Experimental studies of collisions of excited Li(4p) atoms with C2H4, C2H6, C3H8 and theoretical interpretation of the Li-C2H4 system

Collisions of excited Li(4p) states with C2H4, C2H6 and C3H8 are studied experimentally using far-wing scattering state spectroscopy techniques. High-level ab initio quantum mechanical studies of the Li-C2H4 system are conducted to explain the results of the experiment for this system. The recent and present works indicate that knowledge of the internal structure of the perturber (C2H4, C2H6 and C3H8) is essential to fully understand the interaction between the metal and the hydrocarbon molecules. The ab initio calculation shows that the Li(4d) (with little probability under the experimental conditions) and the Li(4p) can be formed directly through the laser pumping. It also shows that the Li(4s) and Li(3d) states can be formed through an electronic diabatic coupling involving a radiationless process. However, the Li(3p), Li(3s) and Li(2p) states can only be formed through a secondary diabatic coupling which is a much less probable process than the primary one. The calculation limited to two C2v sections of the potential energy surfaces (PESs) shows peculiar multi-state crossings that we have never seen in other lithium complexes we studied.