Blueshift and intramolecular tunneling of NH3 umbrella mode in 4He n clusters.
We present diffusion Monte Carlo calculations of the ground and first excited vibrational states of NH(3) (4)He(n) for n< or =40. We use the potential energy surface developed by one of us [M. P. Hodges and R. J. Wheatley, J. Chem. Phys. 114, 8836 (2001)], which includes the umbrella mode coordinate of NH(3). Using quantum Monte Carlo calculations of excited states, we show that this potential is able to reproduce qualitatively the experimentally observed effects of the helium environment, namely, a blueshift of the umbrella mode frequency and a reduction of the tunneling splittings in ground and first excited vibrational states of the molecule. These basic features are found to result regardless of whether dynamical approximations or exact calculations are employed.
Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California-Berkeley, CA 94720-1460, USA. alexandra.viel@univ-rennes1.fr
Alexandra
A
Viel
K Birgitta
KB
Whaley
Richard J
RJ
Wheatley