  We carry out a quantum chemical calculation to obtain the infrared and
electronic absorption spectra of several complex molecules of the interstellar
medium (ISM). These molecules are the precursors of adenine, glycine & alanine.
They could be produced in the gas phase as well as in the ice phase. We carried
out a hydro-chemical simulation to predict the abundances of these species in
the gas as well as in the ice phase. Gas and grains are assumed to be
interacting through the accretion of various species from the gas phase on to
the grain surface and desorption (thermal evaporation and photo-evaporation)
from the grain surface to the gas phase. Depending on the physical properties
of the cloud, the calculated abundances varies. The influence of ice on
vibrational frequencies of different pre-biotic molecules was obtained using
Polarizable Continuum Model (PCM) model with the integral equation formalism
variant (IEFPCM) as default SCRF method with a dielectric constant of 78.5.
Time dependent density functional theory (TDDFT) is used to study the
electronic absorption spectrum of complex molecules which are biologically
important such as, formamide and precursors of adenine, alanine and glycine. We
notice a significant difference between the spectra of the gas and ice phase
(water ice). The ice could be mixed instead of simple water ice. We have varied
the ice composition to find out the effects of solvent on the spectrum. We
expect that our study could set the guidelines for observing the precursor of
some bio-molecules in the interstellar space.

Cosmology and Nongalactic Astrophysics;Earth and Planetary Astrophysics;Chemical Physics