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.

Introduction
Observations
    AKARI IRC Spectra
    Spitzer IRS Spectra
Results
    Continuum Determination
    The Ice Absorption Features
Comprehensive Ice Analysis
    H2O
    Other Ice Species
    Ice Abundances
Discussions
Summary
Acknowledgments
References

• Jaeyeong Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea) Corresponding author
• Woong-Seob Jeong(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Jeong-Eun Lee(Department of Physics and Astronomy, SNU Astronomy Research Center, Seoul National University, Seoul 08826, Republic of Korea) Corresponding author
• Yao-Lun Yang(Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama, 351-0106, Japan)
• Chul-Hwan Kim(Department of Physics and Astronomy, SNU Astronomy Research Center, Seoul National University, Seoul 08826, Republic of Korea)