Considering $\rm CO_2$ snow on Mars and recent cold temperature on the earths' south pole, I am looking for a $\rm CO_2$ phase diagram below 1 millibar that shows the sublimation temperature of $\rm CO_2$ for $\rm CO_2$ partial pressure in earths atmosphere, (i.e. 0.4 millibar).
Found this formula from Giauque & Egan (1937) for the sublimation part of the Phase diagram: p in atm, T in Kelvin. p=0.0131579 * 10^(-(1354.210/T)+8.69903+0.001588T-(4.510710^-6)*T^2)
https://en.wikipedia.org/wiki/File:Carbon_Dioxide_sublimation_curve.png Using Giauque, W.F.; Egan, C.J., Carbon Dioxide. The Heat Capacity and Vapor Pressure of the Solid. The Heat of Sublimation. Thermodynamic and Spectroscopic Values of the Entropy, J. Chem. Phys., 1937, 5, 1, 45-54, https://doi.org/10.1063/1.1749929 (strictly only valid from 154.26K to 195.89K)
Original Giauque-Egan pressure is in centimeter of mercury, conversion to kPa is 1.333224, divide by 101.325 to get atm, rounded to six significant places according to NIST: 0.0131579, temperature is in Kelvin: convert to degrees Celsius using °C = T -273.15
Alternative formula (NIST):
p = 10^ (6.81228 − (1301.67 / (T -3.494))) (p in bar, T in Kelvin)