Microwave spectra of propyne and its [13C] isotopic species: Refined molecular structure of propyne

The ground state microwave spectrum of propyne is remeasured between 60 and 240 GHz with a molecular beam spectrometer. These high resolution measurements allows us to accurately determine the rotational constant and all the determinable quartic and sextic centrifugal distortion constants: B = 8 545 877.12 (12) kHz; D_J = 2.9423 (13) kHz; D_JK = 163.423 (20) kHz; H_J = 0.0097 (40) Hz; H_JK = 0.935 (136) Hz; and H_KJ = 5.23 (27) Hz (95% confidence limits are shown in parentheses). The spectra of the ¹³C]isotopic species are also reinvestigated between 30 and 240 GHz with a video spectrometer. With the accurate rotational constants we derive from those spectra a new r₈ structure is calculated for the CC bond lengths: $\text{r}{}_8\text{(}\text{CC}\text{) = 1.4586 (2)}\text{A}\text{?}$ and $\text{r}{}_8\text{(}\text{CC}\text{) = 1.2066 (2)}\text{A}\text{?}$.