Vibrational spectra of the dimethyl ether radical cation in low-temperature matrices

Dimethyl ether (DME) is a relatively complex molecule detected in various space objects, where it can be subjected to the action of ionizing radiation governing its further chemical evolution. Previously, the primary ionized molecule (radical cation) of DME was extensively characterized by electron paramagnetic resonance (EPR) spectroscopy, while we are unaware of any data on its vibrational spectra. In this work, we report the first assignment of the vibrational features of the DME radical cation using Fourier transform infrared (FTIR) spectroscopy in various low-temperature matrices at 4.5–7 K. The radical cations were generated by X-ray irradiation of argon and krypton matrices containing DME and an electron scavenger (SF6 or CFCl3). EPR spectroscopy was used as a reference tool, and the formation of the radical cations has been proved by its photobleaching with visible and near UV light (445–365 nm) and deuteration of DME. At least three IR absorptions assigned to the vibrational features of the DME radical cation were observed by FTIR spectroscopy, in reasonable agreement with the results of CCSD(T) calculations. In addition, the features of the DME radical cation were found in some molecular matrices (SF6, N2, and CO2) doped by DME without any electron scavenger. We believe that this is one of the first applications of a combined matrix isolation approach, complemented by ab initio calculations, to the characterization of vibrational spectra of non-rigid, relatively complex aliphatic radical cations of potential astrochemical interest.