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Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C _2 H _2 between 7167 and 7217 cm ^−1 , using a frequency-comb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers. We measured the absolute center frequency of sixteen lines belonging to the 2 ${\nu }_{3}+{\nu }_{5}^{1}$ band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a ‘V’-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J -values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 3 and 13 kHz. This is over three orders of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μ m. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene.