rf spectrum and hyperfine structure of formic acid

Several transitions of rf spectrum of K-type doubling of HCOOH were observed, using a molecular beam spectrometer with 1 kHz resolution. The hyperfine structure for about ten transitions is resolved. The spin–rotation coupling constants of the two protons can be deduced. We find Maa1=−7.50±0.2 kHz, Mbb1=−7.2±4 kHz, Mccu1= 7.5±4 kHz, Maau2=−6.55±0.2 kHz, Mbbu2=8.2±4 kHz, Mccu2=−8.6±4kHz. The constants labeled 1 refer to the proton bounded to the oxygen atom.