Mass-Analyzed Threshold Ionization Spectroscopy of 2-Phenylethanol: Probing of Conformational Changes Caused by Ionization

Photoionization and photofragmentation in mass spectrometry with visible and UV lasers

Ever since the introduction of laser technology to the field of mass spectrometry, several disciplines evolved providing solutions to challenging scientific and analytical tasks in research and industry. Among these are techniques involving multiphoton ionization such as Resonance-Enhanced Multiphoton Ionization (REMPI, R2PI) and Mass-Analyzed Threshold Ionization (MATI) spectroscopy, a variant of Zero Kinetic Energy (ZEKE) spectroscopy, that possess the ability to selectively ionize certain preselected compounds out of complex mixtures, for example, environmental matrices, with a high level of efficiency. Another key feature of multiphoton ionization techniques is the ability to control the degree of fragmentation, whereas soft ionization is most highly appreciated in most applications. In cases where rich fragmentation patterns are desired for diagnostic purposes, Photodissociation mass spectrometry (PD-MS) is applied successfully. PD-MS allows for the cleavage of selected chemical bonds. With the introduction of chromophoric labels in PD-MS, it became possible to target certain molecules or groups within a molecule. In this review article, an overview of the basic principles and experimental requirements of REMPI and MATI spectroscopy and PD mass spectrometry are given. By means of selected examples, the latest developments and application possibilities in this field over the past decade with special focus on the German research landscape are pointed out. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 38: 202-217, 2019.

Rotamers of 3,4-difluoroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

We reported the vibronic and cation spectra of 3,4-difluoroanisole. The band origins of the S(1) ←S(0) electronic transition of the cis and trans rotamers appear at 35,505 ± 2 and 35,711 ± 2 cm(-1) and the adiabatic ionization energies are determined to be 67,780 ± 5 and 68,125 ± 5cm(-1), respectively. Most of the observed active vibrations in the electronically excited S(1) and cationic ground D(0) states mainly involve in-plane ring deformation and substituent-sensitive bending vibrations. Analysis of the obtained vibronic and cation spectra suggests that the molecular geometry, symmetry, and vibrational coordinates of the cation in the D(0) state are like those of the neutral species in the S(1) state for these two isomeric species.