We present the combined 2.5–30 μm spectra of four protostars acquired with the infrared camera and the infrared spectrograph on board the AKARI and Spitzer space telescopes, respectively. To analyze the ice absorption features in the 8–22 μm, we first performed a continuum determination process on mid-infrared spectra and applied a method to subtract the silicate absorption. We conducted a global fitting process to the absorption features in the combined infrared spectra using the experimental ice absorbance data to identify the intrinsic absorption of each ice component. We first derived the H2O ice column densities of both stretch and libration modes at 3.05 μm and 13.6 μm simultaneously. We also identified the absorption features containing NH3, CH3OH, CO2, and CO and decomposed their mixed components and compared their ice abundances at different evolutionary stages of the protostars. We explored possible absorptions of the organic ice species such as HCOOH, CH3CHO, and CH3CH2OH in the mid-infrared ranges. The ice analysis method developed in this study can be applied to the ice spectra obtained by the James Webb Space Telescope.

Astrochemistry provides powerful tools to understand various cosmic phenomena, including those in our solar system to the large-scale structure of the universe. In addition, the chemical property of an astronomical body is a crucial factor which governs the evolution of the system. Recent progress in astrophysical theories, computational modelings, and observational techniques requires a detailed understanding of the interactions between the constituents of an astronomical system, which are atoms and molecules within the system. Especially the far-infrared/sub-millimeter wave range, which is called as the last frontier in astronomical observations, contains numerous molecular lines, which may provide a huge amount of new information. However, we need an astrochemical understanding to use this information fully. Although this review is very limited, I would like to stress the importance of astrochemical approach in this overview for the field, which is getting much more attention than ever before.