Knowledge Bank

During the flash photolysis of diazomethane an absorption band has been observed at 3440 {\AA} having a typical $\perp$ band structure with a series of widely spaced sub-bands each of which has a closely spaced fine structure. Spectra obtained with deuterium and carbon 13 substituted diazomethane show that the molecule responsible for this band contains one hydrogen atom and one carbon atom. From the method of production of the spectrum the remaining atoms in the molecule must be nitrogen and the values of the moments of inertia show that there are two nitrogen atoms present. Analysis of the spectra of $HCN2,DNC2$ and $H13CN$ shows that the molecule has the structure with a linear N-C-N chain. Since the carbon atom is near to the centre of mass its exact position and therefore the C - N distances are rather uncertain. However, the other parameters of the molecule which are almost independent of the position of the carbon atom have been accurately determined. They are: $$\begin{array}{lll} for, the, upper, state:& r_{NH} = 1.02_{4} {\AA} r_{N-N} = 2.444 {\AA} \sphericalangle HNC = 119^{\circ}\ for, the, lower, state:& r_{NH} = 1.02_{4} {\AA} r_{N-N} = 2.471 {\AA} \sphericalangle HNC = 115^{\circ}\end{array}$$ While the lengths of the two C-N bonds cannot be determined accurately from the spectroscopic data alone, consideration of the electronic structure of the molecule suggests the the C-N bond next to the hydrogen atom should not be shorter than the other C-N bond. If this is assumed then the spectroscopic data show that the two C-N bonds are very nearly equal.