Laboratory spectroscopy of theoretical ices: Predictions for JWST and test for astrochemical models

Abstract

Context. The gas and ice-grain chemistry of the pre-stellar core L1544 has been the subject of several observations and modelling studies conducted in the past years. The chemical composition of the ice mantles reflects the environmental physical changes along the temporal evolution. The investigation outcome hints at a layered structure of interstellar ices with mainly H${}_2$O in the inner layers and an increasing amount of CO near the surface. The morphology of interstellar ice analogues can be investigated experimentally. Aims. This research presents a new approach of a three-dimensional fit where observational results are first fitted with a gas-grain chemical model. Then, based on the numerical results the laboratory IR spectra are recorded for interstellar ice analogues in a layered and in a mixed morphology. These results can then be compared with future James Webb Space Telescope (JWST) observations. Special attention is paid to the inclusion of the IR inactive species N${}_2$ and O${}_2$. Methods. Ice analogue spectra containing the most abundant predicted molecules were recorded at a temperature of 10 K using a Fourier transform infrared spectrometer. In the case of layered ice we deposited a H${}_2$O-CO-N${}_2$-O${}_2$ mixture on top of a H2O-CH${}_3$OH-N${}_2$ ice, while in the case of mixed ice we examined a H${}_2$O-CH${}_3$OH-N${}_2$-CO composition. Results. Following the changing composition and structure of the ice, we find differences in the absorption bands for most of the examined vibrational modes. The extent of observed changes in the IR band profiles will allow us to analyse the structure of ice mantles in L1544 from future observations by the JWST. Conclusions. The comparison of our spectroscopic measurements with upcoming JWST observations is crucial in order to put stringent constraints on the chemical and physical structure of dust icy mantles, and to explain surface chemistry.

Accepted for publication in A&A, 13 pages, 5 figures

References in corpus (9)

• Observing the gas temperature drop in the high-density nucleus of L 1544
• The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• The dynamics of collapsing cores and star formation
• The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out
• The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
• Band profiles and band strengths in mixed H2O:CO ices
• The complex organic molecular content in the L1498 starless core
• Spectroscopic measurements of CH${}_3$OH in layered and mixed interstellar ice analogues

Cited by in corpus (1)

• Thermal Behavior of Astrophysical Amorphous Molecular Ices