Rotational spectra, structures, and tunneling dynamics of Ar-(H{sub 2}O){sub 2} and Ar-(D{sub 2}O){sub 2}

The authors report the rotational spectra of the weakly bound Ar-(H{sub 2}O){sub 2} and Ar-(D{sub 2}O){sub 2} clusters, studied with a Balle/Flygare pulsed beam FTMW spectrometer. Preliminary results indicate that all of the tunneling paths observed for the (H{sub 2}O){sub 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{sub 1} state transitions could be fitted to a semi-rigid rotor using the Watson Hamiltonian. The rotational constants thereby obtained are listed below (MHz): From the observed splitting of the b dipole transitions for Ar-(D{sub 2}O){sub 2} the donor-acceptor tunneling frequency is found to be 106.3 MHz compared to 1172.5 MHz for the (D{sub 2}O){sub 2} dimer.