  The rotationally resolved spectrum of the B$^2\Pi-$X$^2\Pi$ electronic origin
band transition of $^{13}$C$_6$H is presented. The spectrum is recorded using
cavity ring-down spectroscopy in combination with supersonic plasma jets by
discharging a $^{13}$C$_2$H$_2$/He/Ar gas mixture. A detailed analysis of more
than a hundred fully-resolved transitions allows for an accurate determination
of the spectroscopic parameters for both the ground and electronically excited
state of $^{13}$C$_6$H.
