Mass-selected IR-VUV (118 nm) spectroscopic studies of radicals, aliphatic molecules, and their clusters

Abstract

Mass-selected IR plus UV/VUV spectroscopy and mass spectrometry have been coupled into a powerful technique to investigate chemical, physical, structural, and electronic properties of radicals, molecules, and clusters. Advantages of the use of vacuum ultraviolet (VUV) radiation to create ions for mass spectrometry are its application to nearly all compounds with ionization potentials below the energy of a single VUV photon, its circumventing the requirement of UV chromophore group, its inability to ionize background gases, and its greatly reduced fragmenting capabilities. In this review, mass-selected IR plus VUV (118 nm) spectroscopy is introduced first in a general manner. Selected application examples of this spectroscopy are presented, which include the detections and structural analysis of radicals, molecules, and molecular clusters in a supersonic jet.

IR Spectroscopic Techniques to Study Isolated Biomolecules

“…Although VUV ionization is a more general ionization method, the disadvantage of the method is that conformer selection is compromised. The frequently used 118 nm VUV light, obtained via the tripling of the third harmonic of a Nd:YAG laser in xenon, is capable of producing parent ions of various molecules with ionization energies up to 10.5 eV [85][86][87]. This can, for instance, be used to ionize directly all amino acids.…”

“…Alternatively, using a VUV photon energy sufficient to ionize the molecule, the absorption of an IR photon may open or enhance photodissociation channels upon ionization. As a result, by monitoring the mass-selective ion intensities while scanning the infrared wavelength, an IR-VUV doubleresonance spectrum can be acquired [86,88,89]. …”

Deep Ultraviolet Single‐Photon Ionization Mass Spectrometry

“…It is well known that a synchrotron source and four-wave mixing techniques have the ability to generate tunable DUV light, but the bulky and complicated devices confine their applications for SPI-MS [2]. Alternatively, there is an important finding that 118-nm laser can be generated through high harmonic generation (HHG) of 355-nm laser in a few noble gases such as a Xe-Ar mixture (e.g., 1:10) [64,65]. By allowing the 355-nm laser penetrating through a convenient noble gas cell, the 118-nm DUV lasers have been widely applied for SPI-MS investigations.…”

Gas-phase conformational preference of the smallest saccharide (glycolaldehyde) and its hydrated complexes with bridged hydrogen bonding

“…The recent development of vibrational spectroscopic techniques based on VUV photoionization and its subsequent combination with supersonic-jet expansion techniques (typically pulsed jets) have made it possible to observe the IR spectra of simple and fundamental molecular aggregates in their neutral states. 23,24 This effective approach can provide the information of the geometric structures of molecules, clusters and their intermolecular interactions. 19,[25][26][27][28][29] Furthermore, the vibrational frequencies and intensities of IR absorption, such as modes involving OH, NH, and CH groups, are generally very sensitive probes of hydrogen bonding and other intra-and inter-molecular interactions, which make them excellent probes for investigation of detailed aspects of the structures of biologically relevant ions, radicals, and molecules.…”

“…19,[25][26][27][28][29] Furthermore, the vibrational frequencies and intensities of IR absorption, such as modes involving OH, NH, and CH groups, are generally very sensitive probes of hydrogen bonding and other intra-and inter-molecular interactions, which make them excellent probes for investigation of detailed aspects of the structures of biologically relevant ions, radicals, and molecules. 23 The structure of GA determined by intramolecular hydrogen bonding interaction was previously detected by conventional IR and Raman spectroscopy in the gas phase or in matrix isolation. [30][31][32] The GA-water complex was studied by Fourier transform microwave spectroscopy, where only two lowest conformers referring to cis-cis-water-1 (CC-W-1) and cis-ciswater-2 (CC-W-2) conformer could be found in the gas phase.…”