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首页> 外文期刊>Atmospheric chemistry and physics >Ultraviolet absorption cross sections of carbonyl sulfide isotopologues OCsup32/supS, OCsup33/supS, OCsup34/supS and Osup13/supCS: isotopic fractionation in photolysis and atmospheric implications
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Ultraviolet absorption cross sections of carbonyl sulfide isotopologues OCsup32/supS, OCsup33/supS, OCsup34/supS and Osup13/supCS: isotopic fractionation in photolysis and atmospheric implications

机译：羰基硫同位素同位素OC 32 S，OC 33 S，OC 34 S和O 13 的紫外吸收截面CS：光解和大气影响中的同位素分馏

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We report measurements of the ultraviolet absorption cross sections ofOC32S, OC33S, OC34S and O13CS from 195 to 260 nm. TheOCS isotopologues were synthesized from isotopically-enriched elementalsulfur by reaction with carbon monoxide. The measured cross section ofOC32S is consistent with literature spectra recorded using naturalabundance samples. Relative to the spectrum of the most abundantisotopologue, substitution of heavier rare isotopes has two effects. First,as predicted by the reflection principle, the Gaussian-based absorptionenvelope becomes slightly narrower and blue-shifted. Second, as predictedby Franck-Condon considerations, the weak vibrational structure isred-shifted. Sulfur isotopic fractionation constants (33ε,34ε) as a function of wavelength are not highly structured, and tend tobe close to zero on average on the high energy side and negative on the low energy side.The integrated photolysis rate of each isotopologue at 20 km, the approximate altitude at which most OCS photolysis occurs, was calculated.Sulfur isotopic fractionation constants at 20 km altitude are (?3.7 ± 4.5)‰ and(1.1 ± 4.2)‰ for 33ε and 34ε, respectively, which isinconsistent with the previously estimated large fractionation of over73‰ in 34ε. This demonstrates that OCS photolysis does not produce sulfurisotopic fractionation of more than ca. 5‰, suggesting OCS may indeed be a significant sourceof background stratospheric sulfate aerosols. Finally, the predictedisotopic fractionation constant for 33S excess (33E) in OCSphotolysis is (?4.2 ± 6.6)‰, and thus photolysis of OCS is not expectedto be the source of the non-mass-dependent signature observed in modern andArchaean samples.
机译：我们报告了OC 32 S，OC 33 S，OC 34 S和O 13 CS在195至260 nm之间。通过与一氧化碳反应，从同位素富集的单质硫中合成了OCS同位素。 OC 32 S的测量横截面与使用自然丰度样品记录的文献光谱一致。相对于最丰富的同位素同位素，较重的稀有同位素具有两个作用。首先，如反射原理所预测，基于高斯的吸收包络会变得略微变窄和蓝移。其次，正如弗兰克-康登（Franck-Condon）考虑所预测的那样，弱振动结构发生了红移。硫同位素分馏常数（ 33 ε， 34 ε）与波长的关系不是高度结构化的，并且在高能侧平均接近于零，而在负值附近计算了20 km处每个同位素的积分光解速率，即大多数OCS光解发生的近似高度.20 km高度处的硫同位素分馏常数为（？3.7±4.5）‰和（1.1± 33 ε和 34 ε分别为4.2）‰，这与先前估计的 34 ε中超过73‰的大分馏结果不一致。这表明OCS光解不会产生大于约3的硫同位素分馏。 5‰，表明OCS确实可能是背景平流层硫酸盐气溶胶的重要来源。最后，OCS光解中 33 S过量（ 33 E ）的预测同位素分馏常数为（？4.2±6.6）‰，因此光解在现代和Archaean样本中，预计OCS不会成为非质量依赖性签名的来源。

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