title: Experimental and computational study of crystalline formic acid composed of the higher-energy conformer.
abstract: Crystalline formic acid (FA) is studied experimentally and by first-principles simulations in order to identify a bulk solid structure composed of the higher-energy (cis) conformer. In the experiments, deuterated FA (HCOOD) was deposited in a Ne matrix and transformed to the cis conformer by vibrational excitation of the ground state (trans) form. Evaporation of the Ne host above 13 K prepared FA in a bulk solid state mainly composed of cis-FA. Infrared absorption spectroscopy at 4.3 K shows that the obtained solid differs from that composed of trans-FA molecules and that the state persists up to the annealing temperature of at least 110 K. The first-principles simulations reveal various energetically stable periodic chain structures containing cis-FA conformers. These chain structures contain either purely cis or both cis and trans forms. The vibrational frequencies of the calculated structures were compared to the experiment and a tentative assignment is given for a novel solid composed of cis-FA.
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014, Finland. mikko.o.hakala@helsinki.fi
authors.forename: Mikko
authors.initials: M
authors.lastname: Hakala
authors.forename: Kseniya
authors.initials: K
authors.lastname: Marushkevich
authors.forename: Leonid
authors.initials: L
authors.lastname: Khriachtchev
authors.forename: Keijo
authors.initials: K
authors.lastname: Hämäläinen
authors.forename: Markku
authors.initials: M
authors.lastname: Räsänen
mesh_terms: D003198:Computer Simulation; D005561:Formates / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D005561:Formates; C030544:formic acid