title: Structure, Anharmonic Vibrational Frequencies, and Intensities of NNHNN(+).
abstract: A semiglobal potential energy surface (PES) and quartic force field (QFF) based on fitting high-level electronic structure energies are presented to describe the structures and spectroscopic properties of NNHNN(+). The equilibrium structure of NNHNN(+) is linear with the proton equidistant between the two nitrogen groups and thus of D(∞h) symmetry. Vibrational second-order perturbation theory (VPT2) calculations based on the QFF fails to describe the proton "rattle" motion, i.e., the antisymmetric proton stretch, due to the very flat nature of PES around the global minimum but performs properly for other modes with sharper potential wells. Vibrational self-consistent field/virtual state configuration interaction (VSCF/VCI) calculations using a version of MULTIMODE without angular momentum terms successfully describe this motion and predict the fundamental to be at 759 cm(-1). This is in good agreement with the value of 746 cm(-1) from a fixed-node diffusion Monte Carlo calculation and the experimental Ar-tagged result of 743 cm(-1). Other VSCF/VCI energies are in good agreement with other experimentally reported ones. Both double-harmonic intensity and rigorous MULTIMODE intensity calculations show the proton-transfer fundamental has strong intensity.
authors.affiliation: Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States.
authors.forename: Qi
authors.initials: Q
authors.lastname: Yu
authors.affiliation: Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States.
authors.forename: Joel M
authors.initials: JM
authors.lastname: Bowman
authors.affiliation: Department of Chemistry, Georgia Southern University , Statesboro, Georgia 30460, United States.
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Fortenberry
authors.affiliation: Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States.
authors.forename: John S
authors.initials: JS
authors.lastname: Mancini
authors.affiliation: NASA Ames Research Center , Moffett Field, California 94035-1000, United States.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: T Daniel
authors.initials: TD
authors.lastname: Crawford
authors.affiliation: Department of Chemistry, Harvard University , Cambridge, Massachusetts 02138, United States.
authors.forename: William
authors.initials: W
authors.lastname: Klemperer
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Francisco