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

Abstract

This paper describes a systematic investigation of quasi-bound Rydberg states of calcium monofluoride (CaF) existing between the molecule's υ+ = 0 and 1 ionization thresholds. Experiments utilized ionization-detected optical–optical double resonance spectroscopy to assign states as belonging to one of the six core-penetrating ([Formula: see text] [Formula: see text] 2) or to a core-nonpenetrating ([Formula: see text] [Formula: see text] 3) Rydberg series. Most states observed had effective principal quantum number, ν, between 12 and 18 and one quantum of vibrational excitation in the CaF+ ion-core, although lower ν, υ [Formula: see text] = 2 states were also identified. Core-nonpenetrating states were observed both directly and through avoided crossings with core-penetrating states. Five of the seven [Formula: see text] components in the f-complexes derived from Ca+, 13f and n = 14f, have been identified. We present a detailed analysis of the CaF electronic structure for 12.5 [Formula: see text] ν [Formula: see text] 14.6, υ = 1 using an effective Hamiltonian model to describe CaF+ ion-core-induced [Formula: see text]-mixing between [Formula: see text] [Formula: see text] 3 (s,p, d, and f) Ca+ atomic orbitals. An observed avoided crossing between the 14.19 2Σ+, υ = 1 and 14f ([Formula: see text] = –3), υ = 1 states implies that the previously identified 0.19 Σ+ core-penetrating series has 20–30% f 2υ+-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 is provided in a companion paper by Jungen and Roche in this issue. The effective Hamiltonian model enabled derivation of electrostatic properties of the CaF+ core as well as the 0.14Δ series quantum defect derivative, [dδ/dR]Re+, which governs the exchange of energy between the Rydberg electron and the CaF+ ion-core. The CaF+ electric quadrupole moment, defined with the coordinate origin at the center-of-charge, is 11.3 ± 0.5 a.u. PACS Nos.: 33.40+f, 33.80Eh, 33.15Ry, 33.15Ta