HCOOH high resolution spectroscopy in the 9.18$\mu$m region

We report on higly accurate absolute frequency measurement against a femtosecond frequency comb of 6 saturated absorption lines of formic acid (HCOOH) with an accuracy of 1 kHz. We also report the frequency measurement of 17 other lines with an accuracy of 2 kHz. Those lines are in quasi coincidence with the 9R(36) to 9R(42) CO${}_2$ laser emission lines and are probed either by a CO${}_2$ or a widely tunable quantum cascade laser phase locked to a master CO${}_2$ laser. The relative stability of two HCOOH stabilized lasers is characterized by a relative Allan deviation of 4.5 10${}^{-12}$ ${\tau }^{-1\mathrm{/}2}$. They give suitable frequency references for H${}_2^{+}$ Doppler free two-photon spectroscopy.