title: Isotope effect in normal-to-local transition of acetylene bending modes.
abstract: The normal-to-local transition for the bending modes of acetylene is considered a prelude to its isomerization to vinylidene. Here, such a transition in fully deuterated acetylene is investigated using a full-dimensional quantum model. It is found that the local benders emerge at much lower energies and bending quantum numbers than in the hydrogen isotopomer HCCH. This is accompanied by a transition to a second kind of bending mode called counter-rotator, again at lower energies and quantum numbers than in HCCH. These transitions are also investigated using bifurcation analysis of two empirical spectroscopic fitting Hamiltonians for pure bending modes, which helps to understand the origin of the transitions semiclassically as branchings or bifurcations out of the trans- and cis-normal bend modes when the latter become dynamically unstable. The results of the quantum model and the empirical bifurcation analysis are in very good agreement.
authors.affiliation: Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Jianyi
authors.initials: J
authors.lastname: Ma
authors.forename: Dingguo
authors.initials: D
authors.lastname: Xu
authors.forename: Hua
authors.initials: H
authors.lastname: Guo
authors.forename: Vivian
authors.initials: V
authors.lastname: Tyng
authors.forename: Michael E
authors.initials: ME
authors.lastname: Kellman
mesh_terms: D000114:Acetylene / Q000737:chemistry*; D001665:Binding Sites; D003903:Deuterium / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D003903:Deuterium; D000114:Acetylene