Lifetime measurements of two-photon excited vibronic levels in the low pressure limit: naphthalene

Single vibronic lifetimes of two-photon excited states are measured in the low pressure limit for naphthalene. The two-photon spectrum, besides yielding new states in S₁, is also free of the interference from the neighborhood of the S₂, known from one-photon experiments, and hence unperturbed lifetimes can be measured to higher excess energies. The overall pattern of lifetimes with excess energy including both one-photon and two-photon states shows that the vibronic structure is subordinate to an overall monotonic decrease, much as found earlier for β-naphthylamine. This indicates, at least for naphthalene, that radiationless processes into triplets are dominated by Franck—Condon factors and not by vibronic inductions and promoting modes.