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; DJ = 2.9423 (13) kHz; DJK = 163.423 (20) kHz; HJ = 0.0097 (40) Hz; HJK = 0.935 (136) Hz; and HKJ = 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: r 8( CC) = 1.4586 (2) Å and r 8 ( CC) = 1.2066 (2) Å.