Collision induced modification of spectral lines in the first autoionization region of barium

The spectrum of barium above the first ionization potential is significantly modified by collisions with rare gas atoms. Atomic Ba vapor was produced in a heat-pipe oven. The two ground state electrons of Ba were excited simultaneously using non-resonant two-photon absorption to populate the 5d 3/2 n d 3/2, J = 0, 2 autoionizing states. The spectral region corresponding to this series was studied when Ba atoms were unperturbed, and when they were perturbed by the noble gases Ar, Kr, and Xe. Besides the expected shift and broadening of autoionizing series due to collisions with rare gases, we observed new spectral bands and significant changes to the shape of the existing lines.