THE INFRARED AND MICROWAVE SPECTROSCOPY OF THE ARGON-PROPYNE DIMER

Microwave and infrared measurements are reported for the van der Waals complex Ar-CH3CCH and its isotopomers. The structure is T shaped with equilibrium center-of-mass separation of 3.73 angstrom and an angle of 82-degrees between the molecule symmetry axis and the van der Waals bond. The infrared and microwave spectra are complex due to the effects of a slightly hindered internal rotor. Analysis of the spectral data shows that the dipole moment is almost parallel to the dimer b axis. A modified vibration/rotation Hamiltonian that includes an internal rotor potential is used to show that the barrier to internal rotation is near 10.8 cm-1.