Table 2: Some low energy spectral lines observable by Odin.

Species		 Transition Frequency $E_{\rm u}\;^a$ $n_{\rm crit}\;^b$
    (MHz) (K) (cm-3)

H2O		 110-101 556 936.00 27    3$\times$10$^8\;\;^c$
H218O 110-101 547 676.44 27 3$\times$108
H217O 110-101 552 021.02 26 3$\times$108
NH3 10-00 572 498.07 29     5$\times$10$^7\;\;^c$
15NH3 10-00 572 112.79 29 5$\times$107
O2 33-12 487 249.38 26 103
O2 11-10 118 750.34 6 103
CI 3P1-3P0 492 160.70 24 104
CO 5-4 576 267.93 83    2$\times$10$^5\;\;^c$
13CO 5-4 550 926.30 79 2$\times$105
C18O 5-4 548 830.98 79 2$\times$105
CS 10-9 489 751.05 129 5$\times$107
a Upper state energy.
b Cloud density needed for excitation.
c Will be considerably reduced because of radiative trapping.

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