Photodissociation and photoionisation of atoms and molecules of astrophysical interest
Photodissociation and photoionisation of atoms and molecules of astrophysical interest
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DOI：
10.1051/0004-6361/201628742
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发表时间：
2017-06-01
影响因子：
6.5
通讯作者：
van Dishoeck, E. F.
中科院分区：
文献类型：
--
作者：
Heays, A. N.;Bosman, A. D.;van Dishoeck, E. F.
一组新收集的102个天体化学感兴趣的原子和分子的光解离和光电离截面已经汇编，并简要回顾了所涉及的基本物理过程。它们已被用于计算标准紫外线星际辐射场(ISRF)中的离解和电离率，以及其他与波长有关的辐射场，包括冷恒星和太阳辐射、莱曼-阿尔法主导辐射和宇宙射线诱导的紫外线通量。新的ISRF费率通常与我们以前的汇编在30%范围内一致，但有几个明显的例外。并与PHIDRATES等其他数据库进行了比较。屏蔽区的减少率被计算为粉尘、分子和原子氢、原子C和自屏蔽柱密度的函数。这些屏蔽类型的相对重要性取决于所讨论的原子或分子以及假定的尘埃光学性质。所有的新数据都可以从莱顿的光解离和电离数据库中公开获得。测试和讨论了计算速率对温度和同位素变化的敏感性，以及测量或计算截面的不确定度。用星际-云化学模型对新的速率进行了测试，发现在假设ISRF的情况下，与Leiden数据库的前一次迭代获得的丰度基本一致(在两倍之内)，并且在假设各种恒星辐射的情况下，得到了数量级的变化。与UDfA和KIDA天体化学反应数据库中当前的参数相比，新的参数化尘埃屏蔽因子对许多原子和分子丰度的影响是两倍。新计算的宇宙射线诱导的光解离和电离速率与目前的标准值相差高达5倍。在高温和宇宙射线通量条件下，新的速率将丰富的暗云丰度的平衡丰度改变高达2倍。计算了H2O和NH3光解生成OH、O、NH2和NH的部分截面，得到了与辐射场相关的分支比。
A new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic physical processes involved. These have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (ISRF) and for other wavelength-dependent radiation fields, including cool stellar and solar radiation, Lyman-alpha dominated radiation, and a cosmic-ray induced ultraviolet flux. The new ISRF rates generally agree within 30% with our previous compilations, with a few notable exceptions. Comparison with other databases such as PHIDRATES is made. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic C, and self-shielding column densities. The relative importance of these shielding types depends on the atom or molecule in question and the assumed dust optical properties. All of the new data are publicly available from the Leiden photodissociation and ionisation database. Sensitivity of the calculated rates to variation of temperature and isotope, and uncertainties in measured or calculated cross sections, are tested and discussed. Tests were conducted on the new rates with an interstellar-cloud chemical model, and find general agreement (within a factor of two) in abundances obtained with the previous iteration of the Leiden database assuming an ISRF, and order-of-magnitude variations assuming various kinds of stellar radiation. The newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. Under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. The partial cross sections for H2O and NH3 photodissociation forming OH, O, NH2 and NH are also evaluated and lead to radiation-field-dependent branching ratios.