Aims. We probe the effect of turbulent diffusion on the chemistry at the interface between a cold neutral medium (CNM) cloudlet and the warm neutral medium (WNM). Methods. We perform moving grid, multifluid, 1D, hydrodynamical simulations with chemistry including thermal and chemical diffusion. The diffusion coefficients are enhanced to account for turbulent diffusion. We post-process the steady-states of our simulations with a crude model of radiative transfer to compute line profiles. Results. Turbulent diffusion spreads out the transition region between the CNM and the WNM. We find that the CNM slightly expands and heats up: its CH and H$_2$ content decreases due to the lower density. The change of physical conditions and diffusive transport increase the H$^+$ content in the CNM which results in increased OH and H$_2$O. Diffusion transports some CO out of the CNM. It also brings H$_2$ into contact with the warm gas with enhanced production of CH$^+$, H$_3^+$, OH and H$_2$O at the interface. O lines are sensitive to the spread of the thermal profile in the intermediate region between the CNM and the WNM. Enhanced molecular content at the interface of the cloud broadens the molecular line profiles and helps exciting transitions of intermediate energy. The relative molecular yield are found higher for bigger clouds. Conclusions. Turbulent diffusion can be the source of additional molecular production and should be included in chemical models of the interstellar medium (ISM). It also is a good candidate for the interpretation of observational problems such as warm H$_2$, CH$^+$ formation and presence of H$_3^+$.
On the enhanced cosmic-ray ionization rate in the diffuse cloud towards Zeta Persei
宇宙线通量的空间分布对于理解银河系的星际介质具有重要意义。这种分布可以通过沿着不同的视线研究不同的分子种类来分析，这些分子种类的丰度对宇宙射线电离率很敏感。最近，几个研究小组报告说，与标准值zeta（平均值）= 2.5 e-17 s^-1相比，弥散云中的宇宙射线电离率有所增强，这是在致密分子云中测量的。在早期的工作中，我们报告了宇宙射线率的增强20对HD 185418。McCall等人根据观测到的H $_{3}^+ while Le Petit et al. found a cosmic ray enhancement of ~10 to be consistent with their models for this same sight line. Here we revisit zeta Persei and perform a detailed calculation using a self-consistent treatment of the hydrogen chemistry, grain physics, energy and ionization balance, and excitation physics. We show that the value of zeta deduced from the H$ _{3}^+$的丰度，报告了48对英仙座ζ的增强…
概述了星际介质的主要性质。证据总结表明，星际介质是高度湍流，驱动不同的长度尺度上的各种能量过程。大尺度湍流决定了弥散星际介质中丝状和壳状结构的形成。它还调节了密集、寒冷的分子云的形成。分子云现在被认为是瞬态物体，在HI气体被压缩和冷却的区域形成，时间尺度为1 e7年。在压缩HI板中的超音速湍流是由流体动力学不稳定性与冷却相结合而产生的。湍流耗散由流入的动能输入补偿。当板片的表面密度达到1 e 21 cm^-2的阈值时，最终形成了氢分子，此时进一步冷却会触发恒星形成的开始，这是由于引力坍缩。几百万年后，新形成的恒星和由此产生的超新星将分散它们的分子周围，并产生新的膨胀壳，再次驱动扩散气体中的湍流，并引发下一代冷云的形成。虽然星际介质动力学和恒星形成的一致方案正在出现，但许多细节仍然不清楚，需要对微物理过程进行更详细的研究，并更好地了解超音速可压缩湍流。
