ROTATIONAL SPECTRA, STRUCTURES, AND TUNNELING DYNAMICS OF $Ar-(H_{2}O)_{2}$ AND $Ar-(D_{2}O)_{2}$

Abstract

We report the rotational spectra of the weakly bound $Ar-(H_{2}O)_{2}$ and $Ar-(D_{2}O)_{2}$ clusters, studied with a Balle/Flygare pulsed beam FTMW spectrometer. Preliminary results indicate that all of the tunneling paths observed for the $(H_{2}O)_{2}$ dimer are apparent in the trimer even though the presence of Ar does affect the tunneling frequency and observed splittings. Both the a and b dipole transitions have been observed. The $E_{1}$ $state^{1}$ transitions could be fitted to a semi-rigid rotor using the Watson Hamiltonian. The rotational constants thereby obtained are listed below (MHz): $\begin{array}{cccc}&A&B&C\\Ar-(H_{2}O)_{0}&6253.057(2)&2428.431(1)&1739.564(1)\\Ar-(D_{2}O)_{2}&5517.465(3)&2280.931(1)&1614.026(2)\end{array}$ From the observed splitting of the b dipole transitions for $Ar-(D_{2}O)_{2}$ the donor-acceptor tunneling frequency is found to be 106.3 MHz compared to 1172.5 MHz for the $(D_{2}O)_{2}$ dimer.