Formula omitted] (X = C, Si and Ge): Superalkali cations containing three planar tetracoordinate X atoms

Jin-Chang Guo,Hui-Xia Wu,Guang-Ming Ren,Chang-Qing Miao,Yong-Xia Li

doi:10.1016/j.comptc.2016.03.007

Jin-Chang Guo, Hui-Xia Wu + Show 3 more

Open Access

https://doi.org/10.1016/j.comptc.2016.03.007

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Abstract

A new class of superalkali cations X3Li3+ (X=C, Si and Ge) containing three planar tetracoordinate X atom have been characterized using ab initio methods. These perfect planar high-symmetric (D3h) species are the global minimum of the systems based on extensive stochastic structural searches, followed by high level quantum chemistry calculations. The vertical electron affinities (VEAs) of the X3Li3+ cations range from 2.88 to 3.02eV at OVGF//MP2/6-311+G(3df) level, which are lower than 3.89eV of Cs atom. Thus, they represent the first series of superalkali cations with three ptX (X=C, Si and Ge) atoms. Bonding analyses reveal that there are mainly ionic bonds between X and Li atoms, while there are covalent bonds between X atoms. AdNDP, NICS analyses indicate that X3Li3+ (X=C, Si and Ge) cations are π aromatic with two delocalized π electrons. Large HOMO–LUMO energy gaps 7.62–10.41eV further support their thermodynamic stability. Born–Oppenheimer molecular dynamics (BOMD) investigations indicate that the structures of these ptX species are well maintained during 20ps simulations. The current results may motivate theoretical and experimental studies on novel ptX (X=C, Si and Ge) complexes as well as superalkali species.

Highlights

Establishing the excitation spectrum of a composite system has historically been one of the most effective ways to determine the detailed nature of the interactions between its constituents
The spectrum of nucleon resonances remains poorly established with the basic properties and even the existence of many excited states uncertain
A major program of measurements utilizing polarized photon beams, polarized targets and final-state nucleon polarimeters is currently underway with the goal to achieve a “complete”, model-independent measurement of photoproduction reactions

Summary

Introduction

Establishing the excitation spectrum of a composite system has historically been one of the most effective ways to determine the detailed nature of the interactions between its constituents. In an attempt to address this shortcoming, real photon beams have been used to excite nucleon targets, providing accurate data to constrain partialwave analyses (PWA) and reaction models used to extract information on the excitation spectrum [6,7,8,9,10,11]. The process γ p → K +Λ has the lowest energy threshold for photoproduction reactions with final-state particles containing strange valence quarks This is a crucial channel as many models predict that some poorly established or “missing” resonances couple strongly to strange decay channels [12]. Disentangling the cause of the narrow structure in this mass region is likely to require accurate cross-section and polarization observables for a range of reaction channels

The experiment

Results and interpretation

Conclusions