Diffusion pump silicone oil properties and uses:
     Diffusion pump oil is polymethylphenylsiloxane colorless transparent oily liquid with high phenyl content. The product has extremely low saturated vapor pressure, high temperature resistance, low temperature resistance, oxidation resistance, radiation resistance, stable chemical performance, and high vacuum degree. It is the most ideal liquid medium material in high vacuum systems. It is mainly used as high-vacuum diffusion pump oil in electronics, metallurgy, and instrumentation industries, and can also be used as a high-temperature heat carrier and transfer fluid in instruments. Technical indicators:
     Appearance: colorless or light yellow transparent liquid
     Chromaticity: ≤40 degrees
     Kinematic viscosity: (25°C) 165-185cs
     Refractive index (nD25): 1.5765-1.5785
     Flash point: (open cup method) ≥ 243°C
     Freezing point: ≤-14℃

About silicone oil, please check the details:
https://www.siliconefoam.net/product-linear-vinyl-silicone-oil-iota-273-.html