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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