The Study Of Millimeter-wave Rotational Spectrum Based On Chirped-pulse Fourier Transform

According to the theory of quantum mechanics,all molecules of substances have rotational energy levels.The absorption or emission spectrum of electromagnetic waves accompanied by the transition of molecules on their rotational energy levels is called molecular rotational spectrum.The vast majority of molecular rotational energy level transitions occur in the millimeter wave band from 30 GHz to 300 GHz.The energy required for rotational level transition is much lower than that of molecular vibrational level or electronic level transition,which can make the spectral detection results of molecular rotational spectroscopic instruments have better resolution and sensitivity than those of other types of spectroscopic instruments.As a precision spectral detection and analysis equipment,the molecular structure characteristics measured by rotational spectrometer can be used as the standard of quantum theoretical calculation.In addition,due to the characteristics of millimeter wave rotational spectrum detection frequency band,it is closely related to radio astronomy observation,chemical analysis and pharmaceutical fields,so the development of rotational spectrometer plays a vital role in promoting many fields.Millimeter-wave Chirped-pulse Fourier transform(CP-FT)spectrometer is one of the types of rotational spectrometer,which is the focus of this paper.Firstly,the dissertation introduces the research background of rotational spectroscopy,and analyzes the development process of rotational spectroscopy instruments at home and abroad.After understanding the various types of rotational spectrometers at home and abroad,the basic working principle of the broadband CP-FT spectrometer developed by our laboratory is introduced.In addition,for different spectral research objects,several technologies are combined to improve the sensitivity and working efficiency of the instrument.However,because of the large volume of rotating spectrum instrument system,it is not suitable for field spectrum measurement.Therefore,an integrated design for frequency source is proposed in this dissertation,which can replace the arbitrary waveform generator and signal generator,so as to improve the integration and convenience of the instrument.For the optical system of the spectrometer,the corresponding high-efficiency absorption cell is also designed in this dissertation,so that the millimeter wave excitation source can fully interact with the molecule to be measured and achieve the purpose of enhancing the spectral signal.Finally,after completing the design and construction of millimeter wave CP-FT spectrometer,the millimeter wave rotational spectra of tert-butyl alcohol(TBA)and tert-butyl chloride(TBCl)were measured in laboratory,and the rotational spectral parameters and molecular structure information of TBCl and its isotope substituted compounds were obtained after analysis and fitting.By comparing the consistency with the data calculated by Gaussian software,the excellent performance of the spectrometer built in our laboratory is verified.