A differential mobility analyzer (DMA) is used in atmospheric pressure N₂ to select a narrow range of electrical mobilities from a complex mix of cluster ions of composition (CA)_n(C⁺)_z. The clusters are introduced into the N₂ gas by electrospraying concentrated (∼20 mM) acetonitrile solutions of ionic liquids (molten salts) of composition CA (C⁺ = cation, A⁻ = anion). Mass analysis of these mobility-selected ions reveals the occurrence of individual neutral ion-pair evaporation events from the smallest singly charged clusters: (CA)_nC⁺→(CA)_{n− 1}C⁺+CA. Although bulk ionic liquids are effectively involatile at room temperature, up to six sequential evaporation events are observed. Because this requires far more internal energy than available in the original clusters, substantial heating (∼10 eV) must take place in the ion guides leading to the mass analyzer. The observed increase in IL evaporation rate with decreasing size is drastic, in qualitative agreement with the exponential vapor pressure dependence predicted by Kelvin’s formula. A single evaporation event is barely detectable at n = 13, while two or more are prominent for n ≤ 9. Magic number clusters (CA)₄C⁺ with singularly low volatilities are found in three of the four ionic liquids studied. Like their recently reported liquid phase prenucleation cluster analogs, these magic number clusters could play a key role as gas-phase nucleation seeds. All the singularly involatile clusters seen are cations, which may help understand commonly observed sign effects in ion-induced nucleation. No other charge-sign asymmetry is seen on cluster evaporation.

差分迁移率分析仪 (DMA) 用于在大气压 N ₂下从组成为 (CA) _n (C ⁺ ) _z的簇离子的复杂混合物中选择窄范围的电迁移率。通过电喷雾组成为 CA（C ⁺ = 阳离子，A ^- = 阴离子）的离子液体（熔盐）的浓缩（~20 mM）乙腈溶液，将簇引入 N ₂气体中。这些迁移率选择离子的质量分析揭示了来自最小单电荷簇的单个中性离子对蒸发事件的发生：(CA) _n C ⁺ →(CA) _{n− 1} C ⁺+CA。尽管本体离子液体在室温下实际上是不挥发的，但观察到多达六个连续的蒸发事件。由于这需要比原始簇中可用的更多的内部能量，因此必须在通向质量分析器的离子导向器中进行大量加热（~10 eV）。观察到的 IL 蒸发率随尺寸减小而急剧增加，这与开尔文公式预测的指数蒸气压依赖性定性一致。在n = 13 时几乎无法检测到单个蒸发事件，而当n ≤ 9时，两个或更多是突出的。 幻数簇 (CA) ₄ C ⁺在所研究的四种离子液体中的三种中发现了极低的挥发性。就像他们最近报道的液相预成核簇类似物一样，这些幻数簇可以作为气相成核种子发挥关键作用。看到的所有奇异的非挥发性簇都是阳离子，这可能有助于理解离子诱导成核中常见的符号效应。在团簇蒸发中没有看到其他电荷符号不对称。