Interaction of SO with the Surface of a Water Nanodroplet.

We present a comprehensive computational study of interaction of a SO with water molecules in the gas phase and with the surface of various sized water nanodroplets to investigate the solvation behavior of SO in different atmospheric environments. Born-Oppenheimer molecular dynamics (BOMD) simulation shows that, in the gas phase and at a temperature of 300 K, the dominant interaction between SO and HO is S···O, consistent with previous density-functional theory (DFT) computation at 0 K. However, at the surface of a water nanodroplet, BOMD simulation shows that the hydrogen-bonding interaction of O···H becomes increasingly important with the increase of droplet size, reflecting a marked effect of the water surface on the SO solvation. This conclusion is in good accordance with spectroscopy evidence obtained previously (J. Am. Chem. Soc. 2005, 127, 16806; J. Am. Chem. Soc. 2006, 128, 3256). The prevailing interaction O···H on a large droplet is mainly due to favorable exposure of H atoms of HO at the air-water interface. Indeed, the conversion of the dominant interaction in the gas phase S···O to the dominant interaction on the water nanodroplet O···H may incur effects on the SO chemistry in atmospheric aerosols because the solvation of SO at the water surface can affect the reactive sites and electrophilicity of SO. Hence, the solvation of SO on the aerosol surface may have new implications when studying SO chemistry in the aerosol-containing troposphere.