Dehydrohalogenation and Dehydration Reactions of i-C3H7Br and i-C3H7OH by Sodium Ions Studied by Guided Ion Beam Techniques and Quantum Chemical Methods

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• 作者：E. López ; J. M. Lucas ; J. de Andrés ; M. Albertí ; J. M. Bofill ; A. Aguilar
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：July 14, 2016
• 年：2016
• 卷：120
• 期：27
• 页码：4758-4769
• 全文大小：527K
• 年卷期：0
• ISSN：1520-5215

文摘

Dehydrohalogenation and dehydration reactions of gas-phase i-C₃H₇Br and i-C₃H₇OH molecules induced by collision with Na⁺, all participants being in their electronic ground state, were studied experimentally in our laboratory using a radiofrequency-guided ion beam apparatus and covering the 0.10–10.00 eV center of mass (CM) energy range. In Na⁺ + i-C₃H₇Br collisions the formation of [C₃H₆–Na]⁺ and [HBr–Na]⁺ by dehydrohalogenation was observed and quantified, as well as that of the ion–molecule adduct [Na–i-C₃H₇Br]⁺ together with its decomposition products C₃H₇⁺ and NaBr. In Na⁺ + i-C₃H₇OH collisions the dehydration product [H₂O–Na]⁺ was also found, while [C₃H₆–Na]⁺ was hardly detected. Moreover, the [Na–i-C₃H₇OH]⁺ adduct formation as well as its decomposition into C₃H₇⁺ and NaOH were also quantified. For all these processes, absolute reaction cross sections were measured as a function of the CM collision energy. From measured excitation functions, rate constants for the formation of [C₃H₆–Na]⁺, [HBr–Na]⁺, and [H₂O–Na]⁺ at 303 K were obtained. Complementing the experiments, exhaustive ab initio structure calculations at the MP2 level of theory were performed, giving information on the most relevant features of the potential energy surfaces (PESs) where the dehydrohalogenation, dehydration, and decomposition reactions take place adiabatically for both collision systems. On these PESs different stationary points associated with potential energy minima and transition state barriers were characterized, and their connectivity was ensured using the intrinsic-reaction-coordinate method. The main topology features of the ab initio calculated PESs allowed a qualitative interpretation of the experimental data also exposing the role of the sodium ion as a catalyst in elimination reactions.