Exploration of Vibrationally Resolved Threshold Photoelectron Spectrum of Difluoromethane within Photon Energy Range of 12.45‒14.10 eV^†

Threshold photoelectron spectrum of CH₂F₂ in the photon energy range of 12.45‒14.10 eV was re-investigated by means of a combination of photoelectron-photoion coincidence experiments and density functional theory calculations. A series of vibrational peaks were distinctly observed in this range. Using optimized geometries and vibrational frequencies of the CH₂F₂ neutral and its cation in ground state at the M06-2X/cc-pVTZ level of theory, Franck-Condon factor simulations were conducted. Taking into account anharmonicity influences, a perfect agreement between the simulated and experimental spectra has been achieved. From the reliable vibrational assignments, adiabatic and vertical ionization energies of CH₂F₂ are derived as 12.371 ± 0.010 eV and 13.281 ± 0.010 eV, respectively. In addition, the experimental frequencies of four vibrational modes with a₁ symmetry for CH₂F₂⁺(X²B₁) ions are determined.