We have applied the laser-rf-laser double-resonance method to a molecular ion. Fifty-six hyperfine components of fine-structure transitions (ΔJ=±1) were measured in rotational levels from N=1 to 27 of the ν’’=1 vibrational level of the ${\mathit{X}}^2$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ ground electronic state of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}_2^{+}{}_{}{}^{}$. In order to fit the data, we required seven molecular constants, corresponding to the following interactions: electron spin-rotation fine structure and its centrifugal distortion, Fermi-contact hyperfine structure (hfs), dipolar hfs and its centrifugal distortion, and electric quadrupole and nuclear spin-rotation hfs. The results are in reasonable agreement with theoretical calculations based upon a Hartree-Fock-Roothaan wave function.

• Received 4 April 1991

DOI:https://doi.org/10.1103/PhysRevA.44.4418