| Abstract
| - The dimers formed by formic acid (FA) and furan are investigated by ab initio methods and matrix isolationspectroscopy. Nine complexes with binding energies between −3.91 and −0.82 kcal/mol (MP2/6-311++G(d,p) + ZPE + BSSE) are identified. Another five weaker bound complexes are localized at lower level oftheory only. The binding in the furan−FA dimers can be described in terms of OH···O, CO···H, HO···H,CH···O, OH···π, and CH···π interactions. Therefore, the furan−FA complexes are classified in two types: (1) the dimers where the OH hydrogen of formic acid interacts with the furan molecule and (2) the dimerswhere the main interactions of FA with the furan molecule are via the less acidic CH hydrogen. Duning'sand Pople's triple and double basis sets were used to study the dependence of the geometries and energies ofthe complexes from the basis set. BSSE (basis set superposition error) counterpoise corrections (CP) wereincluded during the geometry optimizations of all dimers at the MP2/6-31G(d,p) level of theory. Matrixisolation spectroscopy allowed us to record the IR spectrum of aggregates between FA and furan. By comparisonof the experimental IR spectrum with calculated IR spectra of a variety of complexes, it was possible toidentify the most stable furan−FA dimer as the major product of the aggregation.
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