Paul Scherrer Institute, General Energy Department, CH-5232 Villigen, Switzerland.
J Chem Phys. 2011 Jan 28;134(4):044302. doi: 10.1063/1.3526747.
In this work we present a deperturbation study of the d (3)Π(g), v=6 state of C(2) by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system (d(3)Π(g)-a (3)Π(u)) unveils the presence of the energetically lowest high-spin state of C(2) in the vicinity of the d (3)Π(g), v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the 1 (5)Π(g) state at rotational quantum numbers N ≤ 11. The spectral complexity for transitions to the v = 6 level of d (3)Π(g) state is further enhanced by an additional perturbation at N = 19 and 21 owing to the b (3)Σ(g)(-), v=19 state. The spectroscopic characterization of both dark states is accessible by the measurement of 122 "window" levels. A global fit of the positions to a conventional Hamiltonian for a linear diatomic molecule yields accurate molecular constants for the quintet and triplet perturber states for the first time. In addition, parameters for the spin-orbit and L-uncoupling interaction between the electronic levels are determined. The detailed deperturbation study unravels major issues of the so-called high-pressure bands of C(2). The anomalous nonthermal emission initially observed by Fowler in 1910 [Mon. Not. R. Astron. Soc. 70, 484 (1910)] and later observed in numerous experimental environments are rationalized by taking into account "gateway" states, i.e., rotational levels of the d (3)Π(g), v=6 state that exhibit significant (5)Π(g) character through which all population flows from one electronic state to the other.
在这项工作中，我们通过双共振四波混频光谱学对 C(2) 的 d(3)Π(g), v=6 态进行了去微扰研究。通过中间能级标记，准确地分配了微扰跃迁的线位置。此外，通过利用该技术的灵敏度和高动态范围，可以获得额外的谱线。这些弱谱特征源自附近的暗态，通过微扰过程获得跃迁强度。对 Swan 体系（d(3)Π(g)-a(3)Π(u)）的（6,5）和（6,4）带中复杂光谱区域的去微扰分析揭示了 C(2) 附近的 d(3)Π(g), v=6 态存在能量最低的高自旋态。d 态的三个自旋分量的项能量曲线在转动量子数 N ≤ 11 时与 1(5)Π(g)态的五个项相交。由于 b(3)Σ(g)(-), v=19 态，在 N = 19 和 21 处的另外一个微扰进一步增强了 d(3)Π(g)态 v=6 能级跃迁的光谱复杂性。通过测量 122 个“窗口”能级，可以获得对两个暗态的光谱特征。对一个线性双原子分子的常规哈密顿量的位置进行全局拟合，首次为五重态和三重态微扰态提供了准确的分子常数。此外，还确定了电子能级之间的自旋轨道和 L 去耦相互作用的参数。详细的去微扰研究揭示了所谓的 C(2)高压带的主要问题。1910 年 Fowler 最初观察到的异常非热发射[Mon. Not. R. Astron. Soc. 70, 484 (1910)]，以及后来在许多实验环境中观察到的非热发射，可以通过考虑“门”态来合理化，即 d(3)Π(g), v=6 态的转动能级，通过这些能级，所有的种群从一个电子态流到另一个电子态，表现出显著的（5）Π(g)特征。
