High Resolution Laser Excitation Spectra and Franck-Condon Factors of A²Π-X²Σ⁺ Electronic Transition of MgF

Magnesium monofluoride (MgF) is proposed as an ideal candidate radical for direct laser cooling. Here, the rotationally resolved laser spectra of MgF for the A²Π-X²Σ⁺ electronic transition system were recorded by using laser induced fluorescence technique. The MgF radicals were produced by discharging SF₆/Ar gas mixtures between the tips of two magnesium needles in a supersonic jet expansion. We recorded a total of 19 vibrational bands belonging to three sequences of Δv=0, ±1 in the region of 348-370 nm. Accurate spectroscopic constants for both X²Σ⁺ and A²Π states are determined from rotational analysis of the experimental spectra. Spectroscopic parameters, including the Franck-Condon factors (FCFs), are determined from the experimental results and the Rydberg-Klein-Rees (RKR) calculations. Significant discrepancies between the experimentally measured and RKR-calculated FCFs are found, indicating that the FCFs are nearly independent of the spin-orbit coupling in the A²Π state. Potential energy curves (PECs) and FCFs determined here provide necessary data for the theoretical simulation of the laser-cooling scheme of MgF.