Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany.
Phys Chem Chem Phys. 2010 Dec 28;12(48):15704-14. doi: 10.1039/c0cp00696c. Epub 2010 Aug 16.
Weakly-bound clusters of the closed-shell benzoyl cation (C(6)H(5)CO(+), PhCO(+)) with Ar and H(2)O are investigated by infrared (IR) spectroscopy, mass spectrometry, and quantum chemical calculations in order to characterize the interaction of a closed shell aromatic cation with a nonpolar and a polar ligand. PhCO(+)-L dimers are produced by electron ionization of benzaldehyde in a supersonic plasma expansion. IR photodissociation (IRPD) spectra of PhCO(+)-L with L = Ar and H(2)O are analyzed in the C-O, C-H, and O-H stretch ranges (2000-3900 cm(-1)). The potential energy surface of the PhCO(+)-L dimers is characterized at the MP2/6-311++G(2df,2pd) level to locate the various minima and determine their energetic and vibrational properties. PhCO(+)-Ar prefers intermolecular π-bonding to the aromatic ring with a bond energy of D(0) = 6 kJ mol(-1). The weak interaction implies that the IRPD spectrum of PhCO(+)-Ar is very close to the IR spectrum of bare PhCO(+). The detection of the C-H and C-O stretch fundamentals provides valuable information about the C-O and C-H bond strengths in this prototypical aromatic acylium ion. Moreover, a variety of weak combination and overtone bands are assigned. The global minimum on the PhCO(+)-H(2)O potential has a planar charge-dipole configuration with D(0) = 41 kJ mol(-1) (with only the two H(2)O protons being out-of-plane), in which the lone pairs of H(2)O interact with the positive partial charges on the carbonyl carbon atom and the proton of the CH group in ortho position. The experimental IRPD spectra are in accord with the calculated global minima. The analysis of the charge distribution shows that the PhCO(+) cation is best represented as an oxocarbenium ion (Ph-C(+)[double bond, length as m-dash]O) with smaller contributions of the ketene structure (Ph(+)[double bond, length as m-dash]C[double bond, length as m-dash]O). This view is supported by the geometrical and vibrational properties of PhCO(+) as well as the shape of the intermolecular PhCO(+)-L dimer potentials.
用红外（IR）光谱、质谱和量子化学计算研究了闭壳苯甲酰阳离子（C（6）H（5）CO（+），PhCO（+））与 Ar 和 H（2）O 的弱束缚簇，以表征闭壳芳香阳离子与非极性和极性配体的相互作用。PhCO（+）-L 二聚体通过苯甲醛在超音速等离子体膨胀中的电子电离产生。分析了 PhCO（+）-L（L = Ar 和 H（2）O）的 IRPD 光谱在 C-O、C-H 和 O-H 伸缩范围（2000-3900 cm（-1））。PhCO（+）-L 二聚体的势能面在 MP2/6-311++G（2df，2pd）水平上进行了特征化，以定位各种最小值并确定它们的能量和振动性质。PhCO（+）-Ar 优先与芳环形成分子间π键，键能为 D（0）= 6 kJ mol（-1）。这种弱相互作用意味着 PhCO（+）-Ar 的 IRPD 光谱非常接近裸露的 PhCO（+）的 IR 光谱。检测 C-H 和 C-O 伸缩基频提供了有关这种典型芳香酰基阳离子中 C-O 和 C-H 键强度的有价值信息。此外，还分配了各种弱组合和泛频带。PhCO（+）-H（2）O 势能上的全局最小值具有平面电荷偶极构型，D（0）= 41 kJ mol（-1）（只有两个 H（2）O 质子不在平面上），其中 H（2）O 的孤对与羰基碳原子上的正部分电荷和邻位 CH 基团的质子相互作用。实验 IRPD 光谱与计算的全局最小值一致。电荷分布分析表明，PhCO（+）阳离子最好表示为氧碳翁离子（Ph-C（+）[双键，长度为 m-dash]O），酮烯结构（Ph（+）[双键，长度为 m-dash]C[双键，长度为 m-dash]O）的贡献较小。这一观点得到了 PhCO（+）的几何和振动性质以及 PhCO（+）-L 二聚体分子间势能的形状的支持。
