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The H atom tunneling dissociation dynamics of the S1 state of meta- or para-cresol has been investigated by using the picosecond time-resolved pump-probe spectroscopy in a state-specific manner. The S1 state lifetime (mainly due to the H atom tunneling reaction) is found to be mode-dependent whereas it quickly converges and remains constant as the rapid intramolecular vibrational energy redistribution (IVR) starts to participate in the S1 state relaxation with the increase of the S1 internal energy (Eint). The IVR rate and its change with increasing Eint have been reflected in the parent ion transients taken by tuning the total energy (hνpump + hνprobe) just above the adiabatic ionization threshold (so that the dissipation of the initial mode-character could be monitored as a function of the reaction time), indicating that the mode randomization rate into the S1 isoenergetic manifolds exceeds the tunneling rate quite early in terms of Eint for m-cresol (≤∼1200 cm−1) or p-cresol (≤∼800 cm−1) compared to the case of phenol (≤∼1800 cm−1). Though the H atom tunneling dynamics of phenol (S1) seems to be little influenced by the methyl substitution on the either m- or p-position, the IVR rate has been found to be strongly accelerated due to the sharply-increasing (S1) density of states with increasing Eint due to the pivotal role of the low-frequency CH3 torsional mode. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase single-stage AC-DC converter for an IPT-based small wind power generation system (WPGS) with an S-S compensation circuit is proposed. It applies a three-phase single-stage AC-DC converter to improve the input power factor (PF), efficiency, and reliability in small WPGSs. Also, inductive power transfer (IPT) was applied to compensate for brush wear in the nacelle of small and medium-sized wind turbines while ensuring electrical safety. In conditions of the three-phase Permanent Magnet Synchronous Generator (PMSG) voltage (80~260 Vrms) for the wind turbine and the load (150~1000 W), it was verified that the desired output voltage below 3% can be controlled through the fixed link voltage (VLink) control without wireless communication. A 1 kW prototype was built and tested to demonstrate its applicability to the rotation of small and medium-sized wind turbine nacelles instead of brushes and slip rings. [ABSTRACT FROM AUTHOR]

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]

Developing coherent excitation methods for quantum emitters ensuring high brightness, optimal single‐photon purity and indistinguishability of the emitted photons has been a key challenge in the past years. While various methods have been proposed and explored, they all have specific advantages and disadvantages. This study investigates the dynamics of the recent swing‐up scheme as an excitation method for a two‐level system and its performance in single‐photon generation. By applying two far red‐detuned laser pulses, the two‐level system can be prepared in the excited state with near‐unity fidelity. The successful operation and coherent character of this technique are demonstrated using a semiconductor quantum dot (QD). Moreover, the multi‐dimensional parameter space of the two laser pulses is explored to analyze its impact on excitation fidelity. Finally, the performance of the scheme as an excitation method for generating high‐quality single photons is analyzed. The swing‐up scheme itself proves effective, exhibiting nearly perfect single‐photon purity, while the observed indistinguishability in the studied sample is limited by the influence of the inevitable high excitation powers on the semiconductor environment of the quantum dot. [ABSTRACT FROM AUTHOR]

Ultrafast charge carrier dynamics of green‐light emitting InP/ZnSe/ZnS core–shell quantum dots (QDs) with three different ZnSe thickness of 2.0 nm (gQD‐20), 2.4 nm (gQD‐24), or 3.3 nm (gQD‐33) are interrogated by femtosecond transient absorption (TA) and femtosecond stimulated Raman spectroscopy (FSRS). Auger‐type cooling of hot electron into the band‐edge level of InP is clearly manifested in the TA spectra, giving its time constant of ≈222, 300, or 349 fs for gQD‐20, gQD‐24, or gQD‐33, respectively, indicating that the state‐filling to the 1S(e) of InP is significantly slowed down with the increase of the mid shell thickness. The global analysis of the whole TA spectra turns out to be extremely useful to explain the dynamic behavior of the heterogeneous ensemble of single and/or bi‐ (or multi‐) excitons in the presence of the Stark‐shift. The hole‐relaxation dynamics into the band‐edge 1S (h) of the core InP is revealed in the bleaching dynamics of the FSR bands corresponding to the phonon mode of InP or ZnSe, giving the estimated lifetime of 1.0–1.4 ps for gQD‐20. The hole‐relaxation dynamics by the phonon emission seem to be little sensitive to the ZnSe shell thickness. [ABSTRACT FROM AUTHOR]

Photofragmentation dynamics of cis and trans isomers of 1,2-dibromoethylene (1,2-DBE) have been investigated by multiphoton excitation using a picosecond (ps) laser pulse. It has been found that the Br2+ product ion preferentially originates from the cis isomer rather than from trans. The Boltzmann-type isotropic low kinetic energy components of the Br+ and Br2+ product state distributions seem to be most likely from the unimolecular reactions of the vibrationally hot cationic ground state generated by the three-photon absorption at the photon energy below ∼38 000 cm−1. The highly anisotropic kinetic energy components of Br+ and Br2+ start to appear at the photon energy above ∼38 000 cm−1, where the Dn (n ≥ 1) − D0 transition is facilitated within the same ps laser pulse as the parent molecule is efficiently ionized by the two-photon absorption. The transition dipole moment of the D4 − D0 transition of the strongest oscillator strength has been theoretically predicted to be parallel to the C–Br bond or C=C bond axis for the trans or cis isomer, respectively. The fast anisotropic with the (β ∼ +2) component in the Br+ product distribution is thus likely from the trans isomer, whereas that of Br2+ (β ∼ −0.5) should be the consequence of the photodissociation of the cis isomer. The isomer-specific reactivity found here in the picosecond multiphoton excitation of 1,2-DBE provides a nice platform for the better understanding of the structure–reactivity relationship under the harsh condition of the strong or ultrashort optical field. [ABSTRACT FROM AUTHOR]