Effect of isotropic collisions with neutral hydrogen on the polarization of the CN solar molecule

Abstract

In this work, we study the solar molecule CN, which presents conspicuous profiles of scattering polarization. We start by calculating accurate potential energy surfaces for the singlet and triplet electronic ground states in order to characterize the collisions between the CN molecule in its X2Σ state and the hydrogen in its ground state 2S. The potential energy surfaces are included in the Schrödinger equation to obtain the scattering matrix and the probabilities of collisions. Depolarizing collisional rate coefficients are computed in the framework of the infinite order sudden approximation for temperatures ranging from T = 2000 K to T = 15 000 K. We give an interpretation of the results and compare the singlet and triplet collisional rate coefficients. We show that, for typical photospheric hydrogen density (nH = 1015−1016 cm−3), the X2Σ state of CN is partially or completely depolarized by isotropic collisions.