Rotational (de-) excitation of C3N- by collision with He atoms

Since their recent detection in the interstellar medium, anions have raised the question of their possible mechanisms of formation, destruction and excitation. Among the observed anions, C3N- is an interesting species owing to its large dipole moment and its remarkable stability, since the electron affinity of C3N is particularly large. In this work, a quantum mechanical treatment of the rotational (de-)excitation of C3N- in collisions with He is reported. Full close-coupling calculations are performed within the rigid rotor approximation for the j = 0 up to 15 rotational levels of C3N- and for collision energies in the range 0.1-2000 cm(-1). These results are complemented for the j = 16 up to 30 rotational levels of C3N-by using two different approximations whose accuracies are tested against close-coupling results. The uniform J-shifting is found to give the most accurate results. At high collision energy, a strong propensity to favour |Delta j| = 2 transitions is observed and discussed. The rate coefficients for the rotational transitions between 1 and 300 K are reported.