Mass analyzed threshold ionization spectra of phenol…Ar₂: Ionization energy and cation intermolecular vibrational frequencies

The phenol⁺…Ar₂ complex has been characterized in a supersonic jet by mass analyzed threshold ionization (MATI) spectroscopy via different intermediate intermolecular vibrational states of the first electronically excited state (S₁). From the spectra recorded via the S₁0⁰ origin and the S₁β_x intermolecular vibrational state, the ionization energy (IE) has been determined as 68 288 ± 5 cm^-1, displaying a red shift of 340 cm^-1 from the IE of the phenol⁺ monomer. Well-resolved, nearly harmonic vibrational progressions with a fundamental frequency of 10 cm^-1 have been observed in the ion ground state (D₀) and assigned to the symmetric van der Waals (vdW) bending mode, β_x, along the x axis containing the C-O bond. MATI spectra recorded via the S₁ state involving other higher-lying intermolecular vibrational states (σ 1s, β 3x, σ 1s β 1x, σ 1 s β 2 x) are characterized by unresolved broad structures.