User Guide
1. Project and Experiment Application
Before submitting a research proposal, please carefully review the beamline introduction and research scope or contact beamline staff to confirm the suitability of your project. Register and submit your proposal via the CAS Major Science and Technology Infrastructure Sharing Service Platform. Once approved and allocated total
beamtime, submit your experiment request on the same platform, ensuring the requested beamtime does not exceed the total allocation.
2. Beamtime Schedule and Operational Status
Users can check the beamtime schedule and current operational status to reasonably request experiment slots based on their research progress.
3. Pre-Experiment Preparation
After beamtime confirmation, users should contact the User Office (yhb@ustc.edu.cn, 0551-63602018) to complete:
• Radiation safety training
• Radiation dosimeter badge application
• User access pass arrangement
• Accommodation inquiries
Before the experiment, users should:
• Review the beamline introduction or user information page for available equipment and experimental precautions.
• Contact beamline staff for further inquiries or additional details.
• Discuss experimental feasibility, preparation, and procedures with beamline scientists.
For experiments at the beamline, users must confirm the following with the beamline scientists:
(1) Sample properties (melting/boiling points, phase, vapor pressure, toxicity, pH, viscosity, etc.)
(2) Appropriate sample introduction method
(3) Sample purity and potential impurity interference
(4) Required pressure and temperature conditions
(5) Energy resolution and mass resolution requirements
(6) Other experiment- or beamline-related details
4. Beamline Research Scope
In-situ detection techniques employ modern analytical instruments to probe microscopic dynamic processes without disturbing the reaction system, enabling the elucidation of reaction mechanisms and intermediate structures.
Mass spectrometry (MS) is a powerful tool for molecular structure identification, offering high sensitivity, rapid analysis, and broad applicability. Molecular beam mass spectrometry (MBMS) can freeze stable and unstable gas-phase products for realtime, online analysis, making it particularly suitable for studying complex gas-phase reaction systems.
Synchrotron radiation, an advanced light source developed since the 1950s, provides high brightness, superior collimation, and tunable wavelengths, serving as a vital tool for fundamental and applied research. Synchrotron vacuum ultraviolet (VUV) light (6–20 eV) is unparalleled for near-threshold photoionization studies, as it enables soft ionization—minimizing fragmentation while ionizing target molecules.
By integrating tunable VUV synchrotron light with MBMS, researchers can:
• Detect reactive intermediates in situ and online.
• Distinguish isomers by scanning photon energy.
This approach is widely applied in combustion, catalysis, and atmospheric chemistry for product diagnostics and mechanistic studies.
Principle of Synchrotron Radiation Photoionization Mass Spectrometry Technology:
The synchrotron radiation photoionization mass spectrometry detection system can be divided into three regions: differential pumping region, ionization region, and mass spectrometry detection region. After exiting the reactor, the reaction products first enter the differential pumping region located approximately 10.0 mm from the reactor outlet. This region primarily consists of a nozzle and a skimmer. The nozzle is fabricated from sintered quartz, featuring a 25° conical angle at its tip with a microaperture through the cone. The aperture diameter depends on experimental pressure: under low-pressure conditions (~30 Torr), the nozzle aperture measures ~350 μm, while at atmospheric pressure (~760 Torr), it is reduced to ~75 μm. A fraction of the products passes through the quartz nozzle aperture, undergoing supersonic expansion to achieve the first-stage differential sampling. The skimmer, made of nickel via vapor chemical deposition, also exhibits a 25° conical angle with a 20 μm aperture at its tip for secondstage differential pumping. After dual-stage differential pumping, the products form a
supersonic molecular beam, effectively reducing the translational temperature of unstable intermediates, increasing molecular mean free path, and minimizing collisions. Under reaction conditions of 760 Torr and 2000 K, this supersonic molecular beam sampling achieves a maximum flow velocity of Mach 25 while maintaining a
temperature as low as 10 K, effectively preserving reactive radicals and unstable intermediates generated during the reaction. The sampled molecular beam then enters the ionization region. To maintain beam integrity and enhance ionization efficiency, the ionization chamber is maintained at high vacuum (10-4–10-5 Pa) using molecular pumps. Within the ionization chamber, the molecular beam intersects perpendicularly
with tunable synchrotron radiation vacuum ultraviolet (VUV) light for ionization. The photon energy is precisely adjusted via a stepper motor and linkage mechanism controlling the grating position. Notably, unlike conventional electron impact ionization, the synchrotron VUV light enables energy-tunable soft ionization tailored
to specific product ionization energies, effectively avoiding or eliminating interference from fragment peaks. The resulting ions are analyzed in a time-of-flight mass spectrometer (TOF-MS). Ion beams are modulated by electrostatic lenses to achieve parallel trajectories, passing through a slit before entering the repeller region of the TOF acceleration electrodes. Accelerated ions travel through a field-free drift region to a reflection electric field, where energy dispersion compensation and focusing enhance mass resolution. Finally, ions are detected by a microchannel plate (MCP) detector, converted to pulse currents, amplified by a VT120 preamplifier into voltage signals, and recorded using a P7888 multichannel data acquisition system (FAST Comtec GmbH, Germany).
Research：
(1) Study on Polycyclic Aromatic Hydrocarbons (PAHs) Formation Pathways The formation of polycyclic aromatic hydrocarbons (PAHs) involves complex physicochemical processes, and elucidating their formation mechanisms holds profound implications for combustion science, environmental atmospheric chemistry, and astrochemistry. At the combustion beamline station of the Hefei Light Source, the molecular beam sampling-synchrotron radiation vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technology enables molecular-level precision diagnostics in intricate reaction systems. This technique uniquely captures and identifies critical reactive intermediates, providing pivotal experimental evidence for exploring and validating complex physicochemical mechanisms. By integrating these findings with precise quantum chemical calculations, the formation mechanisms of intricate PAHs can ultimately be unraveled.
Journal of the American Chemical Society 143 (2021) 20710-20716
(2) Study on Combustion Pathways of Energetic Fuels
As the primary energy source for aerospace propulsion systems and strategictactical weaponry, the combustion of solid propellants is fundamentally a dynamic coupling of complex cascade reactions. Precise elucidation of their microscopic reaction pathways is critical for regulating energy release efficiency and optimizing propulsion system reliability. However, constrained by the limited temporal resolution (>10 ms) and insufficient species selectivity of conventional diagnostic techniques, significant knowledge gaps persist regarding the evolution of key intermediates (e.g., transient radicals, metastable isomers) during the initial decomposition stages of
energetic materials. These limitations severely hinder the development of combustion performance prediction models and the design of novel high-energy, low-sensitivity propellants. By employing molecular beam sampling-synchrotron radiation vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), the research team has
achieved groundbreaking progress in resolving the primary decomposition pathways of typical solid propellant components, including high-energy explosives such as RDX and CL-20. Key gaseous intermediates generated during the early decomposition phase were tracked at millisecond timescales, while numerous high-molecular-weight products (100 < m/z < 450) were simultaneously identified. Integrating experimental
observations with high-precision quantum chemical calculations, the team has, for the first time, uncovered the intrinsic relationship between the cage-like molecular configurations of energetic fuels and their combustion performance, providing unprecedented molecular-level evidence for understanding their high-detonation
velocity characteristics.
Proceedings of the Combustion Institute 40 (2024) 105433
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