Photoelectron spectra of the , , and transitions of , , , and CH3I (top to bottom panels) recorded by Karlsson and co-workers.7 Adapted from Ref. 7.
High-resolution PFI-ZEKE photoelectron spectrum of the transition of in the region of the vibronic ground state of (top panel), and the corresponding calculation shown as stick spectrum (bottom panel) and after convolution with a Gaussian line profile with a FWHM of 0.8 cm−1 representing the instrumental linewidth (middle panel). The experimental spectrum has not been corrected for the field-induced shift (≈−0.84 cm−1) of the ionization energies. The assignment bars label the most intense ΔN = 0 transitions of the dominant (ΔK = K + − K = +1) and the minor (ΔK = K + − K = −2) contributions to the vibronic wavefunction induced by the Jahn-Teller effect.
Schematic diagram of the two-state excitonic model, where either methane (left-hand side) or the halogen atom (right-hand side) is ionized and becomes the electron donor. The gray horizontal lines mark the eigenvalues of the excitonic coupling matrix H exc obtained using Eq. (6) which correspond to the lowest and a higher lying 2E electronic state in the methyl-halide cation. The ionization energies E I are indicated by vertical arrows.
Energy differences between calculated and experimental ionization energies of the methyl-halide cations as a function of the interaction potential V exc. The ΔE I of the lower (E I) and upper 2E electronic states are decreasing and increasing in energy for an increasing interaction potential V exc, respectively. The states from to are shown as black to gray lines of decreasing blackness, and is shown as dotted line because of the large uncertainty in the experimental determination of this ionization energy. The dashed vertical line (V exc = 17 500 cm−1) marks the strength of the interaction potential where ΔE I and are minimized.
Schematic energy diagram presenting the ionization energies E I of methane and the halogen atoms (black vertical arrows), which are coupled by the excitonic matrix H exc (Eq. (6)) by an interaction potential V exc = 17 500 cm−1. The resulting eigenvalues, which represent the lowest and a higher lying 2E state in the methyl-halide cations, are marked by gray horizontal lines, and the corresponding experimental ionization energies66 are marked by black horizontal lines. The energy of the upper 2E electronic state of derived from photoelectron spectra7,66 is marked by a dotted line, because there is a large experimental uncertainty to its energy, see text for details.
Schematic energy diagram presenting the ionization energies E I of methane and of atomic oxygen and sulphur (black vertical arrows), which are coupled in the excitonic matrix H exc (Eq. (6)) by an interaction potential V exc = 17 500 cm−1. The resulting eigenvalues are marked by gray horizontal lines, and the corresponding experimental ionization energies67,68 are marked by black horizontal lines.
Schematic energy diagram presenting the electron affinities EA of methane62 and of atomic oxygen and sulphur69 (black vertical arrows), which are coupled in the excitonic matrix (Eq. (10)) by an interaction potential V exc = 17 500 cm−1. The resulting eigenvalues are marked by gray horizontal lines, and the corresponding experimental electron affinities63,64 are marked by black horizontal lines.
Allowed rovibronic transitions in a photoionizing transition in the molecular symmetry group . The selection rules are the same for even-ℓ and odd-ℓ photoelectron partial waves.
Spin-orbit coupling in the 2E ground state of and .
Main Jahn-Teller coupling parameters in the 2E ground state of and .
Harmonic wave numbers (in cm−1) of the six vibrational modes of , , and in C3v symmetry.
Atomic ionization energies55–57 (in cm−1), determined as the center-of-gravity energies of the neutral and ionic states, and vertical ionization energy of methane58,59 (in cm−1).
Ionization energies and ( and ) to the lowest and a higher lying electronic state of (CH3Y+), determined from photoelectron spectroscopic studies (“Experiment”) and with the exciton-type model of Eq. (6) using an interaction potential V exc = 17 500 cm−1 (“Model”). In the last two columns, the differences between the calculated and experimentally determined ionization energies (ΔE I and ) are presented.
Values of a X(Y), , and , determined with V exc = 17 500 cm−1, and the comparison to ζe of the 2E ground states of and .
Electron affinities for the chalcogen atoms,69 methane,62 ,63 and CH3S (Ref. 64) (in cm−1).
Values of EA, , , and , determined with V exc = 17 500 cm−1, and the comparison to ζe of the 2E ground state of .
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