In i isoelectronic sequence: wavelengths and energy levels for Xe vi through La ix

Spectra of Xe, Cs, Ba, and La produced with a high-voltage spark discharge were observed photographically with the National Bureau of Standards 10.7-m normal- and grazing-incidence spectrographs. Identified lines of the In i isoelectronic sequence were used to determine the energy levels of the 5s25p, 5s5p2, 5s25d, and 5s26s configurations. Their interactions with unobserved configurations that include a 4f electron are discussed. Fitted values of the radial energy integrals were determined from the known levels.