Multidimensional characterization of the conical intersection seam in the normal mode space

Abstract

<p>Multidimensional conical intersection seam has been characterized by utilizing the dynamic resonances in the nonadiabatic transition probability experimentally observed in the predissociation of thioanisole isotopomers.</p>

πσ*-Mediated Nonadiabatic Tunneling Dynamics of Thiophenols in S1: The Semiclassical Approaches

“…Thereafter, the nonadiabatic transition especially in the proximity of the conical intersection occurs with the significantly high probability to govern the overall dynamic outputs such as reaction rates, product yields, branching ratios, or energy disposals. − The nonadiabatic transition probability is extremely sensitive to the nature of the reactive flux with respect to the electronic/nuclear configurations at the conical intersection, and thus its theoretical prediction (or the explanation of the experiment) has been quite challenging especially for polyatomic molecular systems. In this aspect, the πσ*-mediated photochemistry of the heteroaromatic molecular system − has provided the nice platform for many recent years not only for elucidating the mechanism of the ultrafast nonradiative transitions frequently found in biological building blocks but also for the thorough understanding of the conical intersection dynamics. − Among the systems of interest, predissociation dynamics of thioanisole is particularly notable. − Therein, the S 1 /S 2 and S 0 /S 2 conical intersections are encountered along the S–CH 3 bond extension coordinate. The former is close to the vertical transition region whereas the latter is located at the later stage of the reaction.…”

“…Due to the small energy difference (∼3000 cm –1 ) of two final distinct product channels into either C 6 H 5 S·(Ã) or C 6 H 5 S·(X̃), the nonadiabatic transition probability could be precisely estimated from the analysis of product translational energy distributions in a state-specific way. The nonadiabatic dynamics from the well-defined quantum state of the reactant to that of the product gives the resonance-like features in the nonadiabatic transition probability, giving the unprecedented deep insights into the structural and dynamic properties of the conical intersections responsible for the eventual S–CH 3 bond breakage. ,, It has also been found that the reactive flux in S 1 is bifurcated at the first S 1 (ππ*)/S 2 (πσ*) conical intersection into either the Herzberg type-I (electronic) or type-II (vibrational) predissociation process − with distinct reaction rates and nonadiabatic transition probabilities . Very interestingly, the reactive flux of the type-I electronic predissociation is faster to give the higher nonadiabatic transition probability compared to the case of the type-II vibrational predissociation, indicating that the electronic predissociation in which the reactive flux should funnel through the rather narrow conical intersection region fast exhibits the higher nonadiabatic transition probability.…”

Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules

“…The πσ*‐mediated photochemistry, in this aspect, is quite unique as it gives the rational explanation for the ultrafast nonradiative transitions of many heteroaromatic molecular systems upon the electronic excitations, which are often relevant to the photochemical or photobiological activities 6,19–38 . As a matter of fact, spectroscopic and dynamic studies on heteroaromatic systems including phenols, 9,12,39–75 thiophenols, 10–12,76–97 anisoles, 98–102 thioanisoles, 5,103–115 or many others are vast in terms of their diversities and detailed dynamic features. Herein, we focus on the H‐atom detachment reactions of phenols and thiophenols especially in terms of the state‐specific tunneling rate constants.…”

Femtosecond Wavepacket Dynamics Reveals the Molecular Structures in the Excited (S1) and Cationic (D0) States

“…26−37 For instance, the nonadiabatic transition probability has been found to be strongly mode-dependent in the S-CH 3 bond predissociation of the electronically excited (S 1 ) thioanisole. 11,13,14,16,17 The nonadiabatic transition probability is strongly enhanced when (the nuclear configuration of the reactive flux given by) the specific vibronic mode accesses the conical intersection region. From the exploration of the wide range of the phase space, the otherwise formidable task of capturing the conical intersection in terms of the structure and its dynamic role becomes a reality now.…”

“…The mode dependence of the dynamic outputs such as reaction rates and/or product yields has been extremely useful in disentangling the complicated coupling dynamics among numerous vibronic modes associated with the reaction channels. In this aspect, the dynamics around conical intersections have been studied in impressive detail in recent studies on thioanisoles, − thiophenols, − or phenols. − For instance, the nonadiabatic transition probability has been found to be strongly mode-dependent in the S-CH 3 bond predissociation of the electronically excited (S 1 ) thioanisole. ,,,, The nonadiabatic transition probability is strongly enhanced when (the nuclear configuration of the reactive flux given by) the specific vibronic mode accesses the conical intersection region. From the exploration of the wide range of the phase space, the otherwise formidable task of capturing the conical intersection in terms of the structure and its dynamic role becomes a reality now.…”