Electronic spectrum of 17 electronic states of BN molecule: a theoretical study

The potential energy curves (PECs) of the X(3)Π, a(1)Σ(+), b(1)Π, A(3)Σ(+), B(3)Σ(-), c(1)Δ, D(3)Π, 1(5)Π, 3(1)Σ(+), 3(3)Π, 2(1)Π, 2(3)Σ(+), 1(3)Δ, 1(5)Σ(+), 4(3)Π, 2(3)Σ(-) and 1(5)Σ(-) electronic states of the BN molecule are calculated using an ab initio quantum chemical method. The PEC calculations have been made for internuclear separations from 0.06 to 1.20 nm using the complete active space self-consistent field (CASSCF) method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV5Z basis set. To improve the quality of PECs, core-valence correlation and relativistic corrections are included. Relativistic correction calculations are carried out using the third-order Douglas-Kroll Hamiltonian (DKH3) approximation. Core-valence correlation corrections are included using a cc-pCVQZ basis set. Relativistic corrections are calculated at the level of a cc-pVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). These PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. The spectroscopic parameters are determined by fitting the vibrational levels, which are calculated in a direct forward manner from the analytic potential by solving the ro-vibrational Schrödinger equation using Numerov's method. The spectroscopic results have been compared in detail with those reported in the literature. Excellent agreement has been found between the present spectroscopic results and the experimental ones. Using the Breit-Pauli operator, the spin-orbit coupling effect on the spectroscopic parameters is included in the X(3)Π and D(3)Π electronic states. The vibrational level, inertial rotation and centrifugal distortion constants are calculated for each vibrational state of each electronic state. And those of the first 20 vibrational states of each electronic state are reported when the rotational quantum number equals zero. Comparison with the measurements shows that the present results are accurate. The spectroscopic parameters of the c(1)Δ, 1(5)Π, 3(1)Σ(+), 3(3)Π, 2(1)Π, 2(3)Σ(+), 1(3)Δ, 1(5)Σ(+), 4(3)Π and 1(5)Σ(-) electronic states and the vibrational manifolds of all the electronic states obtained here are expected to be reliable predicted results.