Matrix-isolation and ab initio study of the complex between formic acid and xenon

We report on the identification of the complexes of formic acid (FA) and Xe in an argon matrix. The geometries, interaction energies, reaction barriers, and vibrational spectra of the FA⋯Xe complexes are calculated at the MP2 level of theory. The calculations reveal four structures for the trans-FA⋯Xe complex and four structures for the cis-FA⋯Xe complex. In the experiments, two structures of the trans-FA⋯Xe complex are observed after deposition of FA/Xe/Ar matrices, with and without OH⋯Xe interaction (H-bonded and non-H-bonded structures). The cis-FA⋯Xe complex was synthesized by vibrational excitation of the non-H-bonded trans-FA⋯Xe complex. The non-H-bonded and H-bonded structures of the cis-FA⋯Xe complex are observed after the excitation. The decay of the H-bonded and non-H-bonded cis-FA⋯Xe complexes in an argon matrix is, respectively, substantially slower and faster compared to the cis-FA monomer. This observation is explained by the different tunnelling barriers for these species.

► Four trans-FA⋯Xe and four cis-FA⋯Xe complexes are predicted theoretically.
► Two trans-FA⋯Xe and two cis-FA⋯Xe complexes are found experimentally.
► Stabilization of cis-FA is observed in the H-bonded complex.
► Destabilization of cis-FA is observed in the non-H-bonded complex.