Jiuzhong Yang

The vacuum ultraviolet beamline/endstations at NSRL dedicated to combustion research

An undulator-based vacuum ultraviolet (VUV) beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLS II), and could deliver photons in the 5-21 eV range, with a photon flux of 10(13) photons s(-1) at 10 eV when the beam current is 300 mA. The monochromator of the beamline is equipped with two gratings (200 lines mm(-1) and 400 lines mm(-1)) and its resolving power is 3900 at 7.3 eV for the 200 lines mm(-1) grating and 4200 at 14.6 eV for the 400 lines mm(-1) grating. The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflectron time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented here. The ability to detect reactive intermediates (e.g. H, O, OH and hydroperoxides) is advantageous in combustion chemistry research.

Photoionization Mass Spectrometric and Kinetic Modeling of Low‐pressure Pyrolysis of Benzene

Pyrolysis of benzene at 30 Torr was studied from 1360 K to 1820 K in this work. Synchrotron vacuum ultraviolet photoionization mass spectrometry was employed to detect the pyrolysis products such as radicals, isomers and polycyclic aromatic hydrocarbons, and measure their mole fraction profiles versus temperature. A low‐pressure pyrolysis model of benzene was developed and validated by the experimental results. Rate of production analysis was performed to reveal the major reaction networks in both fuel decomposition and aromatic growth processes. It is concluded that benzene is mainly decomposed via H‐abstraction reaction to produce phenyl and partly decomposed via unimolecular decomposition reactions to produce propargyl or phenyl. The decomposition process stops at the formation of acetylene and polyyne species like diacetylene and 1,3,5‐hexatriyne due to their high thermal stabilities. Besides, the aromatic growth process in the low‐pressure pyrolysis of benzene is concluded to initiate from benzene and phenyl, and is controlled by the even carbon growth mechanism due to the inhibited formation of C5 and C7 species which play important roles in the odd carbon growth mechanism.

Extractive Atmospheric Pressure Photoionization (EAPPI) Mass Spectrometry: Rapid Analysis of Chemicals in Complex Matrices.

AbstractExtractive atmospheric pressure photoionization (EAPPI) mass spectrometry was designed for rapid qualitative and quantitative analysis of chemicals in complex matrices. In this method, an ultrasonic nebulization system was applied to sample extraction, nebulization, and vaporization. Mixed with a gaseous dopant, vaporized analytes were ionized through ambient photon-induced ion–molecule reactions, and were mass-analyzed by a high resolution time-of-flight mass spectrometer (TOF-MS). After careful optimization and testing with pure sample solution, EAPPI was successfully applied to the fast screening of capsules, soil, natural products, and viscous compounds. Analysis was completed within a few seconds without the need for preseparation. Moreover, the quantification capability of EAPPI for matrices was evaluated by analyzing six polycyclic aromatic hydrocarbons (PAHs) in soil. The correlation coefficients (R2) for standard curves of all six PAHs were above 0.99, and the detection limits were in the range of 0.16–0.34 ng/mg. In addition, EAPPI could also be used to monitor organic chemical reactions in real time. Graphical Abstractᅟ

Construction and performance of combustion beamline at NSRL

An undulator-based VUV beamline BL03U is constructed at the National Synchrotron Radiation Laboratory. Optical design and performance test results are presented in this paper. The monochromator is a Czerny–Turner configuration with a toroidal collimating mirror, two plane gratings, and a toroidal focusing mirror. Plane gratings with line densities of 200 and 400 l/mm are used to cover the photon energy range of 5–21 eV. A gas absorption spectrum is used to evaluate the beamline performance. The photon energy resolving power (E/ΔE) of the beamline is approximately 3900 at 7.3 eV for the 200 l/mm grating and 4200 at 14.6 eV for the 400 l/mm grating. The photon flux is approximately 5×1012 photons/s/300 mA at energy of 10 eV.

Novel applications of synchrotron VUV photoionization mass spectrometry in combustion and energy research

Combustion of fossil fuels provides more than 80% of the global energy supply nowadays. However, the rapid consumption of fossil fuels has raised great public concerns on energy sustainability and environmental security. Since chemical reactions play the crucial role in combustion and other thermal chemical processes in energy conversion, prior understanding of the chemical reaction mechanisms in these processes is essential for exploring new techniques to improve combustion efficiency and reduce pollutant emissions. This paper reviews our recent efforts in the development of new methods and instruments with synchrotron vacuum ultraviolet (VUV) photoioni- zation mass spectrometry and their applications in combustion and energy research, and presents perspectives of novel methods and applications in the near future.Combustion of fossil fuels provides more than 80% of the global energy supply nowadays. However, the rapid consumption of fossil fuels has raised great public concerns on energy sustainability and environmental security. Since chemical reactions play the crucial role in combustion and other thermal chemical processes in energy conversion, prior understanding of the chemical reaction mechanisms in these processes is essential for exploring new techniques to improve combustion efficiency and reduce pollutant emissions. This paper reviews our recent efforts in the development of new methods and instruments with synchrotron vacuum ultraviolet(VUV) photoioni- zation mass spectrometry and their applications in combustion and energy research, and presents perspectives of novel methods and applications in the near future.

Experimental and Theoretical Study on Pyrolysis of Isopsoralen

The pyrolysis of isopsoralen was studied by synchrotron vacuum ultraviolet photoionization mass spectrometry at low pressure. The pyrolysis products were detected at different photon energies, the ratios of products to precursor were measured at various pyrolysis temperatures. The experimental results demonstrate that the main pyrolysis products are primary CO and sequential CO elimination products (C10H6O2 and C9H6O). The decomposition channels of isopsoralen were also studied by the density functional theory, then rate constants for competing pathways were calculated by the transition state theory. The dominant decomposition channels of isopsoralen and the molecular structures for corresponding products were identified by combined experimental and theoretical studies.