Time-resolved two-color photoacoustic and multiphoton ionization spectroscopy of aniline

The multiphoton ionization and photoacoustic signals from aniline have been detected as a function of time delay between two laser pulses of different wavelength. The first pulse excited the S0 → S1 0--0 transition. The second pulse either excited S1 to a higher singlet state, or a triplet state produced by intersystem crossing to a higher triplet state, depending on the time delay between pulses. Both ionization and dissociation processes are observed. By varying the conditions of excitation it appears that a given amount of energy can be selectively channeled almost exclusively into either ionization or dissociation pathways. The results are explained using a simple Franck--Condon factor model