Discussion of the parity violation and the break of the time-reversal invariance m diatomic molecules has continued for a number of years Experiments an the TIF molecule gave one of the most stringent limits on the electric-dipole moment of the proton and on the T-violating nuclear forces, At present, a new generation of experiments wilh paramagneticdiatomic molecules is underway. These experiments are aimed mainly at the search for the electric-dipole-moment of the electron.In this topical review we enamine theoretical aspects of parity non-conservation in diatomic molecules. We focus on molecular theory leaving aside the nuclear pan of the problem. In this approach the nucleus is characterized by he number of P-odd and P, T-odd moments, namely anapole moment, Schiff moment and magnetic quadrupole moment. Molecular theory has to link lhese moments to the experimentally measured quantities. such as frequency shifts, etc. The other possible sources of the parity non-conservation in molecules are the electronnuclear neutral c m n t interactions and the electricdipole moment of the electron. They are also discussed in lhis review. ' Rizlewicz er al(1982). g Van Zee er al(1978). Knight er al(1981).

Parity nonconservation that originates from the weak interaction of atomic electrons with the nuclei in heliumlike gadolinium and europium is considered. An experiment with a polarized ion beam is discussed. The mixed hyperfine-and weak-quenching effect in Gd 62ϩ and Eu 61ϩ isotopes is shown to lead to an asymmetry of the photon emission relative to the ion beam polarization. With complete beam polarization, the magnitude of the asymmetry in photon counting rates reaches about 0.39ϫ10 Ϫ3 in gadolinium and is about 0.11ϫ10 Ϫ3 in europium.

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