Infrared Characterization of the Products and Rate Coefficient of the Reaction between Criegee Intermediate CH2OO and HNO3

The reactions of Criegee intermediates with HNO3 are important in the polluted urban atmosphere because of their large rate coefficients and the significant concentration of HNO3. Employing a step-scan Fourier-transform spectrometer, we recorded infrared spectra of transient species and end products in the reaction CH2OO + HNO3 upon irradiation of a flowing mixture of CH2I2/HNO3/N-2/O-2 at 308 nm. Eight bands at 1686, 1426, 1348, 1294, 1052, 965, 891, and 825 cm(-1) were assigned to the absorption of the adduct nitrooxymethyl hydroperoxide (NMHP, NO3CH2OOH). Additional products from two dissociation channels were observed. Four bands at 1709, 1325, 1276, and 886 cm(-1) were assigned to H2C(O)ONO2 (with coproduct OH), produced from the fission of the O-O bond of internally hot NMHP (NMHP*). Simultaneous detection of H2CO (1746 cm(-1)), NO2 (1617 cm(-1)), and HO2 (1392 and 1098 cm(-1)) indicated a direct cleavage of the N-OC and C-OO bonds of NMHP*. The relative yields of these three channels in pressure range 10-150 Torr were estimated. At 10 Torr, the absorption of internally excited HNO3 near 885 and 1320 cm(-1) was also detected at an early stage of the reaction. We investigated also the rate coefficient of the reaction CH2OO + HNO(3 )by probing the temporal profiles of the formation of NMHP and NO2 under total pressures of 40 and 70 Torr at 298 K. The rate coefficient k(HNO3) = (2.4 +/- 0.4) x 10(-10 )cm(3) molecule(-1) s(-1) is less than half the only literature value, (5.4 +/- 1.0) x 10(-10) cm(3) molecule(-1) s(-1), reported by Foreman et al. (Angew. Chem. Int. Ed. 2016, 55, 10419-10422).