State-resolved studies of the vibronic structure and reaction dynamics of molecular dications

带有两个正电荷的分子，即分子指示，具有不同寻常的性质。首先，由于两个类电荷的斥力，分子具有很高的能量。这种高能意味着它们对单电荷离子的反应是不同的。其次，两个正电荷之间的排斥力意味着，这些双电荷分子中的许多分子寿命都很短，它们碎裂成一对单电荷离子。然而，对于大多数小分子来说，尽管一对正电荷之间存在排斥，但它们的电子的某些排列提供了足够强的化学键来将分子结合在一起。电子的这些排列产生了分子指令的所谓的长寿命(亚稳态)电子态。在这些亚稳态中，许多小分子粒子可以存活足够长的时间，从而与中性分子发生碰撞并发生化学反应。这项申请建议对申请人开发的一种研究分子指令化学反应的仪器进行广泛的升级。该装置通过鉴定通常在阳离子化学反应中形成的两种带电产物来运行。该仪器使用一种专门设计的质谱仪来检测和识别来自单个反应的带电产物；即所谓的符合实验。在质谱仪中使用位置敏感探测器使实验能够精确地确定两个产物离子在单个反应事件后的移动方式。这种对产物离子运动的研究，即所谓的反应过程的动力学，为化学反应的机理提供了强有力的探索。在目前的配置下，该实验已经揭示了广泛的反应范围，并表明指示反应以不寻常的路径进行。然而，该实验探测反应产物能量的精度目前是有限的，这一应用提出了对光谱仪的重大发展，以显著提高这种能量分辨率。我们建议安装一个更大面积的探测器和改进的定时电子设备，同时加入一个更受控制和限制的中性分子入口处(分子束)。这些改进，加上结合速度成像方法的新设计的质谱仪，将提高光谱仪的能量分辨率，以便能够确定双原子标度的各个振动能级的能量和反应性。速度成像是为激光光谱学发展起来的一种技术，它涉及到质谱计中特殊的电场布置，从而能够准确地确定产物的离子速度。为了在我们的实验中实现速度成像，不使用激光来电离反应产物，涉及到我们开发的新设计的质谱仪，它仍然可以给出准确的产品离子速度，但不会降低质谱仪识别不同物种的能力。我们建议使用升级后的装置来研究现有技术无法探测的双原子原子的能级，并研究最近被认为是行星电离层化学中关键物种的分子原子的反应性和反应机理。

Molecules which carry two positive charges, molecular dications, possess unusual properties. Firstly, due to the repulsion of the two like-charges the molecules are highly energetic. This high energy means that they react differently to singly-charged ions. Secondly, the repulsion between the two positive charges means than many of these doubly charged molecules are very short-lived and they fragment to form a pair of singly-charged ions. However, for most small molecules, certain arrangements of their electrons give strong enough chemical bonds to hold the molecule together despite the repulsion between the pair of positive charges. These arrangements of the electrons generate so-called long-lived ( metastable ) electronic states of molecular dications. In these metastable states many small molecular dications can live for long enough to collide with a neutral molecule and undergo chemical reactions. This application proposes an extensive upgrade to a piece of apparatus developed by the applicant to study the chemical reactions of molecular dications. The apparatus operates by identifying both of the charged products that usually are formed in a dication chemical reaction. The apparatus uses a specially designed mass spectrometer to detect and identify both of the charged products from reaction of an individual dication; a so-called coincidence experiment. Using a position-sensitive detector in the mass spectrometer allows the experiment to precisely determine how both of the product ions are moving following an individual reactive event. Such studies of the motion of the product ions, the so-called dynamics of a reactive process, provide a powerful probe of the mechanism of the chemical reaction. In it's current configuration the experiment has revealed the reactivity of a wide-range of dications and shown that dication reactions proceed by unusual pathways. However, the accuracy with which the experiment can probe the energies of the reaction products is currently limited and this application proposes significant developments to the spectrometer to dramatically improve this energy resolution. We propose to install a larger area detector and improved timing electronics, together the incorporation of a more controlled and constrained inlet (a molecular beam ) for the neutral molecules. These improvements, together with a new design of mass spectrometer which incorporates a velocity imaging methodology, will improve the energy resolution of the spectrometer so that the energies and reactivity of individual vibrational levels of diatomic dications can be determined. Velocity imaging is a technique developed for laser spectroscopy, involving a special arrangement of electric fields in the mass spectrometer, which allows the product ion velocities to be determined accurately. To implement velocity imaging in our experiment, which does not use a laser to ionize the products of the reaction, involves a new design of mass spectrometer, which we have developed, which still gives accurate product ion velocities but does not degrade the ability of the mass spectrometer to identify different species. We propose to use the upgraded apparatus to study the energy levels of diatomic dications which cannot be probed by existing techniques and also to study the reactivity and reaction mechanisms of the molecular dications which have recently been implicated as key species in the chemistry of planetary ionospheres.