Anomalous Intensities in the Infrared Emission of CH⁺ Explained by Quantum Nuclear Motion and Electric Dipole Calculations

The unusual infrared emission patterns of CH⁺, recently detected in the planetary nebula NGC 7027, are examined theoretically with high-accuracy rovibrational wavefunctions and ab initio dipole moment curves. The calculated transition dipole moments quantitatively reproduce the observed J-dependent intensity variation, which is ascribed to underlying centrifugal distortion-induced interference effects. We discuss the implications of this anomalous behavior for astrochemical modeling of CH⁺ production and excitation, and provide a simple expression to estimate the magnitude of this effect for other light diatomic molecules with small dipole derivatives.