Rotational excitation of CN molecules by proton impact

Cross sections for excitation of the ground rotational state of CN by proton impact are presented. The calculations are based on a multi-state impact parameter formulation in which the coupled equations were solved numerically. Comparison is made with cross sections obtained from various approximate solutions of the equations which include the Born, the exponential and the sudden approximations and the range of validity of the impact parameter formulation for small excitation energies is examined.