Isomer B is substantially lower in energy than isomer C, and exhibits full proton transfer from the iodic acid to ammonia, such that the cluster is comprised of two ammoniums, one iodate, and an iodine pentoxide molecule. Isomer A contains the same proton transfer components as isomer B and structurally they both only differ by the orientation and subsequent hydrogen bonds of a terminal IO 3 . Although visually isomer A and B do not appear to differ significantly, their predicted spectra show considerable differences in both fingerprint and NH/ NH 2 stretching regions. Comparing them both directly to the experimental spectrum, we see that isomer A is an excellent match to the experimental spectrum. Isomer A has two transitions in the free NH/ NH 2 stretching region, as does the experiment, whereas isomer B has three transitions there. Moving down to the fingerprint region, we find the relative intensity pattern of isomer A to be more representative to that of the experiment.