Adiabatic index (left panel), normalised internal energy (middle panel), and entropy (right panel) for the H₂ molecule. In the left panel we also show the constants γ = 5/3 and γ = 7/5 . Residuals are for cases 1–7 with respect to case 8. In the left panel cases 1–5 are equal to γ = 7/5 below 1000 K, case 6 is identical to case 7 after 300 K, and case 7 is identical to case 8 until 6000 K; in the middle panel cases 1 to 5 are identical until 1000 K, and case 7 is almost identical to case 8 until 2000 K.