Kinetic energy distributions in ion-induced $\mathrm{CO}$ fragmentation: Signature of shallow states in multiply charged $\mathrm{CO}$

Ion-induced molecular fragmentation of $\mathrm{CO}$ has been studied using time-of-flight mass spectroscopy with position sensitive detectors in multihit coincidence mode. ${\mathrm{Ar}}^{8+}$ ions having a velocity of 1.1 a.u. were used as projectiles. The features observed in the kinetic energy release (KER) spectra for all the detected fragmentation channels are discussed in light of the existing and calculated ab initio potential energy curves. The preference of the symmetric breakup over the asymmetric one is clearly observed. For fragmentation channels originating from the same parent molecular ion, it is observed that the most probable KER value is higher for the dissociation channel having a higher charge on the oxygen ion. Occurrence of sharp peaks in KER spectra of some of the fragmentation channels hints towards the existence of shallow (possibly metastable) excited states of ${\mathrm{CO}}^{q+}$ $(q=4,5)$ molecular ions and calls for further theoretical investigations.

Figure 1

Kinetic energy release spectra for ${\mathrm{CO}}^{2+}$ dissociation. Theoretical values are indicated by vertical lines at the top of the graph.

Figure 2

Kinetic energy release spectra for ${\mathrm{CO}}^{3+}$ dissociation. Theoretical values are indicated by vertical lines at the top of the graph.

Figure 3

Kinetic energy release spectra for ${\mathrm{CO}}^{4+}$ dissociation. Theoretical values are indicated by vertical lines at the top of the graph.

Figure 4

Kinetic energy release spectra for ${\mathrm{CO}}^{5+}$ dissociation. Theoretical values are indicated by vertical lines at the top of the graph.

Figure 5

Kinetic energy release spectra for ${\mathrm{CO}}^{6+}$ dissociation. Theoretical values are indicated by vertical lines at the top of the graph.

Figure 6

Potential energy curves for low lying states of a ${\mathrm{CO}}^{4+}$ molecular ion. Shallow states like $A{}^3\Pi$ can give rise to sharp peaks in KER spectra.