Pei Linsen, Farrar James M
Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.
J Chem Phys. 2015 Aug 28;143(8):084304. doi: 10.1063/1.4929389.
We present a study of the charge transfer reactions of the atomic ions N(+)and O(+) with methanol in the collision energy range from ∼2 to 4 eV. Charge transfer is driven primarily by energy resonance, although the widths of the product kinetic energy distributions suggest that significant interchange between relative translation and product vibration occurs. Charge transfer with CD3OD is more exoergic for N(+), and the nascent parent ion products appear to be formed in excited B̃ and C̃ electronic states, and fragment to CD2OD(+) by internal conversion and vibrational relaxation to the ground electronic state. The internal excitation imparted to the parent ion is sufficient to result in loss of one or two D atoms from the carbon atom. The less exoergic charge transfer reaction of O(+) forms nascent parent ions in the excited à state, and internal conversion to the ground state only results in ejection of single D atom. Selected isotopomers of methanol were employed to identify reaction products, demonstrating that deuterium atom loss from nascent parent ions occurs by C-D bond cleavage. Comparison of the kinetic energy distributions for charge transfer to form CD3OD(+) and CD2OD(+) by D atom loss with the known dynamics for hydride abstraction from a carbon atom provides strong evidence that the D loss products are formed by dissociative charge transfer rather than hydride (deuteride) transfer. Isotopic labeling also demonstrates that chemical reaction in the N(+) + CD3OD system to form NO(+) + CD4 does not occur in the energy range of these experiments, contrary to earlier speculation in the literature.
我们展示了一项关于在约2至4电子伏特的碰撞能量范围内，原子离子N(+)和O(+)与甲醇发生电荷转移反应的研究。电荷转移主要由能量共振驱动，尽管产物动能分布的宽度表明相对平动和产物振动之间发生了显著的交换。对于N(+)而言，与CD3OD的电荷转移更具放能性，新生的母离子产物似乎是在激发的B̃和C̃电子态中形成的，并通过内转换和振动弛豫到基态电子态而裂解为CD2OD(+)。赋予母离子的内部激发足以导致从碳原子上损失一个或两个D原子。O(+)的放能性较低的电荷转移反应在激发的Ã态中形成新生的母离子，而内转换到基态仅导致单个D原子的射出。使用甲醇的选定同位素异构体来识别反应产物，表明新生母离子中氘原子的损失是通过C-D键断裂发生的。将通过D原子损失形成CD3OD(+)和CD2OD(+)的电荷转移的动能分布与从碳原子上夺取氢化物的已知动力学进行比较，提供了强有力的证据，证明D损失产物是通过离解电荷转移而非氢化物（氘化物）转移形成的。同位素标记还表明，在这些实验的能量范围内，N(+) + CD3OD系统中形成NO(+) + CD4的化学反应不会发生，这与文献中早期的推测相反。
