High-Resolution Near-Infrared Spectroscopy of CH₂⁺ and Its Deuterated Isotopologues

Aiming to provide approximate rotational constants for millimeter wave spectroscopists to identify the corresponding species in space, we have recorded the near-infrared spectra of the methylene cation CH₂⁺ and its deuterated isotopologues, CD₂⁺ and CHD⁺, using a high resolution and high sensitivity spectrometer. Detection of CH₂⁺ in space will shed light on interstellar chemistry as it is the intermediate between the abundant CH⁺ and yet to be observed CH₃⁺, which is important in the formation of larger organic molecules. CH₂⁺ and its deuterated isotopologues are also of special interest for theoretical studies because of their unique intramolecular dynamics, i.e., the Renner–Teller interaction and quasi-linearity. This paper will discuss several new bands of CH₂⁺, the Ã(0,5[11],0)⁰ ← X̃(0,0[0],0)¹ and Ã(0,4[11],0)² ← X̃(0,0[0],0)¹ bands of CD₂⁺, which have been identified and analyzed, and the candidate lines for the Ã(0,4[10],0)¹ ← X̃(0,0[1],0)⁰ band of CHD⁺, in comparison with the theoretical predictions by Bunker and colleagues