Experimental Evidence of the Inversion of Angular Momentum During the Transfer of Excitation by Resonant Collisions in the 6P13 State of Mercury

The zero-field level-crossing signal of even isotopes of natural Hg excited by resonant collisions from directly excited ${\mathrm{Hg}}^{198}$ atoms has been observed with circularly polarized light. The signal is proportional to the atomic "orientation" (mean value of the angular momentum of the excited atoms). The sense of this orientation is reversed when the excitation is transferred by collisions from ${\mathrm{Hg}}^{198}$ to other isotopes, as predicted by the theory.