Hydrogen Transfer vs Proton Transfer in 7-Hydroxy-quinoline·(NH3)3: A CASSCF/CASPT2 Study

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• 作者：Antonio Ferná ; ndez-Ramos ; Emilio Martí ; nez-Nú ; ñ ; ez ; Saulo A. Vá ; zquez ; Miguel A. Rí ; os ; Carlos M. Est&eacute ; vez ; Manuela Merchá ; n ; Luis Serrano-Andr&eacute ; s
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：July 5, 2007
• 年：2007
• 卷：111
• 期：26
• 页码：5907 - 5912
• 全文大小：113K
• 年卷期：v.111,no.26(July 5, 2007)
• ISSN：1520-5215

文摘

Multiconfigurational CASSCF and CASPT2 calculations were performed to investigate the enol s/entities/rarr.gif"> ketotautomerization in the lowest singlet excited state of the 7-hydroxyquinoline·(NH₃)₃ cluster. Two differentreaction mechanisms were explored. The first one corresponds to that proposed previously by Tanner et al.(Science 2003, 302, 1736) on the basis of experimental observations and CASSCF optimizations under C_s-symmetry constraints. This mechanism comprises four consecutive steps and involves nonadiabatic transitionsbetween the valence ¹s/gifchars/pi.gif" BORDER=0 >s/gifchars/pi.gif" BORDER=0 >* state and a s/gifchars/pi.gif" BORDER=0 >s/gifchars/sigma.gif" BORDER=0 >* Rydberg-type state, resulting in hydrogen-atom transfer. Single-point CASPT2 calculations corroborate that for C_s-symmetry pathways hydrogen-atom transfer is clearlypreferred over proton transfer. The second mechanism, predicted by CASSCF optimizations without constraints,implies proton transfer along a pathway on the ¹s/gifchars/pi.gif" BORDER=0 >s/gifchars/pi.gif" BORDER=0 >* surface in which one or more ammonia moleculesdepart significantly from the molecular plane defined by the hydroxyquinoline ring. The results suggest thatboth mechanisms may be competitive with proton transfer being somewhat favorable over hydrogen-atomtransfer.