It is shown that the coalescence of the nu(CO) infrared bands of tricarbonyl(eta(4)-norbornadiene)iron cannot be explained on an "intrawell" mechanism and must involve "interwell" dynamics. This leads to the general conclusion that vibrational spectroscopic evidence for chemical exchange (i.e. "interwell") can be obtained by demonstrating that there is extra intensity between spectral bands that cannot be explained by simple overlap of individual bands.