Photodissociation dynamics of ethyl formate at 193 nm-based synchrotron radiation and <i>ab initio</i> calculations: hydrogen elimination and secondary dissociations

This investigation reports the unimolecular dissociation of ethyl formate, CH₃CH₂OOCH, at 193 nm using VUV synchrotron radiation-based phorofragment translational spectroscopy. We obtained the translational energy distributions and determined the fractions of energy released into product translation. Eleven dissociation pathways (five primary and six secondary dissociation reactions) resulted from five detected photofragments (<i>m</i>/<i>z</i> = +1, +15, +29, +30, and +44). Hydrogen elimination, H + CH₃CH₂OOC, was determined as a primary channel whose detection corresponded to 78.8% ± 5.2% of the total H atoms observed. Hydrogen elimination was also identified through two additional secondary dissociations (H + CO₂ (16.8% ± 2.1%) and H + CH₃CHO (4.4% ± 2.2%)) on the microsecond time scale of the experiments. Our electronic structure calculations based on the UCCSD/cc-pVDZ level of theory revealed the energy barriers for relevant secondary dissociation channels. Translational energy distributions constructed from the TOF data recorded and subsequent proposed reaction mechanisms are discussed. Also, considering the unobservable primary products CH₃CH₂OOC, CH₃CH₂O, HCOO, and HCOOCH₂, we suggest several secondary dissociations involving the production of fragments CH₃CH₂, CO₂, CH₃CHO, CH₃, CH₂O, HCO, and H. This investigation provides more detailed insights into the multichannel dissociation mechanisms of ethyl formate.