QCT study of the vibrational and translational role in the H + C2H6(ν1, ν2, ν5, ν7, ν9 and ν10) reactions
- 36 Downloads
Two important issues were analysed in the title reaction: the effects of vibrational excitation, associated with mode selectivity, and the role of translational energy, associated with Polanyi’s rules. Based on a global analytical potential energy surface, PES-2018, recently developed in our group, quasi-classical trajectory (QCT) calculations were performed at total energy of 35 kcal mol−1, either as translation or as a combination of translation and vibration energy. Independent vibrational excitation by one quantum of any of the CH3 stretching modes in ethane leads to similar dynamics pictures of reaction cross sections and H2(v′, j′) rotovibrational and scattering distributions, ruling out mode selectivity. Normal mode analysis showed a cold, non-inverted, H2(v′) product vibrational distribution, while the C2H5(v′) co-product presented many vibrational states, all of them with a low population, practically simulating a classical behaviour. An equivalent amount of energy as translation raises reactivity somewhat less effective than vibrational energy, contrary to that found for the O(3P) + CH4 reaction. Both reactions present “central” barriers, so this opposite behaviour shows the difficulties for a straightforward application of the Polanyi′s rules. The role of vibrational and translational energy on dynamics has been rationalized by the coupling between vibrational modes, which makes analysis of vibrational excitation difficult in polyatomic systems. Finally, the role of the total energy on reactivity and mode selectivity was analysed, concluding that at lower energy, 15 kcal mol−1, translational energy is much more effective than vibrational energy to enhance reactivity, while at intermediate energy, 20 kcal mol−1, the situation is more confusing and strongly dependent on the counting methods used in the QCT calculations. Therefore, very small mode selectivity is found, and translation seems to be more effective in enhancing reactivity than vibration at low collision energies, while this behaviour is reversed as we increase the collision energy, being the turning point around 20 kcal mol−1.
KeywordsVibrational excitation Central barrier reaction Potential energy surface Theoretical study
This work was partially supported by Junta de Extremadura and European Regional Development Fund, Spain (Project Nos. GR18010 and IB16013).
- 2.Espinosa-Garcia J, Corchado JC (2019) Phys Chem Chem Phys 21:13305Google Scholar
- 7.Porter RN, Raff LM (1976) In: Miller WH (ed) Dynamics of molecular collisions, Part B. Plenum Press, New YorkGoogle Scholar
- 8.Truhlar DG, Muckerman JT (1979) In: Bernstein RB (ed) Atom-molecules collision theory. Plenum Press, New YorkGoogle Scholar
- 9.Raff LM, Thompson DL (1985) In: Baer M (ed) Theory of chemical reaction dynamics, vol. 3. CRC Press, Boca RatonGoogle Scholar
- 11.Hase WL, Duchovic RJ, Hu X, Komornicki A, Lim KF, Lu D-H, Peslherbe GH, Swamy KN, Van de Linde SR, Varandas AJC, Wang H, Wolf RJ (1996) QCPE Bull. 16:43Google Scholar
- 29.Zheng J, Zhang S, Lynch BJ, Corchado JC, Chuang Y-Y, Fast PL, Hu W-P, Liu Y-P, Lynch GC, Nguyen KA, Truhlar DG (2010) POLYRATE-2010-A. University of Minnesota, Minneapolis, MNGoogle Scholar
- 30.Kraka E, Dunning TH (1990) In: Advances in molecular electronic structure theory, vol 1, JAI, New York, p 129Google Scholar