Atmospheric significance of water clusters and ozone-water complexes

Ozone-water complexes O3···(H2O)n (n = 1-4) have been theoretically investigated using QCISD and CCSD(T) methods along with the 6-311G(2df,2p), 6-311+G(2df,2p), aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets and extrapolation to CBS limit. For comparison, water clusters (H2O)n (n = 1-4) have also been studied at the same level of theory. The ozone-water complexes are held together by a combination of weak specific hydrogen-bonding and van der Waals interactions. Surprisingly, the hydrogen-bonded complexes are not necessarily the most stable ones. In particular, in the most stable 1:1 complex structure the main stabilizing factors come from van der Waals interactions. The high accuracy of the calculated binding energies provides a reliable basis to discuss the abundance of these clusters in the atmosphere. We predict concentrations up to 9.24 × 10(15), 3.91 × 10(14), and 2.02 × 19(14) molecules·cm(-3) for water dimer, trimer, and tetramer in very hot and humid conditions and that the concentrations of these clusters would remain significant up to 10 km of altitude in the Earth's atmosphere. The concentration of O3···H2O is predicted to be between 1 and 2 orders of magnitude higher than previous estimation from the literature: up to 5.74 × 10(8) molecules·cm(-3) in very hot and humid conditions at ground level and up to 1.56 × 10(7) molecules·cm(-3) at 10 km of altitude of the Earth's atmosphere. The concentrations of the other ozone-water clusters, O3··(H2O)2, O3···(H2O)3, and O3···(H2O)4, are predicted to be very small or even negligible in the atmosphere.