Abstract
Exchange excitation has been directly observed in the excitation of the 63P1,2 states of mercury by transversely polarized electrons. A significant change of polarization of the electrons scattered in the forward direction has been measured for energies between threshold and 7 eV for both states. Above 7 eV the influence of exchange excitation of the 63P1 state decreases rapidly. This in in qualitative agreement with theory. From the measurements, the relative contributions for triplet (exchange) and singlet ('direct') scattering in the excitation of the 63P1 state in mercury were obtained. These can be explained in terms of intermediate coupling.