Photodissociation Dynamics of Phenol

The major photodissociation channel of phenol in UV region in gas phase is OH bond fission. In this work, we focus on the photolysis wavelength around 265~275 nm with ionization wavelength at 118 nm. By the advantage of our homemade multi-mass system, it is easy to tell the difference between dissociation, dissociative ionization of hot molecule, and dissociative ionization of fragment. In phenol photodissociation results, these three channels are founded by fragments C6H5O (m/z 93), C5H6 (m/z 66), and C5H5 (m/z 65). Fragments C6H5O are from hydrogen elimination of phenol. Fragments C5H6 and C5H5 are from dissociative ionization of hot phenol and fragments C6H5O. We use fragments C6H5O and C5H5, which is from C6H5O, to calculate the total kinetic energy release of hydrogen elimination channel, and found that it is bimodal. The slow peak is located at 2000 cm-1 and is from the dissociation of highly vibrational phenol ground state. The fast peak is around 7000 cm-1 and is determined from phenol excited state dissociation. The lifetimes of phenol under photolysis wavelength 269.291 and 275.113 nm are about 96 and 62 μs, respectively, which are much longer than the pump-probe delay time of traditional potodissociation technique. In this study, we prove that it is impossible to detect dissociation channel from such long lifetime of highly vibrational phenol ground state by using traditional technique. We also try to figure out whether the excited A ̃ state phenoxyl radical is produced or not. According to our results, we did not detect the signal of A ̃ state phenoxyl radical. This may due to two possible reasons. First, A ̃ state phenoxyl radical is not generated under photodissociation at 193 nm. Second, the lifetime of A ̃ state phenoxyl radical is too short to be detected in our system.