Molecular Hydration of Carbonic Acid: Ab Initio Quantum Chemical and Density Functional Theory Investigation

Molecular hydration of carbonic acid (H₂CO₃) is investigated in terms of bonding patterns in H₂CO₃···(H₂O) _n [ n = 1-4] hydrogen-bonded clusters within ab initio quantum chemical and density functional theory (DFT) frameworks. Successive addition of water molecules to H₂CO₃···H₂O entails elongation of O-H (hydroxyl) bond as well as contraction of specific intermolecular hydrogen bonds signifying hydration of carbonic acid; these structural features get markedly enhanced under the continuum solvation framework. A comparison between the structurally similar clusters H₂CO₃···(H₂O) _n and HCOOH···(H₂O) _n [ n = 1-3] brings out the structural stability of the former. The present investigation in conjunction with the binding energy behavior of approaching water molecule(s) should serve as a precursor for pathways exploring aqueous dissociation of H₂CO₃ for larger clusters, as well as development of force-field potentials for acid dissociation process.