On the Theory of Ionization and Excitation Yields

The Fowler equation for excitation and ionization yields due to fast electrons in H2 is written down, and an approximation is developed which is expected to be accurate except for source electron energies below perhaps 200 eV. A general form for the solution is developed which is numerically evaluated. Results for the ionization yield, and also for the yield of all electronic excitations, agree within ∼2% with more precise calculations except below ∼300 eV. Extensions to more complex media and to other fast particles are discussed.