Trajectory and Model Studies of Collisions of Highly Excited Methane with Water Using an ab Initio Potential

Quasi-classical trajectory studies have been performed for the collision of internally excited methane with water using an accurate methane–water potential based on a full-dimensional, permutationally invariant analytical representation of energies calculated at a high level of theory. The results suggest that most energy transfer takes place at impact parameters smaller than about 8 Bohr; collisions at higher impact parameters are mostly elastic. Overall, energy transfer is fairly facile, with values for ⟨ΔEdown⟩ and ⟨ΔEup⟩ approaching almost 2% of the total excitation energy. A classical model previously developed for the collision of internally excited molecules with atoms (Houston, P. L.; Conte, R.; Bowman, J. M. J. Phys. Chem. A 2015, 119, 4695–4710) has been extended to cover collisions of internally excited molecules with other molecules. For high initial rotational levels, the agreement with the trajectory results is quite good (R2 ≈ 0.9), whereas for low initial rotational levels it is only fair ...