Test of the triaxial rotor model and the interacting boson fermion approximation model description of collective states inIr191

Coulomb excitation of states in ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$ 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 ${1/2}^{+}$ first excited state, and the ${\mathrm{}(7/2)\mathrm{}}^{+}$ γ-vibrational-like state at 686 keV. The average deviation between experimental and theoretical energies for 20 states is 45 keV for the particle-asymmetric-rigid-rotor model and 125 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 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. These six moderately collective transitions correspond to Δ${\tau }_1$=2 transitions in the U(6/4) and U(6/20) supersymmetry schemes and are strictly forbidden in these schemes. For both supersymmetric schemes there is a lack of detailed agreement with the very collective E2 transitions which have Δ${\tau }_1$=0,±1. 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 ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$ is (4±1)B(E${3)}_{\mathrm{sp}}$.