Minaev Boris
State University of Technology, Cherkassy 18006, Ukraine.
Spectrochim Acta A Mol Biomol Spectrosc. 2005 Dec;62(4-5):790-9. doi: 10.1016/j.saa.2005.03.006. Epub 2005 Aug 15.
Observation of Bose-Einstein condensation in Li27 initiated the interest in the scattering length of two ground state lithium atoms when they approach each other as a radical pair triplet aSigmau+3 state. But some properties of this state are still unknown. In present work, a number of low-lying triplet states of lithium molecule are calculated by multi-configuration self-consistent field (MCSCF) and response techniques with account of spin-orbit coupling, spin-spin coupling and some other magnetic perturbations. The singlet-triplet transition probabilities to the ground state are also presented. Most results are connected with the weakly bound lowest triplet a3Sigmau+ state, whose radiative lifetime and spin-splitting are unknown so far in spite of its great importance in Bose-Einstein condensation. Calculations indicate that this state has a very small spin-splitting, lambdass=-0.01 cm-1, which is negligible in comparison with the line-width in experimental Fourier transform spectra published so far. Similar splitting is obtained for the upper state of the 1(3)Sigmag+--a3Sigmau+ transition. This is in agreement with experimental rovibronic analysis of the 1(3)Sigmag+--a3Sigmau+ band system in which the triplet structure was not resolved. The radiative lifetime of the a3Sigmau+ state is predicted to exceed 10 h.
对锂-27中玻色-爱因斯坦凝聚的观测引发了人们对两个基态锂原子作为自由基对三重态aΣu+3态相互靠近时散射长度的兴趣。但该态的一些性质仍不为人知。在本工作中，利用多组态自洽场（MCSCF）和响应技术，考虑自旋-轨道耦合、自旋-自旋耦合及其他一些磁微扰，计算了锂分子的多个低激发三重态。还给出了到基态的单重态-三重态跃迁概率。大多数结果与弱束缚的最低三重态a3Σu+态有关，尽管它在玻色-爱因斯坦凝聚中非常重要，但其辐射寿命和自旋分裂至今仍未知。计算表明，该态的自旋分裂非常小，λss = -0.01 cm-1，与迄今发表的实验傅里叶变换光谱中的线宽相比可忽略不计。对于1(3)Σg+--a3Σu+跃迁的上态也得到了类似的分裂。这与1(3)Σg+--a3Σu+带系的实验振转分析一致，在该分析中三重态结构未被分辨。预测a3Σu+态的辐射寿命超过10小时。
