Abstract

We investigate the photolytic production of two radical intermediates in the reaction of OH with propene, one from addition of the hydroxyl radical to the terminal carbon and the other from addition to the center carbon. In a collision-free environment, we photodissociate a mixture of 1-bromo-2-propanol and 2-bromo-1-propanol at 193 nm to produce these radical intermediates. The data show two primary photolytic processes occur: C–Br photofission and HBr photoelimination. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling bromine atoms, yielding the distribution of kinetic energies of the nascent C3H6OH radicals + Br. Resolving the velocity distributions of Br(2P1/2) and Br(2P3/2) separately with 2 + 1 REMPI allows us to determine the total (vibrational + rotational) internal energy distribution in the nascent radicals. Using an impulsive model to estimate the rotational energy imparted to the nascent C3H6OH radicals, we predict the percentage of radicals having vib...

Highlights

  • The oxidation of unsaturated hydrocarbons by the hydroxyl radical is an important reaction in both atmospheric and combustion chemistry

  • The addition of the hydroxyl radical to propene offers a wider variety of products than the addition of OH to ethene as the addition to propene may occur via two pathways: addition to the terminal carbon and addition to the center carbon

  • We report the measured speed and angular distributions of the recoiling bromine atoms as well as the resulting distribution of kinetic energies imparted to the fragments upon dissociation

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Summary

Introduction

The oxidation of unsaturated hydrocarbons by the hydroxyl radical is an important reaction in both atmospheric and combustion chemistry. Our experiment focuses on the reaction of OH with propene, a simple unsaturated hydrocarbon with two sites at which addition of the OH may occur. Ethene and propene flame studies have given evidence for the presence of enols, which has increased interest in the product branching resulting from OH-initiated oxidation.[35,36]. The addition of the hydroxyl radical to propene offers a wider variety of products than the addition of OH to ethene as the addition to propene may occur via two pathways: addition to the terminal carbon and addition to the center carbon. Experimental results show the branching between the center and terminal carbon addition favors the terminal carbon, with approximately 65−75% of additions leading to terminal carbon addition.[37−39] Theory has given similar results, yielding predictions of ∼65% of additions to the terminal carbon.[40,41]

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