Excited state energetics of aniline-rare-gas van der Waals complexes

Aniline-Nen and aniline-Arn (n = 1 and 2) complexes were synthesized in continuous and in pulsed supersonic expansions and interrogated by laser-induced fluorescence. Information on the formation kinetics and excited state energetics was obtained

Electron impact mass spectrometry of alkanes in supersonic molecular beams

The electron impact mass spectrometry of straight chain alkanes C8H18-C40H82, squalane, methylstearate, 1-chlorohexadecane, 1-bromohexadecane, and dioctylphthalate was studied by sampling them with supersonic molecular beams. A fly-through Brink-type electron impact ion source was used, utilizing a vacuum background ion filtration technique based on differences between the kinetic energy of the supersonic beam species and that of thermal molecules. The 70-eV electron impact mass spectra of all the alkanes were characterized by a pronounced or dominant molecular weight peak together with all the fragment ions normally exhibited by the standard thermal 70-eV EI mass spectra. In contrast, the NIST library of most of these molecules did not show any molecular weight peak. By eliminating the intramolecular thermal vibrational energy we gained control over the degree of molecular ion fragmentation by the electron energy. At an electron energy of 18 eV the molecular ion dissociation was further reduced considerably, with only a small absolute reduction in the peak height by less than a factor of 2. The effect of vibrational cooling increased with the molecular size and number of atoms. Pronounced differences were observed between the mass spectra of the straight chain triacontane and its branched isomer squalane. Similar mass spectra of octacosane (C28H58) achieved with 70-eV EI in a supersonic molecular beam were obtained with a magnetic sector mass spectrometer by using an electron energy of 14 eV and an ion source temperature of 150 °C. However, this ion source temperature precluded the gas chromatography—mass spectrometry (GC-MS) of octacosane. The GC-MS of alkanes was studied with an ion trap gas chromatograph—mass spectrometer at an ion source temperature of 230 °C. Thermal peak tailing was observed for C20H42 and heavier alkanes, whereas for C28H58 and heavier alkanes the severe peak tailing made quantitative GC-MS impractical. In contrast, no peak tailing existed even with C40H82 for GC-MS in supersonic molecular beams. The minimum detected amount of eicosane (C20H42) was shown to be 60 fg. This was demonstrated by using single ion monitoring with the quadrupole mass analyzer tuned to the molecular weight peak of 282 u. The coupling of electron impact mass spectrometry in supersonic molecular beams with hyperthermal surface ionization and a fast GC-MS inlet is briefly discussed

The pre‐separation of oxygen containing compounds in oxidised heavy paraffinic fractions and their identification by GC‐MS with supersonic molecular beams

The heavy petroleum fractions produced during refining processes need to be upgraded to useable products to increase their value. Hydrogenated heavy paraffinic fractions can be oxidised to produce high value products that contain a variety of oxygenates. These heavy oxygenated paraffinic fractions need to be characterised to enable the control of oxidation processes and to understand product properties. The accurate identification of the oxygenates present in these fractions by electron ionisation (EI) mass spectrometry is challenging due to the complexity of these heavy fractions. Adding to this challenge is the limited applicability of EI mass spectral libraries due to the absence of molecular ions from the EI mass spectra of many oxygenates. The separation of oxygenates from the complex hydrocarbon matrix prior to high temperature GC‐MS (HT‐GC‐MS) analysis reduces the complexity of these fractions and assists in the accurate identification of these oxygenates. Solid phase extraction (SPE) and supercritical fluid chromatography (SFC) were employed as prefractionation techniques. GC‐MS with supersonic molecular beams (SMBs) (also named GC‐MS with cold‐EI) utilises a SMB interface with which EI is done with vibrationally cold sample compounds in a fly‐through ion source (cold‐EI) resulting in a substantial increase in the molecular ion signal intensity in the mass spectrum. This greatly enhances the accurate identification of the oxygenates in these fractions. This study investigated the ionisation behaviour of oxygenated compounds using cold‐EI. The prefractionation by SPE and SFC and the subsequent analysis with GC‐MS with cold‐EI were applied to an oxygenated heavy paraffinic fraction.Supplementary material: Figure A: Mass spectra of n‐eicosane with conventional EI (bottom) and cold‐EI (top). Figure B: Mass spectra of n‐docosane with conventional EI (bottom) and cold‐EI (top). Figure C: Mass spectra of n‐eicosene with conventional EI (bottom) and cold‐EI (top). Figure D: Mass spectra of undecanoic acid with conventional EI (bottom) and cold‐EI (top). Figure E: Mass spectra of tetradecanoic acid with conventional EI (bottom) and cold‐EI (top). Figure F: Mass spectra of 1‐tetradecanol with conventional EI (bottom) and cold‐EI (top). Figure G: Mass spectra of 1‐hexadecanol with conventional EI (bottom) and cold‐EI (top). Figure H: Mass spectra of 1‐heptadecanol with conventional EI (bottom) and cold‐EI (top). Figure I: Mass spectra of 1‐octadecanol with conventional EI (bottom) and cold‐EI (top). Figure J: Mass spectra of 1‐eicosanol with conventional EI (bottom) and cold‐EI (top). Figure K: Mass spectra of 1‐docosanol with conventional EI (bottom) and cold‐EI (top). Figure L: Mass spectra of 2‐hexadecanone at 16.8 min (distribution 1) with conventional EI (bottom) and cold‐EI (top). Figure M: Mass spectra of 2‐heptadecanone at 18.8 min (distribution 1) with conventional EI (bottom) and cold‐EI (top). Figure N: Mass spectra of γ‐stearolactone at 25.1 min (distribution 2) with conventional EI (bottom) and cold‐EI (top). Figure O: Mass spectra of the oxygenate eluting at 45.5 min (distribution 3) with conventional EI (bottom) and cold‐EI (top). Figure P: Mass spectra of the oxygenate eluting at 46.5 min (distribution 3) with conventional EI (bottom) and cold‐EI (top).http://wileyonlinelibrary.com/journal/jms2020-04-01hj2019Chemistr