Slice Imaging Studies of Vibration, Rotational and Electronic Mediated Photodissociation and Photoionization of C2

在这个由化学系化学结构、动力学和机制项目支持的项目中，加州大学戴维斯分校的William Jackson教授和他的研究小组将探索光如何解离双原子分子C2。这种分子吸收近红外和可见光区域的光，这与其他同质双原子分子不同，如H2、N2和O2，这些分子也是由宇宙中大量的原子组成的。因此，C2分子是独一无二的，因为它很容易在碰撞较少的环境中进行光泵浦，这种环境是行星大气，彗星和星际介质的某些区域的特征。这导致与该组中的其他分子相比，该分子在激发态旋转和振动水平上具有更高的种群。这可以改变光解离和光电离的阈值，原子产物的电子态之间的分支，以及C2激发态的单重态和三重态流形之间的耦合。在种子脉冲超声速分子束中，利用聚焦ArF激光器制备了基态单重态σ和第一态三重态π激发振动态的C2。然后利用无聚焦紫外（UV）和/或真空紫外（VUV）激光源制备处于特定激发态的C2， C2自由基可以被光解离或光电离。如果它被光电离，C2+产物可以通过飞行时间质谱仪（TOF-MS）检测到。光解作用会产生三重态P、单线态D和单线态S的碳原子。这些原子可以在切片成像装置的相互作用区域用紫外和紫外激光器电离。这一策略将使我们能够研究电子、振动和旋转能量如何影响光解离成三重态P、单线态D和单线态S碳原子的阈值能量，并确定C2光电离的精确阈值。这项研究将揭示C2分子的特性，相对于其他宇宙中丰富的双原子分子，如氢（H2）和氧（O2）， C2分子仍未被研究。这项研究对我们理解宇宙的演化和生命的起源具有重要意义，因为星际介质中碳氧的比例决定了该区域是富氧还是贫氧。贫氧地区将进化并产生富含碳的颗粒，这些颗粒将具有构成生命基础的成分。杰克逊实验室的研究将有助于确定这种分子的最终稳定性，因为它将确定它在星际和行星际介质中暴露于紫外线辐射时衰变的速度。本研究项目的参与者包括博士后、研究生和本科生。

In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor William Jackson and his research group at the University of California at Davis will explore how light dissociates the diatomic molecule C2. This molecule absorbs light in the near infrared and visible region, which is unlike the other homogenous diatomic molecules, such as H2, N2, and O2, that are also made up of cosmically abundant atoms. As a result the C2 molecule is unique in that it will readily undergo optical pumping in the collision less environments that are characteristic of certain regions of planetary atmospheres, comets, and the interstellar medium. This leads to higher populations in excited rotational and vibrational levels for this molecule compared to others in this group. This can change the thresholds for photodissociation, and photoionization, for branching between electronic states of the atomic products, and for the coupling between the singlet and triplet manifolds of the excited electronic states of C2. A focused ArF laser is used to prepare C2 in excited vibrational states of the ground singlet sigma state and the first excited triplet pi state in a seeded pulsed supersonic molecular beam. Then an unfocused ultraviolet (UV) and/or vacuum ultraviolet (VUV) laser sources will be used to prepare C2 in a particular excited electronic state from which the C2 radical can be either be photodissociated or photoionized. If it is photoionized the C2+ product can be detected via the time-of-flight mass spectrometer (TOF-MS). Photodissociation will produce carbon atoms in the triplet P, singlet D and singlet S electronic states. These atoms can be ionized with the VUV and UV lasers in the interaction region of the slice imaging apparatus. This strategy will allow us to investigate how electronic, vibrational, and rotational energy affect the threshold energy for photodissociation into carbon atoms in the triplet P, singlet D and singlet S electronic states, and determine precise thresholds for photoionization of C2.This research will reveal the properties of the C2 molecule, which remains unstudied relative to other cosmically abundant diatomic molecules such as hydrogen (H2) and oxygen (O2). The research has implications for our understanding of the evolution of the universe and the origins of life because the ratio of carbon to oxygen in the interstellar medium determines whether the region will be oxygen rich or oxygen poor. The oxygen poor regions will evolve and produce carbon rich grains that will have the components that can form the basis of life. The studies in the Jackson laboratory will help to determine the ultimate stability of this molecule since it will define just how fast it will decay when exposed to UV radiation in the interstellar and interplanetary media. Participants in this research program include postdoctoral associates, graduate and undergraduate students.