The vibrational spectrum of the t-HOCO free radical trapped in solid argon

When formic acid is codeposited at 14 K with a beam of excited argon atoms or of F atoms produced in a discharge, t-HOCO is produced in sufficient yield for the infrared detection of most of its vibrational fundamentals. The OH stretching, COH deformation, and torsion vibrations are considerably shifted from the positions previously reported for this species in a CO matrix, consistent with the stabilization of an OC⋅⋅⋅HOCO hydrogen-bonded complex in the earlier experiments. A detailed normal coordinate analysis for t-HOCO isolated in solid argon is reported. In the F-atom reaction studies, the HOC–O⋅⋅⋅HF hydrogen-bonded complex is also stabilized, permitting the comparison of the effects of hydrogen bonding at either end of the molecule. Although there is indirect evidence for the formation of the symmetric H–CO2 species in these experiments, it is not stabilized in concentration sufficient for the identification of its infrared spectrum.