Collective motion in the nuclear shell model IV. Odd-mass nuclei in the sd shell

The U3 coupling scheme is used as the basis for a survey of the odd nuclei in the sd shell. Energy levels and electromagnetic properties are compared with experiment. In the first half of the shell, A < 28, there is agreement, but in the second half the data suggest something much closer to jj coupling. The need for an effective charge also disappears beyond A = 28.