Slow Neutron Capture Gamma Rays inHg200

Coincidence measurements on the gamma rays following slow neutron capture by ${\mathrm{Hg}}^{200}$ have been made with thermal neutrons and at the 34-, 129-, and 175-eV resonances. The two new low-lying levels found at 1.05 and 1.27 MeV constitute the third and fourth excited states of ${\mathrm{Hg}}^{200}$. These new states, together with the previously known second excited state, are shown to be consistent with a two-phonon vibrational triplet. Transitions to several other states were also observed. The transitions from the four capturing states to various low-lying states are summarized.