Vibrational mode-specific dynamics of the F− + CH3CH2Cl multi-channel reaction

• Published in: Physical chemistry chemical physics : PCCP 2022-04, Vol.24 (14), p.8166-8181
• Main Authors: Tajti, Viktor, Czakó, Gábor
• Format: Article
• Language: English
• Subjects: Angle of attack; Channels; Dimensional analysis; Excitation; Failure analysis; Potential energy; Protons; Stretching
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d2cp00685e

We investigate the mode-specific dynamics of the ground-state, C–Cl stretching (v10), CH2 wagging (v7), sym-CH2 stretching (v1), and sym-CH3 stretching (v3) excited F− + CH3CH2Cl(vk = 0, 1) [k = 10, 7, 1, 3] → Cl− + CH3CH2F (SN2), HF + CH3CHCl−, FH⋯Cl− + C2H4, and Cl− + HF + C2H4 (E2) reactions using a full-dimensional high-level analytical global potential energy surface and the quasi-classical trajectory method. Excitation of the C–Cl stretching, CH2 stretching, and CH2/CH3 stretching modes enhances the SN2, proton abstraction, and FH⋯Cl− and E2 channels, respectively. Anti-E2 dominates over syn-E2 (kinetic anti-E2 preference) and the thermodynamically-favored SN2 (wider reactive anti-E2 attack angle range). The direct (a) SN2, (b) proton abstraction, (c) FH⋯Cl− + C2H4, (d) syn-E2, and (e) anti-E2 channels proceed with (a) back-side/backward, (b) isotropic/forward, (c) side-on/forward, (d) front-side/forward, and (e) back-side/forward attack/scattering, respectively. The HF products are vibrationally cold, especially for proton abstraction, and their rotational excitation increases for proton abstraction, anti-E2, and syn-E2, in order. Product internal-energy and mode-specific vibrational distributions show that CH3CH2F is internally hot with significant C–F stretching and CH2 wagging excitations, whereas C2H4 is colder. One-dimensional Gaussian binning technique is proved to solve the normal mode analysis failure caused by methyl internal rotation.