Asymmetry parameters forCO2around the CKand OKionization edges from the anisotropy of the ion distributions

Asymmetry parameter (β) values have been determined from the ${\mathrm{C}}^{+}$, ${\mathrm{O}}^{+}$, and ${\mathrm{CO}}^{+}$ signals in the time-of-flight (TOF) mass spectra and the ${\mathrm{CO}}^{+}$-${\mathrm{O}}^{+}$ signal in the photoion-photoion coincidence (PIPICO) spectra of ${\mathrm{CO}}_2$ excited and/or ionized with monochromatic synchrotron radiation around the C K and O K ionization edges using a rotatable time-of-flight mass spectrometer. Positive β values of 0.4 were found for the ${\mathrm{C}}^{+}$ ions at the C 1${\mathit{s}}^{\mathrm{-}1}$2${\mathrm{\pi }}_{\mathit{u}}^{\mathrm{*}}$ and O 1${\mathit{s}}^{\mathrm{-}1}$2${\mathrm{\pi }}_{\mathit{u}}^{\mathrm{*}}$ resonances, respectively, and negative values between -0.1 and -0.4 were obtained for the other TOF and PIPICO signals at the same photon energies. The difference between these values and the expected value of -1 results from bending the molecule in the excited state before or during its ionic fragmentation. An O-C-O bond angle of 124° was found for ${\mathrm{CO}}_2$ in the C 1${\mathit{s}}^{\mathrm{-}1}$2${\mathrm{\pi }}_{\mathit{u}}^{\mathrm{*}}$ state from the β value for the ${\mathrm{O}}^{+}$-${\mathrm{CO}}^{+}$ PIPICO signal. The β values were close to the isotropic value of zero at all other photon energies for the ${\mathrm{C}}^{+}$ ions. β values for the ${\mathrm{O}}^{+}$ and ${\mathrm{CO}}^{+}$ signals in the TOF spectra and the ${\mathrm{O}}^{+}$-${\mathrm{CO}}^{+}$ signals in the PIPICO spectra were found to be similar.