Absorption Spectrum and Absolute Absorption Cross Sections of CH₃O₂ Radicals and CH₃I Molecules in the Wavelength Range 7473–7497 cm^–1

Abstract

The absorption spectrum of CH3O2 radicals and CH3I molecules has been measured in the range 7473-7497 cm(-1). CH3O2 radicals have been generated by 248 nm laser photolysis of CH3I in the presence of O2, and the relative absorption has been measured by time-resolved continuous-wave cavity ring-down spectroscopy (cw-CRDS). Calibration of the relative absorption spectrum has been carried out on three distinct wavelengths by carefully measuring CH3O2 decays under different experimental conditions and extracting the initial radical concentration (and with this the absolute absorption cross sections) by using the well-known rate constant for the CH3O2 self-reaction. The following, pressure-independent absorption cross sections were determined: 3.41 × 10(-20), 3.40 × 10(-20), and 2.11 × 10(-20) cm(2) at 7748.18, 7489.16, and 7493.33 cm(-1). These values are 2-3 times higher than previous determinations ( Pushkarsky, M. B.; Zalyubovsky, S. J.; Miller, T. A. J. Chem. Phys. 2000, 112 (24), 10695 - 10698 and Atkinson, D. B.; Spillman, J. L. J. Phys. Chem. A 2002, 106 (38), 8891 - 8902). The absorption spectrum of the stable precursor CH3I has also been determined and three characteristic sharp absorption lines with absorption cross sections up to 2 × 10(-21) cm(2) have been observed in this wavelength range.

Experimental and theoretical investigation of the reaction of RO2 radicals with OH radicals: Dependence of the HO2 yield on the size of the alkyl group

“…The HO 2 yield, , has been obtained from the simultaneous measurement of OH and HO 2 concentration time profiles, using a laser photolysis reactor coupled to two identical continuous wave cavity ring down spectroscopy (cw‐CRDS) absorption paths. The experimental setup has already been described in detail . Briefly, the reaction was initiated by the 248 nm photolysis of XeF 2 in the presence of hydrocarbons RH (methane, ethane, propane [all with a purity of 99.95%; Air Liquide, France] or n ‐butane [purity 99.5%; Air Liquide, France]) and H 2 O, leading to the generation of the peroxy radicals and OH radicals through the following reaction sequence: which is followed by reaction (R1).…”

“…The experimental setup has already been described in detail. [13][14][15] Briefly, the reaction was initiated by the 248 nm photolysis of XeF 2 in the presence of hydrocarbons RH (methane, ethane, propane [all with a purity of 99.95%; Air Liquide, France] or n-butane [purity 99.5%; Air Liquide, France]) and H 2 O, leading to the generation of the peroxy radicals and OH radicals through the following reaction sequence:…”

Line parameters measurements and modeling for the ν6 band of CH3I: A complete line list for atmospheric databases

“…[9] in HITRAN database [4] and at room temperature between 7473 and 7497 cm -1 from Ref. [10] in GEISA database [5].…”

A new method for atmospheric detection of the CH<sub>3</sub>O<sub>2</sub> radical

“…At present, CH 3 O 2 is not specifically measured in the atmosphere by any direct or indirect method. Time-resolved continuous-wave cavity ring-down spectroscopy (CRDS), using the ν 12 transition of the A ← X band at ∼ 1.3 µm, has been used to detect CH 3 O 2 directly in a photoreactor (Farago et al, 2013;Bossolasco et al, 2014). However, the detection limit is not sufficiently sensitive to enable tropospheric detection.…”