Chemical States of Fe atoms Implanted into Solid Oxygen

本文利用短寿命的^<57>Mn（T_<1/2>=1.5 min）束流进行了束内穆斯堡尔光谱实验，研究了由^<57>Mn注入固体氧中产生^<57>Fe原子的新化学物质。预计氧的高电子亲和力有利于铁的高价态的产生。^<58>的Fe束（E=63 MeV/nucleon）与Be生产靶发生核弹丸-碎裂反应后产生^<57>Mn粒子作为二次RI束，并在Riken加速器研究设施中使用RIPS（Riken弹丸-碎裂分离器）进行飞行同位素分离器分离。然后，将^<57>Mn通过适当厚度的Al板注入到固体O_2样品中，将束流能量抑制到约20 MeV/核子。在^<57>Mn的注入过程中，在18、32和40 K下测量了光束内穆斯堡尔光谱。得到的光谱在18k时可以用4组洛伦兹重态进行分析。根据同分异构体位移和四极分裂的穆斯堡尔参数，以及从始算分子轨道计算，确定了这4种组分分别为Fe（O_2）、FeO和（O_2）Fe(O_2)，是Fe原子处于高氧化态的化学物质。我们讨论了由^<57>Mn产生的^<57>Fe原子与固体O_2基体之间的反应产物，并与激光烧蚀Fe原子与O_2气体在低温下分离在Ar基体中的产物进行了比较。

We have performed an in-beam Mossbauer spectroscopic experiment using a short-lived ^<57>Mn(T_<1/2>=1.5 min) beam, in order to study the production of the novel chemical species of ^<57>Fe atoms arising from ^<57>Mn implanted into solid oxygen. It is expected that the high electron affinity of oxygen favors the production of high valence states of Fe.^<57>Mn particles were produced as a secondary RI beam following a nuclear projectile-fragmentation reaction of ^<58>Fe beams (E=63 MeV/nucleon) with Be production target, and separated by the in-flight isotope separator using RIPS(Riken Projectile-fragment Separator) in RIKEN Accelerator Research Facility. Subsequently, the ^<57>Mn was implanted into a solid O_2 sample after passing through an Al plate with an appropriate thickness to suppress the beam energy down to about 20 MeV/nucleon. The in-beam Mossbauer spectra were measured at 18, 32 and 40 K during the implantation of ^<57>Mn. The obtained spectrum at 18 K could be analyzed by 4 sets of Lorentzian doublet. From the basis of Mossbauer parameters of the isomer shifts and the quadrupole splittings and the ab-initio molecular orbital calculations, these 4 components were assigned to be Fe(O_2), FeO, and (O_2)Fe(O_2), and a chemical species in a higher oxidation state of Fe atoms. We discussed the reaction products between ^<57>Fe atoms arising from ^<57>Mn and a solid O_2 matrix, compared with the products of laser-ablated Fe atoms with O_2 gas isolated in the Ar matrix at low temperatures.