Comparing the electronic relaxation dynamics of aniline and d(7)-aniline following excitation at 272-238 nm

Femtosecond time-resolved photoelectron spectroscopy experiments have been used to compare the electronic relaxation dynamics of aniline and d(7)-aniline following photoexcitation in the range 272-238 nm. Together with the results of recent theoretical investigations of the potential energy landscape [M. Sala, O. M. Kirkby, S. Guerin and H. H. Fielding, Phys. Chem. Chem. Phys., 2014, 16, 3122], these experiments allow us to resolve a number of unanswered questions surrounding the nonradiative relaxation mechanism. We find that tunnelling does not play a role in the electronic relaxation dynamics, which is surprising given that tunnelling plays an important role in the electronic relaxation of isoelectronic phenol and in pyrrole. We confirm the existence of two time constants associated with dynamics on the 1(1)pi sigma* surface that we attribute to relaxation through a conical intersection between the 1(1)pi sigma* and 1(1)pi pi* states and motion on the 1(1)pi sigma* surface. We also present what we believe is the first report of an experimental signature of a 3-state conical intersection involving the 2(1)pi pi*, 1(1)pi sigma* and 1(1)pi pi* states.