Energy transfer in multi-collision environments; an experimental test of theory: LiH (10;2) in H₂(0;0)

We report separate experimental and theoretical studies of the equilibration of highly excited LiH (v = 10; J = 2) in H₂ at 680 K. Experiments that follow the time evolution of state-to-state population transfer in multi-collision conditions with μs resolution were carried out by Shen and co-workers at Xinjiang University and East China Institute of Science and Technology. At the same time, theoretical computations on the relaxation of this gas mixture were undertaken by McCaffery and co-workers at Sussex University. Rapid, near-resonant, vibration-vibration energy exchange is a marked feature of the initial relaxation process. However, at later stages of ensemble evolution, slower vibration-rotation transfer forms the dominant relaxation mechanism. The physics of the decay process are complex and, as demonstrated experimentally here, a single exponential expression is unlikely to capture the form of this decay with any accuracy. When these separate studies were complete, the evolution of modal temperatures from the Sussex calculations was compared with experimental measurements of these same quantities from Shanghai and Urumqi. The two sets of data were marked by their near identity, within experimental and computational error, representing an experimental validation of the theoretical/computational model developed by the Sussex group and a significant experimental advancement by the group of Shen et al.