Internal Inelastic Scattering Satellite Probed by Molecular-Frame Photoelectron Angular Distributions from ${\mathrm{CO}}_2$

The molecular-frame photoelectron angular distribution (MFPAD) of the satellite accompanying the C $1s$ photoline of the ${\mathrm{CO}}_2$ molecule has been measured at the C $1s(2{\sigma }_g)\to 4{\sigma }_u^{*}$ shape resonance, using electron-ion multicoincidence momentum spectroscopy. The observed MFPAD indicates that the conjugate satellite is excited by internal inelastic scattering. In this scenario, a photoelectron is ejected from the C $1s(2{\sigma }_g)$ orbital along the molecular axis and collides with an O lone-pair electron in the highest occupied molecular orbital $1{\pi }_g$. Then one of the colliding electrons is trapped to the lowest unoccupied molecular orbital $2{\pi }_u^{*}$, while the other is emitted as a satellite photoelectron of ${\sigma }_g$ symmetry, losing the information of the original photoelectron emission direction and parity.

Figure 1

C $1s$ photoelectron spectrum of ${\mathrm{CO}}_2$ recorded at 311.8 eV.

Figure 2

2D plots of MFPADs for (a) the C $1s$ main line and (b) the lowest satellite of ${\mathrm{CO}}_2$ recorded at photon energy of 311.8 eV. The $x$ axis denotes the angle ${\theta }_n$ between the $E$ vector and molecular axis, and the $y$ axis the electron emission polar angle $\theta$ relative to the molecular axis. The electron emission intensity is plotted on a gray linear scale (color scale). These distributions have not been directly measured, but reconstructed from a parametrization of all available MFPADs for various molecular orientations. See text for details.

Figure 3

3D plots of MFPADs for (a) the C $1s$ main line and (b) the lowest satellite of ${\mathrm{CO}}_2$ recorded at photon energy of 311.8 eV, where the $E$ vector is parallel to the molecular axis. These distributions have not been directly measured but instead have been reconstructed from a parametrization of all available MFPADs for various molecular orientations. See text for the details.