The far infrared spectrum of trans-formic acid: An extension up to 175 cm−1

The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009 cm−1) and long path length (72 m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62-300 cm−1, showing transitions from the trans-isomer.Ground state rotational transitions with Ka up to 30, were identified up to 175 cm−1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the Ir representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P.

► The far infrared spectrum of HCOOH was recorded at 0.0009 cm−1 resolution. ► Spectrum was recorded at the far-infrared beamline, Canadian Light Source. ► Rotational transitions of the trans-isomer were identified in the 62-175 cm−1 range. ► 3321 Transitions were assigned and fitted together with 4149 literature data. ► All 8 order parameters L and some 10th parameters P were determined.