Spectra of Symmetric Top and Linear Molecules

It is shown how the vibration-rotation energy manifolds of symmetric top molecules can be built up, and how symmetry species labels can be assigned to the levels. Then electric dipole transitions are discussed, and the formation of the different types of vibration-rotation spectra is examined. Practical rules for the identification of types of transitions in a spectrum are also discussed. The effects of anharmonic, Coriolis, and l -type interactions of vibration-rotation levels on line positions and intensities are also considered. Phase conventions which simplify the vibration-rotation study are identified and suggested. Linear molecules are treated as a particular class of symmetric tops, where the contribution to the angular momentum about the top axis is only vibronic.