Issue 10, 2021

Probing BrCl from photodissociation of CH2BrCl and CHBr2Cl at 248 nm using cavity ring-down spectroscopy

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+g and B3Π (0+) ← X1Σ+ transitions, respectively. Their corresponding spectra were simulated for assignment of rotational lines at a given vibrational level. The quantum yields for Br2 eliminated 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 Br2 fragment, but not the BrCl fragment in the experiments. An ab initio theoretical 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 Br2 and 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 Br2 spectrum, explaining why BrCl fragments cannot be detected in the photolysis of CHBr2Cl.

Graphical abstract: Probing BrCl from photodissociation of CH2BrCl and CHBr2Cl at 248 nm using cavity ring-down spectroscopy

Article information

Article type
Paper
Submitted
08 Dec 2020
Accepted
13 Feb 2021
First published
15 Feb 2021

Phys. Chem. Chem. Phys., 2021,23, 6098-6106

Probing BrCl from photodissociation of CH2BrCl and CHBr2Cl at 248 nm using cavity ring-down spectroscopy

B. Muthiah, T. Kasai and K. Lin, Phys. Chem. Chem. Phys., 2021, 23, 6098 DOI: 10.1039/D0CP06350A

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