Dissociative double photoionization of CO2 molecules in the 36-49 eV energy range: angular and energy distribution of ion products

Dissociative double photoionization of CO2, producing CO+ and O+ ions, has been studied in the 36–49 eV energy range using synchrotron radiation and ion–ion coincidence imaging detection. At low energy, the reaction appears to occur by an indirect mechanism through the formation of CO+ and an autoionizing state of the oxygen atom. In this energy range the reaction leads to an isotropic distribution of products with respect to the polarization vector of the light. When the photon energy increases, the distribution of products becomes anisotropic, with the two ions preferentially emitted along the direction of the light polarization vector. This implies that the molecule photoionizes when oriented parallel to that direction and also that the CO2 2+ dication just formed dissociates in a time shorter than its typical rotational period. At low photon energy, the CO+ and O+ product ions separate predominantly with a total kinetic energy between 3 and 4 eV. This mechanism becomes gradually less important when the photon energy increases and, at 49 eV, a process where the two products separate with a kinetic energy between 5 and 6 eV is dominant

Double Photoionization of CO2 Molecules in the 34-50 eV Energy Range

The double photoionization of CO2 molecules has been studied in the 34-50 eV photon energy range, by the use of synchrotron radiation and detecting electron-ion and electron-ion-ion coincidences. Three processes have been observed: (i) the formation of the CO2 2+ molecular dication, (ii) the production of a metastable (CO2 2+)* that dissociates, with an apparent lifetime of 3.1 μs, giving rise to CO+ and O+ ions, and (iii) the dissociation leading to the same products, but occurring with a lifetime shorter than 0.05 μs. The relative dependence on the photon energy of the cross section for such processes has been measured. While for the production of the molecular dication a threshold is observed, in agreement with the vertical threshold for double ionization of CO2, for the dissociative processes the threshold appears to be lower than that value, indicating the presence of an indirect dissociation, probably leading to the formation of CO+ together with a neutral autoionizing oxygen atom

Anisotropy of the angular distribution of fragment ions in dissociative double photoionization of N2O molecules in the 30-50 eV energy range

The double photoionization of N2O molecules by linearly polarized light in the 30–50 eV energy range has been studied by coupling ion imaging technique and electron-ion-ion coincidence. For the two possible dissociative processes, leading to N++NO+ and O++N2 +, angular distributions of ionic fragments have been measured, finding an evident anisotropy. This indicates that the molecules ionize when their axis is parallel to the light polarization vector and the fragments are separating in a time shorter than the dication rotational period. The analysis of results provides, in addition to the total kinetic energy of ionic fragments, crucial information about the double photoionization dynamics

Angular and energy distribution of fragment ions in dissociative double photoionization of acetylene molecules at 39 eV

The two-body dissociation reactions of the dication, C2H22+, produced by 39.0 eV double photoionization of acetylene molecules, have been studied by coupling photoelectron-photoion-photoion coincidence and ion imaging techniques. The results provide the kinetic energy and angular distributions of product ions. The analysis of the results indicates that the dissociation leading to C2H++H+ products occurs through a metastable dication with a lifetime of 108 +/- 22 ns, and a kinetic energy release (KER) distribution exhibiting a maximum at similar to 4.3 eV with a full width at half maximum (FWHM) of about 60%. The reaction leading to CH2+ + C+ occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10(-12) s). The KER distribution of product ions for this reaction, exhibits a maximum at similar to 4.5 eV with a FWHM of about 28%. The symmetric dissociation, leading to CH+ + CH+, exhibits a KER distribution with a maximum at similar to 5.2 eV with a FWHM of 44%. For the first two reactions the angular distributions of ion products also indicate that the double photoionization of acetylene occurs when the neutral molecule is mainly oriented perpendicularly to the light polarization vector. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720350