The initial vibrational level distribution and relaxation of HCN[X ¹∑⁺ (v₁,0,v₃)] in the CN(X ²∑⁺)+CH₄→HCN+CH₃ reaction system

The reaction of the cyano radical (CN) with methane was studied by time-resolved infrared absorption spectroscopy by monitoring individual rovibrational states of the HCN and CH₃ products. The initial vibrational level distribution of the bendless vibrational levels of HCN(v₁,0,v₃) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. About 20% of the HCN products were observed to be initially produced in the HCN(v₁,0,v₃) vibrational levels, with v₁ and v₃=0,1,2. The CN radical was created by laser photolysis of three different precursors. Each photolyte provided a different initial vibrational level distribution of CN; however, similar initial HCN(v₁,0,v₃) vibrational level distributions were obtained independent of the CN radical precursor. This may indicate that the CN radical does not act as a spectator bond during the course of a reactive encounter for this system. The time dependence of. the CH₃ (000⁰0) ground state was also followed using time-resolved infrared absorption spectroscopy. Preliminary data indicates that a large fraction, if not all, the CH₃ radicals are produced in their ground state in the title reaction.