Direct spectroscopic determination of the degree of orientation of parity-selected NO

If a polar molecule can be selected in a rotational state of definite parity, subsequent orientation of the molecule in an electric field mixes opposite parity states. The degree of mixing reflects the degree of orientation. Therefore, the intensity ratio of spectral lines that correspond to transitions starting from the two parity states being mixed, forms a sensitive and accurate probe of the molecular orientation. If saturation of the spectral lines of interest is avoided, the absolute degree of orientation can be determined, without recourse to other experimental data but line intensities. The method is illustrated for the case of the NO molecule.