# Ionisation of H$_2$O by a strong ultrashort XUV pulse: a model within the single active electron approximation

## TL;DR

This paper introduces a new computational method within the single active electron approximation to study ionisation of water molecules by intense ultrashort XUV pulses, providing efficient and comparative analysis of molecular orientation and phase effects.

## Contribution

A novel, computationally inexpensive approach for modeling ionisation in complex molecules under ultrashort laser pulses within the single active electron framework.

## Key findings

- Ionisation yield varies with molecular orientation and pulse phase.
- The new method produces results comparable to existing approaches.
- Application to water molecule demonstrates practical utility.

## Abstract

We present and discuss a new computationally inexpensive method to study, within the single active electron approximation, the interaction of a complex system with an intense ultrashort laser pulse. As a first application, we consider the one photon single ionisation of the highest occupied molecular orbital of the water molecule by a laser pulse. The ionisation yield is calculated for different orientations of the molecule with respect to the field polarization axis and for different carrier envelope phases of the pulse, and compared against predictions of another single active electron approach.