Studies of copper monofluoride in the b³Π state by microwave-optical double resonance and intermodulated fluorescence

The optical spectrum of copper monofluoride in the yellow has been studied at sub-Doppler resolution to obtain information on the nuclear hyperfine interactions for both ⁶³Cu and ¹⁹F nuclei for the upper state (b³Π). The experimental techniques employed were intermodulated fluorescence and microwave-optical double resonance, the electronic transition being excited with a tunable dye laser. The data obtained were fitted together with earlier Doppler-limited measurements to an effective Hamiltonian and values were determined for most of the molecular parameters involved. The b³Π state of copper monofluoride is heavily perturbed by nearby electronic states and it is noteworthy that the effective Hamiltonian can reproduce the observations to within experimental error. Generally speaking, the Cu and F hyperfine parameters are consistent with an ionic description of the b[su3Π state, arising from the configuration Cu⁺ (3d⁹ 4s¹) F^- (2p⁶). However, some anomalies arise. In particular, the parity-dependent hyperfine parameter, d, for the ⁶³Cu nuclei is determined to be negative, contrary to expectation.