Analysis of Rydberg Series of Ytterbium Monofluoride, YbF

Resonance-enhanced multiphoton ionization (REMPI) is used to characterize Rydberg states of ¹⁷⁴YbF. Assignment of these Rydberg states to series that converge to various rotational and vibrational levels of the ¹⁷⁴YbF⁺ cation leads to an accurate value for the ionization energy <i>IE</i> = 48706.57(8) cm^-1 of YbF. The values for the rotational constants of the YbF⁺ X¹Σ⁺ ground state are found as <i>B</i>_{ν = 0}⁺ = 0.257(1) cm^-1 and <i>B</i>_{ν = 1}⁺ = 0.255(3) cm^-1, while the vibrational transition energy is Δ<i>G</i>_1/2 = 598.86(15) cm^-1. Photoinduced Rydberg ionization (PIRI) measurements via a high-lying Rydberg state have been performed using an infrared free electron laser, confirming the Δ<i>G</i>_1/2 value.