Spin-orbit coupling and vibronic transitions of Ce(CH) and Ce(CH) formed by the Ce reaction with propene: Mass-analyzed threshold ionization and relativistic quantum computation.

A Ce atom reaction with propene is carried out in a pulsed laser vaporization molecule beam source. Several Ce-hydrocarbon species formed by the C-H and C-C bond activation of propene are observed by time-of-flight mass spectrometry, and Ce(CH) (n = 4 and 6) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory, multiconfiguration, and relativistic quantum chemical calculations. The MATI spectrum of each species consists of two vibronic band systems, each with several vibronic bands. Ce(CH) is identified as an inserted species with Ce inserting into an allylic C-H bond of propene and Ce(CH) as a metallocycle through 1,2-vinylic dehydrogenation. Both species have a C structure with the Ce 4f6s ground valence electron configuration in the neutral molecule and the Ce 4f configuration in the singly charged ion. The two vibronic band systems observed for each species are attributed to the ionization of two pairs of the lowest spin-orbit coupled states with each pair being nearly degenerate.