An analysis of the four nuclear quadrupole problem: The microwave spectrum of cyanogen azide

We have derived expressions for the Hamiltonian matrix elements for the coupling of any number of quadrupolar nuclei with the molecular rotation using the Wigner n-j formalism. These expressions have been used to analyse the nuclear quadrupole hyperfine structure of the rotational spectrum of cyanogen azide, NCN₃. The analysis was effected by comparing the experimental high resolution spectral traces with computer simulated traces from which the nuclear quadrupole coupling constants obtained are (MHz)

$\text{x}{}_{\mathrm{aa}}\text{(1) = 4.82 ± 0.02,}\text{x}{}_{\mathrm{bb}}\text{(1) = ?0.70±0.08,}$

$\text{x}{}_{\mathrm{aa}}\text{(2) = ?0.85 ± 0.07,}\text{x}{}_{\mathrm{bb}}\text{(2) = 0.70±0.08,}$

$\text{x}{}_{\mathrm{aa}}\text{(3) = ?0.75 ± 0.07,}\text{x}{}_{\mathrm{bb}}\text{(3) = 0.70±0.05,}$

$\text{x}{}_{\mathrm{aa}}\text{(4) = ?2.27 ± 0.04,}\text{x}{}_{\mathrm{bb}}\text{(4) = 0.70±0.07,}$

Small corrections to the previously reported rotational constants are given.