Spectroscopy of ¹⁷⁵Ir and ¹⁷⁷Ir and deformation effects in odd iridium nuclei

Excited states in ¹⁷⁵Ir and ¹⁷⁷Ir have been identified using (heavy-ion, pxn) reactions and γ-ray spectroscopic techniques. Rotational bands based on intrinsic states arising from the odd-proton parents, h _{9 2},h _{11 2},i _{13 2} and d _{5 2} were established to high spin except for the 5 2⁺[402] bands. Only the h _{9 2} bands show sharp alignment gains compatible with alignment of (i _{13 2})² neutrons. The smooth apparent alignments of the i _{13 2} proton bands can be attributed, at least qualitatively, to a much larger deformation. The complex alignment gains observed in the h _{11 2} bands in these and other iridium isotopes in the range ^173-181Ir are consistent with the effects of mixing with a deformed intruder (equivalently, a low-spin shape change). This conjecture is tested against the in-band decay properties using a three-band model. Examination of the band structure suggests a significant gamma deformation at very low spin, before the change to a more deformed configuration occurs.