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 that follow the equilibration of highly excited LiH (v=10;J=2) in H2 at 680K. Experiments that follow the time evolution of state-tostate population transfer in multi-collision conditions were carried out by Shen and co-workers at Xinjiang University and East China Institute of Science and Technology with µs resolution. 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 processes form 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 were compared with experimental measurements of these same quantities from Shanghai and Urumqui. The two sets of data were found to be identical to within experimental and computational error. This constitutes an important experimental validation of the theoretical/computational model developed by the Sussex group and a significant experimental advance by the group of Shen et.al.