Cysteine (Cys) is unique due to its highly reactive thiol group. It often regulates the biological function of proteins by acting as the redox site. Despite its biological significance, however, the valence electronic structure of Cys under the aqueous environments remains unavailable. Here, we report the VUV photoelectron spectroscopy of Cys aqueous aerosols via a newly built aerosol VUV photoelectron spectroscopy apparatus. The photoelectron spectra of Cys show distinct band shapes at varying pH conditions, reflecting the altered molecular orbital characters when its dominating form changes. The ionization energy of Cys is determined to be 8.98 ± 0.05 eV at low pH. A new feature at a binding energy of 6.97 ± 0.05 eV is observed at high pH, suggesting that the negative charge on the thiolate group becomes the first electron to be removed upon ionization. This work implies that when Cys is involved in redox processes, the charge transfer mechanism may be entirely altered under different pH conditions.

Synchrotron radiation is used to excite Ar to the intermediate states 3p 1/2 5 ͑3dЈ͓3 / 2͔ 1 , 5dЈ͓3 / 2͔ 1 , 5sЈ͓1 / 2͔ 1 , 7sЈ͓1 / 2͔ 1 ͒ and 3p 3/2 5 ͑6d͓1 / 2͔ 1 , 6d͓3 / 2͔ 1 , 8s͓3 / 2͔ 1 ͒, then excited by lasers to the autoionizing Rydberg series 3p 1/2 5 npЈ ͓͑1 / 2͔ 0,1 , ͓3 / 2͔ 1,2 ͒ and nfЈ͓5 / 2͔ 2. For the intermediate states of 5sЈ, 7sЈ, and 8s, the npЈ ͓͑1 / 2͔ 0 and ͓3 / 2͔ 2 ͒ series are observed with high intensity but not the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series when the polarization vectors of two light beams are in parallel; but when they are in orthogonal, the npЈ͓1 / 2͔ 0 series disappears, the npЈ͓3 / 2͔ 2 intensity remains, and the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series show up strongly. The intensity distribution of the npЈ series strongly depends on the intermediate state. The spectra of the npЈ series are assigned according to their intensity variation with the polarization vectors. The quantum defects determined for the series npЈ͓1 / 2͔ 0 ͑n =11-57͒, npЈ͓3 / 2͔ 2 ͑n =11-65͒, npЈ͓3 / 2͔ 1 ͑n =11-31͒, and nfЈ͓5 / 2͔ 2 ͑n =9-74͒ are 1.611Ϯ 0.011, 1.683Ϯ 0.013, 1.688Ϯ 0.010, and 0.016Ϯ 0.005, respectively. Our values are in excellent agreement with theoretical prediction. The spectral line shapes of autoionizing Rydberg states are analyzed with a Beutler-Fano profile. Reduced autoionization linewidths for the npЈ͓1 / 2͔ 0 ͑n =11-16͒ series vary in the range 2549-4145 cm −1 , and the nfЈ͓5 / 2͔ 2 ͑n =9-11͒ series in 186-247 cm −1 in reasonable agreement with theoretical prediction.

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The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.

This work investigates the pyrolysis of n-butylbenzene, which widely exists in transportation fuels and their surrogate mixtures. Both reactive and stable pyrolysis products were comprehensively detected with synchrotron vacuum ultraviolet photoionization mass spectrometry. Their mole fractions versus temperature were also evaluated at 30, 150, and 760 Torr. A kinetic model of n-butylbenzene pyrolysis was developed, and new data were used to validate the model. On the basis of the modeling analysis, the benzylic C–C bond dissociation that forms the benzyl radical and the propyl radical was found to be a key decomposition reaction of n-butylbenzene at all investigated pressures, whereas H abstraction provided increasing contributions with increasing pressure. Compared with small alkylbenzenes, such as toluene and ethylbenzene, n-butylbenzene demonstrates different pyrolysis characteristics and chemistry because of the existence of its long alkyl side chain. n-Butylbenzene has a higher pyrolysis reactivity and lower decomposition temperature regions, which inhibit the further decomposition of the benzyl radical and the formation of highly unsaturated C2–C4 products. As a result, conventional combination reactions between aromatic radicals and highly unsaturated C2–C4 species are only minor formation pathways for indene and naphthalene in n-butylbenzene pyrolysis, while fuel-specific pathways become crucial instead. Furthermore, combination reactions involving the benzyl radical and the phenyl radical are crucial for the formation of many PAHs, especially phenanthrene and fluorene. The results in this work reveal the strong influence of side-chain length on the pyrolysis chemistry of alkylbenzenes and indicate a further need for exploring the influences of other structural features.