Photodissociation of tert-butyl hypochlorite and decomposition of the tert-butoxy radical fragment

The photochemistry of tert-butyl hypochlorite (TBOCl) has been studied in a molecular beam by photofragment translational spectroscopy. After laser excitation at 248 or 308 nm, the TBOCI molecule decays exclusively into a tert-butoxy radical (TBO) and a Cl atom. The photolysis at 248 nm releases almost- equal-to 60% of the available energy into the photofragment recoil which is highly anisotropic (beta = 1.9 +/- 0. 1), implying a direct dissociation mechanism and an electronic transition dipole moment mu over arrow pointing right in the parent molecule that is oriented along the O-Cl bond. Approximately 90% of the nascent TBO radicals formed at 248 nm have sufficient internal energy to undergo a secondary decay into methyl radicals and acetone, while at 308 nm TBO is stable. From a comparison of the time-of-flight distributions of the primary fragments Cl and TBO and on the basis of the dissociation energy D0(1)(TBO - Cl) = 50 kcal/mol of the primary reaction, the threshold energy for the unimolecular decay of TBO is found to be E0 = 20 +/- 3 kcal/mol, a value which is higher than the previously reported gas kinetic activation energy E(a) = 15 kcal/mol.