PHOTOELECTRON PHOTOION COINCIDENCE STUDY OF THE FRAGMENTATION OF VALENCE STATES OF CHF2–CH3+ IN THE RANGE 12–25 eV

Abstract

Using vacuum ultraviolet radiation from a synchrotron source, threshold photoelectron photoion coincidence (TPEPICO) spectroscopy has been used to study the dissociative photoionisation of CHF 2– CH 3 in the photon energy from 11.8 eV to 24.8 eV. Combining with ab initio molecular orbital calculation, fragmentation process and fragmental mechanism of the valence states of parent ion are discussed. For single bond cleavage process, a statistical mechanism might govern the C – C bond cleavage, while the kinetic energy release derived from channel CHF 2– CH 3+ → CH 3– CHF ++ F + e- shows evidence for impulsive mechanism. A two-step increase of signal CF 2– CH 3+/ CHF 2– CH 2+ was observed. The two-step is due to the formation of ion CF 2– CH 3+/ CHF 2– CH 2+ through two different dissociation channels. Both computed molecular orbital character and related G2 dissociation energy support the assumption. The ionisation threshold of 12.02 ± 0.04 eV measured from the TPES and the appearance energies (AEs) identified from the ion yield curves are presented. New or refined upper limit values of enthalpy of formation at 298 K for ion CHF 2+, CF 2– CH 3+ and CHF – CH 3+ are derived.