Abstract
Being the lightest, most mobile atom that exists, hydrogen plays an important role in the chemistry of hydrocarbons, proteins and peptides and most biomolecules. Hydrogen can undergo transfer, exchange and migration processes, having considerable impact on the chemical behavior of these molecules. Although much has been learned about reaction dynamics involving one hydrogen atom, less is known about those processes where two or more hydrogen atoms participate. Here we show that single and double hydrogen migrations occurring in ethanol cations and dications take place within a few hundred fs to ps, using a 3D imaging and laser pump-probe technique. For double hydrogen migration, the hydrogens are not correlated, with the second hydrogen migration promoting the breakup of the C–O bond. The probability of double hydrogen migration is quite significant, suggesting that double hydrogen migration plays a more important role than generally assumed. The conclusions are supported by state-of-the-art molecular dynamics calculations.
Highlights
Being the lightest, most mobile atom that exists, hydrogen plays an important role in the chemistry of hydrocarbons, proteins and peptides and most biomolecules
What allows us to state that the two-body coincidences mainly reflect the dynamics of the cation is the statistical analysis of the individual channels compared to their precursor(s), which is elaborated on in the Supplementary information (SI)
The Newton and Dalitz plots show a considerable dependence on the time delay for each of the pathways leading to H+ + H2O+ + C2H3+
Summary
Most mobile atom that exists, hydrogen plays an important role in the chemistry of hydrocarbons, proteins and peptides and most biomolecules. Hydrogen migration dynamics are revealed through detection of the produced ion fragments Fast nuclear dynamics such as single hydrogen migration, which unfolds on a time scale ranging from a few tens of fs to several hundreds of fs in simple hydrocarbons, have been resolved using such a pump and probe technique[14,15,16]. Several previous studies have considered the formation of H2+ and H3+ from a variety of precursor molecules, which requires the displacement of more than one hydrogen atom[19,21,22,23] In many of these cases, the H2+ and H3+ are formed from hydrogen atoms that are close to each other in the molecule (for example, the two or three H atoms bonded to the same atomic center), and are not due to the migration of H atoms from one molecular site to another. The scrambling and roaming mechanisms are energetically unfavorable and kinematically unlikely, as confirmed by applications of the Rice–Ramsperger–Kassel–Marcus (RRKM) theory to small hydrocarbons[23,27]
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