VUV-absorption cross section as a function of photon wavelength (bottom X-axis) and VUV-photon energy (top X-axis) of CH₄ ice deposited at 8 K, black solid trace. The blue dashed trace is the VUV-absorption cross-section spectrum of gas phase CH₄ adapted from Lee et al. 32. The fit of the solid-phase spectrum, red dotted (single bands, see Table 2) and dashed-dotted trace, is the sum of three Gaussians. It has been offset for clarity.