Equilibrium structures of polyatomic organic molecules

The preceding, somewhat historical, review of spectroscopic structural methods is more-or-less complete up to the 1980s. Of course, many new experimental tools had appeared by this time and were leading to additional high-quality data, often with unprecedented precision. These included Fourier-transform microwave spectroscopy 

It remained, in fact, a great disappointment that the eighteen experimental, very high-quality Iq values of six propane isotopomers could not yield a more dependable structure than that represented by either the ro or rj structures of Table 7. Moreover, since Watson had shown clearly that the mass-dependence of the lo values of isotopomers carried information about the equilibrium structure [30], 

---