SPECTROSCOPIC, KINETIC, AND MECHANISTIC STUDY OF CH2FO2 RADICALS IN THE GAS-PHASE AT 298-K

The ultraviolet absorption spectrum of CH2FO2 radicals and the kinetics and mechanism of their self-reaction have been studied in the gas phase at 298 K. Two techniques have been used: pulse radiolysis UV absorption to measure the spectrum and kinetics and long path length Fourier transform infrared spectroscopy (FTIR) to identify and quantify the reaction products. Absorption cross sections were quantified over the wavelength range 220-300 nm. The measured cross section near the absorption maximum is sigma(CH2FO2)(240 nm) = (4.11 +/- 0.67) x 10(18) cm2 molecule.-1 Errors are statistical (2-sigma) plus our estimate of potential systematic uncertainty (10%). This absorption cross section was then used to derive the observed self-reaction rate constant for reaction 1, defined as -d[CH2FO2]/dt = 2k(abs)[CH2FO2]2, CH2FO2 + CH2FO2 --> products (1), k(iobs) = (4.01 +/- 0.52) x 10(-12) cm3 molecule-1 s-1 (errors are 2-sigma). The only carbon-containing products observed by FTIR spectroscopy were HC(O)F and CH2FOOH, indicating that the majority (> 77%) of the self-reaction proceeds via the channel CH2FO2 + CH2FO2 --> CH2FO + CH2FO + O2 (1a). As part of this work, a rate constant of (3.24 +/- 0.51) x 10(-13) cm3 molecule-1 s-1 was measured for the reaction of Cl atoms with CH3F and a lower limit of 1.2 x 10(-11) cm3 molecule-1 s-1 was determined for the reaction of F atoms with CH3F: Cl (F) + CH3F --> CH2F + HCl (HF).