title: Near-threshold shape resonance in the photoionization of 2-butyne.
abstract: Photoelectron velocity map imaging is combined with one- and two-photon ionization to study the near threshold photoionization of the 2-butyne molecule. In this region, the photoabsorption and photoionization cross sections display a very intense broad feature that is assigned to an l = 4, π(g) shape resonance. The effect of this shape resonance on the vibrational branching ratios and photoelectron angular distributions is explored. Theoretical calculations of the photoionization cross section and photoelectron angular distributions are in good agreement with the experiments. The results for 2-butyne are compared with those of acetylene, propyne, and 1-butyne, none of which show such significant enhancements near threshold, and the differences are rationalized in terms of the symmetries and orbital angular momenta of the highest occupied orbitals and the corresponding shape resonances. Expectations for larger alkynes and alkynyl radicals are also discussed. A preliminary measurement of the ionization energy of the 2-butyne dimer is also presented.
authors.affiliation: Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Xu
authors.forename: U
authors.initials: U
authors.lastname: Jacovella
authors.forename: B
authors.initials: B
authors.lastname: Ruscic
authors.forename: S T
authors.initials: ST
authors.lastname: Pratt
authors.forename: R R
authors.initials: RR
authors.lastname: Lucchese
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D002073:Butanes / Q000737:chemistry*; D019281:Dimerization; D007477:Ions; D055668:Photochemical Processes; D017785:Photons
chemical_list: D000480:Alkynes; D002073:Butanes; D007477:Ions