We have studied the formation of negative ions in a negative Corona Discharge (CD) fed by CO2/N2 mixtures (with 0, 2, 4, 6, 8, 10% N2) using the technique of ion mobility spectrometry-orthogonal acceleration time of flight mass spectrometry (IMS-oaTOF). The composition of the negative ions was found to be dependent on the initial gas composition, the gas flow regime, the concentrations of neutral reactive species formed in the discharge and the trace amounts on water in the gases were found to play an important role in the negative ions formation. In a pure CO2 discharge operating under standard gas flow conditions of IMS (associated with strong interaction of ions with neutral reactive species formed in discharge) the ions CO3− (H2O) and CO4−(H2O) dominated the measured negative ion spectrum while in CO2/N2 mixtures NO3−(H2O)n, NO3−(HNO3) (n = 0, 1) ions prevailed. In the case of reverse gas flow regime (low interaction of ions with neutral reactive species formed in discharge), the negative ions detected were O2−(H2O)n, and O2−.CO2(H2O)n both in pure CO2 and N2/CO2 mixtures. The spectra of negative ions recorded for a gas mixture containing 4% N2 in CO2 were compared with theoretical predictions of negative ion composition in the lower atmosphere of Mars.
Drift Tube Mass Spectrometry Spectrum Martian Atmosphere Dissociative Electron Attachment Short Drift Time
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