Rotational Spectroscopic Investigation on 9-Fluorenone at C-Band (4～8 GHz)
ZHU Yu-xuan1, YANG Xiao-yu1, XU Xin-rong1, SUN Ming1*, JIAO Chao1*, CHEN Qian1*, ZHAO Zhen-lu2, CHEN Wei-qiang2, ZHANG Xin2, LIU Hong-xin2
1. School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
2. Beijing Spacecraft Manufacturing Co. Ltd., Beijing 100094, China
Abstract：9-fluororenone is a typical oxygenated polycyclic aromatic hydrocarbon (PAH), derivative of PAHs containing carbonyl functional groups. Oxygenated PAHs can be formed by direct photolysis or oxidation of parent PAHs. As an inexpensive and nontoxic photocatalyst, 9-fluororenone with such an aromatic carbonyl groupcan act as a prototype molecule for the study of photochemical process, mostly via the time-resolved infrared and resonance Raman spectroscopy. In addition, 9-fluorenone could be a significant target of radio astronomy, because such oxygenated PAHs with decent dipole moments can provide a new and effective way to confirm the existence of PAHs in deep space and reveal the connotation of interstellar medium chemistry. The pure rotational spectra of 9-fluorenone have been gradually captured in the millimeter wave and microwave range. The present work aims is to expand the scope of laboratory observation of 9-fluorenone in the microwave C-band (4～8 GHz), and further support the astrophysical research of this molecule and other PAHs. Specifically, a potential astrophysical molecule, 9-fluorenone, was investigated by a broadband chirped-pulse Fourier transform microwave spectrometer (cp-FTMW) with a heating solenoid valve gas pulse nozzle in the microwave C-band range. In this work, 27 b-type pure rotational transitions of 9-fluorenone were newly measured and assigned. By combining with the microwave data fitting, we obtained precise rotational constants for 9-fluorenone with these values: A=1 445.884 739 29(10) MHz, B=584.871 673 6(71) MHz and C=416.550 607 8(81) MHz. The measured rotational constants of 9-fluorenone were compared with various theoretical and experimental works. The measured spectroscopic parameters were compared with various theoretical and experimental works. The accuracy of rotational constants of this combined fitting is markedly improved. It can be seen that the combined fitting analysis is not only conducive to the accurate characterization of the ground state structure, but also provides the basis for the computational study of such kinds of molecules. The accurate observation of its new rotational transitions in the vibrational ground state also provides more spectroscopic data for the PAH molecule hunting in deep space, which will promote the wider exploration of PAHs in astrophysics. This work also demonstrates the ability of our cp-FTMW spectrometer to detect nonvolatile molecules in supersonic jet expansion using a heated nozzle.
基金资助: The National Natural Science Foundation of China (61627802, U1531107), the National Undergraduate Training Program for Innovation and Entrepreneurship (202010288046Z)
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