Near‐Threshold Photodetachment of WF 5 − Molecular Anions in a Cryogenic Storage Ring
Martin Martschini, David Leimbach, Hubert Gnaser, Dag Hanstorp, Mingchao Ji, Paul Martini, Ansgar Simonsson, Rachel Poulose, Mikael Björkhage, Henning Zettergren, Henning T. Schmidt, Robin GolserABSTRACT
Rationale
The molecular anion WF 5 − constitutes an isobaric interference for the mass spectrometric detection of the HfF 5 − anion. The latter is expected to form an extremely sensitive way of detecting the radionuclide 182 Hf at natural levels using, for example, accelerator mass spectrometry.
Methods
Photoinduced detachment of WF 5 − molecular anions was studied in the Double ElectroStatic Ion Ring ExpEriment (DESIREE), with the ring cooled to cryogenic temperatures (~13 K). Photon energies from 2.5 to 4.5 eV were applied using an OPO laser system for excitation. This energy range covers the threshold for the removal of an electron from that anion species.
Results
Photoinduced reactions were observed which indicate the existence of an energy threshold for WF 5 − anions above which the neutralization yield increases strongly. In that range, the data of the neutral signal could be fitted by a linear function of photon energy E , yielding a threshold energy E th = 3.13 ± 0.01 eV. This result constitutes a substantial improvement both in the range and the resolution of the photon energy as compared to previous data and provides now a rather precise value for that threshold.
Conclusions
This knowledge is required for any attempts to suppress WF 5 − anions by photodetachment in the ultrasensitive detection of the very rare radioisotope 182 Hf using the 182 HfF 5 − analyte anion; for that, the 182 WF 5 − anion would be a stable isobaric mass interference for analyses by accelerator mass spectrometry. The radionuclide 182 Hf is considered of great interest in various astrophysical environments such as nucleosynthetic processes.