IR and UV Spectra of the Matrix‐Isolated Peroxy Radicals CF₃OO,trans‐FC(O)OO, andcis‐FC(O)OO

Abstract

The peroxy radicals CF3OO and FC(O)OO are prepared in high yields by vacuum flash pyrolysis of ROONO2 or ROOOR (R=CF3, FC(O)), highly diluted in inert gases, and subsequent isolation in inert-gas matrices by quenching the product mixtures at low temperatures. The IR spectrum of FC(O)OO was observed for the first time and eight fundamentals as well as several combinations were measured and assigned for both cis and trans rotamers of FC(O)OO. Discrepancies in an earlier assignment of the fundamentals of CF3OO have been eliminated and its IR spectrum is reported fully. The matrix UV spectra of both peroxy radicals (X2A"--> 2(2)A" transition) are in agreement with the gas-phase spectra; however, there are differences in the absorption cross-sections, for which possible reasons are discussed. The X2A"--> 1(2)A' transitions in the near IR region are too weak to be detected with our instrumentation.

The Trifluoromethoxy Carbonyl Peroxy Radical CF3OC(O)OO

“…Assuming a similarity between the CF 3 O group and a fluorine atom, the CF 3 OC(O)OO radical should behave similar to FC(O)OO. Indeed, comparable properties were observed in certain cases: 1) The O 2 moiety is strongly bound to carbon and can only be abstracted by raising the pyrolysis temperature (> 500 8C in the case of FC(O)OO [10] and 300 8C in the case of CF 3 OC(O)OO as discussed above).…”

“…All unidentified IR bands disappeared simultaneously, while the bands of CF 3 O showed a slower decay due to its comparable small absorption cross sections for the light used. [29] CF 3 OO [6,10] was identified as a photolysis product, together with CO 2 and COF 2 . When using UV light with wavelength shorter than 254 nm, the photochemically generated CF 3 OO is also partially photolyzed.…”

“…2) The generation of the peroxy radical from the trioxide precursors FC(O)OOOC(O)F [10,30] or CF 3 OC(O)OOOCkeo(O)OCF 3 [27] is possible by low-pressure flash thermolysis in high yields.…”

“…Its contour is similar to the fluorinated peroxy radical absorption bands of CF 3 OO and FC(O)OO. [10] The transition is therefore assigned to the 2 2 A'' 2 X 2 A'' excitation leading to subsequent dissociation of the radical [Eq. (15) (15) The photolysis product CF 3 OO itself absorbs UV light and this radical partly dissociates during photolysis according to Equation (16).…”

“…The IR [6±10] and UV [11,12] spectroscopic properties of CF 3 OO are well documented, as well as several kinetic studies. [11±17] The radical FC(O)OO is less well studied, the IR [10] and UV [10,18,19] spectra and some kinetic data [18,19] are known. While the related species CF 3 C(O)OO is partly characterized, [20,21] to our knowledge no data are available for CF 3 OC(O)OO.…”