Bond selectivity in the reaction of NH(a 1Δ) with methanol.

Reaction of NH(a 1Δ) with methanol has been studied by a flash photolysis of HNCO at 193 nm at room temperature (298±2 K). Time dependence and relative concentrations for NH, NH2, NHD, CH3O, H, and D are monitored by a laser induced fluorescence (LIF) technique. From the pseudo-first-order analysis of NH(a 1Δ) decay rate, the rate constants for the reactions NH(a 1Δ)+CH3OH→ products (1), and NH(a 1Δ)+CH3OD→products (2) have been determined to be k1=(1.37±0.10)×10-10 cm3 molecule-1 s-1 in the pressure range of 3–20 Torr Ar or 5 Torr He, and k2=(1.33±0.05)×10-10 cm3 molecule-1 s-1 at the pressure of 5 Torr He, respectively. By comparing the LIF intensity of NH(X 3Σ-) in reaction (1) with that in NH(a 1Δ)+Xe reaction system, the contribution of physical quenching in reaction (1) has been evaluated to be less than 2.4%. Also by comparing the LIF intensities of NHD and NH2 in reaction (2) with those in NH(a 1Δ)+D2/H2 reaction systems, the branching ratio between the pathways producing NHD (2b) and NH2 (2c) has been determined to be k(2b)/k(2c)=23±9. It is elucidated that the insertion of NH(a 1Δ) into O–D bond of CH3OD is completely predominant over C–H bond; i.e., the O–D bond is about 69 times more reactive toward insertion of NH(a 1Δ) than a single C–H bond. [ABSTRACT FROM AUTHOR]