Infrared photodissociation spectra of Al+(CH3OH)n (n=1-4) and Al+(CH3OH)n-Ar (n=1-3) were measured in the OH stretching vibration region, 3000-3800 cm-1. For n=1 and 2, sharp absorption bands were observed in the free OH stretching region, all of which were well reproduced by the spectra calculated for the solvated type geometry with no hydrogen bond. On the other hand, for n=3 and 4, there were broad vibrational bands in the energy region of hydrogen bonded OH stretching vibrations, 3000-3500 cm-1. Energies of possible isomers for the Al+(CH3OH)3,4 ions with hydrogen bonds were calculated in order to assign these bands. It is found that the third and fourth methanol molecules form hydrogen bonds with methanol molecules in the first solvation shell, rather than a direct bonding with the Al+ ion. We obtained no evidence of the insertion reaction for the present Al+(CH3OH)n system, which was reported in Al+(H2O)n previously. One possible explanation of the difference between these two systems is that the potential energy barriers between the solvated and inserted isomers in the Al+(CH3OH)n system is too high to form the inserted type isomers.

This is a preprint of an article published by American Chemical Society in Journal of Physical Chemistry A, 2007, available online: http://pubs.acs.org/doi/abs/10.1021/jp067622c.

This work was supported by the Joint Studies Program (2004) of the Institute for Molecular Science. A part of this work was also supported by "Nanotechnology Support Project" and Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.