  The planned measurement of optical resonances in singly-ionised lawrencium (Z
= 103) requires accurate theoretical predictions to narrow the search window.
We present high-precision, ab initio calculations of the electronic spectra of
Lr$^+$ and its lighter homologue lutetium (Z = 71). We have employed the
state-of-the-art relativistic Fock space coupled cluster approach and the AMBiT
CI+MBPT code to calculate atomic energy levels, g-factors, and transition
amplitudes and branching-ratios. Our calculations are in close agreement with
experimentally measured energy levels and transition strengths for the
homologue Lu$^+$ , and are well-converged for Lr$^+$ , where we expect a
similar level of accuracy. These results present the first large-scale,
systematic calculations of Lr$^+$ and will serve to guide future experimental
studies of this ion.

Atomic Physics