UV photodissociation action spectra of protonated formylpyridines.

The first ππ* transition for protonated 2-, 3-, and 4-formylpyridine (FPH) (m/z 108) is investigated by mass spectrometry coupled with photodissociation action spectroscopy at room temperature and 10 K. The photoproduct ions are detected over 35 000-43 000 cm, and the major product channel for 3-FPH and 4-FPH is the loss of CO forming protonated pyridine at m/z 80. For 2-FPH, the CO loss product is present but a more abundant photoproduct arises from the loss of CHO to form m/z 78.

Actinic Wavelength Action Spectroscopy of the IO Reaction Intermediate.

Iodinate anions are important in the chemistry of the atmosphere where they are implicated in ozone depletion and particle formation. The atmospheric chemistry of iodine is a complex overlay of neutral-neutral, ion-neutral, and photochemical processes, where many of the reactions and intermediates remain poorly characterized. This study targets the visible spectroscopy and photostability of the gas-phase hypoiodite anion (IO), the initial product of the I + O reaction, by mass spectrometry equipped with resonance-enhanced photodissociation and total ion-loss action spectroscopies.

Picosecond excited-state lifetimes of protonated indazole and benzimidazole: The role of the N-N bond.

Certain chemical groups give rise to characteristic excited-state deactivation mechanisms. Here, we target the role of a protonated N-N chemical group in the excited-state deactivation of protonated indazole by comparison to its isomer that lacks this group, protonated benzimidazole. Gas-phase protonated indazole and protonated benzimidazole ions are investigated at room temperature using picosecond laser pump-probe photodissociation experiments in a linear ion-trap.

Laser Photodissociation Action Spectroscopy for the Wavelength-Dependent Evaluation of Photoligation Reactions.

The nitrile imine-mediated tetrazole-ene cycloaddition is a widely used class of photoligation. Optimizing the reaction outcome requires detailed knowledge of the tetrazole photoactivation profile, which can only partially be ascertained from absorption spectroscopy, or otherwise involves laborious reaction monitoring in solution. Photodissociation action spectroscopy (PDAS) combines the advantages of optical spectroscopy and mass spectrometry in that only absorption events resulting in a mass change are recorded, thus revealing the desired wavelength dependence of product formation.

Electrostatically Tuning the Photodissociation of the Irgacure 2959 Photoinitiator in the Gas Phase by Cation Binding.

The low-lying electronic states of Irgacure 2959, a Norrish-type I photoinitiator, complexed with a single metal cation are investigated in the gas phase by photodissociation action spectroscopy. Analysis of the band shifts using quantum chemical calculations (TD-DFT and SCS-CC2) reveals the underlying influence of the charge on the key electronic energy levels. Since the cations (H, Li, Na, K, Zn, Ca, and Mg) bind at varying distances, the magnitude of the electric field at the center of the chromophore due to the cation is altered, and this shifts the electronic states by different amounts.

Next-generation derivatization reagents optimized for enhanced product ion formation in photodissociation-mass spectrometry of fatty acids.

Ultraviolet-photodissociation (UVPD) mass spectrometry is an emerging analytical tool for structural elucidation of biomolecules including lipids. Gas phase UVPD of ionised fatty acids (FAs) can promote fragmentation that is diagnostic for molecular structure including the regiochemistry of carbon-carbon double bonds and methyl branching position(s). Typically, however, lipids exhibit poor conversion to photoproducts under UVPD and thus require longer integration times to achieve the signal-to-noise required for structural assignments.

Discrimination between Protonation Isomers of Quinazoline by Ion Mobility and UV-Photodissociation Action Spectroscopy.

The influence of oriented electric fields on chemical reactivity and photochemistry is an area of increasing interest. Within a molecule, different protonation sites offer the opportunity to control the location of charge and thus orientation of electric fields. New techniques are thus needed to discriminate between protonation isomers in order to understand this effect.

Gas phase reactions of iodide and bromide anions with ozone: evidence for stepwise and reversible reactions.

Despite the impacts - both positive and negative - of atmospheric ozone for life on Earth, there remain significant gaps in our knowledge of the products, mechanisms and rates of some of its most fundamental gas phase reactions. This incomplete understanding is largely due to the experimental challenges involved in the study of gas-phase reactions of ozone and, in particular, the identification of short-lived reaction intermediates. Here we report direct observation of the stepwise reaction of the halide anions iodide (I-) and bromide (Br-) with ozone to produce XO3- (where X = I and Br, respectively).

Selecting and identifying gas-phase protonation isomers of nicotineH using combined laser, ion mobility and mass spectrometry techniques.

The detection and assignment of protonation isomers, termed protomers, of gas-phase ions remains a challenge in mass spectrometry. With the emergence of ion-mobility techniques combined with tuneable-laser photodissociation spectroscopy, new experimental combinations are possible to now meet this challenge. In this paper, the differences in fragmentation and electronic spectroscopy of singly protonated (S)-nicotine (nicH+) ions are analysed using action spectroscopy in the ultraviolet region and field asymmetric ion mobility spectrometry (FAIMS).