The magnetic rotation spectrum of formaldehyde: singlet–triplet perturbations in the 41 and 43 levels of the Ã1A2 state of H2CO

Abstract

A survey of the magnetic rotation spectrum (MRS) of formaldehyde in the near ultraviolet is reported. The [Formula: see text] and [Formula: see text] bands of the [Formula: see text] system are also studied under high resolution. The rR and pP 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 rR branches of the [Formula: see text] band are identified.Several strong lines in the MRS are shown to be associated with rR, rP, pR, and pP lines in the absorption spectrum and to reveal the presence of singlet–triplet perturbations. Only one perturbed rotational level is found in the [Formula: see text] band, but for the [Formula: see text] band several rotational levels are found to exhibit such 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 ΔJ = ΔN = ΔKa = 0 interactions with the 415161 level of the ã3A2 state and by ΔJ = ΔN = 0. ΔKa = ± 1 interactions with the 5161 level. The matrix elements are of the order of 0.01–0.10 cm−1.