The direct observation of the photoinduced molecular detachment of halogens X-2 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 pumpprobe spectroscopy of the reaction reveals a fast (tau<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.