Electronic transitions of jet-cooled FeC$_n$ clusters ($n = 3 - 6$) were measured between 230 and 300 nm by a mass-resolved 1+1 resonant two-photon ionization technique. Rotational profiles were simulated based on previous calculations of ground state geometries and compared to experimental observations. Reasonable agreement is found for the planar fan-like structure of FeC$_3$. The FeC$_4$ data indicate a shorter distance between the Fe atom and the bent C$_4$ unit of the fan. The transitions are suggested to be $^{ 3}$A$_{ 2} \leftarrow ^{ 3}$B$_{ 1}$ for FeC$_3$ and $^{ 5}$A$_{ 1} \leftarrow ^{ 5}$A$_{ 1}$ for FeC$_4$. In contrast to the predicted C$_{ \infty \text{ v}}$ geometry, non-linear FeC$_5$ is apparently observed. Line width broadening prevents analysis of the FeC$_6$ spectrum.
Categories: physics.chem-ph