As we can see from the highest energy structure, isomer C (Figure ), the calculated free NH 2 and free OH stretching region shows significant complexity in the NH 2 stretching region that is not found in the experimental spectrum and the fingerprint region of isomer C also does not properly capture the relative peak intensity pattern or number of modes in the NH 2 bending/wagging region. These spectral differences along with the considerably higher energy of this structure in comparison to the other calculated structures is sufficient evidence to eliminate the possibility of this isomer's occurrence in the experiment. Isomer B is much closer in energy to the the lowest energy isomer A, but isomer B does not have a free OH. Although it was mentioned previously that the iodine related vibrational modes pose challenges in being diagnostic of structure, they can still help dismiss unlikely structures. For this cluster, in the experimental spectrum we see a sharp well defined IO related stretching mode just above 800 cm -1 , and the presence of two very faint peaks, one just below 800 cm -1 The experimental CIVP spectrum (top) is compared to the computed harmonic IR spectra (bottom) of the (2, 2, 0) cluster. Isomer A is lowest in energy, followed by isomer B, and isomer C is significantly higher in energy. The main features involve OH stretching and bending modes (peaks in red), NH stretching and bending modes (peaks in blue), and IO stretching modes (peaks in purple). Again, the lowest energy isomer, A, is found to be the likely experimentally present isomer as it has a free OH stretching mode and two free NH stretching modes. The fingerprint relative peak intensity pattern composed of NH bending and wagging modes, an OH bend, and IO stretching modes is also very well replicated. and one just above 600 cm -1 (both denoted by purple lines in the experimental spectrum in Figure ). The low intensity of these peaks is likely due to the N 2 binding energy of about 800 cm -1 as mentioned earlier. These iodine-related peaks are best reproduced in the lowest energy calculated spectrum of isomer A, along with the NH 2 bending/wagging modes and free NH 2 and OH stretching modes. The similarities between the calculated spectrum of isomer A and the experimental spectrum and the determination of isomer A as the lowest energy isomer, suggest that isomer A is the experimentally present structure at the (2, 2, 0) cluster size.