Photoelectron spectroscopy of Rydberg excited states in singly charged molecular ions CS₂ ⁺ by NIR laser pulses

Abstract

We performed photoelectron spectroscopy using femtosecond extreme-ultraviolet (XUV) pulses from a free-electron laser and femtosecond near-infrared (NIR) pulses from a synchronized laser, and succeeded in measuring photoelectrons from highly excited Rydberg states of molecular ions + CS .2 Such excited states are prepared via a sequential process of photoionization and subsequent photoexcitation during a short pulse of XUV, and then a band of the Rydberg excited states is probed with a synchronized NIR pulse. The photoelectron spectrum has been well explained by our hydrogenic Rydberg orbital model. The present result demonstrates that the two-color experiments of XUV free-electron lasers and NIR laser makes it possible to observe highly excited states of molecular ions. This implies that the present approach provides ones a new spectroscopic tool for studying excited states of various molecular ions.