International audienceThe ignition dynamics of a CH4: O2: N2: Ar = 1: 4: 15: 80 mixture by a high-voltage nanosecond discharge is simulated numerically with allowance for experimental data on the dynamics of the discharge current and discharge electric field. The calculated induction time agrees well with experimental data. It is shown that active particles produced in the discharge at a relatively low deposited energy can reduce the induction time by two orders of magnitude. Comparison of simulation results for mixtures with and without nitrogen shows that addition of nitrogen to the mixture leads to a decrease in the average electron energy in the discharge and gives rise to new mechanisms for accumulation of oxygen atoms due to the excitation of nitrogen electronic states and their subsequent quenching in collisions with oxygen molecules. Acceleration of the discharge-initiated ignition is caused by a faster initiation of chain reactions due to the production of active particles, first of all oxygen atoms, in the discharge
Here we report the observation that, depending on the solvent used for the electrospray, 2-nitrophloroglucinol undergoes a deprotona- tion from different sites forming two tautomeric gas phase ions. Those ions differ bythe collision-induced dissociation [CID] spectra and by the gas phase hydrogen/deuterium (H/D) exchange kinetic. We performed H/D exchange in the electrospray ionization (ESI) source by saturation ESI region with vapors of deuterated solvent (D20). It was observed that [2-nitrophloroglucinol-H]- exchanges two -OH hydrogens when MeOD is used as the spray solvent but when the spray solvent is 50:50 MeOD/DO20 we observed an additional two H/D exchanges at the aromatic ring. We propose that the reaction occurs via a keto-enolt tautomerization mechanism which was found to be energetically favorable.
It has previously been reported that different conformations of oligonucleotides may be detected using a gas-phase hydrogen/deuterium (H/D) exchange performed in the collision cell of a mass spectrometer. The presence of different conformers was postulated based on the bimodal shape of the deuterium distribution and on the ion mobility spectrometry data. Here we implement an in-electrospray ionization source H/D exchange to detect the different conformations of oligonucleotides in the region of ion formation. We observed that the number of H/D exchanges depends considerably on the temperature of the desolvating capillary and varies from 25% at 50°C to 80% at 450°C, but no bimodality in the shape of the deuterium distribution was observed. Such results indicate that in the region of ion formation different conformations of oligonucleotide ions rapidly interconvert one into another.
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