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CN-122016734-A - Chirp pulse Fourier transform microwave spectrometer and detection method

CN122016734ACN 122016734 ACN122016734 ACN 122016734ACN-122016734-A

Abstract

The invention discloses a chirped pulse Fourier transform microwave spectrometer and a detection method, which belong to the technical field of microwave spectrum and comprise a pulse sample introduction and reactant in-situ generation system, a segmented chirped pulse generation and radiation system, a signal detection and high-speed acquisition system, a synchronous time sequence control system and a signal processing and automatic acquisition assembly. The invention adopts the chirped pulse Fourier-leaf transformation microwave spectrometer and the detection method, realizes 18-40 GHz continuous broadband coverage through the segmented chirped pulse sequence, integrates a pulse discharge sample injection system, can generate and directly detect high-reactivity intermediates and molecular clusters thereof in situ, fills the technical blank of the 18-40 GHz frequency band broadband high-sensitivity microwave spectrometer, and provides a powerful tool for researching the structure and reaction dynamics of key transient species in atmospheric chemistry, combustion chemistry and astrochemistry.

Inventors

  • LI WEIXING
  • GAO ZHIWEN
  • ZHOU MINGFEI

Assignees

  • 复旦大学

Dates

Publication Date
20260512
Application Date
20260225

Claims (10)

  1. 1. A chirped pulse fourier transform microwave spectrometer, comprising: the pulse sample injection and reactant in-situ generation system comprises a pulse valve and a pulse discharge electrode integrated at a nozzle of the pulse valve, and is used for generating a low-temperature molecular beam containing transient reaction intermediates; the segmented chirp pulse generating and radiating system comprises an arbitrary waveform generator, a frequency multiplier, a microwave power amplifier and a transmitting horn antenna which are sequentially connected, and is used for generating and radiating a series of microwave excitation pulses covering 18-40 GHz frequency bands; The signal detection and high-speed acquisition system comprises a receiving horn antenna, a limiter, a single-pole double-throw switch, a low-noise amplifier and an oscilloscope which are connected in sequence, and is used for receiving and digitizing free induction attenuation signals of molecular radiation; The synchronous time sequence control system comprises a digital delay generator and a signal transmission line, is electrically connected with the systems through the signal transmission line and is used for coordinating the operation time sequence of the systems; The signal processing and automatic acquisition assembly comprises a data processing terminal and automatic acquisition software stored in the terminal, wherein the data processing terminal is respectively and electrically connected with an oscilloscope and a synchronous time sequence control system, and the automatic acquisition software calls a hardware resource control instrument to integrally operate so as to carry out Fourier transform processing on the digitized free induction attenuation signal and generate a broadband microwave spectrum.
  2. 2. The chirped pulse fourier transform microwave spectrometer of claim 1, wherein the pulse discharge electrode is integrated with the pulse valve base, the pulse discharge electrode comprising a ceramic insulating spacer and a brass electrode, the ceramic insulating spacer being spaced from the brass electrode.
  3. 3. A chirped pulse fourier transform microwave spectrometer as defined in claim 2, wherein the pulse discharge electrode is connected to a high voltage discharge circuit controlled by the synchronized timing control system for generating synchronized pulse discharges as the gas pulses pass through to generate radicals, ions or metastable molecules in situ in the supersonic expanding jet.
  4. 4. The chirped pulse fourier transform microwave spectrometer of claim 1 wherein the arbitrary waveform generator is configured to generate 4-6 chirped pulse sequences with bandwidths of 2-6 GHz and center frequency spacing of 5-8 GHz, the frequency combinations of which cover continuous frequency bands of 18-40 GHz after amplification by a frequency multiplier, microwave power amplifier.
  5. 5. The microwave spectrometer of claim 4, wherein the arbitrary waveform generator generates a chirped pulse sequence comprising a plurality of repeated sub-sequences each consisting of a plurality of chirped pulses with sequentially increasing center frequencies within a single trigger period.
  6. 6. The chirped pulse fourier transform microwave spectrometer of claim 1 wherein the limiter is configured to isolate the receive feedhorn from the low noise amplifier during microwave excitation pulse radiation, the oscilloscope having a sampling rate of no less than 80 GS/s.
  7. 7. The chirped pulse fourier transform microwave spectrometer of claim 1, wherein the synchronous timing control system is centered on a digital delay generator to provide accurate trigger signals with adjustable delays for the pulse sample and reactant in-situ generation system, the segmented chirped pulse generation and radiation system, and the signal detection and high-speed acquisition system.
  8. 8. The chirped pulse fourier transform microwave spectrometer of claim 7, wherein the signal processing and automated acquisition software is run on a data processing terminal by invoking hardware resources of an oscilloscope, a synchronous timing control system to perform the steps of: s101, controlling each hardware module to work cooperatively according to a set time sequence; S102, acquiring a free induction attenuation signal of a time domain from an oscilloscope; s103, performing segmented Fourier transform on free induction attenuation signal segments corresponding to different excitation frequency bands; s104, splicing the sub-spectrums obtained by the transformation into a complete 18-40 GHz broadband spectrum; s105, a sectional accumulation average strategy is adopted to perform long-time stable average on the signals so as to improve the signal to noise ratio.
  9. 9. The method for detecting a chirped pulse fourier transform microwave spectrometer according to any of claims 1-8, comprising the steps of: S201, injecting a gaseous mixture containing a precursor into a vacuum cavity through the pulse sample injection and reactant in-situ generation system, triggering synchronous pulse discharge through a pulse discharge electrode integrated in a pulse valve, and generating free radicals, ions or metastable molecules in situ; s202, generating microwave pulses which cover 18-40 GHz by utilizing the segmented chirped pulses and radiating the microwave pulses by a radiation system, and exciting molecules in a vacuum cavity; S203, acquiring a time domain signal of molecular radiation by using the signal detection and high-speed acquisition system; S204, processing the time domain signal by using the signal processing and automatic acquisition software to obtain a broadband molecular rotation spectrum in the range of 18-40 GHz.
  10. 10. The method of claim 9, wherein the gaseous mixture comprises halogenated hydrocarbon, oxygen and water vapor, and wherein the pulsed discharge produces Criegee intermediates, and wherein step S204 comprises performing a segmented Fourier transform and spectral stitching on the time domain signal and using a cumulative average of the signals over 10 7 times.

Description

Chirp pulse Fourier transform microwave spectrometer and detection method Technical Field The invention relates to the technical field of microwave spectrum, in particular to a chirped pulse Fourier transform microwave spectrometer and a detection method. Background The microwave spectroscopy is used as a core technology of molecular structure analysis and species qualitative detection, can realize high-precision measurement of molecular parameters such as bond length, bond angle, dipole moment and the like by capturing a pure rotation transition signal of a molecule, has irreplaceable functions in the fields of chemistry, astronomy, material science and the like, and is a foundation stone for molecular structure analysis, astronomical chemical detection and transient reaction intermediate research. The chirped pulse Fourier transform microwave (CP-FTMW) spectrum technology is used as a core technology branch of microwave spectroscopy, the broadband excitation of molecules is realized by generating frequency chirped pulses, a high-speed digital acquisition module is matched to capture free induction attenuation signals, and a microwave spectrum chart is obtained through Fourier transform processing, so that compared with the traditional microwave spectrum technology, the spectrum acquisition speed, the detection sensitivity and the frequency band coverage range are remarkably improved, and the method has become a mainstream technical scheme of modern microwave spectrum analysis. However, the conventional CP-FTMW spectrometer has obvious technical defects in band coverage and sample injection suitability, and is difficult to meet the requirements of leading edge scientific research: Firstly, the coverage of the frequency band is limited, the frequency band is limited by the performance of key electronic components such as a traveling wave tube amplifier, the working frequency band of the CP-FTMW spectrometer used in the current business and laboratory is more limited to be below 18 GHz, and the broadband and high-sensitivity CP-FTMW spectrometer with the frequency band of 18-40 GHz is in a technical blank state for a long time. The frequency band of 18-40 GHz just covers a large number of small and medium-sized molecules, especially the high-intensity rotation transition signals of key transient species in atmospheric chemistry and interstellar chemistry, and the lack of the frequency band instrument severely limits the deep research of transient species and reaction dynamics mechanisms in the related fields; secondly, the sample injection system has poor suitability, the analyte sample injection system and the spectrum detection unit of the existing spectrometer are designed in a separated mode, in-situ generation and direct detection of transient intermediates with high reactivity and short service life cannot be realized, the species are easy to attenuate and decompose in the transmission process, the detection accuracy and the detection effectiveness are greatly reduced, and the scientific research requirements related to the transient species are difficult to meet. In conclusion, a CP-FTMW spectrometer which works in the frequency band of 18-40 GHz, has high-sensitivity broadband detection capability and integrates an in-situ sample injection function is developed, the bottleneck of the prior art is broken through, and the CP-FTMW spectrometer has important significance in promoting research progress in the fields of reaction dynamics, atmospheric chemistry, astrochemistry and the like. Disclosure of Invention The invention aims to provide a chirped pulse Fourier transform microwave spectrometer and a detection method, which realize continuous, broadband and high-sensitivity operation in the frequency range of 18-40 GHz, integrate a pulse discharge sample injection system and can generate and directly detect a high-reactivity intermediate and a molecular cluster thereof in situ. To achieve the above object, the present invention provides a chirped pulse fourier transform microwave spectrometer, comprising: the pulse sample injection and reactant in-situ generation system comprises a pulse valve and a pulse discharge electrode integrated at a nozzle of the pulse valve, and is used for generating a low-temperature molecular beam containing transient reaction intermediates; the segmented chirp pulse generating and radiating system comprises an arbitrary waveform generator, a frequency multiplier, a microwave power amplifier and a transmitting horn antenna which are sequentially connected, and is used for generating and radiating a series of microwave excitation pulses covering 18-40 GHz frequency bands; The signal detection and high-speed acquisition system comprises a receiving horn antenna, a limiter, a single-pole double-throw switch, a low-noise amplifier and an oscilloscope which are connected in sequence, and is used for receiving and digitizing the free induction attenuation signal of molecular radi