Abstract. Proton transfer reaction (PTR) is a commonly applied ionization technique for mass spectrometers, in which hydronium ions (H3O+) transfer a proton to analytes with higher proton affinities than the water molecule. This method has most commonly been used to quantify volatile hydrocarbons, but later-generation PTR instruments have been designed for better throughput of less volatile species, allowing detection of more functionalized molecules as well. For example, the recently developed Vocus PTR time-of-flight mass spectrometer (PTR-TOF) has been shown to agree well with an iodide-adduct-based chemical ionization mass spectrometer (CIMS) for products with 3–5 O atoms from oxidation of monoterpenes (C10H16). However, while several different types of CIMS instruments (including those using iodide) detect abundant signals also at “dimeric” species, believed to be primarily ROOR peroxides, no such signals have been observed in the Vocus PTR even though these compounds fulfil the condition of having higher proton affinity than water. More traditional PTR instruments have been limited to volatile molecules as the inlets have not been designed for transmission of easily condensable species. Some newer instruments, like the Vocus PTR, have overcome this limitation but are still not able to detect the full range of functionalized products, suggesting that other limitations need to be considered. One such limitation, well-documented in PTR literature, is the tendency of protonation to lead to fragmentation of some analytes. In this work, we evaluate the potential for PTR to detect dimers and the most oxygenated compounds as these have been shown to be crucial for forming atmospheric aerosol particles. We studied the detection of dimers using a Vocus PTR-TOF in laboratory experiments, as well as through quantum chemical calculations. Only noisy signals of potential dimers were observed during experiments on the ozonolysis of the monoterpene α-pinene, while a few small signals of dimeric compounds were detected during the ozonolysis of cyclohexene. During the latter experiments, we also tested varying the pressures and electric fields in the ionization region of the Vocus PTR-TOF, finding that only small improvements were possible in the relative dimer contributions. Calculations for model ROOR and ROOH systems showed that most of these peroxides should fragment partially following protonation. With the inclusion of additional energy from the ion–molecule collisions driven by the electric fields in the ionization source, computational results suggest substantial or nearly complete fragmentation of dimers. Our study thus suggests that while the improved versions of PTR-based mass spectrometers are very powerful tools for measuring hydrocarbons and their moderately oxidized products, other types of CIMS are likely more suitable for the detection of ROOR and ROOH species.

The present study reports for the first time the use of a thiol-functionalized graphene oxide nanocatalyst with impressive activity (>10(5)-fold) in dephosphorylation reactions. The innovative and recyclable nanocatalyst has potential in designing artificial enzymes with targeted multifunctionalities and in detoxification of organophosphorus agents.

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The cyclic imine 1,2,3,6-tetrahydropyrazine (THPyz) has been observed to be the major atmospheric photo-oxidation product of piperazine, a widely used solvent in carbon-capture technology, yet little is known about its own fate. Very few studies have focused on the atmospheric chemistry of imines in general, despite consistently appearing as major products of amine oxidation. In this work, we explore the reaction mechanism of THPyz oxidation initiated by OH radicals, as well as the fate of the first-generation C-centered (alkyl) and N-centered (aminyl) radical products, with quantum chemistry and theoretical kinetics methods. We predict that the major initial reaction steps involve H-abstraction from a carbon adjacent to the amine nitrogen, leading to subsequent formation of a second imine function via the O 2 -addition/HO 2 -elimination pathway. Calculated yields of potentially hazardous products are low but non-negligible. Typically carcinogenic compounds, nitrosamines and nitramines, are expected to have a maximum yield of ∼7% and ∼11%, respectively, under high NO x regimes, considering the uncertainties in the obtained rates. Low yield (1−14%) of an isocyanate is also predicted, formed in a channel following initial H-abstraction from the imine carbon. The aminyl radical formed from OH radical addition to the imine carbon undergoes fast C−C bond scission, leading to an imidic acid. These pathways are minor for OH radical oxidation of THPyz but could be more competitive for other Schiff bases.

Organic peroxy radicals (RO2) are key intermediates in atmospheric chemistry and can undergo a large variety of both uni- and bimolecular reactions. One of the least understood reaction classes of RO2 are their self- and cross-reactions: RO2 + R′O2. In our previous work, we have investigated how RO2 + R′O2 reactions can lead to the formation of ROOR′ accretion products through intersystem crossings and subsequent recombination of a triplet intermediate complex 3(RO···OR′). Accretion products can potentially have very low saturation vapor pressures, and may therefore participate in the formation of aerosol particles. In this work, we investigate the competing H-shift channel, which leads to the formation of more volatile carbonyl and alcohol products. This is one of the main, and sometimes the dominant, RO2 + R′O2 reaction channels for small RO2. We investigate how substituents (R and R′ groups) affect the H-shift barriers and rates for a set of 3(RO···OR′) complexes. The variation in barrier heights and rates is found to be surprisingly small, and most computed H-shift rates are fast: around 108–109 s–1. We find that the barrier height is affected by three competing factors: (1) the weakening of the breaking C–H bond due to interactions with adjacent functional groups; (2) the overall binding energy of the 3(RO···OR′), which tends to increase the barrier height; and (3) the thermodynamic stability of the reaction products. We also calculated intersystem crossing rate coefficients (ISC) for the same systems and found that most of them were of the same order of magnitude as the H-shift rates. This suggests that both studied channels are competitive for small and medium-sized RO2. However, for complex enough R or R′ groups, the binding energy effect may render the H-shift channel uncompetitive with intersystem crossings (and thus ROOR′ formation), as the rate of the latter, while variable, seems to be largely independent of system size. This may help explain the experimental observation that accretion product formation becomes highly effective for large and multifunctional RO2.