Accurate rotational constants for linear interstellar carbon chains: achieving experimental accuracy

Abstract

Linear carbon chain molecular species remain the dominant theme in interstellar chemistry. Their continuous astronomical observation depends on the availability of accurate spectroscopic parameters. Accurate rotational constants are reported for hundreds of molecular species of astrophysical, spectroscopy and chemical interests from the different linear carbon chains; $\mathrm{C}_{{n}}\mathrm{H}$ , $\mathrm{C}_{{n}}\mathrm{H}^{-}$ , $\mathrm{C}_{{n}}\mathrm{N}$ , $\mathrm{C}_{{n}}\mathrm{N}^{-}$ , $\mathrm{C}_{{n}}\mathrm{O}$ , $\mathrm{C}_{{n}}\mathrm{S}$ , $\mathrm{HC}_{{n}}\mathrm{S}$ , $\mathrm{C}_{{n}}\mathrm{Si}$ , $\mathrm{CH}_{3}(\mathrm{CC})_{{n}}\mathrm{H}$ , $\mathrm{HC}_{{n}}\mathrm{N}$ , $\mathrm{DC}_{2{n}+1}\mathrm{N}$ , $\mathrm{HC}_{2{n}}\mathrm{NC}$ , and $\mathrm{CH}_{3}(\mathrm{C}\equiv\mathrm{C})_{{n}}\mathrm{CN}$ using three to four moments of inertia calculated from the experimental rotational constants coupled with those obtained from the optimized geometries at the Hartree Fock level. The calculated rotational constants are obtained from the corrected moments of inertia at the Hartfree Fock geometries. The calculated rotational constants show accuracy of few kHz below irrespective of the chain length and terminating groups. The obtained accuracy of few kHz places these rotational constants as excellent tools for both astronomical and laboratory detection of these molecular species of astrophysical interest. From the numerous unidentified lines from different astronomical surveys, transitions corresponding to known and new linear carbon chains could be found using these rotational constants. The astrophysical, spectroscopic and chemical implications of these results are discussed.