Marlton Samuel J P, Liu Chang, Bieske Evan J
School of Chemistry, The University of Melbourne, Melbourne, Victoria 3010, Australia.
J Chem Phys. 2024 Jan 21;160(3). doi: 10.1063/5.0188157.
The bond dissociation energy of FeCr+ is measured using resonance enhanced photodissociation spectroscopy in a cryogenic ion trap. The onset for FeCr+ → Fe + Cr+ photodissociation occurs well above the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit. In contrast, the higher energy FeCr+ → Fe+ + Cr photodissociation process exhibits an abrupt onset at the energy of the Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) limit, enabling accurate dissociation energies to be extracted: D(Fe-Cr+) = 1.655 ± 0.006 eV and D(Fe+-Cr) = 2.791 ± 0.006 eV. The measured D(Fe-Cr+) bond energy is 10%-20% larger than predictions from accompanying CAM (Coulomb Attenuated Method)-B3LYP and NEVPT2 and coupled cluster singles, doubles, and perturbative triples electronic structure calculations, which give D(Fe-Cr+) = 1.48, 1.40, and 1.35 eV, respectively. The study emphasizes that an abrupt increase in the photodissociation yield at threshold requires that the molecule possesses a dense manifold of optically accessible, coupled electronic states adjacent to the dissociation asymptote. This condition is not met for the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit of FeCr+ but is satisfied for the higher energy Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) dissociation limit.
在低温离子阱中使用共振增强光解离光谱法测量了FeCr⁺的键解离能。FeCr⁺→Fe + Cr⁺光解离的起始点远高于最低的Cr⁺(6S, 3d⁵) + Fe(5D, 3d⁶4s²)解离极限。相比之下，高能的FeCr⁺→Fe⁺ + Cr光解离过程在Cr(7S, 3d⁵4s¹) + Fe⁺(6D, 3d⁶4s¹)极限能量处呈现出突然的起始点，从而能够提取准确的解离能：D(Fe - Cr⁺) = 1.655 ± 0.006 eV和D(Fe⁺ - Cr) = 2.791 ± 0.006 eV。测得的D(Fe - Cr⁺)键能比伴随的CAM（库仑衰减方法）-B3LYP以及NEVPT2和耦合簇单、双和微扰三重态电子结构计算的预测值大10% - 20%，这些计算分别给出D(Fe - Cr⁺) = 1.48、1.40和1.35 eV。该研究强调，阈值处光解离产率的突然增加要求分子在解离渐近线附近拥有密集的可光学访问的耦合电子态流形。对于FeCr⁺的最低Cr⁺(6S, 3d⁵) + Fe(5D, 3d⁶4s²)解离极限，此条件不满足，但对于更高能量的Cr(7S, 3d⁵4s¹) + Fe⁺(6D, 3d⁶4s¹)解离极限则满足。
