Emissivities of γ-rays produced in ¹⁶O¹⁶O interactions. The three curves correspond to three radiation channels: γ-rays from (1) grey long dashed line: decays of “nominal” π⁰-mesons, (2) red dash-dotted line: “hard photons”, and (3) grey short dashed line: decays of “subthreshold” π-mesons. The spectrum of non-thermal nuclei ¹⁶ is assumed a power low in kinetic energy with α_p = 2.85. For the energy spectrum of CRs and the density of gas the following normalisations are used: w_p (≥ 1 GeV nuc⁻¹) = 1 eV cm⁻³; n_O = 1 cm⁻³.