Microwave Magnetic-Dipole Transitions between Excited Electronic States of CN

Abstract

Eleven microwave transitions in the frequency range from 10.5 to 11.5 GHz have been observed between excited electronic states of CN. These correspond to 11 of 13 allowed magnetic-dipole transitions, $\Delta F=0,\pm 1$, in the $K^{\prime }=4\mathrm{}$ perturbation complex between the three hyperfine levels of the perturbed component of the $\Lambda$ doublet of the $A^2{{\Pi }_{\frac{3}{2}}}^{+} \mathrm{}(v=10\mathrm{})\mathrm{}$ level and the three hyperfine levels in each of the perturbed and the unperturbed components of the spin doublet of the $B^2{\Sigma }^{+} \mathrm{}(v=0\mathrm{})\mathrm{}$ level. These transitions and the previously measured 13 electric-dipole transitions determine all 12 hyperfine energy levels of this perturbation complex. The experiment is the first microwave measurement of magnetic-dipole transitions between excited electronic states of a molecule. CN was produced predominately in the metastable $A^2\Pi$ state by a chemical reaction when methylene chloride was added to a nitrogen afterglow. Resonant microwave pumping from the II state increased the population of the three hyperfine levels of each $\Sigma$ state. The population change was detected by measuring an increase in the intensity of the $B^2{\Sigma }^{+}\to X^2{\Sigma }^{+} \mathrm{}(0,0)\mathrm{}$ violet band of CN near 3875 Å.