Extensive new data on the even-parity, J=0Â andÂ 2 bound states of Ca provide an excellent opportunity for the application of multichannel quantum-defect theory (MQDT) to these spectra. A detailed description of the experimental technique of multiphoton ionization spectroscopy is given, followed by an explicit application of MQDT to the case where interacting Rydberg series go to three distinct limits. MQDT parameter sets are obtained for each of the S01, D21, and D23 series of Ca, permitting quantitative determination of the configuration mixing in each bound state. Several previous assignments of members of the D21 series are changed by the analysis. It is found that the quantum defects of the bound energy levels of Ca are determined almost entirely by configuration mixing, with no observable effects of recoupling. This is in contrast to the situation in the rare gases, where angular momentum recoupling has the dominant effect on the quantum defects, with configuration mixing a small additional effect. © 1977 The American Physical Society.