Spectroscopic study of cis-to-trans tunneling reaction of HCOOD in rare gas matrices

The higher energy conformer (cis) of HCOOD is prepared by vibrational excitation of the trans form. The cis conformer decays back to the conformational ground state (trans) via tunneling of deuterium. The tunneling process in HCOOD in rare gas matrices is extremely slow (in scale of weeks). We present new measurements of the tunneling rate constants, which characterize the efficiency of the cis-to-trans conversion process in Ne, Ar, Kr, and Xe matrices. The tunneling rates of HCOOD follow the trend k(Xe)approximate to k(Kr)>k(Ar)approximate to k(Ne), which is anomalous with respect to the reaction barrier of the solvated molecule. We propose a semiempirical energetic scheme of solid state solvation, which is consistent with all experimental observation. The temperature dependence of the tunneling constants rates of HCOOD is very weak compared to HCOOH in all matrices. The fundamental vibrational frequencies of the cis and trans conformers of HCOOD in various matrices are reported.