Astrochemistry as a Tool To Follow Protostellar Evolution: The Class I Stage

The latest developments in astrochemistry have shown how some molecular species can be used as tools to study the early stages of the solar-type star formation process. Among them, particularly relevant are interstellar complex organic molecules (iCOMs) and deuterated molecules. Their analysis gives us information on the present and past history of the protostellar objects. Among the protostellar evolutionary stages, Class I protostars represent a perfect laboratory where the initial conditions for the planet formation process can be studied. Indeed, from a physical point of view, the Class I stage is the bridge between the Class 0 phase, dominated by the accretion process, and the protoplanetary disk phase, when planets form. Despite their importance, few observations of Class I protostars exist, and very little is known about their chemical content. In this paper we review the (few) existing observations of iCOMs and deuterated species in Class I protostars. In addition, we present new observations of deuterated cyanoacetylene and thioformaldehyde toward the Class I protostar SVS13-A. These new observations allow us to better understand the physical and chemical structure of SVS13-A and compare the cyanoacetylene and thioformaldehyde deuteration with other sources in different evolutionary phases.