Infrared spectra of 2-thiocytosine and 5-fluoro-2-thiocytosine; experimental and ab initio studies

IR absorption spectra of 2-thiocytosine and 5-fluoro-2-thiocytosine isolated in low-temperature, inert gas matrices and in thin polycrystalline films are reported. The spectra of amino-thiol tautomeric forms of the compounds were studied for matrix isolated species, whereas the spectra of amino-thione tautomeric forms were observed for polycrystalline films. The experimental spectra were compared with the spectra predicted with the ab initio SCF/6-31G** method. The observed IR absorption bands in the spectra of monomers (amino-thiol forms) were assigned to the theoretically calculated normal modes.