To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone
To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone
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DOI：
10.1021/acs.jpca.9b04640
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发表时间：
2019-07-04
影响因子：
2.9
通讯作者：
Sheps, Leonid
中科院分区：
文献类型：
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作者：
Antonov, Ivan;Voronova, Krisztina;Sheps, Leonid
我们用三种互补的时间分辨光谱方法研究了S-2(pi pi*)>；S-0激发下乙酰丙酮(戊烷-2，4-二酮)的烯醇酮互变异构体在波长2 66和2 48 nm下的气相光化学。与以前的报道相反，以前的报道声称研究了乙酰丙酮的单光子激发，并发现OH和CH3是唯一的重要气相产物，但我们检测到15个独特的初级光产物，并证明其中包括OH和CH3在内的5个初级光产物仅由多光子激发产生。我们将单光子产物分配到六个光化学通道，并表明最重要的途径是光互变异构化为二酮形式，它可能是其他几个产物通道的中间产物。在320~600K温度范围内，测定了S-0催化剂上烯醇酮互变为二酮的平衡常数，并用Vant Hoff方法求出了Delta H=4.1+/-0.3kcal.mol(-1)，Delta S=6.8+/-0.5cal.mol(-1)·K-1。我们将乙酰丙酮中的C-OH键离解能从理论和实验测定的90kcal.mol(-1)修正为新值121.7 kcal.mo1。我们的实验和电子结构计算证明，一些产物通道，包括光互变异构化，发生在S-0上，而另一些可能发生在激发三重态表面上。虽然S二号的大振子强度
We investigate the gas-phase photochemistry of the enolone tautomer of acetylacetone (pentane-2,4-dione) following S-2(pi pi*) -> S-0 excitation at lambda = 266 and 248 nm, using three complementary time-resolved spectroscopic methods. Contrary to earlier reports, which claimed to study one-photon excitation of acetylacetone and found OH and CH3 as the only important gas-phase products, we detect 15 unique primary photoproducts and demonstrate that five of them, including OH and CH3, arise solely by multiphoton excitation. We assign the one-photon products to six photochemical channels and show that the most significant pathway is phototautomerization to the diketone form, which is likely an intermediate in several of the other product channels. Furthermore, we measure the equilibrium constant of the tautomerization of the enolone to diketone on S-0 from 320 to 600 K and extract Delta H = 4.1 +/- 0.3 kcal.mol(-1) and Delta S = 6.8 +/- 0.5 cal.mol(-1).K-1 using a vant Hoff analysis. We correct the C-OH bond dissociation energy in acetylacetone, previously determined as 90 kcalmol1 by theory and experiment, to a new value of 121.7 kcal.mol(-1). Our experiments and electronic structure calculations provide evidence that some of the product channels, including phototautomerization, occur on S-0, while others likely occur on excited triplet surfaces. Although the large oscillator strength of the S-2