  Since molecules are ubiquitous in space, the study of the 'Molecular
Universe' could unfold the mystery of the existing Interstellar medium. Star
formation is linked to the chemical evolution processes. Thus, an analysis of
the formation of stars coupled with the chemical evolution would give a clear
insight into the entire process. For example, various evolutionary stages of
star formation could be probed by observing various molecules. Chemical
diagnostics of these regions could be used to extract the physical properties
(e.g., density, temperature, ionization degree, etc.) of these regions.
Radiative transfer calculations are worthwhile in estimating physical
parameters of the region where molecules are detected. However, the radiative
transfer calculations are limited due to insufficient molecular data, such as
spectroscopic information or collisional excitation probabilities of many
interstellar species. Complex organic molecules are detected in various
environments ranging from the cold gas in prestellar cores to the warm gas on
solar system scales close to individual protostars. A comparative study of the
relative abundances of molecules could provide insights into the beginning of
chemical complexity and the link to our solar system. In my thesis, I would
mainly investigate the physical properties and kinematics of different
star-forming regions using radiative transfer modeling. The observed spatial
differentiation between various key molecules is used to explain their physical
structure or evolution and various microphysical effects. In addition, some key
molecules are used to study the various evolutionary phases. This simulated
data is useful for interpreting the observed data of different telescopes like
IRAM 30m, GBT, ALMA, Herschel, SOFIA, etc.
