IBER 2023

Photodissociation dynamics and alignment of CH2BrI in the third absorption band at 193 nm

6 Sept 2023, 18:35

1h

Department of Physics, University of Coimbra

Poster Communication Poster Session

Speaker

Prof. Luis Bañares (Universidad Complutense de Madrid)

Description

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).