College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2014 Jan 3;117:109-19. doi: 10.1016/j.saa.2013.07.093. Epub 2013 Aug 8.
The potential energy curves (PECs) of 28 Ω states generated from 9 Λ-S states (X(2)Π, 1(4)Π, 1(6)Π, 1(2)Σ(+), 1(4)Σ(+), 1(6)Σ(+), 1(4)Σ(-), 2(4)Π and 1(4)Δ) are studied for the first time using an ab initio quantum chemical method. All the 9 Λ-S states correlate to the first two dissociation limits, N((4)Su)+Se((3)Pg) and N((4)Su)+Se((3)Dg), of NSe radical. Of these Λ-S states, the 1(6)Σ(+), 1(4)Σ(+), 1(6)Π, 2(4)Π and 1(4)Δ are found to be rather weakly bound states. The 1(2)Σ(+) is found to be unstable and has double wells. And the 1(6)Σ(+), 1(4)Σ(+), 1(4)Π and 1(6)Π are found to be the inverted ones with the SO coupling included. The PEC calculations are made by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification. The spin-orbit coupling is accounted for by the state interaction approach with the Breit-Pauli Hamiltonian. The convergence of the present calculations is discussed with respect to the basis set and the level of theory. Core-valence correlation corrections are included with a cc-pCVTZ basis set. Scalar relativistic corrections are calculated by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. All the PECs are extrapolated to the complete basis set limit. The variation with internuclear separation of spin-orbit coupling constants is discussed in brief for some Λ-S states with one shallow well on each PEC. The spectroscopic parameters of 9 Λ-S and 28 Ω states are determined by fitting the first ten vibrational levels whenever available, which are calculated by solving the rovibrational Schrödinger equation with Numerov's method. The splitting energy in the X(2)Π Λ-S state is determined to be about 864.92 cm(-1), which agrees favorably with the measurements of 891.80 cm(-1). Moreover, other spectroscopic parameters of Λ-S and Ω states involved here are also in fair agreement with available measurements. It demonstrates that the spectroscopic parameters reported here can be expected to be reliable predicted ones.
首次使用从头算量子化学方法研究了 28 Ω 态从 9 Λ-S 态（X(2)Π、1(4)Π、1(6)Π、1(2)Σ(+)、1(4)Σ(+)、1(6)Σ(+)、1(4)Σ(-)、2(4)Π 和 1(4)Δ）产生的势能曲线（PECs）。所有 9 Λ-S 态都与 NSe 自由基的前两个离解极限 N((4)Su)+Se((3)Pg) 和 N((4)Su)+Se((3)Dg)相关联。在这些 Λ-S 态中，1(6)Σ(+)、1(4)Σ(+)、1(6)Π、2(4)Π 和 1(4)Δ被发现是相当弱束缚态。1(2)Σ(+)被发现是不稳定的，具有双势阱。并且，当包括 SO 耦合时，1(6)Σ(+)、1(4)Σ(+)、1(4)Π 和 1(6)Π 被发现是倒置的。势能曲线计算是通过完全活性空间自洽场方法进行的，然后通过内部收缩多参考组态相互作用方法与戴维森修正相结合。自旋轨道耦合通过 Breit-Pauli 哈密顿量的态相互作用方法来计算。根据基集和理论水平讨论了当前计算的收敛性。用 cc-pCVTZ 基集包含核价相关校正。用 cc-pV5Z 基集的三阶 Douglas-Kroll 哈密顿近似计算标量相对论修正。所有的势能曲线都被外推到完全基集极限。简要讨论了一些势能曲线上每个势能面都有一个浅势阱的 Λ-S 态的自旋轨道耦合常数随核间距的变化。在可用的情况下，通过求解 Numerov 方法的 rovibrational Schrödinger 方程来计算前十个振动能级，从而确定 9 Λ-S 和 28 Ω 态的光谱参数。在 X(2)Π Λ-S 态中确定自旋轨道耦合能分裂能约为 864.92 cm(-1)，与测量值 891.80 cm(-1)非常吻合。此外，这里涉及的 Λ-S 和 Ω 态的其他光谱参数也与可用的测量值吻合较好。这表明这里报告的光谱参数可以预期是可靠的预测值。
