An ab Initio Calculation of BH−2Rovibronic Energies: A Very Small Singlet–Triplet Splitting

✍ Scribed by J.-P. Gu; R.J. Buenker; G. Hirsch; Per Jensen; P.R. Bunker

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 458 KB
• Volume: 178
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.0171

✦ Synopsis

For each of the X ˜3B 1 , a ˜1A 1 , and b ˜1B 1 electronic states of the BH 0 2 molecular ion we have calculated over 50 ab initio points on the potential energy surfaces using the MRD-CI method for all eight electrons. Analytical functions were fitted through the points for each state, and the functions for the a ˜and b ˜states were such that the surfaces remain degenerate at all linear configurations. For the X ˜state the rotation-vibration energies were calculated from the surface using the MORBID Hamiltonian, and for the a ˜and b ˜states the rovibronic energies were calculated using the RENNER Hamiltonian. For the X ˜state we obtain r e Å 1.2034 A ˚, a e Å 129.5Њ, and a barrier to linearity of 2226 cm 01 . The vibrational wavenumbers are determined to be n 1 Å 2353 cm 01 , n 2 Å 883 cm 01 , and n 3 Å 2498 cm 01 . For the a ˜state we determine r e Å 1.2369 A ˚, a e Å 105.7Њ, a barrier height to linearity of 6071 cm 01 , and the vibrational wavenumbers n 1 Å 2070 cm 01 , n 2 Å 986 cm 01 , and n 3 Å 2059 cm 01 . For the b ˜state we determine r e Å 1.1936 A ˚, a e Å 135.9Њ, a barrier height to linearity of 1069 cm 01 , and the vibrational wavenumbers n 1 Å 2399 cm 01 , n 2 Å 915 cm 01 , and n 3 Å 2591 cm 01 . The most interesting result we obtain is that the singlet-triplet splitting T 0 (a ˜1A 1 ) is only 153 cm 01 for 11 BH 0 2 . Hence singlet-triplet perturbations will significantly affect the levels of the ground state.