Absorption Spectrum of Cd I Vapor at 30 Å Using the Background Radiation of the 2.5-GeV Bonn Synchrotron

New resonances have been observed in the absorption spectrum of neutral cadmium vapor at wavelengths around 30 Å. These are believed to be at present the shortest-wavelength metal-vapor absorption features recorded optically. The 2.5-GeV electron synchrotron at Bonn University was used as a background source of continuous radiation. Hartree-Fock calculations enabled identification of the resonances as caused by excitation from the $3d$ shell, although somewhat larger differences between computed and observed wavelengths were found than were expected.