Lamb-dip ro-vibrational spectroscopy of buffer-gas-cooled acetylene

Wepresent an original opto-mechanical scheme which, effectively coupling a Lambdip saturated-absorption cavity ring-down spectrometer to a buffer-gas-cooling (BGC) source, allows us to determine the absolute frequency of the acetylene (ν1 + ν3) R(1)e transition at 6561.0941 cm−1 with an overall (statistical + systematic) uncertainty as low as 1.2 kHz. By improving the previous record with buffer-gas-cooled molecules by one order of magnitude, our achievement opens the door to new kind of ultra-precise low-temperature spectroscopic studies.