Table 1:

Chemical surface reactions.

Solid s	Surface reaction r	Key species
TiO2[s]	TiO2 TiO2[s]	TiO2
rutile	Ti + 2 H2O TiO2[s] + 2 H2	Ti
(1)	TiO + H2O TiO2[s] + H2	TiO
(A)	TiS + 2 H2O TiO2[s] + H2S + H2	TiS
SiO2[s]	SiO2 SiO2[s]	SiO2
silica	SiO + H2O SiO2[s] + H2	SiO
(3)(B)	SiS + 2 H2O SiO2[s] + H2S + H2	SiS
Fe[s]	Fe Fe[s]	Fe
solid iron	FeO + H2 Fe[s] + H2O	FeO
(1)	FeS + H2 Fe[s] + H2S	FeS
(B)	Fe(OH)2 + H2 Fe[s] + 2 H2O	Fe(OH)2
MgO[s]	MgO MgO[s]	MgO
periclase	Mg + H2O MgO[s] + H2	Mg
(3)	2 MgOH 2 MgO[s] + H2	1/2MgOH
(B)	Mg(OH)2 MgO[s] + H2O	Mg(OH)2
MgSiO3[s]	Mg + SiO + 2 H2O MgSiO3[s] + H2	Mg, SiO
enstatite	Mg + SiS + 3 H2O MgSiO3[s] + H2S + 2 H2	Mg, SiS
(3)	2 MgOH + 2 SiO + 2 H2O 2 MgSiO3[s] + 3 H2	MgOH, 1/2SiO
(C)	2 MgOH + 2 SiS + 2 H2O 2 MgSiO3[s] + 2 H2S + 2 H2	MgOH, 1/2SiS
	Mg(OH)2 + SiO 2 MgSiO3[s] + H2	Mg(OH)2, SiO
	Mg(OH)2 + SiS + H2O MgSiO3[s] + H2S+ H2	Mg(OH)2, SiS
Mg2SiO4[s]	2 Mg + SiO + 3 H2O Mg2SiO4[s] + 3 H2	Mg, SiO
forsterite	2 MgOH + SiO + H2O Mg2SiO4[s] + 2 H2	MgOH, SiO
(3)	2 Mg(OH)2 + SiO Mg2SiO4[s] + H2O + H2	Mg(OH)2, SiO
(C)	2 Mg + SiS + 4 H2O Mg2SiO4[s] + H2S + 3 H2	Mg, SiS}
	2 MgOH + SiS + 2 H2O Mg2SiO4[s] + H2S + 2 H2	MgOH, SiS}
	2 Mg(OH)2 + SiS Mg2SiO4[s] + H2 + H2S	Mg(OH)2, SiS}
Al2O3[s]	2 AlOH + H2O Al2O3[s] + 2 H2	1/2AlOH
aluminia	2 AlH + 3 H2O Al2O3[s] + 4 H2	1/2AlH
(3)	Al2O + 2 H2O Al2O3[s] + 2 H2	Al2O
(D)	2 AlS + 3 H2O Al2O3[s] + 2 H2S + H2	1/2AlS
	2 AlO2H Al2O3[s] + H2O	1/2AlO2H

r assumed to form the solid materials s. The efficiency of the reaction is limited by the collision rate of the key species. The notation 1/2 in the r.h.s. column means that only every second collision (and sticking) event initiates one reaction. Data sources for the supersaturation ratios (and saturation vapour pressures): (1) Helling & Woitke (2006); (2) Nuth & Ferguson (2006); (3) Sharp & Huebner (1990). Data sources for the pure solid refractive indices: (A) Posch (2008); (B) Palik (1985,1991); (C) Jäger et al. (2003); (D) Palik (1991), Begemann et al. (1997).