present the first two-dimensional potential energy surface (2D-PES) for the ground electronic state of the C-5(X-1 sigma(+))-He((XS)-S-1) van der Waals system, obtained using an explicitly correlated coupled-cluster method with single, double, and perturbative triple excitations (RCCSD(T)-F12). This PES is subsequently used in quantum close-coupling (CC) scattering calculations. Collisional excitation cross-sections of the rotational levels of C-5 by He were calculated for energies up to 1500 cm(-1) using the standard (CC) method. The thermal dependence of the corresponding rate coefficients is given for the low and moderate temperature T <= 300 K regime of interstellar molecular clouds. This is the first study on the collisional rate coefficients for this system and may have important implications for the astrophysical detection of C-5(X-1 sigma(+)) and modeling of carbon-rich media.

Automated summary

This study presents the first two-dimensional potential energy surface (2D-PES) for the C-5(X-1 sigma(+))-He((XS)-S-1) van der Waals system and calculates collisional rate coefficients, aiding in the accurate estimation of the abundance of the C-5 radical in the interstellar medium.