Abstrakt
UV PHOTOFRAGMENTATION OF ISOLATED ALKYL CHLORIDES: VELOCITY MAP IMAGING AND MOLECULE DYNAMICS STUDY I.S.Vinklárek(a), J.Suchan(b), J.Rakovský(a), K.Moriová(a), V.Poterya(a), P.Slavíček(b), M.Fárník(a) (a) Department of Dynamics of Molecules and Clusters, J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejskova 2155/3, 182 23 Prague 8 - Czech Republic (b) Department of Physical Chemistry, University of Chemistry and Technology, Prague, Technicka 5, 16628, Prague - Czech Republic This study follows up on our recent research of methyl chloride (CH3Cl), in which we demonstrated different dynamics of photodissociation in the clusters compared with isolated molecules [1,2], and molecule dynamics (MD) simulation of freon photodissociation [3].
Radiation-induced dissociation in supersonic beam of three selected alkyl chlorides, i.e., n-propyl-, i-propyl- and n-pentyl-chloride, were investigated by velocity map imaging combined with MD simulations [3]. The molecule fragmentation was triggered by 193 nm excitation to the dissociative A-band region followed by resonantly enhanced ionization probe pulse to detect ground or spin-orbit excited Cl-fragments.
The energy-resolved distributions show that Cl-fragment kinetic energy is almost independent on the paternal molecule and that around 50% of the available energy after photodissociation is stored in inner modes of hydrocarbon fragment compared to only 10% in the case of CH3Cl. This agrees well with both MD simulations and classical spectator model, which assumes low rigidity of investigated molecules.
The angle-resolved distributions of Cl fragments combined with quantum yield ratio of Cl*/Cl fragments indicate according to model described in [2] enhanced spin-orbital coupling in A-band region correlated with hydrocarbon group prolongation. This leads to strong absorption to 3Q0 state (30%) and around 60% probability of intersystem crossing between 1Q1 and 3Q0 states in both directions.
MD simulation of spin-orbital coupling within the dissociation model are currently in progress. These outcomes have impact on our future experiments with alkyl chlorides incorporated in water cluster environment mimicking the atmospheric aerosols.
References [1] I.S. Vinklárek, J.
Rakovský, V. Poterya and M.
Fárník, J. Phys.
Chem. A 124, 38 (2020). [2] D.
Townsend, S.K. Lee, A.G.
Suits, J. Phys.
Chem. A 108, 39 (2004). [3] J.
Suchan, D. Hollas, B.F.E.
Curchod, and P. Slavíček, Faraday discussions 212 (2018).