Ground state “supercombination differences” as the method of determination of splittings for faintly polar symmetric top molecules: the CHD3 molecule

A method, called the procedure of supercombination differences, has been developed in order to determine the a1−a2 (K = 3) ground state splittings for symmetric top molecules from infrared spectra. By forming normal combination differences corresponding to both the components and then their differences the splittings were evaluated for the CHD3 molecule up to J = 20 with the aid of 11 rotation-vibration bands. By applying the theoretical J dependence of the splittings they could be well explained with one parameter 2h3 = 2.2960(90) × 10−10 cm−1.