The OH Product State Distribution from the Photodissociation of Hexafluoroacetylacetone

Abstract

Hexafluoroacetylacetone (1,1,1,5,5,5-hexafluoro-2,4-pentanedione) in the supersonic jet, which exists as its enolic form, has been found to give the OH radical as a result of photodissociation induced by the π−π* transition. The nascent OH product state distributions are measured at the photolysis wavelengths of 293.5 and 266 nm. As in the case of the acetylacetone photodissociation, no fluorescence is observed even in the energy region near the origin, indicating ultrafast nonradiative decay of the excited state. The OH fragment is found to be vibrationally cold, and its rotational state distributions are peaked at N = 3 at both pump wavelengths used in this work. The OH fragment is slightly more populated in the 2Π3/2 state than it is in the 2Π1/2 state. The Π-/Π+ ratios are found to be unity, suggesting that there is no preferential alignment of the pπ electronic orbital of the OH radical with respect to its plane of rotation. The strength of the intramolecular hydrogen bond and its dynamic role in the chemical bond dissociation of hexafluoroacetylacetone are discussed and compared with the acetylacetone photodissociation dynamics.