UV Photolysis OF ortho-halogenated thiophenol : The role of hydrogen bonding in photodissociation dynamics

Abstract

The experimental techniques of velocity-map ion imaging and resonance-enhanced multiphoton ionization spectroscopy have been used to investigate the dynamics of D atom loss processes from gas phase ortho-halogenated thiophenol-(d1), following photolysis at many wavelengths within the range of vibronic bands of S1 electronic state and further higher excited state. In case of 2-fluorothiophenol-(d1), a dependence of the relative yields of two reaction channels ( ground, X and the first excited state, A of 2-FC6H4S∙ radical ) is observed within S1 (ππ*) region. We’ve expected that molecular planarity by intramolecular hydrogen bonding of F∙∙∙D affects bifurcation dynamics of the second CI, considering previous finding. And relative contribution of S1 (ππ*) & S2 (nσ*) electronic states is investigated along energetics. To shed light on this behavior, potential energy surface (PES) along related reaction coordinates (SD elongation & CSD bending angle & CCSD torsion angle), vertical excitation energy, Frank-Condon simulation and radical energetics are performed using CASPT2, SA-CASSCF, TD-DFT levels. According to chemical intuition, we are doing experiment on effects strength of hydrogen bond upon fragmentation mechanism using 2-chlorothiophenol-(d1). Comparison electronic spectrum of S1 (ππ*) state and branching ratio with the results of 2-fluorothiophenol-(d1) will serve to highlight intramolecular hydrogen bonding effect on photodissociation dynamics.