Schematic of the scattering geometry depicting the various angles employed. A coplanar geometry (ψ = 0°) is defined when the momenta of all three electrons lie in the detection plane. The analyzer angles (ξ1 and ξ2) are measured with respect to the incident electron beam k 0 in this plane. Noncoplanar geometries can also be accessed in this apparatus by lifting the electron gun out of the detection plane, although this feature was not utilized here.
A typical coincidence binding energy spectrum obtained for CH4. These data were measured in a coplanar geometry with outgoing electron energies of 20 eV at ξ = 45°. The two peaks correspond to the two highest orbitals, i.e., the 1t2 and 2a1 orbitals as labeled. The orbitals are easily resolved, so that the TDCS from each orbital is uncontaminated by its neighbor. The width of the HOMO is significantly increased from that due solely to the experimental resolution due to Jan–Teller distortion.21
Comparison between experimental EMS data (dots)21 and the square modulus of the Fourier transform of the orientational averaged molecular wavefunctions, , (lines) which were used to calculate the TDCS used in this study.
TDCS from the 1t2 HOMO state of CH4 for coplanar symmetric kinematics. The energies of the outgoing electrons are shown on the respective plots. The experimental data (dots) and results from the molecular three-body distorted wave approximation (lines) are depicted. The experimental and theoretical data have been independently normalised to unity at the peak for each energy.
As for Fig. 4, for the 2a1 NHOMO state of CH4.
A comparison of the TDCS from the M3DW calculation for the 1t2 (solid line) and 2a1 (dashed line) normalized to unity at the peak. The theory predicts very similar structure for both states, although the absolute magnitudes are different.
TDCS for the equivalent states within the isoelectronic species, i.e., the 2a1 orbital of CH4 and the 2s inner atomic state of Ne. The upper figures show results for the molecule at 20 and 5 eV outgoing energies, as in Fig. 4. The bottom panel shows the TDCS from the 2s state of neon collected under the same kinematics. The experimental data (points) are compared with theoretical predictions from the distorted wave calculations (solid line) for CH4 and the distorted wave born approximation (dotted line) for neon.
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