Molecules MH3 (M = Cr, Mo, W) are pyramidal: CCSD(T) ab initio study of structure and vibrational dynamics

Ab initio calculations were carried out on chromium, molybdenum, and tungst en trihydrides. The equilibrium parameters of the ground states, vibrationa l frequencies, IR intensities and the inversion barriers of the molecules w ere calculated at the CCSD(T) level with large basis sets. The relative ene rgies to the excited states were evaluated by the EOM-CCSD method. All mole cules were found to have pyramidal (C-3 nu) equilibrium structures. The cal culated inversion barriers of CrH3, MoH3, and WH3 are 1353, 1086, and 472 c m(-1) respectively. The vibrational levels corresponding to the totally sym metric H-M-H bending mode were predicted using the discrete variable repres entation approach. The tunneling splitting and rates were also evaluated wi thin the Wentzel-Kramers-Brillouin approximation. The available experimenta l data are discussed in light of results from the ab initio calculations.