Theoretical study of HBeO

Using multi-reference configuration interaction (MRCI) and coupled-cluster RCCSD(T) ab initio methods three-dimensional potential energy surfaces (PES) have been generated for the X 2Π and A 2Σ+ states of HBeO. The two components of the X 2Π electronic ground state form a linear-linear Renner-Teller pair. The HBeO structure is calculated to lie 11,917 cm−1 above the BeOH isomer. A barrier on the A′ PES of 10,920 cm−1 relative to the HBeO minimum does not permit a spontaneous rearrangement. From variational Renner-Teller calculations the rovibronic levels of the X 2Π state of the HBeO radical have been evaluated for J=12andJ=32. The eigenstates can not be unequivocally assigned by harmonic quantum numbers due to anharmonic resonances involving all three vibrational modes. In contrast with previous studies A 2Σ+ state is calculated above the X 2Π (Te = 9389 cm−1). For some higher doublet and quartet states of BeOH and HBeO, MRCI vertical electronic transition energies are reported.