The $4f^6\to 4f^{5}5d^1$ absorption spectrum of the ${\mathrm{Sm}}^{2+}$ ions incorporated in a ${\mathrm{SrCl}}_2$ single crystal was recorded at $4.2\mathrm{K}$ in the $15000–45000{\mathrm{cm}}^{-1}$ spectral range. The overall spectrum is very satisfactorily simulated by theoretical calculations performed in the frame of the semi-empirical Hamiltonian model. The calculations enabled the assignment of all bands observed in the spectrum as well as a prediction of some experimentally unobserved transitions in the $45000–55000{\mathrm{cm}}^{-1}$ region. The rich vibronic structure observed for absorption bands in the $15000–25000{\mathrm{cm}}^{-1}$ spectral region is dominated by the vibronic progressions in the totally symmetric $\mathrm{Sr}\text{−}\mathrm{Cl}$ stretching mode of $\sim 213{\mathrm{cm}}^{-1}$ upon the thirteen zero phonon lines and local vibration modes at $\sim 81{\mathrm{cm}}^{-1}$ and $\sim 116{\mathrm{cm}}^{-1}$. This multiphonon vibronic spectrum is very well reproduced by the model calculation.

• Received 9 February 2007

DOI:https://doi.org/10.1103/PhysRevB.76.115125