Spectral narrowing and infrared laser fragmentation of jet-cooled UO2(hfaa)2 TMP and UO2(hfaa)2 THF: Volatile uranyl compounds

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Abstract
The temperature dependence of the CO2 laser‐induced decomposition spectral linewidths and yields for jet‐cooled UO2(hfaa)2 TMP and UO2(hfaa)2 THF molecules has been studied using laser‐induced fluorescence detection and photoionization time‐of‐flight mass spectrometry on a pulsed supersonic beam of uranyl molecules seeded into a helium carrier gas. The two uranyl species, although chemically very similar, show a remarkable difference in the temperature dependence of the linewidth. For UO2(hfaa)2 TMP, the linewidth decreases upon cooling by a factor of ∼15, while the UO2(hfaa)2 THF linewidth decreases by only a factor of ∼2.6 over the same temperature range. The differences in the linewidth behavior are reflected in the yield curves for the laser‐induced reaction for the cooled molecules. These results for UO2(hfaa)2 TMP, to our knowledge, represent the first measurements of the temperature dependence of a T2 line broadening process for an isolated gas phase molecule. Detection of beam molecules as well as molecular decomposition fragments by multiphoton ionization is found to be ∼103 times more efficient than detection by resonant two‐color photoionization.