Rotational spectra and structures of the van der Waals dimers of argon with 2-fluoropyridine and 3-fluoropyridine.

The ground state rotational spectra of the van der Waals dimers of 2-fluoropyridine and 3-fluoropyridine with argon have been investigated using both Fourier transform microwave (FTMW) and chirped-pulse Fourier transform microwave (cp-FTMW) spectroscopies between 4 and 26 GHz. The rotational constants and 14N nuclear quadrupole coupling constants derived from fitting the observed transitions were used to estimate the van der Waals coordinates of the two complexes. These are in good agreement with the lowest energy structures determined via MP2 calculations (6-311++G(2d, 2p)) and have the Ar atom sitting above the plane of the aromatic ring. The center of mass separation of the two moieties in the dimers is between 3.5 and 3.6 A and the Ar atom lies 5–11° off the monomer c′-axis toward the nitrogen atom of the pyridine backbone.