Infrared spectrum of the methane ice at 15 K, before irradiation. In a) the absorbance scale has been enlarged to make the less intense combination bands of all CH₄ assignments visible and b) zoom of the ν₃ (this band is slightly saturated, but it does not significantly change the band profile) and ν₄ assignments. The vibration modes at 1302 and 1298 cm^-1 are considered as centered at 1300 cm^-1.