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The photodissociation of dihalomethanes have received significant attention due to its role in producing pollutant species and ozone depletion.[1] Moreover, CH$_2$BrI presents an intricate structure of excited electronic states and a high bond selectivity. For instance, the A absorption band was attributed to C-I dissociation, while the A' band corresponds to C-Br bond fission.[2] However, the third band (B band) has not been investigated deeply.[3]
The detection of atomic iodine I($^2$P$_{3/2,1/2}$) and bromine Br($^2$P$_{3/2,1/2}$), using a combination of laser pump-and-probe and slicing imaging techniques coupled to (2+1) REMPI, show the presence of two main contributions. Combining the experimental results with high ab initio calculations, we assigned the faster contribution to a predissociation through the 9A' state. Meanwhile, the slower contribution was attributed to a secondary dissociation after absorbing a second 193 nm photon. Due to geometrical restrictions, this process was favored through the C-Br dissociation rather than the C-I bond cleavage. The calculated anisotropy parameter supports the proposed mechanism.
References
[1] A. Saiz-Lopez et al., Chem. Rev. 112, 1773 (2012); W. R. Simpson et al., Chem. Rev. 115, 4035 (2015).
[2] S. Marggi Poullain et al., Phys. Chem. Chem. Phys. 20, 3490 (2018).
[3] L. J. Butler et al., J. Chem. Phys. 86, 2051 (1987).
