Calculation of the fine structure and intensity of the singlet-triplet transitions in the imidogen radical

摘要

The singlet-triplet transition moments are calculated for the NH radical by multiconfiguration self-consistent field (MCSCF) method with a quadratic response (QR) technique. The band systems in the visible region (b(l) Sigma(+)-> X-3 Sigma(-) and a(1) Delta -> X-3 Sigma(-)) of the NH radical are analyzed in comparison with previous ab initio treatments and with the recent experimental data in attempt to solve some discrepancies. The b(1)Sigma(+)-> X(3)Sigma(Omega)(-) transition moments ratio for the two spin sublevels Omega = 1 and Omega = 0 of the ground state is well reproduced and the radiative lifetime of the b(1) Sigma(+) state (tau(b) = 58 ms) is obtained in a good agreement with the experimental value tau(b)= 53((+1 7)(-13)) 3[1 3 ms. The A(3) Pi <- a(1) Delta transition probability is calculated for the first time and found to be in an excellent agreement with the recent optical pumping measurements of the NH radical in a molecular beam, where Population transfer from the metastable a(1)Delta state to the ground X(3)Sigma(-) state is achieved. For the at a(1)Delta -> X-3 Sigma-transition some improvement is achieved in comparison with the previous ab initio results, but the calculated radiative lifetime (tau(a) = 3.9 s) is still much lower than the recent measurement provides (tau(a)= 12.5 s). The zero field splitting and spin-rotation coupling constants are calculated for the ground state by different methods and advantage of the density functional theory is stressed. (c) 2004 Elsevier B.V. All rights reserved.