Time-Dependent Center-of-Gravity Metric Determines Key Dynamical Features of Doorway-Mediated Intersystem Crossing

Traditional statistical models provide only a phenomenological description of intersystem crossing, the spin−orbit-induced mixing of optically bright and dark excited electronic states with different values of total electron spin, S. The statistical models do not identify the dominant energy flow pa...

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Bibliographic Details
Published in:The journal of physical chemistry letters 2010-07, Vol.1 (14), p.2144-2148
Main Authors: Bittinger, Kyle L, Virgo, Wilton, Field, Robert W
Format: Article
Language:English
Subjects:
Kinetics, Spectroscopy
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Summary:Traditional statistical models provide only a phenomenological description of intersystem crossing, the spin−orbit-induced mixing of optically bright and dark excited electronic states with different values of total electron spin, S. The statistical models do not identify the dominant energy flow pathways and the state-specific mechanisms responsible for the mixing of zero-order bright state character into dark states. A time-dependent center of gravity metric, described herein, is sensitive to deterministic patterns of bright state−dark state mixing that deviate from mechanism-free statistical pictures. The center of gravity metric may be applied to incoherently excited, time-gated, high-resolution spectra of small molecules in a narrow energy region surrounding each selectable transition into an optically bright rovibronic state. The metric reveals the characteristic behavior caused by the nonstochastic bias in the local distribution of fractional bright state character, as well as the magnitude of the matrix element between bright and dark states. We use a simple two-state model to illustrate the metric, and then apply the metric to several transitions in the S1−S0 spectrum of acetylene. The metric is robust with respect to measurement deficiencies common in laser-induced fluorescence spectroscopy, and may be applied to numerically characterize state-specific mechanisms of intersystem crossing beyond the scope of statistical Golden Rule models.
ISSN:1948-7185
1948-7185
DOI:10.1021/jz100526g