The structures of more than thirty H2nNOn+2+ (n = 2-4) complexes have been optimized in ab initio MP2/6-31+G* calculations. Relative energies of the species identified have been established in G2MP2 theoretical calculations and applied to an examination of the thermochemistry of the NO2+(H2O)(n-1) + H2O --> NO2+ + (H2O)(n) --> HNO3(H3O+)(H2O)(n-2) --> HNO3 + H3O+(H2O)(n-2) reactions. The nature of the most stable cluster varies with size, An ion-centered NO2+(H2O)(2) is the global minimum energy structure on the H4NO4+ surface, while an HNO3(H3O+)(H2O)(2) complex is most stable on H8NO6+. On the H6NO5+ surface NO2+(H2O)(3), HNO3-(H3O+)(H2O) and H2NO3+(H2O)(2) clusters lie within 1 kcal/mol of each other.