Study on spectroscopic parameters and molecular constants of HCl（X1∑＋） molecule by using multireference configuration interaction approach

Equilibrium internuclear separations, harmonic frequencies and potential energy curves （PECs） of HCI（X1∑＋） molecule are investigated by using the highly accurate valence internally contracted multireference configuration interaction （MRCI） approach in combination with a series of correlation-consistent basis sets in the valence range. The PECs are all fitted to the Murrell-Sorbie function, and they are used to accurately derive the spectroscopic parameters （De, Do, ωeXe, αe and Be） Compared with the available measurements, the PEC obtained at the basis set, aug-cc-pV5Z, is selected to investigate the vibrational manifolds. The constants Do, De, Re, We, ωeXe, Ore and Be at this basis set are 4.4006 eV, 4.5845 eV, 0.12757 rim, 2993.33 cm^-1, 52.6273 cm^-1, 0.2981 cm^-1 and 10.5841 cm^-1, respectively, which almost perfectly conform to the available experimental results. With the potential determined at the MRCI/aug-cc-pV5Z level of theory, by numerically solving the radial Schrodinger equation of nuclear motion in the adiabatic approximation, a total of 21 vibrational levels are predicted. Complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced, which are in excellent agreement with the available Rydberg-Klein-Rees data. Most of these theoretical vibrational manifolds are reported for the first time to the best of our knowledge.