The discovery of the methyl cation (CH+
3) was reported in 2023 by Berné and co-workers. As they note, CH+
3 has been thought to be an important contributor in gas-phase astrochemistry for forty years. But due to its symmetry, CH+
3 has no permanent dipole moment and thus cannot be detected via rotational spectroscopy.

The methyl cation was identified via two vibrational modes using the James Webb Space Telescope (JWST) toward a protoplanetary disk centered on the red dwarf d203-506 in the Orion Bar. New spectroscopic work by Changala and co-workers enabled deeper analysis of the JWST data. The animations below show the two IR-active vibrational features that were detected: the out-of-plane ν₂ mode and the doubly degenerate, in-plane ν₄ mode.

The methyl or methenium cation can be formed by ionizing the methyl radical, CH₃. Both species are trigonal planar. CH₃ only becomes tetrahedral (as in methane or the methyl group in many compounds) when a fourth covalent bond is formed to carbon.