Cavity Ring-Down Absorption Spectroscopy: Optical Characterization of ICl Product in Photodissociation of CH 2 ICl at 248 nm

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2018-10, Vol.122 (42), p.8344-8353
• Main Authors: Paredes-Roibás, Denís, Balaganesh, Muthiah, Kasai, Toshio, Gavira-Vallejo, José María, Lin, King Chuen
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.8b07012

Iodine monochloride (ICl) elimination from one-photon dissociation of CH ICl at 248 nm is monitored by cavity ring-down absorption spectroscopy (CRDS). The spectrum of ICl is acquired in the transition of B Π ← X Σ and is confirmed to result from a primary photodissociation, that is, CH ICl + hν → CH + ICl. The vibrational population ratio is determined with the aid of spectral simulation to be 1:(0.36 ± 0.10):(0.11 ± 0.05) for the vibrational levels ν = 0, 1, and 2 in the ground electronic state, corresponding to a Boltzmann-like vibrational temperature of 535 ± 69 K. The quantum yield of the ICl molecular channel for the reaction is obtained to be 0.052 ± 0.026 using a relative method in which the scheme CH Br → CH + Br is adopted as the reference reaction. The ICl product contributed by the secondary collisions is minimized such that its quantum yield obtained is not overestimated. With the aid of the CCSD(T)//B3LYP/MIDI! level of theory, the ICl elimination from CH ICl is evaluated to follow three pathways via either (1) a three-center transition state or (2) two isomerization transition states. However, the three-center concerted mechanism is verified to be unfavorable.