BARC/PUB/2018/0122

 
 

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

 
     
 
Author(s)

SenGupta, S.; Saha, A.; Awadhesh Kumar; Naik, P. D.
(RPCD)

Source

ChemistrySelect, 2018. Vol. 3 (10): pp. 2781-2788

ABSTRACT

Cl 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 (TDDFT) 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.

 
 
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