pVTZ Basis Sets Research Articles

Hyperhardness and hypersoftness of atoms and their ions

ContextThe theory of reactivity based on cDFT has been supplemented with the new method of calculating the atomic and local indices. With the use of previously derived relationship of the electron density gradient to the softness kernel and to the linear response function, we deliver theoretical analysis to obtain significant reactivity indices—the electron density derivatives: local softness and local hypersoftness together with the global hyperhardness index and the derivative of the global softness with respect to the number of electrons. The local derivatives have been applied in the calculation of responses of atoms to perturbation by an external potential by the alchemical approach. The vital role of the local softness has been confirmed; the potential role of the hypersoftness has been indicated.MethodOur original theoretical scheme has been numerically illustrated with the results obtained with electron density calculations with B3LYP method implemented in Gaussian 16 package. The aug-cc-pvqz basis set has been routinely applied, except for the Ca atom (cc-pvqz). Using the pVTZ basis set recommended by Sadlej was necessary for the potassium atom.Graphical

An insight into the structure and vibrations of 4–nitroindole and 7–nitroindole by spectroscopic and DFT methods

The structure of 4−nitroindole (4NI) and 7−nitroindole (7NI) is optimised by B3LYP level using 6 − 31++G** and cc−pVTZ basis sets. The FT−IR and FT−Raman and NMR spectra of 4NI and 7NI are analysed in detail and compared. The observed 1H and 13C NMR chemical shifts are found good correlation with theoretical chemical shifts calculated by GIAO method. The vibrational frequencies of 4NI and 7NI have been precisely assigned and analysed. The electron density and electrostatic potential of 4NI is more than that 7NI molecule. The bond orbital analysis (NBO) is carried out. The dual Fukui descriptors (Δfk), the dual local softness (Δsk) and the multiphilicity descriptors (Δωk) have clearly reveals that the atoms N1, C2, C3, C4, C8 are more favourable for nucleophilic attack in both 4NI. In the case of 7NI molecule N1, C2, C3, C5, C7 are more prone to nucleophilic attack. The local reactivity descriptors favours electrophilic attack at the carbon atom C9 of 4NI and 7NI molecules.

Energy profile, structure, spectroscopic and quantum chemical investigations of trans–3,4–(methylenedioxy)cinnamic acid

Abstract The molecular structural parameters and thermodynamic properties of trans–3,4–(methylenedioxy)cinnamic acid have been determined by B3LYP method by using 6–311++G** and cc–pVTZ basis sets. The vibrational frequencies of the compound have been precisely assigned, analysed and the theoretical results are compared with FT-IR and FT-Raman data. The energies of important MOs of the compound are also evaluated from DFT method. The frontier orbital energy gap (ELUMO–EHOMO) is found to be 4.1032 eV. The hydrogen and carbon chemical shifts are elaborately discussed. The dual descriptors Δfk, Δsk and Δωk reveals that the order of reactivity towards nucleophilic attack is C1 > O13 > O12 > C3 > C8 > C6. The minimum and maximum limits of the electrostatic potential observed in MDCA is –1.448e × 10–2(red) and +1.448e × 10–2 (blue). Thus, the present investigation provides complete structural, vibrational and reactivity characteristics of the compound .

An experimental and theoretical investigation on the structure, vibrations and reactivity properties of pharmacologically active compounds 3–acetylindole and indole–3–acetamide

The structure, electronic properties, vibrational fundamental modes and thermodynamic properties of 3–acetylindole (3AI) and indole–3–acetamide (3IAM) compounds are investigated. The most stable geometry, structural parameters and vibrational wavenumbers are determined by using B3LYP method with 6–311++G∗∗ and cc–pVTZ basis sets. FT–IR and FT–Raman spectrum of the compounds are recorded in the range of 4000–400 and 4000–100 cm−1, respectively. The molecular electrostatic potential and total electron density of the compounds have been analysed. The chemical reactivity and site selectivity of the molecules have been investigated by utilising global and local reactivity descriptors.

Conformations, structure, vibrations, chemical shift and reactivity properties of isoquinoline–1–carboxylic acid and isoquinoline–3–carboxylic acid – Comparative investigations by experimental and theoretical techniques

The most stable conformer of isoquinoline–1–carboxylic acid (IQ1CA) and isoquinoline–3–carboxylic acid (IQ3CA) are determined and the geometry has been optimised with B3LYP method using high level 6–311++G** and cc–pVTZ basis sets. The structure, electronic properties, vibrational fundamental modes, thermodynamic properties and chemical shifts of the compounds are investigated. The vibrational fundamental modes are assigned and analysed by utilising FT–IR and FT–Raman spectrum of the compounds recorded in the range of 4000–400 and 4000–100 cm−1, respectively. The LUMO–HOMO energy difference is determined to explain the charge transfer within the molecule. The molecular electrostatic potential and total electron density of the molecules are determined to explain the size, shape and the reactive sites (polar) of the molecules. The 1H and 13C NMR chemical shifts of the compounds are determined by Gauge Invariant Atomic Orbital (GIAO) method using DMSO–d6 solvent by B3LYP/cc–pVTZ method. The local and global chemical reactivity properties of the compounds have been investigated with the help of global and local reactivity descriptors.

Structure, Vibrations, Molecular Orbitals, Reactivity Properties of 3-Trifluoromethylphenylchloroformate by FT-IR, FT-Raman, FT-NMR and DFT Studies

The geometry of 3-trifluoromethylphenylchloroformate (FMPCF) was optimized with B3LYP method using 6–311++G** and cc–pVTZ basis sets. The molecular structural parameters and thermodynamic properties of the compound have been determined. The vibrational frequencies of the fundamental modes of the compound have been precisely assigned, analyzed and the theoretical results were compared with the experimental data. The energies of important molecular orbitals of the compound are also evaluated from DFT method. The Frontier orbital energy gap (ELUMO–EHOMO) is found to be 6.2143 eV. The extreme limits of the electrostatic potential is +8.301e × 10–3 to –8.301e × 10–3 while the total electron density spreads between +3.835e × 10–2 to –3.835e × 10–2. 1H NMR and 13C NMR chemical shifts are measured and compared with their gauge independent atomic orbital (GIAO) calculated values. The n(O7) →π*(C13–O14) and π(C1–C6) →π*(C2–C3) transitions are best stablized with 48.40 and 21.03 kcal mol–1, respectively. In 3-trifluoromethylphenylchloroformate, the atoms C13 is favourable for electrophilic attack. The atoms C2 and C8 are more favourable for nucleophilic attack. The dual descriptors (Δfk, Δsk and Δωk) revealed that the order of nucleophilic attack is C1 > C4 > C2 > C8 > C5. Thus, the present investigation provides complete structure, vibrations and reactivity characteristics of the compound.

Energy profile analysis, spectroscopic investigations (FT–IR, FT–Raman and FT–NMR), electronic properties, structure‒activity aspects and DFT studies of (1,3‒benzodioxol‒5‒yl)acetic acid

Abstract The interaction of electromagnetic interaction by comprehensive theoretical and experimental FT‒IR, FT‒Raman and FT‒NMR spectroscopic studies of (1,3‒benzodioxol‒5‒yl)acetic acid (BDA) have been carried out. DFT/B3LYP method with 6‒311++G** and cc‒pVTZ basis sets have been used to determine the molecular properties of BDA. Five different conformers I, II, III, IV and V of BDA has been determined by potential energy profile. The most stable BDA molecule adopts a non‒planar (puckered) conformation I. The total energy, heat capacity, entropy, vibrational energy and zero point energy calculated by B3LYP/cc‒pVTZ basis sets are 106.34 kcal mol‒1, 40.22 kcal mol‒1 K‒1, 103.44 kcal mol‒1, 104.56 kcal mol‒1 and 99.72 kcal mol‒1, respectively. The total electron density of the BDA molecule spread between + 5.53e ×10‒2 and ‒5.531e ×10‒2. The electrostatic potential are lie in the range ± 1.123e ×10‒2. In BDA molecule n(O12) → π* C11‒O13 interaction is strongly stablised by 42.5 kcal mol‒1. The carbon atoms C3 and C4 are highly deshielded due to –I effect of highly electronegative oxygen. The symmetrical O‒C‒O vibration is blue shifted by 20 and 24 cm‒1 in FT‒IR and FT‒Raman spectra, respectively, when compared to methylenedioxy benzene. The reactivity order for the electrophilic attack is C9 > C10 > C11 while the reactivity order for the nucleophilic attack is C10 > C9 > C3.

Structure, electronic, spectroscopic and reactivity investigations of pharmacologically active compound 1–acetyl–3–indolecarboxaldehyde – An experimental and theoretical approach

The experimental and theoretical studies on the structure and vibrations of 1–acetyl–3–indolecarboxaldehyde (AIC) have been carried out by utilising FT–IR, FT–Raman, FT–NMR and quantum chemical density functional theory (DFT) method. The FT–IR and FT–Raman spectra are recorded in the region 4000–400 cm−1 and 4000–100 cm−1, respectively. The geometry of AIC is optimised by B3LYP method with 6–31G**, 6–311++G** and cc–pVTZ basis sets. The more stable minimum energy conformer has been found by analyzing the potential energy profile. The fundamental vibrational frequencies, infrared intensities, Raman intensities and bonding features of this compound are determined. The HOMO and LUMO energy difference show that, the charge transfer occurs within the molecule. The electrostatic potential and thermodynamic properties of the compound at the different temperatures have been calculated. 1H and 13C NMR chemical shifts of the compound are determined by Gauge Invariant Atomic Orbital (GIAO) by using B3LYP/6–311++G** method. The electrostatic potential of AIC lie in the range +1.22e × 10−2 to −1.22e × 10−2. The limits of total electron density of the complex is +4.906e × 10−2 to −4.906e × 10−2.

Conformational analysis, spectroscopic, structure–activity relations and quantum chemical simulation studies of 4–(trifluoromethyl)benzylamine

The FT–IR and FT–Raman spectra of 4–trifluoromethylbenzylamine (TFMBA) have been recorded in the range 4000–450 and 4000–100 cm−1 respectively. The conformational analysis of the compound has been carried out to attain stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT–Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers obtained theoretically from the B3LYP gradient calculations employing the standard high level 6–311++G** and cc–pVTZ basis sets for the optimised geometry of the compound. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The 1H (400 MHz; CDCl3) and 13C (100 MHz; CDCl3) nuclear magnetic resonance (NMR) spectra were also recorded. The electronic properties, highest occupied molecular orbital and lowest unoccupied molecular orbital energies are measured by DFT approach. The charges of the atoms by natural bond orbital (NBO) analysis are determined by B3LYP/cc–pVTZ method. The structure–chemical reactivity relations of the compound are determined through chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods.

Energy profile, spectroscopic (FT–IR, FT–Raman and FT–NMR) and DFT studies of 4–bromoisophthalic acid

The stable conformer of 4−bromoisophthalic acid (BIPA) has been identified by potential energy profile analysis. All the structural parameters of 4−bromoisophthalic acid are determined by B3LYP method with 6–311++G**, 6−31G** and cc−pVTZ basis sets. The fundamental vibrations are analysed with the use of FT−IR (4000–400 cm−1) and FT−Raman (4000−100 cm−1) spectra. The harmonic vibrational frequencies are theoretically calculated and compared with experimental FTIR and FT−Raman frequencies. The 1H and 13C NMR spectra have been analysed and compared with theoretical 1H and 13C NMR chemical shifts calculated by gauge independent atomic orbital (GIAO) method. The electronic properties, such as HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies are determined by B3LYP/cc−pVTZ method. The electron density distribution and site of chemical reactivity of BIPA molecule have been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP). Stability of the molecules arising from hyperconjugative interactions, charge delocalizations have been analysed by using natural bond orbital (NBO) analysis. The thermodynamic properties and atomic natural charges of the compound are analysed and the reactive sites of the molecule are identified. The global and local reactivity descriptors are evaluated to analyse the chemical reactivity and site selectivity of molecule through Fukui functions.

Simulations on the structure, vibrations and electronic properties of 1,2–epoxy–3–phenoxy propane and 1,2–epoxy–3–( p –tolyloxy)propane by FT–IR, FT–Raman, FT–NMR and DFT methods

Abstract Complete structural, electronic and vibrational properties of 1,2–epoxy–3–phenoxy propane (EPOP) and 1,2–epoxy–3–(p–tolyloxy)propane (ETOP) molecules have been investigated with the help of FT–IR, FT–Raman and FT–NMR spectra of the compounds with the support of the theoretical calculations carried out by DFT/B3LYP method of calculations with 6–311 + + G** and cc–pVTZ basis sets. Various possible conformers of the compounds are determined by analyzing the potential energy profile. In EPOP, the stable conformer I is more stable than the second II by 0.1776 kcal mol–1. Similarly, the conformer I of ETOP is more stable than the conformer II 0.8435 kcal mol–1. The various modes of vibrational frequencies are assigned and analysed with the help of FT–IR and FT–Raman spectra. The electronic properties, such as HOMO and LUMO energies are determined. In both the cases of EPOP and ETOP, the HOMO space distribution reveals that all the carbon atoms of the phenyl ring, the methyl carbon atom and the methylene hydrogen atoms H8 and H9 are more favourable for electrophilic attack. The lone pair donor orbital, n(O10) → π*C11–C16 interaction in EPOP is strongly stabilised by 29.34 kcal mol–1. In the case of ETOP compound, πC12–C13 → π*C11–C16 interaction has more stabilisation energy, 21.34 kcal mol–1. The stabilisation energy of lone pair donor orbital, n(O10) → σ*C11–C16 is 28.80 kcal mol–1. 1H and 13C chemical shifts of the molecules are calculated by GIAO method and discussed. For EPOP, the hydrogen atoms H4, H5 and H6 present in the epoxy ring shows peaks at 2.72, 2.85 and 3.32 ppm, respectively. In the case of ETOP the epoxy hydrogen shows up field peak at 2.70, 2.84 and 2.30 ppm, because of the presence of hyperconjugative effect of the methyl group. The chemical reactivity and site selectivity of the molecule has been determined with the help of global and local reactivity descriptors. The Δfk, Δsk and Δωk values of ETOP suggests that C14 and C11 carbon atoms are more prone to nucleophilic attack while in EPOP the Δfk and Δωk values shows that C14 and C11 is the active sites for the nucleophilic attack but Δsk is only favourable for C11 and not for C14 atom.

Spectra, electronic structure and molecular docking investigations on 3-(phenyl(p-tolylamino)methyl)naphthalen-2-ol – An experimental and computational approach

A combined experimental and theoretical study on synthesis, molecular structure, vibrational analysis, natural bond orbitals, electronic structure, hyperpolarizability, thermochemical properties has been reported for 3-(phenyl(p-tolylamino)methyl) naphthalen-2-ol (PTMN). The FT-IR spectrum was recorded in the range 4000–400 cm−1 and FT-Raman spectrum was recorded in the range 4000–50 cm−1. Sadlej pVTZ basis set was used to calculate the molecular geometry and the vibrational spectra. Natural bond orbital analysis (NBO) were calculated for PTMN using Density Functional Theory (DFT) based on B3LYP/6-311G(d,p) model chemistry. The potential energy distribution (PED) was derived to deepen the understanding on different modes of vibrations which are contributed by respective wavenumber. The molecular structure of PTMN was confirmed also with the simulation of NMR spectrum was performed using GIAO strategy by using B3LYP/6-311G(d,p). The non-linear nature of PTMN was confirmed by hyperpolarizabilty examination. The docking results suggest that the PTMN might exhibit inhibitory activity against protein induce Alopecia disease. The experimental UV–Visible spectra was recorded in the region of 600–200 nm and correlated with simulated spectra by suitable solvated PBEPBE/6-311G(d,p) model. The properties of HOMO-LUMO energies were measured by DFT approaches. In addition, the molecular electrostatic potential (MEP) was computed and investigated. Thermal properties are theoretically calculated that are obtained from the thermochemistry results against a range of temperatures.

An insight into the structure, vibrations, electronic and reactivity properties of the tautomers 1–(diaminomethylene)thiourea and 2–imino–4–thiobiuret

The conformational analysis of 1–(diaminomethylene)thiourea (MTU) has been done to find out the more stable conformer. The more stable geometry of MTU and 2–imino–4–thiobiuret (ITB) are optimised with B3LYP method using 6–311++G** and cc–pVTZ basis sets. The molecules are not planar. The complete molecular structural parameters and thermodynamic properties of the optimised geometry have been determined. The molecule of MTU is not a planar but twisted. The MEP of MTU lies in the region from +1.175e × 10−2 to −1.175e × 10−2 while the total electron density spread between +6.371e × 10−2 and −6.371e × 10−2. The MEP of ITB distributed between +1.179e × 10−2 and −1.179e × 10−2 while the total electron density of ITB lies in the region +7.729e × 10−2 and −7.729e × 10−2. The energies of important MOs of the compound were also evaluated from DFT method. The LUMO shows that the nitrogen and sulphur atoms are the most nucleophilic attacking sites whereas the HOMO reveals that nitrogen, sulphur and carbon atoms are for the electrophilic substitutions. The vibrational frequencies of the fundamental modes of the compounds have been precisely assigned, analysed and the theoretical results were compared with the experimental wavenumbers. 1H and 13C NMR isotropic chemical shifts were determined and the assignments are compared with the experimental values. In MTU molecule, the n → π* transitions such as n(N5) → π*C4–S6 and n(N1) → π*C2–N3 interactions are strongly stabilised by 66.60 and 41.24 kcal mol−1, respectively. In the case of ITB compound, the stabilisation energy of lone pair donor orbital, n(N5) → σ*C4–S6 is 46.03 kcal mol−1. The dual descriptors Δfk, Δsk and Δωk values clearly indicate that the order of nucleophilic attack in MTU is S6 > N11 > N1 > N5 > N3 while in ITB the order follows as N1 > N11 > N5>S6 > N3.

Potential energy profile, structural, vibrational and reactivity descriptors of trans–2–methoxycinnamic acid by FTIR, FT-Raman and quantum chemical studies

The stable conformers of trans–2–methoxycinnamic acid (trans–2MCA) are determined by potential energy profile analysis. The energies of the s–cis and s–trans conformers of trans–2MCA determined by B3LYP/cc–pVTZ method are −612.9788331 Hartrees and −612.9780953 Hartrees, respectively. The vibrational and electronic investigations of the stable s–cis and s–trans conformers of trans–2–methoxycinnamic acid have been carried out extensively with FTIR and FT–Raman spectral techniques. The s–cis conformer (I) with a (C16–C17–C18–O19) dihedral angle equal to 0° is found to be more favoured relative to the one s–trans (II) with (C16–C17–C18–O19) = 180°, possibly due to delocalization, hydrogen bonding and steric repulsion effects between the methoxy and acrylic acid groups. The DFT studies are performed with B3LYP method by utilizing 6–311++G** and cc–pVTZ basis sets to determine the structure, thermodynamic properties, vibrational characteristics and chemical shifts of the compound. The total dipole moments of the conformers determined by B3LYP/cc–pVTZ method are 3.35 D and 4.87 D for s–cis and s–trans, respectively. It reveals the higher polarity of s–trans conformer of trans–2MCA molecule. The electronic and steric influence of the methoxy group on the skeletal frequencies has been analysed. The energies of the frontier molecular orbitals and the LUMO-HOMO energy gap have been determined. The MEP of s–cis conformer lie in the range +1.374e × 10−2 to −1.374e × 10−2 while for s–trans it is +1.591e × 10−2 to −1.591e × 10−2. The total electron density of s–cis conformer lie in the range +5.273e × 10−2 to −5.273e × 10−2 while for s–trans it is +5.403e × 10−2 to −5.403e × 10−2. The MEP and total electron density shows that the s–cis conformer is less polar, less reactive and more stable than the s–trans conformer. All the reactivity descriptors of the molecule have been discussed. Intramolecular electronic interactions and their stabilisation energies have analysed by NBO method.

Conformation analysis of copper(II) etioporphyrin-II by combined gas electron diffraction/mass-spectrometry methods and DFT calculations

Molecular structure of copper(II) etioporphyrin-II (CuEP-II) has been studied by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) method in synchronous mode. The experimental results were complemented by DFT calculations using the B3LYP and PBE functionals with pVTZ basis sets for describing H, C, N atoms and cc-pVTZ for describing Cu atom. The CuEP-II molecule was found to possess quasiplanar geometry of macroheterocycle. DFT calculations predict six conformers for the molecule, which differ by the orientation of the ethyl groups with respect to the macrocycle. Energy differences of five conformers are less, than 0.1kJ/mol (UPBE) or 0.3kJ/mol (UB3LYP). Rotation barriers of single ethyl-group are 14.6 and 19.8kJ/mol (UPBE), 15.7 and 21.6kJ/mol (UB3LYP). Sixth conformer has relatively high energy. Structural parameters of the CuEP-II molecule yielded by DFT calculations are, in general, in a good agreement with the GED data. Structural analysis indicated that the gas-phase electron diffraction method is robust for determination of the macroheterocyclic fragment, but is not enough sensitive to conformational composition of CuEP-II. Substitution effect in pyrrole fragments of CuP, CuOFP, CuOMP and CuEP-II complexes has been analyzed.

Molecular and Ionic Clusters of Rubidium Fluoride: Theoretical Study of Structure and Vibrational Spectra

In this study, the geometrical structure and vibrational spectra of the trimer molecule Rb3F3 and ionic clusters Rb2F+, RbF2-, Rb3F2+, and Rb2F3- were studied by density functional theory (DFT) with hybrid functional B3P86 and Moller–Plesset perturbation theory of second order (MP2). The effective core potential with Def2–TZVP (6s4p3d) basis set for rubidium atom and aug–cc–pVTZ (5s4p3d2f) basis set for fluorine atom were used. The triatomic ions have a linear equilibrium geometric structure of D∞h symmetry, whereas for pentaatomic ions Rb3F2+, Rb<sub23F3- and trimer molecule Rb3F3 different isomers have been revealed. For the ions Rb3F2+, Rb2F3- three isomers were confirmed to be equilibrium; the linear (D∞h ), the planar cyclic (C2v ) and the bipyramidal (D3h ) while for trimer Rb3F3, two isomers were found; the hexagonal (D3h ) and the “butterfly-shaped” (C2v ) configuration.

Theoretical Study of Structure and Vibrational Spectra of Molecular and Ionic Clusters Existing in Vapour over Rubidium Chloride

The geometrical structure and the vibrational spectra of dimer Rb2Cl2, trimer Rb3Cl3, tetramer Rb4Cl4 molecules and heptaatomic Rb4Cl3+, Rb3Cl4– ions were studied. The cluster molecules and ions had been detected in equilibrium vapour over rubidium chloride previously. The quantum chemical calculations by DFT with hybrid functional B3P86 and MP2 methods were performed. The effective core potential with Def2–TZVP (6s4p3d) basis set for rubidium atom and full electron aug–cc–pVTZ (6s5p3d2f) basis set for chlorine atom were used. The equilibrium configuration was confirmed to be rhomb of symmetry D2h for dimer Rb2Cl2, distorted cube (Td) for tetramer Rb4Cl4 and polyhedral (C3v) for heptaatomic ions Rb4Cl3+ and Rb3Cl4–. For the trimer molecule Rb3Cl3 two isomers have been revealed: hexagonal (D3h) and butterfly-shaped (C2v), the latter has lower energy and is proved to be predominant in equilibrium vapour in a broad temperature range.

The Predicted Spectrum and Singlet–Triplet Interaction of the Hypermetallic Molecule SrOSr

In accordance with previous studies in our group on Be, Mg, and Ca hypermetallic oxides, we find that SrOSr has a linear X̃1Σ(g)+ ground electronic state and a very low lying first excited ã3Σ(u)+ triplet electronic state. No gas-phase spectrum of this molecule has been assigned yet, and to encourage and assist in its discovery we present a complete ab initio simulation, with absolute intensities, of the infrared absorption spectrum for both electronic states. The three-dimensional potential energy surfaces and the electric dipole moment surfaces of the X̃1Σ(g)+ and ã3Σ(u)+ electronic states are calculated using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on complete active space self-consistent field (CASSCF) wave functions applying a Sadlej pVTZ basis set for both O and Sr and the Stuttgart relativistic small-core effective core potential for Sr. The infrared spectra are simulated using the MORBID program system. We also calculate vertical excitation energies and transition moments for several excited singlet and triplet electronic states in order to predict the positions and intensities of the most prominent singlet and triplet electronic absorption bands. Finally, for this heavy molecule, we calculate the singlet–triplet interaction matrix elements between close-lying vibronic levels of the X̃ and ã electronic states and find them to be very small.

CASSCF and MR–CISD study of the n−4s and n−4pe Rydberg states of the CF3Cl

The low-lying n−4s (S2 and T2) and n−4pe (S3 and T3) Rydberg states of the CF3Cl have been studied at the CASSCF, MR–CISD, MR–CISD+Q and MR–AQCC levels using the mixed aug–cc–pVDZ/d–aug–cc–pVDZ and aug′–cc–pVTZ/d′–aug′–cc–pVTZ basis sets. Spin–orbit corrections for the singlet energies, vertical excitation energies and oscillator strengths have been computed. The effect of the inclusion of K+L or only the K inner shell chlorine orbitals in the frozen core space at the post-CASSCF levels has also been discussed. Good agreement with available experimental and with previous high-level theoretical results has been achieved.

Theoretical investigations of the nature of interaction of Br 2 with hydrogen halide

The interactions of the Br 2 with hydrogen halide have been investigated by performing calculations at the second-order perturbation theory based on the Møller–Plesset partition of the Hamiltonian with the Sadlej PVTZ basis set. The X–Br type geometry and hydrogen-bonded geometry are investigated in these interactions. The calculated interaction energies show that the X–Br type structures are more stable than the corresponding hydrogen-bonded structures. To study the nature of the intermolecular interactions, symmetry-adapted perturbation theory (SAPT) calculations were carried out and the results indicate that the X–Br interactions are dominantly electrostatic and dispersion energy in nature, while dispersion energy governs the hydrogen bonding interactions.