Thermal desorption of astrophysical relevant ice mixtures of acetaldehyde and acetonitrile from olivine dust

TL;DR

This study investigates how water, acetonitrile, and acetaldehyde ice mixtures desorb from olivine dust grains under astrophysical conditions, revealing that a significant fraction of molecules can remain on grains up to higher temperatures, affecting molecular distribution in space.

Contribution

It provides new laboratory data on thermal desorption of key astrochemical molecules from olivine dust, highlighting the retention of molecules at higher temperatures than previously assumed.

Findings

Approximately 40% of molecules remain on grains up to 200 K.

Desorption occurs at 100 K for acetaldehyde and 120 K for acetonitrile.

Retention of molecules influences the location of snowlines in protoplanetary disks.

Abstract

Millimeter and centimeter observations are discovering an increasing number of interstellar complex organic molecules (iCOMs) in a large variety of star forming sites, from the earliest stages of star formation to protoplanetary disks and in comets. In this context it is pivotal to understand how the solid phase interactions between iCOMs and grain surfaces influence the thermal desorption process and, therefore, the presence of molecular species in the gas phase. In laboratory, it is possible to simulate the thermal desorption process deriving important parameters such as the desorption temperatures and energies. We report new laboratory results on temperature-programmed desorption (TPD) from olivine dust of astrophysical relevant ice mixtures of water, acetonitrile, and acetaldehyde. We found that in the presence of grains, only a fraction of acetaldehyde and acetonitrile desorbs at about 100 K and 120 K respectively, while 40% of the molecules are retained by fluffy grains of the order of 100 {\mu}m up to temperatures of 190-210 K. In contrast with the typical assumption that all molecules are desorbed in regions with temperatures higher than 100 K, this result implies that about 40% of the molecules can survive on the grains enabling the delivery of volatiles towards regions with temperatures as high as 200 K and shifting inwards the position of the snowlines in protoplanetary disks. These studies offer a necessary support to interpret observational data and may help our understanding of iCOMs formation providing an estimate of the fraction of molecules released at various temperatures.