Theoretical insights into the structure, stability, thermochemistry, and bonding in hydrated N2O clusters

Abstract

Abstract We have investigated the structure, stability, thermochemistry, and bonding in microhydrated N2O clusters (N2O‧Wn (n = 1–12)). To do this we used various theoretical methods and techniques including density functional theory (DFT), quantitative molecular electrostatic potential surface (MESP), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction analysis (NCI). A detailed density functional search shows that N2O lies on the top of the water molecules and water molecules tend to form a cage structure. The existence of water in cage geometry and segregation of N2O unveils the presence of weak bonding between N2O and water cluster. The computed adsorption energy (ΔEabs), association energy (AE), and incremental association energy (ΔEIA) were all negative which means the complexes are stabilized. In small size clusters the most stable isomer dominates the relative population at all temperatures. In cluster with 6 and more water all the isomers contribute at the high atmospheric temperature. The formation of all the hydrated N2O complexes is enthalpically favored over the range of atmospheric altitudes. In general, the free energy change and enthalpy change decrease with the increase in altitude. The enthalpy change for the clusters unveils a distinct inflection at the tropopause. MESP analysis shows a higher Vs,max value on the hydrogen atom of a water molecule at the terminal end which helps for the addition of water molecules. QTAIM and NCI analyses reveal that N2O-water complexes are predominately stabilized by weak noncovalent interactions like N‧‧‧OW, O‧‧‧Ow, and O‧‧‧Hw. Overall, this work helps in understanding the structure, and stability of hydrated N2O molecules at different altitudes of the atmosphere.