Photodissociation of CH2BrCHBrC(O)Cl at 248 nm: probing Br2as the primary fragment using cavity ring-down spectroscopy

The photodissociation of 2,3-dibromopropionyl chloride (CH2BrCHBrC(O)Cl, 2,3-DBPC) at 248 nm was carried out to study Br2as the primary molecular product in the B3Π+0u← X1Σ+gtransition using cavity ring-down absorption spectroscopy. The rotational spectra (v′′ = 0-2) were acquired and assigned with the aid of spectral simulation. It is verified that the obtained Br2fragment is attributed to the one-photon dissociation of 2,3-DBPC and is free from contributions of secondary reactions. The vibrational ratio of the Br2population ofv(0):v(1):v(2) is equal to 1:(0.58 ± 0.12):(0.23 ± 0.09), corresponding to the Boltzmann vibrational temperature of 623 ± 38 K. The quantum yield of Br2eliminated from 2,3-DBPC is estimated to be 0.09 ± 0.04. The dissociation pathways of 2,3-DBPC and its potential energy surfaces were calculated using density functional theory. By employing the CCSD(T)//M062X/6-31+g(d,p) level of theory, transition state barriers and corresponding reaction energies were calculated for the Br, Cl, Br2, BrCl, HBr and HCl elimination channels. The unimolecular rate constant for Br2elimination was determined to be 2.09 × 105s?1using Rice-Ramsperger-Kassel-Marcus (RRKM) theory, thus explaining the small quantum yield of the Br2channel. ? the Owner Societies 2021.