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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.

Vibrational spectra of the pyrazine and the pyrazine-Ar cation in the electronic ground state (D 0) have been measured via several intermediate states of the first excited state (S 1) by mass-analyzed threshold ionization spectroscopy. Additionally, ab-initio calculations at the DFT, CIS and MP2 level of theory have been conducted to compare experimental findings with theory. For the pyrazine monomer a negative anharmonic behavior for combination bands containing the 16a or the 1 vibration could be observed for the first time. It was found that the 16a vibration has to be considered when discussing the nature of the vibronic coupling in the first excited state (S 1) as well as in the ionic ground state (D 0). For some vibrations a new assignment is given in the first excited state (S 1) and the ionic ground state (D 0). An earlier discussed appearance of internal vibrational redistribution (IVR) by activating the 516a1 vibrational state in the first electronically excited state (S 1) is rejected due to the results of the presented measurements. For the pyrazine-Ar complex the ionization energy, as well as the binding energy in the ionic and the neutral ground state could be determined. These values are given by 74632 ± 5 cm-1, 630 cm-1 ± 20 cm-1 and 349 cm-1 ± 20 cm-1, respectively. The van-der-Waals vibrations in the first excited state could be reassigned and the frequencies of these vibrations have been found to be 12 cm-1, 27 cm-1 and 39 cm-1.

For the first time, vibrational spectra of the pyridine cation in the electronic ground state have been measured via several intermediate states (0(0), 16b0(2), 16b0(4), 6a0(1), 6b(1), 16a0(1), 10a0(1) and 12(1)) by Mass-Analyzed Threshold Ionization (MATI) spectroscopy. From the MATI spectra, the adiabatic ionization energy of pyridine has been determined to be 74,185 +/- 6 cm(-1) (9.1978 +/- 0.0008 eV). Several vibronic modes in the ionic ground state could be assigned for the first time. An intensity gain of vibrations having b1 symmetry could be observed by activating the ion ground state. Also, a breakdown of the "delta nu = 0 propensity rule" for the excitation via the 16b(2) and 16b(4) states of the first excited states are displayed in the recorded spectra. In conjunction with ab initio calculations these observations can be explained by a strong geometrical distortion along the 16b vibration in the first excited state, leading to a "boat distortion".

A laser spectroscopic investigation of phenol...Ar(n) (n = 1-6) clusters in the first electronically excited state (S(1)) and the cationic ground state (D(0)) is reported. Resonance enhanced two-photon ionisation (R2PI) spectra have been recorded for the investigation of the S(1) state. The origins of S(1)← S(0) (S(1)0(0)) transition of phenol...Ar(n) (n = 1, 2,4-6) are all red shifted compared to the S(1)0(0) state of the monomer by 33 cm(-1), 67 cm(-1), 10 cm(-1), 20 cm(-1), 44 cm(-1), respectively. However, the origin of the phenolAr(3) cluster is blue shifted by 25 cm(-1). For the investigation of the ionic ground state photoionization efficiency (PIE) and mass-analyzed-threshold ionization (MATI) spectroscopy have been applied. The spectra of phenol...Ar(3) and phenol...Ar(4) yield values for the ionization energy (IE) of 68,077 ± 15 cm(-1) and 67,948 ± 15 cm(-1). With the combination of theoretical methods and R2PI, PIE and MATI spectroscopy, the major species present have been positively identified.