Schofield Keith
Materials Research Laboratory, University of California, Santa Barbara, California 93106-5121, USA.
J Phys Chem A. 2006 Jun 1;110(21):6938-47. doi: 10.1021/jp0564187.
Although the "Golden" years of spectroscopy and the major studies on ionization processes now are behind us, as with many branches of science, much yet remains to be gleaned from such topics that is both full of interest and of significance to present day research. Presented here is one such overlooked example, an observation that relates to both these fields. An analysis is presented for the periodic table concerning the gas-phase thermochemical nature of MO+ and MO2+ ions. Unexpectedly, a pattern of 18 elements has been identified that exhibit the potential for having long-lived MO+ ions. Normally such molecular ions are expected to decay extremely rapidly by dissociative recombination with electrons, but in particular, 12 of this group behave not like molecules but rather as atomic ions. These are the diatomic oxide ions of Sc, Y, La, Zr, Hf, Ce, Pr, Nd, Pm, Gd, Tb, and Th. In the gas phase, they decay by much slower three-body recombination channels. As may be noted, these elements are located in the first two columns of the transition elements, among the earlier rare earths and an actinide. From all the elements, UO2+ is the only dioxide ion that behaves similarly. These findings now elevate the potential importance of these ions and should facilitate their spectral characterization. Moreover, subsequent comparisons with spectra of well-known isoelectronic and isovalent neutral monoxides and other diatomics will help in the stimulation of further theoretical advances. In addition, once characterized, an ease of spectrally monitoring such ionic states will provide a useful analytical tool.
尽管光谱学的“黄金”时代以及关于电离过程的主要研究如今已成为过去，但与许多科学分支一样，从这些对当今研究既充满趣味又具有重要意义的主题中，仍有许多有待发掘。这里展示的就是一个被忽视的例子，一个与这两个领域都相关的观察结果。本文对元素周期表中MO⁺和MO₂⁺离子的气相热化学性质进行了分析。出乎意料的是，已确定有18种元素呈现出具有长寿命MO⁺离子的潜力。通常，这类分子离子预计会通过与电子的解离复合而极快速地衰变，但特别值得注意的是，这一组中的12种元素的行为不像分子，而更像原子离子。它们是Sc、Y、La、Zr、Hf、Ce、Pr、Nd、Pm、Gd、Tb和Th的双原子氧化物离子。在气相中，它们通过慢得多的三体复合通道衰变。可以注意到，这些元素位于过渡元素的前两列、早期稀土元素以及一种锕系元素之中。在所有元素中，UO₂⁺是唯一表现类似的二氧化物离子。这些发现现在提升了这些离子的潜在重要性，并应有助于对其进行光谱表征。此外，随后与著名的等电子和等化合价中性单氧化物及其他双原子分子的光谱进行比较，将有助于推动进一步的理论进展。另外，一旦进行了表征，对这类离子态进行光谱监测的简便性将提供一种有用的分析工具。
