I just ran across this reference again while writing this comment (same one as I mentioned here so I thought I would add it to the mix explicitly.
The paper is quite thorough and interesting, and I think deserves a careful read.
New estimates for the sublimation rate for ice on the Moon Edgar L. Andreas, Icarus 186 (2007) 24–30:
This is pretty amazing, the vapor pressure has been experimentally measured over a range of ten orders of magnitude!
Fig. 1. Measurements or reference data for the saturation vapor pressure over a planar surface of pure water ice from Hilsenrath et al. (1960), Jancso et al. (1970), Bryson et al. (1974), Buck (1981), and Marti and Mauersberger (1993). The functional expressions for esat,i are from Buck (1981), Wagner et al. (1994), and
Murphy and Koop (2005) and are given in Eqs. (2)–(4). The Murphy and Koop curve is under the Buck and Wagner et al. curves in the region where they all overlap.
Here is the punch line, and it packs quite a punch! Note the annotation of 1 molecule per square centimeter per hour, and the fact that every major tick mark on the y axis represents ten orders of magnitude!
Fig. 2. The sublimation rate for a planar surface of pure ice calculated using the expressions from Buck (1981), Wagner et al. (1994), and Murphy and Koop (2005)
for esat,i in Eq. (1). The left axis gives the sublimation rate as a mass flux; its units are µg cm−2 h−1. The right axis gives the sublimation rate as the number of
molecules of water vapor leaving a square centimeter of the ice surface per hour. The arrow shows where the sublimation rate is only 1 molecule cm−2 h−1.