Infrared Spectroscopy of Protonated Methanol-Water Clusters -Effects of Heteromolecules in Hydrogen Bond Network- Ken-ichiro Suhara, Asuka Fujii and Naohiko Mikami Department of Chemistry, Graduate School of Science, Tohoku University

Introduction Hydrogen bond networks in large-size protonated clusters IR photodissociation spectroscopy of OH-stretching vibrations Size-dependent development of the hydrogen bond network structures in large-size clusters 1. local structures in protic solvent 2. proton motion in condensed phases Microscopic models for

Size dependence of hydrogen bond network structures Methanol molecule ･ 3-coordination at the maximum ･ Donation of only one proton The bicyclic structure formation is completed at n = 7 More complicated cage structures can not be formed (n > 7) net ~10 < n H + (H 2 O) n cage 21 ≤ n chain n < ~10 Miyazaki et al., Shin et al. (2004) Strictly restricted structure ! Totally different preferences between the hydrogen bond networks of water and methanol H + (MeOH) n n = 7 Chang et al., and Fujii et al. (1999&2005) The terminal of network development

Wu et al., J. Phys. Chem. A IR spectroscopy and DFT calculations H + (MeOH) n (H 2 O) m, m + n = 4 M3W1 Coexistence of H 3 O + and CH 3 OH 2 + ion cores Previous study Mass spectrometry for H + (MeOH) n (H 2 O) m Proton switching from the alcohol to the water site at n = 9, m = 1 & n = 10, m = 2 ? Garvey et al., J. Phys. Chem. A Presence of magic numbers n = 9, m = 1 & n = 10, m = 2 Garvey et al., J. Am. Chem. Soc Structures in the protonated water-methanol mixed clusters ?

This study A structural analysis of protonated water-methanol mixed clusters H + (MeOH) n (H 2 O) m, (n = , m = 1 & 2) by IR spectroscopy Hydrogen bond network including heteromolecules

Mass spectrometry size(n+m) Ion intensity Ion intensity size n H + (MeOH) n (H 2 O) 1 Garvey et al., J. Am. Chem. Soc magic number The magic number was not observed in our mass spectrum No magic number… Proton switching?

IR spectra of H + (MeOH) n (H 2 O) m, (m = 0, 1) m = 0m = 1 n = n = n>7: similar IR spectra to H + (MeOH) n+1 Disappearance of free OH peaks No drastic change of the IR spectra at n = No evidence for proton switching

H + (MeOH) n (H 2 O) 1 tricyclic structurebicyclic structure Disappearance of the free OH band in n > 6 Definition of symbols Free OH n = 7 n = 5 n = 4 n = n = 3 n = 6

Conclusion IR spectroscopy of H + (MeOH) n (H 2 O) m, (m = 1 & 2) No magic number in the mass distribution No spectroscopic evidence for the proton switching Structural convergence to the tricyclic structure for m = 1