Knowledge Bank

$H+(H2O)n$ complexes in the intermediate size range $(n=10-30)$ are studied by infrared photodissociation spectroscopy near the symmetric and asymmetric stretching vibrations of water $(3657cm-1,3756cm-1)$. The complexes fragment by the loss of intact, multiple water molecules and their infrared spectra are compared to the predictions of theory. The spectrum for the magic number $n=21$ cluster shows only one distinct feature in the O-H region indicating all the water molecules occupy similar binding sites. Surprisingly, a single band is also observed for $n=22$ and no photodissociation is observed for the calculated fundamental of the $H3O+$ ion core near $2500cm-1$. Possible interpretations of the above results will be discussed.