Theoretical study of the complex between formic acid and argon

Quantum chemical calculations on the structure, energetics and vibrational spectra of the van der Waals complex between formic acid (FA) and argon are presented. Both conformers of FA were considered in the calculations and for both forms a planar structure with an almost linear interaction path between argon and the OH-tail of the molecular is the most stable complex configuration. The computed interaction energies at the CCSD(T)/6-311++G(2d,2p),6-311 + G(3df)[Ar]//MP2(full)/6-311++G(2d,2p),6-311 + G(3df)[Ar] level of theory are - 1.50 and - 2.01 kJ mol(-1) for the trans-(HCOOHAr)-Ar-... and cis-(HCOOHAr)-Ar-... complexes, respectively. Calculations reveal three other local minima for both complexed conformers of which a local minimum structure featuring interaction between argon and the carbonyl group of the molecule is characterised for the first time. The intra- and intermolecular stretching modes were found to be most affected by BSSE-correction applied during the optimisation of the complex equilibrium structure. The intramolecular stretching modes were noted to decrease and the intermolecular stretching modes to increase compared to calculations without the BSSE-correction. (C) 2004 Published by Elsevier B.V.