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 σ_CH2FO2 (240 nm) = (4.11 ± 0.67) × 10^-18 cm² molecule.^-1 Errors are statistical (2σ) 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_obs[CH₂FO₂]², CH₂FO₂ + CH₂FO₂ → products (1). k_1obs = (4.01 ± 0.52) × 10^-12 cm³ molecule^-1 s^-1 (errors are 2σ). 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) × 10^-13 cm³ molecule^-1 s^-1 was measured for the reaction of Cl atoms with CH₃F and a lower limit of 1.2 × 10^-11 cm³ molecule^-1 s^-1 was determined for the reaction of F atoms with CH₃F: Cl (F) + CH₃F → CH₂F + HCl (HF).