High-spin states up to (29/$2^{+}$) and (29/$2^{\mathrm{-}}$) in ${}_{}{}^{71}{}_{}{}^{}\mathrm{As}$ have been studied via the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{19}$F,α2p) reaction at 62 MeV using in-beam γ-ray spectroscopic techniques. Based on a particle-γ coincidence measurement a new decay sequence of negative parity has been assigned to ${}_{}{}^{71}{}_{}{}^{}\mathrm{As}$. Lifetimes for some E2 transitions were extracted from Doppler-shifted line shapes observed in coincidence mode, and experimental transition quadrupole moments were determined. They indicate a moderate to high collectivity in both the positive-parity yrast band and the new negative-parity decay sequence at high spins. Total Routhian surfaces calculated for states of both parities reveal strong triaxial shapes at high spins. A noncollective structure of 19/$2^{\left(\mathrm{-}\right)}$ and 21/$2^{\left(\mathrm{-}\right)}$ states is interpreted as a three-quasiparticle excitation.

• Received 23 March 1994

DOI:https://doi.org/10.1103/PhysRevC.50.716