The lowest energy calculations displayed in Figure and, exhibit similar binding arrangements to each other with slight modifications. Isomer C, which is 17.38 kcal/mol higher in energy than isomer A, explores the likely spectrum of a structure where the iodic acid does not donate its proton to an ammonia. This structure is still quite high in energy compared to the lowest energy calculation and is therefore energetically improbable to be experimentally present. Comparing the experimental spectral features to those of isomer C also results in an unlikely match. The experimental relative intensity pattern of the NH 2 bending/wagging modes is not well reproduced in isomer C's spectrum. There are two peaks around 1200 cm -1 (one of which is an OH bend), that do not exist within the experimental spectrum. The iodine-related vibrational mode relative intensity pattern in Figure : The experimental CIVP spectrum (top) is compared to the computed harmonic IR spectra (bottom) of the (2, 1, 1) cluster. Isomer A is lowest in energy, followed by isomer B, and isomer C is again significantly higher in energy. The main features involve NH stretching and bending modes (peaks in blue) and IO stretching modes (peaks in purple). Isomer A is found to be the experimentally present isomer as it reproduces the relative peak intensity pattern of the NH modes particularly well in both the fingerprint region and higher energy stretching region. Isomer A is also the lowest energy isomer. isomer C's spectrum is also quite different from that of the experiment. Between 800 and 900 cm -1 several equal intensity transitions are predicted in isomer C's spectrum whereas in the experimental spectrum there are three transitions in this region, of ascending intensity with ascending wavenumber. There are significantly more transitions in the free NH/ NH 2 stretching region in the calculated spectrum of isomer C than in the experimental spectrum.