# Probing the role of excited states in ionization of acetylene

## TL;DR

This study models acetylene ionization using VUV laser pulses and finds that excited states significantly influence ionization efficiency, harmonic generation, and photoelectron spectra, depending on laser wavelength and molecular alignment.

## Contribution

It demonstrates the impact of excited states on ionization and harmonic generation in acetylene, using time-dependent density functional theory with various laser wavelengths.

## Key findings

- Ionization is maximized when molecules align with laser polarization.
- Excited states enhance high harmonic generation yield.
- Photoelectron spectra are significantly affected by excited state populations.

## Abstract

Ionization of acetylene by linearly-polarized, vacuum ultraviolet (VUV) laser pulses is modelled using time-dependent density functional theory. Several laser wavelengths are considered including one that produces direct ionization to the first excited cationic state while another excites the molecules to a Rydberg series incorporating an autoionizing state. We show that for the wavelengths and intensities considered, ionization is greatest whenever the molecule is aligned along the laser polarization direction. By considering high harmonic generation we show that populating excited states can lead to a large enhancement in the harmonic yield. Lastly, angularly-resolved photoelectron spectra are calculated which show how the energy profile of the emitted electrons significantly changes in the presence of these excited states.