A quantum chemical study of negatively charged methanol clusters

Abstract

We performed high-level quantum chemical density functional theory calculations on negatively charged methanol clusters containing up to six monomers. The calculations suggest that there exist stable methanol cluster anions and that these anions are more stable than similar cluster anions of water. Linear hydrogen bonded methanol chains are observed to bind the excess electron on dipole bound states. The orientation and the size of the excess electron were characterized by the position of the center of mass and the radius of gyration of the highest occupied molecular orbital (HOMO). The electron occupies a large diffuse orbital concentrated outside the molecular frame in the molecular dipole direction. The tendencies of the dipole moments, the vertical electron detachment energies, and the size of the HOMOs all fit in the same cooperative trend, suggesting stronger interactions in larger anions. We also located stable cluster anions which can serve as model systems for the solvated electron in liquid methanol. Multiple O–H⋯e− interactions with dominantly bond-oriented arrangement toward the solvated electron are probably strongly favored in the liquid phase for energetic reasons. Although the size of the excess electron is still significantly larger than expected from quantum molecular dynamics simulations, the general decreasing trend of the radius of gyration with increasing cluster size is reassuring. Similarly to the O–H⋯e− interactions, we located C–H⋯e− interactions between appropriately oriented methyl hydrogens and the excess electron in a large anion of six methanol molecules. We propose the interactions of both the hydroxyl hydrogens and the methyl hydrogens with the excess electron to be considered hydrogen bonds.