  We observe vibronic transitions in CaD$^+$ between the 1$^{1}\Sigma$ and
2$^{1}\Sigma$ electronic states by resonance enhanced multiphoton
photodissociation spectroscopy in a Coulomb crystal. The vibronic transitions
are compared with previous measurements on CaH$^+$. The result is a revised
assignment of the CaH$^+$ vibronic levels and a disagreement with CASPT2
theoretical calculations by approximately 700 cm$^{-1}$.
