论文标题

电氢分子的吸收光谱

Absorption spectra of electrified hydrogen molecules

论文作者

Walker, Mark A.

论文摘要

分子氢通常在其旋转状态之间只有弱的四极杆过渡,但是在静态电场中,它获得了偶极矩和一组允许的过渡。在这里,我们使用H2分子的静态电响应张量的自由计算来构建扰动的振动振动本特征系统及其基态吸收。我们将注意力限制在两种与星际介质中凝结的氢分子相关的简单场合构型:均匀的电场和点状电荷的场。能量本质是振动和角动量本征态的混合物,因此有许多过渡满足偶极选择规则。我们发现,在具有高振动激发的状态中,混合最强,导致光学和接近红外的数百种吸收线。这些光谱与无场分子的光谱大不相同,因此,如果它们出现在天文数据中,则很难分配。此外,在凝结的环境中,激发状态可能会寿命很短,从而使吸收线的外观具有分散的外观。因此,我们建议电动H2作为弥漫性星际带(DIB)的可能载体。我们进一步认为,原则上,有可能用这个载体来解释所有DIB。但是,尽管有电化,但仍需要过渡,并且需要大量的冷凝H2列,从而使我们目前对ISM的理解很难调和这种可能性。

Molecular hydrogen normally has only weak, quadrupole transitions between its rovibrational states, but in a static electric field it acquires a dipole moment and a set of allowed transitions. Here we use published ab initio calculations of the static electrical response tensors of the H2 molecule to construct the perturbed rovibrational eigensystem and its ground state absorptions. We restrict attention to two simple field configurations that are relevant to condensed hydrogen molecules in the interstellar medium: a uniform electric field, and the field of a point-like charge. The energy eigenstates are mixtures of vibrational and angular momentum eigenstates so there are many transitions that satisfy the dipole selection rules. We find that mixing is strongest amongst the states with high vibrational excitation, leading to hundreds of absorption lines across the optical and near infrared. These spectra are very different to that of the field-free molecule, so if they appeared in astronomical data they would be difficult to assign. Furthermore in a condensed environment the excited states likely have short lifetimes to internal conversion, giving the absorption lines a diffuse appearance. We therefore suggest electrified H2 as a possible carrier of the Diffuse Interstellar Bands (DIBs). We further argue that in principle it may be possible to account for all of the DIBs with this one carrier. However, despite electrification the transitions are not very strong and a large column of condensed H2 would be required, making it difficult to reconcile this possibility with our current understanding of the ISM.

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