School of Biomedical, Biomolecular & Chemical Sciences, The University of Western Australia, M313, Crawley, 6009, Australia.
J Phys Chem A. 2010 Apr 15;114(14):4762-9. doi: 10.1021/jp909237n.
Infrared vibrational predissociation spectra are recorded for Br(-)-(NH(3))(n) (n = 1-4) and I(-)-NH(3) clusters in the N-H stretch region (3040-3460 cm(-1)). To aid spectral assignments and clarify structures of the Br(-)-(NH(3))(n) clusters, ab initio calculations are performed at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels of theory. The Br(-)-NH(3) and I(-)-NH(3) dimers are predicted to have structures in which the NH(3) molecule is attached to the halide anion by a single hydrogen-bond. The dominant infrared band for Br(-)-NH(3) at 3171 cm(-1) corresponds to a hydrogen-bonded N-H stretch vibrational mode, whereas two weaker bands are assigned to a symmetric stretch vibration of the nonbonded N-H groups (3347 cm(-1)) and to an ammonia-based bending overtone (3293 cm(-1)) deriving infrared intensity through Fermi interaction with the H-bonded N-H stretch mode. The corresponding I(-)-NH(3) spectrum is dominated by the H-bonded N-H stretch band at 3217 cm(-1), with three weaker bands at 3240, 3305, and 3360 cm(-1) assigned to two bending overtone vibrations and the nonbonded N-H symmetric stretch vibration, respectively. Spectra of the Br(-)-(NH(3))(n), n = 2-4, clusters are similar to the I(-)-NH(3) spectrum, exhibiting evidence for strong Fermi interactions between the H-bonded N-H stretch vibrational mode and ammonia-based bending overtones. On the basis of the infrared spectra and ab initio calculations, the larger Br(-)-(NH(3))(n) clusters are deduced to have structures in which the NH(3) molecules are attached to the Br(-) by single H-bonds, but not necessarily to one other.
记录了 Br(-)-(NH(3))(n) (n = 1-4) 和 I(-)-NH(3) 团簇在 N-H 伸缩区域 (3040-3460 cm(-1)) 的红外振动预解离光谱。为了帮助谱带归属和阐明 Br(-)-(NH(3))(n) 团簇的结构，在 MP2/aug-cc-pVDZ 和 MP2/aug-cc-pVTZ 理论水平上进行了从头算计算。预测 Br(-)-NH(3) 和 I(-)-NH(3) 二聚体具有 NH(3) 分子通过单个氢键连接到卤化物阴离子的结构。Br(-)-NH(3) 的主要红外带位于 3171 cm(-1)，对应于氢键 N-H 伸缩振动模式，而两个较弱的带分别分配给非键合的 N-H 基团的对称伸缩振动 (3347 cm(-1)) 和源自与氢键 N-H 伸缩模式的 Fermi 相互作用获得红外强度的氨弯曲泛频 (3293 cm(-1))。相应的 I(-)-NH(3) 光谱主要由 3217 cm(-1)处的氢键 N-H 伸缩带主导，3240、3305 和 3360 cm(-1) 处的三个较弱带分别分配给两个弯曲泛频振动和非键合的 N-H 对称伸缩振动。Br(-)-(NH(3))(n)，n = 2-4，团簇的光谱与 I(-)-NH(3) 光谱相似，表明氢键 N-H 伸缩振动模式与氨弯曲泛频之间存在强烈的 Fermi 相互作用。基于红外光谱和从头算计算，推断较大的 Br(-)-(NH(3))(n) 团簇具有 NH(3) 分子通过单个氢键连接到 Br(-)的结构，但不一定连接到另一个。
