Basis Set Level Research Articles

Probing Dynamics in Higher-Lying Electronic States with Resonance-Enhanced Femtosecond Stimulated Raman Spectroscopy.

Femtosecond stimulated Raman scattering (FSRS) measurements typically probe the structural dynamics of a molecule in the first electronically excited state, S1. While these measurements often rely on an electronic resonance condition to increase signal strength or enhance species selectivity, the effects of the resonance condition are usually neglected. However, mode-specific enhancements of the vibrational transitions in an FSRS spectrum contain detailed information about the resonant (upper) electronic state. Analogous to ground-state resonance Raman spectroscopy, the relative intensities of the Raman bands reveal displacements of the upper potential energy surface due to changes in the bonding pattern upon S n ← S1 electronic excitation, and therefore provide a sensitive probe of the ultrafast dynamics in the higher-lying state, S n. Raman gain profiles from the wavelength-dependent FSRS spectrum of the model compound 2,5-diphenylthiophene (DPT) reveal several modes with large displacement in the upper potential energy surface, including strong enhancement of a delocalized C-S-C stretching and ring deformation mode. The experimental results provide a benchmark for comparison with calculated spectra using time-dependent density functional theory (TD-DFT) and equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD), where the calculations are based on the time-dependent formalism for resonance Raman spectroscopy. The simulated spectra are obtained from S1-S n transition strengths and the energy gradients of the upper (S n) potential energy surfaces along the S1 normal mode coordinates. The experimental results provide a stringent test of the computational approach, and indicate important limitations based on the level of theory and basis set. This work provides a foundation for making more accurate assignments of resonance-enhanced excited-state Raman spectra, as well as extracting novel information about higher-lying excited states in the transient absorption spectrum of a molecule.

Theoretical Study of the Histidine-catalyzed Asymmetric Aldol Reaction of Acetone and Benzaldehyde.

The mechanism of histidine-catalyzed asymmetrical aldol reaction of acetone with benzaldehyde was studied by using B3LYP method of density functional theory at the levels of 6-31G(d,p) and cc-pvdz basis sets. The calculation results showed that the reaction mechanism included four steps: (I) nucleophilic attack of histidine on acetone to form alcohol intermediate Inter-A through the transition state TS1 (considered a rate control step because the activation energy (49.95 kcal/mol) was relatively high); (II) dehydration of the alcohol intermediate to form the cis- or trans-enamine through the transition states TS3 and TS4 with the energy barriers of 36.12 and 38.15 kcal/mol; (III) electrophilic addition of cis-enamine or trans-enamine with benzaldehyde to form imine Inter-C or Inter-E through the transition states TS8, TS9, TS10, and TS11 (energy barriers 18.43, 22.34, 13.24, and 13.24 kcal/mol, respectively); (IV) after combination of the imine intermediate with water through the transition states TS12, TS13, TS14, and TS15 (energy barriers 22.79, 34.6, 28.2, 25.12 kcal/mol, respectively), removal of the histidine catalys to obtain the final S or R aldol product. Through analyzing the potential energy profile of reaction, we found that the histidine-catalyzed reaction of acetone with benzaldehyde was more energetically favorable to obtain the R-product (ee value >99%). Solvent effects computed with a polarizable continuum model (PCM) indicated that the DMSO and water can reduce the reaction energy barrier.

X-ray crystal structure, Hirshfeld surface analysis and DFT study of some cis-5‑hydroxy‑2-phosphono-2,5-dihydrofurans

The structures of two cis-5‑hydroxy‑2-phosphono-2,5-dihydrofurans C24H23O5P (1) and C26H27O5P (2), were investigated by using various spectroscopic tools including IR, NMR (1H, 31P, 13C) spectroscopy, mass spectrometry and single crystal X-ray diffraction. Intermolecular interactions were studied by Hirshfeld surface analysis. The structures of both compounds were also optimized by density functional theory (DFT) calculations using B3LYP hybrid functionals with 3–21 g* level basis set. The experimentally determined parameters were compared with those calculated theoretically and they were found to complement each other with a very good correlation.

An investigation of molecular mechanism and the role of Te-bridged-atom in the formation of polysubstituted pyridines via Hetero-Diels–Alder reaction of isotellurazole with acetylenic dienophile: a molecular electron density study

An electron localization function (ELF) analysis and a detailed computational study of the hetero-Diels-Alder (HDA) reaction between isotellurazole and acetylenic dienophile have been performed. Then, B3LYP/Lanl2dz + 6-31+g(d) basis set level has been used to characterize the molecular mechanism and reactivity. The conceptual and computational DFT show that the most favorable regioisomeric product is the ortho/endo adduct, for which the energetic cost is 39.4 kcal/mol. Furthermore, ELF topological analysis envisages that the electron density of the pseudo-radical centers of the most electrophilic and nucleophilic atoms of the molecules come mainly from the charge transfer which takes place along the reaction pathway. The high asynchronicity of the bond formation means that two-stage one-step is the most appropriate mechanism for this reaction. However, the weak electronic contribution of the heavy chalcogen-bridged Tellurium atom in the C1-Te-N2 sequence has increased the activation barrier of the reaction. Otherwise, it has assisted the easy removal of the atom in the intermediary cycloadduct in the end of the reaction leading to the polysubstituted pyridine. So, despite the fact that Te atom is electronically rich, it plays a marginal role for improving reactivity of this [4+2] cycloaddition process. Synopsis. The mechanism of the Hetero-Diels-Alder (HDA) reaction of isotellurazole with acetylenic dienophile has been studied carefully. The quantum chemical calculations and an electron localization function analysis show that the weak electronic contribution of the heavy chalcogen-bridged Tellurium atom in the C1-Te-N2 sequence has decreased the activation barrier of the reaction. Besides, it has assisted the easy removal of this atom in the intermediary cycloadduct at the end of the reaction to make possible the synthesis of pyridine ring system (high polarized bonds). Equally, the electronic density analysis of several formed radicals permits us to conclude that two-stage one-step is the mechanism of the HDA reaction

Experimental, DFT Studies and Biological Evaluation of S‐methyl‐β‐N‐(3‐(2‐nitrophenyl)allylidene)dithiocarbazate

AbstractS‐Methyl‐β‐N‐(3‐(2‐nitrophenyl)allylidene)dithiocarbazate (HL), Schiff base of S‐methyl dithiocarbazate, was synthesized by 1:1 condensation between S‐methyl dithiocarbazate and trans‐o‐Nitrocinnamaldehyde. It's in‐vitro cytotoxicity is assayed against two habitually infection causing bacteria strains including gram‐positive Staphylococcus aureus and gram‐negative Escherichia coli for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in concentration. This nitrogen‐sulfur based Schiff base (HL) was characterized by Mass, FT‐IR, 1H‐NMR, 13C‐NMR, Raman, and UV‐Vis spectroscopic techniques. Theoretical quantum chemical calculation has been performed using DFT in combination with B3LYP exchange correlation functional and 6‐311++ G (d, p) basis sets level. The computed parameters were: Chemical potential of compound (μ) −0.174 eV, HOMO‐LUMO energy gap −0.11093 eV, chemical hardness (ɳ) −0.055 eV, softness (S) 2.164 eV, ionization energy (IE) −0.23026 eV, electron affinity (EA) −0.11933 eV, the electronegativity (EN) 0.174 eV, dipole moment (D) 1.3383 Debye and relative stabilization energy −1536.982 eV. In the theoretical FT‐IR spectrum analysis 81 fundamental vibrational modes has be observed because of non‐linear structure of HL, with potential energy distribution percentage (PED%) by using VEDA‐4 (Vibrational energy distribution analysis) software. Theoretically calculated parameters like 1H‐NMR, 13C‐NMR, FT‐IR, UV‐VIS, Raman, electrostatic potential and HOMO‐LUMO energy gap were in conformity with experimental results.

Theoretical Study of the Electronic and Optical Properties to Design Dye-Sensitivity for Using in Solar Cell Device

In this work, the structural and optoelectronic properties of phenanthrene-1,3,4-thaidiazoles oligomers were calculated using density functional theory (DFT) at B3LYP/6-31G(d) basis set level, to evaluate their possible application as organic semiconductor materials in photovoltaic and solar cell devices. For this reason, the energy gaps, frontier orbital (HOMO, and LUMO) distributions, total energies, Fermi level energies, work functions and maximum wavelength absorption, vertical absorption energies, and oscillator strengths have been investigated and discussed. The structures of phenanthrene-1,3,4-thiadiazoles oligomers are expanded from 1 to 10 thiadiazole monomeric units, to examine the increase of thiadiazole monomeric units on the optoelectronic properties. We observed that increased the number of monomeric units lead to significantly enhance the optoelectronic properties, which caused to decrease the gap energy from 3.69 eV in the structure with one thiadiazole ring just to 2.36 eV with 10 units. These changes give the shift of maximum absorption wavelengths from 376 to 578 nm. Consequently, these molecules have main absorption bands within the solar spectrum, to give the best performance for photovoltaic and organic solar cells devices.

Synthesis, characterization, thermal and DFT studies of S-methyl-β-N-(3-(2-nitrophenyl)allylidene)dithiocarbazate as anti-bacterial agent

S-Methyl-β-N-(3-(2-nitrophenyl)allylidene)dithiocarbazate (HL), Schiff base of S-methyl dithiocarbazate, was synthesized by 1:1 condensation between S-methyl dithiocarbazate and trans-o-nitro cinnamaldehyde. It's in-vitro cytotoxicity is assayed against two habitually infection causing bacteria strains including gram-positive Staphylococcus aureus and gram-negative Escherichia coli for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in concentration. This nitrogen-sulfur based Schiff base (HL) was characterized by Mass, FT-IR, 1H-NMR, 13C NMR, Raman, and UV–Vis spectroscopic techniques. Theoretical quantum chemical calculation has been performed using DFT in combination with B3LYP exchange correlation functional and 6–311++ G (d, p) basis sets level. The computed parameters were: Chemical potential of compound (μ) −0.174 eV, HOMO-LUMO energy gap −0.11093 eV, chemical hardness (ɳ) −0.055 eV, softness (S) 2.164 eV, ionization energy (IE) −0.23026 eV, electron affinity (EA) −0.11933eV, the electronegativity (EN) 0.174 eV, dipole moment (D) 1.3383 Debye and relative stabilization energy −1536.982 eV. In the theoretical FT-IR spectrum analysis 81 fundamental vibrational modes has be observed because of non-linear structure of HL, with potential energy distribution percentage (PED%) by using VEDA-4 package. Theoretically calculated parameters like 1H-NMR, 13C NMR, FT-IR, UV-VIS, Raman, electrostatic potential and HOMO-LUMO energy gap were in conformity with experimental results. Thermal reactivity of the ligand was studied by TGA decomposes completely to give gaseous products.

Towards a better comprehension of interactions in the crystalline N-acetylbenzylamine and its sulphur analogue N-benzyl-ethanethioamide. IR, Raman, DFT studies and Hirshfeld surfaces analysis

This paper presents the investigation results of the polarized IR spectra of the hydrogen bond in crystals of N-acetylbenzylamine and its sulphur analogue N-benzyl-ethanethioamide. The spectra were measured at 298 and 77 K by a transmission method, with the use of polarized light. The Raman spectroscopy, Hirshfeld surfaces analysis and DFT studies have been also reported. Theoretical calculations of the isolated molecule were performed by using density functional theory (DFT) method at B3LYP/6-311(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311++G(3df,2pd) basis set levels. The geometrical parameters of analyzed compounds are in good agreement with the XRD experiment. The vibrational frequencies were calculated and subsequently values have been compared with the experimental Infrared and Raman spectra. It has been shown that the observed and calculated frequencies are found to be in good agreement, as well as the analysis of the Hirshfeld surface has been well correlated to the spectroscopic studies. Additionally, the highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), the energy gap between EHOMO and ELUMO (ΔEHOMO–LUMO), molecular electrostatic potential and global reactivity descriptors viz. chemical potential, global hardness and electrophilicity have been calculated. In N-acetylbenzylamine the presence of the N-benzylamide fragment is essential for activity.

Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with Double and Triple W-P and W-As Bonds.

Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH3 and HE═WH2 molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH3 to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W-H stretching region are assigned to the molecules with loss of H from W, E≡WH2. The electronic structure calculations show that the E≡WH3 molecules have a W-E triple bond, the HE═WH2 molecules have a W-E double bond, and the H2E-WH molecules have a W-E single bond. The formation of multiple E-W bonds leads to increasing stability for the isomers.

Computational Investigation of Structure and Reactivity of Methyl Hydrazinecarbodithioate

In this study, we theoretically investigated Methyl hydrazinecarbodithioate by quantum chemical calculations for geometry optimization, vibration frequencies, and electronic structure parameters. The geometry optimization by DFT, ab initio MP2 method and the frequency calculation by DFT method was performed at the highest available Pople style 6-311G++(3df,3pd) basis set level. The semi-empirical calculations were performed by the latest PM7 method. The theoretically obtained results were compared with the experimental data. Conformational behavior, frontier molecular orbitals, molecular electrostatic potential, electron localization function, and non-covalent interaction plots were also analyzed. The study explained the geometry, conformational flexibility and relative stability of different conformers.

DFT Studies of Carbon Structures Supported Vanadia Catalysts for Oxidative Dehydrogenation of Propane: Kinetic and Thermodynamic

The detailed mechanism for oxidative dehydrogenation of propane on the 1 VO4(CH3 )3 surface has been studied in depth with density functional theory (DFT) calculations at the B3LYP level and standard split-valance basis set, 6-31+G*. Monomeric vanadia specie was considered and modeled as catalysis. In addition, the mechanisms of the two complete catalytic cycle, involving the regeneration of the reduced catalyst using O2 gaseous have been reported. The reaction proceeds in two subsequent steps which at the first, one hydrogen abstracting by the vanadium of V= O1 group with about 48.35 cal/mol activation energy is the rate determining step. Subsequently, second intermediate has been formed through a bond formed between the propyl radical and O2 atom (V-O2). In continue, the O1 atom abstracts one hydrogen atom from the methyl group with a 131.63 kcal/ mol barrier to form propene by passing to second transition state. The results of our calculations have found that all the reactions involve vanadyl oxygen (V=O1), with the bridging oxygen (V-O-C) serving to stabilize the isopropyl radical intermediate.

Straightening the Hierarchical Staircase for Basis Set Extrapolations: A Low-Cost Approach to High-Accuracy Computational Chemistry.

Because the one-electron basis set limit is difficult to reach in correlated post-Hartree-Fock ab initio calculations, the low-cost route of using methods that extrapolate to the estimated basis set limit attracts immediate interest. The situation is somewhat more satisfactory at the Hartree-Fock level because numerical calculation of the energy is often affordable at nearly converged basis set levels. Still, extrapolation schemes for the Hartree-Fock energy are addressed here, although the focus is on the more slowly convergent and computationally demanding correlation energy. Because they are frequently based on the gold-standard coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)], correlated calculations are often affordable only with the smallest basis sets, and hence single-level extrapolations from one raw energy could attain maximum usefulness. This possibility is examined. Whenever possible, this review uses raw data from second-order Møller-Plesset perturbation theory, as well as CCSD, CCSD(T), and multireference configuration interaction methods. Inescapably, the emphasis is on work done by the author's research group. Certain issues in need of further research or review are pinpointed.

Deterministic Construction of Nodal Surfaces within Quantum Monte Carlo: The Case of FeS.

In diffusion Monte Carlo (DMC) methods, the nodes (or zeroes) of the trial wave function dictate the magnitude of the fixed-node (FN) error. In standard DMC implementations, the nodes are optimized by stochastically optimizing a short multideterminant expansion in the presence of an explicitly correlated Jastrow factor. Here, following a recent proposal, we pursue a different route and consider the nodes of selected configuration interaction (sCI) expansions built with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm. By increasing the size of the sCI expansion, these nodes can be systematically and deterministically improved. The present methodology is used to investigate the properties of the transition metal sulfide molecule FeS. This apparently simple molecule has been shown to be particularly challenging for electronic structure theory methods due to the proximity of two low-energy quintet electronic states of different spatial symmetry and the difficulty to treat them on equal footing from a one-electron basis set point of view. In particular, we show that, at the triple-ζ basis set level, all sCI results-including those extrapolated at the full CI (FCI) limit-disagree with experiment, yielding an electronic ground state of 5Σ+ symmetry. Performing FN-DMC simulation with sCI nodes, we show that the correct 5Δ ground state is obtained if sufficiently large expansions are used. Moreover, we show that one can systematically get accurate potential energy surfaces and reproduce the experimental dissociation energy as well as other spectroscopic constants.

Synthesis, characterization, crystal structure and quantum chemical investigations of three novel coumarin-benzenesulfonohydrazide derivatives

Coumarin derivatives are an important class of heterocyclic compounds due to their physical and biological properties. Coumarin derivatives have been identified with many significant electro-optical properties and biological activities. Three novel coumarin derivatives containing benzene sulfonohydrazide group were synthesized by condensation reaction. The synthesized compounds were characterized by various spectroscopic techniques (Mass, 1H/13C NMR and FTIR). Thermal and optical properties were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and UV–Vis spectroscopic studies. Finally their structures were confirmed by single crystal X-ray diffraction (XRD) studies. The three compounds exhibit diverse intermolecular interactions, as observed by the crystal packing and Hirshfeld surface analysis. Further, their structures were optimized by density functional theory (DFT) calculations using B3LYP hybrid functionals with 6-311G+(d,p) level basis set. The Mulliken charge, molecular electrostatic potential (MEP), frontier molecular orbitals (HOMO-LUMO) were investigated. The experimentally determined parameters were compared with those calculated theoretically and they complement each other with a very good correlation. The transitions among the molecular orbitals were investigated using time-dependent density functional theory (TD-DFT) and the electronic absorption spectra obtained showed very good agreement with the experimentally measured UV–Vis spectra. Furthermore, non-linear optical (NLO) properties were investigated by calculating polarizabilities and hyperpolarizabilities. All three compounds exhibit significantly high hyperpolarizabilities compared to the reference material urea, which makes them potential candidates for NLO applications.

Benchmarking study on time-dependent density functional theory calculations of electronic circular dichroism for gas-phase molecules

Time-dependent density functional (TDDFT) theory has become a popular method to calculate electronic excited states. The electronic circular dichroism (ECD) spectra of chiral molecules can be computed by TDDFT to resolve their absolute configurations. In this work, we evaluated the performance of TDDFT to calculate ECD of three chiral molecules whose vibronic CD spectra in a supersonic jet were recently reported. We tested seven different functionals (PBEPBE, PBE1PBE, B3LYP, mPW1PW91, M06-2X, CAM-B3LYP, and ωB97X-D) with different levels of the Pople basis set to predict the rotatory strengths of both vertical and adiabatic excitations of the chiral molecules. The 6-311++G(d,p) basis set is appropriate for the ECD calculation, and the augmentation of the diffuse function improves the quality of basis set in calculating the rotatory strength. The simulations of vibronic CD spectra under the adiabatic Hessian scheme in Cartesian coordinates have been feasible only with the M06-2X, CAM-B3LYP, and ωB97X-D functionals. The rotatory strength signs for the 0–0 transition of (1R, 2S)-ephedrine and (S)-2-amino-1-phenylethanol agree well with the experimental results. For the (1S, 2S)-pseudoephedrine conformers, the rotatory strength signs predicted using those three functionals are consistent with each other but do not coincide with the experimental results. The PBEPBE and B3LYP functionals are not robust for geometry optimizations in TDDFT because the calculations using these functionals do not provide reasonable equilibrium geometries for some conformers in the S1 state. Comparison with the conformation-specific CD spectra provides the unambiguous assessment of the DFT functionals suitable for ECD calculations.

Synthesis, Characterization and Preliminary Study on Acetylpyrazine N(4)Butylthiosemicarbazone as a Potential CDK2 Inhibitor Combined with DFT Calculations

In this study, a new thiosemicarbazone ligand, namely acetylpyrazine N(4)butylthiosemicarbazone (APBT), was synthesized and characterized using 1H and 13C nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies. Quantum chemical calculations were performed using density functional theory at the B3LYP/6-311++G(d,p) basis set level. The optimized molecular geometry of APBT is discussed based on X-ray structural reports from the literature. The assignment of the vibrational frequencies was done based on a potential energy distribution analysis using the vibrational energy distribution analysis (VEDA) 4 software. The energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) was evaluated to study the reactivity and stability of the compound. Global chemical reactivity and local reactivity descriptors of reactants and the product (APBT) were calculated to study the reaction mechanism. The region of interaction during the reaction to form APBT was determined using molecular electrostatic potential analysis. Finally, a preliminary study of the title compound as a cyclin-dependent kinase (CDK) inhibitor was further evaluated by performing a docking calculation.

Effect of Methylation on 2-Hydroxypyridine in Ground State: Theoretical Study

A systematic study on the methyl substituted 2-hydroxypyridine molecule is presented in this paper to investigate the methylation effect in the ground electronic state (S0) using ab initio calculations. The minimum energy conformation of these molecules was evaluated using Hartree-Fock (HF), second order Mollar Plesset perturbation (MP2) and B3LYP density functional level of theories and TZVP Gaussian type basis set. B3LYP/TZVP level of theory was used for the natural bond orbital (NBO) calculations to get insight into the substitution energy of the stationary states and also to estimate the role of Lewis and non-Lewis (delocalization) energies. The present study reveals that stabilization of these molecules is due to the change in nuclear-electron interaction energy. However, the local interactions to methyl group are the responsible term for the delocalization energy contribution.

What Function Is Optimal for CCSD(T) Complete Basis Extrapolation for OH Stretching Potential of Water Molecules?

A procedure to calculate the complete basis set limits of electronic energy of water molecules is developed based on two levels of extrapolation scheme. A three‐point fitting scheme with the energies computed at the levels of basis function, aug‐cc‐pVXZ for X = 4–6, is employed to obtain accurate energies of a monomer and a dimer of water. Three extrapolation functions considered in this article are found to work excellently to give accurate Hartree–Fock (HF) energies of water molecules. However, the three functions give slightly different values up to 1–2 mHartree for the complete basis limit of electronic correlation energy. The best performing extrapolating function for the five‐point fitting scheme with a larger set of basis functions for X = 2–6 has been determined aiming for the extrapolation from the lowest two levels of basis sets, double and triple zeta basis functions. For this purpose, an exponential function is suggested for HF energy while an exponential function with a square root exponent is suggested for electronic correlation energy. The optimal exponents of the two functions have been determined.

Growth, structural, optical, mechanical and quantum chemical analysis of unidirectional grown bis(guanidinium) 5-sulfosalicylate (BGSSA) single crystal

Bis(guanidinium) 5-sulfosalicylate single crystal was grown by using Sankaranarayanan-Ramasamy (SR) method from the solution of methanol and water in equimolar ratio. Good quality crystal with 50 mm length and 10 mm in diameter was grown. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm the crystal structure and it was found to be orthorhombic. UV–Vis–NIR spectroscopic study revealed that the SR method grown crystal had good optical transparency with wide optical band gap of 4.4 eV. The presence of the functional groups and modes of vibrations were identified by FTIR spectroscopy recorded in the range 4000–400 cm−1. The mechanical strength of the grown crystal was confirmed using Vickers microhardness tester by applying load from 25 g to 100 g. Density functional theory (DFT) method with B3LYP/6-31-G (d,p) level basis set was employed and hence the optimized molecular geometry, first order hyperpolarizability, dipole moment, thermodynamic functions, molecular electrostatic potential and frontier molecular orbital analysis of the grown BGSSA sample was computed and analysed.

Spectra and dissociation properties of Freon 31 under electric field

ABSTRACTFreon 31 is a carcinogenic substance. It is of great significance for studying its degradation under external electric field. The bond length, energy, dipole moment, orbital energy lever distribution, infrared spectra, and dissociation properties of Freon 31 molecule under the external field are investigated using the density functional theory on basis set level of B3LYP/6-311++G(d, p). In addition, the effects of electric field on ultraviolet–visible absorption spectra of the molecule are studied with CIS/6-311G++(d, p) method. The results indicate that spectra and dissociated properties under electric field have changed significantly. As the electric field (0–0.04 atomic units) along negative direction of y-axis increases, the bond length of carbon–chlorine bond gradually increases and tends to break; the bond length of carbon–fluorine bond gradually decreases. The energy gap first increases and then decreases changing with electric field. The infrared spectra and ultraviolet–visible absorption spectra exhibit blue shift or bathochromic shift under electric field. Moreover, the potential energy surface of Freon 31 about Carbon–Chlorine bond is scanned by the same basis set with configuration interaction - single excitation (CIS) method. The result shows the barrier of dissociation gradually decreases with the electric field. When the intensity of electric field is equal to 0.04 atomic units, the barrier has disappeared. In addition, the molecule is induced to fragmentation due to carbon–chlorine bond breaking. The results offer important reference to the degradation of contaminants.