Quantum Chemical Rovibrational Characterization of CH₂ClH⁺, a Low-Energy Isomer of Ionized Chloromethane

Abstract

The astrophysical detection of chloromethane indicates that a low-energy form of the cation, the methyl chloronium cation (CH 2 ClH + ), may also be found in similar regions. Quantum chemical computations are providing what have been previously benchmarked as reliable vibrational frequencies and spectroscopic constants for this openshell cation. The ν 3 Cl−H stretch at 2630.5 cm −1 has a relatively large intensity and sits at 3.80 μm in a fairly unpopulated region of most astronomical infrared spectra, where it could more readily be distinguished from polycyclic aromatic hydrocarbons or other complex organic species. The 1.48 D center-of-mass computed dipole moment of CH 2 ClH + makes it observable rotationally, and its differences in structure and rotational constants from chloromethane will distinguish this cation isomer from its neutral counterpart. Such would have application for observational analysis with either groundbased radio telescopes or from the upcoming James Webb Space Telescope.