Knowledge Bank

We have observed the $k=3$ splittings in the $\nu 2$ state of $PH3$ using radiofrequency-infrared double-resonance. The microwave sidebands on $CO2$ laser lines were used as the infrared radiation source. The observed splittings together with those earlier reported by Carlotti $etal.1$ do not agree with the simple $(J+3)\ast (J-3)\ast$ formula, contrary to the similar splittings in the ground state reported by Klemperer and his $colleagues.2$ A more pronounced anomaly has been reported for the $k=6$ and $k=9$ doublings in the $3\nu 2$ and $4\nu 2$ states of $PH3.\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ We explain the anomaly for the $\nu 2$ state by taking into account the Coriolis interactions between $\nu 2k=3$ levels and various $\nu 4k-\ell |=3n$ levels. The results explain this anomaly well. We have obtained the following splitting parameters for various doublings: \begin{eqnarray*}\Delta_{(\nu_{2},k=3,\ell=0)}& = & 357(40)Hz\ \Delta_{(\nu_{4},k=2,\ell=-1)} & = & 594(70)kHz\end{eqnarray*}