Rydberg series and autoionization resonances in the Y I absorption spectrum

The absorption spectrum of yttrium vapour has been photographed in the spectral range 1650 to 2250 À, with a 10 m spectrograph. Series of autoionization resonances, which converge on excited states of the Y+ ion have been identified, as combinations with the doublet ground-state of YI, 5s24d 2D3/2,5/2. Although the lines of these series show broadened and often asymmetrical profiles, the lines are sufficiently well defined to fix a value for the first ionization potential of Y I, which differs from the previously accepted value by approximately 2500 cm-1. In addition, approximately 400 new Y I lines, which involve excited levels below the first ionization limit of Y I, namely 4s21So, have been found. The majority of these are unclassifiable at present but, the value for the first ionization-potential being known from the resonances above-mentioned, two series of the character 5s24d 2D3/2, 5/2-5s2nf2Fo have been identified. In addition to the identifications of series, 152 new lines below the 5s21So limit identify 76 new levels of Y I, of odd parity.