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

The J = 1-0 transitions of (CH+)-C-12, (CH+)-C-13, and (CD+)-C-12 in the ground X-1 Sigma(+) 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 (CH+)-C-13 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 C-13 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 (1)Sigma molecule are caused by the large rotational energy and relatively small excitation energy of the excited A(1)Pi state. The effective g-factor and the spin-rotation coupling constant obtained by ab initio calculations agree very well with the experimentally determined values. (C) 2010 American Institute of Physics. [doi:10.1063/1.3514914]