Temperature Dependence of Optical Absorption Lines from Iron Atoms in a Krypton Matrix

The optical absorption spectrum of iron atoms isolated in a krypton matrix contains two narrow lines at λ=3004±0.5 and 2969±1.0 {}. These lines are related to the two multiplet lines 3d⁶4s⁵D₄-3d⁷(a⁴F)4p⁵D₄^∘ and 3d⁶4s²⁵D₄-3d⁷(a⁴F)4p⁵D₃^∘. The linewidths (full width at half-maximum) at a matrix temperature of 4 K are 42 ±{} 1.5 and 38 ±{} 4 cm^-1, respectively. The lines are asymmetric (high-energy tail) and the linewidths increase with increasing temperature. From the line-shape analysis of the 3004 {} line at 4.2 and 20.5 K, the effective Debye temperature of solid krypton as probed by iron atoms is determined: The temperature dependence of linewidth yields ΘD=60±5 K; the asymmetry of the line gives ΘD=53±6 K.