State-to-state photodissociation of CO2(v2=0 and 1) at 157 nm via the O(1D) + CO(X1Σ+) channel was studied by using the sliced velocity map imaging technique. Both the O(1D) and CO(X1Σ+)...

In this work, the CO2 Vacuum Ultraviolet (VUV) photodissociation dynamics of the dominant O(1D) channel near 155 nm have been studied using Velocity Map Imaging (VMI) technique. Correlations among the...

Short-chain fatty acids (SCFAs) are important metabolites produced by the gut microbiome as a result of the fermentation of non-digestible polysaccharides. The most abundant SCFAs are acetic acid, propionic acid, and butyric acid which make up 95% of this group of metabolites in the gut. Whilst conventional analysis SCFAs is done using either blood or fecal samples, SCFAs can also be detected in exhaled breath using proton transfer reaction-time-of-flight- mass spectrometry (PTR-ToF-MS) using H3O+ for ionization. However, no investigation has been performed to characterize the reactions of SCFAs with H3O+ and with other reagent ions, such as O2+ and NO+. Gas-phase samples of acetic acid, propionic acid, and butyric acid were analyzed with SRI/PTR-ToF-MS under dry and humid conditions. The ions generated and their distribution was determined for each reagent ion. It was found the humidity did not influence the product ion distribution for each SCFA. Using H3O+ as a reagent ion, SRI/PTR-ToF-MS analysis of an exhaled breath sample was performed in real-time to demonstrate the methodology. The presence of SCFAs in exhaled breath was confirmed by thermal desorption—gas chromatography—mass spectrometry (TD-GC-MS). Breath sampling repeatability was within acceptable limits (<15%) for an analytical methodology for each investigated SCFA. Nutritional intervention studies could potentially benefit from real-time monitoring of exhaled SCFAs as an alternative to measuring SCFAs invasively in blood or fecal samples since it is non-invasive, and requires minimal time investment from participants.

The traditional three-electrode Velocity Map Imaging (VMI) electrostatic lens developed by Eppink and Parker has proven to be a useful tool in a wide range of applications in molecular dynamics, including photodissociation experiments taking place in a molecular beam. However, in some other cases, such as crossed molecular beam experiments, the large diameter (typically ∼ 70 mm) of this conventional VMI lens can be inconvenient. We describe here a VMI lens with a much smaller diameter (down to ∼ 20 mm) using tubular electrodes. The performance is evaluated by imaging O + fragments produced by the photodissociation of O 2 at around 225 nm, and by inelastic scattering of NO with Ar. Our results suggest that the recorded images are of acceptable quality compared to those from a standard lens while achieving a fourfold reduction of the VMI lens diameter.