Determination of Intermediates of the UO2F2 Aerosol Formation under Different Water Conditions
CHRISTIAN MARK SALVADOR, Jason Richards, Shannon Mahurin, Meng-Dawn Cheng,
Oak Ridge National Laboratory Abstract Number: 31
Working Group: Aerosol Chemistry
AbstractUranyl fluoride (UO
2F
2) is produced in gas-phase UF6 hydrolysis. Understanding the particle formation of UO
2F
2 is critical for nuclear forensics. Formation of the uranyl aerosol requires the production of several precursors or intermediate species. Here, we probed the production of the intermediates using a Molecular Beam Mass Spectrometer (MBMS). UF
6 (200 ppm) and water vapor (300 ppm and 3000 ppm) were flown at 1.0 LPM each in separate gas-phase hydrolysis experiments. Triplicate analyses of each condition were run to ensure the reliability of the peaks observed from the reaction products. More than 15 masses showed significant enhancement (>30%) compared to the baseline condition. Interestingly, four common peaks (m/z 79, 81, 96, and 634), were found in the two reaction conditions, suggesting possibly different reaction pathways. The masses < 100 m/z were attributed to (HF)
3F, (HF)
4, and (H
2O)
2 ·(HF)
3, which are the expected HF clusters generated from the hydrolysis. The overall peaks were classified into four groups: Water/HF clusters: [(H2O)
2·(HF)
6F)] monomers:[(UF
5OH·(HF)
4·F, UF
5OH·(H
2O)
6·(HF)
3 and (UF
5OH)·(HF)
2·(H2O)
4)], dimers:[(UO
2F
2)
2·H
2O, (UF
5OH)·(UO
2F
2)·H
2O, and (UF
5OH)
2·(HF)
2] and trimers:[UF
5·UO
2F
2·UO
2F
2, UF
5·UO
2F
2·UO
2F
2, and UO
2F
2·U
2O
2F
9H]. This is the first time that molecules embedded with the UF
5OH core was experimentally discovered, although the possibility of this structure being part of the reaction intermediates was suggested previously by computational modeling about 5 years ago. The reaction pathways of the intermediates and their implications in different water vapor conditions will be discussed in the presentation.