Multi-mass velocity map imaging study of the 805 nm strong field ionization of CF3I

Abstract

Multi-mass velocity map imaging studies of charged fragments formed by near infrared strong field ionization together with covariance map image analysis offer a new window through which to explore the dissociation dynamics of several different highly charged parent cations, simultaneously – as demonstrated here for the case of CF₃I^Z+ cations with charges Z ranging from 1 to at least 5. Previous reports that dissociative ionization of CF₃I⁺ cations yields CF₃⁺, I⁺ and CF₂I⁺ fragment ions are confirmed, and some of the CF₃⁺ fragments are deduced to undergo secondary loss of one or more neutral F atoms. Covariance map imaging confirms the dominance of CF₃⁺ + I⁺ products in the photodissociation of CF₃I²⁺ cations and, again, that some of the primary CF₃⁺ photofragments can shed one or more F atoms. Rival charge symmetric dissociation pathways to CF₂I⁺ + F⁺ and to IF⁺ + CF₂⁺ products and charge asymmetric dissociations to CF₃ + I²⁺ and CF₂I²⁺ + F products are all also identified. The findings for parent cations with Z ≥ 3 are wholly new. In all cases, the fragment recoil velocity distributions imply dissociation dynamics in which coulombic repulsive forces play a dominant role. The major photoproducts following dissociation of CF₃I³⁺ ions are CF₃⁺ and I²⁺, with lesser contributions from the rival CF₂I²⁺ + F⁺ and CF₃²⁺ + I⁺ channels. The CF₃²⁺ fragment ion images measured at higher incident intensities show a faster velocity sub-group consistent with their formation in tandem with I²⁺ fragments, from photodissociation of CF₃I⁴⁺ parent ions. The measured velocity distributions of the I³⁺ fragment ions contain features attributable to CF₃I⁵⁺ photodissociation to CF₃²⁺ + I³⁺ and the images of fragments with mass to charge (m/z) ratio ∼31 show formation of I⁴⁺ products that must originate from parent ions with yet higher Z.