RESUMEN
The kinetics of the reaction of hydroxyl radical (OH) with dimethyl methylphosphonate (DMMP, (CH3O)2CH3PO) (reaction 1) OH + DMMP â products (1) was studied at the bath gas (He) pressure of 1 bar over the 295-837 K temperature range. Hydroxyl radicals were produced in the fast reaction of electronically excited oxygen atoms O(1D) with H2O. The time-resolved kinetic profiles of hydroxyl radicals were recorded via UV absorption at around 308 nm using a DC discharge H2O/Ar lamp. The reaction rate constant exhibits a pronounced V-shaped temperature dependence, negative in the low temperature range, 295-530 K (the rate constant decreases with temperature), and positive in the elevated temperature range, 530-837 K (the rate constant increases with temperature), with a turning point at 530 ± 10 K. The rate constant could not be adequately fitted with a standard 3-parameter modified Arrhenius expression. The data were fitted with a 5-parameter expression as: k1 = 2.19 × 10-14(T/298)2.43exp(15.02 kJ mol-1/RT) + 1.71 × 10-10exp(-26.51 kJ mol-1/RT) cm3molecule-1s-1 (295-837 K). In addition, a theoretically predicted pressure dependence for such reactions was experimentally observed for the first time.