Probing BrCl from photodissociation of CH2BrCl and CHBr2Cl at 248 nm using cavity ring-down spectroscopy
Journal
Physical Chemistry Chemical Physics
Journal Volume
23
Journal Issue
10
Pages
6098-6106
Date Issued
2021
Author(s)
Muthiah B
Kasai T
KING-CHUEN LIN
Abstract
Photodissociation of di- and tri-halogenated methanes including CH2BrCl and CHBr2Cl at 248 nm was investigated using cavity ringdown absorption spectroscopy (CRDS). The spectra of the BrCl(v′′ = 2, 3) and Br2(v′′ = 1, 2) fragments were probed over the wavelength range of 594.5-596 nm in the B3Π+0u← X1Σ+gand B3Π (0+) ← X1Σ+transitions, respectively. Their corresponding spectra were simulated for assignment of rotational lines at a given vibrational level. The quantum yields for Br2eliminated from CHBr2Cl and BrCl from CH2BrCl were determined to be 0.048 ± 0.018 and 0.037 ± 0.014, respectively. The photodissociation of CHBr2Cl yielded only the Br2fragment, but not the BrCl fragment in the experiments. Anab initiotheoretical method based on the CCSD(T)//B3LYP/6-311g(d,p) level was employed to evaluate the potential energy surface for the dissociation pathways to produce Br2and BrCl from CHBr2Cl, which encountered a transition state barrier of 445 and 484 kJ mol?1, respectively. The corresponding RRKM rate constants were calculated to show that the branching ratio of (Br2/BrCl) is ?20. The BrCl spectrum is expected to be obscured by the much larger Br2spectrum, explaining why BrCl fragments cannot be detected in the photolysis of CHBr2Cl. ? the Owner Societies 2021.
Subjects
Absorption spectroscopy; Chlorine compounds; Light measurement; Photodissociation; Photolysis; Potential energy; Quantum chemistry; Rate constants; Branching ratio; Cavity ring down spectroscopies; Cavity ring-down; Dissociation pathways; Rotational lines; Transition state; Vibrational levels; Wavelength ranges; Bromine compounds; ab initio calculation; absorption spectroscopy; article; cavity ring down spectroscopy; conformational transition; dissociation; halogenation; photolysis; quantum yield; rate constant; simulation
Type
journal article