Mateo David, Eloranta Jussi
Department of Chemistry and Biochemistry, California State University at Northridge , 18111 Nordhoff Street, Northridge, California 91330, United States.
J Phys Chem A. 2014 Aug 21;118(33):6407-15. doi: 10.1021/jp501451y. Epub 2014 Apr 1.
On the basis of electronic structure calculations, the structure of intrinsic positive charge solvated in superfluid helium is identified as triatomic He3(+) ion, which is bound to the surrounding ground state helium atoms through the charge–charge induced dipole interaction in a pairwise additive manner. Bosonic density functional theory calculations show that this ion forms the well-known Atkins’ snowball solvation structure where the first rigid helium shell is effectively disconnected from the rest of the liquid. Evaluation of the total energy vs helium droplet size N shows distinct regions related to the completion of solvent shells near N = 16 and N = 47. These regions can be assigned to magic numbers observed in positively charged helium droplets appearing at N = 15 and in the range between 20 and 50 helium atoms. The calculated added mass for the positive ion in bulk superfluid helium (18 mHe) is much smaller than the previous experiments suggest (30–40 mHe), indicating that there may be yet some unidentified additional factor contributing to the measured effective mass. Both previous experiments and the present calculations agree on the effective mass of the negative charge (240–250 mHe). The main difference between the solvated negative and positive charges in liquid helium is that the latter forms a chemically bound triatomic molecule surrounded by highly inhomogeneous liquid structure whereas the former remains as a separated charge with a smoothly varying liquid density around it.
基于电子结构计算，超流氦中溶剂化的本征正电荷结构被确定为三原子He3(+)离子，它通过电荷 - 电荷诱导偶极相互作用以成对相加的方式与周围的基态氦原子结合。玻色子密度泛函理论计算表明，该离子形成了著名的阿特金斯雪球溶剂化结构，其中第一个刚性氦壳层与液体的其余部分有效分离。总能量相对于氦滴尺寸N的评估显示出与N = 16和N = 47附近溶剂壳层完成相关的不同区域。这些区域可归因于在N = 15出现的带正电氦滴以及20至50个氦原子范围内观察到的幻数。计算得到的体超流氦中正离子的附加质量（18mHe）远小于先前实验表明的值（30 - 40mHe），这表明可能存在一些尚未确定的额外因素对测量的有效质量有贡献。先前的实验和目前的计算在负电荷的有效质量（240 - 250mHe）上是一致的。液氦中溶剂化的负电荷和正电荷之间的主要区别在于，后者形成一个被高度不均匀的液体结构包围的化学键合三原子分子，而前者则作为一个分离的电荷，其周围液体密度平滑变化。
