Estimated values for C2H4 from the polynomial in:
Fray, N., and B. Schmitt 2009.  Sublimation of ices of astrophysical
interest: A bibliographic review.  Planet. Space Sci. 57, 2053-2080.
 T(K)     P(bar)
 55.00   1.45e-12
 56.00   3.18e-12
 57.00   6.77e-12
 58.00   1.41e-11
 59.00   2.85e-11
 60.00   5.64e-11
 61.00   1.09e-10
 62.00   2.07e-10
 63.00   3.83e-10
 64.00   6.97e-10
 65.00   1.24e-09
 66.00   2.18e-09
 67.00   3.76e-09
 68.00   6.38e-09
 69.00   1.07e-08
 70.00   1.75e-08
 71.00   2.85e-08
 72.00   4.55e-08
 73.00   7.19e-08
 74.00   1.12e-07
 75.00   1.73e-07
 76.00   2.63e-07
 77.00   3.97e-07
 78.00   5.91e-07
 79.00   8.72e-07
 80.00   1.27e-06
 81.00   1.84e-06
 82.00   2.64e-06
 83.00   3.75e-06
 84.00   5.29e-06
 85.00   7.39e-06
 86.00   1.02e-05
 87.00   1.41e-05
 88.00   1.93e-05
 89.00   2.61e-05
 90.00   3.51e-05
 91.00   4.70e-05
 92.00   6.25e-05
 93.00   8.25e-05
 94.00   1.08e-04
 95.00   1.41e-04
 96.00   1.84e-04
 97.00   2.37e-04
 98.00   3.04e-04
 99.00   3.88e-04
100.00   4.94e-04
101.00   6.24e-04
102.00   7.86e-04
103.00   9.85e-04
104.00   1.23e-03
