Ab initio study of the torsional motion in tolane

Xu, Dong; Cooksy, Andrew L.

doi:10.1016/j.theochem.2007.03.028

Cited by 13 publications

(9 citation statements)

References 48 publications

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“…We will use here the optimized scaling factors as originally developed 24 (c mk = 6/5; c mm = c kk = 1/3) due to the remarkable improvement obtained with respect to the unscaled method for various chemical problems of the greatest interest. [33][34][35][36][37][38][39][40] Note that the original MP2 method is recovered if c mk = c mm = c kk = 1. Interactions between chains are dominated by weak forces which produce physical binding between chains and consequently drive the solid-state assembly found in experimental studies.…”

Section: Computational Methodologymentioning

confidence: 99%

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

Sancho‐García

Pérez-Jiménez

2007

Phys. Chem. Chem. Phys.

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The difference between the length of the central carbon-carbon bond and that of the adjacent flanked double bonds in polymers such as polyacetylene is closely related to their electronic properties and plays a central role in their conductivity upon doping. Simple as it seems, this bond length alternation (BLA) is a difficult test for many theoretical methods. Accurate coupled-cluster (CC) benchmark values are difficult to obtain even for small- and medium-sized oligoacetylenes due to their intrinsic computational limitations. Here we present a computationally much cheaper alternative to obtain accurate benchmark BLA values, even for large polyacetylene oligomers, by using the so-called spin-component scaled Møller-Plesset perturbation theory up to second order (SCS-MP2). Comparison between these new benchmark BLA with those provided by density functional theory (DFT) calculations shows a large dispersion of the results depending on the amount of exact exchange used in the exchange-correlation functional. We find that the percentage of exact exchange needed to accurately reproduce the new benchmark BLA is much larger than previously thought when comparison was made with values obtained using the MP2 method.

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Section: Computational Methodologymentioning

confidence: 99%

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

Sancho‐García

Pérez-Jiménez

2007

Phys. Chem. Chem. Phys.

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“…[34][35][36] In addition, extensive computational modeling of the phenyl torsional motion has been carried out, including studies of the possible role of ps* states in the excited state dynamics. [35][36][37][38] Similar condensed phase studies have been carried out for diphenyldiacetylene (DPDA). A recent study by Thulstrup et al, showed that the absorption features of DPDA arise from a combination of both planar and perpendicular phenyl orientations.…”

Section: Introductionmentioning

confidence: 91%

The excited states and vibronic spectroscopy of diphenyldiacetylene and diphenylvinylacetylene

Sebree

Zwier

2012

Phys. Chem. Chem. Phys.

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Laser induced fluorescence (LIF) excitation scans and dispersed fluorescence (DFL) spectra have been recorded for two four-carbon α,ω-diphenyl systems, diphenyldiacetylene (DPDA, φ-C≡C-C≡C-φ) and trans-diphenylvinylacetylene (DPVA, φ-CH≡CH-C≡C-φ) as isolated molecules cooled in a supersonic expansion. While these molecules have similar conjugation length, they exhibit strikingly different vibronic spectroscopy and photophysics. The near-UV LIF excitation spectrum of diphenyldiacetylene has its electronic origin at 32,158 cm(-1), and a strong progression in the C≡C stretch (2156 cm(-1)). All transitions are inherently broad, with widths of ~30 cm(-1) fwhm or greater. The S(1) origin DFL spectrum is composed of sharp transitions with Franck-Condon activity mirroring that in the excitation spectrum, and broad emission shifted well to the red ascribable to phosphorescence on the μs timescale. Using ab initio calculations, it is possible to show that DPDA exists as a single, planar conformer with D(2h) symmetry. In contrast, trans-diphenylvinylacetylene shows intense sharp transitions in both LIF and DFL spectra with an S(0)-S(1) origin of 31,183.2 cm(-1) and long progressions involving the in-plane fundamentals ν(53) (bridge-phenyl bending) and ν(51) (bridge-phenyl stretch). A sharp reduction in fluorescence yield in DPVA occurs within 300 cm(-1) of the S(1) origin. Possible causes for the photophysical processes occurring in the two molecules are discussed.

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“…In fact, as noted by Bunker and Jensen [48], 'except in ultrahigh resolution spectroscopic studies ethane can be considered to be a rigid molecule and the possibility of torsional tunneling can be neglected'. It is also of interest to note that for tolane (diphenyl-acetylene) υ 0 = 533 [49].…”

Section: And Its Modelsmentioning

confidence: 99%

Modelling rotations, vibrations, and rovibrational couplings in astructural molecules – a case study based on the H⁺₅ molecular ion

et al. 2015

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One-dimensional (1D) and two-dimensional (2D) models are investigated, which help to understand the unusual rovibrational energy-level structure of the astronomically relevant and chemically interesting astructural molecular ion H + 5 . Due to the very low hindering barrier characterising the 1D torsion-only vibrational model of H + 5 , this model yields strongly divergent energy levels. The results obtained using a realistic model for the torsion potential, including the computed (near) degeneracies, can be rationalised in terms of the model with no barrier. Coupling of the torsional motion with a single rotational degree of freedom is also investigated in detail. It is shown how the embedding-dependent rovibrational models yield energy levels that can be rationalised via the 2D vibrational model containing two independent torsions. Insight into the complex rovibrational energy level structure of the models and of H + 5 is gained via variational nuclear motion and diffusion Monte Carlo computations and by the analysis of the wavefunctions they provide. The modelling results describing the transition from the zero barrier limit to the large barrier limit should prove to be useful for the important class of molecules and molecular ions that contain two weakly coupled internal rotors. IntroductionThe simplest and exactly solvable quantum chemical models that are traditionally employed to understand highresolution spectra of gas-phase molecules are based on the harmonic oscillator (HO) and rigid rotor (RR) approximations of the vibrations and the rotations, respectively. In cases when the results based on the RRHO approximation, perhaps after a slight extension based on second-order perturbation theory [1][2][3][4][5], provide a good qualitative and even a semiquantitative understanding of spectral regularities, the molecule of interest can be considered to be 'semirigid'. These are molecules for which the electronic state that is being investigated contains a single, well-defined, and relatively deep minimum. For semirigid molecules, the timescales for the vibrational and rotational motions are sufficiently different to allow their approximate separation, the vibrational spacing decreases as the vibrational excitation increases, the vibrational states have well-defined symmetries provided by the point group characterising the unique equilibrium structure, and the rotational states can be assigned to a certain vibrational state. The RRHO treatment is familiar to most chemists as excellent textbooks exist which describe slightly anharmonic molecular vibrations [6,7] as

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Ab initio study of the torsional motion in tolane

Cited by 13 publications

References 48 publications

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

The excited states and vibronic spectroscopy of diphenyldiacetylene and diphenylvinylacetylene

Modelling rotations, vibrations, and rovibrational couplings in astructural molecules – a case study based on the H⁺₅ molecular ion

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Ab initio study of the torsional motion in tolane

Cited by 13 publications

References 48 publications

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

Improved accuracy with medium cost computational methods for the evaluation of bond length alternation of increasingly long oligoacetylenes

The excited states and vibronic spectroscopy of diphenyldiacetylene and diphenylvinylacetylene

Modelling rotations, vibrations, and rovibrational couplings in astructural molecules – a case study based on the H+5 molecular ion

Contact Info

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Modelling rotations, vibrations, and rovibrational couplings in astructural molecules – a case study based on the H⁺₅ molecular ion