Gnaser Hubert, Martschini Martin, Leimbach David, Karls Julia, Hanstorp Dag, Indrajith Suvasthika, Ji Mingchao, Martini Paul, Simonsson Ansgar, Zettergren Henning, Schmidt Henning T, Golser Robin
University of Vienna, Faculty of Physics, Isotope Physics - VERA Laboratory, A-1090 Wien, Austria.
Department of Physics, University of Gothenburg, SE-41296 Gothenburg, Sweden.
J Chem Phys. 2022 Jul 28;157(4):044304. doi: 10.1063/5.0097896.
Spontaneous and photo-induced decay processes of HfF and WF molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13 K) and the extremely low residual gas pressure (∼10 mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450 nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF anions at about 3.5 eV, above which the neutralization yield increases strongly. By contrast, HfF ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (∼5.2 eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope Hf using the HfF anion while effectively reducing the interfering stable isobar W in the analyte ion WF . The radionuclide Hf is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years ago.
在双静电离子环实验（DESIREE）中研究了HfF和WF分子阴离子的自发衰变过程和光致衰变过程。由于DESIREE的低温（13K）和极低的残余气体压力（约10毫巴），能够在长时间尺度（几十毫秒）上观察到这些反应。对于光致反应，采用了240至450nm范围内的激光波长。发现这两种阴离子物种都会通过电子脱离或碎片化进行自发衰变。几毫秒后，观察到辐射冷却过程降低了通过这些过程进一步衰变的概率。光致反应表明WF阴离子存在约3.5eV的能量阈值，高于该阈值，中和产率会大幅增加。相比之下，即使对于本实验中使用的最高光子能量（约5.2eV），HfF离子在光子相互作用时基本上不会增强中性粒子的产生。这种抑制对于在加速器质谱中使用HfF阴离子高效检测极其稀有的同位素Hf非常有利，同时能有效减少分析物离子WF中干扰性稳定同量异位素W的影响。放射性核素Hf在天体物理环境中具有重要意义，因为它是研究几百万年前可能在太阳系附近发生的核合成事件的潜在候选物质。
