\begin{table}%t1 
      \caption{Chemical surface reactions.} 
        %\centerline
{
          \begin{tabular}{cll}
          \hline \hline 
            {Solid $s$} & {Surface reaction $r$} & {Key species} \\ 
            \hline 
            TiO$_2$[s] & TiO$_2$ $\longrightarrow$ TiO$_2$[s]   & TiO$_2$ \\ 
            rutile     & Ti + 2 H$_2$O $\longrightarrow$ TiO$_2$[s] + 2 H$_2$ & Ti \\
              (1)      & TiO + H$_2$O $\longrightarrow$ TiO$_2$[s] + H$_2$ & TiO    \\ 
              (A)      & TiS + 2 H$_2$O $\longrightarrow$ TiO$_2$[s] + H$_2$S + H$_2$ & TiS \\ \hline 
            SiO$_2$[s] & SiO$_2$ $\longrightarrow$ SiO$_2$[s] & SiO$_2$ \\ 
            silica     & SiO + H$_2$O $\longrightarrow$ SiO$_2$[s] + H$_2$ & SiO    \\ 
             (3)(B)    & SiS + 2 H$_2$O $\longrightarrow$ SiO$_2$[s] + H$_2$S + H$_2$ & SiS \\ \hline   
            Fe[s]      & Fe $\longrightarrow$ Fe[s] & Fe \\ 
            solid iron & FeO + H$_2$ $\longrightarrow$ Fe[s] + H$_2$O & FeO \\
              (1)      & FeS + H$_2$ $\longrightarrow$ Fe[s] + H$_2$S & FeS \\ 
              (B)      & Fe(OH)$_2$ + H$_2$ $\longrightarrow$ Fe[s] + 2 H$_2$O & Fe(OH)$_2$ \\ \hline 
            MgO[s]     & MgO $\longrightarrow$ MgO[s] & MgO \\ 
            periclase  & Mg + H$_2$O $\longrightarrow$ MgO[s] + H$_2$ & Mg \\
              (3)      & 2 MgOH $\longrightarrow$ 2 MgO[s] + H$_2$ & $1/2$MgOH\\
              (B)      & Mg(OH)$_2$ $\longrightarrow$ MgO[s] + H$_2$O & Mg(OH)$_2$\\ \hline
            MgSiO$_3$[s]& Mg + SiO + 2 H$_2$O $\longrightarrow$ MgSiO$_3$[s] + H$_2$ & $\min\{$Mg, SiO$\}$\\ 
            enstatite  & Mg + SiS + 3 H$_2$O $\longrightarrow$ 
                              MgSiO$_3$[s] + H$_2$S + 2 H$_2$ & $\min\{$Mg, SiS$\}$\\ 
              (3)      & 2 MgOH + 2 SiO + 2 H$_2$O $\longrightarrow$ 
                              2 MgSiO$_3$[s] + 3 H$_2$ & $\min\{1/2$MgOH, 1/2SiO$\}$ \\
              (C)      & 2 MgOH + 2 SiS + 2 H$_2$O $\longrightarrow$
                              2 MgSiO$_3$[s] + 2 H$_2$S + 2 H$_2$ & $\min\{1/2$MgOH, 1/2SiS$\}$ \\
                       & Mg(OH)$_2$ + SiO $\longrightarrow$
                              2 MgSiO$_3$[s] +  H$_2$ & $\min\{$Mg(OH)$_2$, SiO$\}$ \\ 
                       & Mg(OH)$_2$ + SiS + H$_2$O $\longrightarrow$ 
                              MgSiO$_3$[s] + H$_2$S+ H$_2$ & $\min\{$Mg(OH)$_2$, SiS$\}$ \\ \hline
            Mg$_2$SiO$_4$[s] & 2 Mg + SiO + 3 H$_2$O $\longrightarrow$
                                    Mg$_2$SiO$_4$[s] + 3 H$_2$ & $\min\{1/2$Mg, SiO$\}$\\
            forsterite & 2 MgOH + SiO + H$_2$O $\longrightarrow$ 
                              Mg$_2$SiO$_4$[s] + 2 H$_2$ & $\min\{1/2$MgOH, SiO$\}$\\ 
              (3)      & 2 Mg(OH)$_2$ + SiO $\longrightarrow$ 
                              Mg$_2$SiO$_4$[s] + H$_2$O + H$_2$ & $\min\{1/2$Mg(OH)$_2$, SiO$\}$ \\ 
              (C)      & 2 Mg + SiS + 4 H$_2$O $\longrightarrow$ 
                              Mg$_2$SiO$_4$[s] + H$_2$S + 3 H$_2$ & $\min\{1/2$Mg, SiS\} \\
                       & 2 MgOH + SiS + 2 H$_2$O $\longrightarrow$ 
                              Mg$_2$SiO$_4$[s] + H$_2$S + 2 H$_2$ & $\min\{1/2$MgOH, SiS\}\\
                       & 2 Mg(OH)$_2$ + SiS $\longrightarrow$ 
                              Mg$_2$SiO$_4$[s] + H$_2$ + H$_2$S & $\min\{1/2$Mg(OH)$_2$, SiS\} \\ \hline
             Al$_2$O$_3$[s] & 2 AlOH + H$_2$O $\longrightarrow$ Al$_2$O$_3$[s] + 2 H$_2$ & 1/2AlOH \\ 
              aluminia   &  2 AlH + 3 H$_2$O $\longrightarrow$ Al$_2$O$_3$[s] + 4 H$_2$& 1/2AlH\\
              (3)        & Al$_2$O + 2 H$_2$O $\longrightarrow$ Al$_2$O$_3$[s] + 2 H$_2$ & Al$_2$O\\ 
              (D)        & 2 AlS + 3 H$_2$O $\longrightarrow$ Al$_2$O$_3$[s] + 2 H$_2$S + H$_2$ & 1/2AlS\\
                         & 2 AlO$_2$H $\longrightarrow$ Al$_2$O$_3$[s] + H$_2$O & 1/2AlO$_2$H\\
	     \hline 
          \end{tabular}}
          \medskip
\par
           $r$ 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)
          \citet{HW06}; (2) \citet{Nu06}; (3) \citet{Sh90}.
          Data sources for the pure solid refractive indices: (A)
          \citet{Po99}; (B) \citet{Pa85,Pa91}; (C) \citet{Ja03};
        (D) \citet{Pa91}, \citet{Be97}.
        \label{tab:chemreak2} 
      \end{table}