Pulsed laser photolysis–laser-induced fluorescence measurements on the kinetics of CN(v= 0) and CN(v= 1) with O2, NH3 and 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.