Study on theoretical analysis of C4F7N infrared spectra and detection method of mixing ratio of the gas mixture

Abstract

SF6 gas is widely used in power industry because of its good insulation, but it's an extremely potent greenhouse gas. To actively respond to climate change, the research of new environment-friendly gas insulating medium is an important research direction. C4F7N gas is the most potential environmentally friendly insulating gas instead of SF6 applied in high-voltage electrical equipment. C4F7N/CO2 gas mixture insulation equipment has been gradually promoted and used. The insulation performance of the gas mixture can be obtained by determining the content of C4F7N in the gas mixture. Therefore, the detection of mixture ratio of C4F7N gas has important engineering significance. In this paper, the geometric structure of C4F7N molecule is optimized based on density functional theory. Four methods of GGA-PBE, GGA-BLYP, GGA-PW91 and B3LYP were selected to determine the best density functional theory method for calculating the spectral properties of C4F7N molecules. A method for detecting the mixture ratio of C4F7N/CO2 based on infrared spectroscopy is proposed. The results show that: the B3LYP method is the best for the calculation of C4F7N infrared spectrum. A peak processing algorithm based on multi-scale wavelet transform was proposed. After the infrared overlapping peaks of C4F7N/CO2 gas mixture in the band of 750 ∼ 785 cm−1 were processed, the fitting effect has been improved overall. After peak processing, the band consists of four subpeaks, the inversion error can be reduced from 4.8 to 2.7 by using the sub-peak 2 as the eigenvalue of concentration inversion. The research results provide an effective method for detecting the mixing ratio of C4F7N/CO2 gas mixture.