Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism.

Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism.
Chemosphere. 2020 Aug;253:126747
Authors: Deng X, Tang Y, Song X, Liu K, Gu Z, Zhang B
Abstract
The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and time-resolved ion-yield (TR-IY) techniques. Following excitation to the origin of S1 (ππ∗) state of m- and o-FPhOH, H atoms elimination mediated by tunneling through the potential barrier under the S1 (ππ∗)/S2 (πσ∗) conical intersection (CI) has been observed as a Gaussian feature signal centered at a total kinetic energy release (TKER) of ∼6000 cm-1 for both molecules. The quantum tunneling mechanism has been identified as the main decay pathway of S1 state for m-FPhOH, and the tunneling lifetime of 2.1 ns has been obtained from the TR-VMI measurements of H fragments. This tunneling mechanism is further confirmed by the studies on the selective O-H deuterated species, m-FPhOD, and consolidated by our theoretical calculations. However, the photolysis dynamics is quite different for the photoexcited o-FPhOH. The much lower yield of the H atoms originating from tunneling hinders the extraction of a reliable tunneling lifetime for o-FPhOH. Our theoretical calculations exhibit a broader and higher potential barrier exists beneath the S1/S2 CI of o-FPhOH, which increase the difficulty f...

Source: Chemosphere - May 30, 2020 Category: Chemistry Authors: Deng X, Tang Y, Song X, Liu K, Gu Z, Zhang B Tags: Chemosphere Source Type: research