On the binding of electrons to nitromethane: Dipole and valence bound anions

Abstract

Articles you may be interested inDecay dynamics of nascent acetonitrile and nitromethane dipole-bound anions produced by intracluster chargetransfer J.Low-energy photoelectron imaging spectroscopy of nitromethane anions: Electron affinity, vibrational features, anisotropies, and the dipole-bound state J. Chem. Phys. 130, 074307 (2009); 10.1063/1.3076892 Dipole bound and valence state coupling in argon-solvated nitromethane anionsConventional ͑valence͒ and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe(n f ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*Ϸ13Ϯ1 which is characteristic of the formation of dipole-bound anions ͓͑CH 3 NO 2 ͒ϭ3.46 D͔. However, the breadth ͑⌬nϷ5, FWHM͒ of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ''doorway'' dipole anion state. Studies of the electric field detachment of CH 3 NO 2 Ϫ formed through the Xe(n f ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 12Ϯ3 meV. Photodetachment of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ͑valence bound͒ anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ͑vЈϭ0, vЉϭ0͒ transitions in the photoelectron spectra of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ yields adiabatic electron affinities of 0.26Ϯ0.08 and 0.24Ϯ0.08 eV, respectively.

Low-energy photoelectron imaging spectroscopy of nitromethane anions: Electron affinity, vibrational features, anisotropies, and the dipole-bound state

“…1͒. The vibrational spacing found in the PE spectrum reported by Compton et al 1 is consistent with both the NO 2 bending mode and the NO 2 wagging mode of the neutral molecule. In this paper, we present low-energy PE imaging results for the CH 3 NO 2 − anion, revealing much more detail.…”

“…The uncertainty in the AEA determination of Compton et al 1 was due to the shape of the PE spectrum, which is dominated by an extended vibrational progression, peaking at a vertical detachment energy of about 0.9 eV. The AEA determination was done by using the last discernible peaks at the low binding energy side of the spectrum.…”

“…1͔͒ to bind an excess electron not only in a valencelike state but also in a state that is more accurately described as a dipole-bound state. 1,2,6,8 The binding energy of the valencelike state is comparatively small, 1 below several of the fundamental vibrational transitions in the anion, making it an ideal model system for the investigation of the interaction of vibrational excitation and electron emission. 3,5 Interestingly, the signature of the dipolebound state of CH 3 NO 2 − has not been found in photoelectron ͑PE͒ spectroscopy so far.…”

“…3,5 Interestingly, the signature of the dipolebound state of CH 3 NO 2 − has not been found in photoelectron ͑PE͒ spectroscopy so far. 1 The adiabatic electron affinity ͑AEA͒ of CH 3 NO 2 has been determined to be ͑260Ϯ 80͒ meV by Compton et al 1 by using the last discernible peaks on a very extended and congested vibrational progression as bracketing features. The error bars were intended to cover the range of possible origin assignments of a vibrational progression with ͑80Ϯ 9͒ meV ͑645 cm −1 ͒ spacing, yielding possible EAs of about 180, 260, or 340 meV.…”

“…The interaction of nitromethane ͑CH 3 NO 2 ͒ with lowenergy electrons and the properties of the CH 3 NO 2 − anion have been the subject of many studies, both experimentally [1][2][3][4][5] and theoretically. 6,7 One very remarkable feature of CH 3 NO 2 is that it has a sufficiently high dipole moment ͓ = 3.46 D ͑Ref.…”