Fundamental vibrational transitions of hydrogen chloride detected in CRL 2136 ^{⋆,⋆⋆,⋆⋆⋆}

¹ Universitäts-Sternwarte München, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany
e-mail: mgoto@usml.lmu.de
² Subaru Telescope, 650 North A‘ohoku Place, Hilo, HI 96720, USA
³ Gemini Observatory, 670 North A‘ohoku Place, Hilo, HI 96720, USA
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA

Received: 8 July 2013
Accepted: 14 August 2013

Abstract

Aims. We would like to understand the chemistry of dense clouds and their hot cores more quantitatively by obtaining more complete knowledge of the chemical species present in them.

Methods. We have obtained high-resolution infrared absorption spectroscopy at 3–4 μm toward the bright infrared source CRL 2136.

Results. The fundamental vibration-rotation band of HCl has been detected within a dense cloud for the first time. The HCl is probably located in the warm compact circumstellar envelope or disk of CRL 2136. The fractional abundance of HCl is (4.9–8.7) × 10^-8, indicating that approximately 20% of the elemental chlorine is in gaseous HCl. The kinetic temperature of the absorbing gas is 250 K, half the value determined from infrared spectroscopy of ¹³CO and H₂O. The percentage of chlorine in HCl is approximately that expected for gas at this temperature. The reason for the difference in temperatures between the various molecular species is unknown.