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Electron driven molecular dissociation

电子驱动分子解离

基本信息

批准号：
ST/I000151/1
负责人：
金额：
$ 10.18万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Training Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FI000151%2F1
关键词：
Electron driven molecular dissociation

项目摘要

Astrophysically small molecules exist not just in quiescent cool clouds, which themselves are weakly ionized and therefore contain electrons, but also in much more active astrophysical regions such as planetary nebulae and diffuse interstellar clouds. These regions often contain significant numbers of free, quasi-thermal electrons, up to 10-4 compared to H2. These electrons can effect chemical change and drive observable spectroscopy processes (see A.J. Lim, I. Rabadan and J. Tennyson, MNRAS, 306, 473 (1999) for example); the cross sections between electrons and molecular ions are particularly large. Additionally electron molecule collisions are important elsewhere, for example they are the main driver behind planetary aurorae and many molecular masers. Models of all these regimes require data which is largely unknown and, in many cases, cannot be determined from laboratory based measurements. Over the last two decades the UCL group has developed the UK molecular R-matrix codes to provide a first principles, quantum mechanical treatment of the collision between low energy electrons and small molecules. This code has been used to treat collisions leading to rotational excitation involving important astrophysical ions (see for example A. Faure and J. Tennyson, MNRAS, 325, 443 (2001), A. Faure, J.D. Gorfinkiel and J. Tennyson, MNRAS 347, 323 (2004)). Recent observations of molecular emissions from C-shocked regions of the ISM (Jimenez-Serra et al, ApJ 650, L135 (2007)) showed that it is possible to recover local electron densities by using our electron molecule collisions calculations. Low-energy electrons also destroy molecules through dissociative recombination (DR for ions) and dissociative attachment (DA for neutrals). Cross sections for these processes are often hard to obtain. The present proposal is for a PhD student who will use the QuantemolN implementation of the UK polyatomic R- matrix code to study electron collisions with molecules of astrophysical interest and obtain dissociative cross sections. To do this the student will develop and test an add-on DA/DR estimator for Quantemol-N. A preliminary DA estimator developed by the company will provide the starting point for this work. The QuantemolN code, which will be provided by the company, is very suitable for these studies since it is an expert system which greatly increases the ease and speed with which a user can perform very technically demanding electron collision calculations. In return the student will assist the company in adding further features to this code to treat DA and DR. This project is proposed now since this feature has recently been requested by a Japanese industrial client of the company and a number of other users have expressed a strong interest. Adding to this functionality of the code is a strategic aim of Quantemol. The student will be provided training in performing electron molecule collision calculations, interpreting the results and using them in astronomical models and to interpret astronomical spectra. S/he will interact with people directly observing the processes, several of whom (for example Dr J Rawlings and Dr S Viti) are at UCL. S/he will also experience working with a small start up company which gives the opportunity to be involved both in the software development and in the interaction with other users of the code. This proposal follows a highly successful CASE studentship award to Dr HN Varambhia who used Quantemol-N to do studies on HCN, HNC, CS, CO and other astrophysically important systems (Eg Varambhia et al, Electron-impact rotational excitation of the carbon monosulfide (CS) molecule, MNRAS in press) which has been of immense benefit to the company by raising its scientific profile which led to new orders for the existing Quantemol-N package and interest in the others, from both the UK and abroad. Varambhia also added an electron impact ionization estimator to Quantemol-N.

天体物理上的小分子不仅存在于静止的冷云中，冷云本身是弱电离的，因此含有电子，而且还存在于更活跃的天体物理区域，如行星状星云和弥散星际云。这些区域通常包含大量的自由准热电子，与H2相比高达10-4。这些电子可以影响化学变化并驱动可观察到的光谱过程（例如，见A.J. Lim， I. Rabadan和J. Tennyson， MNRAS, 306,473 (1999)）；电子和分子离子之间的横截面特别大。此外，电子分子碰撞在其他地方也很重要，例如，它们是行星极光和许多分子脉泽背后的主要驱动力。所有这些制度的模型所需要的数据在很大程度上是未知的，而且在许多情况下，无法通过基于实验室的测量确定。在过去的二十年里，UCL小组开发了英国分子r矩阵代码，为低能电子和小分子之间的碰撞提供了第一原理，量子力学处理。该代码已用于处理导致涉及重要天体物理离子的旋转激发的碰撞(例如参见A. Faure和J. Tennyson， MNRAS, 325, 443 （2001)， A. Faure， J.D. Gorfinkiel和J. Tennyson, MNRAS 347, 323(2004)）。最近对ISM c激波区分子发射的观测（Jimenez-Serra et al, apj650, L135(2007)）表明，通过我们的电子分子碰撞计算，可以恢复局部电子密度。低能电子还通过离子的解离重组（DR）和中性的解离附着（DA）破坏分子。这些过程的横截面通常很难得到。目前的建议是为一名博士生，他将使用英国多原子R矩阵代码的QuantemolN实现来研究与天体物理学感兴趣的分子的电子碰撞并获得解离截面。为此，学生将开发和测试Quantemol-N的附加DA/DR估计器。该公司开发的初步数据处理估计器将为这项工作提供起点。QuantemolN代码将由该公司提供，非常适合这些研究，因为它是一个专家系统，大大提高了用户执行技术要求很高的电子碰撞计算的便利性和速度。作为回报，该学生将协助公司在此代码中添加进一步的功能来治疗DA和dr。该项目现在被提出，因为该公司的一个日本工业客户最近要求使用该功能，并且许多其他用户也表达了强烈的兴趣。增加代码的这种功能是Quantemol的战略目标。学生将接受训练，进行电子分子碰撞计算，解释结果，并将其用于天文模型和解释天文光谱。他/她将与直接观察过程的人互动，其中一些人（例如J罗林斯博士和S维蒂博士）是伦敦大学学院的。他/她还将有在小型初创公司工作的经验，这将使他/她有机会参与软件开发以及与其他代码用户的互动。这个提议是一个非常成功的案例博士奖学金奖HN Varambhia曾经Quantemol-N研究HCN, HNC, CS,公司和其他天体物理学重要的系统(例如Varambhia et al,电子轰击旋转励磁的碳一硫化物(CS)分子,MNRAS新闻)已经极大的好处,该公司通过提高其科学配置文件导致新订单现有Quantemol-N包和对他人的兴趣,从英国和海外。Varambhia还为Quantemol-N添加了一个电子冲击电离估计器。