Time filter

Source Type

Mineo H.,Institute of Atomic and Molecular Science | Fujimura Y.,National Chiao Tung University
Journal of Physics: Conference Series | Year: 2015

We propose an ultrafast quantum switching method of π-electron rotations, which are switched among four rotational patterns in a nonplanar chiral aromatic molecule (P)-2,2'- biphenol and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses. Coherent π-electron dynamics are generated by applying the linearly polarized UV pulse laser to create a pair of coherent quasidegenerated excited states. We also plot the time-dependent π-electron ring current, and discussed ring current transfer between two aromatic rings. © Published under licence by IOP Publishing Ltd. Source

Takahashi K.,University of Colorado at Boulder | Takahashi K.,Institute of Atomic and Molecular Science | Plath K.L.,University of Colorado at Boulder | Axson J.L.,University of Colorado at Boulder | And 3 more authors.
Journal of Chemical Physics | Year: 2010

The early time dynamics of vibrationally excited glyoxylic acid and of its monohydrate 2,2-dihydroxyacetic acid are investigated by theoretical and spectroscopic methods. A combination of "on-the-fly" dynamical simulations and cavity ring-down spectroscopy on the excited O-H stretching vibrational levels of these molecules observed that conformers that possess the correct structure and orientation react upon excitation of Δ v OH =4,5, while the structurally different but near isoenergetic conformers do not undergo unimolecular decay by the same direct and fast process. Experiment and theory give a femtosecond time scale for hydrogen atom chattering in the vibrationally excited glyoxylic acid. This process is the precursor for the concerted decarboxylation of the ketoacid. We extrapolate the results obtained here to suggest a rapid subpicosecond overall reaction. In these light-initiated reactions, relatively cold hydroxycarbenes, stable against further unimolecular decay, are expected products since most of the excitation energy is consumed by the endothermicity of the reaction. Glyoxylic acid and its monohydrate are atmospherically relevant ketoacids. The vibrational overtone initiated reactions of glyoxylic acid leading to di- and monohydroxycarbenes on subpicosecond time scales are potentially of importance in atmospheric chemistry since the reaction is sufficiently rapid to avoid collisional dissipation. © 2010 American Institute of Physics. Source

Chen S.-Y.,National Chiao Tung University | Lee Y.-P.,National Chiao Tung University | Lee Y.-P.,Institute of Atomic and Molecular Science
Journal of Chemical Physics | Year: 2010

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of CH3 CO and O2; IR absorption spectra of CH3 C (O) OO and α -lactone were observed. Absorption bands with origins at 1851±1, 1372±2, 1169±6, and 1102±3 cm-1 are attributed to t -CH3 C (O) OO, and those at 1862±3, 1142±4, and 1078±6 cm-1 are assigned to c -CH3 C (O) OO. A weak band near 1960 cm-1 is assigned to α -lactone, cyc- CH2 C (=O) O, a coproduct of OH. These observed rotational contours agree satisfactorily with simulated bands based on predicted rotational parameters and dipole derivatives, and observed vibrational wavenumbers agree with harmonic vibrational wavenumbers predicted with B3LYP/aug-cc-pVDZ density-functional theory. The observed relative intensities indicate that t -CH3 C (O) OO is more stable than c -CH3 C (O) OO by 3±2 kJ mol-1. Based on these observations, the branching ratio for the OH+α -lactone channel of the CH3 CO+ O2 reaction is estimated to be 0.04±0.01 under 100 Torr of O2 at 298 K. A simple kinetic model is employed to account for the decay of CH 3 C (O) OO. © 2010 American Institute of Physics. Source

Kumar P.,Institute of Atomic and Molecular Science | Hu L.-H.,Southern Taiwan University of Science and Technology
Journal of Alloys and Compounds | Year: 2016

Flower-like self-assembly of vanadium pentoxide (V2O5) has been synthesized via a facile, eco-friendly and bottom-up approach using hydrothermal process at low temperature with high-yield for the first time. This hierarchical flower-like structure is found to be accumulated with numerous plate-like subunits, and each unit seems to be a complete structure of randomly grown hexagonal nano/micro plates. A possible reaction mechanism for the formation of hierarchical flower-like structures of V2O5 has also been proposed. The reduction process (from V5+to V4+ or some mix oxidation states)is carried out through sulphur-reduction by using an advanced homemade CVD system with argon as the carrier gas at different temperatures. The sulphur reduced V2O5 structure formed shows excellent lithium storage and rate capability. After sulphur-reduction, the specific capacity of the flower-like V2O5 as the cathode material can achieve 400 mAh g-1, 300 mAh g-1, 250 mAh g-1 and 100 mAh g-1 at different rates of 0.07C, 1C, 2.3C and 29 C, respectively between 1.75 V and 4 V. © 2015 Elsevier B.V. Source

Nayak A.P.,University of Texas at Austin | Pandey T.,Indian Institute of Science | Voiry D.,Rutgers University | Liu J.,University of Texas at Austin | And 10 more authors.
Nano Letters | Year: 2015

Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure-property relation due to the rich band structure of MoS2. Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibrational properties of the MoS2 family can be extended to other 2D TMDs. These results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications. © 2014 American Chemical Society. Source

Discover hidden collaborations