UV‐Absorption spectrum of the methylperoxy radical and the kinetics of its disproportionation reaction at 300 K

Abstract

Molecular modulation spectroscopy combined with ultraviolet spectroscopic techniques have been used to observe the behavior of the CH,O, radicals generated in the gas phase by near-ultraviolet modulated photolysis of flowing C1,-CH,-O2 mixtures. The kinetics of the disproportionation reaction (1)and the absorption cross-sections of CH30, were measured by computer fitting of the modulated absorption traces obtained i n t h e wavelength range 220 to 270 n m a t 300 K and 240 torr. The rate constant for the elementary self-reaction k , = k,,,, + h l , b , + k,,,, was determined to be 13.61 i 0.55, x 10 l3 cm3 molecule -' s '. The parameter kubs/r (where kobi is the observed apparent second-order rate constant) was measured from the decay curves in the dark phase of the modulated photolysis period in the wavelength range 230-260 nm, and had a value 1.16 x lo5 cm s a t 250 nm. At 250 nm the absorption cross-section was determined as u(CH302i = 4.14 x 10 -'' cm' molecule ', leading to a value of kobs = (4.8 ? 0.5) x 10 s -' . In addition, the absorption spectrum of CH.?O, was measured in the range 210-295 nm using diode array spectroscopy. A detailed review of all previous studies concerning the kinetics and spectrum of the CH.,O, radical is presented, and a recommended spectrum. representing an average from selected recent studies, is proposed.cm' molecule

UV absorption spectra of HO2, CH3O2, C2H5O2, and CH3C(O)CH2O2 radicals and mechanism of the reactions of F and Cl atoms with CH3C(O)CH3

“…As shown in Fig. 4B, the shape of the spectrum measured here is in excellent agreement with those of McAdam et al 19, Moortgat et al 20, Simon et al 21, Lightfoot and Jemi‐Alade 22, Jenkin and Cox 23, Maricq and Wallington 24, and the recommendation of Tyndall et al 4. The UV absorption spectrum of CH 3 O 2 is well established.…”

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

“…The measurements of the absorption cross-section by Simon et al (1990) form the basis of our recommendation of σ (250 nm)=3.9×10 −18 cm 2 molecule −1 . Thus, we recommend k obs =4.8×10 −13 cm 3 molecule −1 s −1 at 298 K. Taking the branching ratio of k 2 /k=0.37 at 298 K yields the value of k at 298 K given above.…”

Atmospheric chemistry of benzaldehyde: UV absorption spectrum and reaction kinetics and mechanisms of the C6H5C(O)O2 radical

“…25). Benzp CH3O2, 240 nm \ 4.55 ] 10~18 aldehyde absorbs signiÐcantly at the measurement wavelengths (see Fig.…”