EXCITATION OF H-2 VIBRATIONAL LEVELS (V LESS-THAN-OR-EQUAL-TO 4) BY LOW-ENERGY ELECTRON-IMPACT

An ab initio L2-basis-set theory for low-energy electron-molecule scattering is applied to the excitation of the nu =1, 2, 3 and 4 vibrational levels of H2 by slow electrons (1-10 eV), with or without simultaneous rotational excitation. An optical potential including direct, exchange and polarisation terms is expanded in a diagrammatic perturbation series and used in the framework of the T-matrix expansion method of Rescigno, McCurdy and McKoy (1975). Calculated integral and differential cross sections agree well with all available experimental data. The static-exchange approximation, on the other hand, gives poor results (2-4 times too low), with the error increasing as one goes to higher vibrational excitations. Polarisation is thus indispensable in a reliable description of vibrational excitation processes.