Fragmentation of valence electronic states of CHF2CF3+ studied by threshold photoelectron–photoion coincidence (TPEPICO) techniques in the photon energy range 12–25 eV

Vacuum ultraviolet synchrotron radiation and threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy have been used to study the decay dynamics of the valence electronic states of CHF\(_2\)CF\(_3^+\). The threshold photoelectron spectrum (TPES) and ion yield curves of the observed fragments have been recorded in the photon energy range 12-25 eV. Electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. Using a combination of the measured TPES and ab initio molecular orbital calculations, we conclude that the CHF\(_2\)CF\(_3^+\) cation adopts a staggered C\(_s\) geometry, the \(X\)~ \(^2\)A' ground state being formed by electron removal from the 18a' -bonding orbital of CHF\(_2\)CF\(_3\). Upon ionisation, large geometry changes and broad spectral bands are both predicted and observed. The next outer-valence orbitals of CHF\(_2\)CF\(_3\), 17a' and 11a", are predominantly associated with fluorine 2p orbitals located on the CHF\(_2\) group. Translational kinetic energy releases are determined from fixed-energy TPEPICO-TOF spectra. The ground state of CHF\(_2\)CF\(_3^+\) dissociates through CC bond cleavage with a relatively small release of energy. By contrast the \(A\)~ and \(B\)~ states dissociate rapidly by an impulsive mechanism with a larger fractional release of energy to CHFCF\(_3^+\) + F. Upper limits for the ionization threshold of CHF\(_2\)CF\(_3\) (12.70 \(\pm\) 0.05 eV) and the enthalpy of formation of CHFCF\(_3^+\) at 298 K (299 \(\pm\) 7 kJ mol-1, respectively) are determined.