We developed a low-resolution, high intensity monochromator composed of one multilayer mirror, two plane Pt mirrors, and a filter to investigate core-electron excitation effects induced by a photochemical reaction. We used a Mo/B4C multilayer mirror, which exhibits a high reflectivity at the L-shell absorption edge of Si (100 eV). We also examined the photoinduced fragmentation of SIH4 and Si2H6 molecules at the absorption edge using a synchrotron radiation beam. We confirmed that core-electron excitation initiated the fragmentation of these molecules into multiple ionization particles.