The nearest neighbor level spacing and Delta(3) distributions indicate that the vibrational spectrum of CH2((a(1)) over tildeA(1)) is largely chaotic. Nevertheless, regular localized states coexist with the chaotic ones and they are related to overtone states of the principal vibrational modes. Periodic orbits accompanied by a stability analysis identify these states and explain their topologies and localization in configuration space. Particularly, the bending vibrational mode which is associated to the isomerization pathway which connects two equivalent minima separated by a linear symmetric saddle point, shows the dip in energy level spacings at the region of the saddle point. The corresponding wave functions are identified by periodic orbits emanated from saddle-node bifurcations below and above the barrier of isomerization. (C) 2004 Elsevier B.V. All rights reserved.