We formulate a least squares function in the constants (now variables) k1 and k2 using the data from the chemical a.

Input := 


SSa[k1_,k2_] = Sum[(asol[adata[[n,1]]] -  adata[[n,2]])^2,

                 {n,1, Length[adata]}];

Input := 


solak = FindMinimum[SSa[k1,k2],{k1,.1},{k2,.2}]

Output =


{0.0000535918, {k1 -> 0.063221, k2 -> 0.2}}