title: Mid- and Far-IR Spectra of H5(+) and D5(+) Compared to the Predictions of Anharmonic Theory.
abstract: H5(+) is the smallest proton-bound dimer. As such, its potential energy surface and spectroscopy are highly complex, with extreme anharmonicity and vibrational state mixing; this system provides an important benchmark for modern theoretical methods. Unfortunately, previous measurements covered only the higher-frequency region of the infrared spectrum. Here, spectra for H5(+) and D5(+) are extended to the mid- and far-IR, where the fundamental of the proton stretch and its combinations with other low-frequency vibrations are expected. Ions in a supersonic molecular beam are mass-selected and studied with multiple-photon dissociation spectroscopy using the FELIX free electron laser. A transition at 379 cm(-1) is assigned tentatively to the fundamental of the proton stretch of H5(+), and bands throughout the 300-2200 cm(-1) region are assigned to combinations of this mode with bending and torsional vibrations. Coupled vibrational calculations, using ab initio potential and dipole moment surfaces, account for the highly anharmonic nature of these complexes.
authors: †Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
authors: Timothy C
authors: TC
authors: Cheng
authors: ‡Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors: Ling
authors: L
authors: Jiang
authors: ‡Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors: Knut R
authors: KR
authors: Asmis
authors: §Department of Chemistry, Emory University, Atlanta, Georgia 30332, United States.
authors: Yimin
authors: Y
authors: Wang
authors: §Department of Chemistry, Emory University, Atlanta, Georgia 30332, United States.
authors: Joel M
authors: JM
authors: Bowman
authors: †Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
authors: Allen M
authors: AM
authors: Ricks
authors: †Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
authors: Michael A
authors: MA
authors: Duncan
keywords: infrared spectroscopy; interstellar ions; ion spectroscopy; mass spectrometry; photodissociation; shared proton