Ab initio molecular orbital calculations on NO+(H2O)(n) cluster ions. 2. Thermodynamic values for stepwise hydration and nitrous acid formation

Ab initio molecular orbital calculations have been used to compute thermody namic constants (DeltaH degrees, DeltaS degrees, DeltaG degrees) for the st epwise hydration reactions of NO+(H2O)(n), and for the competing rearrangem ent reaction which produces HONO and H+(H2O)(n) (for n less than or equal t o 4). Geometry optimizations and harmonic frequency calculations were perfo rmed at the MP2/6-311++G(2d,p) level, and relative energies were computed a t the MP2/augcc-pVTZ level with MP2/6-311++G(2d,p) optimized geometries. Th e geometry changes and energetics of these competing solvation and rearrang ement reactions have been studied, and reasons are proposed to explain why NO+(H2O)(n+1) formation is the dominant process for n = 1 and n = 2 but HON O + H+(H2O)(n) formation contributes for n = 3 and becomes more important f or n = 4.