A quantum chemical study of negatively charged methanol clusters

We performed high-level quantum chemical density functional theory calculat ions on negatively charged methanol clusters containing up to six monomers. The calculations suggest that there exist stable methanol cluster anions a nd that these anions are more stable than similar cluster anions of water. Linear hydrogen bonded methanol chains are observed to bind the excess elec tron on dipole bound states. The orientation and the size of the excess ele ctron were characterized by the position of the center of mass and the radi us of gyration of the highest occupied molecular orbital (HOMO). The electr on occupies a large diffuse orbital concentrated outside the molecular fram e in the molecular dipole direction. The tendencies of the dipole moments, the vertical electron detachment energies, and the size of the HOMOs all fi t in the same cooperative trend, suggesting stronger interactions in larger anions. We also located stable cluster anions which can serve as model sys tems for the solvated electron in liquid methanol. Multiple O-H ... e(-) in teractions with dominantly bond-oriented arrangement toward the solvated el ectron are probably strongly favored in the liquid phase for energetic reas ons. Although the size of the excess electron is still significantly larger than expected from quantum molecular dynamics simulations, the general dec reasing trend of the radius of gyration with increasing cluster size is rea ssuring. Similarly to the O-H ... e(-) interactions, we located C-H ... e(- ) interactions between appropriately oriented methyl hydrogens and the exce ss electron in a large anion of six methanol molecules. We propose the inte ractions of both the hydroxyl hydrogens and the methyl hydrogens with the e xcess electron to be considered hydrogen bonds. (C) 1999 American Institute of Physics. [S0021-9606(99)30221-X].