Communication: Long-lived neutral H₂ in hydrogen migration within methanol dication

The ejection of triatomic hydrogen molecular ions HD₂ ⁺ and D₃⁺ from CD₃OH²⁺ is investigated by first-principle molecular dynamics simulation. Two C-D chemical bonds are found to be broken to form a neutral D₂ moiety that vibrates, rotates, and moves for a relatively long period of time (20-330 fs) towards a transition state leading to the ejection of HD₂⁺ or D₃⁺. The formation of such a long-lived neutral D ₂ moiety within a hydrocarbon molecule interprets well the recent experimental findings of the long lifetime of doubly charged energized hydrocarbon molecules prior to the ejection of H₃⁺.