Pulsed laser photolysis–laser-induced fluorescence measurements on the kinetics of CN(v= 0) and CN(v= 1) with O2, NH3and NO between 294 and 761 K

Abstract

Time-resolved laser-induced fluorescence (LIF) measurements have been carried out on the kinetics of CN(v= 0) and CN(v= 1) radicals with O2, NH3 and NO at temperatures between 294 and 761 K. The radicals were generated by pulsed laser photolysis of NCNO at 532 nm, and the decays of concentration were monitored using a dye laser tuned to lines in either the (0,0) or (0,1) band of the CN(B2Σ+–X2Σ+) system. The observed rate constants all decrease with temperature, and accurate values have been determined for the parameters which decribe these variations (see table 4). With O2 and NH3, the rate constants for CN(v= 0) are slightly larger (e.g. 23 and 56% at 295 K) than for CN(v= 1). It appears that the reactions (CN + O2 and CN + NH3) must occur over potential-energy surfaces which are initially attractive. With NO, CN(v= 1) is removed very rapidly [k295=(7.6 ± 0.2)×10–11 cm3 molecule–1 s–1], almost certainly because of vibrational relaxation in collisions in which a complex forms and then redissociates. For CN(v= 0)+ NO the rate constant is pressure-dependent and has been investigated only in a limited range. However, at a total pressure of 30 Torr the rate constant shows a strong negative temperature dependence. The results are consistent with reaction by a radical association mechanism, with no evidence for the channel leading to CO + N2.