Dynamics of OH formation in the photodissociation of enolic-acetonylacetone at 193nm

Abstract

Abstract The photodissociation dynamics of enolic-acetonylacetone (H3C C(O) CH2 CH C(OH) CH3), in gas phase, is studied using Laser Photolysis–Laser Induced Fluorescence (LP–LIF) technique at room temperature. The nascent state distribution of the OH radical is probed formed after photo-excitation of the parent molecule to its π C = C − π C = C * state using 193 nm laser light. The ro-vibrational distribution of the nascent OH photofragment is measured using LIF in collision free conditions. The rotational distribution is Boltzmann-like, and characterized by a single rotational temperature of 650 ± 50 K. The spin-orbit and Λ-doublet ratios of OH fragment formed in the dissociation process are also determined. For OH producing channel, the average translational energy partitioned into the photofragment pairs in the center-of-mass co-ordinate is found to be 25.0 ± 4.0 kcal/mol, corresponding to a fT value of 0.43. The experimental studies along with theoretical calculations employing time-dependent density functional theory (TD-DFT) along with ab initio molecular orbital (MO) theory suggest that the initially prepared π C = C − π C = C * state crosses over to a nearby σ* repulsive state along the C O bond, from where the dissociation takes place. The dynamics of OH formation is compared with that of acetylacetone photodissociation and effect of H-bonding is discussed.