Signatures of Reaction Mechanisms Encoded in the Vibrational Population Distribution of Small-Molecule Products: Photodissociation of Symmetric -Triazine Using 266 nm Radiation.

We utilize rotationally resolved Chirped-Pulse Fourier Transform millimeter-wave spectroscopy to study photodissociation dynamics of 1,3,5-Triazine ( symmetric -Triazine) to form 3 HCN molecules. The state-specific vibrational population distribution (VPD) of the photofragments contains mechanistic details of the reaction. This photodissociation is performed using 266 nm radiation transverse to a seeded supersonic jet. The vibrational cooling inefficiency in the jet preserves the VPD of the photofragments, while rotational cooling enhances the signal of low-J pure-rotational transitions. The multiplexed nature of the spectrometer enables simultaneous sampling of several "vibrational satellites" of the J = 1 ← 0 transition of HCN. Excited state populations along the HCN bend ( v 2 ) and CN stretch ( v 3 ) modes are observed, which show ≥3.2% vibrational excitation of the photofragments. Observation of an at least bimodal VPD, along the even-v states of v 2 , implies an asymmetric partitioning of vibrational energy among the HCN photofragments. This suggests a sequential dissociation mechanism of symmetric -Triazine initiated by 266 nm radiation.