Spectroscopic Study of the I₂ Formation from the Photolysis of Iodomethanes (CHI₃, CH₂I₂, CH₃I, and CH₂ICl) at Different Wavelengths

Abstract

Emission spectra following the photolysis of iodomethanes (CHI3, CH2I2, CH3I, and CH2ICl) at 266 nm were recorded in a slow flow cell. In addition to emission from the electronically excited species including CH (A(2)Δ, B(2)Σ(-), and C(2)Σ(+)), C2 (d(3)Πg), and atomic iodine ((4)P(o)), a series of emission bands was observed in the 12,000-19,000 cm(-1) region. The dominant structure of these emission bands was verified as the I2 B(3)Π(+)(0,u)-X(1)Σ(+)g emission at the 532 nm excitation, and the observed I2 was formed from collisions between iodine atoms generated from the C-I bond dissociation in these iodomethanes. The I2 emission spectra following the photolysis of CH2I2 at different wavelengths were acquired, and the threshold energy for the first C-I bond cleavage was determined to be 208 ± 1 kJ mol(-1). We also obtained the emission spectra of pure I2 at several visible excitation wavelengths for comparison with those from the photolysis of iodomethanes, and a least-squares global fit of the observed I2 emission bands yields more accurate anharmonicity parameters for the vibrational structure in the I2 B-X transition.

Direct photoisomerization of CH2I2vs. CHBr3 in the gas phase: a joint 50 fs experimental and multireference resonance-theoretical study

“…favouring the ylide. Finally, although photoelimination of molecular halogen was suggested for CHBr 3 and CH 2 I 2 on excitation with lowenergy UV photons, 22,52,[96][97][98] albeit in a small quantum yield for the latter molecule, the resonance form representing a carbenedihalogen complex possibly involved does not carry any significant weight (45%) along both MEPs.…”

Cavity Ring-Down Absorption Spectroscopy: Optical Characterization of ICl Product in Photodissociation of CH2ICl at 248 nm

“…Tu et al . used the laser-induced fluorescence (LIF) technique to study the photolysis of different polyhalomethanes such as CHI 3 , CH 2 I 2 , CH 3 I, and CH 2 ICl at 266 nm in a slow flow cell at ambient temperature.…”

“…The quantum yields of I* and Cl* obtained lie in between 0.22 and 0.55 at various photolysis wavelengths; among them, I* yields a larger value for each wavelength. 7,8 Tu et al 9 nm in a slow flow cell at ambient temperature. Among the emission spectra of CH, C 2 , and I 2 observed, they reported that most of the observed I 2 molecules result from the collisional product between the atomic iodine from photodissociation, instead of any molecular elimination channels.…”

Reactivity of CHI3 with OH Radicals: X-Abstraction Reaction Pathways (X = H, I), Atmospheric Chemistry, and Nuclear Safety

“…Further studies on CHI 3 aimed to characterize its photodissociation, spectroscopic, and thermodynamic properties. Tu et al 13 conducted spectroscopic measurements of four halogenated methanes including CHI 3 as photodissociation is one of the main paths of their removal in the troposphere. The authors have identified emission bands originating from the species such as CH, C 2 , and atomic and molecular iodine; in addition, accurate anharmonicity parameters for I 2 have been obtained.…”