Matrix Isolation and Ab Initio Study on the CHF 3 ···CO Complex.

Intermolecular complexes between CHF3 and CO have been studied by ab initio calculations and IR matrix isolation spectroscopy. The computations at the MP2 and CCSD(T) levels of theory indicated five minima on the potential energy surface (PES). The most energetically favorable structure is the C(CO)-H(CHF3) coordinated complex (C, symmetry) with the stabilization energy of 0.84 kcal/mol as computed at the CCSD(T) level (with ZPVE and BSSE corrections). This is the only structure experimentally found in argon and krypton matrixes, whereas the weaker non hydrogen-bonded complexes predicted by theory were not detected. The vibrational spectrum of this complex is characterized by a red-shift of the CF3 asymmetric stretching, splitting of the C-H bending mode, and blue-shifts of the C-H and C-O stretching vibrations as compared to the monomer molecules. The observed complexation-induced shifts of CHF3 and C-O fundamentals are in good agreement with the computational predictions. It was shown that both MP2 and CCSD(T) calculations generally provided a reasonable description of the vibrational properties for the weak intermolecular complexes of fluoroform.