Infrared Spectroscopy of Perdeuterated Protonated Water Clusters in the Vicinity of the Clathrate Cage
We report infrared predissociation spectra of size-selected D+(D2O)(n) clusters in the size range n = 18-24 for comparison to previous studies of the corresponding H+(H2O)(n) species (Shin, J.-W.; Hammer, N. I.; Diken, E. G.; Johnson, M. A.; Walters, R. S.; Jaeger, T. D.; Duncan, M. A.; Christie, R. A.; Jordon, K. D. Science 2004, 304, 1137). For n = 18-20, two "free" OD stretch bands are observed and assigned to D2O molecules in acceptor-acceptor-donor (AAD) and acceptor-donor (AD) hydrogen bonding arrangements. Only the AAD band is observed for the n = 21 perdeuterated species. This behavior is identical to that observed previously for the corresponding H+(H2O)(n) Clusters. Similar to the all-H protonated species, the AD "free" OD stretch band is also absent for the perdeuterated n = 22 cluster but returns for clusters larger than n = 22. Like the H+(H2O)(n) systems, the perdeuterated clusters have no spectral band in the lower frequency range where the signature of the hydronium cation is predicted. These observations shed new light on the intriguing spectroscopy and dynamics of large protonated water clusters.