band that are not reproduced by our FC simulations, peaks B1-B17 (Table ). The spacing of these features is consistently ~120 cm -1 above that of an allowed transition (as is the case for B1-B9, B13, B17) or ~240 cm -1 above another "B" feature (as is the case for B9 → B11, B10 → B12, B12 → B14, B13 → B15, B14 → B16). The similarity of these spacings with that of our measured value for the v2 bending frequency (122(18) cm -1 ) suggests these features arise from transitions terminating in odd quanta of the non-totally symmetric v2 mode. We thus assign peaks B1-B17 to transitions of this type to neutral levels with πu vibrational symmetry.