Table 2. Abundances of C, O, CO, H, and H2

 	H2Oa	Cb		Ob		COb		Hb		H2b
Obs.c	…	<1013		<2.5 × 1013	<1017	…	…
Max.d	0	1.8 × 108	1.6 × 1015	4.3 × 1013	…	…
 	0.10	6.4 × 108	1.2 × 1014	2.4 × 1014	2.4 × 1014	8.1 × 1014
 	0.25	1.2 × 108	1.3 × 1013	6.0 × 1013	3.5 × 1014	3.2 × 1015
 	0.50	4.4 × 107	7.6 × 1012	2.6 × 1013	4.0 × 1014	7.1 × 1015
 	1.00	1.5 × 107	5.6 × 1012	1.1 × 1013	4.6 × 1014	1.4 × 1016
 	wete	5.9 × 106	2.3 × 1013	2.4 × 1013	1.2 × 1017	4.0 × 1015
Avg.d	0.25	6.7 × 107	1.1 × 1013	4.6 × 1013	2.5 × 1014	2.7 × 1015
Min.d	0.25	2.4 × 107	8.3 × 1012	2.8 × 1013	1.6 × 1014	1.8 × 1015
aThe near-surface H2O vapor abundance. The values are relative to the O2 density of 7.4 × 109 cm-3. A value of 0.25 is adopted as our reference model.
bThe column-integrated density in units of cm-2. H and H2 are allowed to escape.
cThe observed upper limits of column density for C, O, and CO [Strobel et al., 2002].
dThe calculated abundances for maximum, averaged, and minimum solar fluxes.
e“Wet” refers to the model where three-body chemical reactions are not enhanced on the surface. In this model, the best fits of O2 and H2O surface densities are 3.2 × 1010 and 4.8 × 109 cm-3, respectively.