The effect of internal energy partitioning on the reactivity of radical intermediates

The first step in the atmospheric oxidation pathway for a volatile organic compound (VOC) is often the reaction with a radical such as hydroxyl or NO 3. The reaction results in a highly reactive radical intermediate which can either undergo isomerization or dissociation, or it can undergo additional oxidation reactions until it enters the condensed phase in the form of an aerosol. It is imperative to understand the mechanisms and relative reaction rates of these initial oxidation steps. This thesis describes our investigation of two radical species common in oxidation pathways. These highly reactive radicals are generated under vacuum by photodissociation of a halogenated precursor. We used a combination of a velocity map imaging apparatus and a crossed laser-molecular beam scattering apparatus to detect the velocities of photoproducts of the initial dissociation and the products of the secondary dissociation of internally excited photofragments. The measurement of the kinetic energy of the dissociating fragments under collisionless conditions allows for the calculation of the internal energy of the radicals, allowing us to characterize the behavior of the radicals as a function of this internal energy.;The generation of the radicals by photodissociation is a commonly used technique for producing radicals in high yield without affecting its subsequent dynamics. However, in some cases the photodissociation can generate a large amount of rotation in the resulting radical, particularly when the halogen atom in the photolytic precursor is in an off-center position. We introduce a recently proposed modified impulsive model for approximating the rotational energy imparted to the radical, and make predictions about how the subsequent reaction pathways of the radical may be affected by this rotation. We discuss our results of the investigation of the photodissociation of acetyl chloride to Cl + CH3CO, and the photodissociation of 2-bromoethanol-d4 to Br + CD2CD2OH, and how that photodissociation affects the subsequent dissociation of internally excited acetyl radicals and 2-hydroxyethyl radicals.