title: Calculation of the fine structure and intensity of the singlet-triplet transitions in the imidogen radical.
abstract: 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(1)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((-13)(+17)) 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 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.
authors.affiliation: State University of Technology, Cherkassy 18006, Ukraine. boris@theochem.kth.se
authors.forename: Boris
authors.initials: B
authors.lastname: Minaev
authors.forename: Lyudmila
authors.initials: L
authors.lastname: Yaschuk
authors.forename: Vitalina
authors.initials: V
authors.lastname: Kukueva
mesh_terms: D005609:Free Radicals / Q000737:chemistry*; D007094:Imides / Q000737:chemistry*; D015394:Molecular Structure
chemical_list: D005609:Free Radicals; D007094:Imides