Abstract Ca +–Ar 2 complexes are investigated with mass-selected photodissociation spectroscopy and with high-level ab initio calculations. Theory finds two minima with comparable energies for the ground state, a linear Ar–Ca +–Ar structure and a C 2 v Ca +– Ar 2 structure with a significant argon dimer interaction. The latter is computed to be slightly lower in energy. Electronic spectroscopy finds a sharp spectrum near the forbidden Ca +( 2 D– 2 S) atomic interval. Two vibronic progressions are assigned that have significantly different linewidths. Analysis of the spectrum establishes that the complex is most likely linear.