Features of the formation of the spin polarization of an alkali metal at the resolution of hyperfine sublevels in the $^2S_{1/2}$ state

The optical orientation of the angular momenta of alkali atoms in the presence of a buffer gas (molecular nitrogen) has been studied experimentally. It has been shown that, even at a low concentration of molecular nitrogen in the cell, the excitation of $^{133}$Cs atoms from the lower hyperfine level with $F=3$, which belongs to the ground $^2S_{1/2}$ state, results in a larger amplitude of the magnetic resonance than the excitation from the hyperfine level with $F=4$. This result has been theoretically explained under the assumption that the spin state of the alkali atomic nucleus does not change at collision with a nitrogen molecule, which is accompanied by a nonradiative transition of the alkali atom from the excited $^2P_{1/2}$ state to the ground $^2S_{1/2}$ state.