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Rotational spectroscopy of singly $^{13}$C substituted isotopomers of propyne and determination of a semi-empirical equilibrium structure

Submillimeter spectra of three isotopomers of propyne containing one $^{13}$C atom were recorded in natural isotopic composition in the region of 426 GHz to 785 GHz. Additional measurements were carried out near 110 GHz. Combining these with earlier data resulted in greatly improved spectroscopic parameters which permit reliable extrapolations up to about 1.5 THz. Coupled cluster quantum-chemical calculations were carried out in order to assess the differences between equilibrium and ground state rotational parameters of these and many other isotopic species to evaluate semi-empirical equilibrium structural parameters. In addition, we estimated the main spectroscopic parameters of the isotopomers of propyne with two $^{13}$C atoms, which have not yet been studied in the laboratory, but which may be detectable in astronomical sources with a large amount of $^{13}$C compared to the dominant $^{12}$C.