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Mode-dependent H atom tunneling dynamics of the O–H bond predissociation of the S1 phenol has been theoretically analyzed. As the tunneling is governed by the complicated multi-dimensional potential energy surfaces that are dynamically shaped by the upper-lying S1(ππ*)/S2(πσ*) conical intersection, the mode-specific tunneling dynamics of phenol (S1) has been quite formidable to be understood. Herein, we have examined the topography of the potential energy surface along the particular S1 vibrational mode of interest at the nuclear configurations of the S1 minimum and S1/S2 conical intersection. The effective adiabatic tunneling barrier experienced by the reactive flux at the particular S1 vibrational mode excitation is then uniquely determined by the topographic shape of the potential energy surface extended along the conical intersection seam coordinate associated with the particular vibrational mode. The resultant multi-dimensional coupling of the specific vibrational mode to the tunneling coordinate is then reflected in the mode-dependent tunneling rate as well as nonadiabatic transition probability. Remarkably, the mode-specific experimental result of the S1 phenol tunneling reaction [K. C. Woo and S. K. Kim, J. Phys. Chem. A 123, 1529–1537 (2019)] (in terms of the qualitative and relative mode-dependent dynamic behavior) could be well rationalized by semi-classical calculations based on the mode-specific topography of the effective tunneling barrier, providing the clear conceptual insight that the skewed potential energy surfaces along the conical intersection seam (strongly or weakly coupled to the tunneling reaction coordinate) may dictate the tunneling dynamics in the proximity of the conical intersection. [ABSTRACT FROM AUTHOR]

[Ca.sub.2+] is a highly versatile intracellular signal that regulates many different cellular processes, and cells have developed mechanisms to have exquisite control over [Ca.sup.2+] signaling. Epidermal growth factor (EGF), which fails to mobilize intracellular [Ca.sup.2+] when administrated alone, becomes capable of evoking [[Ca.sup.2+].sub.i] increase and exocytosis after bradykinin (BK) stimulation in chromaffin cells. Here, we provide evidence that this sensitization process is coordinated by a macromolecular signaling complex comprised of inositol 1,4,5-trisphosphate receptor type 1 (I[P.sub.3]R1), cAMP-dependent protein kinase (PKA), EGF receptor (EGFR), and an A-kinase anchoring protein, yotiao. The I[P.sub.3]R complex functions as a focal point to promote [Ca.sup.2+] release in two ways: (1) it facilitates PKA-dependent phosphorylation of I[P.sub.3]R1 in response to BK-induced elevation of cAMP, and (2) it couples the plasmalemmal EGFR with I[P.sub.3]R1 at the [Ca.sup.2+] store located juxtaposed to the plasma membrane. Our study illustrates how the junctional membrane I[P.sub.3]R complex connects different signaling pathways to define the fidelity and specificity of [Ca.sub.2+] signaling.

The πσ*‐mediated photochemistry of heteroaromatic molecules has provoked the investigation of the conical intersection dynamics. The Born–Oppenheimer approximation fails at the conical intersection where the S1 (ππ*) and S2 (πσ*) states cross. The nonadiabatic transitions are much influenced by the nuclear configuration of the reactive flux particularly in the curve‐crossing region encountered along the reaction pathway. In this article, we focus on the tunneling dynamics of phenols and thiophenols. The O (S)H bond cleavage occurs via tunneling through the barrier which is dynamically shaped by the upper‐lying S1/S2 conical intersection in terms of the couplings at the individual branching planes as well as along the (3N‐8) dimensional seam coordinates. State‐specific tunneling rates and their interpretation are given for phenol, substituted phenols, thiophenol, ortho‐substituted thiophenols, and benzenediols including their 1:1 water clusters. The completely orthogonal modes to the tunneling coordinate are very critical in the dynamic shaping of the reaction barrier. [ABSTRACT FROM AUTHOR]

Conical intersection seam comprised of crossing surfaces of two lowest excited states of dimethyl sulfide (DMS) has been directly accessed by the one-photon excitation from the ground equilibrium state. Since the S–C bond rupture takes place promptly, the molecular structure on the excited state effectively belongs to CS symmetry. Namely, excited states of 11B1 and 11A2 in C2V become 11A′′ and 21A′′ states in CS, respectively, and the optical transition from the ground equilibrium state to the dissociating molecule at the conical intersection seam is symmetry-allowed to facilitate the nonadiabatic transition on the 21A′′ state, leading eventually to the CH3S + CH3 products. The dynamic study of DMS, in this sense, gives the great opportunity to unravel the vibronic structure of the conical intersection seam by the conventional one-photon excitation method. In this work, utilizing the photofragment excitation (PHOFEX) spectroscopic method, the vibronic structures of DMS and its isotope analogs (CD3SCD3, CH3SCD3) at the conical intersection seam have been revealed, providing accurate lifetimes and detailed dynamics associated with individual vibronic transitions. The lifetime of the excited DMS is estimated to be ∼100 fs, indicating that the dissociation is complete within one single oscillation in the conical intersection region. It is also found that the symmetric CSC stretching mode is strongly coupled to the reaction coordinate, as manifested by our experimental finding that the fragmentation yield of the S–CD3 bond is enhanced compared to that of the S–CH3 bond in the CH3SCD3 dissociation reaction only when the CSC symmetric stretching vibrational mode is excited at the conical intersection region. This work demonstrates that the better understanding of the excited state could make the bond-selective chemistry into reality. [ABSTRACT FROM AUTHOR]

The dynamic role of the intramolecular hydrogen bond in the S 1 relaxation of cis -2-chlorophenol (2-CP) or cis -2-chlorothiophenol (2-CTP) has been investigated in a state-specific manner. Whereas ultrafast internal conversion is dominant for 2-CP, the H-tunneling competes with internal conversion for 2-CTP even at the S 1 origin. The S 0 -S 1 internal conversion rate of 2-CTP could be directly measured from the S 1 lifetimes of 2-CTP- d 1 (Cl-C 6 H 4 -SD) as the D-tunneling is kinetically blocked, allowing distinct estimations of tunneling and internal conversion rates with increasing the energy. The internal conversion rate of 2-CTP increases by two times at the out-of-plane torsional mode excitation, suggesting that the internal conversion is facilitated at the nonplanar geometry. It then sharply increases at ∼600 cm -1 , indicating that the S 1 /S 0 conical intersection is readily accessible at the extended C-Cl bond length. The strength of the intramolecular hydrogen bond should be responsible for the distinct dynamic behaviors of 2-CP and 2-CTP.

Mode-dependent H atom tunneling dynamics of the O-H bond predissociation of the S 1 phenol has been theoretically analyzed. As the tunneling is governed by the complicated multi-dimensional potential energy surfaces that are dynamically shaped by the upper-lying S 1 (ππ*)/S 2 (πσ*) conical intersection, the mode-specific tunneling dynamics of phenol (S 1 ) has been quite formidable to be understood. Herein, we have examined the topography of the potential energy surface along the particular S 1 vibrational mode of interest at the nuclear configurations of the S 1 minimum and S 1 /S 2 conical intersection. The effective adiabatic tunneling barrier experienced by the reactive flux at the particular S 1 vibrational mode excitation is then uniquely determined by the topographic shape of the potential energy surface extended along the conical intersection seam coordinate associated with the particular vibrational mode. The resultant multi-dimensional coupling of the specific vibrational mode to the tunneling coordinate is then reflected in the mode-dependent tunneling rate as well as nonadiabatic transition probability. Remarkably, the mode-specific experimental result of the S 1 phenol tunneling reaction [K. C. Woo and S. K. Kim, J. Phys. Chem. A 123, 1529-1537 (2019)] (in terms of the qualitative and relative mode-dependent dynamic behavior) could be well rationalized by semi-classical calculations based on the mode-specific topography of the effective tunneling barrier, providing the clear conceptual insight that the skewed potential energy surfaces along the conical intersection seam (strongly or weakly coupled to the tunneling reaction coordinate) may dictate the tunneling dynamics in the proximity of the conical intersection.

The S-H bond tunneling predissociation dynamics of thiophenol and its ortho -substituted derivatives (2-fluorothiophenol, 2-methoxythiophenol, and 2-chlorothiphenol) in S 1 (ππ*) where the H atom tunneling is mediated by the nearby S 2 (πσ*) state (which is repulsive along the S-H bond extension coordinate) have been investigated in a state-specific way using the picosecond time-resolved pump-probe spectroscopy for the jet-cooled molecules. The effects of the specific vibrational mode excitations and the SH/SD substitutions on the S-H(D) bond rupture tunneling dynamics have been interrogated, giving deep insights into the multidimensional aspects of the S 1 /S 2 conical intersection, which also shapes the underlying adiabatic tunneling potential energy surfaces (PESs). The semiclassical tunneling rate calculations based on the Wentzel-Kramers-Brillouin (WKB) approximation or Zhu-Nakamura (ZN) theory have been carried out based on the ab initio PESs calculated in the (one, two, or three) reduced dimensions to be compared with the experiment. Though the quantitative experimental results could not be reproduced satisfactorily by the present calculations, the qualitative trends among different molecules in terms of the behavior of the tunneling rate versus the (adiabatic) barrier height or the number of PES dimensions could be rationalized. Most interestingly, the H/D kinetic isotope effect observed in the tunneling rate could be much better explained by the ZN theory compared to the WKB approximation, indicating that the nonadiabatic coupling matrix elements should be invoked for understanding the tunneling dynamics taking place in the proximity of the conical intersection.

The S 1 -state decaying rates of the three different benzenediols, catechol, resorcinol, and hydroquinone, and their 1:1 water clusters have been state-specifically measured using the picosecond time-resolved parent ion transients obtained by the pump (excitation) and probe (ionization) scheme. The S 1 lifetime of catechol is found to be short, giving τ ∼ 5.9 ps at the zero-point level. This is ascribed to the H-atom detachment from the free OH moiety of the molecule. Consistent with a previous report ( J. Phys. Chem. Lett. 2013 , 4 , 3819-3823), the S 1 lifetime gets lengthened with low-frequency vibrational mode excitations, giving τ ∼ 9.0 ps for the 116 cm -1 band. The S 1 lifetimes at the additional vibronic modes of catechol are newly measured, showing the nonnegligible mode-dependent fluctuations of the tunneling rate. When catechol is complexed with water, the S 1 lifetime is enormously increased to τ ∼ 1.80 ns at the zero-point level while it shows an unusual dip at the intermolecular stretching mode excitation (τ ∼ 1.03 ns at 146 cm -1 ). Otherwise, it is shortened monotonically with increasing the internal energy, giving τ ∼ 0.67 ns for the 856 cm -1 band. Two different asymmetric or symmetric conformers of resorcinol give the respective S 1 lifetimes of 4.5 or 6.3 ns at their zero-point levels according to the estimation from our transients taken within the temporal window of 0-2.7 ns. When resorcinol is 1:1 complexed with H 2 O, the S 1 decaying rate is slightly accelerated for both conformers. The S 1 lifetimes of trans and cis forms of hydroquinone are measured to be more or less same, giving τ ∼ 2.8 ns at the zero-point level. When H 2 O is complexed with hydroquinone, the S 1 decaying process is facilitated for both conformers, slightly more efficiently for the cis conformer.

Molecular structures in the electronically excited (S 1 ) and cationic (D 0 ) states of 2-fluorothioanisole (2-FTA) have been precisely refined from the real-time dynamics of the femtosecond (fs) wavepacket prepared by the coherent excitation of the Franck-Condon active out-of-plane torsional modes in the S 1 ← S 0 transition at 285 nm. The simulation to reproduce the experiment in terms of the beating frequencies gives the nonplanar geometry of 2-FTA in S 1 , where the out-of-plane dihedral angle (φ) of the S-CH 3 moiety is 51° with respect to the molecular plane. The behavior of the fs wavepacket in terms of the amplitudes and phases with the change of the probe (ionization) wavelength (λ probe = 300-330 nm) provides the otherwise veiled structure of the cationic D 0 state. While the 2-FTA cation adopts the planar geometry (φ = 0°) at the global minimum, it is found to have a vertical minimum at φ ≈ 135° from the perspective of the D 0 ← S 1 vertical transition. Ab initio calculations support the experiment quite well although the simulation using the model potentials could improve the match with the experiment, giving the new interpretation for the previously disputed photoelectron spectroscopic results.

Fermi resonances in the first electronically excited (S 1 ) state of phenol have been observed in real time. Quantum beats associated with coherent superposition of Fermi resonant eigenstates are manifested as temporal oscillations of the ionization cross sections of which the amplitudes are strongly dependent on the total ionization energy. This indicates that coherently excited eigenstates are effectively decomposed into their zeroth-order states, providing the unique opportunity for the investigation of nonstationary state dynamics in real-time. Energy gaps (Δν̃) of eigenstates within the laser coherence width have been most precisely determined up to date, giving Δν̃ ∼ 3.302 ± 0.001 or 1.655 ± 0.001 cm -1 for the 1 1 /4 1 10b 1 or 12 2 /8a 1 Fermi doublets, respectively. Dephasing rate suddenly increases as the S 1 internal energy becomes above ∼1500 cm -1 , revealing the important role of energy randomization dynamics during the H atom tunneling process of phenol in S 1 .