Overview of desorption parameters of volatile and complex organic molecules

Abstract

Context. Many molecules observed in the interstellar medium are thought to result from the thermal desorption of ices. Parameters such as the desorption energy and pre-exponential frequency factor are essential in describing the desorption of molecules. Experimental determinations of these parameters are missing for many molecules, including those found in the interstellar medium. Aims. The objective of this work is to expand the number of molecules for which desorption parameters are available, by collecting and re-analysing experimental temperature programmed desorption data that are present in the literature. Methods. We used transition state theory (TST) in combination with the Redhead equation to determine the desorption parameters. Experimental data and molecular constants (e.g. mass, moment of inertia, etc.) were collected and given as input. Results. Using the Redhead-TST method, the desorption parameters for 133 molecules were determined. The Redhead-TST method is found to provide reliable results that agree well with desorption parameters determined on the basis of more rigorous experimental methods. The importance of using accurately determined pre-exponential frequency factors to simulate desorption profiles is highlighted here. The large amount of data allows us to look for trends, with the most important being the relationship log10(v) = 2.65ln(m) + 8.07, where ν is the pre-exponential frequency factor and m is the mass of the molecule. Conclusions. The data collected in this work allow for the thermal desorption of molecules to be modeled, with the aim of helping improve our understanding of changes in the chemical and elemental composition of interstellar environments.