Study of the Synchrotron Photoionization Oxidation of Alpha-Angelica Lactone (AAL) Initiated by O(3P) at 298, 550, and 700 K

In recent years, biofuels have been receiving significant attention because of their potential for decreasing carbon emissions and providing a long-term renewable solution to unsustainable fossil fuels. Currently, lactones are some of the alternatives being produced. Many lactones occur in a range of natural substances and have many advantages over bioethanol. In this study, the oxidation of alpha-angelica lactone initiated by ground-state atomic oxygen, O(3P), was studied at 298, 550, and 700 K using synchrotron radiation coupled with multiplexed photoionization mass spectrometry at the Lawrence Berkeley National Lab (LBNL). Photoionization spectra and kinetic time traces were measured to identify the primary products. Ketene, acetaldehyde, methyl vinyl ketone, methylglyoxal, dimethyl glyoxal, and 5-methyl-2,4-furandione were characterized as major reaction products, with ketene being the most abundant at all three temperatures. Possible reaction pathways for the formation of the observed primary products were computed using the CBS–QB3 composite method.

Combined Experimental and Theoretical Study on Photoionization Cross Sections of Benzonitrile and o/m/p-Cyanotoluene

Toluene is one of the most abundant aromatic compounds in the atmosphere of Titan, and CN group has been regarded as an indicator for observing aromatic compounds in interstellar medium due to the large dipole moments resulted from the CN substituents. In the present work, the photoionization cross-sections (PICS) of benzonitrile and o/m/p-cyanotoluene, which are the products of CN + toluene were obtained at the photon energy ranging from ionization threshold to 14 eV combining experimental and theoretical methods. The synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was employed, and theoretical calculations based on the frozen-core Hartree-Fock approximation and Franck-Condon simulations were carried out to cross-verify the measurements. In addition, the generalized charge decomposition analysis was used to investigate the characteristics of ionized molecular orbitals. Our results are valuable for quantifying these key species (especially by the SVUV-PIMS technique) and estimating related parameters such as dissociation rates in interstellar space.

Combined Experimental and Theoretical Study on Photoionization Cross Sections of Benzonitrile and o/m/p-Cyanotoluene

Toluene is one of the most abundant aromatic compounds in the atmosphere of Titan, and CN group has been regarded as an indicator for observing aromatic compounds in interstellar medium due to the large dipole moments resulted from the CN substituents. In the present work, the photoionization cross-sections (PICS) of benzonitrile and o/m/p-cyanotoluene, which are the products of CN + toluene were obtained at the photon energy ranging from ionization threshold to 14 eV combining experimental and theoretical methods. The synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was employed, and theoretical calculations based on the frozen-core Hartree-Fock approximation and Franck-Condon simulations were carried out to cross-verify the measurements. In addition, the generalized charge decomposition analysis was used to investigate the characteristics of ionized molecular orbitals. Our results are valuable for quantifying these key species (especially by the SVUV-PIMS technique) and estimating related parameters such as dissociation rates in interstellar space.

Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide, an Isoprene-Derived Criegee Intermediate, with Formic Acid: Experiment and Theory

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1‑hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO2 upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis.