Electronic Structures and Transition Properties of BeSe and BeTe Molecules.

The electronic structure of BeSe and BeTe molecules has been investigated using the CASSCF/(MRCI + Q) method at the spin-free and spin-orbit level. The potential energy curves, the permanent dipole moment, the spectroscopic constants , , ω, and , and the dissociation energy are determined in addition to the vertical transition energy T. The molecules' percentages of ionic character are deduced, and the trends of the spectroscopic constants of the two molecules are compared and justified. A ro-vibrational study is performed using the canonical function approach to calculate the constants , , and and the turning points and . All the ground-state vibrational levels have also been investigated. The radiative lifetimes of vibrational transitions among the electronic ground states are also discussed. The results for BeSe have been compared with the previously published data while those for BeTe molecules are presented here for the first time.