Energy Distribution Of Molecules Research Articles

Intermolecular Forces Dictate Vibrational Energy Transfer in Plasmonic-Molecule Systems.

Plasmonic materials are a promising category of photocatalysts for solar energy harvesting and conversion. However, there are some significant obstacles that need to be overcome to make plasmonic catalysts commercially available. One major challenge is to obtain a systematic understanding of how to design and optimize plasmonic systems from the perspective of both plasmonic materials and reagent molecules to achieve highly efficient and selective catalysis. It is well-known that the contributions of plasmon-molecule interactions such as plasmon-induced resonant energy transfer and charge transfer to the catalytic mechanism are rather complicated and possibly multifold. Observation of these phenomena is challenging due to the highly heterogeneous nature of plasmonic substrates as well as the large difference in sizes and optical cross sections between plasmonic materials and molecules. In this work, we use a molecular perspective to examine the crucial process of energy transfer between plasmons and molecules, with the goal of determining which experimental parameters can be used to control this energy flow. We employ ultrafast surface-enhanced anti-Stokes and Stokes Raman spectroscopy to investigate vibrational energy transfer in plasmonic-molecule systems. By comparing the energy transfer kinetics of five different aromatic thiols on the picosecond time scale, we find that intermolecular forces play an important role in energy distribution in molecules adsorbed to plasmonic materials, which changes the amount of energy deposited onto the molecule and the lifetime of the energy deposited. Our work implies that careful consideration of catalyst loading and molecule adsorption geometry is crucial for enhancing or suppressing the rate and efficiency of plasmon-driven energy transfer.

Investigation of multiphoton-excited molecules by the method of Raman scattering spectroscopy at an overtone and compound vibrational frequencies

The multiphoton-excited CF3Br molecules are investigated by the method of Raman light scattering spectroscopy at frequencies of overtones and compound vibrations. It is demonstrated that highly nonequilibrium energy distribution of molecules is formed under excitation. The physical parameters characterizing this distribution, including the part of excited molecules and their average excitation level, are determined. The pattern of vibrational energy distribution formed in the CF3Br molecules under multiphoton excitation is reconstructed.

Molecular dynamics simulation of the energy distributions of molecules in liquid solutions

Abstract A solution is modelled as a classical 2D molecular system consisting of two types of molecules having different interaction parameters. The interaction is modelled by Lennard - Jones - type potentials. Molecular Dynamics simulations of solutions of soft molecules imbedded into a bath of rather hard solvent molecules are performed. From the molecular dynamics trajectories we derive the energy distributions and study local energy excitations of the solute and the solvent molecules. In particular the dynamics of activation processes (high energy events) is investigated for a special model: We simulate the thermal equilibrium of one molecule with Lennard-Jones 8-6-interactions imbedded into a bath of molecules with 18-6 interactions. It is shown that in thermal equilibrium a region of temperatures and densities exists, where the mean one-particle energy has a relative maximum. In this region the potential part of the thermal energy is preferably partitioned to the solvent molecules. Further we show that the energy distribution of the soft molecules shows longer tails than that of the hard molecules. On the basis of these distributions it is concluded that energy spots at the solute molecules may appear which possibly could lead to the enhancement of solute reactions.

Vibrational Temperatures of Some Molecules in a Hollow Cathode Discharge

Abstract Investigation of vibrational energy distributions of molecules excited in a hollow cathode discharge has been presented here. The vibrational temperatures of the CN, N2 and N2 + molecules have been measured at different experimental conditions. The excitation processes in HCD have been discussed.

Vibrational energy distribution in molecules excited by infrared radiation in the collisionless regime

An investigation is made of the excitation kinetics of polyatomic molecules in the quasicontinuum. An approach is proposed to allow for a gradual transfer of molecules from lower levels to the quasicontinuum without making a detailed study of their population kinetics. A solution of the diffusion equation in the quasicontinuum is used to derive analytic expressions for the vibrational energy distribution function of the molecules under the conditions of collisionless photodissociation experiments. Expressions are also derived for the dissociation yield and the average energy absorbed by the molecules as a function of the laser radiation energy flux. The results of the calculations show good agreement with the experimental data for CF3I and SF6 molecules.

Diagnostics of pulsed molecular beams and free jets with pyroelectric detectors and TEA CO2 lasers

A pyroelectric detector with a time resolution of 3–5 μs and a TEA CO2 laser have been used in diagnostics of a pulsed molecular beam (a free jet). The kinetic energy distribution of molecules was determined by using time-of-flight measurements both with a laser and without it. A combination of the laser with the pyroelectric detector makes it possible to determine the kinetic energy distribution of molecules in a selected internal state and to measure the energy absorted by the molecules of the beam from a laser pulse. The results obtained for pure SF6 and the SF6 seeded in He have been presented and analyzed. The advantages and the disadvantages of the method are being discussed in comparison with other available methods of diagnostics of molecular beams and free jets.

Energy transfer in the quenching of singlet molecular oxygen - III. Application of statistical theory

The vibrational energy distribution in molecules which have quenched O2(1∑+g) to O2(1∆g) or O2(1∆g) to O2(3∑-g) is interpreted in terms of the statistical theory. This theory is extended to include cases where initial rotational and translational energy contributes to vibrational excitation of the products. A common linear surprisal plot is observed in the quenching both of O2(1∑) and O2(1∆) by a number of molecules. Strongly inverted vibrational distributions with ⋋v= - 7.5 are inferred for both products of the quenching step.

Discussion on energy distribution in molecules in relation to chemical reactions

It often happens that the empirical observations of chemistry reveal the working of principles which can be easily interpreted in terms of physical theories, but which might have been difficult to predict. One need only mention the question of the nature of valency as one of the most conspicuous examples. For this reason it is useful if problems lying on the border line of physics and chemistry are discussed from both points of view. The present theme is the distribution of energy in molecules and its relation to the phenomena of chemical change. We know that the transference of energy from one molecule to another and, in particular, the accompanying interconversion of translational and internal energy depend upon specific mechanisms which give rise to phenomena of great interest. I need only mention the influence of hydrogen and certain other gases in maintaining the energy distribution in unimoleculer reactions, the variation of the velocity of sound with frequency, due to the finite time required for the establishment of equilibrium in the energy distribution among the internal degrees of freedom, and lastly that curious inability of solvent molecules to degrade the light energy absorbed by fluorescent substances.