  Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest
organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them
having two rotational isomeric (rotameric) forms: trans and cis where the trans
form is energetically more stable. In this article, we study computational
energetics and anharmonic vibrational spectrum of TFA including overtone and
combination vibrations. We also studied experimental photoisomerization and
photodecomposition channels of HCOSH molecules with different wavelengths. We
suggest that TFA is a potential sulfur containing candidate molecule for
interstellar and planetary observations and discuss these in a light of
different radiation environments in space. More generally, we discuss that
infrared radiation driven photo-isomerization reactions may be a common
phenomenon in such environments and can affect the chemical reaction pathways
of organic and other interstellar molecules.
