(a) Potential energy (V) is plotted as a function of the I to CN center of mass (COM) distance, R(I–CNCOM), in the linear (θ = 0°) geometry. The red circle highlights the conical intersection region between the 1Π1 and states. (b) V is plotted as a function of the angle between the R vector and CN axis, θ, for R(I–CNCOM) = 3.2 Å. In both panels, the ground-state wave function for the anion, Ψ(R, θ), is shown (dotted trace), and the grey box represents the Franck-Condon region. Also, the electronic ground state of the anion has been shifted by −0.4 eV to have better agreement with the measured transitions to the 3Π2 and 3Π1 states.
Composite photoelectron spectrum of ICN−. The broad peak at ∼ 3.2 eV corresponds to high-lying vibrational levels of the ground electronic state, 1Σ+. The ground-state origin lies more than 1 eV lower in binding energy and is not observed. The next three sharp features are the first three excited states of ICN (3Π2, 3Π1, and ). The broad asymmetric peak at ∼ 5.25 eV consists of transitions to the conical intersection (CI) region (1Π1 and ) and has some overlap with the dissociative electronic state. For comparison, the inset shows the photoelectron spectrum of IBr−.25
Composite photoelectron spectra of ICN− (black) and ICN−·Ar (red) showing transitions to the 3Π2 and 3Π1 states. Solvation by Ar results in a 30 meV shift to higher binding energy and a sharpening of the peaks for both electronic states. The shoulder on the higher binding energy side of the 3Π2 feature becomes more prominent in the ICN−·Ar spectrum and lies ∼20 meV above the main peak, which is consistent with the calculated I–CN stretch frequency of the 3Π2 state.
Thermochemical cycles used to determine EA(ICN) and D0( 2Σ+ I–CN−). The two thermochemical cycles involve either EA(CN) (Ref. 45) or D0( 1Σ+ I–CN) (Ref. 21) values from previous measurements, along with the measured VDE(3Π1 ICN) and calculated D0(3Π1 I–CN) values from this work.
Calculated spectroscopic properties of ICN − ( 2Σ+) and ICN ( 1Σ+, 3Π2, and 3Π1) from this work, along with previously measured values for ICN ( 1Σ+).
Summary of experimentally determined values: dissociation energy (D0), adiabatic electron affinity (EA), and term energies (T0).
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