V-shaped temperature dependences and pressure dependence of elementary reactions of hydroxyl radicals with several organophosphorus compounds

Author

Xiaokai Zhang, New Jersey Institute of TechnologyFollow

Document Type

Dissertation

Date of Award

5-31-2023

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

Lev N. Krasnoperov

Second Advisor

Alexei Khalizov

Third Advisor

Farnaz A .Shakib

Fourth Advisor

Xianqin Wang

Fifth Advisor

Mirko Schoenitz

Abstract

Organophosphorus compounds have brought increasing attention since they are widely used as flame-retardants, which can take effect in combustion via reactions with reactive radicals. These reactions are influenced by variables such as temperature and pressure, resulting in a temperature and pressure dependent rate constant. Studying this reaction kinetics has great importance in both combustion reaction and atmospheric environment.

This study is focused on kinetics of several elementary reactions of combustion importance. The kinetics of hydroxyl radicals were studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 295 - 837 K temperature range and the 1 - 30 bar pressure range. Hydroxyl radical was generated by photolysis of N₂O/H₂O/He. The time-resolved OH absorption profiles were fitted by different models to get the reaction rate constant at corresponding reaction conditions.

Three such reactions were experimentally studied, reactions of OH with trimethyl phosphate (TMP), dimethyl methyl phosphonate (DMMP), and trimethyl phosphite (TMPi). All three compounds exhibit the features predicted for elementary reactions with "negative" (submerged) barriers, where V-shaped temperature dependencies are observed (negative at low and positive at elevated temperatures). For reaction OH + DMMP, bath gas pressure dependence was also observed (1 ? 30 bar, He). These reactions are suggested to have "transition states" with the ground state lying below the ground state of the reactants, presumably caused by the "long-range electrostatic interactions" in the "transition states".

Recommended Citation

Zhang, Xiaokai, "V-shaped temperature dependences and pressure dependence of elementary reactions of hydroxyl radicals with several organophosphorus compounds" (2023). Dissertations. 1673.
https://digitalcommons.njit.edu/dissertations/1673