Knowledge Bank

The $X$$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$$\Pi 3/2$ hydroxyl (OH) radical has been isolated in superfluid $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$He nanodroplets and probed with infrared laser depletion spectroscopy. From an analysis of the Stark spectrum of the \textit{Q}(3/2) transition, the $\Lambda$-doublet splittings are determined to be 0.198(3) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ and 0.369(2) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ in the ground and first excited vibrational states, respectively. These splittings are 3.6 and 7.2 times larger than their respective gas phase values. A factor of 1.6 increase in the \textit{Q}(1/2) $\Lambda$-doublet splitting was previously reported for the helium solvated $X$$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$$\Pi 1/2$ NO radical [K. von Haeften, A. Metzelthin, S. Rudolph, V. Staemmler, and M. Havenith, Phys. Rev. Lett. 95, 215301 (2005)]. A simple model is presented that predicts the observed $\Lambda$-doublet splittings in helium solvated OH and NO. The model assumes a small parity dependence of the rotor's effective moment of inertia and predicts a factor of 3.6 increase in the OH ground state (J=3/2) $\Lambda$-doubling when the \textit{B}$\mathrm{0<mrow\; data-mjx-texclass="ORD">e</mrow>}$ and \textit{B}$\mathrm{0<mrow\; data-mjx-texclass="ORD">f</mrow>}$ rotational constants differ by less than one percent.