Measurement and calculation of the fine structure changing collision cross sections in the Mg+ and Ca+ resonance states by helium

Using laser ablation of solid samples in a buffer gas atmosphere, free magnesium and calcium ions are produced within a confined volume of a laser produced plasma above the sample surface. The fine structure transfer cross sections of the Mg⁺ and Ca⁺ resonance states by collisions with helium are measured at different gas temperatures by laser induced fluorescence. The experimental results are compared with theoretical cross sections of fine structure changing collisions taking into account radial and angular mixing of the relevant molecular terms. Good agreement between theory and experiment is obtained in the case of Mg⁺-He. For Ca⁺-He, the theoretical and experimental data do not agree. Possible systematic errors in the fine structure transfer measurements of Ca⁺ by helium are discussed.