Accurate calculations of spectroscopic properties for the 13 K–S states and the 23 X states of BO radical including the spin–orbit coupling effect Zunlue Zhu, Wei Yu, Shuai Wang, Jinfeng Sun, Deheng Shi ⇑ College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China highlights  PECs are extrapolated to the CBS limit.  Effect of SO coupling on the spectroscopic parameters is evaluated.  Spectroscopic parameters of 13 K–S states and 23 X states are obtained.  Effect of core–valence correlation and scalar relativistic corrections is included.  Franck–Condon factors and radiative lifetimes of some transitions are calculated. graphical abstract The spectroscopic properties of 23 X states generated from the 13 K–S states of BO radical are studied. Of the 13 K–S states, the F 2 P,1 2 U and 1 2 D states possess the double well. The 1 4 P,C 2 P,1 2 R  and 2 2 R  states possesses one well with one barrier. The A 2 P,1 4 P and F 2 P are the inverted states with the SO cou- pling effect included. All the states possess the deep well except for the 1 2 U. The PECs are calculated by the CASSCF method followed by the icMRCI approach with Davidson correction. Core–valence correlation and scalar relativistic corrections are taken into account. The PECs are extrapolated to the CBS limit. The SO coupling effect is accounted for. The spectroscopic parameters are evaluated. The Franck–Condon fac- tors and radiative lifetimes of transitions from the B 2 R + ,C 2 P,D 2 R + ,1 2 R  and 1 4 P K–S states to the ground state are calculated for several low vibrational levels. The spectroscopic parameters reported here can be expected to be reliably predicted ones. 0.1 0.2 0.3 0.4 0.5 0.6 -99.9 -99.8 -99.7 -99.6 7 5 6 4 2 3 1 Potential energy /Hartree Internuclear separation /nm B( 2 Pu) + O( 1 Dg) B( 2 Pu)+O( 3 Pg) PECs of seven states of the BO radical 1-A 2 Π; 2-1 4 Σ - ; 3-1 2 Σ - ; 4-C 2 Π; 5-2 2 Σ - ; 6-1 4 Π; 7-F 2 Π article info Article history: Received 22 January 2014 Received in revised form 13 March 2014 Accepted 3 April 2014 Available online 18 April 2014 Keywords: Potential energy curve Spectroscopic parameter Franck–Condon factor Radiative lifetime Spin–orbit coupling effect abstract The spectroscopic properties of 23 X states generated from the 13 K–S states of BO radical are studied for the first time for internuclear separations from about 0.07 to 1.0 nm. Of the 13 K–S states, each of the F 2 P,1 2 U and 1 2 D states is found to possess the double well. Each of the 1 4 P,C 2 P,1 2 R  and 2 2 R  states possesses one well with one barrier. The A 2 P,1 4 P and F 2 P are the inverted states with the spin–orbit coupling effect taken into account. All the states possess the deep well except for the 1 2 U. The potential energy curves (PECs) are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. Core–valence correlation and scalar relativistic corrections are included into the calculations. The PECs are extrapolated to the complete basis set limit. The spin–orbit coupling effect is accounted for by the state interaction approach with the Breit–Pauli Hamiltonian. The spectroscopic parameters are evaluated, and compared with the available measurements and other theoretical results. The Franck–Condon factors and radiative lifetimes of the transitions from the B 2 R + ,C 2 P,D 2 R + ,1 2 R  and http://dx.doi.org/10.1016/j.saa.2014.04.023 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel./fax: +86 373 3326375. E-mail address: scattering@sina.com.cn (D. Shi). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 42–54 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa