Infrared emission from UV-irradiated mixtures of CH2I2 and O2 probed with a step-scan FTIR spectrometer

Chen, Ting-Yu

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https://hdl.handle.net/2142/100841 Copy

Description

Title

Infrared emission from UV-irradiated mixtures of CH2I2 and O2 probed with a step-scan FTIR spectrometer

Author(s)

Chen, Ting-Yu

Contributor(s)

Lee, Yuan-Pern

Issue Date

2018-06-19

Keyword(s)

Dynamics and kinetics

Abstract

The Criegee intermediates, carbonyl oxides proposed by Criegee in 1949 as key intermediates in the ozonolysis of alkenes, play important roles in organic chemistry and atmospheric chemistry. The simplest Criegee intermediate is CH2OO. In the reaction of O3 with C2H4, some CH2OO thus produced are internally excited so that they decompose to form OH, CO, CO2, and other compounds. Recently a new scheme for production of CH2OO in laboratories, ultraviolet (UV) irradiation of diiodomethane (CH2I2) in O2, has enabled direct detection of CH2OO with various methods and stimulated active research on Criegee intermediates. Even though ∼ 25% of CH2OO was reported to decompose at pressure smaller than 60 Torr,a and infrared absorption of internally excited CO and CO2 was reported,b no investigation on the dynamics of the decomposition products in the reaction CH2I + O2 has been reported. We employed a step-scan Fourier-transform infrared (FTIR) spectrometer to record temporally resolved emission upon irradiation of mixtures of CH2I2, O2, and Ar at 248 and 308 nm. IR emission of CO, CO2, OH, CH2I, and H2CO in the region 1860 − 4900 cm−1was recorded. At total pressure 8 Torr and irradiation wavelength 248 nm, rotationally resolved lines of CO (v ≤ 11, J ≤ 19) in region 1860 − 2300 cm−1were observed; the rotational distribution is Boltzmann with temperature near 300 K, but the vibrational distribution is bimodal, with two components having averaged vibrational energies of 99 and 18 kJ mol−1 . Emission of OH (v ≤ 3, J ≤ 5.5) in region 2980 − 3600 cm−1was observed with ambient rotational distribution and average vibrational energy of 41 kJ mol−1 . The branching ratio of CO : OH is 60:40. Emission of highly internally excited CO2 was also observed; its average internal energy was estimated. The effects of pressure and irradiation wavelength on the emission of these species will be discussed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100841

DOI

10.15278/isms.2018.TD04

Copyright and License Information

Copyright 2018 Ting-Yu Chen

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