Text this: Laser spectroscopy of the $$^2{\mathrm{S}}_{1/2}{-}^2{\mathrm{P}}_{{1}/2}$$ 2 S 1 / 2 - 2 P 1 / 2 , $$^2{\mathrm{P}}_{3/2}$$ 2 P 3 / 2 transitions in stored and cooled relativistic C $$^{3+}$$ 3 + ions