Combining a laser vaporization cluster source, a velocity scan system, and a time-of-flight mass spectrometer, we measured velocity distributions of few-atom cobalt clusters (${\mathrm{\text{Co}}}_n$, $n=6-60$) suspended in a helium carrier gas and expanded into vacuum. The velocity distributions provide information about the cluster size dependence of the translational temperature, flow velocity, and velocity slip with respect to the helium carrier gas. The system of clusters in a carrier gas is found to violate the equipartition theorem. Although the clusters in the expansion do not thermalize with the helium gas, they do experience significant, size-dependent internal cooling. While expanding into vacuum, the clusters collide, at least a couple of hundred times, super-elastically with the carrier gas, thereby transferring internal vibrational energy into self-acceleration and increasing the flow velocity of the gas as a whole. It also is demonstrated that the proposed velocity distribution measurements can be used to test whether a source produces thermalized clusters.

中文翻译：

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氦载气中金属团簇的尺寸依赖性速度分布和温度

结合激光汽化团簇源，速度扫描系统和飞行时间质谱仪，我们测量了少数原子钴团簇的速度分布（${\mathrm{\text{有限公司}}}_{ñ}$， $ñ=6-60$）悬浮在氦气载气中并膨胀为真空。速度分布提供了有关簇温度与氦载气的平移温度，流速和速度滑动的簇大小相关性的信息。发现载气中的簇系统违反了等分定理。尽管膨胀中的簇不随氦气热化，但它们确实经历了明显的，取决于尺寸的内部冷却。在膨胀成真空时，这些团簇与载气至少发生了数百次超弹性碰撞，从而将内部振动能量转化为自加速作用，并整体上提高了气体的流速。