Excitation of $3F^{\circ}$ Levels of Strontium Atoms in Collisions with Slow Electrons

The excitation of the spectral series $5s4d\,^3D_{1, 2, 3} - 5snf\,^3F^{\circ}_{2, 3, 4}$ in collisions of slow monoenergetic electrons with strontium atoms is investigated experimentally. In three investigated series, the dependence of the cross sections on the principal quantum number of the upper level $n$ conforms strictly to the power law, which is indicative of the absence of perturbation of the $5snf\,^3F^{\circ}$ levels. The obtained results are compared with the available experimental and theoretical values.