Vibrational Frequency Analysis Research Articles

First-principles study on structural, vibrational, elastic, piezoelectric, and electronic properties of the Janus BiXY ( X=S,Se,Te and Y=F,Cl,Br,I ) monolayers

Broken inversion symmetry in atomic structure can lead to the emergence of specific functionalities at the nanoscale. Therefore, realizing 2D materials in Janus form is a growing field, which offers unique features and opportunities. In this paper, we investigate the structural, vibrational, elastic, piezoelectric, and electronic properties of Janus $\mathrm{Bi}XY$ ($X=\mathrm{S}$, Se, Te and $Y=\mathrm{F}$, Cl, Br, I) monolayers based on first-principle methods. The structural optimization and vibrational frequency analysis reveal that all of the proposed structures are dynamically stable. Additionally, ab initio molecular dynamics simulations verify the thermal stability of these structures even at elevated temperatures. The mechanical response of the Janus $\mathrm{Bi}XY$ crystals in the elastic regime is investigated in terms of in-plane stiffness and the Poisson ratio, and the obtained results ascertain their mechanical flexibility. The piezoelectric stress and strain coefficient analysis demonstrates the appearance of strong out-of-plane piezoelectricity, which is comparable with the Janus transition metal dichalcogenide monolayers. The calculated electronic band structures reveal that except for BiTeF, all Janus $\mathrm{Bi}XY$ monolayers are indirect band gap semiconductors, and their energy band gaps span from the infrared to the visible part of the optical spectrum. Subsequently, large Rashba spin splitting is observed in electronic band structures when the spin-orbit coupling is included. The obtained results point out Janus 2D $\mathrm{Bi}XY$ structures as promising materials for a wide range of applications in nanoscale piezoelectric and spintronics fields.

A Study on the Classification Effect of sEMG Signals in Different Vibration Environments Based on the LDA Algorithm.

Myoelectric prosthesis has become an important aid to disabled people. Although it can help people to recover to a nearly normal life, whether they can adapt to severe working conditions is a subject that is yet to be studied. Generally speaking, the working environment is dominated by vibration. This paper takes the gripping action as its research object, and focuses on the identification of grasping intentions under different vibration frequencies in different working conditions. In this way, the possibility of the disabled people who wear myoelectric prosthesis to work in various vibration environment is studied. In this paper, an experimental test platform capable of simulating 0–50 Hz vibration was established, and the Surface Electromyography (sEMG) signals of the human arm in the open and grasping states were obtained through the MP160 physiological record analysis system. Considering the reliability of human intention recognition and the rapidity of algorithm processing, six different time-domain features and the Linear Discriminant Analysis (LDA) classifier were selected as the sEMG signal feature extraction and recognition algorithms in this paper. When two kinds of features, Zero Crossing (ZC) and Root Mean Square (RMS), were used as input, the accuracy of LDA algorithm can reach 96.9%. When three features, RMS, Minimum Value (MIN), and Variance (VAR), were used as inputs, the accuracy of the LDA algorithm can reach 98.0%. When the six features were used as inputs, the accuracy of the LDA algorithm reached 98.4%. In the analysis of different vibration frequencies, it was found that when the vibration frequency reached 20 Hz, the average accuracy of the LDA algorithm in recognizing actions was low, while at 0 Hz, 40 Hz and 50 Hz, the average accuracy was relatively high. This is of great significance in guiding disabled people to work in a vibration environment in the future.

The influence of transition metal (Mn, Fe, Co, Cu) doping on the electronic and vibrational properties of indium nitride nanocage: A DFT study

Density functional theory (DFT) method is used to analyse the electronic and vibrational properties of an indium nitride (InN) Nanocage doped withtransition metals(TMs). To investigate the impact of doping, an Indium atom is replaced with a TM atom (Mn, Fe, Co, and Cu) to produce transition metal doped Nanocages. According to present study, these transition metal doped indium nitride Nanocages are remarkably stable, and their HOMO-LUMO energy gaps are significantly lower than the pristine In12N12 Nanocage. To study the electronic property in details global reactivity descriptors such as hardness, ionisation potential, electron affinity and electrophilicity are calculated. Vibrational frequency analysis ensures that all the structures are real minima on the potential energy surface that means they are dynamically stable. The IR and Raman spectra reported here are intended to provide chemical insight into the characterization of these unidentified structures, allowing for further experimental study.

Synthesis, spectral characterization, crystal structures, and DFT study of three new La(III) 2-amino-1-cyclopentene-1-carbodithioate complexes

• Three lanthanum(III) 2-amino-1-cyclopentene-1-carbodiothioate (ACDA) were obtained. • It is reported the first structural determinations of a rare earth ACDA complexes. • The ACDA is bonded to the lanthanum in a S,S coordination mode. • The DFT calculations for all the ACDA lanthanide complexes is in favor of the S,S mode. The synthesis and characterization of the first three La(III) 2-amino-1-cyclopentene-1-carbodithioate (ACDA) complexes is reported including two ionic complexes, [NEt 3 H][La(ACDA 4 )] ( 1 ), [N( n - Bu) 4 ][La(ACDA 4 ] ( 2 ) and [La(ACDA) 3 )(1,10-phenanthroline)] ( 3 ). The single-crystal X-ray structures of 1 – 3 correspond to the first known structural determination of ACDA rare earth complexes. Compounds 1 – 3 show an S,S coordination mode, and due to hydrogen bonding present in the ligands, secondary interactions were observed. DFT calculations for all the lanthanide series indicate that the ACDA ligand binds in an isobidentate fashion through low covalent M–S bonds, as evidenced by natural population analysis. Furthermore, the S,S coordination mode is overwhelmingly preferred over the N,S coordination, as demonstrated by free energy calculations from the vibrational frequency analysis.

Evaluation of Wear of Disc Brake Friction Linings and the Variability of the Friction Coefficient on the Basis of Vibroacoustic Signals

The article presents the results of friction and vibroacoustic tests of a railway disc brake carried out on a brake stand. The vibration signal generated by the friction linings provides information on their wear and offers evaluation of the braking process, i.e., changes in the average friction coefficient. The algorithm presents simple regression linear and non-linear models for the thickness of the friction linings and the average coefficient of friction based on the effective value of vibration acceleration. The vibration acceleration signals were analyzed in the amplitude and frequency domains. In both cases, satisfactory values of the dynamics of changes above 6 dB were obtained. In the case of spectral analysis using a mid-band filter, more accurate models of the friction lining thickness and the average coefficient of friction were obtained. However, the spectral analysis does not allow the estimation of the lining thickness and the friction coefficient at low braking speeds, i.e., 50 and 80 km/h. The analysis of amplitudes leads to the determination of models in the entire braking speed range from 50 to 200 km/h, despite the lower accuracy compared to the model, based on the spectral analysis. The vibroacoustic literature presents methods of diagnosis of the wear of various machine elements such as bearings or friction linings, based on amplitude or frequency analysis of vibrations. These signal analysis methods have their limitations with regard to their scope of use and the accuracy of diagnosis. There are no cases of simultaneous use of different methods of analysis. This article presents the simultaneous application of the amplitude and frequency methods in the analysis of vibroacoustic signals generated by brake linings. Moreover, algorithms for assessing the wear of friction linings and the average coefficient of friction were presented. The algorithm enables determination of the time at which the friction linings should be replaced with new ones. The final algorithm analyzes the vibration acceleration signals using both amplitude analysis for low braking speeds, as well as spectral analysis for medium and high braking speeds.

Synthesis of Antibacterial Disulfide Derivatives and its Computational Molecular Docking Against Penicillin Binding Protein

The present studies were designed to synthesize the three disulfide derivatives bearing S-S bond formation, their characterization and explore the antibacterial activity using in silico analysis. They were synthesized by the condensation reaction of 2-(2-(2-aminophenyl) disulfanyl) benzeneamine with 3-bromo-2-hydroxy-5-nitrobenzaldehyde; 5-bromo-2-hydroxybenzaldehyde and 3, 5-dichloro-2-hydroxy-benzaldehyde, respectively. The crystal structure of the compound has been crystallized in the Orthorhombic system of the space group Pbca with eight molecules in the unit cell. The compounds were elucidated by various spectroscopic methods. The molecular docking study was also performed against penicillin binding protein 4 (PBP4) active site pocket and E. coli DNA Gyrase B ATPase domain to evaluate the possible mechanism of antibacterial property of synthesized disulfide derivatives. Results revealed that these disulfide derivatives possess higher binding affinity for active site of PBP4 and Gyrase B ATPase domain. The present study demonstrated that indigenously synthesized disulfide compounds have potential to inhibit the PBP4 and Gyrase B ATPase domain and can be developed as antibacterial lead compounds. Furthermore, the LC-BLYP study provided the optimized geometry, vibrational frequency analysis and the HOMO-LUMO gap while TD-LCBLYP calculations gave the simulated UV-Visible spectra of disulfide derivatives.

Analysis of Thickness Vibration Frequencies of FBAR as Layered Structures with Piezoelectric Plates

Analysis of Thickness Vibration Frequencies of FBAR as Layered Structures with Piezoelectric Plates

Spectral tuning of 11-cis retinal in conjugation with Au14 cluster and concomitant effect on isomerization: A theoretical outlook

The present study explores the optical properties of retinal molecules in presence of small gold cluster (Au 14 ), where the cluster motifs are varied through O h , D 2h and C 4v symmetries. The constructive interference of the transition dipole moments (TDMs) in retinal-gold nanoconjugates is responsible for most intense electronic transitions. The charge transfer transition from the occupied Au cluster orbital to the unoccupied retinal orbital is playing significant role in the spectral shift of the conjugates. The vibrational frequency analysis of 11-cis retinal and its conjugate (Au 14 in D 2h symmetry) reveal that the different vibrational modes associated with the isomerization process are red shifted in the conjugate. The conjugation of isolated retinal with gold probes makes the process of 11-cis to all-trans isomerization thermodynamically favorable. The entire evaluation reflects the effect of gold cluster in the spectral tuning of retinal molecules and reveals its relevant consequences on photoisomerization and hence the process of vision.

Electronic and vibrational spectroscopy of ethyl methyl carbonate: A comparative experimental and theoretical study

A detailed spectroscopic study on ethyl methyl carbonate, a green solvent, has been carried out by recording vacuum ultraviolet and infrared spectra. The vacuum ultraviolet photoabsorption spectrum is recorded using synchrotron radiation from Photophysics beamline at the Indus-1 synchrotron radiation source at RRCAT, Indore, India in the wavelength region of 7–11.5 eV. Infrared spectra in gas phase as well as matrix isolated case are recorded using an indigenously developed laboratory low temperature experimental facility and a Fourier transform infrared spectrometer in the 500–4000 cm−1 region. Geometry optimization, vibrational frequency analysis of neutral & ionized ethyl methyl carbonate and electronic excited state energy information has been obtained using quantum chemical calculations. The observed ir spectral features could be assigned to the fundamental vibrational modes of the molecule. The vacuum ultraviolet region comprising a broad continuum is assigned to valence transitions having high oscillator strengths and overlying weak bands to ns, np, nd type Rydberg transitions. Potential energy curves of the ground and first few low lying excited states generated provided additional insights into their nature and further interpretation of observed experimental spectra. In this paper we report the first electronic absorption spectrum in 7 to 11.5 eV region, its spectroscopic analysis and identification of vibrational modes in the infrared spectra for ethyl methyl carbonate. Results of quantum chemical simulations carried out to obtain nature of excited states, energies and vibrational frequencies using GAMESS (USA) quantum chemistry code are also reported in this paper.

Proton Conduction Mechanism for Anhydrous Imidazolium Hydrogen Succinate Based on Local Structures and Molecular Dynamics.

Anhydrous organic crystalline materials incorporating imidazolium hydrogen succinate (Im-Suc), which exhibit high proton conduction even at temperatures above 100 °C, are attractive for elucidating proton conduction mechanisms toward the development of solid electrolytes for fuel cells. Herein, quantum chemical calculations were used to investigate the proton conduction mechanism in terms of hydrogen-bonding (H-bonding) changes and restricted molecular rotation in Im-Suc. The local H-bond structures for proton conduction were characterized by vibrational frequency analysis and compared with corresponding experimental data. The calculated potential energy surface involving proton transfer (PT) and imidazole (Im) rotational motion showed that PT between Im and succinic acid was a rate-limiting step for proton transport in Im-Suc and that proton conduction proceeded via the successive coupling of PT and Im rotational motion based on a Grotthuss-type mechanism. These findings provide molecular-level insights into proton conduction mechanisms for Im-based (or -incorporated) H-bonding organic proton conductors.

First-principle study of Ag-Au double wall nanotube and nanowire

A stable hollow (5,5)@(10,10) coaxial silver-gold tube is predicted based on density functional theory. Results show that the average binding energy of the nanostructures increases monotonically as the length of the nanotube grows. The strands of the outer sheet are wound up helically, nearly but not exactly parallel to the tube axis. However, the inner sheet differs from it, which grows by concatenating the repeated unit of a pentagonal prism with rotation in a pentagonal prism structure without rotation. It is a new isomer that is different from previous literature. The statically stability of the Ag-Au nanotube is emphasized by the vibrational frequency analysis with no imaginary frequency. The inner diameter is larger than that of the pristine gold nanotube. So, here a large hollow Ag-Au double wall nanotube is predicted theoretically and the theoretical calculation results may have potential applications in microelectronic industry, especially for application of Ag-based nanomaterial.

Rhodium Single‐Atom Catalysts on Titania for Reverse Water Gas Shift Reaction Explored by First Principles Mechanistic Analysis and Compared to Nanoclusters

AbstractThe thermocatalytic reduction of CO2 by H2 often proceeds via two competing reaction mechanisms – the reverse water gas shift reaction (rWGSR, CO2+H2⇌CO+H2O) and methanation (CO2+4H2⇌CH4+2H2O). Atomically dispersed Rh1 catalysts on TiO2 show high selectivity toward the rWGSR compared with larger Rh nanoclusters, but the origin of this size‐dependent selectivity has not been fully explained. Here we report density functional theory (DFT) calculations and microkinetic simulations that clarify the Rh1 active sites and rWGSR pathway on anatase TiO2(101), as well as the high rWGSR selectivity of Rh1 compared with supported Rhx (x=2–8 atoms) nanoclusters. DFT‐computed formation energies, vibrational frequency analysis, and microkinetic modeling suggest three plausible active sites: Rh1 on titania (Rh1/TiO2(101)), Rh1 with a nearby hydroxyl group (Rh1OH/TiO2(101)), and Rh1 near an oxygen vacancy at a three‐fold coordinated site (Rh1 near O3cvac). Predicted turnover frequencies and apparent activation barriers for Rh1 indicate a faster reaction involving CO2 dissociation assisted by a support oxygen vacancy via Rh1 near O3cvac, as well as slower reactions involving Rh1OH/TiO2(101) or Rh1/TiO2(101) through a COOH intermediate. These Rh1 sites are selective toward CO rather than CH4 because of the weak adsorption of CO, large barrier for C−O bond dissociation, and the lack of nearby metal sites for H2 dissociation, in contrast to Rhx nanoclusters, including Rh2 dimers.

Characterization of titanium influences on structure and thermodynamic stability of novel C20-nTin nanofullerenes (n=1-5): a density functional perspective.

In this survey, effects of titanium heteroatom(s) on structural parameters and thermodynamic stability of C20 fullerene and its C20-nTin derivatives (n = 1-5) are compared and contrasted, at DFT levels of theory. The results show that in going from C19Ti1 to C15Ti5, binding energy increases while absolute value heat of atomization decreases. According to vibrational frequency analysis, excepting C16Ti4-1, the other optimized structures give no imaginary frequency as true minima. The calculated binding energy of 887.12kcalmol-1/atom displays C15Ti5 as the most thermodynamically stable heterofullerene. It has Cs symmetry and contains five titanium atoms alternatively in equatorial position. The substitutional doping of C20 fullerene leads to high Mülliken charge distribution upon the surfaces of the resulted heterofullerenes especially C19Ti1 as suitable hydrogen storage. The contour plots indicate the most negative electrostatic potential by red color for C atoms, whereas the most positive electrostatic potential by yellow color for Ti heteroatoms. The contour plots and multiwfn analysis exhibit charge transfer from titanium heteroatoms to the neighboring carbon atoms. Furthermore, the resulted electron density maps from multiwfn qualitatively confirm the contour plot's findings. The hydrogen adsorption is an endothermic process for C20 fullerene and exothermic process for C20-nTin heterofullerenes. Major criteria examined for thermodynamic stability; from C19Ti1 to C15Ti5, binding energy and hydrogen adsorption increase while heat of atomization decreases.

A DFT study of Se-decorated B12N12 nanocluster as a possible drug delivery system for ciclopirox

Despite the significant role of ciclopirox as a novel anticancer agent to treat various cancers such as breast, liver, colorectal and bladder, it has some adverse effects and poor solubility in water. Hence, the enhancement of ciclopirox polarity is crucial in biological systems. In this work, the effect of selenium decoration on the interaction of ciclopirox drug molecule with B12N12 was investigated using density functional theory (DFT) calculations. Based on structural analysis, CO group of ciclopirox was chemisorbed on the boron and selenium atoms of B12N12 and Se-B12N12 nanoclusters, respectively. It was found that the selenium decoration significantly improves the reactivity of B12N12 toward ciclopirox. A short recovery time (~2.13 s) was predicted for ciclopirox desorption from the Se-B12N12 nanocluster surface. The vibrational frequency analysis was conducted to survey the vibration frequencies of bonds formed in the CPX/nanocluster complex. The charge transfer process was studied using charge decomposition analysis (CDA). Furthermore, Quantum theory of atoms in molecules (QTAIM) analysis revealed that the non-covalent interactions between CPX and nanoclusters are essential for the delivery process. Finally, electronic properties analysis showed that energy band gap of Se-B12N12 nanocluster is significantly reduced from 0.2835 to 0.2121 a.u after ciclopirox adsorption.

A comparison of the chemical bonding and reactivity of Si8H8O12 and Ge8H8O12: A theoretical study.

We have analyzed the chemical bonding and reactivity in the cubic molecule octahydridosilsesquioxane, Si8H8O12, and its counterpart Ge8H8O12 by means of ab initio quantum chemical methods and group theory. Density functional theory and MP2 methods combined with the basis sets 6-311+G(d) and 6-311++G(2d,p) were used for geometry optimization and vibrational frequency analysis. The geometries of Si8H8O12 and Ge8H8O12 are unstable under Oh symmetry and distort to the rare Th molecular symmetry. The energy gained from this pseudo-Jahn-Teller distortion ranges from 0.78 to 6.14 kcal mol-1 depending on methodological treatment. The Fukui functions and the molecular electrostatic potential were both used as DFT-based reactivity descriptors. Our study shows that Si8H8O12 and Ge8H8O12 are both hard amphoteric molecules. The cavity within each cage is acidic and able to encapsulate hard small bases such as F-. The exterior of the cages is basic and can form stable exohedral complexes with hard acids, as in the case of H+. The insertion of F- in Si8H8O12 and Ge8H8O12 cages gives the most stable endohedral complexes of the series studied, characterized by formation energies of -3.50 and -3.45 eV at CAM-B3LYP/6-311+G(d) and -3.61 and -3.68 eV at the MP2/6-311++G(d,p) level, respectively. The calculated formation energies of the exohedral and endohedral complexes align with the DFT reactivity descriptor analysis.

Molecular structure and spectra of danthron and emodin studied by FTIR, Raman spectroscopy and DFT techniques

In this work, experimental and theoretical studies on danthron and emodin are presented. Experimentally, Fourier transform infrared (FTIR), Raman and UV–Vis spectra of danthron and emodin were recorded. The structure and vibrational frequencies of the molecules were calculated using density functional theory (DFT) with the B3LYP functional using the triple zeta (TZVP) basis set. Among various possible structures of danthron and emodin, it was found that the most stable structures involve intramolecular hydrogen bonds between two OH and C=O groups. The theoretical IR spectra of the most stable conformations of danthron and emodin correlate well with their experimental FTIR. Detailed vibrational frequency analysis was done for all the vibrational modes obtained and were assigned to the ring vibrations along with the stretching and bending of specific bond vibrations. The bands obtained from the experimental FTIR and Raman spectra of both the molecules correlate well with their theoretical data.

Thermodynamic stability, structural and electronic properties for the C20-nAln heterofullerenes (n = 1-5): a DFT study.

DFT calculations are utilized to compare and contrast the substituted aluminum-heterofullerenes, C20-nAln (with n = 1-5) from thermodynamically view point, at density functional theory (DFT). Vibrational frequency analysis confirms that apart from C15Al5, all studied species are true minima. Considering the optimized geometries shows that all heterofullerenes are isolated-pentagon cage and none collapse to open deformed as segregated structure. The highest binding energy (5.56eV/atom) and absolute heat of atomization (3323.68kcalmol-1) reveals open-shell C19Al1 as the most stable thermodynamic heterofullerene. The most NICS (0) (isotropic and anisotropic parameters, -49.58 and - 46.47ppm, respectively) introduces closed-shell C18Al2-2 as the most aromatic structure. Also, closed-shell C16Al4-1 heterofullerene emerges with the most polarizability (307.71a.u.) and hence activity to interact with the surrounding polar species. The lowest and the highest charge transfer on the surfaces of C20 and C16Al4-2 without weak Al-Al bond, as the worst and the best candidate, respectively, provokes further investigation on impossible and possible application for hydrogen storage, respectively. We wish that the present survey will stimulate new experiments.

Optimisation of a Spindle Body Considering the Vibration Prediction of the Entire Milling Centre Construction

Static and dynamic properties of machine tools have a decisive influence on their accuracy. In case of HSM machine tools, the phenomena associated with them are additionally strengthened by high machining parameters. In order to predict a machine tool behaviour at the design stage, it is necessary to use numerical methods to simulate for its simulation. Thanks to the use of this type of software, it is possible to perform the next step, i.e. the optimisation of the structure. In case of machine tools, due to the multiplicity of factors affecting its accuracy, this should be a multicriterial optimisation. This article presents the results of a vertical milling centre spindle body optimisation using the Finite Element Method. The results of static stiffness and vibration frequency analysis for three bodies (i.e. the body of the form and dimensions proposed by the constructor, the body after parametric optimisation and the body after the form and parametric optimisation including use of different materials) were compared. The optimisation tools available in the ANSYS system were used for the simulation. The calculations were preceded by experimental research and modifications of dynamic parameters performed on their basis using the author's methodology to determine the behaviour of a partially existing structure for different masses of the body being optimised.

Investigating the effect of edge and basal plane surface functionalisation of carbonaceous anodes for alkali metal (Li/Na/K) ion batteries

Alkali metal ion batteries are instrumental in the widespread implementation of electric vehicles, portable electronics, and grid energy storage. From experimental characterisation of hard carbons, these carbon anodes were shown to contain a variety of functional groups. Through density functional theory simulations, the effect of functional groups (O, OH, NH2, and COOH) on edges and basal plane surfaces of carbonaceous materials on the adsorption of lithium, sodium, and potassium are investigated. These simulations show that the functionalisation of H-terminated edges and curved surfaces rather than basal planes is more energetically favourable and thus more likely to be present. Comparison of experimental FTIR and computational vibrational frequency analysis confirmed the occurrence of the investigated functional groups (O, OH, NH2, and COOH) in the synthesised hard carbon materials. Metal adsorption on the functionalised models showed that adsorption energies were stronger on the functionalised basal plane in comparison to the functionalised edge sites and contribute to the metal ion immobilization and consequent irreversible capacity loss. The metal adsorption on the curved surface was further improved by the addition of functional groups, benefitting the initial lithiation/sodiation/potassiation of the carbon anode. Hence, the morphology of the functionalised carbon systems plays an important role in the charge/discharge performance of carbonaceous anodes.

The suppression of intramolecular charge transfer emission by tautomerism in 2-(4′-amino-2′-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine: Intramolecular proton transfer versus intermolecular proton transfer

2-(4′-Aminophenyl)-1H-imidazo[4,5-c]pyridine (APIP-c) emits twisted intramolecular charge transfer (TICT) emission in methanol. However, when hydroxyl group was introduced in APIP-c, the hydroxy compound 2-(4′-amino-2′-hydroxyphenyl)-1H-imidazo[4,5-c]pyridine (AHPIP-c) does not emit TICT emission in methanol. But it undergoes excited state intramolecular proton transfer (ESIPT) to emit tautomer emission. The cause for the suppression of TICT by ESIPT in AHPIP-c was not clear. Therefore, DFT calculations were performed using polar continuum model with explicit methanol molecule to understand the cause. The vibrational frequency analyses were performed to know the strength of the bond in the ground and excited states. The potential energy curves for both intra- and intermolecular proton transfer processes were constructed in the ground and excited states. Our theoretical studies reveal that the relative strength of the intermolecular hydrogen bond and intramolecular hydrogen bond plays a crucial role in determining the dominating excited state process.