Quantum Chemical Calculation Of The Excited State Potential Energy Surface Of H₂O～+ By Using The CASSCF Method

The H2O+ cation has been of great importance for elementary research processes in astrophysics, physical chemistry, biophysics, the origin of lives and the search forlives in outer space. The X2B1 and A2A1 electronic states are subject to theRenner-Teller effect, resulting in a complicated A2A1 -X2B1 emission spectrum andassignment. It is very necessary to have theoretical data to reference. Nowadays, it is an important step to study the potential energy surface of H2O+ considering few data of the excited state of it.In the present paper, the excited potential surface of H2O+ is calculated by using CASSCF method with GAUSSIAN98 program. We discussed the selection of complete active space(CAS), the orbitals within the initial guess and results with different basis sets during CASSCF calculation. At the same time, we calculated the excited potential surface of H2O+ at the CAS(3,4)/6-31+G(d, p) level, then fitted to analytical expression. The potential surface obtained is agreed very well with the result from MRD-CI method .