Structure of the Low-Lying Energy Levels ofHg200

The decay scheme of ${\mathrm{Tl}}^{200}$→${\mathrm{Hg}}^{200}$ has been reinvestigated with a Ge(Li) detector. The construction of the level scheme allows us to remove some of the ambiguities of previous investigations. From spectrum and angular-correlation measurements, the spin and parity of the 1029.5-keV third excited level of ${\mathrm{Hg}}^{200}$ is established as $0^{+}$. The low-energy level scheme of ${\mathrm{Hg}}^{200}$ is interpreted as due to the perturbation of the vibrational spectrum of bosons by a quadrupole interaction.