The Zeeman effect and hyperfine interactions in J = 1-0 transitions of CH + and its isotopologues

The J = 1 − 0 transitions of \documentclass[12pt]{minimal}\begin{document}$^{12}$\end{document} 12 CH \documentclass[12pt]{minimal}\begin{document}$^+$\end{document} + , \documentclass[12pt]{minimal}\begin{document}$^{13}$\end{document} 13 CH \documentclass[12pt]{minimal}\begin{document}$^+$\end{document} + , and \documentclass[12pt]{minimal}\begin{document}$^{12}$\end{document} 12 CD \documentclass[12pt]{minimal}\begin{document}$^+$\end{document} + in the ground \documentclass[12pt]{minimal}\begin{document}$X^1\Sigma ^+$\end{document} X 1 Σ + state have been unambiguously identified by using an extended negative glow discharge as an ion source. Unexpectedly large Zeeman splittings have been observed, and the \documentclass[12pt]{minimal}\begin{document}$^{13}$\end{document} 13 CH \documentclass[12pt]{minimal}\begin{document}$^+$\end{document} + line exhibits nuclear spin-rotation hyperfine splitting in addition to the Zeeman effect. The nuclear spin-rotation coupling constant was determined to be 1.087(50) MHz for the \documentclass[12pt]{minimal}\begin{document}$^{13}$\end{document} 13 C species. The rotational g -factor is found to be -7.65(29), in terms of the nuclear magneton for the J = 1 and v = 0 state, more than an order of magnitude larger than values for typical diamagnetic closed shell molecules. These larger than usual magnetic interactions for a \documentclass[12pt]{minimal}\begin{document}$^1\Sigma$\end{document} 1 Σ molecule are caused by the large rotational energy and relatively small excitation energy of the excited \documentclass[12pt]{minimal}\begin{document}$A^1\Pi$\end{document} A 1 Π state. The effective g -factor and the spin-rotation coupling constant obtained by ab initio calculations agree very well with the experimentally determined values.