  We study multiple ionization in proton collisions with water, methane, and
ammonia molecules using an independent-atom model. Previous work on total (net)
capture and ionization cross sections is extended to treat the multiple
ionization channels explicitly. We present the theoretical framework to treat
charge-state correlated processes within the independent-atom model approach
which uses the geometric screening introduced for different molecular
geometries and orientations. Comparison of results is made for the target
molecules $\rm H_2O, CH_4, NH_3$ with an emphasis on $q$-fold electron removal.
Coincident measurements of produced molecular fragments can be used to estimate
this quantity. We find very good agreement for the model calculations for the
water molecule, where data exist for $q=1-4$. For methane we observe reasonable
agreement with $q=1,2$, and for ammonia only for $q=1$, i.e., the experimental
data show little support for a direct multiple ionization channel in the latter
case.
