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Matrix isolation infrared and ab initio study of the hydrogen bonding between formic acid and water

2004; Elsevier BV; Volume: 60; Issue: 13 Linguagem: Inglês

10.1016/j.saa.2004.03.004

1873-3557

Lisa George, Wolfram Sander,

Spectroscopy and Quantum Chemical Studies

The infrared spectra of the formic acid–water complexes isolated in argon matrices are reported. Both supersonic jet expansion and a conventional effusive source followed by trapping in solid argon at 10 K are used to obtain the matrices. The experimental IR spectra are compared to the data obtained from high level ab initio (MP2) and DFT (B3LYP) calculations with 6-311++G(d,p) and aug-cc-pVTZ basis sets. The complex formation results in red shifts in the CO and OH stretching vibrations and a blue shift in the CO stretching vibration of formic acid. The OH stretching modes of water also exhibit pronounced red shifts. Both the MP2 and B3LYP calculations located three minima corresponding to cyclic HCOOH⋯H2O complexes with two hydrogen bond interactions. The binding energies are −10.3, −5.1, and −3.5 kcal mol−1, respectively, for the three complexes at the MP2/ aug-cc-pVTZ level, corrected for the basis set superposition error (BSSE) using the Boys−Bernardi counterpoise scheme. Comparison of the calculated frequencies of the three complexes with the matrix IR spectrum reveals that the lowest energy complex is formed. In addition, a complex of formic acid with two water molecules is observed.