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The $A~2\Pi u-X~2\Pi g$ system of $CS2+$ isolated in solid Ne was investigated by laser-induced fluorescence. Dispersed fluorescence spectrum in the range 475-570 nm and fluorescence excitation spectrum in the range 410-480 nm showed distinct vibrational progressions. Previous $studies1,2$ reported irregular vibrational spacings for the $A~$ and $X~$ states due to Fermi resonance. We have carefully determined the line positions of the $A~-X~$ system of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C32S2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>},13C32S2+$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C34S2+$. By comparison of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$-isotopic shifts relative to $\mathrm{<mrow\; data-mjx-texclass="ORD">34</mrow>}S$-isotopic shifts for the corresponding lines, we were able to assign each component of the Fermi polyad. Our new assignments for the $X~$ state are different from previous ones, for example: the (1,2,0) and (2,0,0) are interchanged, and the (1,4,0) and (3,0,0) are also interchanged; these new assignments agree with recent theoretical $calculations3$. Similarly, we also propose new assignments for the vibronic lines of the $A~$ state.