Low-lying multiphonon states in ${}^{136}\mathrm{Ba}$ have been populated with the inelastic neutron scattering reaction. Excitation functions were performed at neutron energies from 2.2 to 3.9 MeV, and $\gamma$-ray angular distributions were measured at 2.5, 3.0, and 3.5 MeV. Lifetimes have been determined using the Doppler-shift attenuation method, and electromagnetic transition rates have been deduced. The previously assigned $2_{1,\mathrm{ms}}^{+}$ mixed-symmetry state at 2128.9 keV has been confirmed and is not greatly fragmented. For the first time in the $N=80$ isotones, a $3_{2,\mathrm{ms}}^{+}$ two-phonon mixed-symmetry state is proposed. In addition, the $2_5^{+}$ and the $4_3^{+}$ levels at 2222.7 and 2356.4 keV, respectively, decay with large $B(M1)$ values to the two-phonon $2_2^{+}$ and $4_1^{+}$ states, respectively, which suggests two-phonon mixed-symmetric character. Their excitation energies, however, are not consistent with this interpretation.

• Received 14 July 2008

DOI:https://doi.org/10.1103/PhysRevC.78.034317