Matrix Isolation and Ab Initio Study of Trans-Trans and Trans-Cis Dimers of Formic Acid

Six trans-trans and five trans-cis dimeric structures of formic acid (HCOOH) are revealed by ab initio Calculations. Four trans-trans and two trans-cis chillers are identified in the IR absorption spectra ill argon matrices. The trans-cis dimers are obtained by narrow-band IR excitation of the vibrational transitions of the trans-trans dimers. Two trans-trans (tt3 and tt6) and one trans-cis (tc4) dimer are characterized experimentally for the first time. The tunneling decay rates of two trans-cis dimers (tc1 and tc4) are evaluated at different temperatures. A greater lifetime of the trans-cis dimers at elevated temperatures compared to the cis-monomer suggests that the high-energy conformers call be stabilized upon hydrogen bonding.