Triplet state nonradiative lifetimes of collision-free aniline and aniline–argon complexes above the S1 origin

Triplet state lifetimes have been measured for collision-free aniline and aniline–argon complexes in a pump-probe photoionization experiment. The triplet state populations are due to intersystem crossing from optically pumped S1 vibronic states. The measured triplet decay rates as a function of excess energy above the T1 origin show behavior which is not exponential with respect to excess energy, increasing much more rapidly than similar molecules studied by this technique. It is postulated that this could be due to increased spin-orbit coupling caused by the T2 charge transfer state. The results for the aniline–argon complex are used to estimate a ∼275 cm−1 van der Waals bond energy in the highly excited triplet as well as to aid the understanding of both the S1–T and the T-S0 nonradiative processes.