Photolysis of HCOOH monomer and dimer in solid argon: Raman characterization of in situ formed molecular complexes

Raman spectroscopy combined with the matrix isolation technique was employed to study the 193-nm photodecomposition products of formic acid in an argon matrix. The Raman-active fundamentals belonging to the CO2 + H-2 and CO + H2O photoproducts were assigned. Also, bands due to Fermi resonance between the stretching vibration (nu(1)) and the overtone of the bending mode (2 nu(2)) of CO2 were identified. Both ortho-and para-H-2 molecules were identified from their rotational lines S-0(1) and S-0(0), respectively. These bands appeared upon matrix annealing as well as after prolonged photolysis. Additionally, photolysis of FA dimers produces oxalic acid and its secondary photoproducts, CO2 + CO + H2O. All experimental studies were supported by ab initio calculations.