Revealing the Ultrafast Energy Transfer Pathways in Energetic Materials: Time-Dependent and Quantum State-Resolved.

Intramolecular vibrational energy transfer is gaining tremendous attention as a regulator of condensed-phase behavior and reactions. In polyatomic molecules, this transfer is an ultrafast process involving multiple modes with numerous quantum states. The inherent complexity and rapid evolution of these processes pose significant challenges to experimental observation, and the high computational costs make full quantum mechanical calculations impractical with current technology.

Impact of the uniaxial strain on terahertz modulation characteristics in flexible epitaxial VO film across the phase transition.

Exploring flexible electronics is on the verge of innovative breakthroughs in terahertz (THz) communication technology. Vanadium dioxide (VO) with insulator-metal transition (IMT) has excellent application potential in various THz smart devices, but the associated THz modulation properties in the flexible state have rarely been reported. Herein, we deposited an epitaxial VO film on a flexible mica substrate via pulsed-laser deposition and investigated its THz modulation properties under different uniaxial strains across the phase transition.

Femtosecond coherent anti-Stokes Raman spectroscopy study of vibrational dynamics of liquid chloroform.

Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) was used to study the dynamics of the vibrational modes of liquid chloroform. The vibrational modes were selectively excited and their coherent vibrational dynamics were obtained. Some subtle features that are difficult to distinguish in the ordinary spontaneous Raman spectrum, such as overtones and combinations of some fundamental vibrational modes, were recognized from the CARS transients.

Vibrational energy redistribution in crystalline nitromethane simulated by molecular dynamics.

molecular dynamics simulations (AIMD) are systematically performed to study the Vibrational Energy Redistribution (VER) in solid nitromethane (NM) by combining normal mode decomposition and short-time Fourier transform technique. After the selective excitations of all fourteen intramolecular vibrational modes above 400 cm, four three-dimensional (3D) excitation and detected vibrational spectra are obtained. The evolution of the kinetic energy proportion of all vibrations are also given and discussed quantitatively.

Elucidating the Coupling Mechanisms of Rapid Intramolecular Vibrational Energy Redistribution in Nitromethane: Ab Initio Molecular Dynamics Simulation.

Ab initio molecular dynamics simulations are presented to investigate the intramolecular vibrational energy redistribution (IVR) of an isolated nitromethane molecule. A number of IVR processes are simulated by monitoring the kinetic energy of vibrational modes under selective low-lying vibrational excitations from their ground states (Δν = 1 or 2). Evolution of the normal-mode kinetic energy gives the ultrafast energy transfer processes from parent modes to daughter modes intuitively.

Ab initio molecular dynamics simulation of vibrational energy redistribution of selective excitation of C-H stretching vibrations for solid nitromethane.

Vibrational energy redistribution (VER) of energetic materials plays an important role in transferring the injected energy to the hot spots, but it is extremely challenging to understand the mechanism of VER from experimental or theoretical studies. Here, we combined nonequilibrium molecular dynamics with density functional theory to study the processes of VER for solid nitromethane after the selective excitation of the C-H stretching vibration. The VER processes are traced by monitoring the normal-mode kinetic energies of both excited and unexcited vibrations.

Predicting the Initial Thermal Decomposition Path of Nitrobenzene Caused by Mode Vibration at Moderate-Low Temperatures: Temperature-Dependent Anti-Stokes Raman Spectra Experiments and First-Principals Calculations.

The lack of understanding of the initial decomposition micromechanism of energetic materials subjected to external stimulation has hindered its safe storage, usage, and development. The initial thermal decomposition path of nitrobenzene triggered by molecular thermal motion is investigated using temperature-dependent anti-Stokes Raman spectra experiments and first-principles calculations to clarify the initial thermal decomposition micromechanism. The experiment shows that the symmetric nitro stretching, antisymmetric nitro stretching, and phenyl ring stretching vibration modes are active as increasing temperature below 500 K.

Correction: Tracking intramolecular energy redistribution dynamics in aryl halides: the effect of halide mass.

[This corrects the article DOI: 10.1039/C8RA04979C.].

Tracking intramolecular energy redistribution dynamics in aryl halides: the effect of halide mass.

Selective excitation of C-H, C-C, CX and CX stretching vibrational modes in an orderly manner, detection of intramolecular energy redistribution and vibrational coupling in the electronic ground state of aryl halides are performed by time- and frequency-resolved Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy. Intramolecular energy flow from parent modes to daughter modes is observed in the experiment. According to the experimental results, it is found that the up-hill vibrational energy flow from lower frequency modes to higher frequency ones is counterintuitive and energy redistribution efficiencies are controlled by the mass of the halide.

Measuring the carrier dynamics of photocatalyst micrograins using the Christiansen effect.

The optical measurement of photocatalyst materials is subject to Mie scattering when the particle size is comparable to the wavelength of the probe light. A novel approach was developed to deal with this scattering problem in the transient spectroscopy of photocatalyst micrograins using the Christiansen effect because the probe light in the vicinity of the Christiansen frequency can be transmitted. Scattering theory was used to analyze the transient spectra of micrograins and estimate the extinction coefficient at the Christiansen frequency.

Visualizing Intramolecular Vibrational Redistribution in Cyclotrimethylene Trinitramine (RDX) Crystals by Multiplex Coherent Anti-Stokes Raman Scattering.

The femtosecond time-resolved multiplex coherent anti-Stokes Raman scattering (CARS) technique has been performed to investigate intramolecular vibrational redistribution (IVR) through vibrational couplings in 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) molecules. In the multiplex CARS experiment, the supercontinuum (SC) was used as broad-band Stokes light to coherently and collectively excite multiple vibrational modes, and quantum beats arising from vibrational couplings among these modes were observed. The IVR of RDX is visualized by a topological graph of these vibrational couplings, and with analysis of the topological graph, two vibrational modes, both of which are assigned to ring bending, are confirmed to have coupling interactions with most of the other vibrational modes and are considered to have a tendency of energy transfer with these vibrational modes.

A Long-Lived Mononuclear Cyclopentadienyl Ruthenium Complex Grafted onto Anatase TiO2 for Efficient CO2 Photoreduction.

This work shows a novel artificial donor-catalyst-acceptor triad photosystem based on a mononuclear C5 H5 -RuH complex oxo-bridged TiO2 hybrid for efficient CO2 photoreduction. An impressive quantum efficiency of 0.56 % for CH4 under visible-light irradiation was achieved over the triad photocatalyst, in which TiO2 and C5 H5 -RuH serve as the electron collector and CO2 -reduction site and the photon-harvester and water-oxidation site, respectively.

Photogenerated Intrinsic Free Carriers in Small-molecule Organic Semiconductors Visualized by Ultrafast Spectroscopy.

Confirmation of direct photogeneration of intrinsic delocalized free carriers in small-molecule organic semiconductors has been a long-sought but unsolved issue, which is of fundamental significance to its application in photo-electric devices. Although the excitonic description of photoexcitation in these materials has been widely accepted, this concept is challenged by recently reported phenomena. Here we report observation of direct delocalized free carrier generation upon interband photoexcitation in highly crystalline zinc phthalocyanine films prepared by the weak epitaxy growth method using ultrafast spectroscopy.

Temporal evolution of photothermal-induced Rayleigh wave and plate deformation as an interference in the transient kinetics of photoinduced carrier recombination of a rutile titanium dioxide single crystal.

The dynamic properties of photothermal processes occurring after the initial photogenerated carrier recombination in the flash photolysis of a semiconductor plate sample probed with a reflected infrared beam are reported in this work. Transient kinetics pertaining to the photothermal processes always appear as interfering signals in that of the photogenerated carrier recombination and should be distinguished and excluded. We observed that the photothermal-induced Rayleigh wave occurs immediately after the photogenerated carrier recombination that is then followed by the photothermal-induced flexural vibration of the sample substrate with a set of intrinsic frequencies as reported in our previous work (Appl.

Carrier recombination-incited substrate vibrations after pulsed UV-laser photolysis of TiO2 thin single-crystal plate and nanoparticle films.

Photo-induced carrier generation and recombination have been regarded as important steps in understanding the photocatalytic reactions on the surfaces of semiconductors such as TiO2. During the investigation of a photocatalytic water-splitting reaction on the surface of semiconductor TiO2 (rutile) single-crystal plate and sintered-nanoparticle (anatase) films coated on a CaF2 plate, a pulsed 355 nm laser was used for band-gap excitation and a continuous-working, mid-infrared laser as the probe to trace the kinetics of the photogenerated electrons. Fast oscillations with periods of 10-50 μs were observed.