On the configurations nsnp(n+1)p in Al I, Ga I, In I, and Tl I

New data for optically allowed transitions to levels of nsnp(n+1)p (n=4,5 and 6 in Ga, In and Tl respectively) are presented. The structure is analysed by the technique of partial plots and the identifications obtained by Roig (1975) for Al I are thereby carried through to Tl I. The identifications obtained for In I are in substantial agreement with earlier results, but the photoabsorption data reveal that some changes of designation are needed. For Ga I, there is a disagreement between the experimentally based assignments and structure calculations based on scaled Hartree-Fock parameters.