Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
J Chem Phys. 2011 Jul 21;135(3):034309. doi: 10.1063/1.3615505.
Lanthanum dimer (La(2)) was studied by mass-analyzed threshold ionization (MATI) spectroscopy and a series of multi-configuration ab initio calculations. The MATI spectrum exhibits three band systems originating from ionization of the neutral ground electronic state, and each system shows vibrational frequencies of the neutral molecule and singly charged cation. The three ionization processes are La(2)(+) (a(2)∑(g)(+)) ← La(2) (X(1)∑(g)(+)), La(2)(+) (b(2)Π(3/2, u)) ← La(2) (X(1)∑(g)(+)), and La(2)(+) (b(2)Π(1/2, u)) ← La(2) (X(1)∑(g)(+)), with the ionization energies of 39,046, 40,314, and 40,864 cm(-1), respectively. The vibrational frequency of the X(1)Σ(g)(+) state is 207 cm(-1), and those of the a(2)Σ(g)(+), b(2)Π(3/2, u) and b(2)Π(1/2, u) are 235.7, 242.2, and 240 cm(-1). While X(1)Σ(g)(+) is the ground state of the neutral molecule, a(2)Σ(g (+) and b(2)Π(u) are calculated to be the excited states of the cation. The spin-orbit splitting in the b(2)Π(u) ion is 550 cm(-1). An X(4)Σ(g)(-) state of La(2)(+) was predicted by theory, but not observed by the experiment. The determination of a singlet ground state of La(2) shows that lanthanum behaves differently from scandium and yttrium.
镧二聚体（La(2)）的研究采用质量分析阈值电离（MATI）光谱和一系列多组态从头算计算。MATI 光谱显示三个带系统源自中性基态的电离，每个系统都显示中性分子和单电荷阳离子的振动频率。三个电离过程为 La(2)(+) (a(2)∑(g)(+)) ← La(2) (X(1)∑(g)(+))、La(2)(+) (b(2)Π(3/2, u)) ← La(2) (X(1)∑(g)(+))和 La(2)(+) (b(2)Π(1/2, u)) ← La(2) (X(1)∑(g)(+))，其电离能分别为 39046、40314 和 40864 cm(-1)。X(1)Σ(g)(+)态的振动频率为 207 cm(-1)，a(2)Σ(g)(+)、b(2)Π(3/2, u)和 b(2)Π(1/2, u)的振动频率分别为 235.7、242.2 和 240 cm(-1)。虽然 X(1)Σ(g)(+)是中性分子的基态，但 a(2)Σ(g)(+)和 b(2)Π(u)被计算为阳离子的激发态。b(2)Π(u)离子的自旋轨道分裂为 550 cm(-1)。理论预测了 La(2)(+)的 X(4)Σ(g)(-)态，但实验未观察到。La(2)的单重基态的确定表明镧的行为与钪和钇不同。
