Molecular frame photoelectron angular distribution for oxygen 1s photoemission from CO_2 molecules

We have measured photoelectron angular distributions in the molecular frame (MF-PADs) for O 1s photoemission from CO2, using photoelectron-O+–CO+ coincidence momentum imaging. Results for the molecular axis at 0, 45 and 90° to the electric vector of the light are reported. The major features of the MF-PADs are fairly well reproduced by calculations employing a relaxed-core Hartree–Fock approach. Weak asymmetric features are seen through a plane perpendicular to the molecular axis and attributed to symmetry lowering by anti-symmetric stretching motion

Carbon K-shell photoelectron angular distribution from fixed-in-space CO2 molecules

Measurements of photoelectron angular distributions for carbon K-shell ionization of fixed-in-space CO2 molecules with the molecular axis oriented along, perpendicular and at 45 degrees to the electric vector of the light are reported. The major features of these measured spectra are fairly well reproduced by calculations employing a relaxed-core Hartree-Fock approach. In contrast to the angular distribution for K-shell ionization of N-2, which exhibits a rich structure dominated by the f-wave (l = 3) at the shape resonance, the angular distribution for carbon K-shell photoionization of CO2 is quite unstructured over the entire observed range across the shape resonance

Symmetry-Dependent Multielectron Excitations near the C 1s Ionization Threshold and Distortion of the Shape Resonance in CO 2

Satellite bands accompanying the C 1s photoline for the CO 2 molecule parallel to the electric vector of the incident radiation E are found to be more intense than those for CO 2 perpendicular to E in the shape resonance region. This indicates that multielectron excitations are caused in part by the interaction of the outgoing C 1s photoelectron with the valence electrons. The photoelectron-impact valence excitations couple with the C 1s single-hole ionization and distort the shape resonance significantly. We assign the broad resonance at ϳ312 eV to a distorted S u shape resonance. DOI: 10.1103/PhysRevLett.89.023006 PACS numbers: 33.60.Fy, 34.80. -i Photoabsorption spectra of small molecules exhibit resonant features both below and above the inner-shell thresholds. The resonances above the thresholds, assigned to shape resonances, are conventionally described as oneelectron phenomena associated either with temporary trapping of the photoelectron by the molecular potential Such multielectron transitions in molecules induced by a single photon have so far mostly been interpreted as results of a shake-up mechanism. Here a core electron absorbs the photon angular momentum. In a dipole transition it is either emitted to the continuum or to an excited state. The valence electrons are now no longer in an eigenstate of the altered potential and relax in a monopole transition either to a bound state or to the continuum. The electron emitted to the continuum is then observed either as a normal or conjugate satellite of the main photoline. From atomic double ionization and ionization with excitation, it is known however that, in addition to shakeup/ shakeoff, two electron processes can also be induced by an electron-electron scattering (see In the present Letter we provide experimental evidence for the existence of the PEVE interaction within a CO 2 molecule. Our experiment is based on the simple idea that (i) the probability of normal shakeup/shakeoff drops when the photon frequency approaches the ionization threshold This PEVE interaction calls for a reevaluation of the concept of shape resonances. They are conventionally regarded as one-electron phenomena, i.e., interference of the photoelectron wave described as occurring in the rigid molecule (valence electrons and nuclear motions are independent of the photoelectron motion). The importance of the PEVE coupling suggests that one describe this interference as occurring in the soft molecule: due to the PEVE coupling the valence-excited molecular configurations assist in the intramolecular interference. We will show that this coupling shifts upward the position of the shape resonance considerably. In the preset experiment, we have investigated the dependence of the satellite excitations accompanying C 1s photoionization in CO 2 on the symmetry of the transitions in the vicinity of the shape resonance. We recorded C 1s photoelectron spectra for CO 2 whose molecular axis is parallel or perpendicular to E . To probe the direction of the molecular axis for each photoelectron emission, we use coincidence detection between the photoelectron and the fragment ions 023006-1 0031-9007͞02͞ 89(2)͞023006(4)$20.0

Symmetry-Dependent Multielectron Excitations near the C 1s Ionization Threshold and Distortion of the Shape Resonance in CO2

Satellite bands accompanying the C 1s photoline for the CO2 molecule parallel to the electric vector of the incident radiation E are found to be more intense than those for CO2 perpendicular to E in the shape resonance region. This indicates that multielectron excitations are caused in part by the interaction of the outgoing C 1s photoelectron with the valence electrons. The photoelectron-impact valence excitations couple with the C 1s single-hole ionization and distort the shape resonance significantly. We assign the broad resonance at ∼312 eV to a distorted Σu shape resonance

Molecular frame photoelectron angular distribution for oxygen 1s photoemission from CO 2 molecules

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