Reorientation ofMCenters in KCl

The dependence of the $M$-center reorientation efficiency on $M^{+}$ concentration indicates that at low temperatures, $M$ centers reorient indirectly by absorbing light, forming $M^{+}$ centers which then absorb and rotate. Reoriented $M$ centers are produced only after reoriented $M^{+}$ centers capture electrons. We further show that $M^{+}$ centers reorient with high efficiency during the radiationless transition, $2p{\pi }_u\to 2p{\sigma }_u$.