Knowledge Bank

Magnetic circular dichroism parameters have been calculated for the $N(1\Sigma g+2440)\to Q(3\Pi lu$, $3\Pi o+u$, $1\Pi u$ 2431) and $N\to V(1\Sigma u+$ 1441) transition of the halogens, in order to account for the observed MCD $spectra.1$ The experimental MCD spectra are dominated by B-terms and the calculations indicate that the expected A-term for the Q($\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u$ 2431) transition is hidden under a B-term which arises from the magnetic field mixing of this state with the V state. This mechanism alone accounts for the Cl2 spectrum. For the cases of $Br2$ and $I2$, spin-orbit coupling between the appropriate component states of the configuration (2431) accounts$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ for the observed absorption intensity to $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi 1u$ and this coupling has also been used in the MCD calculations. Also a coupling scheme favored by Mulliken$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ to account for the observed absorption intensity to $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi 0+u$ found to give the beat fit for the MCD spectrum. In this model the state $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi 0+g$ (2341) is assumed to mix with the ground state.