ABSOLUTE MEASUREMENTS OF PHOTOABSORPTION CROSS-SECTIONS, PHOTOIONIZATION CROSS-SECTIONS, AND PHOTOIONIZATION QUANTUM YIELDS OF SILANE IN THE 13-40 EV REGION

The absolute values of the photoabsorption cross section of silane have been measured in the energy region between 13 and 40 eV. The photoionization quantum yields have also been measured in the 13-22 eV region. Using these values, we have evaluated the absolute photoionization cross sections and the total cross sections for nonionizing processes, i.e., neutral fragmentations. The photoabsorption cross sections show a broad peak at around 14.6 eV and a vibrational structure between 16 and 18 eV. These structures are superimposed on the spectra of direct transitions to the ionization continuum. The decaying features of the superexcited states corresponding to these two bands are shown to be very different from each other. Corresponding to the broad absorption peak located at around 14.6 eV, considerable deviations from unity in the photoionization quantum yields are observed. This means that the superexcited states at this energy decay through fast neutral fragmentation rather than autoionization. On the other hand, the superexcited states, which appear as the vibrational structure between 16 and 18 eV, decay predominantly through autoionization over the neutral fragmentation.