Time-resolved dynamics in acetonitrile cluster anions

Excited state dynamics of acetonitrile cluster anions, ( CH 3 CN ) n - , were investigated using time-resolved photoelectron imaging (TRPEI) for 20 ⩽ n ⩽ 50. The clusters were excited and then photodetached with femtosecond pump and probe pulses at 790 and 395 nm, respectively. Excited state lifetimes varied between 200 and 270 fs over this size range, showing no obvious size trend. Experimental evidence indicates that we are exciting ‘isomer II’ clusters in which the excess electron is valence-bound to a solvated anionic dimer core. The absence of an obvious size-dependence in the excited state lifetimes is consistent with such a structure.