Inelastic scattering of PO+ by H2 at interstellar temperatures

IF 4.7 3区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
Pooja Chahal, Apoorv Kushwaha, T J Dhilip Kumar
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引用次数: 0

Abstract

Phosphorous species are of great interest in interstellar chemistry since they are the basic blocks for building life here on Earth. Modelling the abundance and environment of recently detected PO+ under non Local Thermodynamic Equilibrium (LTE) requires rotational spectra of the molecule along with accurate collisional rates with the most abundant species, hydrogen and helium. A new 4D ab initio potential energy surface (PES) of PO+ - H2 collision is calculated using CCSD(T)/CBS(DTQ) methodology considering rigid rotor approximation. The region containing the minima of the PES is augmented using neural networks (NN) model while very high potentials (>2500 cm−1) and asymptotic region have been approximated using Slater and R−4 functions respectively. The close coupling calculations have been performed using MOLSCAT software for both ortho and para-H2. The rate coefficients have been reported for transitions j − j′ = 1 − 0, 2 − 1, 3 − 2 and 5 − 4 through which PO+ has been experimentally detected in ISM. The rate coefficients for even and odd transitions of PO+ with para-H2 are compared with that of helium and are found to be 1.1-2.0 times higher. For even transitions (Δj = 2), the ortho-H2 rates are 10% higher than para-H2 rates. However, the trend reverses in the case of odd transitions (Δj = 1) when higher J transitions are considered at low temperatures. At higher temperatures, the ortho rates cross the para-H2 rates and become larger than the latter. The new rate coefficients with both ortho and para-H2 will enable accurate modelling of the PO+ abundance in the interstellar medium under non-LTE conditions.
星际温度下 H2 对 PO+ 的非弹性散射
磷物种是构建地球生命的基本要素,因此在星际化学中具有重大意义。在非局部热力学平衡(LTE)条件下模拟最近探测到的 PO+ 的丰度和环境需要该分子的旋转光谱以及与最丰度物种氢和氦的精确碰撞率。采用 CCSD(T)/CBS(DTQ) 方法计算了 PO+ - H2 碰撞的新 4D 原子势能面 (PES),并考虑了刚性转子近似。包含 PES 最小值的区域使用神经网络 (NN) 模型进行了增强,而极高电位(>2500 cm-1)和渐近区域则分别使用 Slater 和 R-4 函数进行了近似。使用 MOLSCAT 软件对正位和对位 H2 进行了紧密耦合计算。报告了 j - j′ = 1 - 0、2 - 1、3 - 2 和 5 - 4 转变的速率系数,在 ISM 中通过这些转变实验检测到了 PO+。将 PO+ 与对位 H2 的偶数和奇数跃迁的速率系数与氦的速率系数进行比较后发现,PO+ 的速率系数是氦的 1.1-2.0 倍。对于偶数转变(Δj = 2),正H2的速率比对H2的速率高10%。然而,当考虑低温下的高 J 转变时,奇数转变(Δj = 1)的趋势则相反。在较高温度下,正交速率超过了对位 H2 速率,变得大于后者。含有正H2和对H2的新速率系数将有助于在非LTE条件下对星际介质中的PO+丰度进行精确建模。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
9.10
自引率
37.50%
发文量
3198
审稿时长
3 months
期刊介绍: Monthly Notices of the Royal Astronomical Society is one of the world''s leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research and the design of astronomical instruments.
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