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