Bergeat Astrid, Morales Sébastien B, Naulin Christian, Kłos Jacek, Lique François
Univ. Bordeaux, CNRS, ISM, UMR 5255, Talence, France.
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, United States.
Front Chem. 2019 Mar 28;7:164. doi: 10.3389/fchem.2019.00164. eCollection 2019.
Fine-structure populations and collision-induced energy transfer in atoms are of interest for many fields, from combustion to astrophysics. In particular, neutral carbon atoms are known to play a role in interstellar media, either as probes of physical conditions (ground state P spin-orbit populations), or as cooling agent (collisional excitation followed by radiative decay). This work aims at investigating the spin-orbit excitation of atomic carbon in its ground electronic state due to collisions with molecular deuterium, an isotopic variant of H, the most abundant molecule in the interstellar medium. Spin-orbit excitations of C(P ) by H or D are governed by non-adiabatic and spin-orbit couplings, which make the theoretical treatment challenging, since the Born-Oppenheimer approximation no longer holds. Inelastic collisional cross-sections were determined for the C(P) + D → C(P ) + D (with = 1 and 2) excitation process. Experimental data were acquired in a crossed beam experiment at low collision energies, down to the excitation thresholds (at 16.42 and 43.41 cm, respectively). C-atoms were produced mainly in their ground spin-orbit state, P, by dissociation of CO in a dielectric discharge through an Even-Lavie pulsed valve. The C-atom beam was crossed with a D beam from a second valve. The state-to-state cross-sections were derived from the C(P ) ( = 1 or 2) signal measured as a function of the beam crossing angle, i.e., as a function of the collision energy. The results show different quantum behaviors for excitation to C(P) or C(P) when C(P) collides with -D or -D. These experimental results are analyzed and discussed in the light of highly accurate quantum calculations. A good agreement between experimental and theoretical results is found. The present data are compared with those obtained for the C-He and C-H collisional systems to get new insights into the dynamics of collision induced spin-orbit excitation/relaxation of atomic carbon.
原子中的精细结构布居和碰撞诱导的能量转移在从燃烧到天体物理学等许多领域都备受关注。特别是，已知中性碳原子在星际介质中发挥作用，既作为物理条件的探针（基态P自旋轨道布居），也作为冷却剂（碰撞激发后接着辐射衰变）。这项工作旨在研究处于基电子态的原子碳与分子氘（氢的一种同位素变体，是星际介质中最丰富的分子）碰撞时的自旋轨道激发。H或D对C(P)的自旋轨道激发受非绝热和自旋轨道耦合支配，这使得理论处理具有挑战性，因为玻恩 - 奥本海默近似不再成立。确定了C(P) + D → C(P ) + D（ = 1和2）激发过程的非弹性碰撞截面。在低碰撞能量下，直至激发阈值（分别为16.42和43.41厘米），通过交叉束实验获取了实验数据。C原子主要通过在介电放电中通过Even - Lavie脉冲阀使CO解离而产生于其基自旋轨道态P。C原子束与来自第二个阀的D束交叉。态 - 态截面是从作为束交叉角（即碰撞能量的函数）测量的C(P )（ = 1或2）信号推导出来的。结果表明，当C(P)与 -D或 -D碰撞时，激发到C(P)或C(P)呈现出不同的量子行为。根据高精度量子计算对这些实验结果进行了分析和讨论。实验结果与理论结果吻合良好。将当前数据与C - He和C - H碰撞系统获得的数据进行比较，以获得对碰撞诱导原子碳自旋轨道激发/弛豫动力学的新见解。
