Study on spectroscopic parameters and molecular constants of HCl(X^1Σ^+) 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.

Spectroscopic investigations on NO^+(X^1Σ^+, a^3Σ^+, A^1Π) ion using multi-reference configuration interaction method and correlation-consistent sextuple basis set augmented with diffuse functions

Three low-lying electronic states （X1∑, a3∑＋, and A1II） of NO＋ ion are studied using the complete active space self-consistent-field （CASSCF） method followed by highly accurate valence internally contracted multi-reference configuration interaction （MRCI） approach in combination of the correlation-consistent sextuple basis set augmented with diffuse functions, aug-cc-pV6Z. The potential energy curves （PECs） of the NO＋（X1∑＋, a3∑＋, A1II） are calculated. Based on the PECs, the spectroscopic parameters Re, De, We, WeXe, ae, Be, and D0 are reproduced, which are in excellent agreement with the available measurements. By numerically solving the radial SchrSdinger equation of nuclear motion using the Numerov method, the first 20 vibrational levels, inertial rotation and centrifugal distortion constants of NO＋（X1∑＋, a3∑＋, A1II） ion are derived when the rotational quantum number J is equal to zero （J = 0） for the first time, which accord well with the available measurements. Finally, the analytical potential energy functions of these states are fitted, which are used to accurately derive the first 20 classical turning points when J = 0. These results are compared in detail with those of previous investigations reported in the literature.

Investigations on analytic potential energy function, spectroscopic parameters and vibrational manifolds (J = 0) of the SD + (X^3 Σ^- ) ion

This paper investigates the spectroscopic properties of the SD^＋（X^3∑^-） ion by employing the coupled-cluster singles-doubles-approximate-triples [CCSD（T）] theory combining with the quintuple correlation-consistent basis set augmented with diffuse functions （aug-cc-pV5Z） of Dunning and co-workers. The accurate adiabatic potential energy function is obtained by the least-squares fitting method with the 100 ab initio points, which are calculated at the unrestricted CCSD（T）/aug-cc-pV5Z level of theory over the internuclear separation range from 0.09 to 2.46 nm. Using the potential, it accurately determines the spectroscopic parameters （De, ωeХe, αe and Be）. The present De, Re, We, ωeХe, αe and Be results are of 3.69119 eV, 0.13644 nm, 1834.949 cm^-1, 25.6208 cm^-1, 0.1068 cm^-1 and 4.7778 cm^-1, respectively, which are in remarkably good agreement with the experimental findings. A total of 29 vibrational states has been predicted by numerically solving the radial Schrodinger equation of nuclear motion when the rotational quantum number J equals zero. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reported when J = 0 for the first time, which are in good accord with the measurements wherever available.