Measured data for alpha N2 from:
Borovik, E.S., S.F. Grishin, and E. Grishina 1960.  The vapor pressure of nitrogen and hydrogen at low pressures.  Sov. Phys. Tech. Phys. (Engl. transl.) 5, 506-511.
T(K)     P(bar)
21.20   1.47e-13
21.60   3.07e-13
22.00   6.13e-13
22.50   1.60e-12
23.00   3.33e-12
24.00   1.73e-11
25.00   6.67e-11
26.00   2.53e-10
26.40   4.27e-10
