Paramagnetic Resonance Absorption in Phenanthrene in Its Phosphorescent State

Abstract

Electron paramagnetic resonance absorption in phenanthrene in its lowest photoexcited triplet state has been investigated at the boiling point of N₂. The measurements have been made on phenanthrene molecules, oriented in diphenyl host crystals, at the frequency ∼2.3×10¹⁰ cycle sec^—1 and also at lower frequencies at almost zero field (76 to 3 G). Taking the long principal magnetic axis in the plane of the phenanthrene molecule to be the x axis, the short axis in the plane to be the y axis, and the normal to the plane to be the z axis, the results have been described by the spin Hamiltonian, $$\mathcal{H}\mathrm{=|\beta |}\mathbf{H}\mathrm{·g·}\mathbf{S}+\mathbf{S}\mathrm{·T·}\mathbf{S},$$ where $$\begin{array}{c}\text{S=1,}\\ T_{\mathrm{zz}}\text{/hc≡D/hc=±0.100430\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}\text{,\hspace{0.17em}\hspace{0.17em}σ{D/hc}=0.000010\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}},\\ {\mathrm{-T}}_{\mathrm{yy}}{\mathrm{/hc=T}}_{\mathrm{xx}}\text{/hc≡E/hc=∓0.046576\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}\text{,\hspace{0.17em}\hspace{0.17em}σ{E/hc}=0.000009\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}},\\ g_{\mathrm{zz}}{\text{=+2.00209,\hspace{0.17em}\hspace{0.17em}σ{g}}_{\mathrm{zz}}\text{}=0.00005,}\\ g_{\mathrm{yy}}{\text{=+2.00279,\hspace{0.17em}\hspace{0.17em}σ{g}}_{\mathrm{yy}}\text{}=0.00005,}\\ g_{\mathrm{xx}}\text{=+2.0041.}\end{array},$$ A preliminary investigation of the hyperfine structure has been made. These results have been compared with published calculations.