Sommerfeld Thomas
Department of Chemistry and Physics, Southeastern Louisiana University, Hammond, Louisiana 70402, USA.
J Phys Chem A. 2008 Nov 20;112(46):11817-23. doi: 10.1021/jp8057004. Epub 2008 Oct 28.
Dipole-bound anions of small water clusters (H2O) N- (N >or= 2) are well-known from experiment and theory. In contrast, the smallest ammonia cluster anion detected so far is the 13-mer (NH3)13-. Here dipole-bound states of small ammonia clusters (NH3)N- (N = 2, 3, 4) are investigated using coupled-cluster ab initio methods. The trimer is found to be the smallest ammonia cluster able to form a dipole bound state, and its vertical detachment energy is predicted to be 27 meV, somewhat smaller than that of the water dimer. For the ammonia tetramer dipole-bound states with triple-acceptor monmers are identified akin to the well-studied double-acceptor binding motif of water cluster anions. Moreover, a (NH3)6-)hexamer that has been considered as a model for a cavity-bound state is examined. Ab initio results for this system challenge the notion that an electron localized in an ammonia cavity can be thought of as a delocalized radical anion.
小水团簇（H₂O）N⁻（N≥2）的偶极束缚阴离子已为实验和理论所熟知。相比之下，迄今检测到的最小氨团簇阴离子是十三聚体（NH₃）₁₃⁻。本文采用耦合簇从头算方法研究了小氨团簇（NH₃）N⁻（N = 2、3、4）的偶极束缚态。发现三聚体是能够形成偶极束缚态的最小氨团簇，其垂直脱附能预计为27毫电子伏，略小于水二聚体的垂直脱附能。对于氨四聚体，确定了具有三受体单体的偶极束缚态，类似于对水团簇阴离子深入研究的双受体结合模式。此外，还研究了被视为腔束缚态模型的（NH₃）₆⁻六聚体。该体系的从头算结果对电子定域于氨腔中可被视为离域自由基阴离子这一观点提出了挑战。
