Mechanisms and time-resolved dynamics for trihydrogen cation (H3+) formation from organic molecules in strong laser fields

Nagitha Ekanayake,Kanaka Raju Pandiri,Peyman Feizollah,Ben Berry,Daniel Rolles,James E Jackson,Travis Severt,Christopher A Mancuso,Marcos Dantus,Benjamin G Levine,Balram Kaderiya,Artem Rudenko,Bethany Jochim,Shashank Pathak,B Scott Fales,Muath Nairat,Kevin D Carnes,Itzik Ben-Itzhak

doi:10.1038/s41598-017-04666-w

Nagitha Ekanayake, Kanaka Raju Pandiri + Show 16 more

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https://doi.org/10.1038/s41598-017-04666-w

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Abstract

Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds to break and form. We present evidence for the existence of two different reaction pathways for H3+ formation from organic molecules irradiated by a strong-field laser. Assignment of the two pathways was accomplished through analysis of femtosecond time-resolved strong-field ionization and photoion-photoion coincidence measurements carried out on methanol isotopomers, ethylene glycol, and acetone. Ab initio molecular dynamics simulations suggest the formation occurs via two steps: the initial formation of a neutral hydrogen molecule, followed by the abstraction of a proton from the remaining CHOH2+ fragment by the roaming H2 molecule. This reaction has similarities to the H2 + H2+ mechanism leading to formation of H3+ in the universe. These exotic chemical reaction mechanisms, involving roaming H2 molecules, are found to occur in the ~100 fs timescale. Roaming molecule reactions may help to explain unlikely chemical processes, involving dissociation and formation of multiple chemical bonds, occurring under strong laser fields.

Highlights

Strong-field laser-matter interactions often lead to exotic chemical reactions
Taking into account the importance of having a definitive understanding of H3+ formation dynamics in polyatomic molecules under strong-field conditions, we experimentally and theoretically consider H3+ formation from organic molecules via two distinct pathways following double ionization of the precursor molecule: (i) association of three hydrogen atoms initially bound to the same carbon atom [Fig. 1(a)], and (ii) association of two hydrogen atoms bound to a carbon atom with a hydrogen atom from a neighboring chemical group [Fig. 1(b)]
First principles molecular dynamics simulations for the formation of H3+ from a doubly charged methanol molecule based on the single reference configuration interaction singles and doubles (CISD) method have previously been reported[38]

Summary

Introduction

Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds to break and form. Ab initio molecular dynamics simulations suggest the formation occurs via two steps: the initial formation of a neutral hydrogen molecule, followed by the abstraction of a proton from the remaining CHOH2+ fragment by the roaming H2 molecule. This reaction has similarities to the H2 + H2+ mechanism leading to formation of H3+ in the universe. It is known that strong-field laser-molecular interactions lead to reactions involving multiple bond cleavage and formation processes, and the relative yields of such reactions can be manipulated to some extent by tailored femtosecond pulses[9, 10]. We explore two types of precursor molecules: those containing three hydrogens bound to a single carbon atom (i.e. methyl group), as well as those containing only two hydrogen atoms bound to a carbon atom containing a hydroxyl group

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