Effect of oxidation on excited state dynamics of neutral TiO (n < 10, x < 4) clusters.

Excited state lifetimes of neutral titanium oxide clusters (TiO, n < 10, x < 4) were measured using a sequence of 400 nm pump and 800 nm probe femtosecond laser pulses. Despite large differences in electronic properties between the closed shell stoichiometric TiO clusters and the suboxide TiO (x = 1-3) clusters, the transient responses for all clusters contain a fast response of 35 fs followed by a sub-picosecond (ps) excited state lifetime. In this non-scalable size regime, subtle changes in the sub-ps lifetimes are attributed to variations in the coordination of Ti atoms and localization of charge carriers following UV photoexcitation. In general, clusters exhibit longer lifetimes with increased size and also with the addition of O atoms. This suggests that the removal of O atoms develops stronger Ti-Ti interactions as the system transitions from a semiconducting character to a fast metallic electronic relaxation mechanism.