Ionization-detected optical-optical double resonance spectroscopic studiesof moderate energy Rydberg states of calcium monofluoride

This paper describes a systematic investigation of quasi-bound Rydberg stat es of calcium monofluoride (CaF) existing between the molecule's v(+) = 0 a nd 1 ionization thresholds. Experiments utilized ionization-detected optica l-optical double resonance spectroscopy to assign states as belonging to on e of the six core-penetrating (l less than or equal to 2) or to a core-nonp enetrating (l greater than or equal to 3) Rydberg series. Most states obser ved had effective principal quantum number, v, between 12 and 18 and one qu antum of vibrational excitation in the CaF+ ion-core, although lower v, v g reater than or equal to 2 states were also identified. Core-nonpenetrating states were observed both directly and through avoided crossings with core- penetrating states. Five of the seven L components in the f-complexes deriv ed from Ca+, 13f and n = 14f, have been identified. We present a detailed a nalysis of the CaF electronic structure for 12.5 less than or equal to v le ss than or equal to 14.6, v = 1 using an effective Hamiltonian model to des cribe CaF+ ion-core-induced l-mixing between l less than or equal to 3 (s,p ,d, and f) Ca+ atomic orbitals. An observed avoided crossing between the 14 .19 (2)Sigma (+), v = 1 and 14f (L = -3), v = 1 states implies that the pre viously identified 0.19 Sigma (+) core-penetrating series has 20-30% f (2)S igma (+)-character. The effective Hamiltonian approach accounts for much of the data, however, a complete accounting requires the use of multichannel quantum defect theory (MQDT). An MQDT analysis of the data presented here i s provided in a companion paper by Jungen and Roche in this issue. The effe ctive Hamiltonian model enabled derivation of electrostatic properties of t he CaF+ core as well as the 0.14 Delta series quantum defect derivative, [d delta /dR](Re)(+), which governs the exchange of energy between the Rydber g electron and the CaF+ ion-core. The CaF+ electric quadrupole moment, defi ned with the coordinate origin at the center-of-charge, is 11.3 +/- 0.5 a.u .