SPIN-VIBRONIC PERTURBATIONS IN THE $^{1}A_{2}$ STATE OF $CH_{2}O$

Author Institution: Photochemistry Unit, University of Western OntarioIn the singlet $\pi^{*}\leftarrow n$ transitions of $CH_{2}O$, some 30 lines of the $2^{2}_{0} 4^{1}_{0}$ vibronic band show an observable Zeeman effect. Each magnetically-sensitive line lies close to the resonance, of crossing point, of a group of mild perturbations observed in the zero-field spectrum in sub-bands with $K^{\prime} = 0 - 6$. The pattern denotes an upper state perturbation in which the resonance shifts progressively from $J^{\prime} = 12$ at $K^{\prime} = 0$ to $J^{\prime} = 16$ at $K^{\prime} = 6$, and is considered to result from the interaction $^{1}A_{2}\leftarrow{p}\rightarrow ^{3}A_{2}$. The perturbed singlet state $2^{2}4^{1} (30658 cm^{-1}$) is a vibronic $B_{2}$ state. The nature of the perturbation ($\Delta K = 0$) proves that the perturbing triplet state has vibronic species $B_{2}$ or $B_{1}$. A rotational analysis of this triplet vibronic state has been carried out, based upon `extra’ lines in the spectrum. The coupling scheme will be discussed