Anisotropy in multiple ionisation of CO by ion collisions at intermediate interaction strengths

Abstract

Multiple ionisation of the CO molecule following the impact of 100-700 keV He 2+ ions was studied. Fragments arising from the dissociation of n CO 5)were recorded using the coincidence momentum imaging technique. By measuring the angular distribution of the fragment ions in coincidence, and applying the axial recoil approximation, the angle between the axis of the molecule and the direction of the projectile was determined. Strong anisotropy was observed for high degree of ionisation. The dependence of the anisotropy on the interaction strength and the projectile energy was studied and the results were compared with the predicted values in the literature for diatomic molecules. Furthermore, an asymmetry in the angular distribution owing to the heteronuclear nature of the molecule was observed and quantified, showing that the anisotropy is not entirely a geometric effect as has been presented in earlier works.

Triple ionisation of OCS: orientation dependence in the case of ion impact

“…It is clear from the angular distribution of O + and S + that ionisation probability is high for the orientation in which the oxygen atom points towards the projectile. The result is similar for the CO molecule, reported in our earlier papers [22,23]. For C 2+ impact, high negative value of the anisotropy parameter indicates a higher ionisation probability for the perpendicular orientation of the molecule and thus in this case no forward-backward asymmetry can be expected.…”

“…two fragments (which are measured in the experiment) with respect to the projectile directly gives us the angle made by the molecular axis with the projectile [22].…”

“…In recent papers [22,23], we have discussed the orientation dependence of multiple ionisation of the CO molecule. Together with anisotropy, asymmetry was observed, owing to the heteronuclear nature of CO molecule.…”

Orientation dependence of multiple ionisation of a diatomic molecule under proton impact

“…However, in a study of multiple ionisation of CO and NO in a strong laser field, Li et al [24] found that in both molecules ionisation is enhanced when the electric field of the laser points toward the O atom. In a recent paper [25] we have discussed the asymmetry in multiple ionisation of the CO molecule under the impact of He 2+ in the intermediate interaction strength regime (0.76k2.0). We showed that the heteronuclear nature of CO gives rise to an asymmetry in the ionisation process, and that a higher degree of ionisation is more likely to be achieved when the projectile first encounters the oxygen atom rather than the carbon atom.…”

Production of Metastable CO3+ through the Strong-Field Ionization and Coulomb Explosion of Formic Acid Dimer

“…CO is the second most abundant molecule in interstellar space, − making its high charge states particularly important. CO 2+ was first identified in 1931 and has since been analyzed in many experimental − and theoretical studies. − The cross-sections and ionization energies of CO n + (as high as n = 9) have been studied with a variety of techniques, including electron impact, , fast ion collisions, − vacuum ultraviolet (VUV) photoionization, ,, multiphoton ionization (MPI), , and strong-field ionization (SFI). − The predissociation lifetime of CO 2+ is measured ranging from tens of nanoseconds to several seconds. , Yet, CO 3+ has so far eluded direct observation by mass spectrometry. The distinct absence of CO 3+ in mass spectra directly has stimulated the hypothesis that it contains no metastable potential.…”