15min:

KENSUKE TONO AND KOICHI TSUKIYAMA, Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo, 162-8601, Japan.

Photodissociation spectra of the protonated methanol cluster ions, H⁺(CH₃OH)_n (n=4-8), were measured in the range of 900-2300 cm^-1 by using a infrared free electron laser. A broad spectral feature was observed at about 1600 cm^-1 in each spectrum. We assign this feature to the OH⁺ stretching vibration, which is coupled with the OH bending motion in the HOH⁺ group. The small vibrational wavenumber suggests that the O-H⁺ bond is very weak.

Structure optimizations by the density functional theory show that H⁺ is equally shared by two oxygen atoms at n=4,5. This result also demonstrates the weak bonding between H⁺ and oxygen. The binding features of H⁺ in the cluster ions will be discussed.