标题： 分子超冷等离子体的形成与衰变 显示英文标题

标题： On the formation and decay of a molecular ultracold plasma

摘要： 双共振光激发分子束中的二氧化氮，产生了一组密集的$50f(2)$激发态，这些状态演化形成自由电子等离子体，被困在 NO$^+$空间电荷的势阱中。 等离子体以分子束的速度移动，并在通过接地栅极时产生电子飞行时间信号，该信号测量等离子体的大小和被捕获电子的数量。 这种等离子体以符合电子温度低至 5 K 的速率膨胀，比通常观察到的原子超冷等离子体更冷。 分子 NO$^+$正离子与电子的复合形成了被超过二氧化氮化学键两倍能量激发的中性分子，由此引发了一个问题：即中性碎片化是否在塑造从激发气体到等离子体的短期演化过程中能量和粒子密度再分布中起作用。 为了探讨这个问题，我们将用于原子超冷等离子体的耦合速率方程模型适应于描述我们系统中电子-激发态和电子-离子碰撞的能量粒度雪崩。 在原子形式的基础上，增加激发态预解离通道和双体、电子-正离子解离复合通道，我们研究了这种弛豫如何将粒子密度和能量分布在激发态、自由电子和中性碎片上。 这项研究的结果表明了一些分子碎片化通道可能影响等离子体状态的机制。 显示英文摘要

摘要： Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of $50f(2)$ Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO$^+$ spacecharge. The plasma travels at the velocity of the molecular beam, and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K, colder that typically observed for atomic ultracold plasmas. The recombination of molecular NO$^+$ cations with electrons forms neutral molecules excited by more than twice the energy of the NO chemical bond, and the question arises whether neutral fragmentation plays a role in shaping the redistribution of energy and particle density that directs the short-time evolution from Rydberg gas to plasma. To explore this question, we adapt a coupled rate-equations model established for atomic ultracold plasmas to describe the energy-grained avalanche of electron-Rydberg and electron-ion collisions in our system. Adding channels of Rydberg predissociation and two-body, electron- cation dissociative recombination to the atomic formalism, we investigate the kinetics by which this relaxation distributes particle density and energy over Rydberg states, free electrons and neutral fragments. The results of this investigation suggest some mechanisms by which molecular fragmentation channels can affect the state of the plasma.