Photodissociation dynamics of pyridine

Abstract

Photodissociation of pyridine, 2,6-d2-pyridine, and d5-pyridine at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Six dissociation channels were observed at 193 nm, including C5NH5 --> C5NH4 + H (10%) and five ring opening dissociation channels, C5NH5 --> C4H4 + HCN, C5NH5 --> C3H3 + C2NH2, C5NH5 --> C2H4 +C3NH, C5NH5 --> C4NH2 + CH3 (14%), and C5NH5 --> C2H2 + C3NH3. Extensive H and D atom exchanges of 2,6-d2-pyridine prior to dissociation were observed. Photofragment translational energy distributions and dissociation rates indicate that dissociation occurs in the ground electronic state after internal conversion. The dissociation rate of pyridine excited by 248-nm photons was too slow to be measured, and the upper limit of the dissociation rate was estimated to be 2x10(3) s(-1). Comparisons with potential energies obtained from ab initio calculations and dissociation rates obtained from the Rice-Ramsperger-Kassel-Marcus theory have been made.

Photodissociation dynamics of pyrimidine

“…The dissociation barrier height is about 10 and 20 kcal/ mol lower than the barrier heights of the analogous dissociation channels of pyridine, HCN elimination and C 2 H 2 elimination, respectively. 3 It is about 50 kcal/ mol lower than the barrier height of the analogous C 2 H 2 elimination channel for benzene. 2,4 The generation of HCN from three-body dissociation ͓reaction ͑3b͔͒ is an energetic possibility.…”

“…However, pyridine exhibits a much richer dissociation dynamics and has a faster dissociation rate at 193 nm. 3 Six dissociation channels were observed at 193 nm, including C 5 NH 5 → C 5 NH 4 +H ͑10%͒ and five ring opening dissociation channels, C 5 NH 5 → C 4 H 4 + HCN, C 5 NH 5 → C 3 H 3 +C 2 NH 2 , C 5 NH 5 → C 2 H 4 +C 3 NH, C 5 NH 5 → C 4 NH 2 +CH 3 ͑14%͒, and C 5 NH 5 → C 2 H 2 +C 3 NH 3 . Extensive H and D atom exchanges of 2 , 6-d 2 -pyridine prior to dissociation were observed.…”

“…Most of the dissociation barrier heights of pyridine are lower than that of benzene. 3,4 As a result, ring opening dissociation channels play a very important role in photodissociation of pyridine at 193 nm.…”

Specific fragmentation of the K‐shell excited/ionized pyridine derivatives studied by electron impact: 2‐, 3‐ and 4‐methylpyridine

“…[17,18] Ni and coworkers studied dissociation of pyridine [19] and 4-methylpyridine [20] by 193-nm laser excitation and proposed the dissociation channels from the neutral excited states. They observed six dissociation channels of pyridine by the 193-nm excitation -a hydrogen-atom elimination channel; C 5 H 5 N → C 5 H 4 N + H and five ring-opening dissociation channels; C 5 H 5 N → C 4 H 4 + HCN, C 5 H 5 N → C 3 H 3 + C 2 H 2 N, C 5 H 5 N → C 2 H 4 + C 3 HN, C 5 H 5 N → C 4 H 2 N + CH 3 and C 5 H 5 N → C 2 H 2 + C 3 H 3 N. They also found H-atom migrations before dissociation.…”

Observation and Identification of Metastable Excited States in Ultrafast Laser-Ionized Pyridine

“…These extinction voltages, and the corresponding This particular decay channel has been previously documented in pyridine and pyrazine [25,26].…”