Spectroscopic and kinetic investigation of methylene amidogen by cavity ring-down spectroscopy

Cavity ring-down spectroscopy (CRDS) has been used to study room-temperature chemical reactions of the methylene amidogen radical (H2CN). The radical was prepared by 193 nm photolysis of formaldoxime, H2CNOH --> H2CN + OH. CRDS signals from both H2CN and OH [A - X (1,0) band] were observed in the wavelength region 278-288 nm. By comparison of the strengths of the OH and H2CN signals, the oscillator strength of H2CN electronic transition in the 279-288 nm wavelength region was measured to be 4.5 x 10(-4). To correct for the loss of the OH signal due to reactions of OH, the room-temperature rate constant for the reaction of OH with formaldoxime was measured, k(H2CNOH + OH) = (1.5 +/- 0.4) x 10(-12) cm(3) molecule(-1) s(-1). Reaction of H2CN with a number of stable molecules [O-2, C2H4, CO, CH4, H-2] could not be observed, and an upper limit to the reaction rate constants, < 1 x 10(-15) cm(3) molecule(-1) s(-1), was derived. Self-recombination was the main removal process for the H2CN radical under the conditions of the experiment, with the rate constant k(H2CN + H2CN) = (7.7 +/- 2.5) x 10(-12) cm(3) molecule(-1) s(-1). At high photolysis laser energies, for which the H2CNOH fractional dissociation was high, it was possible to study the reaction of H2CN with OH. A value of the rate constant for the OH + H2CN reaction, k(OH + H2CN) = 6 x 10(-12) cm(3) molecule(-1) s(-1), was derived.