The core-penetrating Rydberg series of the CaF molecule: At the borderline between valence and Rydberg states

Abstract

This paper reports the results of a pulsed optical–optical double resonance study of three new low energy Rydberg states and the previously known but not rotationally analyzed F 2Π state [C. A. Fowler, Phys. Rev. 59, 645 (1941)] of the CaF molecule. The v=0 levels of these four electronic states are in the energy region 36 000–39 800 cm−1 (n*≊3-4). Molecular constants (A,p,q) or γ, and B were measured for all of the states. The F′ 2Σ+ state at 36 125 cm−1 (n*=3.177) is particularly important because it is the lowest and previously unobserved member of the ′p′ 2Σ+ Rydberg series. The assignment of the F′ state as the lowest member of the ′p′ 2Σ+ series corrects a mistaken assignment of the C′ 2Σ+ state as the lowest member of the ′p′ 2Σ+ series [J. E. Murphy, J. M. Berg, A. J. Merer, N. A. Harris, and R. W. Field, Phys. Rev. Lett. 65, 1861 (1990)].