Dissociation of aliphatic hydrocarbons by controlled electron impact: Vibrational and rotational energy distributions of the excited CH radicals

Abstract

Abstract Emission spectra of CH(A 2 Δ -X 2 Π ) produced in collisions of acetylene, ethyelen and ethane with electrons (17–100 eV) have been measured and the rovibrational distributions of CH(A 2 Δ ) have been obtained. The rovibrational distributions of CH(A 2 Δ ) apparently depended on the incident electron energy, indicating the existence of more than two dissociation processes. The ratio of the vibrational populations, ( P ( ν ′ = 1)/ P ( ν ′ = 0)), varied from 0.45, 0.3 and 0.3 at 17 eV to 0.8, 0.75 and 0.7 at 100 eV, and the rotational temperatures, T r ( ν ′ = 0), varied from 3200, 5000 and 4300 K at 17 eV to 2500, 3800 and 3800 K at 100 eV for acetylene, ethylene and ethane, respectively. Component 1, which has the lowest threshold, is vibrationally cooler and rotationally hotter than components 2 and 3. The intermediate states for the formation of component 1 are σ c-c bonding Rydberg states. The emission and formation cross sections of CHA 2 Δ ) separated into each vibrational level were determined.