FTIR and millimeter wave investigation of the 71 and 91 states of formic acid HCOOH and H13COOH

High resolution FTIR spectra of the two overlapping bands ν7 and ν9 of the 13C species of formic acid have been measured and analyzed. Rotational transitions in the millimeter wave region were measured and included in the analysis. As in the parent species, there is a strong Coriolis interaction between the 71 and 91 states. The corresponding IR bands of the parent species have been remeasured and new MMW transitions recorded. The analysis of the spectra for the two species provides an opportunity to consider a reduction of the Hamiltonian employed for the analysis of this type of interacting system of states. Parameters with low correlations could be obtained. Several interstellar features coincide with transitions predicted from these parameters.