Intensity-resolved ionization yileds of aniline with femtosecond laser pulses

TL;DR

This study investigates the ionization behavior of aniline and benzene molecules under intense femtosecond laser pulses, revealing a novel resonant multiphoton ionization process through advanced 3D imaging techniques.

Contribution

The paper introduces a new method for measuring intensity-dependent ionization yields free from volumetric artifacts, uncovering a previously unobserved resonant multiphoton process in aniline.

Findings

Identification of a resonant-like multiphoton ionization process.

Demonstration of a technique for volumetric-free ionization yield measurement.

Evidence supporting a stepwise ionization mechanism via the pi-sigma* state.

Abstract

We present experimental results for the ionization of aniline and benzene molecules subjected to intense ultrashort laser pulses. Measured parent molecular ions yields were obtained using a recently developed technique capable of three-dimensional imaging of ion distributions within the focus of a laser beam. By selecting ions originating from the central region of the focus, where the spatial intensity distribution is nearly uniform, volumetric-free intensity-dependent ionization yields were obtained. The measured data revealed a previously unseen resonant-like multiphoton ionization process. Comparison of benzene, aniline and Xe ion yields demonstrate that the observed intensity dependent structures are not due to geometric artifacts in the focus. Finally we attribute the ionization of aniline to a stepwise process going through the pi-sigma^star state which sits 3 photons above the ground state and 2 photons below the continuum.