Spectroscopic and Kinetic Investigation of Methylene Amidogen by Cavity Ring-Down Spectroscopy

Abstract

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 × 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) × 10-12 cm3 molecule-1 s-1. Reaction of H2CN with a number of stable molecules [O2, C2H4, CO, CH4, H2] could not be observed, and an upper limit to the reaction rate constants, < 1 × 10-15 cm3 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) × 10-12 cm3 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 × 10-12 cm3 molecule-1 s-1, was derived.