The 193-nm Photodissociation of NCO

Abstract

The 193-nm photolysis of the NCO radical has been investigated. NCO was generated from the reaction of CN + O2, where the CN was produced by 193-nm photolysis of C2N2 close to the nozzle of a pulsed jet. A second 193-nm photon dissociated the NCO radical during the same laser pulse. At this photon energy both the N−CO and the NC−O bonds may break. N(2D,2P) and CO products have been detected using vacuum ultraviolet laser induced fluorescence. A direct measurement of the N(2D):N(2P) branching ratio yielded an upper limit of 72 ± 18. The CO vibrational distribution was modeled with prior distributions for each of the contributing channels with coproducts N(4S,2D,2P). Combination of the results from the prior model and the direct measurement yielded a branching ratio of N(4S):N(2D):N(2P) of (5.1 ± 1.8):(93.6 ± 4.8):(1.3 ± 0.3). For the N(2D) + CO product channel, the average energy disposal into product relative translation (8%) and CO vibration (24%) was determined, leaving 68% of the available energy to appear as CO rotation. This observation suggests that the geometry of the dissociating state of NCO is likely bent.