The Theory of the Magnetic Quenching of Iodine Fluorescence and ofΛ-Doubling inΠ03States

A theoretical basis is given for Turner's proposal that the magnetic quenching of iodine fluorescence is a predissociation phenomenon. To this end it is shown that a magnetic field introduces matrix elements in the Hamiltonian function between the ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{+}$ and ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{-}$ (or possibly the ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{+}$ and ${{}_{}{}^3{}_{}{}^{}\Sigma _0^{}{}_{}{}^{}}^{+}$) states, respectively stable and unstable in ${\mathrm{I}}_2$. This confirms Mulliken's assignment of ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{+}$ to the upper state of the halogen visible bands. The magnetic field has a unique role for so-called $0^{+}$, $0^{-}$ levels because perturbations between these particular states cannot arise from rotational distortion, the cause of the usual Kronig predissociation, or from electric fields unless they are very large or else markedly inhomogeneous. The magnetic quenching should be independent of the rotational quantum number (section 5) and should depend on field strength in the form $\frac{b{\mathfrak{H}}^2}{(a+b{\mathfrak{H}}^2)}$. The observed mode of frequency dependence demands that in ${\mathrm{I}}_2$ the potential curves of ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{+}$, ${{}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}}^{-}$ states, which are the two components of a $\Lambda$-doublet, be extremely close for certain values of $r$ or else actually cross each other. This crossing is shown to be theoretically possible under certain conditions. The possibility of magnetic predissociation in other molecules is also discussed. The predissociation due to collision observed by Turner, Kaplan, and others probably arises because electric fields can blend $u$ and $g$ states, and also $0^{+}$ and $0^{-}$ states if inhomogeneous.