Femtosecond dynamics of photoinduced molecular detachment from halogenated alkanes. I. Transition state dynamics and product channel coherence

Abstract

The direct observation of the photoinduced molecular detachment of halogens X2 from halogenated alkanes RCHX2 is presented. Three-photon excitation at 312 nm produces molecular halogens and a carbene; the halogen products are formed predominantly in the D′ state. Femtosecond pump–probe spectroscopy of the reaction reveals a fast (τ<50 fs) dissociation with no evidence of intramolecular vibrational redistribution. This is consistent with a prompt dissociation without intermediates. The experimental results demonstrate vibrational coherence in the halogen product, which requires that the reaction proceed by a concerted mechanism.