Isotopically invariant dunham parameters and the potential function of the HCl molecule

The isotopically invariant Dunham parameters U _mj , Δ _mj ^H and Δ _mj ^Cl were determined by simultaneously fitting the line centers of vibration-rotation transitions of six isotopic HCl forms in the ground electronic state. Fitting included relations between U _mj values. The parameters of the isotopically invariant potential of HCl were determined using independent U _m0 and U _m1 values. The contributions to the vibrational terms of H³⁵Cl caused by violation of the Born-Oppenheimer approximation were calculated.