Highly resolved infrared spectra of pure CO₂ ice (15–75 K)^⋆

¹ Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513 2300 RA, Leiden, The Netherlands
e-mail: isokoski@strw.leidenuniv.nl
² Department of Physics and Astronomy, The University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
³ Current address: New York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA

Received: 20 March 2013
Accepted: 14 May 2013

Abstract

Context. The ν₂ bending mode of pure CO₂ ice around 15.2 μm exhibits a fine double-peak structure that offers a sensitive probe to study the physical and chemical properties of solid CO₂ in space. Current laboratory spectra do not fully resolve the CO₂ ice features.

Aims. To improve the fitting of the observed CO₂ features, high-resolution solid-state infrared spectra of pure CO₂ ice are recorded in the laboratory for a series of astronomically relevant temperatures and at an unprecedented level of detail.

Methods. The infrared spectra of pure CO₂ ice were recorded in the 4000 to 400 cm^-1 (2.5–25 μm) region at a resolution of 0.1 cm^-1 using Fourier transform infrared spectroscopy.

Results. Accurate band positions and band widths (FWHM) of pure CO₂ ice are presented for temperatures of 15, 30, 45, 60, and 75 K. The focus of this spectroscopic work is on the CO₂ (ν₂) bending mode, but more accurate data are also reported for the ¹²CO₂ and ¹³CO₂ (ν₃) stretching mode, and CO₂ (ν₁+ν₃) and (2ν₂+ν₃) combination bands.