Cold collision and the determination of the X²Σ_1/2(v = 1,  N = 1) → A²Π_1/2(v′ = 0, J′ = 1/2) frequency with buffer-gas-cooled MgF molecules

We report a detailed experimental study of the cold collision of magnesium mono-fluoride (MgF) with buffer gas and compare the cryogenic molecular beam source of two different inner structures of cell. The collision cross section with helium is measured to be ∼0.8×10⁻¹⁴cm² at 7.5 K, which is suitable for buffer-gas cooling. The absorption spectrum around 368.7 nm at low-lying rotational states is assigned and the accurate frequency of X²Σ_1/2(v = 1, N = 1) → A²Π_1/2(v′ = 0, J′ = 1/2) transition is determined to be 812.959246 THz, which is essential for constructing the quasi-closed cycling between vibrational states. Our study is an important complement to laser cooling of MgF molecules.