Systematic Behavior in Alkaline Earth Spectra: A Multichannel Quantum Defect Analysis

“Two-electron” atoms are more complex than “one-electron” atoms because of electron-electron interactions. This leads to spectra that are not well understood. Using multiple photon excitation and ionization detection, we have extensively studied Rydberg series of states in Ca, Sr, and Ba. The spectroscopic data were interpreted by using multichannel quantum defect theory (MQDT). In this context, systematic trends in the atom series Ca, Sr, and Ba are discussed.