Evidence of anharmonicity in the vibrational spectrum of protonated ethylene

McCoy, Anne B.; Duncan, M. A.

doi:10.1016/j.jms.2022.111704

Cited by 3 publications

(12 citation statements)

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“…The definitions of these coordinates are also provided in Figure . On the basis of harmonic and VPT2 calculations, the 1–0 transitions in the last three of these vibrations have been assigned to the peaks at 2158, 3033, and 3113 cm –1 in the spectrum reported by Ricks et al , This spectrum is reproduced in Figure . Additionally, the transition at 2840 cm –1 recently has been assigned as a transition to the state with one quantum of excitation in the breathing motion of the bridging proton as well as one quantum of excitation in the proton transfer vibration .…”

Section: Resultsmentioning

confidence: 93%

“…On the basis of harmonic and VPT2 calculations, the 1–0 transitions in the last three of these vibrations have been assigned to the peaks at 2158, 3033, and 3113 cm –1 in the spectrum reported by Ricks et al , This spectrum is reproduced in Figure . Additionally, the transition at 2840 cm –1 recently has been assigned as a transition to the state with one quantum of excitation in the breathing motion of the bridging proton as well as one quantum of excitation in the proton transfer vibration . On the basis of these assignments, we focus on the states with one quantum of excitation in each of these four vibrations as well as the state with one quantum of excitation in both the breathing and the proton transfer vibrations.…”

Section: Resultsmentioning

confidence: 93%

“…We now turn our attention to vibrationally excited states, which are calculated using the fixed-node approximation, described above. As noted in the Introduction, spectra have been reported for the H + (C 2 H 4 ) isotopologue of the ethyl cation, ,, and we begin our discussion with the excited state energies of this ion. We focus on excitations involving four vibrations.…”

Section: Resultsmentioning

confidence: 99%

“… a Ground state energy is reported relative to the potential minimum. All excited state energies are reported relative to the ground state. b See Figure for definitions and illustrations of the vibrations. c Refs and . d Average based on 5 (ground state) or 10 (excited state) DMC simulations with 50 000 walkers and Δτ = 1 a.u., as described in the text. Standard deviations are provided in parentheses. e Results of VPT2 calculations at the MP2/aug-cc-pVTZ level of theory …”

Section: Resultsmentioning

confidence: 99%

“…The spectrum also contains several weaker features between 2500 and 3000 cm –1 , which were recently assigned to transitions to states with two quanta of excitation in the HCH bends and to the state with one quantum of excitation in the two vibrations of the bridging proton in the CH + C plane. These assignments were made on the basis of a combination of second order vibrational perturbation theory (VPT2) based on MP2/aug-cc-pVTZ calculations, and reduced dimensional calculations . All of these spectral assignments and calculations relied on the premise that the ground state of the ethyl cation is localized in a single minimum on the potential surface.…”

Section: Introductionmentioning

confidence: 99%

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Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)

2023

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The structure and spectra of ethyl cation, H + (C 2 H 4 ), and its deuterated analogues are investigated using diffusion Monte Carlo (DMC). These calculations all show that the ground state wave function for H + (C 2 H 4 ) is localized near the minimum energy configuration in which the excess proton is in a bridging configuration, although the amplitude of the vibrational motions of the bridging proton is large. Deuteration of the bridging proton reduces the amplitude of this motion, while deuteration of only the ethylenic hydrogen atoms in H + (C 2 D 4 ) has little effect on the amplitude of the motion of the bridging proton. Excited states that are accessed by spectroscopically observed transitions in H + (C 2 H 4 ) are calculated using fixed-node DMC. The calculated and measured frequencies for the states with one quantum of excitation in the ethylenic CH stretching vibrations show good agreement. We also explore the excited state with one quantum of excitation in the proton transfer vibration of the bridging proton and obtain a frequency of 616 cm −1 for H + (C 2 H 4 ). This frequency increases to 629 cm −1 in H + (C 2 D 4 ). Deuteration decreases this frequency to 491 and 495 cm −1 in D + (C 2 H 4 ) and D + (C 2 D 4 ), respectively. The effects of partial deuteration on the frequencies of the CH stretching vibrations, and the corresponding probability amplitudes are also explored. Finally, we report the vibrationally averaged rotational constants for the four isotopologues of ethyl cation considered in this study.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)

2023

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Investigation of the Proton-Bound Dimer of Dihydrogen Phosphate and Formate Using Infrared Spectroscopy in Helium Droplets

Torres-Boy,

Taccone,

Kirschbaum

et al. 2024

J. Phys. Chem. A

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Understanding the structural and dynamic properties of proton-bound complexes is crucial for elucidating fundamental aspects of chemical reactivity and molecular interactions. In this work, the proton-bound complex between dihydrogen phosphate and formate, and its deuterated counterparts, is investigated using IR action spectroscopy in helium droplets. Contrary to the initial expectation that the stronger phosphoric acid would donate a proton to formate, both experiment and theory show that all exchangeable protons are located in the phosphate moiety. The experimental spectra show good agreement with both scaled harmonic and VPT2 anharmonic calculations, indicating that anharmonic effects are small. Some H-bending modes of the nondeuterated complex are found to be sensitive to the helium environment. In the case of the partially deuterated complexes, the experiments indicate that internal dynamics leads to isomeric interconversion upon IR excitation.

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Infrared spectroscopy of the syn-methyl-substituted Criegee intermediate: A combined experimental and theoretical study

Zou,

Hassan,

Roy

et al. 2024

The Journal of Chemical Physics

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An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies.

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Evidence of anharmonicity in the vibrational spectrum of protonated ethylene

Cited by 3 publications

References 25 publications

Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)

Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)

Investigation of the Proton-Bound Dimer of Dihydrogen Phosphate and Formate Using Infrared Spectroscopy in Helium Droplets

Infrared spectroscopy of the syn-methyl-substituted Criegee intermediate: A combined experimental and theoretical study

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Evidence of anharmonicity in the vibrational spectrum of protonated ethylene

Cited by 3 publications

References 25 publications

Isotope Effects on Ground and Excited States of Ethyl Cation, H+(C2H4)

Isotope Effects on Ground and Excited States of Ethyl Cation, H+(C2H4)

Investigation of the Proton-Bound Dimer of Dihydrogen Phosphate and Formate Using Infrared Spectroscopy in Helium Droplets

Infrared spectroscopy of the syn-methyl-substituted Criegee intermediate: A combined experimental and theoretical study

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Product

Resources

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Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)

Isotope Effects on Ground and Excited States of Ethyl Cation, H⁺(C₂H₄)