Vibrational Potential

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Jaan Laane - One of the best experts on this subject based on the ideXlab platform.

  • Vibrational Potential Energy Surfaces in Ground and Excited Electronic States
    Frontiers and Advances in Molecular Spectroscopy, 2018
    Co-Authors: Jaan Laane, Esther J. Ocola, Hye J. Chun
    Abstract:

    Abstract Infrared and Raman spectra of molecules, often of vapor samples at high temperatures and/or utilizing special sample cells, have been utilized to investigate molecular structures, conformations, and Vibrational Potential energy surfaces (PESs) in electronic ground states. Similarly, laser-induced fluorescence (LIF) and ultraviolet spectra have provided the data for investigating electronic excited states. Theoretical ab initio and density functional theory (DFT) calculations have complemented the experimental work. The focus of the work has been on cyclic and bicyclic molecules that possess large-amplitude motions such as the ring-puckering and ring-twisting vibrations. We first discuss molecules with intramolecular π-type hydrogen bonding in cyclic and bicyclic alcohols and amines. This type of bonding is achieved only when the ring puckering or ring twisting and OH or NH 2 torsional coordinates are at their optimal positions. Second, we review the Raman spectra of 1,3-butadiene that allowed us to calculate the torsional Potential energy function for this molecule. Third, we examine the ultraviolet electronic spectra of pyridine and several fluoropyridines and discuss their Potential energy functions in electronic excited states. Fourth, we present our experimental data and theoretical calculations for the two-dimensional PESs of three unusual molecules. In each case, the characteristics of the energy levels and their corresponding wave functions are discussed in detail. Fifth, the PESs for the torsional vibrations of stilbenes are reviewed. Sixth, we summarize our results for the ground and excited states of several bicyclic aromatics including the remarkable 1,3-benzodioxole molecule, which possesses the anomeric effect. Lastly, we describe our results on the LIF spectra of cyclic ketones that generally possess double-minimum PESs for the carbonyl inversion vibrations in their S 1 (n, π⁎) excited states.

  • theoretical calculations and Vibrational Potential energy surface of 4 silaspiro 3 3 heptane
    Journal of Chemical Physics, 2014
    Co-Authors: Esther J. Ocola, Niklas Meinander, Cross Medders, Jaan Laane
    Abstract:

    Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering Potential energy surface (PES) of the form V = a(x14 + x24) – b(x12 + x22) + cx12x22, where x1 and x2 are the ring-puckering coordinates for the two rings. The presence of sufficiently high Potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.

  • Vibrational Potential Energy Surfaces in Electronic Excited States
    Frontiers of Molecular Spectroscopy, 2009
    Co-Authors: Jaan Laane
    Abstract:

    Publisher Summary Potential energy functions concentrate on the use of the harmonic oscillator. Potential functions that are not harmonic, however, can be much more informative, especially if their energy minima do not correspond to the coordinate origins. Several spectroscopic methods, including infrared and ultraviolet absorption, Raman, jet-cooled laser-induced fluorescence, and cavity ringdown, have been utilized to map out the Vibrational quantum states of molecules in their ground and excited electronic states. Data on the higher excited Vibrational levels for large-amplitude vibrations such as ring-puckering, ring-twisting, ring-flapping, and internal rotation allow one- or two-dimensional Potential energy surfaces to be accurately determined. In many cases, ab initio and/or DFT computations are utilized to complement the experimental work. Following a discussion of theory, experimental methods, and computational methods, the spectroscopic results and PESs for several types of molecules are presented. First, the PESs for the carbonyl wagging vibration of seven cyclic ketones in their S1(n, π*) excited states are reviewed. Except for 2-cyclopentenone (2-CP), which is conjugated and planar, the PESs have a barrier to planarity, which increases with angle strain. PESs for the ring-bending and ring-twisting vibrations were also determined for these ketones in both their ground and excited states. The LIF study of trans-stilbene and two substituted stilbenes allowed two-dimensional PESs for the internal rotations of the phenyl groups to be calculated for both ground and S1(π, π*) states.

  • Spectroscopic determination of Vibrational Potential energy surfaces in ground and excited electronic states
    Journal of Electron Spectroscopy and Related Phenomena, 2006
    Co-Authors: Jaan Laane, Juan Yang
    Abstract:

    Abstract Vibrational Potential energy surfaces (PESs) for selected vibrations can provide detailed information on the conformational changes of non-rigid molecules in both ground and excited electronic states. These have been investigated using several spectroscopic techniques including laser-induced fluorescence (LIF), both fluorescence excitation spectroscopy (FES) and single Vibrational level fluorescence (SVLF) or dispersed fluorescence (DF), infrared (IR) and ultraviolet (UV) absorption, and laser Raman spectroscopy. These methods allow detailed quantum energy maps for the ground electronic state (S 0 ) and excited electronic states [S 1 (π,π * ) and S 1 (n,π * )] to be established. Knowledge of these states allows the PESs to be determined in terms of the relevant molecular vibrations. The results for coumaran and 1,4-benzodioxan (14BZD) will be presented. Coumaran is puckered in both S 0 and S 1 (π,π * ) states with inversion barriers of 154 and 34 cm −1 , respectively, and the energy minima lie at dihedral angles of 25° and 14°. 14BZD is twisted in both S 0 and S 1 (π,π * ) states with high barriers to planarity. In the electronic excited state the inversion barrier is reduced considerably.

  • spectroscopic determination of the two dimensional Vibrational Potential energy surfaces for the ring puckering and ring flapping modes of indan in its s0 and s1 π π electronic states
    Journal of Chemical Physics, 2002
    Co-Authors: Zane Arp, Niklas Meinander, Jaebum Choo, Jaan Laane
    Abstract:

    The vapor-phase far-infrared, mid-infrared, ultraviolet, Raman, and laser-induced fluorescence spectra of indan have been recorded and analyzed. The far-infrared spectra, which are very similar to those previously reported, together with the Raman and dispersed fluorescence (SVLF) spectra of the jet-cooled molecules were used to reassign the ring-puckering and ring-flapping energy levels for the S0 ground state. These were then utilized to calculate a two-dimensional Vibrational Potential energy surface (PES) which nicely fits all of the assigned puckering and flapping levels. The PES has a barrier of 488 cm−1 as compared to a previously reported value of 1979 cm−1, which was based on a one-dimensional analysis and earlier assignments. The dihedral angle of puckering is ±30°. Fluorescence excitation spectra of jet-cooled indan together with ultraviolet absorption spectra were used to assign the flapping and puckering levels in the S1(π,π*) electronic excited state. The PES for this state has a barrier of ...

Niklas Meinander - One of the best experts on this subject based on the ideXlab platform.

  • theoretical calculations and Vibrational Potential energy surface of 4 silaspiro 3 3 heptane
    Journal of Chemical Physics, 2014
    Co-Authors: Esther J. Ocola, Niklas Meinander, Cross Medders, Jaan Laane
    Abstract:

    Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering Potential energy surface (PES) of the form V = a(x14 + x24) – b(x12 + x22) + cx12x22, where x1 and x2 are the ring-puckering coordinates for the two rings. The presence of sufficiently high Potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.

  • spectroscopic determination of the two dimensional Vibrational Potential energy surfaces for the ring puckering and ring flapping modes of indan in its s0 and s1 π π electronic states
    Journal of Chemical Physics, 2002
    Co-Authors: Zane Arp, Niklas Meinander, Jaebum Choo, Jaan Laane
    Abstract:

    The vapor-phase far-infrared, mid-infrared, ultraviolet, Raman, and laser-induced fluorescence spectra of indan have been recorded and analyzed. The far-infrared spectra, which are very similar to those previously reported, together with the Raman and dispersed fluorescence (SVLF) spectra of the jet-cooled molecules were used to reassign the ring-puckering and ring-flapping energy levels for the S0 ground state. These were then utilized to calculate a two-dimensional Vibrational Potential energy surface (PES) which nicely fits all of the assigned puckering and flapping levels. The PES has a barrier of 488 cm−1 as compared to a previously reported value of 1979 cm−1, which was based on a one-dimensional analysis and earlier assignments. The dihedral angle of puckering is ±30°. Fluorescence excitation spectra of jet-cooled indan together with ultraviolet absorption spectra were used to assign the flapping and puckering levels in the S1(π,π*) electronic excited state. The PES for this state has a barrier of ...

  • FAR-INFRARED, RAMAN, AND DISPERSED FLUORESCENCE SPECTRA, Vibrational Potential ENERGY SURFACE, AND THE ANOMERIC EFFECT OF 1,3-BENZODIOXOLE
    Journal of the American Chemical Society, 1999
    Co-Authors: Sachie Sakurai, Niklas Meinander, Kevin F. Morris, Jaan Laane
    Abstract:

    The far-infrared and Raman spectra of 1,3-benzodioxole vapor have been recorded and analyzed. Forty-one infrared and six Raman bands were assigned to transitions between the various ring-puckering energy levels in the ground and excited ring-flapping states. The determination of the energy levels was assisted by analysis of the single vibronic level fluorescence spectra of the jet-cooled molecules. The puckering levels change substantially in the flapping excited state, indicating substantial interaction between the two Vibrational modes. From the spectroscopic data, a two-dimensional Vibrational Potential energy surface was determined. This has a barrier to planarity of 164 cm-1 and energy minima at puckering and flapping angles of ±24° and ∓3°, respectively. This molecule has a lower barrier to planarity than 1,3-dioxole, reflecting the influence of the benzene ring on the anomeric effect. Nevertheless, the anomeric effect is clearly the origin of the nonplanarity of this bicyclic ring system.

Jaebum Choo - One of the best experts on this subject based on the ideXlab platform.

Delin Shen - One of the best experts on this subject based on the ideXlab platform.

  • Distribution of Vibrational Potential energy in molecular systems
    The Journal of Chemical Physics, 1999
    Co-Authors: Huw O. Pritchard, S. Raj Vatsya, Delin Shen
    Abstract:

    It is shown that for a collection of n classical harmonic oscillators, the long-time distribution of Potential energies P is approximated by sinm(πP) for n⩾4, where m=(8n/π2−1/√2) and P is scaled to lie between 0 and 1. As n→∞, the distribution tends to a δ-function centered about P=0.5. When coupling is present between the oscillators, the effective value of m is reduced, so that the breadth of the Potential energy distribution reflects the degree of randomization in the system.

D. J. List - One of the best experts on this subject based on the ideXlab platform.

  • Solvent and pressure‐induced perturbations of the Vibrational Potential surface of acetonitrile
    The Journal of Chemical Physics, 1992
    Co-Authors: Dor Ben-amotz, Meng Rong Lee, Seung Y. Cho, D. J. List
    Abstract:

    Raman‐scattering studies at both ambient pressures and in a high‐pressure diamond‐anvil cell are used to measure gas‐to‐liquid Vibrational frequency shifts of three normal modes of acetonitrile, CH3CN (ν1, CH stretch; ν2, CN stretch; and ν4, CC stretch) dissolved in various solvents (methylenechloride, chloroform, carbontetrachloride, toluene, pyridine, acetone, and methanol). The results are compared with calculated repulsive and attractive solvation force‐induced perturbations of polyatomic Vibrational Potential surfaces. Repulsive solvation forces are modeled using recently developed analytical ‘‘hard‐fluid’’ expressions for heteronuclear two‐cavity distribution functions in hard‐sphere fluids, while attractive forces are assumed to contribute a van der Waals(linearly density‐dependent) mean field. Results for the CN and CC stretches of acetonitrile compare favorably with theoretical predictions, while the CH stretch appears to experience a nonlinearly density‐dependent attractive frequency shift at hi...