Vacuum ultra-violet spectra of formic and acetic acids
The absorption spectra of gaseous formic acid and its deuterated analogues have been photographed between 1100 and 1800 Å. The previously known Rydberg series has been extended and other series identified so that the ionization energy can be given as 11.329 ± 0.002 eV. All Rydberg transitions show progressions with quanta about 1500 cm–1 assigned to ν′3, and although the CO bond length is probably increased there is no evidence for non-planarity in Rydberg states as there is for the (n, π*) state.
The absorption spectrum of acetic acid has also been studied between 1100 and 2600 Å but, because of diffuseness, assignments can only be given by comparison with formic acid.
The spectrum of trifluoroacetic acid has been studied between 1700 and 2600 Å and the discrete bands previously identified with this acid have been shown to be due to CS2 impurity.