SI-referenced HCOOH spectroscopy at the sub-ppt level

We report on a new determination of the ν6, J′=21,Ka′=2,Kc′=20←J″=21,Ka″=3,Kc″=19 HCOOH rovibrational line centroid at 9.17μm with 7.1 Hz statistical uncertainty (2×10−13), a 100-fold improvement with respect to previous measurements. It involves a Fabry-Perot saturated-absorption spectrometer referenced to the Système International through a frequency comb. We elaborate a detailed line shape model that allows retrieving the transit-time width and accurate determination of the pressure and power shifts and broadening. We also give the nitrogen and air pressure shift and broadening coefficients.