Rydberg states and ionization potential of calcium monofluoride

61 vibronic states of CaF in the region 41 930–45 905 ${\mathrm{cm}}^{\mathrm{-}1}$ are observed by optical-optical double resonance, rovibronically assigned, and shown to belong to 37 Rydberg electronic states. These states are organized into six core-penetrating (l≤2), mixed-l Rydberg series, from which we obtain an improved value of the CaF ionization potential, 47 005±20 ${\mathrm{cm}}^{\mathrm{-}1}$. All previously observed low Rydberg and valence states of CaF fit smoothly into these six Rydberg series, which form the complete set of l≤2 series. Using this information, absolute quantum defects have been determined and the series are assigned nominally (i.e., dominant l character) as d (Δ, Π, and Σ), p (Π and Σ), and s (Σ).