  In an effort to further our interest in understanding basic chemistry of
interstellar molecules, we carry out here an extensive investigation of the
stabilities of interstellar carbon chains; Cn, H2Cn, HCnN and CnX (X=N, O, Si,
S, H, P, H-, N-). These sets of molecules accounts for about 20% of all the
known interstellar and circumstellar molecules, their high abundances therefore
demand a serious attention. High level ab initio quantum chemical calculations
are employed to accurately estimate enthalpy of formation, chemical reactivity
indices; global hardness and softness; and other chemical parameters of these
molecules. Chemical modeling of the abundances of these molecular species has
also been performed. Of the 89 molecules considered from these groups, 47 have
been astronomically observed, these observed molecules are found to be more
stable with respect to other members of the group. Of the 47 observed
molecules, 60% are odd number carbon chains. Interstellar chemistry is not
actually driven by the thermodynamics, it is primarily dependent on various
kinetic parameters. However, we found that the detectability of the odd
numbered carbon chains could be correlated due to the fact that they are more
stable than the corresponding even numbered carbon chains. Based on this
aspect, the next possible carbon chain molecule for astronomical observation in
each group is proposed. The effect of kinetics in the formation of some of
these carbon chain molecules is also discussed.
