The gas phase ultraviolet spectrum and stability of 1,1-dihydroxyacetone (the geminal diol of methylglyoxal) are investigated using spectroscopic and computational methods. Experimental gas phase electronic spectra recorded in the ultraviolet–visible range were used to follow the hydration of methylglyoxal. We show that upon the addition of water, methylglyoxal hydrates to form the geminal diol. The electronic spectra of methylglyoxal and its geminal diol conformers were calculated using TD-DFT and LR-CC methods to facilitate experimental peak assignments. The lowest energy electronic transition of the diol is experimentally measured and compared with the results of the theoretical calculations. We find that upon formation of the diol, the lowest-energy transition of methylglyoxal (centered around ∼430 nm) vanishes, and the remaining transitions, including the methylglyoxal diol absorptions (λ_max = 240 nm), fall outside the available solar actinic flux in the troposphere. This likely has significant impacts on the ultimate fate of methylglyoxal in the atmosphere.

中文翻译：

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甲基乙二醛气相水合的紫外光谱

使用光谱和计算方法研究了气相紫外光谱和1，1-二羟基丙酮（甲基乙二醛的双酚）的稳定性。在紫外-可见光范围内记录的实验气相电子光谱用于跟踪甲基乙二醛的水合作用。我们表明，在添加水后，甲基乙二醛水合物形成双生二醇。使用TD-DFT和LR-CC方法计算甲基乙二醛及其双二醇构象异构体的电子光谱，以促进实验峰分配。实验测量了二醇的最低能量电子跃迁，并将其与理论计算结果进行了比较。我们发现，在形成二醇后，甲基乙二醛的最低能级跃迁（约430 nm附近）消失，其余跃迁消失，_最大= 240 nm），超出对流层中可用的太阳光化通量范围。这可能会对大气中甲基乙二醛的最终命运产生重大影响。