The main results of research:
1) The 'expanded' local mode approach and the general isotopic substitution theory were used to estimate the relations between spectroscopic parameters of the Td symmetric isotopic species, XY4, on the one hand, and with different isotopologues, on the other hand. Test calculations were made for methane molecule.
2) The 'expanded' local mode approach and symmetric properties were derived for six atomic Х2Y4 type molecules of D2h symmetry. Test calculations were made for C2H4 molecule.
3) High resolution spectra of C2D4, GeH4, SiH4, CH3D were investigated.