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Two color resonant mass analyzed threshold ionization (MATI) spectroscopy was applied in order to investigate the ionic properties of the structural isomers of trichlorobenzene (TCB) above the ionization threshold. For the first time, vibrational spectra of the 35 Cl 3 and 35 Cl 2 37 Cl isotopomers of 1,2,3-, 1,2,4- and 1,3,5-trichlorobenzene cations in their electronic ground state have been measured via different S 1 intermediate states by mass analyzed threshold ionization (MATI) spectroscopy. Additionally ab initio calculations at DFT (density functional theory) and TDDFT (time-dependent density functional theory) have been performed to compare experimental findings with theory. From the MATI spectra the adiabatic ionization energies of the three isomers 1,2,3-TCB, 1,2,4-TCB and 1,3,5-TCB could be determined to 74289 ± 6 cm −1 , 72779 ± 6 cm −1 and 74900 ± 100 cm −1 , respectively. Several vibrational modes of the isotopomers have been assigned by comparison of the experimental and theoretical results.

The phenol(+)...Ar(2) 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 (S(1)). From the spectra recorded via the S(1)0(0) origin and the S(1)β(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 (D(0)) 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 S(1) state involving other higher-lying intermolecular vibrational states (σ(s)(1), β(x)(3), σ(s)(1)β(x)(1), σ(s)(1)β(x)(2)) are characterized by unresolved broad structures.

For the first time, vibrational spectra of the 35Cl2 and 35Cl37Cl isotopomers of o-, m-, and p-dichlorobenzene cations in the electronic ground state have been measured via S1 intermediate states by mass analyzed threshold ionization (MATI) spectroscopy. Additionally, ab initio calculations at DFT (density functional theory), CIS (configuration interaction singles), and CASSCF (complete active space self-consistent field) levels of theory have been conducted to compare experimental findings with theory. From the MATI spectra, adiabatic ionization energies of the ortho, meta, and para isomers have been determined to be the same for each pair of investigated isotopomers to 73,237 +/- 6, 72,191 +/- 6, and 73,776 +/- 6 cm(-1), respectively. Several vibrational modes, including fundamentals, combinations, and progressions have been assigned by comparing the experimental and theoretical results. The appearance of overtone progressions involving the 7a mode could be explained by a geometry change of all three isomers during ionization in the direction of this mode by retraining the symmetry of the molecules. Although the general spectral features of the investigated isotopomers are similar, frequencies of some vibrations are slightly different up to a few wavenumbers depending on the involvement of the chlorine atoms in the molecular motion.

The various dissociation thresholds of phenol(+)···Ar(3) complexes for the consecutive loss of all three Ar ligands were measured in a molecular beam using resonant photoionization efficiency and mass analyzed threshold ionization spectroscopy via excitation of the first excited singlet state (S(1)). The adiabatic ionization energy is derived as 68077 ± 15 cm(-1). The analysis of the dissociation thresholds demonstrate that all three Ar ligands in the neutral phenol···Ar(3) tetramer are attached to the aromatic ring via π-bonding, denoted phenol···Ar(3)(3π). The value of the dissociation threshold for the loss of one Ar ligand from phenol(+)···Ar(3)(3π), ∼190 cm(-1), is significantly lower than the binding energy measured for the π-bonded Ar ligand in the phenol(+)···Ar(π) dimer, D(0) = 535 ± 3 cm(-1). This difference is rationalized by an ionization-induced π → H isomerization process occurring prior to dissociation, that is, one Ar atom in phenol(+)···Ar(3)(3π) moves to the OH binding site, leading to a structure with one H-bonded and 2 π-bonded ligands, denoted phenol(+)···Ar(3)(H/2π). The dissociation thresholds for the loss of two and three Ar atoms are also reported as 860 and 1730 cm(-1). From these values, the binding energy of the H-bound Ar atom can be estimated as 870 cm(-1).