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

TL;DR

This study calculates collisional effects of neutral hydrogen on the polarization of the CN molecule in the solar atmosphere, revealing significant depolarization at typical photospheric densities.

Contribution

It provides new accurate potential energy surfaces and collisional rate coefficients for CN-H collisions, enhancing understanding of polarization depolarization mechanisms.

Findings

CN polarization is significantly affected by hydrogen collisions.

Depolarization occurs at typical photospheric hydrogen densities.

Results improve modeling of solar molecular polarization.

Abstract

Our work is concerned with the case of the solar molecule CN which presents conspicuous profiles of scattering polarization. We start by calculating accurate PES for the singlet and triplet electronic ground states in order to characterize the collisions between the CN molecule in its $X \; ^2\Sigma$ state and the hydrogen in its ground state $^2S$. The PES are included in the Schr\"oodinger 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 $T= 15000$ K. Interpretation of the results and comparison between singlet and triplet collisional rate coefficients are detailed. We show that, for typical photospheric hydrogen density ($n_{H} = 10^{15}-10^{16}$ cm$^{-3}$), the $X \; ^2\Sigma$ state of CN is partially or completely depolarized by isotropic collisions.