Desorption of hot molecules from photon irradiated interstellar ices

TL;DR

This study experimentally investigates photodesorption processes of benzene and water ices under laser irradiation, revealing three distinct mechanisms and their energetic characteristics, which impact interstellar gas-phase chemistry understanding.

Contribution

It provides the first detailed measurements of photodesorption mechanisms and energies for benzene and water ices relevant to astrophysics.

Findings

Identified three photodesorption processes with distinct energy signatures.

Measured high translational temperatures of desorbed molecules.

Implications for gas-phase chemistry in interstellar medium.

Abstract

We present experimental measurements of photodesorption from ices of astrophysical relevance. Layers of benzene and water ice were irradiated with a laser tuned to an electronic transition in the benzene molecule. The translational energy of desorbed molecules was measured by time-of-flight (ToF) mass spectrometry. Three distinct photodesorption processes were identified - a direct adsorbate-mediated desorption producing benzene molecules with a translational temperature of around 1200 K, an indirect adsorbate-mediated desorption resulting in water molecules with a translational temperature of around 450 K, and a substrate-mediated desorption of both benzene and water producing molecules with translational temperatures of around 530 K and 450 K respectively. The translational temperature of each population of desorbed molecules is well above the temperature of the ice matrix. The implications for gas-phase chemistry in the interstellar medium are discussed.