Photodissociation Dynamics of BrCH2CH2ONO at 193 nm: Probing the Unimolecular Dissociation Pathways of the CH2CH2ONO Radical
The University of Chicago
The purpose of this study is to explore the photodissociation dynamics of BrCH2CH2ONO at 193 nm. The experiments are designed to use BrCH2CH2ONO as a photolytic precursor to generate the CH2CH2ONO radical, a radical of potential importance in atmospheric chemistry, using a crossed laser-molecular beam scattering apparatus with electron bombardment. This radical could be a model system of the interaction between a tropospherically abundant molecule (like NO2) and an unsaturated hydrocarbon (like CH2CH2). Past studies have shown that at 351 nm the O-NO bond is cleaved, however, we see that excitation at 193 nm raises BrCH2CH2ONO to an excited state repulsive in the C-Br bond that allows us to photolytically cleave the C-Br bond. Radicals are difficult to study under bulk conditions due to their high reactivity, so employing collision-free conditions allows for the study of particular radicals like CH2CH2ONO. Initial experiments show that C-Br photofission occurs in some of the photoexcited molecules, so we can study the subsequent unimolecular decomposition of the CH2CH2ONO radical. With the aid of electronic structure theory (Gaussian 09), two different product channels with relatively low barriers to dissociation have been determined: one producing NO and the other producing NO2. Characterization of the unimolecular dissociation pathways of the CH2CH2ONO radical allows for the determination of the unique product branching ratios between different channels, and an overall greater understanding of the potentially atmospherically relevant interaction between NO2 and CH2CH2.