Photodetachment and photodissociation of the linear OCuO− molecular anion: energy and time dependence of Cu− production

Abstract

A photodissociative study of CuO₂⁻ is presented using a combination of energy and time domain photoelectron spectroscopy. Ion source conditions are used that solely produce linear OCuO⁻. Photodissociation of this isomer to produce Cu⁻ + O₂ is conclusively demonstrated at wavelengths between 765 and 340 nm. Nanosecond pulsed photoexcitation at wavelengths shorter than 340 nm produces single photon detachment transitions from the first excited state of CuO₂⁻. At longer wavelengths narrow Cu⁻ fragment transitions are observed as a result of a sequential two photon process. In addition, the longer wavelengths produce a weak, broad two photon dependent signal, the result of detachment of the dissociating linear isomer. Time resolved pump–probe measurements reveal a long timescale growth (up to 150 ps) of the Cu⁻ fragment yield, consistent with the unfavorable starting geometry for the dissociative process and indicating a potential energy surface which has one or more substantial barriers to dissociation.