Knowledge Bank

Molecular-beam electric-resonance, electric-resonance optothermal, pulsed-nozzle Fourier-transform, and submillimeter absorption spectroscopy have been used to measure the microwave and submillimeter spectra of Ar-$NH3$ for the two $\sum$ and two $\Pi$ states correlating asymptotically with $Ar+NH3$ ($j=1,|k|=1$). For a number of the transitions $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ quadrupole hyperfine structure has been resolved and relative intensity measurements have been made. The two $\sum$ states are found to lie below the two $\Pi$ states and are separated by approximately the inversion splitting of free $NH3$. For the $\Pi$ states the $NH3$ inversion tunneling is nearly quenched, being only weakly allowed through Coriolis interactions with the nearby $\sum$ states. The strong Coriolis interactions also give rise to a ``pure-inversion” K=0 type Q-branch with a band origin at - 22.7 GHz. All the above are interpreted using a model internal-rotation inversion Hamiltonian, leading to detailed information about the anisotropy of the intermolecular potential.