Kinetics of the Gas-Phase Reaction of Hydroxyl Radicals with Dimethyl Methylphosphonate (DMMP) over an Extended Temperature Range (273-837 K)

Xiaokai Zhang; Daria A Barkova; Pavel V Koshlyakov; Ilya E Gerasimov; Evgeni N Chesnokov; Lev N Krasnoperov

doi:10.3390/molecules27072301

Kinetics of the Gas-Phase Reaction of Hydroxyl Radicals with Dimethyl Methylphosphonate (DMMP) over an Extended Temperature Range (273-837 K)

Molecules. 2022 Apr 1;27(7):2301. doi: 10.3390/molecules27072301.

Authors

Xiaokai Zhang¹, Daria A Barkova², Pavel V Koshlyakov², Ilya E Gerasimov², Evgeni N Chesnokov², Lev N Krasnoperov¹

Affiliations

¹ Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA.
² Institute of Chemical Kinetics and Combustion, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk, Russia.

Abstract

The kinetics of the reaction of hydroxyl radical (OH) with dimethyl methylphosphonate (DMMP, (CH₃O)₂CH₃PO) (reaction 1) OH + DMMP → 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.

Keywords: DMMP; V-shaped temperature dependence; dimethyl methylphosphonate; hydroxyl; kinetics; laser photolysis; pressure dependence; radical; transient absorption.