Affiliations: Department of Chemistry, University of Warwick, Coventry, UK
Note:  Current address: Lawrence Berkeley National Laboratories, University of California, Berkeley, CA 94720, USA.
Note:  Current address: School of Chemistry, University of Bristol, Cantocks Close, BS8 1TS, UK.
Note:  Corresponding author: Vasilios G. Stavros, Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK. E-mail: [email protected]
Abstract: This work brings together previous work on catechol (1,2-dihydroxybenzene) and resorcinol (1,3-dihydroxybenzene) with recent results from experiments on hydroquinone (1,4-dihydroxybenzene). The experiments utilise time-resolved ion yield and velocity map imaging techniques to demonstrate how the position of the OH functional groups influences the excited state dynamics of these molecules. The mechanisms responsible for these dynamics are explored, with the focus on H-atom tunnelling mediated photodissociation. In all cases, tunnelling occurs beneath a conical intersection formed between the excited 11ππ* state and the 11πσ* state, which is dissociative along the O–H stretch coordinate. Tunnelling beneath this barrier yields high kinetic energy (~5000–7000 cm−1) H-atoms. The excited state lifetime of these molecules ranges from hundreds of femtoseconds to several nanoseconds and is found to be dependent on excitation energy as well as the relative positions of the OH functional groups.