Three types of anionic fragments are observed in the photodissociation of nitromethane cluster anions, (CH3 NO2) n-, n=1-6, at 355 nm: NO2- (CH3 NO2) k, (CH 3 NO2)k-, and OH- (k<n). The fragmentation trends are consistent with the parent clusters containing a monomer-anion core, CH3 NO2-, solvated by n-1 neutral nitromethane molecules. The NO2- (CH3 NO2) k and OH- fragments formed from these clusters are described as core-dissociation products, while the (CH3 NO 2) k- fragments are attributed to energy transfer from excited CH3 NO2- into the solvent network or a core-dissociation-recombination (caging) mechanism. As with other cluster families, the fraction of caged photofragments shows an overall increase with increasing cluster size. The low-lying A2 A′ and/or B 2 A′ electronic states of CH3 NO2 - are believed responsible for photoabsorption leading to dissociation to NO2- based fragments, while the C 2 A″ state is a candidate for the OH- pathway. Compared to neutral nitromethane, the photodissociation of CH3 NO 2- requires lower energy photons because the photochemically active electron occupies a high energy π orbital (which is vacant in the neutral). Although the electronic states in the photodissociation of CH3 NO2 and CH3 NO2- are different, the major fragments, CH3 + NO2 and CH 3 + NO2-, respectively, both form via C-N bond cleavage.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry