THE SIGNIFICANCE OF AUTOIONIZATION PROCESSES DURING NONRESONANT ONE-COLOR 2-PHOTON IONIZATION OF NEUTRAL SILVER AND COPPER ATOMS AT LAMBDA = 248 NM

Recent experimental ionization efficiency data (photoion signal as a f unction of laser intensity) for nonresonant two-photon ionization of A g and Cu at lambda = 248 nm show strong deviations from the expected l aser intensity dependence of the nonresonant two-photon ionization pro cess. In addition, the comparison of the ionization efficiency data of the photoions Ag+ and Cu+ shows drastic differences between silver an d copper. These deviations are explained by considering a two-photon e xcitation 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 au toionization processes and non-ionizing radiative de-excitation scheme s must also be taken into account. The importance of these processes f or quantitative surface analysis using secondary neutral mass spectrom etry in combination with nonresonant two-photon postionization is addr essed.