Potential formation of three pyrimidine bases in interstellar regions
  Work on the chemical evolution of pre-biotic molecules remains incomplete
since the major obstacle is the lack of adequate knowledge of rate coefficients
of various reactions which take place in interstellar conditions. In this work,
we study the possibility of forming three pyrimidine bases, namely, cytosine,
uracil and thymine in interstellar regions. Our study reveals that the
synthesis of uracil from cytosine and water is quite impossible under
interstellar circumstances. For the synthesis of thymine, reaction between
uracil and :CH2 is investigated. Since no other relevant pathways for the
formation of uracil and thymine were available in the literature, we consider a
large gas-grain chemical network to study the chemical evolution of cytosine in
gas and ice phases. Our modeling result shows that cytosine would be produced
in cold, dense interstellar conditions. However, presence of cytosine is yet to
be established. We propose that a new molecule, namely, C4N3OH5 could be
observable in the interstellar region. C4N3OH5 is a precursor (Z isomer of
cytosine) of cytosine and far more abundant than cytosine. We hope that
observation of this precursor molecule would enable us to estimate the
abundance of cytosine in interstellar regions. We also carry out quantum
chemical calculations to find out the vibrational as well as rotational
transitions of this precursor molecule along with three pyrimidine bases.
