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Î.sup.3 -carene is a prominent monoterpene in the atmosphere, contributing significantly to secondary organic aerosol (SOA) formation. However, knowledge about Î.sup.3 -carene oxidation pathways, particularly regarding their ability to form highly oxygenated organic molecules (HOMs), is still limited. In this study, we present HOM measurements during Î.sup.3 -carene ozonolysis under various conditions in two simulation chambers. We identified numerous HOMs (monomers: C.sub.7-10 H.sub.10-18 O.sub.6-14 ; dimers: C.sub.17-20 H.sub.24-34 O.sub.6-18) using a chemical ionization mass spectrometer (CIMS). Î.sup.3 -carene ozonolysis yielded higher HOM concentrations than α-pinene, with a distinct distribution, indicating differences in formation pathways. All HOM signals decreased considerably at lower temperatures, reducing the estimated molar HOM yield from â¼ 3 % at 20 °C to â¼ 0.5 % at 0 °C. Interestingly, the temperature change altered the HOM distribution, increasing the observed dimer-to-monomer ratios from roughly 0.8 at 20 °C to 1.5 at 0 °C. HOM monomers with six or seven O atoms condensed more efficiently onto particles at colder temperatures, while monomers with nine or more O atoms and all dimers condensed irreversibly even at 20 °C. Using the gas- and particle-phase chemistry kinetic multilayer model ADCHAM, we were also able to reproduce the experimentally observed HOM composition, yields, and temperature dependence.

This paper describes instrumentation and procedures developed to measure H.sub.2 and Ne in polar ice core samples. Gases are extracted from ice core samples by melting under vacuum. Measurements are conducted by gas chromatographic separation with detection by a pulsed helium ionization detector (He-PDD). The analytical system was developed for field analysis of ice core samples immediately after drilling. This minimizes the potential for exchange of these highly permeable gases between the ice core and the modern atmosphere. The design, operation, and performance of the instrument are discussed using data from the initial deployment to Summit, Greenland. The results demonstrate the feasibility of ice core analysis of H.sub.2 and Ne with precision of 8.6 % and 10.2 % (1Ï) respectively.

Ab initio investigation of the spectroscopic constants, bond dissociation energies of germanium monohalides, germanium dihalides and their ionic systems, viz. GeX, GeX.sup.-, GeX.sup.+, GeX.sub.2, GeX.sub.2.sup.- and GeX.sub.2.sup.+ (X = F, Cl, Br and I) have been carried out using correlation consistent triple-zeta basis sets for F and Cl and similar triple-zeta basis sets with RECPs for Ge, Br and I atoms. Geometry and frequency of all the neutral and ionic systems of germanium halides are obtained using MP2, CCSD(T) and QCISD(T) methods. The energetics are obtained at the CCSD(T)//MP2, QCISD(T)//MP2, CCSD(T) and QCISD(T) levels. Electron affinity (EA) and ionization potential (IP) of the monohalides and dihalides are reported to be consistent with the data available in literature. The bond dissociation energies (BDEs) to various dissociation asymptotes for most of the ionic systems are to be reported new in literature. The BDEs of the neutral germanium dihalides GeX.sub.2 are calculated by using the BDEs of GeX.sub.2.sup.- and GeX.sub.2.sup.+ ions and EA and IP of the associated neutral systems. A good agreement is found between the calculated values and the data wherever available. The BDEs of GeX.sub.2 for higher halogen member are reported to be new in literature. The enthalpies of formation for atomization and ionization of the neutral GeX.sub.2 dihalides are also reported here. The enthalpies of ionization are reported first time in literature and found consistent with other group IV dihalides. The reported molecular properties may be helpful to understand the chemistry involved in the plasma-assisted fabrication process of the Ge-based modern microelectronic devices, as well as will serve as a future reference.

The reaction between methanol radical cations and methane, producing methyl radicals and protonated methanol, is pivotal to both astrochemical and atmospheric processes. Methanol and methane are the most abundant organic molecules in space and Earth’s atmosphere and central to molecular synthesis under different environmental conditions. Here, we present a combined experimental and theoretical investigation of the ion–molecule reaction between CH[sub.3]OH[sup.•+] and CH[sub.4]. The study explores the reaction mechanism and energetics under ionized conditions utilizing quantum chemical methods and experimental data. The findings reveal that the reaction’s non-thermal behavior becomes pronounced when CH[sub.3]OH[sup.•+] is vibrationally excited by photon absorption above the ionization threshold, as can happen in the presence of ionizing agents like cosmic rays. Conversely, in thermal equilibrium conditions, the reaction accelerates as temperatures decrease, as suggested by canonical rate coefficient calculations. The products can initiate further chemical reactions, shaping molecular networks in the interstellar medium and affecting atmospheric trace gas balances.

The ability to image invisible gases has applications in industrial and environmental monitoring settings, but is technologically challenging to embed in a low-cost device. For example, imaging methane gas has applications among gas utility companies for routine pipeline monitoring and storage facility inspection. Video rate gas imaging conveys the direction of dispersal and hence the location of a leak source, helping users to improve their efficiency of response to hazardous events. Conventional approaches to detecting methane gas leaks have mainly been based upon flame ionization detectors, but such technology measures concentration at only a single point, making locating the source of the leak a difficult and slow process. One approach to gas imaging is to use a focal plane array (FPA) to image the methane directly. As an alternative to using a FPA, it is possible to use a single photo-detector and an infrared laser, wavelength tuned to an absorption line of the gas, which is raster scanned over a scene and the resulting backscattered light collected and measured.

Mechanistic arguments relative to matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) address observations that predominately singly charged ions are detected. However, recently a matrix assisted laser ablation method, laserspray ionization (LSI), was introduced that can use the same sample preparation and laser as MALDI, but produce highly charged ions from proteins. In MALDI, ions are generated from neutral molecules by the photon energy provided to a matrix, while in LSI ions are produced inside a heated inlet tube linking atmospheric pressure and the first vacuum region of the mass spectrometer. Some LSI matrices also produce highly charged ions with MALDI ion sources operated at intermediate pressure or high vacuum. The operational similarity of LSI to MALDI, and the large difference in charge states observed by these methods, provides information of fundamental importance to proposed ionization mechanisms for LSI and MALDI. Here, we present data suggesting that the prompt and delayed ionization reported for vacuum MALDI are both fast processes relative to producing highly charged ions by LSI. The energy supplied to produce these charged clusters/droplets as well as their size and time available for desolvation are determining factors in the charge states of the ions observed. Further, charged droplets/clusters may be a common link for ionization of nonvolatile compounds by a variety of MS ionization methods, including MALDI and LSI.

Revealing structural isomerism in nanoparticles using single-crystal X-ray crystallography remains a largely unresolved task, although it has been theoretically predicted with some experimental clues. Here we report a pair of structural isomers, Au38T and Au38Q , as evidenced using electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and indisputable single-crystal X-ray crystallography. The two isomers show different optical and catalytic properties, and differences in stability. In addition, the less stable Au38T can be irreversibly transformed to the more stable Au38Q at 50 °C in toluene. This work may represent an important advance in revealing structural isomerism at the nanoscale.

Positive-ion laser desorption/ionization (LDI) of fullerenes contained in soot as produced by the Krätschmer-Huffman process delivers a wide range of fullerene molecular ions from C56+• to above C300+•. Here, the collision cross section (CCS) values of those fullerene molecular ions are determined using a trapped ion mobility-quadrupole-time-of-flight (TIMS-Q-TOF) instrument. While CCS values in the range from C60+• to C96+• are already known with high accuracy, those of ions from C98+• onward had yet to be determined. The fullerene molecular ions covered in this work have CCS values from about 200 to 440 Å2. The fullerene molecular ion series is evenly spaced at C2 differences in composition, and thus, small CCS differences of just 2.2–3.5 Å2 were determined across the entire range. Fullerene M+• ions may be employed as mobility calibrants, in particular, when very narrow 1/K0 ranges are being analyzed to achieve high TIMS resolving power. In addition, due to the simple elemental composition, M+• ions of fullerenes could also serve for mass calibration. This study describes the determination of CCS values of fullerene molecular ions from C56+• to C240+• and the application of ions from C56+• to C220+• to calibrate the ion mobility scale of a Bruker timsTOFflex instrument in any combination of LDI, matrix-assisted laser desorption/ionization (MALDI), and electrospray ionization (ESI) modes in the CCS range from about 200 to 420 Å2. This use was exemplified along with ions from Agilent Tune Mix, leucine-enkephalin, angiotensin I, angiotensin II, and substance P.

The systematic study of the temperature and pressure dependence of matrix-assisted ionization (MAI) led us to the discovery of the seemingly impossible, initially explained by some reviewers as either sleight of hand or the misinterpretation by an overzealous young scientist of results reported many years before and having little utility. The “magic” that we were attempting to report was that with matrix assistance, molecules, at least as large as bovine serum albumin (66 kDa), are lifted into the gas phase as multiply charged ions simply by exposure of the matrix:analyte sample to the vacuum of a mass spectrometer. Applied heat, a laser, or voltages are not necessary to achieve charge states and ion abundances only previously observed with electrospray ionization (ESI). The fundamentals of how solid phase volatile or nonvolatile compounds are converted to gas-phase ions without added energy currently involves speculation providing a great opportunity to rethink mechanistic understanding of ionization processes used in mass spectrometry. Improved understanding of the mechanism(s) of these processes and their connection to ESI and matrix-assisted laser desorption/ionization may provide opportunities to further develop new ionization strategies for traditional and yet unforeseen applications of mass spectrometry. This Critical Insights article covers developments leading to the discovery of a seemingly magic ionization process that is simple to use, fast, sensitive, robust, and can be directly applied to surface characterization using portable or high performance mass spectrometers. Graphical Abstract ᅟ

Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (-50 and -30 .sup.\" C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization-atmospheric pressure interface-time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C.sub.8-10 monomers and C.sub.18-20 dimers as the major compounds in the particles (diameter up to ⼠100 nm). Particularly, for the system with isoprene added, C.sub.5 (C.sub.5 H.sub.10 O.sub.5-7) and C.sub.15 compounds (C.sub.15 H.sub.24 O.sub.5-10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C.sub.5 and C.sub.15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J.sub.1.7 nm) and compared with previous studies, we found lower J.sub.1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.