Astrochemistry as a tool to follow the protostellar evolution: the Class
  I stage
  The latest developments in astrochemistry have shown how some molecular
species can be used as a tool to study the early stages of the solar-type star
formation process. Among them, the more relevant species are the interstellar
complex organic molecules (iCOMs) and the deuterated molecules. Their analysis
give us information on the present and past history of protostellar objects.
Among the protostellar evolutionary stages, Class I protostars represent a
perfect laboratory in which to study the initial conditions for the planet
formation process. 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 towards 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.
