Stropoli Santino J, Khuu Thien, Boyer Mark A, Karimova Natalia V, Gavin-Hanner Coire F, Mitra Sayoni, Lachowicz Anton L, Yang Nan, Gerber R Benny, McCoy Anne B, Johnson Mark A
Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA.
Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
J Chem Phys. 2022 May 7;156(17):174303. doi: 10.1063/5.0083078.
We report vibrational spectra of the H-tagged, cryogenically cooled X · HOCl (X = Cl, Br, and I) ion-molecule complexes and analyze the resulting band patterns with electronic structure calculations and an anharmonic theoretical treatment of nuclear motions on extended potential energy surfaces. The complexes are formed by "ligand exchange" reactions of X · (HO) clusters with HOCl molecules at low pressure (∼10 mbar) in a radio frequency ion guide. The spectra generally feature many bands in addition to the fundamentals expected at the double harmonic level. These "extra bands" appear in patterns that are similar to those displayed by the X · HOD analogs, where they are assigned to excitations of nominally IR forbidden overtones and combination bands. The interactions driving these features include mechanical and electronic anharmonicities. Particularly intense bands are observed for the v = 0 → 2 transitions of the out-of-plane bending soft modes of the HOCl molecule relative to the ions. These involve displacements that act to break the strong H-bond to the ion, which give rise to large quadratic dependences of the electric dipoles (electronic anharmonicities) that drive the transition moments for the overtone bands. On the other hand, overtone bands arising from the intramolecular OH bending modes of HOCl are traced to mechanical anharmonic coupling with the v = 1 level of the OH stretch (Fermi resonances). These interactions are similar in strength to those reported earlier for the X · HOD complexes.
我们报道了H标记的、低温冷却的X·HOCl（X = Cl、Br和I）离子 - 分子复合物的振动光谱，并通过电子结构计算以及在扩展势能面上对核运动的非谐理论处理来分析所得的谱带模式。这些复合物是通过X·(HO)团簇与HOCl分子在射频离子导向器中低压（约10毫巴）下的“配体交换”反应形成的。除了在双谐波水平预期的基频外，光谱通常还具有许多谱带。这些“额外谱带”呈现出与X·HOD类似物所显示的模式相似的模式，在X·HOD类似物中，它们被归因于名义上红外禁阻的泛音和组合带的激发。驱动这些特征的相互作用包括机械非谐性和电子非谐性。对于HOCl分子相对于离子的面外弯曲软模式的v = 0 → 2跃迁，观察到特别强的谱带。这些跃迁涉及到一些位移，这些位移会破坏与离子的强氢键，从而导致驱动泛音带跃迁矩的电偶极矩有很大的二次依赖性（电子非谐性）。另一方面，HOCl分子内OH弯曲模式产生的泛音带可追溯到与OH伸缩振动的v = 1能级的机械非谐耦合（费米共振）。这些相互作用的强度与先前报道的X·HOD复合物的相互作用强度相似。
