Excited-state chromium atom distributions produced in the KrF* laser multiphoton dissociation of a series of chromium compounds

Abstract

The 248-nm laser multiphoton dissociation (MPD) of a series of chromium compounds has been investigated in the gas phase by using emission spectroscopy to detect the excited-state photoproducts. In the 248-nm MPD of all compounds studied, chromium atoms are formed in a variety of excited states. Atomic chromium is formed in the MPD of the (arene)chromium tricarbonyls via a two-channel dissociation mechanism. The predominant pathway for the formation of the ground electronic state as well as the lowest energy excited states is by a sequential absorption/fragmentation mechanism, where the product of the one-photon dissociation of the parent (arene)chromium tricarbonyl absorbs an additional photon and dissociates to Cr(I). Formation of the first two Cr(I) excited states is found to be quenched by the addition of a buffer gas. The higher energy Cr(I) states are formed exclusively by a direct dissociation process, where the parent (arene)chromium tricarbonyl absorbs multiple photons prior to dissociation. The distribution of excited chromium atoms formed in the direct channel is found to be statistical for all systems and independent of the nature of the arene ligand. The distribution of Cr(I) states formed via the sequential dissociation channel is, however, strongly dependent on the ligand vibrational density of states. The final distribution of excited Cr(I) states formed in this direct process differs for the different types of compounds examined, but no direct correlation with the dissociation energies was found. © 1989 American Chemical Society.