Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules

Tsybizova, Alexandra; Fritsche, Lukas; Gorbachev, Vladimir; Miloglyadova, Larisa; Chen, Peter

doi:10.1063/1.5124227

Cited by 12 publications

(25 citation statements)

References 53 publications

(41 reference statements)

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“…Thermodynamic equilibrium means that both the monomers and dimers, in our case, must be volatile enough to establish a sufficient steady-state concentration, and thermally stable enough that they do not undergo a thermal reaction other than the reversible association. Consequently, high-temperature, high-pressure mass spectrometric determination of equilibria, as had been reported by Meot-Ner, can be used for a limited range of small molecules, or for unimolecular equilibria such as interconversion between conformers of a given ion . The temperature-dependent equilibria for pyridines/pyridinium ions versus their proton-bound dimers have provided bond dissociation energies for the parent pyridine and analogues with a limited range of small alkyl substituents .…”

Section: Discussionmentioning

confidence: 95%

“…A control experiment, based on an intramolecular competition, indicated that the high value, i.e., the 45 kcal/mol, is unlikely to be correct . We have reported a further independent experimental investigation of dispersion interactions based on gas-phase molecular torsion balances, and it also finds that the dispersion-corrected quantum chemical methods appear to overbind significantly . Given the magnitude of the discrepancy, the universality of London dispersion interactions, and the centrality of the determination to the confidence in experiment, theory, or both, we judged it imperative to validate the T-CID method itself with increasingly large molecules in the gas phase.…”

Section: Introductionmentioning

confidence: 99%

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Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

et al. 2020

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Accurate bond dissociation energies for large molecules are difficult to obtain by either experimental or computational methods. The former methods are hampered by a range of physical and practical limitations in gas-phase measurement techniques, while the latter require incorporation of multiple approximations whose impact on accuracy may not always be clear. When internal benchmarks are not available, one hopes that experiment and theory can mutually support each other. A recent report found, however, a large discrepancy between gas-phase bond dissociation energies, measured mass spectrometrically, and the corresponding quantities computed using density functional theory (DFT)-D3 and DLPNO-CCSD(T) methods. With the widespread application of these computational methods to large molecular systems, the discrepancy needs to be resolved. We report a series of experimental studies that validate the mass spectrometric methods from small to large ions and find that bond dissociation energies extracted from threshold collision-induced dissociation experiments on large ions do indeed behave correctly. The implications for the computational studies are discussed.

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Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

et al. 2020

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“…The synthesis of 3,5-bis(3,5-di-tert-butylbenzyl)pyridine, used in the gas-phase studies here, was reported in our previous work. 10 The ions of interest were prepared upon electrospray ionization of a 10 -6 M methanol solution of the 3,5-bis(3,5-di-tert-butylbenzyl)pyridine. HPLC-grade methanol was purchased from Sigma-Aldrich and used without further purification.…”

Section: Methodsmentioning

confidence: 99%

Perturbation of Pyridinium CIVP Spectra by N₂ and H₂ Tags: An Experimental and BOMD Study

et al. 2020

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In cryogenic ion vibrational predissociation (CIVP) spectroscopy, the influence of the tag on the spectrum is an important consideration. Whereas for small ions there have been several studies showing that the tag effects can be significant, these effects are less understood for large ions, or for large numbers of tags. Nevertheless, it is commonly assumed that if the investigated molecular ion is large enough, the perturbations arising from the tag are small, and can therefore be neglected in the interpretation. In addition, it is generally assumed that the more weakly bound the tag is, the less it perturbs the CIVP spectrum. Under these assumptions, CIVP spectra are claimed to be effectively IR absorption spectra of the free molecular ion. Having observed unexpected splittings in otherwise unproblematic CIVP spectra of some tagged ions, we report Born-Oppenheimer molecular dynamics (BOMD) simulations that strongly indicate that mobility among the more weakly bound tags leads to the surprise splittings. We compared the behavior of two tags commonly used in CIVP spectroscopy (H2 and N2) with a large pyridinium cation. Our experimental results surprisingly show that the more weakly bound tag can, under the appropriate circumstances, perturb the CIVP spectra more than the more strongly bound tag, by not just shifting, but also splitting the observed bands. The more weakly bound tag had significant residence times at several spectroscopically distinct sites on the molecular ion. This indicates that the weakly bound tag is likely to sample several binding sites in the experiment, some of which involve interaction with the reporter chromophore.

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“…Many characteristic chromophores, such as O-H or N-H stretching in complexes, can suffer from Fermi resonance with one or multiple otherwise dark overtones of low-lying modes in the investigated molecule. 37 Isotopic labeling is an effective technique to shift interacting vibration levels, and can easily be implemented via hydrogen-deuterium exchange by spraying from a deuterated, protic solvent. The isotopically substituted O-D and N-D modes move into the spectroscopically convenient, and otherwise nearly empty region between 2100 and 2700 cm −1 , making these chromophores easily distinguishable even from the otherwise nearby C-H stretching modes.…”

Section: Application For Labeled Organic Compoundsmentioning

confidence: 99%

Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions

Gorbachev

Miloglyadova

Tsybizova

et al. 2021

Review of Scientific Instruments

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Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy (CIVP) to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by high signal-to-noise ratio and low FWHM-values, allowing the assignment of two compounds with just a few wavenumbers difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG DFG system are compared and discussed.

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Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules

Abstract: Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules.

Cited by 12 publications

References 53 publications

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Perturbation of Pyridinium CIVP Spectra by N₂ and H₂ Tags: An Experimental and BOMD Study

Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions

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Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules

Abstract: Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules.

Cited by 12 publications

References 53 publications

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Perturbation of Pyridinium CIVP Spectra by N2 and H2 Tags: An Experimental and BOMD Study

Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions

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Perturbation of Pyridinium CIVP Spectra by N₂ and H₂ Tags: An Experimental and BOMD Study