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

Emission spectra of CH(A2Δ-X2Π) produced in collisions of acetylene, ethyelen and ethane with electrons (17–100 eV) have been measured and the rovibrational distributions of CH(A2Δ) have been obtained. The rovibrational distributions of CH(A2Δ) 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, Tr(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 σc-c bonding Rydberg states. The emission and formation cross sections of CHA2Δ) separated into each vibrational level were determined.