The Altitude Distribution of Iron Monoxide in the Mesosphere

Cosmic dust enters the mesosphere and ablates into a hot gas which later condenses into meteoritic smoke, leaving behind some atomic iron in the gas phase. This atomic iron has been measured extensively with iron lidars at several sites. The atomic iron reacts with ozone to form iron oxide, FeO. The FeO reacts with atomic oxygen to recycle the atomic iron, Fe. This balance between production and loss leads to a significant stable concentration of molecular FeO. Although there are side cycle reactions of FeO with other gases, they are not important above 80 km. The reaction of Fe with ozone leads to a chemiluminescent airglow emission which has been previously measured by the authors from the OSIRIS spectrograph on the ODIN satellite. The intensity of this airglow emission from FeO(5delta) is proportional to the product of the atomic iron concentration and the ozone concentration. Since the rate of reaction for the reaction of FeO with atomic oxygen is also in equilibrium with rate of reaction of Fe with ozone, the airglow intensity can be used to derive the ground state FeO density if the atomic oxygen concentrations are available. The atomic oxygen can be derived from other airglow emissions, particularly the A band of O2 which is also observed simultaneously by the OSIRIS instrument. The observed ground state FeO profile will be compared with model calculations by the authors. Since this is the first measurement of the altitude profile of ground state FeO, there are no other experimental measurements with which to compare the ground state FeO.