DIFFUSION MONTE CARLO STUDY OF VIBRATIONAL EXCITED STATES OF PROTONATED ETHYLENE (H⁺(C₂H₄))

Moonkaen, Pattarapon

Permalink

https://hdl.handle.net/2142/122667 Copy

Description

Title

DIFFUSION MONTE CARLO STUDY OF VIBRATIONAL EXCITED STATES OF PROTONATED ETHYLENE (H⁺(C₂H₄))

Author(s)

Moonkaen, Pattarapon

Contributor(s)

• McCoy, Anne B.
• Finney, Jacob M.

Issue Date

2023-06-22

Keyword(s)

Vibrational structure/frequencies

Abstract

Carbocations are a class of important organic intermediates, which exist in hydrocarbon plasmas and are believed to play a role in the chemistry in the interstellar medium. Protonated ethylene (H⁺(C₂H₄)) is one such carbocation, which is formed from the smallest alkene. It is also important in mass spectrometry as it appears in the mass spectra of many organic molecules and it is used as the protonating agent in chemical-ionization mass spectrometry. High-level electronic structure calculations predict that the minimum energy structure is the non-classical one in which the excess proton is equidistant from the two carbon atoms. This was confirmed by the IR spectrum of H⁺(C₂H₄) obtained by the Dopfer and Duncan groups. In this work, we use fixed-node Diffusion Monte Carlo (DMC), based on a potential with CCSD(T)-level accuracy to obtain excited state wave functions and vibration frequencies. The analysis of excited state wave functions confirms that the ion is localized in the non-classical minimum on the potential. It also allows us to explore the couplings among the motions of the hydrogen atoms. The frequencies obtained from the DMC calculations are compared to the experimental frequencies in the IR spectrum. Based on this, one of the weak features between 2500 and 3000 cm−¹ in the spectrum is assigned to the combination band of the proton transfer and breathing mode. Lastly, extensions of DMC to calculations of intensity will be discussed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122667

DOI

https://doi.org/10.15278/isms.2023.7200

Owning Collections