Collisional excitation of fine-structure levels in hydrogen-like ions by distant proton-ion encounters

We assess the accuracy of approximations used to calculate the long-range component of proton impact, fine-structure changing, collision strengths in positive ions. In particular we rediscuss an approximation introduced to calculate collision strengths for the electron impact excitation of hydrogen-like ions, and adopted for the case of proton impacts. A more accurate approximation is introduced. The results of the calculations are in harmony with previous close-coupling calculations