The ν1 band in N2O3

The ν1 fundamental band in N2O3 was recorded in absorption at high spectral resolution with a Fourier Transforms interferometer, under jet cooled experimental conditions. The rotational structure, corresponding to 44 K rotational temperature, could be analysed, leading to a set of precise upper state parameters. The absence of b-type lines in the spectrum, expected to occur from the direction of the Q1 normal coordinate with respect to the principal axes of inertia, is fully justified by ab initio calculations performed at the MP2/6–31G∗ level, confirming the decisive role of the polarizing NO2 chromophore in tilting the corresponding induced dipole moment towards the direction of the a axis. The calculations also provide equilibrium geometry parameters.