星周环境中UV和软X射线对苯分子的解离
Dissociation of the benzene molecule by UV and soft X-rays in circumstellar environment
摘要：
苯分子，存在于原行星状星云CRL 618中，被来自热中心恒星的紫外线和X射线光子及其快速风电离和解离。由这些过程产生的离子物种和自由基可以导致新的有机分子的形成。本工作的目的是利用同步辐射和飞行时间质谱研究苯分子的光电离和光解离过程。在对应于真空紫外（21.21 eV）和软X射线（282-310 eV）光谱区域的不同能量下记录质谱。从苯解离光电离的离子的生产在这里被量化，表明C6 H6是更有效地通过软X-射线比UV辐射，其中50%的电离的苯分子存活到UV解离，而只有约4%抵抗X-射线碎片。H+和小分子碳氢化合物如C_2H_2 ~+、C_3H_3 ~+和C_4H_2 ~+的部分离子产额被确定为光子能量的函数。测定了绝对光电离和离解光电离截面。从这些值，苯分子的半衰期，由于在CRL 618中的UV和X射线光子通量得到。
英文摘要：
Benzene molecules, present in the proto-planetary nebula CRL 618, are ionized and dissociated by UV and X-ray photons originated from the hot central star and by its fast wind. Ionic species and free radicals produced by these processes can lead to the formation of new organic molecules. The aim of this work is to study the photoionization and photodissociation processes of the benzene molecule, using synchrotron radiation and time of flight mass spectrometry. Mass spectra were recorded at different energies corresponding to the vacuum ultraviolet (21.21 eV) and soft X-ray (282-310 eV) spectral regions. The production of ions from the benzene dissociative photoionization is here quantified, indicating that C6H6 is more efficiently fragmented by soft X-ray than UV radiation, where 50% of the ionized benzene molecules survive to UV dissociation while only about 4% resist to X-rays. Partial ion yields of H+ and small hydrocarbons such as C2H2+, C3H3+ and C4H2+ are determined as a function of photon energy. Absolute photoionization and dissociative photoionization cross sections have also been determined. From these values, half-life of benzene molecule due to UV and X-ray photon fluxes in CRL 618 were obtained.
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