Terahertz spectroscopy of the CHD radical (${\begin{array}{}{}^{\mathrm{􏽥}}\\ \mathit{X}\end{array}}^{\hspace{0.17em}\mathrm{3}}{\mathit{A}}^{\mathrm{\prime \prime }}$)

¹ Department of Environmental ScienceFaculty of Science, Toho University, 2-2-1 Miyama, Funabashi 274-8510, Japan
e-mail: ozeki@env.sci.toho-u.ac.jp
² Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, CERLA, Université Lille 1, 59655 Villeneuve d’Ascq Cedex, France
e-mail: stephane.bailleux@univ-lille1.fr

Received: 2 November 2010
Accepted: 26 November 2010

Abstract

Context. Pure rotational spectra in the field-free condition of the CH₂ and CD₂ isotopologues of the methylene radical have already been reported, whereas only six rotational transitions of the mono-deuterated species, CHD, detected by FIR-LMR spectroscopy have been.

Aims. Spectra of the mono-deuterated methylene radical in its ground electronic state ($\begin{array}{}{}_{\mathrm{􏽥}}\\ \mathit{X}\end{array}{ }^{\mathrm{3}}{\mathit{A}}^{\mathrm{\prime \prime }}$) were observed in the field-free condition for the first time in the frequency region below 1 THz.

Methods. CHD was generated in a positive column discharge in a CH₂D₂ – Ar mixture cooled with liquid nitrogen.

Results. Two rotational transitions, each split into three fine-structure components, were measured. The B and C rotational constants, the ϵ_bb and ϵ_cc spin-rotation constants, and the β spin-spin constant were revised.

Conclusions. The reported frequencies are suitable for astronomical searches.