Systematics of the excitation energy of the1+scissors mode and its empirical dependence on the nuclear deformation parameter

From the data on dipole excitations obtained in photon scattering experiments we extract and tabulate the mean values of the excitation energy of the $1^{+}$ scissors mode in nuclei of the mass region $130<A<\mathrm{}200.\mathrm{}$ The centers of gravity of the observed $M1\mathrm{}$ strength distributions are always close to 3 MeV including several moderately deformed transitional nuclei. In particular, the data exhibit a weak dependence of the scissors mode energy on the deformation parameter. Including roughly the deformation dependence of pairing effects we could modify an earlier estimate based on a schematic random phase approximation and get a simple formula which yields qualitative agreement with the data.