Stars are born in interstellar space within dense
regions of large clouds of dust and gas. In its earliest stages, the emission
from the young star itself is obscured from us, since the dust absorb the
visible light emitted by the star. But with radio observations of wavelength in
the millimeter and sub-millimeter regime, it is possible to detect the
so-called protostars, because of the effect of their presence on the
surroundings. Protostars emit an enormous amount of heat, which will increase
the temperature of the nearby dust and gas. Molecules can form both on the icy
surfaces of dust grains and in the gas phase. Far away from the protostar,
where the temperature is low, molecules will be frozen into the ice layer that
covers the dust grains, while close to the protostars, where the temperature is
high, the ice and the molecules will evaporate off the grains. The field of
astrochemistry - or molecular astrophysics - has evolved fast in recent years,
due to major technological advancements for radio telescopes. But some of the
most central questions still remain unanswered: how, where and when are complex
organic molecules formed around young stars? How complex can these molecules
become? Is there a difference in the chemistry for high- and low-mass
protostars?


The work in this thesis aim to provide answer for these questions by searching
for molecules where they have not been detected before and by comparing the
relative abundance of different molecules to models and laboratory work as well
as between different sources. The analysis is based on observations of two
high-mass sources, W51/e2 and G34.3+0.2, with the IRAM 30 m single dish
telescope, and of a low-mass protostar, IRAS16293-2422, with the Atacama Large Millimeter/submillimeter
Array. We have successfully made a number of new detections: a tentative
detection of ethylene glycol for the first time in G34.3+0.2, while confirming
the previous marginal detection of ethylene glycol in W51/e2. For the first time
toward a low-mass protostar, we have made firm detections of acetone, propanal
and ethylene oxide in IRAS16293-2422. For some relative abundance ratios, we
find that these are seemingly correlated to the source luminosity, thus we see
a difference between high- and low-mass protostars. But for other ratios we
find no significant difference between them. Chemical models and laboratory
studies fail to reproduce the observed range of high- and low-mass sources.
Modified models and laboratory work as well as more observations are therefore
needed to further develop our understanding of the chemistry occurring in
star-forming regions.