Electronic excitation of formaldehyde by low-energy electrons: A theoretical study using the complex Kohn variational method

We report results of a fully ab initio treatment of electronic excitation in a polyatomic molecule by electron impact. We have calculated total and differential cross sections for exciting the two lowest (n{→}π*{)}¹$,3${A}₂$ excited states of ${H}₂$CO for collision energies between 5 and 20 eV. The calculations were carried out in a three-state close-coupling approximation using the complex Kohn variational method. The absence of any backward peaking in the cross sections calculated for the ³A₂ state is reminiscent of a rigorous selection rule for Σ⁺-Σ^- transitions in linear molecules. However, with no experimental studies available for comparison, the present results must be regarded as predictive.