some useful physical constant

electron mass: 9.10938188e-31 Kg
Ar: 6.63352e-26 Kg
Xe: 2.1801e-25 kg
1 bar = 750.06 Torr
R=62.36367 L·Torr·K^-1·mol^-1
= 8.20574587 × 10^-5 m³·atm·K^-1·mol^{-1
1 Torr = 3.21875E22 particle/m^3}