Excited-state ions in femtosecond time-resolved mass spectrometry: An investigation of highly excited chloroamines

We have investigated the processes induced by femtosecond laser pulses in chloroamines, with a focus on the generation and observation of a highly reactive radical and on the involvement and general importance of excited-state ions in time-resolved mass spectrometry investigations of gaseous molecules. We have found that 280 nm femtosecond pulses lead to an ultrafast breakage of the N-CI bond on the repulsive S ₁ surface, and that resulting radical is long-lived. When exposing the molecule to 420 nm photons a multiphoton ionization takes place to generate ions; these ions can then be excited with a 280 nm photon. The evidence is unambiguous since we observe a distinct temporal evolution of the ion current with no photoelectrons to match. We suggest that the involvement of excited-state ions is a general phenomenon in time-resolved photoionization studies.