Chlorine atom formation dynamics in the dissociation of halogenated pyridines after photoexcitation at 235 nm: A resonance enhanced multiphoton ionization-time of flight (REMPI-TOF) study

•First results on Cl atom formation in the photodissociation of halogenated pyridines.•Absorption spectra for both the compounds were also obtained.•Various mechanisms for Cl atom formation are reported.•Excited state calculation is performed for various states.•Fluorine substitution increases the cross-over possibility from π-π* to π-σ* state.

The photodissociation dynamics of halogen substituted pyridines, namely, 3-chloropyridine (ClPy) and 3-chloro-2,4,5,6-tetrafluoropyridine (ClFPy), has been studied around 235 nm by detecting chlorine atoms in their spin orbit states Cl(2P3/2) and Cl∗(2P1/2) using the REMPI-TOF technique. We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio, for chlorine atom elimination channels. The TOF profiles for Cl and Cl∗ are found to be independent of laser polarization suggesting a zero value for β, within the experimental uncertainties. For 3-chloropyridine, the average translational energies for Cl and Cl∗ elimination channels are determined to be 3.7 ± 1.0 and 7.0 ± 1.5 kcal/mol, respectively. Similarly, for 3-chloro-2,4,5,6-tetrafluoropyridine, the average translational energies for Cl and Cl∗ elimination channels are determined to be 8.0 ± 1.5 and 9.0 ± 1.5 kcal/mol, respectively. The theoretical calculation suggests that the fluorine substitution increases the possibility of cross over to the π-σ∗ state from the initially prepared π-π∗ state.

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