PHOTODETACHMENT OF TRAPPED NEGATIVE GOLD IONS - I - EXPERIMENTAL METHODS AND NEAR-THRESHOLD CROSS-SECTIONS

In this paper and in a subsequent one, we present relative and absolut e measurements of photodetachment cross sections of negative gold ions in an RF trap. Several laser devices needed to be used. Absolute meas urements are possible only when saturation occurs for a reasonable foc using of the laser and are deduced from the variations of photoelectro n yield versus laser pulse energy. We describe the principle behind ou r measurements and we report on the results obtained in the energy ran ge from threshold up to about 4000 cm(-1) above threshold. In this reg ion, we essentially observe a slow departure from Wigner's law (always less than 50%).