Resolution of Transient States of Nitrile Anions via Photodissociation Action Spectroscopy; Our Progress to Date The 2 traces show resonant Cu atomic transitions acquired using two different techniques: {top trace} Resonant 2-Photon Ionization spectroscopy and {bottom trace} R(1+1)3PI where (1+1) indicates the simultaneous absorption of 2 photons from the same laser. The signals evident in the lower trace were acquired using significantly higher laser intensities and provide more structure. The intense sharp features are assigned as a 2-photon Rydberg series (2D5/2 ← 2S1/2) converging to the copper ionization limit (sharp threshold). The state which non-resonantly couples the ground state to the 2D5/2 is a superposition composed primarily of the copper spin orbit components seen in the top trace. The observed state term energies (twice the dye laser frequency) and those published in the NIST database, plotted as a function of 1/n2 for the 2D5/2 ← 2S1/2 Rydberg series. The Rydberg formula predicts linear behavior in the limit as n→∞. Extrapolation to this limit permits the determination of the quantum defect for electrons in d-orbital angular momentum states. For copper, this value is 0.92 ± 0.03