Ethanium

Ethanium was first detected by infrared spectroscopy among the ions produced by electrical discharges in rarefied methane or ethane gas.

[1] Ethanium can also be produced by irradiating methane containing traces of ethane with an electron beam at low pressure (about 2 mmHg).

[3] At about 1 mmHg and 30 °C, ethanium dissociates very slowly to ethenium and H2, across an energy barrier of about 10 kcal/mol; the decomposition is considerably faster at 92 °C.

The alternative "classical" structure would have the charge and the extra hydrogen bound to only one of the two atoms, i.e. a methylated methanium ion.

However, there are other configurations with near-minimum energy, including one where the two CH3 subgroups are slightly staggered (with Cs symmetry), another where one of the carbons of a C2H+5 ion is loosely bound to an H2 molecule 0.250 nm away.