MAGNETIC ROTATION SPECTROSCOPY OF SINGLET METHYLENE

Author Institution: Department of Chemistry, University of California BerkeleyThe Doppler-limited spectra of singlet methylene $(\tilde{b} ^{l}B_{1}\leftarrow\tilde{a} ^{1}A_{1})$,have been observed by direct absorption and magnetic rotation spectroscopy (MRS). Since magnetic rotation is exhibited only by singlet methylene states that are coupled to the triplet manifold, this technique is extremely sensitive to even weak singlet-triplet perturbations. The magnetic activity is observed in greater than 80\% of transitions (studied between $16000 cm^{-1}$ and $17000 cm^{-1})$) indicating strong coupling between singlet and triplet manifolds. Large magnetic effects are observed in vibronic transitions originating from $7_{16}$, $4_{31}$, and $4_{32}$ levels, in good agreement with perturbation analysis of triplet methylene rotational LMR $spectra.^{1}$ This work will lead to a better understanding of electronic structure of methylene and a more accurate determination of the singlet-triplet splitting, as well as a re-evaluation of the $\tilde{b} ^{1}B_{1}\leftarrow\tilde{a} ^{1}A_{1}$ spectrum. $^{1}$T. J. Sears, private communication