# Stability of CN molecule

The $\ce{CN}$ molecule has been observed spectroscopically in comets where pressure has been estimated to be as low as $10^{-10}\ \mathrm{mmHg}$. Draw a Lewis structure for $\ce{CN}$. Suggest an explanation as to why this species can persist in a comet but is unstable under normal terrestrial conditions?

Having drawn the Lewis structure, the molecule is a free radical, hence it is very unstable. Would the species be unstable under terrestrial conditions due to a higher temperature (hence pressure) there? Or more specifically, how does a change in pressure effect a free radical molecule?

• Temperature is unrelated to pressure. As for the radical, it is stable by itself, but very reactive (=unstable) when it meets another radical (or just about anything else, for that matter), which happens more often when there is more stuff around. – Ivan Neretin Jan 21 '16 at 20:29
• @IvanNeretin I'm not a native english speaker, but reactive not means unstable. For example the complex of cobalt with EDTA is very very stable in water but if you have cobalt in water as a complex like $[Co(H_2O)_6]^{3+}$ it is absolutely unstable but to totally inert, then if you add a bit of EDTA you will never get the complexe of Co with EDTA if you don't heat up your solution... – ParaH2 Jan 21 '16 at 20:52
• Neither am I. Sure, these two words are not synonyms, but in this particular context they can be used this way. OK, I should have said "extremely reactive to everything around (including itself), and hence unstable". – Ivan Neretin Jan 21 '16 at 21:04
• Some molecules are inherently unstable, CN, CN- or even CN+ aren't. – Mithoron Jan 21 '16 at 21:16
• Is there a direct relationship of the stability of a molecule to the pressure it is undergoing? @IvanNeretin – mnmakrets Jan 22 '16 at 2:28

$\ce{NC-CN <=> 2CN}$