PFI-ZEKE photoelectron spectrum of CH2F2, ionisation potential and ionic fragmentation appearance potentials

Abstract

The first vibrationally resolved pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of difluoromethane from its adiabatic ionisation potential (formation of the C_2v conformer of CH₂F₂⁺) to the onset of the first ionic fragmentation channel is presented. Precise values for the adiabatic ionisation potential (12.7252 ± 0.0009 eV) and the appearance potentials of the H loss product (13.065 ± 0.003 eV) and the F loss product (14.30 ± 0.06 eV) of the cation are reported. Ab initio harmonic calculations were performed at the MP2 level with quadruple-ζ basis sets in an attempt to assign the newly observed vibrational structure which, in its previously published low resolution form, led to numerous speculations regarding its true origin. The adiabatic ionisation potential and the fragmentation appearance potentials for the three lowest dissociation channels are also predicted in the complete basis set limit of CCSD(T) theory.