Triplet vs pi sigma* state mediated N-H dissociation of aniline

Abstract

UV-excited aromatic molecules with N-H/O-H moieties often possess an important nonradiative relaxation pathway, from an optically bright pi pi* state to a dark dissociative pi sigma* state. We apply a new time-selected photofragment translational spectroscopy method to disclose a previously unknown triplet-mediated N-H dissociation of aniline prevented by the multiphoton dissociative ionization in conventional methods. We further determined the branching fractions of aniline dissociated in the pi sigma*, triplet, and ground states at 248 nm. Additionally, we selectively captured the population changes in the singlet and triplet states with ionization from different laser wavelengths, 355 or 266 nm, in time-resolved photoion yields. The combination of experimental data enables us to uniquely determine the relative ionization cross sections of the singlet and triplet states at an ionization laser wavelength of 266 nm and allows us to extensively measure the rate constants of intersystem crossing and the branching fractions at various excitation wavelengths. Published under license by AIP Publishing.