Centrifugal distortion constants of pentafluorobenzene from its pure rotation spectrum

The centrifugal distortion analysis of the pure rotational spectrum of pentafluorobenzene in the frequency region of 8 to 18 GHz involvingJ upto 54 has yielded the following rotational and quartic centrifugal distortion constants: $$begin{gathered} A'' = 1480 cdot 8665 pm 0 cdot 0026 MHz, tau = - 1 cdot 751 pm 0 cdot 20 kHz, hfill B'' = 1030 cdot 0782 pm 0 cdot 0025 MHz, tau _2 = - 0 cdot 567 pm 0 cdot 066 kHz, hfill C'' = 607 cdot 5152 pm 0 cdot 0026 MHz, tau _{aaaa} = - 0 cdot 765 pm 0 cdot 068 kHz, hfill tau _{bbbb} = - 0 cdot 612 pm 0 cdot 065 kHz, hfill tau _{cccc} = - 0 cdot 547 pm 0 cdot 068 kHz. hfill end{gathered} $$