H-Bonding of Formic Acid with Its Decomposition Products: A Matrix Isolation and Computational Study of the HCOOH/CO and HCOOH/CO₂ Complexes.

The infrared spectra of formic acid/argon matrix layers deposited after flowing over a drying agent show distinct new bands when compared to matrix layers deposited without going through a drying process. The new bands are assigned as due to a formic acid/carbon monoxide H-bonded complex. Several complexes of HCOOH/CO/H2O and HCOOH/CO2 composition have been characterized in B3LYP and MP2 calculations. Comparison with experimental results indicate that the best agreement is obtained for a 1:1 HCOOH-CO hydrogen bonded complex formed between formic acid and CO originating from the decomposition process HCOOH → CO + H2O. Spectral and computational evidence is presented for the formation of HCOOH/CO2 complexes as a result of the HCOOH → CO2 + H2 decomposition path.