Time-dependent density functional theory investigation of the formation of H3+ from alkanes*

The formation of H3+ from ethane, propane, and butane dications was investigated with time-dependent density-functional theory (TDDFT) simulations. This approach offers the benefit of simultaneously addressing nuclear and electronic dynamics, enabling the investigation of electronic excitation, charge transfer, ionization, and nuclear motion. For each dication we determined the ground-state HOMO, the branching ratios of all dissociation channels, and the mechanism leading to H3+. The simulated branching ratios for ethane and propane are similar, while butane is markedly lower. Ethane follows the minimum-energy pathway (MEP) proposed previously; propane forms H3+ mainly via H2 roaming. In butane, H3+ formation proceeds via both the MEP and H2 roaming, with the H2 roaming pathway being more productive.