Infrared photodissociation spectroscopy and density-functional calculations of protonated methanol cluster ions: Solvation structures of an excess proton

Solvation structures of an excess proton in protonated methanol cluster ions, H+(CH3OH)(n) (n= 5-8), were investigated by photodissociation spectroscopy in the middle infrared region (900-2300 cm(-1)) and by using density-functional theory. This work indicates that the excess proton is delocalized between two methanol molecules. Spectral features observed in the range 1400-1800 cm(-1) are attributed to vibrational modes involving collective motion of the shared proton and the two ligand molecules. At n= 6-8, broad spectral features in the region above 1800 cm(-1) suggest coexistence of isomers in which the excess proton and a methanol molecule are tightly bound to form an ion core, CH3OH2+. (c) 2008 American Institute of Physics.