Chemical Composition of Gas-Phase Positive Ions during Laboratory Simulations of Titan’s Haze Formation

The organic haze in the atmosphere of Saturn’s moon Titan affects the moon’s atmospheric and surface properties. Ions are known to play an important role in haze formation chemistry; however, the role of ions in laboratory simulations of haze formation is poorly characterized. Here, we use a high-resolution time-of-flight mass spectrometer with an atmospheric pressure interface to chemically characterize the ambient gas-phase cations formed as haze is produced by the far ultraviolet photolysis of CH4 in N2. These experiments show that the chemical composition of the cations is complex. High molecular weight ions up to m/z 400 are observed, with organic nitrogen ions, including ions with multiple nitrogen atoms, accounting for the majority of the identified ion peaks. Many of the ions identified in this work have been observed in Titan’s upper atmosphere by the Cassini Ion and Neutral Mass Spectrometer. While the chemistry in this study is likely more representative of Titan’s lower atmosphere than of its upper atmosphere, the results presented here suggest that ion composition, including the composition of organic nitrogen ions, may be variable and diverse throughout Titan’s atmosphere. This in turn has potential implications for haze growth and the formation of complex molecules