Theoretical investigations of spectroscopic parameters and molecular constants for electronic ground state of Cl 2 and its isotopes
The potential energy curve of the Cl2(X1?g +) is investigated by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with the largest correlation-consistent basis set, aug-cc-pV6Z, in the valence range. The theoretical spectroscopic parameters and the molecular constants of three isotopes, 35Cl2, 35Cl37Cl and 37Cl2, are studied. For the 35Cl2(X1?g +), the values of D0, De, Re, ?e, ?e?e, ?e and Be are obtained to be 2.3921 eV, 2.4264 eV, 0.19939 nm, 555.13 cm?1, 2.6772 cm?1, 0.001481 cm?1 and 0.24225 cm?1, respectively. For the 35Cl37Cl(X1?g +), the values of D0, De, Re, ?e, ?e?e, ?e and Be are calculated to be 2.3918 eV, 2.4257 eV, 0.19939 nm, 547.68 cm?1, 2.6234 cm?1, 0.00140 cm1 and 0.23572 cm?1, respectively. And for the 37Cl2(X1?g+), the values of D0, De, Re, ?e, ?e?e, ?e and Be are obtained to be 2.3923 eV, 2.4257 eV, 0.19939 nm, 540.06 cm?1, 2.5556 cm?1, 0.00139 cm?1 and 0.22919 cm?1, respectively. These spectroscopic results are in good agreement with the available experimental data. With the potential of Cl2 molecule determined at the MRCI/aug-cc-pV6Z level of theory, the total of 59 vibrational states is predicted for each isotope when the rotational quantum number J equals zero (J = 0). The theoretical vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J = 0, which are in excellent accordance with the available experimental findings.