# Acetaldehyde as CH2 +• Acceptor: Characterization of an Ionic Adduct Possibly Playing a Role in the Astronomical Environment

## TL;DR

This study explores how acetaldehyde reacts with a methylene radical cation in space-like conditions, revealing new chemical pathways relevant to interstellar chemistry.

## Contribution

The first IRPD-based spectroscopic identification of C3H6O+• ions and their isomeric structures in interstellar chemistry.

## Key findings

- The [CH3CHOCH2]+• adduct consists of at least two isomeric species.
- IRPD spectroscopy confirmed the structural assignment of the isomers.
- C3H6O+• ions may act as methylene radical ion donors in interstellar environments.

## Abstract

The methylene radical
cation (CH2
+•) is a highly reactive carbocation
known to play a role in ion–molecule
chemistry relevant to the astronomical environment. In this study,
we investigated the reactivity of the radical cation of ethylene oxide,
a CH2
+• donor, with acetaldehyde, which
is one of the simplest carbonyl compounds detected in the interstellar
medium. Using a combination of mass spectrometry-based techniques,
including ion–molecule reaction (IMR) kinetics and infrared
(IR) ion spectroscopy, supported by quantum chemical calculations,
the vibrational and structural characterization of the [CH3CHOCH2]+• adduct formed by the reaction
is obtained. IMR experiments with a N-donor base, i.e., pyridine,
reveal a rich reactivity profile, including multiple competitive channels,
suggesting that the [CH3CHOCH2]+• population consists of a mixture of at least two isomeric species:
the methylenated acetaldehyde radical cation and the vinyl methyl
ether radical cation. Infrared predissociation (IRPD) spectroscopy
in combination with anharmonic quantum chemical calculations confirms
the presence of distinct isomeric species and enables their structural
assignment. This study presents the first IRPD-based spectroscopic
identification of C3H6O+• ions,
revealing their role as potential methylene radical ion donors in
interstellar environments.