FAR-INFRARED VRT SPECTROSCOPY OF 2 WATER TRIMER ISOTOPOMERS - VIBRATIONALLY AVERAGED STRUCTURES AND REARRANGEMENT DYNAMICS

We report the measurement of far-infrared vibration-rotation tunnellin g parallel bands of two partially deuterated water trimer isotopomers: (D2O)(2)DOH and (H2O)(2)DOH at 97.2607 cm(-1) and similar to 86 cm(-1 ), respectively. The hydrogen bond rearrangement dynamics of the two m ixed trimers can be described by the simplified molecular symmetry G(8 ), which accounts for both the flipping and bifurcation tunnelling mot ions previously established for (H2O)(3) and (D2O)(3). The observed do nor tunnelling quartet, rather than triplet, splitting indicates that the two homogeneous monomers (D2O or H2O) in each mixed trimer experie nce slightly different environments. Vibrationally averaged structures of(H2O)(3), (D2O)(3), and (D2O)(2)DOH were examined in a Monte Carlo simulation of the out-of-plane flipping motions of the free atoms. The simulation addresses both the symmetric top behaviour and the negativ e zero-point inertial defect for (H2O)(3) and (D2O)(3), which were ins ufficiently counted in all previous structure models. The average grou nd state O-O separations, which are correlated to other angular coordi nates, were determined to be 2.84 +/- 0.01 Angstrom for all three spec ies. The simulated difference in hydrogen bond nonlinearity also suppo rts the inequivalency of the two homogeneous monomers. The structural simulation shows that the unique H in (D2O)(2)DOH is free, while a tor sional analysis suggests the unique D in (H2O)(2)DOH is bound within t he cyclic ring. Both bands can be assigned to the pseudorotational tra nsitions which correlate to those found in the pure trimers.