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Table 4
Summary of the effect of each free parameter on the surface chemistry and on the distribution of results (shown in the Appendix).
| Parameter | Effect on the surface chemistry | Distributions of abundances for stable species | Distributions of abundances for radicals |
| Multilayer versus bulk approach | The multilayer approach – decreases the formation of stable species – traps reactive species in the mantle |
– X(CO) > 10-5 for 88% (ML), 50% (bulk) cases – X(H2O) > 10-5 for 60% (ML), 93% (bulk) cases – X(CH3OH) > 10-5 for 15% (ML), 55% (bulk) cases |
– X(OH) > 10-9 for 75% (ML), 1% (bulk) cases – X(HCO) > 10-9 for 25% (ML), 2% (bulk) cases |
| Porosity | The increase of porosity – traps volatile and diffusing particles – increases the formation rate of stable species |
– X(H2CO) > 10-7 for 52% (smooth), 61% (porous) cases – X(CH3OH) > 10-7 for 51% (smooth), 61% (porous) cases |
– X(OH) > 10-6 for 55% (smooth), 20% (porous) cases |
| Density | The increase of density – decreases the formation of stable species formed by hydrogenation reactions |
– X(H2O) > 10-5 for 2% (dense), 85% (sparse) cases with X(H2O) → 2 × 10-4 – X(CH3OH) > 10-5 for 0% (dense), 35% (sparse) cases with X(CH3OH) → 9 × 10-5 |
– X(OH) > × 10-6 for 0% (sparse), 75% (dense) cases |
| Temperature | The increase of temperature – strongly increases the desorption of H and O – decreases the rates of hydrogenation reactions – decreases the abundance of stable species formed by these reactions |
– X(CH3OH) > 10-7 for 65% (cold), 45% (warm) cases – X(H2CO) > 10-7 for 60% (cold), 45% (warm) cases |
– X(OH) > 10-6 for 55% (cold), 48% (warm) cases |
| Grain size ad | The increase of the grain size – increases the mantle thickness – does not influence the integrated mantle composition |
Same evolution of distributions for all stable species | Same evolution of distributions for all radicals |
| Initial abundance of atomic oxygen | The increase of Xini(O): – increases the formation of water (and other molecules formed from reactions involving O) – slightly decreases the formation of molecules formed from CO |
– X(H2O) > 2 × 10-5 for 0% (low-O), 65% (high-O) cases with X(H2O) → 2 × 10-4 – No influence is seen for CO, H2CO and CH3OH |
– X(OH) > 4 × 10-6 for 0% (low-O), 50% (high-O) cases with X(OH) → 4 × 10-5 |
| Diffusion energy | The increase of the diffusion energy – decreases the diffusion rate of mobile species – decreases the formation rate of stable species – slightly increases the survival of radicals |
– X(H2O) > 5 × 10-6 for 87% (fast), 74% (slow) cases – X(CH3OH) > 10-7 for 80% (fast), 30% (slow) cases – X(H2CO) > 10-7 for 75% (fast), 40% (slow) cases |
Same evolution of distributions for all radicals |
| Activation energies | The increase of activation energies – strongly decreases the formation rate of H2CO and CH3OH – strongly decreases the survival of radicals HCO and CH3O – slightly increases the reaction rates of reactions involving O – slightly increases the formation of water |
– X(CO) > 10-5 for 35% (low-Ea), 98% (high-Ea) cases – X(H2CO) > 10-7 for 83% (low-Ea), 25% (high-Ea) cases – X(CH3OH) > 10-6 for 80% (low-Ea), 5% (high-Ea) cases |
– X(HCO) > 10-10 for 90% (low-Ea), 0% (high-Ea) cases – X(CH3O) > 10-10 for 70% (low-Ea), 0% (high-Ea) cases |
| Site size | The increase of the site sizes – decreases the formation time of layers – increases the mantle thickness – does not influence the integrated mantle composition |
Same evolution of distributions for all stable species | Same evolution of distributions for all radicals |
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