The excitation of gas molecules in flue gas by electron impact is calculated with a Monte Carlo (MC) algorithm for electron dynamics in partially ionized gases. The MC algorithm is straightforward for any mixture of molecules for which cross sections are available. Electron drift is simulated in the first case for homogeneous electric fields and in the second case for secondary electrons which are produced by electron-beam irradiation. The electron energy distribution function, , the energy branching and the rate of excitation are calculated for standard gas mixtures of Ar - , and O. These fundamental process parameters are needed for the study of reactions to remove from flue gas. The calculated results indicate that the production of highly excited molecules in the high electric field of a streamer corona discharge has an efficiency similar to that of electron-beam irradiation.