One photon dissociation and multiphoton dissociative ionization of bromochlorodifluoromethane (CF2BrCl) at 267 nm region

Abstract

The photodissociation dynamics of CF2BrCl have been studied near 267 nm using time-of-flight mass spectrometry combined with ion velocity imaging. The bromine atoms are probed via 2+1 resonance enhanced multiphoton ionization. The one-photon dissociation channels of CF2BrCl produce bromine atoms in both ground state Br(2P3/2) and excited state Br(2P1/2). Translational energy and angular distributions for each channel are derived from the two-dimensional images of both of the bromine atoms using the back-projection method. The time of flight mass spectra indicate that the CF2Cl+ ions are also formed with the focused laser in the 259–270 nm region. Six images were taken in this wavelength region and they show the typical characteristics recently reported by several groups that are attributed to dissociative ionization arising from multiphoton absorption. The changes in the energy and angular distributions of CF2Cl+ as a function of wavelength are described in terms of a resonance enhanced multiphoton dissociative ionization mechanism involving excitation to Rydberg states above and below the ionization potential of CF2BrCl. The translational energy distributions at different wavelengths clearly indicate that there is a competition between neutral dissociation and dissociative ionization from the initial super-excited states reached by three photons. The angular distributions suggest that there exist strong coupling between Rydberg electron in p-type orbital and the ion core, which affects the spin–orbit coupling in the fragment Br atom. It is also proposed that curve crossing similar to that observed in the one photon dissociation between repulsive ionic states of CF2BrCl+ leads to the formation of both Br(2P3/2) and Br(2P1/2) as the counterparts of the observed CF2Cl+.