Infrared predissociation spectroscopy of protonated methyl cyanide, CH3CNH+

Aravindh N Marimuthu,Frank Huis In’T Veld,Sven Thorwirth,Britta Redlich,Sandra Brünken

doi:10.1016/j.jms.2021.111477

Aravindh N Marimuthu, Frank Huis In’T Veld + Show 3 more

Open Access

https://doi.org/10.1016/j.jms.2021.111477

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Abstract

The gas phase vibrational spectrum of CH3CNH+ is investigated using a messenger infrared predissociation (IRPD) action spectroscopic method. Vibrational bands were recorded in the 300-1700 cm−1 and 2000-3300 cm−1 regions making use of the widely tunable free electron laser for infrared experiments, FELIX, coupled to a cryogenic ion trap instrument. Band assignments were aided by high-level quantum-chemical calculations, which showed excellent agreement with the experimental data. Effects of the neon atom used as messenger in the IRPD method are investigated in detail. The data presented here will support astronomical searches for the CH3CNH+ ion in space, and provide a basis for high-resolution ro-vibrational and pure rotational studies in vibrationally excited states.

Highlights

Methyl cyanide (CH3CN, known as acetonitrile) was among the first polyatomic molecules detected during radio-astronomical observations of the interstellar medium (ISM) [1]
In the present study we have investigated CH3CNH+ at the coupled-cluster singles and doubles (CCSD) level augmented by a perturbative treatment of triple excitations, CCSD(T) [34], in combination with atomic natural orbital (ANO0, ANO1, and ANO2) basis sets from Almlöf and Taylor [35] as well as the correlation-consistent valence basis set cc-pVDZ [36] in the frozen core approximation
The measured IRPD spectra for [C2H4N]+ with Ne as a tagging agent are displayed in Figs. 3 and 4, compared to the calculated spectrum of the energetically lowest lying isomer, CH3CNH+

Summary

Introduction

Methyl cyanide (CH3CN, known as acetonitrile) was among the first polyatomic molecules detected during radio-astronomical observations of the interstellar medium (ISM) [1]. As methyl cyanide has a proton affinity of 788ð8Þ kJ/mol [12], much larger than that of H2, its protonated version (CH3CNH+) might form efficiently via exothermic proton transfer from Hþ3 to CH3CN in the interstellar medium [13]. Another efficient formation pathway of protonated methyl cyanide is via radiative association of CHþ3 and HCN.

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Conclusion