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Cavity ringdown spectroscopy (CRDS) was used to study room temperature chemical reactions of the methylene amidogen radical $(CH2N)$. The radical was prepared by 193 nm photolysis of formaldoxime, $CH2NOH\to CH2N+OH$. CRDS signal from both $CH2N$ and OH [A-X (1,0) band] was observed in the wavelength region 278-288 nm. By comparison of the OH and $CH2N$ signals, absorption cross section of the $CH2N$ was determined. To correct for the loss of OH radical by reaction, the rate constant of the reaction of OH with formaldoxime was measured, $k(CH2NOH+OH)=2.5\ast 10-12$ molecule $cm3s-1$. Reaction of $CH2N$ with stable molecules such oxygen, hydrogen and methane could not be observed and only an upper limit of the reaction rate constants, molecule $cm3s-1$, could be derived. Self-recombination was the main removal process for the $CH2N$ radical under the conditions of our experiment.