Polyakova E, Stolyarov D, Wittig C
Department of Chemistry, Columbia University, New York, New York 10027, USA.
J Chem Phys. 2006 Jun 7;124(21):214308. doi: 10.1063/1.2198844.
The photoexcitation of NO embedded in superfluid Hen nanodroplets having n approximately 10(4) has been examined. Two-photon excitation prepares electronically excited states (NO()), most notably, the embedded analog of the A 2Sigma state of gas phase NO. Vertical excitation to this low Rydberg state is blueshifted and broadened relative to its gas phase counterpart because of the repulsive electron-helium interaction. Transport to the droplet surface is believed to be facile in the superfluid. For example, NO prefers (energetically) to reside at the droplet surface rather than at the droplet center, in contrast to NO. Photoionization of surface-bound NO* occurs over a significant photon energy range. This yields small cluster ions NO+Hek) with approximately 90% of these clusters having k< or =10. The variation of ion yield with photon energy displays a precipitous change in the region of 24 300-24 400 cm(-1) for all values of k. Possible photoionization mechanisms are discussed and it is suggested that intermediate levels with high-n Rydberg character play a role. This work underscores the important role played by transport in the photophysics of species embedded in the superfluid host.
对嵌入超流氦纳米液滴（n约为10⁴）中的一氧化氮（NO）的光激发进行了研究。双光子激发产生电子激发态（NO*），最显著的是气相NO的A 2Σ态的嵌入类似物。由于电子与氦之间的排斥相互作用，垂直激发到这个低里德堡态相对于其气相对应物发生了蓝移并展宽。在超流体中，向液滴表面的传输被认为是容易的。例如，与NO相反，NO*（在能量上）更倾向于驻留在液滴表面而不是液滴中心。表面结合的NO*的光电离发生在相当大的光子能量范围内。这产生了小簇离子NO + Heₖ，其中约90%的这些簇具有k≤10。对于所有k值，离子产率随光子能量的变化在24300 - 24400 cm⁻¹区域显示出急剧变化。讨论了可能的光电离机制，并表明具有高n里德堡特征的中间能级起到了作用。这项工作强调了传输在嵌入超流体主体中的物种的光物理过程中所起的重要作用。
