Side‐On versus End‐On Bonding of O₂ to the FSO₃ Radical: Matrix Isolation and Ab Initio Study of FSO₅

Abstract

Dedicated to Professor Friedhelm Aubke on the occasion of his 75th birthdayOxy radicals of non-metals such as nitrogen, chlorine, or sulfur play an important part in atmospheric chemistry. They generally form weak complexes with dioxygen. A recent study [1] on the kinetics of formation and the decomposition of the FSO 3 /O 2 complex attracted our interest. The intermediate formed by laser flash photolysis (l = 193 nm) of FSO 2 OF in the presence of O 2 features a strong visible absorption at 450 nm and was claimed to be the chainlike trioxy radical FSO 2 OOO.[1] The oxygenated radical was found to dissociate unimolecularly on a millisecond timescale to yield FSO 3 + O 2 .[1] The short lifetime prevented further spectroscopic investigations. Previously we studied in noble gas matrices O 2 complexes of several oxy radicals such as CF 3 O/O 2 , [2] SF 5 O/O 2 , [3] and ClO 4 /O 2 .[4] However, dioxygen complexes of polyoxy radicals such as FSO 3 have not yet sufficiently been characterized. Herein we report the matrix isolation and a combined UV/Vis/infrared spectroscopic and quantum-chemical characterization of the FSO 3 /O 2 complex. The infrared spectra of the precursor for the synthesis of FSO 3 , the peroxide FSO 2 OOSO 2 F (S 2 O 6 F 2 ), [5,6] isolated in solid argon at 14 K or in neon at 6 K, revealed no impurities, but did show splitting of the bands owing to the presence of several rotamers. Increasing the temperature of the spray-on nozzle during matrix deposition changed the relative intensities of these splittings, and bands associated with the FSO 3 radical, [7] formed by thermal dissociation of S 2 O 6 F 2 according to Equation (1), appear in the IR matrix spectra.S 2 O 6 F 2 is almost completely dissociated at a pyrolysis temperature of 160 8C, as demonstrated in Figure 1 (upper trace). In contrast to previous matrix experiments, [7] much weaker bands of HSO 3 F, H 2 O, CO 2 , HF, and S 2 O 5 F 2 are found in the spectra.The thermolysis products of S 2 O 6 F 2 were trapped in a Ne matrix containing 10 % of O 2 to investigate the reaction of FSO 3 radicals with molecular oxygen. Part of the IR spectrum of this experiment is displayed in Figure 1 (middle trace). It reveals a strong decrease in intensity of all bands attributed to FSO 3 and the appearance of new broad IR bands of the

A theoretical study of the thermal stability of the FS(O2)OSO2 radical and the recombination kinetics with the FSO3 radical

“…SO 2 bond dissociation enthalpy of 8.5 ± 1 kcal mol À1 which is in very good agreement with the reported one of 7.7 ± 1 kcal mol À1[15]. This value is similar to the predicted for the FS(O 2 )O-OO bond, % 10 kcal mol À1[12,13,76] but it is somewhat smaller than the estimated for CF 3 O-SO 2 at the BAC-G3MP2//B3LYP/6-311+G(3df) level, 19.1 kcal mol À1[8].…”

“…3, exhibits a strong band located at about 195 nm (e % 1840 M À1 cm À1 ) and a broad absorption band at about 345 nm (e % 600 M À1 cm À1 ). It is interesting to note that the first band lies in the wavelengths region where the SO 2 exhibits a strong absorption, near 200 nm [86], while the second one resembles the band observed near 360 nm for the weakly bonded FS(O 2 )OOO radical isolated a 6 K in an Ne matrix [13].…”

“…Species of varied stability have been postulated to participate in the reaction mechanisms, in which the fluorosulphate radical, FSO 3 , is involved. In fact, the stable species FS(O 2 )ONO [9], FS(O 2 )ONO 2 [10,11] and the labile complexes FS(O 2 )OOO [12,13], FS(O 2 )OSF 4 [14,15] and FS(O 2 ) OSO 2 [15,16] have been reported. The FSO 3 is an interesting radical formed by direct association of F atoms with SO 3 [17].…”

Dihalogenated Methylperoxy Radicals: Spectroscopic Characterization and Photodecomposition by Release of HO.

“…[26b] Furthermore,t he bands for the SÀOs tretching mode at 648.2/635.4cm À1 shifts by 18.2 cm À1 (Dv calcd = 18.1 cm À1 ). Similar to the photochemistry of CH 3 [27] subsequentU Vi rradiationo fF S(O)OOC (k) in the O 2 -dopedA r-matrix yields FS(O) 3 OOC (l) which dissociates to SO 3 (m) and FOOC (n) under irradiation conditions ( Figure 1C).…”

“…(→CH 3 SO 3 ⋅) and FSO 3 /O 2 (→FS(O) 3 OO . ), subsequent UV irradiation of FS(O)OO . (k) in the O 2 ‐doped Ar‐matrix yields FS(O) 3 OO .…”