Coulomb excitation of states in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ up to J=(21/2) has been observed with 160-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ and 617-MeV ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ ions. Most of these states are grouped into three rotational-like bands based on the ${\mathrm{}(3/2)\mathrm{}}^{+}$ ground state, the ${\mathrm{}(1/2)\mathrm{}}^{+}$ first excited state, and the ${\mathrm{}(7/2)\mathrm{}}^{+}$ γ-vibrational-like state at 621 keV. The average deviation between experimental and theoretical energies for 18 states is 54 keV for the particle-asymmetric-rigid-rotor model and 66 keV for the interacting boson-fermion approximation model [limited to broken Spin(6) symmetry and only the $d_{3/2}$ orbital is considered]. The overall agreement of both model predictions with experimental γ-ray yields for the collective transitions within the ${\mathrm{}(3/2)\mathrm{}}^{+}$ band is quite good.

For interband transitions originating in the K${=(1/2)\mathrm{}}^{+}$ and ${\mathrm{}(7/2)\mathrm{}}^{+}$ bands, the interacting boson-fermion approximation model tends to underestimate the γ-ray yields by one to two orders of magnitude. In ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ there are eight Δ${\tau }_1$≥2 and six Δ${\sigma }_1$=1 transitions which are forbidden in the U(6/4) and U(6/20) supersymmetry schemes. The interacting boson-fermion approximation model tends to underestimate the B(E2) values of two of these transitions with moderate collectivity by at least one order of magnitude. The interband transition ${\mathrm{}(3/2)\mathrm{}}^{\mathcal{’}}$→(3/2) (Δ${\tau }_1$=2 transition) with moderate collectivity is not a special situation in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ but a general feature in ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. For the remainder of the forbidden transitions in the supersymmetry schemes, the experimental B(E2) values are an order of magnitude smaller than the collective ones.

Both supersymmetry schemes and the broken Spin(6) model reproduce the collective E2 transitions with Δ${\tau }_1$=1 reasonably well. The triaxial rotor model description of the experimental energies and the collective E2 transitions is the most successful approach. The B(E3) for excitation of several negative-parity states in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ is (3.3±2.0)B(E${3)}_{\mathrm{sp}}$.

• Received 20 June 1986

DOI:https://doi.org/10.1103/PhysRevC.35.968