Infrared complex refractive index of astrophysical ices exposed to cosmic rays simulated in the laboratory

TL;DR

This study provides a comprehensive catalog of 39 infrared complex refractive indices for 13 astrophysical ices processed by cosmic rays, crucial for modeling interstellar ice chemistry and spectra.

Contribution

First-time presentation of a detailed infrared complex refractive index catalog for 13 cosmic-ray processed astrophysical ices, calculated using a novel NKABS method.

Findings

Catalog of 39 (n, k) indices for 13 ices from 2.0 to 16.6 micrometers.

Data enables accurate radiative transfer modeling of protostellar disks.

Demonstrated importance of these indices in reproducing YSO spectra.

Abstract

In dense and cold regions of the interstellar medium (ISM), molecules may be adsorbed onto dust grains to form the ice mantles. Once formed, they can be processed by ionizing radiation coming from stellar or interstellar medium leading to formation of several new molecules in the ice. Among the different kind of ionizing radiation, cosmic rays play an important role in the solid-phase chemistry because of the large amount of energy deposited in the ices. The physicochemical changes induced by the energetic processing of astrophysical ices are recorded in a intrinsic parameter of the matter called complex refractive index (CRI). In this paper, we present for the first time a catalogue containing 39 complex refractive indices (n, k) in the infrared from 2.0 - 16.6 micrometer for 13 different water-containing ices processed in laboratory by cosmic ray analogs. The calculation was done by using the NKABS (acronym of determination of N and K from ABSorbance data) code, which employs the Lambert-Beer and Kramers-Kronig equations to calculate the values of n and k. The results are also available at the website: http://www1.univap.br/gaa/nkabs-database/data.htm. As test case, a H2O:NH3:CO2:CH4 ice was employed in a radiative transfer simulation of a prototoplanetary disk to show that these data are indispensable to reproduce the spectrum of YSOs containing ices.