Recent experimental ionization efficiency data (photoion signal as a function of laser intensity) for nonresonant two-photon ionization of Ag and Cu at λ = 248 nm show strong deviations from the expected laser intensity dependence of the nonresonant two-photon ionization process. In addition, the comparison of the ionization efficiency data of the photoions Ag+and Cu+shows drastic differences between silver and copper. These deviations are explained by considering a two-photon excitation process of the internal 4d (Ag) or 3d (Cu) electron followed by autoionization of the short-lived excited atomic states produced. In the case of Cu, the competition between the de-excitation due to autoionization processes and non-ionizing radiative de-excitation schemes must also be taken into account. The importance of these processes for quantitative surface analysis using secondary neutral mass spectrometry in combination with nonresonant two-photon postionization is addressed. © 1993.
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