Minaev Boris, Yaschuk Lyudmila, Kukueva Vitalina
State University of Technology, Cherkassy 18006, Ukraine.
Spectrochim Acta A Mol Biomol Spectrosc. 2005 Apr;61(6):1105-12. doi: 10.1016/j.saa.2004.06.026.
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.
通过采用二次响应（QR）技术的多组态自洽场（MCSCF）方法计算了NH自由基的单重态-三重态跃迁矩。结合之前的从头算处理方法和最近的实验数据，对NH自由基在可见光区域的能带系统（b(1)Σ⁺→X(3)Σ⁻和a(1)Δ→X(3)Σ⁻）进行了分析，试图解决一些差异。基态两个自旋子能级Ω = 1和Ω = 0的b(1)Σ⁺→X(3)ΣΩ⁻跃迁矩比得到了很好的再现，并且b(1)Σ⁺态的辐射寿命（τb = 58 ms）与实验值τb = 53（-13）（+17）ms吻合良好。首次计算了A(3)Π←a(1)Δ跃迁概率，发现与最近在分子束中对NH自由基的光泵浦测量结果非常吻合，其中实现了从亚稳a(1)Δ态到基态X(3)Σ⁻态的粒子转移。对于a(1)Δ→X(3)Σ⁻跃迁，与之前的从头算结果相比有了一些改进，但计算得到的辐射寿命（τa = 3.9 s）仍然远低于最近测量得到的值（τa = 12.5 s）。通过不同方法计算了基态的零场分裂和自旋-旋转耦合常数，并强调了密度泛函理论的优势。
