Search for the OH ( X 2 Π) Meinel Band Emission in Meteors as a Tracer of Mineral Water in Comets: Detection of N 2 + ( A-X )

Abstract

We report the discovery of the N₂ ⁺ A-X Meinel band in the 780-840 nm meteor emission from two Leonid meteoroids that were ejected less than 1,000 years ago by comet 55P/Tempel-Tuttle. Our analysis indicates that the N₂ ⁺ molecule is at least an order of magnitude less abundant than expected, possibly as a result of charge transfer reactions with meteoric metal atoms. This new band was found while searching for rovibrational transitions in the X²Π electronic ground state of OH (the OH Meinel band), a potential tracer of water bound to minerals in cometary matter. The electronic A-X transition of OH has been identified in other Leonid meteors. We did not detect this OH Meinel band, which implies that the excited A state is not populated by thermal excitation but by a mechanism that directly produces OH in low vibrational levels of the excited A²Σ state. Ultraviolet dissociation of atmospheric or meteoric water vapor is such a mechanism, as is the possible combustion of meteoric organics.