[qam1]

Now if they detect molecular O2, then my ears would perk up very rapidly!

Not necessary, Mercury's atmosphere contains 5.6% molecular Oxygen and I don't think there is life there.

[Hunble]

You are correct of course and you had me curious.

The key is Mercury's rather unusual temperature variations:

min 90K
mean 440K
max 700 K

For molecular O2 to form, the temperature must be low enough.

P.S. For those who do not understand temps in Kelvin, 273 K is the freezing point of water, or 0 degrees Centigrade.