In this region in isomer B, the relative intensity pattern is not well reproduced as there are a couple transitions (somewhat overlapped) just above 1300 cm -1 that do not exist in the experimental spectrum. Although the transitions in the IO stretching region just above 800 cm -1 in the isomer A spectrum are not as well resolved as they are in the experiment, the ascending relative intensity pattern is present with ascending wavenumber unlike in the predicted spectrum of isomer B. Taken together, isomer A is assigned as the experimentally present structure for the (2, 1, 1) cluster.