Knowledge Bank

Magnetic rotation spectra of the $401$ and $403$ bands of the $A~1A2-X~1A1$ system of formaldehyde have been photographed under high resolution . The and branches of these bands are found to be active and it is noted that the intensities appear to increase more rapidly with increasing $Ka$ in the MRS than in the absorption spectrum. The $43$ and $61$ levels are in Coriolis interaction at higher $Ka$ values, and some branches of the $601$ band are identified in the MRS. Several strong lines in the MRS are shown to be associated with and lines in the absorption spectrum and to reveal the presence of singlet- triplet perturbations. Only one perturbed rotational level is found in the $401$ band , but for the $403$ band several rotational levels are found to exhibit local perturbations, e.g., $190,19,191,19,171,16,102,8,102,9,112,9,173,14,173,15,183,15,$ and $183,16$. These perturbations are produced by $\Delta J=\Delta N=\Delta Ka=0$ interaction with the $415161$ level of the $a3A2$ state and by $\Delta J=\Delta N=0,\Delta Ka=\pm 1$ interactions with the $5161$ level. The matrix elements are of the order of $0.01–0.10cm-1$.