Computational investigations on the HO + CHBrO reaction: mechanisms, products, and atmospheric implications.

Using quantum chemistry methods, mechanisms and products of the CHBrO + HO reaction in the atmosphere were investigated theoretically. Computational result indicates that the dominant product is CHBrOOH + O formed on the triplet potential energy surface (PES). While CBrO + OH + HO produced on the singlet PES is subdominant to the overall reaction under the typical atmospheric condition below 300 K. Due to higher energy barriers surmounted, other products including CBrO + HO, CBrO + HOH, CHO + HOBr, CHBrO + HO + Br, and CHBrOH + O make minor contributions to the overall reaction. In the presence of OH radical, CHBrOOH generates CHBrO and CBrO + HO subsequently, which enters into new Br-cycle in the atmosphere. The substitution effect of alkyl group and halogens plays negligible roles to the dominant products in the RO + HO (X = H, CH, CHOH, CHF, CHCl, CHBr, CHCl, and CHBr) reactions in the atmosphere.