Probing the nano-structure of protonated water clusters by vibrational predissociation spectra and Monte Carlo simulations

IV-7: Probing the nano-structure of protonated water clusters by vibrational predissociation spectra and Monte Carlo simulations

Jer-Lai Kuo, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Huan-Cheng Chang, Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan

Abstract

We have examined the structure of protonated water [H+(H2O)n ] clusters by both theoretical and experimental methods. The size-dependent structual features observed by vibrational predissociation spectra (VPS) at around 150K are (1) ring-structures appear at n=7 evident by the presence of 3-coordinated dangling OH (3coord-dH), (2) mixture of multiple-ring and cage structures are mostly like for n>10 as 3coord-dH become the dominating feature, and (3) for n=21 and 28, VPS is characterized by single 3coord-dH peak indicating clathrated cage structures. More importantly, we found precise transition sizes are sensitive to experimental temperature. Extensive Monte Carlo simulations were therefore carried out to sysmatically investigate the low-energy minima and to gauge the finite temperature effects. Our calculations found that at the experimental temperature, the structures of these clusters are far from their global minima counterparts.