An observation of thev₁rotation-vibration band of the NCO radical by laser magnetic resonance spectroscopy

The v 1 (‘symmetric’ stretch) fundamental of the NCO radical in the [Xtilde] 2Π state has been studied by CO laser magnetic resonance at 7·8 μm. Only a single rotational transition, R 1(3/2), is close enough to a laser line to give a magnetic resonance spectrum. By using values for the spin-orbit coupling and rotational constants from recent optical work, a value for the band origin, v 1 - 1/2α A of 1272·9707(2) cm-1 has been obtained. The orbital contribution to the magnetic moment of NCO in the (1, 0, 0) level is found to be about 20 per cent smaller than expected. Such a result is quantitatively explicable in terms of the Fermi resonance between the (1, 0, 0) and the (0, 2, 0) levels of NCO.