re: H2O2 isn't very stable. Do they explain that?
H2O2 or an oxidant like it may have been the chemical that caused the false positive with G. Levin's experiment.
H2O2 would be produced through photo-dissociation and recombination, e.g.
CO2 + photon = CO + O
H2O + O = H2O2
The H2O2 would be destroyed as fast as it was being produced. The Martian atmosphere is saturated with water vapor due to the sublimation of ice.
The formation of ozone in the Earth's upper atmosphere follows a similar process.
Gary