Quantum chemical study of the umbrella inversion of the ammonia molecule

Ghosh, Dulal C.; Jana, Jibanananda; Biswas, Raka

doi:10.1002/1097-461x(2000)80:1<1::aid-qua1>3.3.co;2-4

Cited by 6 publications

(21 citation statements)

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“…Despite decades of theoretical investigations and a large body of high quality spectroscopic data, investigations of ammonia's PES and analyses of its spectra continue to be active fields of research (see e.g. [1][2][3][4][5][6][7] for some recent reports).…”

Section: Introductionmentioning

confidence: 99%

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Chen

Pearson

Pickett

et al. 2006

Journal of Molecular Spectroscopy

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Section: Introductionmentioning

confidence: 99%

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Chen

Pearson

Pickett

et al. 2006

Journal of Molecular Spectroscopy

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“…From Koopmans' theorem, the ionization potential is the energy of HOMO with negative and the electron affinity is the orbital energy of LUMO with negative sign. Now, combining Koopmans' theorem a further approximation to the above equations is obtained: where Δε is the gap between the HOMO and the LUMO Whereas the global hardness and related properties are independent of any particular molecular orbital (MO) theory and cover all levels of MO theories equally well 20, 28, and whereas it is demonstrated that the conclusions of DFT can be effectively tested by semiempirical theories 5, 16, 20, 24, 33 and there is an advantage with the eigenvalues of semiempirical methods 43, and whereas the computation of density functional quantities is designed approximately, and the approximate nature of Koopmans' theorem is well documented in the chemical literature 56, we invoked the CNDO/2 method of Pople and coworkers 57 in the present investigation. Because the remarkable change in shape prior to the event of chemical reaction occurs through sharp angular deformation of the molecules, the theoretical parameters are computed as a function of angular distortion optimizing the bond lengths at each stage of deformation.…”

Section: Methods Of Computationmentioning

confidence: 99%

“…Chattaraj 22 reviewed the connection between the HOMO–LUMO gap and stability in various situations. Ghosh and coworkers 23–25 and Ghosh 26 demonstrated that the HOMO–LUMO gap can be used to correlate the order of stability and reactivity of structurally related molecules and monitor the physical process of inversion and internal rotation of molecules. The physical process of reorganization of shapes of BX 3 systems prior to the event of chemical reaction occurs through an intramolecular structural deformation following the normal modes of vibration of the molecule.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, the process of charge transfer initiates under the driving force of fixed chemical potentials of the interacting chemical systems and as the process continues the geometry of the adduct supermolecule is decided by the chemical potential equalization principle. The new paradigm of electronic structure has been numerically tested in a number of calculations computing the values of global hardness η for a variety of individual molecules during the process of structural inversion, deformation, and internal rotation, in various types of simple reactions, and in correlating the order of stability and reactivity of structurally related molecules 23–26, 32–43. These quantities are useful to study the molecular stability of different conformers 26.…”

Section: Introductionmentioning

confidence: 99%

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Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH₃) and boron trifluoride (BF₃) as a function of angles of reorganization from planar (D_3h) to pyramidal (C_3v) shape

Ghosh

Jana

2003

Int J of Quantum Chemistry

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ABSTRACT:In chemical response the BH 3 and BF 3 molecules undergo the physical process of planar (D 3h ) to pyramidal (C 3v ) reorganization in shape as the condition precedent to the event of chemical reaction under the requirement of symmetry. A frontier orbital and density functional study of the variation of the stability of electronic structures and chemical reactivity of associated with the physical process of D 3h to C 3v geometry reorganization has been performed. The theoretical parameters viz. eigenvalues of HOMO and LUMO, the HOMO and LUMO energy gap, the global hardness and global softness, the chemical potential, the condensed Fukui function, and local softness of B atom, the reaction site, have been computed over a wide range of ЄXBX angles. The nature of variation in the intrinsic chemical reactivity, global and local, of the molecules associated with their geometry reorganization during the chemical event of charge transfer interaction involving their frontier molecular orbitals has been quantitatively explored. The hardness profiles as a function of reaction coordinates are consistent with the principle of maximum hardness (PMH). Results demonstrate that the hardness and softness are not a static and invariable property of molecules but a dynamic and variable function of molecular structure. The hardness parameters and the HOMO-LUMO gap of the molecules are so modified with the distortion of molecular geometry that, after a certain stage of molecular deformation, the profiles of such parameters of the molecules intersect and cross each other, signifying that the relative order of the intrinsic hardness of their equilibrium geometry is reversed. The intrinsically hard molecule BF 3 becomes softer than the intrinsically soft molecule BH 3 as a consequence of structural distortion. The increase in chemical reactivity computed in terms of density functional parameters are transparent and justified in terms of the profiles of the eigenvalues of the frontier orbitals. The profiles of chemical potential reveal the inherent difference in the tendency of backdonation from two molecules. The computed values of Fukui functions and local softness parameters of the B atom site demonstrate that the concept of local softness can be exploited for a theoretical analysis and understanding of the characteristic chemical events of the molecules under consideration. The profiles of the Fukui functions and local softness parameters of the two molecules seem to reflect and reveal their intrinsic difference in the tendency of receiving donation in the LUMO (electrophilicity) and that of backdonation from the HOMO (nucleophilicity) and the inherent difference of overall reactivity of the two molecules by a simultaneous operation of two opposing processes of charge transfer.

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“…The tricovalent nitrogen compounds undergo a rapid inversion of structure through the quantum mechanical tunneling effect, and the rate of tunneling is faster the lower and the thinner the potential barrier is 1–6. Recently, Ghosh et al 7 have performed a detailed study of the phenomenon of the umbrella inversion of ammonia using the paradigms of molecular orbital and density functional theories (MOT and DFT). An intuitive structure and dynamics of the mechanism of the evolution of the equilibrium shape into the transition‐state conformation prior to the inversion has been suggested, and it has been shown that the MOT and DFT provide appropriate and adequate description of the physical process of evolution of the molecular shape from the equilibrium geometry to the transition state for inversion and attempt to meaningfully locate the physical origin of the barrier of the process of inversion.…”

Section: Introductionmentioning

confidence: 99%

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF₃) molecule

Ghosh

Jana

Bhattacharyya

2002

Int J of Quantum Chemistry

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ABSTRACT:The physical process of the umbrella inversion of the nitrogen trifluoride molecule has been studied invoking the formalisms of the density functional theory, the frontier orbital theory, and the molecular orbital theory. An intuitive structure and dynamics of evolution of the transition state for the event of inversion is suggested. The physical process of dynamic evolution of the molecular conformations between the equilibrium (C 3v ) shape and the planar (D 3h ) transition state has been followed by a number of molecular orbital and density functional parameters like the total energy, the eigenvalues of the frontier orbitals, the highest occupied molecular orbital and lowest unoccupied molecular orbital, the (HOMO-LUMO) gap, the global hardness and softness, and the chemical potential. The molecular conformations are generated by deforming the FNF angle through steps of 2 • from its equilibrium value, and the cycle is continued till the planar transition state is reached, and the geometry of each conformation is optimized with respect to the length of the N-F bond. The geometry optimization demonstrates that the structural evolution entails an associated slow decrease in the length of the N-F bond. The dipole moment at the equilibrium form is small and that at the transition state is zero and shows a strange behavior with the evolution of conformations. As the molecular structure begins to distort from its equilibrium shape by opening of the FNF angle, the dipole moment starts increasing very sharply, and the trend continues very near to the transition state but abruptly vanishes at the transition state. A rationale of the strange variation of dipole moment as a function of evolution of conformations could be obtained in terms of quantum mechanical hybridization of the lone pair on the N atom. The pattern of charge density reorganization as a function of geometry evolution is a continuous depletion of charge from the F center and piling up of charge on the N center. The continuous shortening of bond length and the pattern of variation of net charge densities on atomic sites with evolution of molecular conformations predicts that the bond moment would decrease continuously. The quantum mechanical hybridization of the lone pair of the central N atom shows that the percentage of s character of the lone-pair hybrid on the N atom decreases at a very accelerated rate, and the lone pair at the transition state is accommodated in a pure p orbital. The result of the continued destruction of asymmetry of GHOSH, JANA, AND BHATTACHARYYA charge distribution in the lone pair on the central N atom due to the elimination of contribution of the s orbital with evolution of molecular conformations is the sharp decrease in lone-pair moment. The decrease in bond moment is overcompensated by the sharp fall of its offsetting component, the lone-pair moment, resulting in a net gain in dipole moment with the evolution of molecular geometry. Since the offsetting component decreases very sharply, the net effect is a sharp rise ...

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Quantum chemical study of the umbrella inversion of the ammonia molecule

Cited by 6 publications

References 0 publications

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH₃) and boron trifluoride (BF₃) as a function of angles of reorganization from planar (D_3h) to pyramidal (C_3v) shape

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF₃) molecule

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Quantum chemical study of the umbrella inversion of the ammonia molecule

Cited by 6 publications

References 0 publications

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Measurements of 14NH3 in the ν2=1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion–rotation levels

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH3) and boron trifluoride (BF3) as a function of angles of reorganization from planar (D3h) to pyramidal (C3v) shape

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF3) molecule

Contact Info

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About

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH₃) and boron trifluoride (BF₃) as a function of angles of reorganization from planar (D_3h) to pyramidal (C_3v) shape

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF₃) molecule