TENTATIVE IDENTIFICATION OF FORMALDEHYDE IN THE MARTIAN ATMOSPHERE

Solar occultation observations of the Martian atmosphere near the limb of the planet were performed during the Phobos mission by means of th e Auguste infrared spectrometer in the ranges 2707-2740 and 5392-5272 cm-1 with a resolving power of almost-equal-to 1300. The spectra exhib it features at 2710 and 2730 cm-1 which have not been identified previ ously. After applying a set of corrections to the data and examining t he spectra of various molecules, we are led to conclude that the best candidate for the above-mentioned features is formaldehyde (CH2O). It was observed in eight of the nine successful occultation sequences, ma inly between 8 and 20 km with an average mixing ratio of 0.5(-0.3)+0.8 ppm (there are no good data below 8 km). The observations are perform ed in equatorial spring conditions. The altitude distribution of forma ldehyde reveals correlation with the permanent haze opacity.