Ultrafast dynamics of aniline in the 294-234 nm excitation range: The role of the πσ* state

The ultrafast relaxation of jet-cooled aniline was followed by time-resolved ionization, after excitation in the 294-234 interval. The studied range of energy covers the absorption of the two bright pi pi* excitations, S-1 and S-3, and the almost dark S-2 (pi sigma*) state. The employed probe wavelengths permit to identify different ultrafast time constants related with the coupling of the involved electronic surfaces. A tau(1) = 165 +/- 30 fs lifetime is attributed to dynamics along the S-2 (pi sigma*) repulsive surface. Other relaxation channels as the S-1 -> S-0 and S-3 -> S-1 internal conversion are also identified and characterized. The work provides a general view of the photophysics of aniline, particularly regarding the role of the pi sigma* state. This state appears as minor dissipation process due to the ineffective coupling with the bright S-1 and S-3 states, being the S-1 -> S-0 internal conversion the main non-radiative process in the full studied energy range. Additionally, the influence of the off-resonance adiabatic excitation of higher energy electronic states, particularly S-3, is also observed and discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3615544]