Molecular elimination of methyl formate in photolysis at 234 nm: Roaming vs. transition state-type mechanism
- Citation:
- Chao, M-H, Tsai P-Y, Lin K-C. 2011. Molecular elimination of methyl formate in photolysis at 234 nm: Roaming vs. transition state-type mechanism. Physical Chemistry Chemical Physics. 13:7154-7161., Number 15
Abstract:
Ion imaging coupled with (2 + 1) resonance-enhanced multiphoton ionization (REMPI) technique is employed to probe CO(v″ = 0) fragments at different rotational levels following photodissociation of methyl formate (HCOOCH 3) at 234 nm. When the rotational level, J″CO, is larger than 24, only a broad translational energy distribution extending beyond 70 kcal mol-1 with an average energy of about 23 kcal mol -1 appears. The dissociation process is initiated on the energetic ground state HCOOCH3 that surpasses a tight transition state along the reaction coordinate prior to breaking into CO + CH3OH. This molecular dissociation pathway accounts for the CO fragment with larger rotational energy and large translational energy. As J″CO decreases, a bimodal distribution arises with one broad component and the other sharp component carrying the average energy of only 1-2 kcal mol-1. The branching ratio of the sharp component increases with a decrease of J″CO; (7.3 ± 0.6)% is reached as the image is probed at J″CO = 10. The production of a sharp component is ascribed to a roaming mechanism that has the following features: a small total translational energy, a low rotational energy partitioning in CO, but a large internal energy in the CH3OH co-product. The internal energy deposition in the fragments shows distinct difference from those via the conventional transition state. © the Owner Societies 2011.
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