Microwave spectroscopic investigation and structural determination of the Ar-difluoropyridine van der Waals complexes

The ground state rotational spectra of the van der Waals dimers of 2,3-, 2,4-, 2,5-, 2,6-, and 3,5-difluoropyridine with argon were investigated in the range of 4 to 26 GHz using both Fourier transform microwave (FTMW) and chirped pulse Fourier transform microwave (cp-FTMW) spectroscopy. The spectroscopic parameters derived from fitting the observed transitions were used to estimate the van der Waals coordinates of the five weakly bound complexes and to quantitatively describe their internal dynamics using a pseudodiatomic model. The experimental structures are in fair agreement with MP2 calculations (6-311++G(2d, 2p)) and have the centers of mass of the two moieties separated by 3.486 to 3.545 Å with the Ar atom lying 2-10° from the c' axis of the ring monomer.