The microwave spectra and structures of Ar-AgX (X=F,Cl,Br)

The rotational spectra of the complexes Ar-AgF, Ar-AgCl, and Ar-AgBr have b een observed in the frequency range 6-20 GHz using a pulsed jet cavity Four ier transform microwave spectrometer. All the complexes are linear and rath er rigid in the ground vibrational state, with the Ar-Ag stretching frequen cy estimated as similar to 140 cm(-1). Isotopic data have been used to calc ulate an r(0) structure for Ar-AgF, while for Ar-AgCl and Ar-AgBr partial s ubstitution structures have also been obtained. To reduce zero-point vibrat ional effects a double substitution method (r(d)) was employed to calculate the structures of Ar-AgCl and Ar-AgBr. The Ar-Ag bond distance has been fo und to be rather short and to range from 2.56 Angstrom in Ar-AgF to 2.64 An gstrom in Ar-AgBr. Ab initio MP2 and density functional theory calculations for Ar-AgF and Ar-AgCl model the geometries and stretching frequency well, and predict an Ar-Ag bond energy in Ar-AgF of similar to 23 kJ mol(-1). Th ese results indicate that the Ar-AgX complexes are more strongly bound than typical van der Waals complexes. Analysis of the halogen nuclear quadrupol e coupling constants was unable to confirm whether extensive electron rearr angement occurs upon formation of the complexes. (C) 2000 American Institut e of Physics. [S0021-9606(00)02202-9].