Direct Experimental Evidence for Reverse Internal Conversion in the Relaxation Pathway of the Excited Anions

We report here direct experimental evidence of reverse internal conversion taking place in the excited nitrobenzene anion, revealed by photoelectron spectra acquired by electron detection at the much-delayed time with respect to the laser-anion interaction time along the time-of-flight. Especially, autodetached photoelectrons from the dipole bound states which are in quasi-equilibrium with vibrationally hot anions have been clearly observed concurrently with thermionic emission at the much-delayed time (up to 120 ns). Not only does this work confirm a proposed mechanism in previous reports, but also it demonstrates that the reverse internal conversion is robust across multiple electronically excited states of nitrobenzene anion, suggesting that it may play an important role in governing energy relaxation pathways of excited anionic states.