Search for: All records

The recent discovery and spectroscopic measurements of${}^{27}\mathrm{O}$and${}^{28}\mathrm{O}$suggests the disappearance of the$N=20$shell structure in these neutron-rich oxygen isotopes.

We measured one- and two-proton removal cross sections from${}^{27}\mathrm{F}$and${}^{29}\mathrm{Ne}$, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations.

The invariant mass technique was used to reconstruct the two-body (${}^{24}\mathrm{O}+n$) and three-body (${}^{24}\mathrm{O}+2n$) decay energies from knockout reactions of${}^{27}\mathrm{F}$(106.2 MeV/u) and${}^{29}\mathrm{Ne}$(112.8 MeV/u) beams impinging on a${}^9\mathrm{Be}$target.

The one-proton removal from${}^{27}\mathrm{F}$strongly populated the ground state of${}^{26}\mathrm{O}$and the extracted cross section of$3.4_{-1.5}^{+0.3}$mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from${}^{29}\mathrm{Ne}$an upper limit of 0.08 mb was extracted for populating states in${}^{27}\mathrm{O}$decaying though the ground state of${}^{26}\mathrm{O}$.

The measured upper limit for the population of the ground state of${}^{26}\mathrm{O}$in the two-proton removal reaction from${}^{29}\mathrm{Ne}$indicates a significant difference in the underlying nuclear structure of${}^{27}\mathrm{F}$and${}^{29}\mathrm{Ne}$.

Published by the American Physical Society2024 

Abstract. Short-lived highly reactive atmospheric species, such as organic peroxy radicals (RO2) and stabilized Criegee intermediates (SCIs), play an important role in controlling the oxidative removal and transformation of many natural and anthropogenic trace gases in the atmosphere. Direct speciated measurements of these components are extremely helpful for understanding their atmospheric fate and impact. We describe thedevelopment of an online method for measurements of SCIs and RO2 inlaboratory experiments using chemical derivatization and spin trappingtechniques combined with H3O+ and NH4+ chemicalionization mass spectrometry (CIMS). Using chemical derivatization agentswith low proton affinity, such as electron-poor carbonyls, we scavenge allSCIs produced from a wide range of alkenes without depleting CIMS reagentions. Comparison between our measurements and results from numericmodeling, using a modified version of the Master Chemical Mechanism, showsthat the method can be used for the quantification of SCIs in laboratoryexperiments with a detection limit of 1.4×107 molecule cm−3for an integration time of 30 s with the instrumentation used in this study. Weshow that spin traps are highly reactive towards atmospheric radicals andform stable adducts with them by studying the gas-phase kinetics of thereaction of spin traps with the hydroxyl radical (OH). We also demonstrate that spin trapadducts with SCIs and RO2 can be simultaneously probed and quantified under laboratory conditions with a detection limit of 1.6×108 molecule cm−3 for an integration time of 30 s for RO2 species with the instrumentation used in this study. Spin trapping prevents radical secondary reactions and cycling, ensuring that measurements are not biased by chemical interferences, and it can be implemented for detecting RO2 species in laboratory studies and potentially in the ambient atmosphere. 

Abstract. An improved understanding of the fate and properties of atmospheric aerosolparticles requires a detailed process-level understanding of fundamentalfactors influencing the aerosol, including partitioning of aerosolcomponents between the gas and particle phases. Laboratory experiments withlevitated particles provide a way to study fundamental aerosol processesover timescales relevant to the multiday lifetime of atmospheric aerosolparticles, in a controlled environment in which various characteristicsrelevant to atmospheric aerosol can be prepared (e.g., highsurface-to-volume ratio, highly concentrated or supersaturated solutions,changes to relative humidity). In this study, the four-carbon unsaturatedcompound butenedial, a dialdehyde produced by oxidation of aromaticcompounds that undergoes hydration in the presence of water, was used as amodel organic aerosol component to investigate different factors affectinggas–particle partitioning, including the role of lower-volatility“reservoir” species such as hydrates, timescales involved inequilibration between higher- and lower-volatility forms, and the effect ofinorganic salts. The experimental approach was to use a laboratory systemcoupling particle levitation in an electrodynamic balance (EDB) withparticle composition measurement via mass spectrometry (MS). In particular,by fitting measured evaporation rates to a kinetic model, the effectivevapor pressure was determined for butenedial and compared under differentexperimental conditions, including as a function of ambient relativehumidity and the presence of high concentrations of inorganic salts. Even underdry (RH<5 %) conditions, the evaporation rate of butenedial isorders of magnitude lower than what would be expected if butenedial existedpurely as a dialdehyde in the particle, implying an equilibrium stronglyfavoring hydrated forms and the strong preference of certain dialdehydecompounds to remain in a hydrated form even under lower water contentconditions. Butenedial exhibits a salting-out effect in the presence ofsodium chloride and sodium sulfate, in contrast to glyoxal. The outcomes ofthese experiments are also helpful in guiding the design of future EDB-MSexperiments.