The formation of fourfold energy clusters in high J-multiplets of tria
tomic waterlike molecules is analyzed theoretically. The semiclassical
method is used to determine the rovibrational energy surfaces and the
effective adiabatic rotational Hamiltonians for the ground and excite
d bending states in these molecules. The adiabatic separation of the r
otational and the internal molecular motion used in this paper enables
significant insight into the mechanism of the strong rotation-vibrati
on interaction in rapidly rotating molecules. The critical values of t
he angular momentum J(c), at which the bifurcation responsible for the
clusterization effect occurs, are calculated. The results from the pr
evious classical studies [see I. N. Kozin and I. M. Pavlichenkov, J. C
hem. Phys. 104, 4105 (1996)] and quantum mechanical calculations [O. L
. Polyansky, P. Jensen, and J. Tennyson, J. Chem. Phys. 101, 7651 (199
4)] on the structure of the J-multiplects in the H2O molecule are revi
sed and the formation of the fourfold energy clusters can now be consi
dered well understood. (C) 1998 American Institute of Physics.