Isomers of ions in space and planetary atmospheres Experimental and theoretical studies

by David Sundelin (Stockholm University)

Tuesday 27 May 2025, 14:00 → 17:00 Europe/Stockholm

AlbaNova FB51 (AlbaNova Main Building)

Abstract
The list of detected molecules in space has grown rapidly in recent years. Identified compounds now include both nitrogen
and oxygen bearing species and detection is being made in a variety of different regions. Isomers have also become
increasingly interesting, as their interconversion often is hindered by an energy barrier unlikely to be overcome given the
energy-scarce conditions in space, they readily act as different species. In order to describe the chemical environments in
space, model calculations are being performed, heavily relying on detailed knowledge about the abundances and reactivity
of these species. However, the abundances and formation pathways of many compounds still remain largely unknown.
This thesis presents two experimental studies: i) the possible selective generation of the [CH3N]+ isomers and their
reactivity with hydrocarbons methane, ethene, ethyne, propene, propadiene and propyne and the alcohol methanol, and
ii) the infrared-predissociation spectroscopy of the [CH3N]+ and [C3H3]+ isomers (and the deuterated isotopologues of the
latter). Both isomeric pairs have been proposed to exist on Titan as well as to act as key intermediates in the synthesis
of heavier compounds, potentially including aerosols, tholins and amino acids. Theoretical calculations accompanies the
above experiments, presenting potential energy surfaces of the reactions and predicted vibrational band positions.
The results show that the reactions of [CH3N]+ isomers with the hydrocarbons and the alcohol do lead to heavier
compounds in exoergic pathways feasible to occur in space and on Titan. Products identified by our calculations includes
protonated acrylonitrile, hydrogen cyanide and protonated pyrrole. The reactivity is also isomer dependent, highlighting
the importance of isomer consideration in computational modeling of chemical networks in space. The obtained IRPD
spectrum allows for identification of these species and pave the way for detection of them with infrared telescopes in space.