Table 1: Chemical surface reactions r assumed to form one new unit of the solid material s in the grain mantel. The efficiency of the reaction is limited by the key species, which has the lowest abundance among the reactants. The notation ${\scriptstyle{}^1\!\!/\!{}_2}$ in the r.h.s. column means that only every second collision (and sticking) event initiates one reaction of kind r to form the dust species s (see $\nu ^{\rm key}_r$ in Eqs. (24), (29)).
Index r Solid s Surface reaction Key species (growth)
1 TiO2[s] TiO2 $\longrightarrow$ TiO2[s] TiO2
2 rutile TiO + H2O $\longrightarrow$ TiO2[s] + H2 TiO
3   TiS + 2 H2O $\longrightarrow$ TiO2[s] + H2S + H2 TiS
4 SiO2[s] SiO2 $\longrightarrow$ SiO2[s] SiO2
5 silica SiO + H2O $\longrightarrow$ SiO2[s] + H2 SiO
6   SiS + 2 H2O $\longrightarrow$ SiO2[s] + H2S + H2 SiS
7 Fe[s] Fe $\longrightarrow$ Fe[s] Fe
8 solid iron FeO + H2 $\longrightarrow$ Fe[s] + H2O FeO
9   Fe(OH)2 + H2 $\longrightarrow$ Fe[s] + 2 H2O Fe(OH)2
10 Mg2SiO4[s] 2 Mg + SiO + 3 H2O $\longrightarrow$ Mg2SiO4[s] + 3 H2 $\min\{{\scriptstyle{}^1\!\!/\!{}_2}$Mg, SiO$\}$
11 forsterite 2 Mg(OH)2 + SiO $\longrightarrow$ Mg2SiO4[s] + H2O + H2 $\min\{{\scriptstyle{}^1\!\!/\!{}_2}$Mg(OH)2, SiO$\}$
12   2 MgOH + SiO + H2O $\longrightarrow$ Mg2SiO4[s] + 2 H2 $\min\{{\scriptstyle{}^1\!\!/\!{}_2}$MgOH, SiO$\}$
13 Al2O3[s] 2 AlOH + H2O $\longrightarrow$ Al2O3[s] + 2 H2 ${\scriptstyle{}^1\!\!/\!{}_2}$AlOH
14 corundum 2 AlH + 3 H2O $\longrightarrow$ Al2O3[s] + 4 H2 ${\scriptstyle{}^1\!\!/\!{}_2}$AlH
15   Al2O + 2 H2O $\longrightarrow$ Al2O3[s] + 2 H2 Al2O
16   2 AlS + 3 H2O $\longrightarrow$ Al2O3[s] + 2 H2S + H2 ${\scriptstyle{}^1\!\!/\!{}_2}$AlS
17   2 AlO2H $\longrightarrow$ Al2O3[s] + H2O ${\scriptstyle{}^1\!\!/\!{}_2}$AlO2H


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