Cl‐Radical Formation in UV Photodissociation of Tetrachlorocyclopropene: A REMPI Study

Abstract

AbstractCl atoms in both ground [Cl(2P3/2)] and excited spin orbit states [Cl*(2P1/2)] were detected as photodissociation products of tetrachlorocyclopropene (TCCP) at 235 nm by Resonance Enhanced Multiphoton Ionisation – Time of Flight (REMPI‐TOF) technique. From the experimental REMPI‐TOF profile, the anisotropy parameter (β) for both the channels was found to be nearly zero. TOF profiles of both the Cl and Cl* channels could be fitted into single component translational energy distributions, with average energy of 7.7 and 8.6 kcal mol−1 respectively. Time Dependent – Density Functional Theory (TD‐DFT) calculations using mpw1pw91/aug‐cc‐pVTZ level of theory suggested that, near 235 nm, the initially excited nCl—π* state of TCCP may cross over to the nearby dissociative states, from where Cl/Cl* can be formed directly. Otherwise, the excited molecules may relax rapidly to the ground state, where the lowest energy dissociation channel is the C—C bond cleavage (ΔH=30.4 kcal mol−1), as C—Cl bond breaking channels need high energy (ΔH=73.7 kcal mol−1 and 85.5 kcal mol−1). The biradical product of C—C bond breaking may rearrange to tetrachloroallene molecule with four equivalent C—Cl bonds, which can subsequently undergo C—Cl bond dissociation to produce Cl/Cl* atoms.