1. Changchun University of Science and Technology, Changchun, Jilin 130022, China
2. National Institute of Metrology, Beijing 100029, China
3. Key Laboratory of Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
Abstract：The refractive index of monatomic gases such as argon is an important parameter for the verification of the ab initio calculations based on quantum mechanics. The refractive index of argon from 234 K to 303 K and 0 kPa to 750 kPa was measured accurately using a cylindrical microwave resonator. Microwave resonance frequencies of four TM modes at different pressures in a cylindrical cavity were measured. After the correction of the non-ideal factors, the refractive index of argon was obtained by the comparison of the microwave resonance frequencies in vacuum and in gases. The uncertainty of microwave resonance frequency in the cylindrical cavity is 2×10-8, and the inconsistence between the argon refractive index from four modes is less than 1×10-6. The first dielectric virial coefficients of argon are obtained by calculating the refractive index of argon, and the results show a good agreement with the published results. The refractive index measurement of other gases can be carried out in the future using the experimental apparatus.
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2019, Vol. 40 
