Forbidden electric dipole rotation and rotation–vibration transitions in H2+

Previous studies of the interaction between the rotation–vibration levels of the 1sσg and 2pσu electronic states of H2+ have focussed on explaining the large hyperfine structure observed in some rovibronic transitions between these electronic states. The interaction is an ortho–para interaction between levels of the two electronic states and it gives electric dipole intensity to forbidden rotation and rotation–vibration transitions within each electronic state. We determine the transition moments and Einstein A factors for the most significant of these transitions and point out their relevance to the problem of observing interstellar H2+.