Signatures of quantum phase transitions (QPTs) and excited state quantum phase transitions (ESQPTs) in the bending motion of eight XYZ triatomic molecules (HCN, HNC, NiCN; CaOH, CaOD, MgOH, MgOD and OCS), the large-amplitude bending degree of freedom of a tetratomic molecule (HNCS), and four symmetric XY2 triatomic molecules (H2O, D2O, H 2S, H2Se) are investigated in an attempt to understand their dependence on the composition of the molecular species. It is shown that the isomerizing HCN/HNC system leads to quasi-linearity, that the water molecule H2O displays a dramatic effect at Ex ? 11,000 cm -1 with clear indication of an ESQPT at about vibrational quantum number ?b = 8, and that the heavy water molecule D2O is expected to undergo an ESQPT at ?b = 10. © 2013 Elsevier B.V. All rights reserved.