An ab initio computational study of the properties of a weakly bound complex formed between the recently discovered argon-containing compound HArF and N-2 was undertaken at the MP2/6-311G** level of theory. The complex N-2...HArF was found to have a zero-point vibrational energy corrected binding energy of 396 cm(-1) with respect to the monomer subunits. This complex exhibits a large harmonic vibrational frequency blue shift of 195 cm(-1) for the Ar-H stretching vibration mode with a diminished infrared intensity for this mode on formation of the complex. This surprising result prompted a study to understand the source of the blue shift and the results were compared with corresponding computations for the N-2...HF complex, which has the same proton acceptor but which shows the usual red shift of the H-F stretching mode. (C) 2003 American Institute of Physics.