Experimental and computational study of crystalline formic acid composed of the higher-energy conformer |
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Authors: | Hakala Mikko Marushkevich Kseniya Khriachtchev Leonid Hämäläinen Keijo Räsänen Markku |
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Affiliation: | Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014, Finland. mikko.o.hakala@helsinki.fi |
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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. |
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