Photodissociation is an important loss mechanism for atmospheric hydroperoxides (R-O-OH) leading to the production of OH radicals via the rupture of the weak O-O bond. Photodissociation can either occur through electronic excitation to a repulsive excited electronic state or, alternatively, through unimolecular dissociation on the ground electronic surface. Here we present the first results from the unimolecular dissociation of peroxyformic acid (PFA) initiated by exciting the molecule to its fifth OH stretching overtone state (6nOH) occurring in the vicinity of 615nm. The OH stretch in PFA exhibits a large anharmonicity due to internal hydrogen bonding and we identify the 6nOH vibrational level through a Birge-Spooner plot using information available for the lower overtones. Based on the estimated heat of formation of PFA and its fragments, the O-O bond dissociation energy (D0) in PFA is estimated to be 44.8 kcal/mol. Thus, exciting room temperature PFA molecules at 615 nm is expected to leave the OH + HCO2 fragments with roughly 3.3 kcal/mol of available energy. We have used laser induced fluorescence (LIF) to detect the OH fragment from this near threshold unimolecular reaction and have determined the partitioning of the available energy in to its rotational and translational degrees of freedom. In addition, the LIF probe provides information about partitioning of the energy into the OH fragment’s spin-orbit and lambda-doublet states. By applying energy and momentum conservation, we can determine the translational and internal energy in the partner HCO2 fragment. These results, along with the insight they provide regarding the unimolecular dissociation dynamics of HC(O)OOH, will be presented.

Vibrational overtone induced unimolecular dissociation of peroxyformic acid

2019 Fall National Meeting

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