FTIR studies on the gas phase laser-induced decomposition of CF3CH2ONO

The unimolecular decomposition of CF₃CH₂O (2,2,2-trifluoroethoxy) radical generated from 355 nm pulsed nanosecond laser photolysis of CF₃CH₂ONO (2,2,2-trifluoroethylnitrite) in the gas phase has been studied using Fourier transform infrared absorption spectroscopy. The radical preferentially dissociates via its C–H bond cleavage to yield CF₃CHO (trifluoroacetaldehyde) as the major product. The infrared spectrum of formaldehyde, one of the products of C–C bond dissociation of CF₃CH₂O was not observed under a range of nitrite and argon buffer gas pressures. Similar results were obtained when thermal heating and broadband xenon lamp irradiation of the nitrite were carried out. The addition of high pressures of NO further decreased the production of CF₃CHO since recombination of NO with the trifluoroethoxy radical competes with the unimolecular dissociation process. Surprisingly, CF₃CDO was also the only product observed when the deuterated species CF₃CD₂ONO was photolysed by the 355 nm laser. These observations contradicted MP2/aug-cc-pVTZ calculations which were found to favour the C–C bond dissociation channel. However, 355 nm photolysis of CF₃CH₂ONO in the presence of O₂ yielded trifluoroethylnitrate, CF₃CH₂ONO₂ as the main product while CF₃CHO and CF₂O were also observable at much lower yields.