Knowledge Bank

Microwave and fur-infrared spectra of the $H3N-HOH$ dimer were recorded from 36 to 86 GHz and from 520 to 800 GHz in a planar supersonic jet. The microwave data extended the previous $K=0$ manifold measurements of Herbine and Dyke $\mathrm{<mrow\; data-mjx-texclass="ORD">[1]</mrow>}$ to higher frequency and also provided a complimentary set of ground state transitions in the $K=1$ manifold. The far-infrared data contained 2 sets of 3 bands, one set shifted from the other by an approximately constant 113 MHz splitting. The bands were assigned to $lm‘,K‘>\leftarrow lm"",K"">$ transitions $10,\pm 1>\leftarrow 10,0>,l\pm 1,0>\leftarrow l\pm 1,\pm 1>$, and $l\pm 1,\pm 2>\leftarrow l\pm 1,\pm 1>$, where m is the $NH3$ internal rotation quantum number. The 113 MHz splitting arises from the in-plane water tunnelling motion. From these data were obtained rotational constants and structural parameters. Non-linear least-squares fits to an internal rotor Hamiltonian also provided a limit on the height of the barrier to rotation for the $NH3$ monomer. [FIGURE].