Knowledge Bank

We report the observation of the lowest $\Pi$ bending vibration for both $ArH79Br$ and $ArH81Br$ in a continuously operated planar free jet expansion. The spectra were recorded with a high resolution tunable far infrared spectrometer which utilizes a metal-insulator-metal point contact diode to generate the difference frequency between two $CO2$ laser $frequencies(1)$. The results are compared with recent calculations by $Hutson(2)$ which employ a potential energy surface optimized to reproduce ground state microwave data for this species, and the agreement is found to be excellent. The data indicate strong coupling between the radial and angular degrees of freedom at angles sampled by the II state. Comparison with related systems will be made.