Bifurcation tunneling dynamics in the water trimer

Abstract

Recent far-infrared vibration–rotation–tunneling experiments have probed intricate details of the hydrogen bond tunneling dynamics in the water trimer through excitation of intermolecular vibrational transitions to states of sequentially increasing energy. The experimentally observed bifurcation splitting in the water trimer evolves from an equally spaced quartet in the vibrational ground state to a slightly asymmetrical quartet for intermediate torsional vibrational states lying below 100 cm−1. Even more asymmetric bifurcation splittings have been observed in the out-of-plane librational band of (H2O)3 near 520 cm−1. These patterns may be caused by the bifurcation and flip rearrangements becoming comparable in magnitude. Alternatively, some of the data can be fitted by introducing tunneling matrix elements corresponding to multiple elementary rearrangements. Analysis of the observed bifurcation tunneling splittings of (D2O)3 confirms that the dominant bifurcation pathway includes the torsional flipping motion of the neighboring water molecules. Quantification of the bifurcation matrix elements of (D2O)3 furthermore reveals that these vary within each torsional manifold.