Fine structure in the o. decay of mass-separated Pb and Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well as a-x-t and a-e-t coincidence events were collected. The o. decay of Pb revealed feeding to a low-lying 0+ state at 328(12) keV inHg.This state can be interpreted as being the bandhead of the deformed rotational band observed previously in in-beam studies. In the a decay of Hg, feeding towards the Srst excited 2+ state at 153 keV and the 0~+ state at 478 keV in Pt was observed. The hindrance factor of the a decay towards the excited 0+ state gives information about the particle-hole character of the states connected in the a decay. A two-level mixing calculation is introduced. From the fixing in Pt and the a-decay hindrance factors, small mixing is deduced for ground states of neutron-de6cient Hg and Pb nuclei.

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