Real-time observation of electronic, vibrational, and rotational dynamics in nitric oxide with attosecond soft x-ray pulses at 400 eV

Nariyuki Saito,Nobuhiro Kosugi,Yi Wu,Nobuhisa Ishii,Jiro Itatani,Hiroki Sannohe,Teruto Kanai,Andrew Chew,Seunghwoi Han,Zenghu Chang

doi:10.1364/optica.6.001542

Abstract

Photoinduced quantum dynamics in molecules have hierarchical temporal structures with different energy scales that are associated with electron and nuclear motions. Femtosecond-to-attosecond transient absorption spectroscopy (TAS) using high-harmonic generation (HHG) with a photon energy below 300 eV has been a powerful tool to observe such electron and nuclear dynamics in a table-top manner. However, comprehensive measurements of the electronic, vibrational, and rotational molecular dynamics have not yet been achieved. Here, we demonstrate HHG-based TAS at the nitrogen K-edge (400 eV) for the first time, and observe all the electronic, vibrational, and rotational degrees of freedom in a nitric oxide molecule at attosecond to sub-picosecond time scales. This method of employing core-to-valence transitions offers an all-optical approach to reveal complete molecular dynamics in photochemical reactions with element and electronic state specificity.

Highlights

The observation of electronic and nuclear dynamics in molecules initiated by light is critical for understanding fundamental mechanisms in photoinduced chemical and physical processes [1]
We demonstrate that electronic, vibrational, and rotational dynamics at attosecond to sub-picosecond time scales can be simultaneously observed by high-harmonic generation (HHG)-based transient absorption spectroscopy (TAS) in the soft X-ray (SX) region
Around the delay origin, the nitric oxide (NO) 1s-Rydberg peaks are modulated in the presence of a strong IR field

Summary

Introduction

The observation of electronic and nuclear dynamics in molecules initiated by light is critical for understanding fundamental mechanisms in photoinduced chemical and physical processes [1]. TAS has unique advantages over other techniques: it is unaffected by the existence of strong laser fields, state-specific even if the probe pulse has a broadband spectrum, and free of the space charge problem. Because of these characteristics, TAS is one of the most ideal techniques for laser-based pump-probe experiments for a wide range of atoms and molecules. By using TAS in the extreme ultraviolet (XUV) region below ~100 eV, real-time observations of electronic processes such as autoionization [7, 8], valence electron motion [9], tunnel ionization [10], the emergence of laser-dressed states [11] and nuclear dynamics [12-14] have been demonstrated. Short-wavelength SX pulses are expected to enable element-specific TAS in complex molecules in various environments such as in solvents [26] or on surfaces

Methods

Results

Conclusion