On Extracting Subfemtosecond Data from Femtosecond Quantum Dynamics Calculations: The Methane Cation

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• 作者：T. Mondal ; A. J. C. Varandas
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2014
• 出版时间：September 9, 2014
• 年：2014
• 卷：10
• 期：9
• 页码：3606-3616
• 全文大小：517K
• ISSN：1549-9626

文摘

Motivated by recent measurements of the subfemtosecond structural rearrangement in the methane cation using high-harmonic generation technology, here, we attempt an ab initio quantum dynamics study to explore such an event by modeling the experiments. This is done by calculating the ratio of the squared autocorrelation functions of wave packets that evolve on the X虄²T₂ electronic manifold of the isotopes CD₄⁺ and CH₄⁺, in full dimensionality including nonadiabatic coupling. We have found good agreement with the experimental data, and additionally predict an unexpected maximum in the above ratio at 鈭?.85 fs, thence outside the experimentally covered time-delay window. We further predict the above structural rearrangements to occur in 鈭?.85 fs, and we propose a mechanism for this via a five-dimensional hypersurface developed from the JT active bending vibrations of e and t₂ symmetry. Recurrences of such a maximum are also found with an interval of time delays, and the average of such intervals suggested corroboration of the oscillation time between the T_d and the C_2v geometries of CH₄⁺. Furthermore, we perform a dynamics study up to 200 fs, and we unravel the underlying details of the first photoelectron band of CD₄.