Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0356, USA.
J Chem Phys. 2012 Jul 14;137(2):024309. doi: 10.1063/1.4730911.
Several absorption bands exist in the vacuum ultraviolet (VUV) region of carbon monoxide (CO). Emission spectra indicate that these bands are all predissociative. Experimental results of CO photodissociation by vacuum ultraviolet photons (90 to 108 nm; ∼13 to 11 eV) from the Advanced Light Source synchrotron by measurement of the oxygen isotopic composition of the products are presented here. A large (few hundred per mil) range of oxygen isotopic compositions are observed in the CO photodissociation product and are wavelength dependent. Slope values (δ('17)O/δ('18)O) ranging from 0.72 to 1.36 were observed in the oxygen three-isotope space (δ('18)O vs. δ('17)O), which anti-correlated with increasing synchrotron photon energy, and indicates a dependency on the upper electronic state specific dissociation dynamics (e.g., perturbation and coupling associated with a particular state). An unprecedented magnitude in isotope fractionation was observed for photodissociation at 105 and 107 nm and is found to be associated with accidental predissociation of the vibrational states (ν = 0 and 1) for the upper electronic state E(1)Π. A significant temperature dependency in oxygen isotopic fractionation was observed, indicating a rotational level dependency in the predissociation process.
一氧化碳（CO）在真空紫外（VUV）区域存在多个吸收带。发射光谱表明这些带都是预解离的。本文介绍了用同步辐射真空紫外光（90 至 108nm；～13 至 11eV）照射 CO 得到的实验结果，通过测量产物的氧同位素组成来研究 CO 的光解。在 CO 光解产物中观察到很大（几百个千分比）范围的氧同位素组成，且与波长有关。在氧三同位素空间（δ('18)O 与 δ('17)O）中观察到斜率值（δ('17)O/δ('18)O）范围从 0.72 到 1.36，与同步辐射光子能量的增加呈反相关，表明与上电子态特定的解离动力学有关（例如，与特定态相关的微扰和耦合）。在 105nm 和 107nm 处的光解观察到前所未有的同位素分馏程度，与上电子态 E(1)Π 的振动态（ν = 0 和 1）的意外预解离有关。在氧同位素分馏中观察到显著的温度依赖性，表明在预解离过程中存在与转动能级有关的依赖性。
