The chemistry used to make a rare argon-carbene cation may hold the key to hydrocarbon formation on Saturn's largest moon, claim European researchers.

Detlef Schröder from the Academy of Sciences in Prague, Czech Republic, and co-workers have made a noble-gas compound by colliding argon with dications. Using experimental and theoretical studies they showed that bromomethane (CH₃Br) can be ionised to the molecular dication CH₃Br²⁺ - that can rearrange to the tautomer CH₂BrH²⁺. The reaction of this dication with argon leads to the argon-carbene cation (ArCH₂⁺).¹ Schröder also made the corresponding carbene cation for other noble gases, including krypton and xenon.

Their work could shed light on the mysteries of the upper part of Titan's atmosphere - the ionosphere - that is known to consist of complex hydrocarbons. Previously scientists have struggled to explain how these are formed. 

Stephen Price, from University College London, UK, agrees saying that 'in recent years the bond-forming chemistry of molecular doubly-charged ions has been implicated in environments as varied as the interstellar medium and planetary ionospheres.'  And Schröder has shown before that dications are involved in the growth of hydrocarbons on Titan.² 

Compounds containing noble-gases are rare because they are notoriously difficult to make. With most needing to contain highly electronegative elements - such as fluorine, iodine, oxygen - that are capable of attacking the closed-shell configuration of electrons of the noble gas atoms. 

Price adds that, 'the synthesis of argon-carbon bonds using doubly-charged molecular reagents, further extends the range of fields in which the chemistry of gas-phase dications is potentially important.'  

Emma Shiells