Tunneling dynamics in water tetramer and pentamer

We present a theoretical study of the structures, energetics and tunneling dynamics of the cyclic water tetramer and pentamer, both of which have recently been observed experimentally. The very good agreement between vibrationally averaged rotational constants from diffusion quantum Monte Carte calculations and experimental values confirms that the structures are cyclic. We calculate a splitting for a tunneling motion that is a likely cause for doublets observed experimentally in the far infrared spectrum of (D2O)(4). Predictions of tunneling splittings yet to be observed in the water pentamer are made. (C) 1996 American lnstitute of Physics.