Molecular Internal Energy Research Articles

1511 REMPIを用いた窒素分子線の回転エネルギー分布計測(OS15-2 先端的熱流体計測法,オーガナイズドセッション)

In order to analyze high Knudsen number flows, it is important to understand the interactions of gas molecules and solid surfaces. Molecular beams have been used to study these interactions. Properties such as the translational energy and momentum of a molecular beam have been analyzed very well; however, there are very few reports analyzing the rotational energy of diatomic or polyatomic molecular beam experimentally. Resonantly enhanced multi-photon ionization (REMPI) is a spectroscopic technique, which is able to measure molecular internal energy distribution in very low density gas flows. In this study, we have detected and analyzed the rotational energy distribution in a nitrogen molecular beam by 2R+2 REMPI.

Spectroscopic properties of ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate

We report the synthesis and photophysical properties of ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate (EDMAADCy) in neat solvents of different polarity. The relation between molecular conformations of molecule under study and spectral behavior has been studied using steady-state spectroscopic technique, electrochemical measurements, and quantum-chemical calculations. The fluorescence spectra of EDMAADCy possess, in medium polar solvents, two bands. Theoretical studies of the TICT phenomenon have been made in order to explain the dual emission of the molecule under study. Calculated electric dipole moments in the ground and excited states, for perpendicular and flatted conformers, have been compared with experimentally determined data. Additionally, the results of spectroscopic measurements were used to calculate, according to Marcus theory, the outer-sphere solvent reorganization energy and the internal molecular reorganization energy.

DIADORIM: a Monte Carlo Program for liquid simulations including quantum mechanics and molecular mechanics (QM/MM) facilities: applications to liquid ethanol

This paper presents a Metropolis Monte Carlo (MMC) computer program developed to simulate liquids and solutions including QM/MM facilities: the energy from intermolecular interactions is calculated with classical force field functions and the internal molecular energies are calculated using Quantum Chemistry methods. The following facilities were implemented: (i) the semiempirical MOPAC 6 quantum chemistry package was included as a subroutine of the main MMC simulation program; (ii) alternatively, an interface with an external data bank was developed to allow the use of energies previously obtained; (iii) calculation in NpT and NVT ensembles are available; (iv) the trajectory generated along the MMC sampling can be saved using standard xtc file format allowing trajectory visualization and data analysis using external programs. The program was used to calculate thermodynamical and structural properties of liquids ethanol (ET) in the NpT ensemble at 1.0 atm and 298 K. Bond angles and bond distances of ethanol molecules were kept constant but torsions along the dihedral angle defined by the H-O-C-C atoms were sampled in the simulation. QM/MM calculations were performed using the MOPAC AM1, PM3 and MNDO Hamiltonians to calculate the internal molecular energy. Calculations using internal energies obtained with OPLS-AA force field, ab initio HF/6-31g*, MP2/6-31g* and B3LYP/6-31g* calculations were performed. The dihedral angles distributions obtained with different methodologies reveal extraordinary qualitative and quantitative differences. However, the pair energies and radial distributions functions obtained with the different methodologies are in good agreement. The values calculated for the density and enthalpy of vaporization of liquid ethanol are in good agreement with experimental data.

Model for polarized and depolarized Rayleigh Brillouin scattering spectra in molecular gases

Numerical models for Rayleigh-Brillouin scattering (RBS) spectra from molecular gases are obtained and discussed in this paper. The current publicly-available S6 model is for polarized RBS spectra only, despite the existence of both polarized and depolarized RBS light in many real applications. One of the new models (Q9) can be used to calculate both polarized and depolarized RBS spectra. In addition, this model has a solid physical ground because it is based on the correct Waldmann-Snider equation in which molecular internal energy is treated quantum-mechanically.

Determination of reorganization energy of fluorenone and 4-hydroxyfluorenone in neat and binary solvent mixtures

Steady-state absorption and fluorescence measurements of fluorenone and 4-hydroxyfluorenone in neat and binary solvent mixtures were used to explore the reorganization energy in liquid system. The results of spectroscopic measurements were used to calculate, according to Marcus theory, the outer-sphere solvent reorganization energy, λ 0, and the internal molecular reorganization energy, λ in. Preferential solvation of fluorenone and 4-hydroxyfluorenone in binary solvent mixtures has been studied by monitoring the outer-sphere solvent reorganization energy. In cyclohexane–tetrahydrofuran mixtures, the deviation from linearity in the λ 0 versus the solution polarity is due to non-specific dipolar solvent–solute interactions. For cyclohexane–ethanol binary mixtures, both non-specific and specific (hydrogen bond) interactions contribute to the observed changes.

5,10-Methylene-5,6,7,8-tetrahydrofolate conformational transitions upon binding to thymidylate synthase: molecular mechanics and continuum solvent studies

We applied the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) approach to evaluate relative stability of the extended (flat) and C-shaped (bent) solution conformational forms of the 5,10-methylene-5,6,7,8-tetrahydrofolate (mTHF) molecule in aqueous solution. Calculations indicated that both forms have similar free energies in aqueous solution but detailed energy components are different. The bent solution form has lower intramolecular electrostatic and van der Waals interaction energies. The flat form has more favorable solvation free energy and lower contribution from the bond, angle and torsion angle molecular mechanical internal energies. We exploit these results and combine them with known crystallographic data to provide a model for the progressive binding of the mTHF molecule, a natural cofactor of thymidylate synthase (TS), to the complex forming in the TS-catalyzed reaction. We propose that at the time of initial weak binding in the open enzyme the cofactor molecule remains in a close balance between the flat and bent solution conformations, with neither form clearly favored. Later, thymidylate synthase undergoes conformational change leading to the closure of the active site and the mTHF molecule is withdrawn from the solvent. That effect shifts the thermodynamic equilibrium of the mTHF molecule toward the bent solution form. At the same time, burying the cofactor molecule in the closed active site produces numerous contacts between mTHF and protein that render change in the shape of the mTHF molecule. As a result, the bent solution conformer is converted to more strained L-shaped bent enzyme conformer of the mTHF molecule. The strain in the bent enzyme conformation allows for the tight binding of the cofactor molecule to the productive ternary complex that forms in the closed active site, and facilitates the protonation of the imidazolidine N10 atom, which promotes further reaction.

Phase diagrams for an ideal gas mixture of fermionic atoms and bosonic molecules

We calculate the phase diagrams for a harmonically trapped ideal gas mixture of fermionic atoms and bosonic molecules in chemical and thermal equilibrium, where the internal energy of the molecules can be adjusted relative to that of the atoms by use of a tunable Feshbach resonance. We plot the molecule fraction and the fraction of Bose-condensed molecules as functions of the temperature and internal molecular energy. We show the paths traversed in the phase diagrams when the molecular energy is varied either suddenly or adiabatically. Our model calculation helps to interpret the adiabatic phase diagrams obtained in recent experiments on the Bose–Einstein condensation to Bardeen–Cooper–Schrieffer crossover, in which the condensate fraction is plotted as a function of the initial temperature of the Fermi gas measured before a sweep of the magnetic field through the resonance region.

On the relation between Zenkevich and Wiener indices of alkanes

A relatively complicated relation was found to exist between the quantity U recently introduced by Zenkevich (providing a measure of internal molecular energy), and the Wiener index W (measuring molecular surface area and intermolecular forces). We now report a detailed analysis of this relation and show that, in the case of alkanes, its main features are reproduced by the formula U = ??W + ? + ??1; where ?1 is the number of methyl groups, and ?, ? and ? are constants, depending only on the number of carbon atoms. Thus for isomeric alkanes with the same number of methyl groups, U and W are linearly correlated.

Energy exchange in reactive scattering of hydrogen molecules from a Cu surface

The energy exchange between a D 2 molecule and the phonon states of a copper surface has been modelled using quantum wavepackets. For processes where the molecule gains internal energy, we predict a gain in molecular energy near the excitation threshold. This gain decreased with increasing translational energy, and was insensitive to the final state of the molecule. For non-activated processes, with a decrease in molecular internal energy, a net loss of energy to the substrate was found. This loss increased as the change in internal energy of the molecule increased. These results are in good agreement with experimental observation.

Theoretical and Predictive Modelling of Physical Properties of Polymers

The application of Boltzmann statistics to a complete distribution of molecular conformation energies of simplified homo- and copolymer models gives meaningful information about temperatures at which phase transitions take place in the bulk. We have calculated in the conformation statistical distribution (CSD) approximation Helmholtz free energy variation versus temperature δF = δU-TδS. where U and S are, respectively, the internal molecular energy and the Gibbs statistical entropy of the considered polymeric model. The deepest minima correspond to glass-transition temperature (T g ) and melting temperature (T m ) of modelled polymers, while the remaining peaks are relied to some other transitions, the existence of which is also experimentally proven. The adopted method is able to give T g and T m as a function of the molecular weight of polymers. Some indications can also be achieved about the instability of polymers. The same procedure has been applied to copolymers and blends and has given acceptable results for T g and T m as functions of the material microstructure and composition. Other thermal and mechanical properties, such as moduli, mobilities, chemical resistance to oxidation, physical tendency to miscibility, have been directly or indirectly estmated.

Effects of ion excitation on charge transfer reactions of the Mars, Venus, and Earth ionospheres

The absolute reaction cross sections and reaction rate coefficients as a function of photoionisation energy for 25 ion–molecule reactions (charge transfer reactions except for one) have been measured between the most abundant species present as ions or neutral in the Mars, Venus and Earth ionospheres: O 2, N 2, NO, CO, Ar and CO 2. This study shows the strong influence of electronic as well as vibrational internal energy on most ion–molecule reactions. In particular endothermic charge transfer reactions are driven by electronic excitation of O 2 + and NO + ions in their a 4 Π u and a 3 Σ + metastable states, respectively. Moreover, it is shown that lifetimes of these metastable states are sufficient to survive the mean free path in the lowest part of ionospheres and therefore express their enhanced reactivity. The reactions of O 2 + with NO as well as the reactions of CO 2 + with NO, O 2, CO and to a less extent N 2 are driven by vibrational excitation. N 2 + and CO + reactions vary much less with photon energy than the other ones, except for the case of reactions with Ar. The effects of the molecular ion internal energy content on their reactivity must be included in the ionospheric models for most of the reactions investigated in the present work. It is also the case for the effect of collision energy on the CO ++M reactions as we expect that a significant proportion of these CO + could be produced with translational energy by dissociation of doubly charged CO 2 2+, in particular in the Mars ionosphere. Recommended effective rate constant values are given as a function of VUV photon energy.

A study of the unimolecular decomposition of internal-energy-selected furan molecular ions by threshold-photoelectron–photoion coincidence spectroscopy

The unimolecular decomposition of internal-energy-selected furan molecular ions has been studied by means of threshold-photoelectron–photoion coincidence spectroscopy. Monochromatic synchrotron radiation was used as the ionisation source, and the molecular ion internal energy was established through the detection of a threshold electron. A pulsed electric field was applied to extract the ions from the interaction region and direct them towards a time-of-flight mass spectrometer. Breakdown curves were measured for photon energies up to 30 eV, and these have allowed appearance energies for a wide range of fragment ions to be determined. In the threshold region the breakdown curves have been measured for various ion residence times by introducing electronic delays between the detection of the threshold electron and the application of the ion extraction field. The breakdown curves have been modelled using the RRKM (Rice, Ramsperger, Kassel and Marcus)/QET (quasi-equilibrium theory) approach, and this has allowed activation energies and transition state geometries to be deduced. The threshold photoelectron spectra of furan-h 4 and furan-d 4 have been measured from the ionisation threshold to 28 eV, and vibrational structure has been observed and assigned in the bands due to the X 2 A 2 , the A 2 B 1 and the G 2 A 1 states. Vibrational progressions discernible between 16.2 and 17.3 eV have been attributed to autoionisation from a p-type Rydberg series converging onto the G 2 A 1 state ionisation threshold.

Collisional relaxation and internal energy redistribution in NO 2 investigated by means of laser-induced thermal grating technique

Optical scattering from laser-induced thermal gratings (LITGs) was employed in investigations of molecular relaxation processes in gas mixtures containing a small amount of NO 2 diluted with different buffer gases (N 2,Ar,CO 2). The thermal gratings were generated by the thermalization of the molecular internal energy stored in the NO 2 molecules after laser resonant excitation of the 2 B 1← 2 A 1 Huber–Douglas band. The temporal evolution of LITGs was detected by scattering a cw read-out laser beam. A theoretical simulation of experimental results was performed in which the linearized hydrodynamic equations relevant to collisions responsible for the relaxation process were solved by following a two-step rate equations approach.

Analysis of water–ethanol nucleation rate data with two component nucleation theorems

We generalize the second nucleation theorem to multicomponent systems. Nucleation theorems are used to extract the molecular composition and excess internal energy of the critical cluster from experimental nucleation rates in a water–ethanol mixture. The excess internal energy is found to depend only weakly on temperature and to be almost solely a function of the molecular numbers of water and ethanol in the cluster. We estimate the contribution of the kinetic pre-factor to our analysis, and find that it is small in the case of the first theorem, but significant for the second theorem. We find that capillarity approximation fails to predict the experimental critical size and excess energy in this highly nonideal system.

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.

Internal energy content of n‐butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two‐photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright © 1999 John Wiley & Sons, Ltd.

PARAMETRIC STUDY OF THE RESIDUAL GAS IN SPARK IGNITION ENGINES

ABSTRACT The residual gas xr affects the number of moles of unburned mixture. Consequently it affects the mixture's molecular mass, specific heats, gas constant, internal energy and enthalpy of formation and entropy. Its magnitude affects volumetric efficiency and engine torque and power directly, whereas thermal efficiency and emissions are affected by the change in thermodynamic properties of the working fluid. A parametric study covers the variables which affect xr namely compression ratio,equivalence ratio φ, inlet air temperature Ti, ratio of exhaust and intake pressures pc/pi, and fuel. A computer program was devised to calculate xr,Tr, Tl and specific heat release, and the consequent performance namely power, ηth and bmep. Results show the relative importance of the parameters such as rc,φ, pc/pi and fuel type on residual gas particulars, and fuel on power and ηth whereas for bmep the pc/pi acquires additional importance.

Molecular amplification and generation of microwaves

This paper is a general introduction to the field of amplification and generation of microwaves using molecular rather than electronic processes. The basic physical properties of molecular systems as related to amplification are reviewed. The properties of molecular amplifiers, such as gain, bandwidth, saturation power, and noise figure are discussed and several specific types of amplifiers are described. These include the molecular-beam maser, the "hot-grid cell", amplifiers excited by radio-frequency pulses and by "adiabatic fast passage", and amplifiers based on multilevel molecular internal energy systems, including "optically pumped" amplifiers. Molecular amplifiers may add very little noise to the signal to be amplified: noise figures under 1 dB can be obtained. With suitable feedback, such amplifiers become oscillators of extremely high spectral purity. High gains can be achieved using regeneration, but bandwidths are relatively small. These range from the order of tens of kilocycles for amplifiers using a gaseous molecular system, to megacycles, using solids. Molecular amplifiers saturate at low input powers, of the order of microwatts. Variations of the devices discussed may provide a means of generating millimeter and submillimeter waves.

Molecular excitation in sprites

We have determined the molecular internal energy distribution in the N2 B³IIg state from the fluorescence measured during the observations of sprites during 1995. Spectrally resolved data from two different instruments and three different sprites are compared with theoretical spectra to obtain excited state vibrational distributions. Energy dependent electron excitation cross‐sections and laboratory data were used to estimate the energies of electrons producing the red sprite radiance. Implications for chemical production in the mesosphere and critical future measurements are discussed.

Computer simulation of the supercritical carbon dioxide fluid (II) internal energy and structure of carbon dioxide system containing one benzene molecule

Using potential models based on ab initio quantum chemical calculations, we study a supercritical CO 2 fluid containing one benzene molecule using Monte Carlo simulations. First, molecular average internal energy is calculated for the whole system and for the first solvation shell of the benzene molecule. This analysis shows that the CO 2 molecules in the first solvation shell have a large energetic stabilization owing to the shape of the solute. In addition to the stabilization, the solute-solvent interactions in the first solvation shell show large fluctuations for both the in-plane and out-of-plane parts. Secondly, an orientational distribution function is defined to investigate the CO 2 fluid structure. This function indicates that the CO 2CO 2 intermolecular configuration has a large dependence on the temperature of the system for both the whole system, and for the first solvation shell of the solute. Moreover, the benzene molecule is confirmed to control the mutual arrangement between neighboring CO 2 molecules.