Visible-Light Photoionization of Aromatic Molecules in Water-Ice: Organic Chemistry across the Universe with Less Energy

TL;DR

This study demonstrates that visible light can ionize polycyclic aromatic hydrocarbons in water-ice, revealing new low-energy pathways for organic chemistry in space and planetary environments.

Contribution

First evidence that visible photons can cause ionization of PAHs in water-ice, expanding understanding of astrochemical processes with lower energy requirements.

Findings

Visible photons cause ionization of PAHs in water-ice.

Ionization energy is reduced by 4.4 eV compared to gas phase.

Implications for organic chemistry in space environments.

Abstract

Ionization of gas-phase organic molecules such as polycyclic aromatic hydrocarbons (PAHs) requires vacuum ultraviolet photons at wavelengths shorter than 200 nm (~6-9 eV). We present here for the first time that visible photons - accessible through sunlight - can cause photoionization of trapped PAHs in cryogenic water-ice, accounting for 4.4 eV less ionization energy than in the gas phase. This finding opens up new reaction pathways involving low-energy ionization in many environments where water and organic matter coexist. This include the interstellar medium, molecular clouds, protoplanetary disks, and planetary surfaces and atmospheres (including Earth).