Infrared action spectroscopy as tool for probing gas-phase dynamics: protonated dimethyl ether, (CH₃)₂OH⁺, formed by the reaction of CH₃OH₂⁺ with CH₃OH

Abstract

Methanol is one of the most abundant interstellar Complex Organic Molecules (iCOMs) and represents a major building block for the synthesis of increasingly complex oxygen-containing molecules. The reaction between protonated methanol and its neutral counterpart, giving protonated dimethyl ether, ${\left({\text{CH}}_3^{}\right)}_2^{}{\text{OH}}^{+}$, along with the ejection of a water molecule, has been proposed as a key reaction in the synthesis of dimethyl ether in space.

Here, gas phase vibrational spectra of the ${\left({\text{CH}}_3^{}\right)}_2^{}{\text{OH}}^{+}$ reaction product and the ${\left[{\text{C}}_2^{}{\text{H}}_9^{}{\text{O}}_2^{}\right]}^{+}$ intermediate complex(es), formed under different pressure and temperature conditions, are presented. The widely tunable free electron laser for infrared experiments, FELIX, was employed to record these vibrational fingerprint spectra using different types of infrared action spectroscopy in the 600-1700 cm${}^{-1}$ frequency range, complemented with measurements using an OPO/OPA system to cover the $\text{O}-\text{H}$ stretching region $3400-3700{\mathrm{c}\mathrm{m}}^{-1}$. The formation of protonated dimethyl ether as a product of the reaction is spectroscopically confirmed, providing the first gas-phase vibrational spectrum of this potentially relevant astrochemical ion.

GRAPHICAL ABSTRACT

Keywords:

• Infrared action spectroscopy
• ion-molecule reactions
• cold ion spectroscopy
• interstellar complex organic molecules (iCOMs)
• astrochemistry

Acknowledgments

We would like to dedicate this work, which combines ion reactivity with spectroscopic probing, to the memory of our mentor and colleague Dieter Gerlich, who was a pioneer in the study of ion-molecule reactivity and spectroscopy. Dieter's innovative developments of numerous versatile techniques to guide, trap and cryogenically cool ions have been and will be an inspiration to our research.

We gratefully acknowledge the support of Radboud University and of NWO for providing the required beam time at the FELIX Laboratory, and the skillful assistance of the FELIX staff. We thank the Cologne Laboratory Astrophysics group for providing the FELion ion trap instrument for the current experiments and the Cologne Center for Terahertz Spectroscopy funded by the Deutsche Forschungsgemeinschaft (DFG, grant SCHL 341/15–1) for supporting its operation. V.R. also acknowledges funding for a PhD fellowship from the Dept. Physics, University of Trento.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The original contributions presented in the study are included in the article and in the Electronic Supplementary Material. Gaussian log files for the theoretical calculations performed (structures, energies and spectra) are made available as ASCII files in the Zenodo repository accessible via https://doi.org/10.5281/zenodo.7868559. Further inquiries can be directed to the corresponding author.

Additional information

Funding

The research leading to these results has received funding from LASERLAB-EUROPE (grant agreement no. 871124, European Union's Horizon 2020 research and innovation programme), from the Deutsche Forschungsgemeinschaft (DFG, grant SCHL 341/15–1), from NWO Exact and Natural Sciences through the use of supercomputer facilities at SURFsara in Amsterdam (NWO Rekentijd grant 2021.055), from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska Curie grant agreement No 811312 for the project ‘Astro-Chemical Origins’ (ACO) and from MUR PRIN 2020 project n. 2020AFB3FX ‘Astrochemistry beyond the second period elements’.