High-harmonic transient grating spectroscopy of NO2 electronic relaxation

TL;DR

This study combines theoretical simulations and experimental high-harmonic transient grating spectroscopy to investigate the ultrafast electronic relaxation dynamics of NO2 molecules following UV excitation, revealing vibrational dynamics underlying electronic transitions.

Contribution

It provides the first combined theoretical and experimental analysis of NO2 electronic relaxation using high harmonic transient grating spectroscopy, demonstrating the technique's ability to encode vibrational dynamics.

Findings

Fast oscillations of electronic character observed

Quantitative agreement between experiment and simulation

Vibrational dynamics are encoded in the transient signals

Abstract

We study theoretically and experimentally the electronic relaxation of NO2 molecules excited by absorption of one ~400 nm pump photon. Semi-classical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occuring on the same timescale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO2, high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.