The initial vibrational state distribution of HCN X̃ ¹Σ⁺ (v₁,0,v₃) from the reaction CN(²Σ⁺)+C₂H₆→ HCN+C₂H₅

The reaction of the cyano radical (CN) with ethane was studied using time-resolved infrared absorption spectroscopy to monitor individual rovibrational states of the HCN product. A method is described that can be used to determine the initial vibrational state distribution at pressures of several Torr. This technique was applied to the title reaction to determine that the vibrational states of HCN(v₁,0,v₃), where v ₁,v₃ = 0, 1, and 2, were not directly populated in the title reaction to any significant extent. The initial vibrational energy content of the CN radical was also varied but did not influence the initial population in the HCN vibrational levels probed in this experiment. The time dependence of HCN(v₁,0,v₃) was followed and interpreted in terms of bimolecular rate constants for vibrational relaxation with ethane. The title reaction is mode specific in its energy disposal in that at least every HCN product appears to have at least one quantum of bending excitation, likely in combination with stretching vibrations.