Gas-Phase Infrared Action Spectroscopy of CH 2 Cl + and CH 3 ClH + : Likely Protagonists in Chlorine Astrochemistry

Two fundamental halocarbon ions, CH 2 Cl + and CH 3 ClH + , were studied in the gas phase using the FELion 22-pole ion trap apparatus and the Free Electron Laser for Infrared eXperiments (FELIX) at Radboud University, Nijmegen (the Netherlands). The vibrational bands of a total of four isotopologs, CH 2 35,37 Cl + and CH 3 35,37 ClH + , were observed in selected wavenumber regions between 500 and 2900 cm −1 and then spectroscopically assigned based on the results of anharmonic force field calculations performed at the CCSD(T) level of theory. As the infrared photodissociation spectroscopy scheme employed probes singly Ne-tagged weakly bound complexes, complementary quantum-chemical calculations of selected species were also performed. The impact of tagging on the vibrational spectra of CH 2 Cl + and CH 3 ClH + is found to be virtually negligible for most bands; for CH 3 ClH + –Ne, the observations suggest a proton-bound structural arrangement. The experimental band positions as well as the best estimate rotational molecular parameters given in this work provide a solid basis for future spectroscopic studies at high spectral resolutions.