Ershov Kirill S, Kochubei Sergei A, Kiselev Vitaly G, Baklanov Alexey V
Novosibirsk State University , 2, Pirogova Street, 630090 Novosibirsk, Russia.
Institute of Chemical Kinetics and Combustion , 3, Institutskaya Street, 630090 Novosibirsk, Russia.
J Phys Chem A. 2018 Feb 1;122(4):1064-1070. doi: 10.1021/acs.jpca.7b10396. Epub 2018 Jan 19.
The UV-photodissociation at 266 nm of a widely used TiO precursor, titanium tetraisopropoxide (Ti(OPr), TTIP), was studied under molecular-beam conditions. Using the MS-TOF technique, atomic titanium and titanium(II) oxide (TiO) were detected among the most abundant photofragments. Experimental results were rationalized with the aid of quantum chemical calculations (DLPNO-CCSD(T) and DFT). Contrary to the existing data in the literature, the new four-centered acetone-elimination reaction was found to be the primary decomposition process of TTIP. According to computational results, the effective activation barrier of this channel was ∼49 kcal/mol, which was ∼13 kcal/mol lower than that of the competing propylene elimination. The former process, followed by the dissociative loss of an H atom, was a dominating channel of TTIP unimolecular decay. The sequential loss of isopropoxy moieties via these two-step processes was supposed to produce the experimentally observed titanium atoms. In turn, the combination of these reactions with propylene elimination can lead to another detected species, TiO. These results indicate that the existing mechanisms of TTIP thermal and photoinitiated decomposition in the chemical-vapor deposition (CVD) of titanium dioxide should be reconsidered.
在分子束条件下，研究了一种广泛使用的TiO前驱体四异丙醇钛（Ti(OPr)₄，TTIP）在266 nm处的紫外光解离。使用质谱-飞行时间（MS-TOF）技术，在最丰富的光解碎片中检测到了原子钛和氧化钛（II）（TiO）。借助量子化学计算（DLPNO-CCSD(T)和DFT）对实验结果进行了合理解释。与文献中的现有数据相反，发现新的四中心丙酮消除反应是TTIP的主要分解过程。根据计算结果，该通道的有效活化能垒约为49 kcal/mol，比竞争的丙烯消除反应的活化能垒低约13 kcal/mol。前一过程随后伴随着一个H原子的解离损失，是TTIP单分子衰变的主要通道。通过这两步过程依次损失异丙氧基部分应该会产生实验中观察到的钛原子。反过来，这些反应与丙烯消除反应的结合会导致另一种检测到的物种TiO。这些结果表明，在二氧化钛化学气相沉积（CVD）中，TTIP热分解和光引发分解的现有机制应该重新考虑。
