Rotational and vibrational energy transfer in impulsive ion-molecule collisions

We study rotational and vibrational energy transfer in large angle scattering of ions from molecules in the energy range of atomic unit. In such a collision, the interaction time is much shorter than the rotational period of the molecule. Sometimes, the interaction time becomes even shorter than the vibrational period. We have proposed a new model (hard potential model) for rotational and vibrational energy transfer in a limit of sudden collision. This model is a natural extension of the previously proposed hard-shell model where only the rotational degree of freedom is taken into account. Using the two models, we have studied systematically how energy-loss spectrum changes with collision energy. Here we study the dependence on mass of the projectile in collisions between closed-shell ions and N$_{2}$. Through the comparison between models and CT calculation, we find that the collision is sudden both rotationally and vibrationally for H$^{+}$-N$_{2}$, rotationally sudden and vibrationally non-sudden for Li$^{+}$-N$_{2}$, and non-sudden both rotationally and vibrataionally for Na$^{+}$ with N$_{2}$. Non-sudden phenomenon in the case of Na$^{+}$ - N$_{2}$ is related to a double collision mechanism. Comparison with experimental measurements will be given.