One-phonon states of heavy vibrational nuclei with mixed proton-neutron symmetry have recently been made accessible by the technique of projectile Coulomb excitation. Gamma-rays following Coulomb excitation of the nuclides 136,138Ce and 134Xe have been measured with the Gammasphere-array run in singles-mode. M1, E2, and E3 transition matrix elements from low-spin states were measured relative to the known values. The strength distributions up to about 2.7�MeV serve for identifying the main fragment of the one-quadrupole phonon mixed-symmetry state. The data are presented and their significance is discussed.