Submillimeter-wave spectrum of CH₂D⁺

Abstract

Aims. Recently a tentative identification of CH 2 D+ in interstellar space has been reported. To facilitate astronomical identifications, laboratory measurements of precise rest frequencies for the rotational lines of CH 2 D + should be carried out. Methods. A submillimeter-wave spectrometer is used for detection of CH 2 D + . The CH 2 D + ion is generated in an extended negative glow discharge operated at liquid nitrogen temperature. The optimum gas mixture is found to be CH 4 (∼3 mTorr), CD 4 (∼1 mTorr), and H 2 (∼2 mTorr) in helium buffer. Results. Four rotational lines have been detected in the frequency range of 280−890 GHz. The measured frequencies agree very well within a MHz with the predictions given by Rösslein et al. from the infrared spectra. Conclusions. Two rotational lines of this ion have been tentatively identified toward Ori IRc2. The rest frequencies obtained here should facilitate identifications and analysis of astronomical spectra.

Double resonance rotational spectroscopy of CH2D+

“…In total we detected 21 rotational lines. These are summarized in Table 1 and are compared to the 4 rotational lines measured by Amano (2010), whose conservative error limits are confirmed and improved by at least one order of magnitude in this work. Surprisingly, our measured values also agree extremely well with the very first prediction of rotational transitions of CH 2 D + given by Rösslein et al (1991).…”

“…Thus, excluding this line, our data were used as input to an asymmetric rotor model (Western 2016). Transitions from previous publications (Jagod et al 1992;Amano 2010;Gärtner et al 2013) were not included here as they did not significantly improve the ground state constants. The obtained rotational constants for the ground state of CH 2 D + are summarized in Table 2.…”

“…Those searches and tentative detections used predicted CH 2 D + transition frequencies based on laboratory data available at that time. The first predictions of the rotational transition frequencies were provided by the IR data by Rösslein et al (1991) and Jagod et al (1992), and those were later refined by the high-resolution IR work by Gärtner et al (2010Gärtner et al ( , 2013 and, in particular, by the first four pure rotational lines measured by Amano (2010). More recently, two fundamental rotational transitions were measured in the Cologne laboratories (Brünken et al 2014b) using a helium attachment technique at 4 K (Brünken et al 2014a).…”

Terahertz spectroscopy of the CHD radical (\hbox{$\widetilde{\textit{X}}^{\,\mathsf{3}}\textit{A}''$})

“…In the gas phase chemical models of both dense and diffuse molecular clouds, the methylene radical is thought to be one of the fundamental molecules of the carbon chemistry, and it is produced primarily by dissociative recombination of the methyl ion, CH + 3 (Herbst 2001;Vejby-Christensen et al 1997). Recently tentative detection of the mono-deuterated methyl ion, CH 2 D + have been reported toward an infrared source in the vicinity of Orion (Lis et al 2009), along with its supporting laboratory spectroscopic measurements (Amano 2010;Gärtner et al 2010). Monodeuterated methylene CHD can be produced from this ion or its counterpart ion, CHD + 2 , by dissociative recombination with an electron as shown in the chemical reactions: …”

(New) molecular ions in the interstellar medium

“…Second, the fractionation reaction between CH + 3 and HD leading to CH 2 D + , studied in a low temperature ion trap [21], has a significant exothermicity of about 600 K, allowing the reaction to occur at ∼50-60 K in medium warm environments (to the interstellar standards). Third, the spectroscopy of this molecular ion has encountered recent interest both in the Terahertz spectroscopic range [22] and in the infrared [23], where extremely high resolution measurements allow to derive rotational frequencies at a much better accuracy than in previous studies [24,25]. Nevertheless, the frequencies available from ground state telescopes have not been directly experimentally studied and a possible unambiguous astrophysical detection would be of great interest.…”