Dissociation of acetone radical cation (CH₃COCH₃⁺˙ → CH₃CO⁺+CH₃˙): An ab initio direct classical trajectory study

Controlling tunnelling in methane loss from acetone ions by deuteration

“…At an internal energy of 80-100 kJ mol À1 , acetone ions dissociate by two paths, either by the loss of a CH 3 radical by simple bond rupture or by the loss of CH 4 , which clearly involves a rearrangement, as shown in Fig. 16 Methane loss can only occur by tunnelling below the energy of its transition state, and will contribute to the reaction dynamics if this energy level lies close by the methyl-loss product energies. The two ion products formed are the acetyl ion (CH 3 CO + ) and the ketene ion (CH 2 CO + ).…”

“…The two ion products formed are the acetyl ion (CH 3 CO + ) and the ketene ion (CH 2 CO + ). The computational conclusion of Anand and Schlegel, 16 that the methane loss transition sate lies below the threshold to methyl-loss, has been both accepted 17 and called into question 18 in later photoionization studies. In a study of mixed isotopes, Lifshitz and Tzidony reported a CD 3 H yield 70 times higher than that of CH 3 D in the metastable methane loss from CH 3 COCD 3 + , 13 i.e.…”

“…14 However, in a subsequent study, Osterheld and Brauman reported a much lower KIE by IR multiphoton dissociation (IRMPD) and concluded that tunnelling was not needed to account for methane abstraction dynamics, 15 a conclusion later corroborated by Anand and Schlegel in an ab initio trajectory study. 16 Methane loss can only occur by tunnelling below the energy of its transition state, and will contribute to the reaction dynamics if this energy level lies close by the methyl-loss product energies. However, without internal energy selection, achieved by matrix cooling in neutrals and threshold photoionization by tuneable monochromatic radiation in ions, mechanistic insights can become blurred.…”

“…17,18 The branching ratios reported in the IRMPD study 15 are vastly different from our observations (vide infra), which suggests that a different, potentially non-statistical or isotope sensitive sequential photodissociation reaction route was sampled by Osterheld and Brauman. The computational conclusion of Anand and Schlegel, 16 that the methane loss transition sate lies below the threshold to methyl-loss, has been both accepted 17 and called into question 18 in later photoionization studies.…”

Ab initio and semi-empirical Molecular Dynamics simulations of chemical reactions in isolated molecules and in clusters

“…The method was used to study the formation 12 and protonation of nitric acid, 13 as well as related systems; 14 photodetachment of an anion complex, (F À )(H 2 O) 4 , 15 S N 2 reactions; 16 unimolecular dissociation of H 2 CO and related molecules; 17,18 abstraction reactions of H atoms 19 and a few others. As the merits of MP2 in MD calculations became increasingly recognized, many more applications of the method were reported, including additional studies of nitric acid formation; [20][21][22][23][24] ionization dynamics (and the reverse process of electron capture); [25][26][27][28][29][30][31] S N 2 reactions; [32][33][34] dynamics in the transition state region, also in the context of unimolecular reactions; [35][36][37][38] hydrogen atom abstraction and elimination reactions [39][40][41][42][43][44] and a host of other processes. In the last several years, the use of MD-MP2 has become quite extensive, especially for polyatomic systems of small to moderate sizes.…”