Independent linear combinations of spectroscopic constants for axially symmetric molecules

The problems of indeterminacy and correlation of spectroscopic constants of axially symmetric molecules are discussed in the dependence on the selection rules of the data set used in analysis of high resolution infrared spectra. Derivation of independent linear combinations of the correlated spectroscopic parameters, for several cases of the allowed and forbidden bands, is carried out for the most important molecular point groups, up to the third order theory. The significance of the forbidden, overtone and hot band transitions in the separate determination of individual constants is also evaluated.