M1 transitions involving the D states of quarkonia.

We derive expressions for the decay rates of the M1 transitions (1) n /sup 1/D/sub 2/left-right-arrown' /sup 3/S/sub 1/, (2) n/sup 3/D/sub 1/left-right-arrown' /sup 1/S/sub 0/, and (3) n/sup 1/D/sub 2/left-right-arrown' /sup 3/D/sub 1/ including their leading relativistic corrections. Using the potential proposed by Gupta, Radford, and Repko we also numerically calculate the decay widths for some of these transitions in both the cc-bar and the bb-bar bound systems. In general the M1 decay rates in the bb-bar systems are found to be extremely small, of the order of a few electron volts or less. But in the cc-bar system the M1 decay 1/sup 1/D/sub 2/left-right-arrow1/sup 3/S/sub 1/ may have a significant branching ratio, its partial decay width being more than 2 keV. The inclusion of coupled-channel mixing leads to only small corrections.