Barrier Height Titration by Tunable Photoionization Combined with Chemical Monitoring: Unimolecular Keto/Enol Tautomerization of the Acetamide Cation Radical

Abstract

By using a new “titration” technique, the activation barrier for the strictly unimolecular 1,3‐hydrogen migration 1.+→2.+ has been determined (0.74±0.06 eV; see reaction profile). With this technique the internal energy of 1.+ is controlled by variable photoionization of acetamide and the chemistry of the resulting enol ion 2.+ is then probed by structure‐specific ion–molecule reactions.

Fragment‐controllable mass spectrometric analysis of organic compounds with an infrared laser desorption/tunable vacuum ultraviolet photoionization technique

“…Secondly, fragment-free mass spectrometry can be obtained via nearthreshold photoionization due to the tunability of synchrotron VUV light. 22 Organic mixtures can be identified and characterized in situ with this 'soft' ionization. Moreover, isomers can be distinguished by measuring their photoionization efficiency (PIE) spectrum.…”

Deep Ultraviolet Single‐Photon Ionization Mass Spectrometry

“…In addition to the direct identification capability, the limits of detection using such SPI-MS were found to be as low as ~40 ppb [75]. It is worth mentioning that, although ion mobility-based detection [3][4][5] is widely used for nitro-containing explosives, as known of a screening tool at airports, the conventional technology is not applicable to all explosive-related chemicals; also, any false negative and positive detection rates may be problematic. In this point, SPI-MS could be one of the most promising techniques for trace detection and identification of explosives.…”

“…Simply by measuring the ions abundance relating to their mass-to-charge ratios, mass spectrometry is known as the most powerful tool for identifying the quantity and type of chemicals present in a sample. According to the ionization strategies, mass spectrometry can be classified into hard ionization techniques (typically by direct electron impact, i.e., EI method) [1] and soft ionization techniques which usually include photoionization (PI) [2][3][4][5][6][7][8], chemical ionization (CI) [9,10], matrix-assisted laser desorption/ionization (MALDI) [11], and electrospray ionization (ESI) [12]. Comparing with the EI technique which readily brings rigorous fragmentation for organic compounds, soft ionization techniques find their own advantages of maximal ionization efficiency without using high-energy electron impact.…”

Energy Partitioning in Single-Electron Transfer Events between Gaseous Dications and Their Neutral Counterparts

“…[40][41][42]60 In order to address this particular, still unanswered problem [Scheme 2(c)], at the end of research collaboration we return to the hydrocarbon dications and apply a specific mass-spectrometric technique which is referred to as reactive monitoring with synchrotron radiation. 48,66 In this type of experiment, the bimolecular reactivity of a mass-selected gaseous ion generated via photoionization is probed as a function of the energy of the ionizing photons under otherwise strictly constant conditions. Thereby, the effect of the increasing internal energy content of the nascent photo(di)cations upon ionization with more energetics photons can be probed, which can be used to ensure ground-state reactivity, 23,24,30,31 to probe the involvement of excited states, 67 or to determine the height of activation barriers.…”