Comparison of fast and slow-contraction chemodynamical models. (a) H₂ number density, ﹩{n}_{{{\rm{H}}}_{2}}﹩. (b) Gas kinetic temperature, T_k (solid), and dust temperature, T_d (dashed). (c) Deuteration ratio, x(N₂D⁺)/x(N₂H⁺). (d) Ortho-to-para ratio of H₂, OPR(H₂). (e) Ortho-to-para ratio of H₂D⁺, OPR(H₂D⁺). Orange and blue curves correspond to snapshots at t = 0.42 Ma (fast) and t = 5.1 Ma (slow), respectively, chosen when both reach a central density of ﹩{n}_{{{\rm{H}}}_{2}}(0)=1.1\times 1{0}^{7}﹩ cm⁻³. The initial uniform density 5 × 10³ cm⁻³, a 10 K singular isothermal sphere (SIS) reference, the initial T_k = T_d = 10 K, and the initial OPR(H₂) = 3 are indicated. Boltzmann OPR(H₂) and OPR(H₂D⁺) corresponding to the T_k profile are noted. The dotted vertical line marks the outer boundary used in the non-LTE radiative-transfer modeling (7.63 kau).