ROVIBRONIC (2)B(1)(PI(U))-(2)A(1) SPECTRUM OF THE BH2 RADICAL

Based on ab initio electronic structure calculations, the three-dimensional potential energy functions for the A2B1 (PI(u))-X2A1 linear/bent Renner-Teller sytem of BH2 have been generated and used in beyond Born-Oppenheimer calculations of the rovibronic energy levels by a variational approach accounting for anharmonicity, rotation-vibration and electronic angular momenta coupling effects. The vibronic levels (J = K(a)) for energies up to 15 500 cm-1 for the bending levels and up to 10 000 cm-1 for the stretching and combination levels are given. All experimentally known vibronic energy differences have been reproduced with an accuracy of better than 6 cm-1. The electron-nuclear motion and anharmonic coupling effects have been analysed.