“…This is beautifully borne out by ex periment (222,223). The spectra in the molecules CHXY 2 with X, Y = CI, CF3, F, D have been analyzed with a model similar to the one for CHX3 (but more complex) and algorithms developed by the Zurich group (223) in several publications (208, [222][223][224][225]. The order of magnitude of the couplings is similar to the one shown in Table 1 for symmetric tops, with Fermi resonance constants of the order of up to 100 em -I and a number of further couplings.…”