Controlling H3+ Formation From Ethane Using Shaped Ultrafast Laser Pulses

Tiana Townsend,Charles J Schwartz,T Severt,K D Carnes,Bethany Jochim,Kanaka Raju P,E Wells,Peyman Feizollah,I Ben-Itzhak,S N Tegegn,S Zhao,J L Napierala,Naoki Iwamoto,A Solomon

doi:10.3389/fphy.2021.691727

Tiana Townsend, Charles J Schwartz + Show 12 more

Open Access

https://doi.org/10.3389/fphy.2021.691727

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Abstract

An adaptive learning algorithm coupled with 3D momentum-based feedback is used to identify intense laser pulse shapes that control H3+ formation from ethane. Specifically, we controlled the ratio of D2H+ to D3+ produced from the D3C-CH3 isotopologue of ethane, which selects between trihydrogen cations formed from atoms on one or both sides of ethane. We are able to modify the D2H+:D3+ ratio by a factor of up to three. In addition, two-dimensional scans of linear chirp and third-order dispersion are conducted for a few fourth-order dispersion values while the D2H+ and D3+ production rates are monitored. The optimized pulse is observed to influence the yield, kinetic energy release, and angular distribution of the D2H+ ions while the D3+ ion dynamics remain relatively stable. We subsequently conducted COLTRIMS experiments on C2D6 to complement the velocity map imaging data obtained during the control experiments and measured the branching ratio of two-body double ionization. Two-body D3+ + C2D3+ is the dominant final channel containing D3+ ions, although the three-body D + D3+ + C2D2+ final state is also observed.

Highlights

The intramolecular migration of hydrogen continues to be an active area of investigation in ultrafast science [1,2,3,4,5,6,7,8,9,10,11] with implications for topics ranging from combustion [12] to peptide dissociation [13] and characterizing conformational differences in molecules [14, 15]
By using the D3C-CH3 isotopologue of ethane we were able to separate two different types of dissociation processes leading to the formation of trihydrogen cations: D+3 formation which involves atoms from only one side of the molecule and D2H+ that involves atoms from both sides of the molecule
The laser pulses optimized with an adaptive search strategy were more effective at improving the D2H+:D+3 ratio while maintaining the overall ion yield than the most effective pulses found with a systematic scan of pulse dispersion parameters

Summary

Introduction

The intramolecular migration of hydrogen continues to be an active area of investigation in ultrafast science [1,2,3,4,5,6,7,8,9,10,11] with implications for topics ranging from combustion [12] to peptide dissociation [13] and characterizing conformational differences in molecules [14, 15]. In some cases the migration of hydrogen leads to the formation of new molecular ions, such as H+3 [5, 16,17,18,19,20,21], by processes such as H2 roaming or double hydrogen migration [18, 19, 22, 23]. The formation of H+3 is usually a multi-step process that often involves the association of hydrogen atoms from different sites of the parent molecule. In methanol (CH3OH), there is clear evidence that H+3 may form when a roaming H2 from the methyl side abstracts the hydroxyl proton in addition to alternative mechanisms that only involve the methyl side. For ethanol (CH3CH2OH) and several slightly longer alcohol molecules, multiple pathways to H+3 formation exist that involve hydrogen migration, the relative importance of these pathways decreases as the carbon chain length increases [19, 20]

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