Infrared Characterization of the Products and Rate Coefficient of the Reaction between Criegee Intermediate CH 2 OO and HNO 3 .

The reactions of Criegee intermediates with HNO 3 are important in the polluted urban atmosphere because of their large rate coefficients and the significant concentration of HNO 3 . Employing a step-scan Fourier-transform spectrometer, we recorded infrared spectra of transient species and end products in the reaction CH 2 OO + HNO 3 upon irradiation of a flowing mixture of CH 2 I 2 /HNO 3 /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, NO 3 CH 2 OOH). Additional products from two dissociation channels were observed. Four bands at 1709, 1325, 1276, and 886 cm -1 were assigned to H 2 C(O)ONO 2 (with coproduct OH), produced from the fission of the O-O bond of internally hot NMHP (NMHP*). Simultaneous detection of H 2 CO (1746 cm -1 ), NO 2 (1617 cm -1 ), and HO 2 (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 HNO 3 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 CH 2 OO + HNO 3 by probing the temporal profiles of the formation of NMHP and NO 2 under total pressures of 40 and 70 Torr at 298 K. The rate coefficient k HNO3 = (2.4 ± 0.4) × 10 -10 cm 3 molecule -1 s -1 is less than half the only literature value, (5.4 ± 1.0) × 10 -10 cm 3 molecule -1 s -1 , reported by Foreman et al. ( Angew. Chem. Int. Ed. 2016 , 55 , 10419-10422).