Müller S, Mudrich M, Stienkemeier F
Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany.
J Chem Phys. 2009 Jul 28;131(4):044319. doi: 10.1063/1.3180819.
We systematically investigate the formation and stability of snowballs formed by femtosecond photoionization of small alkali clusters bound to helium nanodroplets. For all studied alkali species Ak = (Na,K,Rb,Cs) we observe the formation of snowballs Ak(+)He(N) when multiply doping the droplets. Fragmentation of clusters Ak(N) upon ionization appears to enhance snowball formation. In the case of Na and Cs we also detect snowballs Ak(2) (+)He(N) formed around Ak dimer ions. While the snowball progression for Na and K is limited to less than 11 helium atoms, the heavier atoms Rb and Cs feature wide distributions at least up to Ak(+)He(41). Characteristic steps in the mass spectra of Cs-doped helium droplets are found at positions consistent with predictions on the closure of the first shell of helium atoms around the Ak(+) ion based on variational Monte Carlo simulations.
我们系统地研究了与氦纳米液滴结合的小碱金属团簇经飞秒光电离形成雪球的过程及其稳定性。对于所有研究的碱金属物种Ak =（Na、K、Rb、Cs），我们观察到在对液滴进行多重掺杂时会形成雪球Ak(+)He(N)。电离时团簇Ak(N)的碎片化似乎会增强雪球的形成。在Na和Cs的情况下，我们还检测到围绕Ak二聚体离子形成的雪球Ak(2) (+)He(N)。虽然Na和K的雪球增长限于少于11个氦原子，但较重的原子Rb和Cs至少在Ak(+)He(41)之前具有广泛的分布。在掺Cs氦液滴的质谱中，特征峰出现在与基于变分蒙特卡罗模拟对Ak(+)离子周围氦原子第一壳层闭合的预测相一致的位置。
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