High accuracy measurements on the ground state rotational spectrum of formaldehyde (H2CO) up to 2 THz

In making use of the Cologne Sideband spectrometer for Terahertz Applications (COSSTA), the pure rotational spectrum of H2CO in its ground vibrational state has been investigated in the frequency range from 1.76 to 2.01 THz with an absolute frequency accuracy ranging from 20 to 50 kHz for strong, isolated lines. Additionally, the rotational spectrum has been reinvestigated in the 0.830 to 0.957 THz region with the Cologne Terahertz spectrometer. The accurate new line frequencies were subjected to a combined fit with previously published data employing standard A- and S-reduced Watson-type Hamiltonians.