Knowledge Bank

Electric field spectra are obtained by modulating the ultraviolet absorption of gases with an alternating electric field, using a lock-in amplifier to select the signal at a frequency double that of the $field1,2$. With formaldehyde under high resolution the major effect is broadening of the rotational lines of low J; it is thus possible to pick out from the complex absorption spectrum the first members of rotational sub-bands and in this way one can unambiguously assign those subbands (with $K\le 2$) for which the molecular asymmetry is important. Results are to be presented.