ArF Laser Photodissociation Dynamics of 1,4-Pentadien-3-ol: Laser-Induced Fluorescence Observation of OH Rovibrational States

Abstract

On photoexcitation at 193 nm, the 1 (π, π*) excited 1,4-pentadien-3-ol appears to be undergoing rapid internal conversion producing a highly energized ground electronic state, which is followed by dissociation to CH 2 = CH-CH-CH=CH 2 (pentadienyl) and OH radicals as primary products. While the laser-induced fluorescence (LIF) showed that only 1.1% of the nascent OH (X 2 Π) are produced in the vibrationally excited state with v = 1, there is no OH produced with v = 2. The rotational state distribution of OH is found to fit a Boltzmann distribution, characterized by a rotational temperature, T r o t , of 1250 ′ 100 K for the v = 0 and T c o t of 1020 ′ 100 K for the v = 1 vibrational states. By measuring the Doppler spectroscopy of the v = 0 and v = 1 states of OH, an average relative translational energy of the photofragments is found to be 41.8 ′ 5.0 and 37.4 ′ 5.0 kJ mol - 1 , respectively. The real time formation of OH shows a dissociation rate constant of the 1,4-pentadien-3-ol to be (2.0 ′ 0.4) x 10 7 s - 1 . The above dissociation rate in relation to statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory suggests a resonance stabilization energy of the pentadienyl radical to be 70 kJ mol - 1 .