During a severe geomagnetic storm the IO 7774 ¿ triplet was observed to have an intensity of the order of 15R, reduced to the zenith. Theoretical calculations using electron density profiles obtained with the Arecibo incoherent scatter radar show that the measured intensities cannot be explained by either radiative or ion-ion recombination reactions. A possible correlation between the airglow enhancement and Dst has been found. Excitation by heavy neutral atoms or ions, for example, oxygen or O+, precipitating into the thermosphere is put forward as a possible explanation for enhanced 7774 ¿ emission during this magnetic storm.