Conformer-specific VUV-MATI spectroscopy of methyl vinyl ketone: stabilities and cationic structures of the s-trans and s-cis conformers

Abstract

Methyl vinyl ketone (MVK), a volatile compound with photochemical activity, has received considerable attention in the fields of environmental chemistry and atmospheric chemistry. We explored the conformational stabilities of MVK...

Identification of individual conformers in C4H6O isomers using conformer-specific vibrational spectroscopy

“…In addition, the 0-0 band positions for the s-cis conformers in the two isomers corroborated the AIE values determined in previous studies. 9,10 The assignments of the peaks observed in the IR hole-burn spectra of the individual conformers in the two isomers are listed in Table 2 alongside the calculated results and previously reported values. Owing to the vibrational excitations for the s-cis conformers of MVK and CA in the S 0 state, the 0-0 band signals were depleted by 4.3% and 20.9%, respectively.…”

“…[1][2][3][4] Such techniques reduce conformational complexity by utilizing the adiabatic cooling of molecules that results from supersonic expansion in the absence of the non-equilibrium kinetic effect. 5,6 Subsequent investigations have revealed that molecules with a sufficiently low conformer interconversion barrier exist in conformational equilibrium even at low temperatures, [7][8][9] whereas conformers with a high interconversion barrier retain their original composition during cooling via supersonic expansion. [10][11][12] For the former case, identifying peaks that correspond to a specic conformer in measured vibrational spectra requires additional exploration of the vibrational temperature-dependent conformational population, which, in turn, depends on the constructed potential energy surfaces associated with conformational interconversion.…”

“…1 . 31–34 Before recent studies using single-photon vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy and the Franck–Condon (FC) simulations, 9,10 most investigations involving the conformations of these two isomers only examined the temperature-dependence of the peaks corresponding to each neutral conformer in vibrational or rotational spectra. This contributed to the fact that CA and MVK have very short lifetimes, that is, a few hundred femtoseconds, in the excited electronic state owing to the substituent effect of the methyl group on electronic relaxation rates.…”

“…However, the theoretical predictions regarding the preferential conformation for MVK were inconsistent with the recent experimental results, suggesting that the uncertainty in the calculated energy values can originate from the use of incorrect functions and/or densities. 9 Consequently, we were motivated to obtain identifiable vibrational spectra of individual conformers ( i.e. , s- trans and s- cis ) in the two isomers, and thus provide indisputable experimental data regarding the conformational populations while also elucidating how the conformational stabilities in the two isomers change relative to the position of the methyl group.…”

Explaining and Fixing DFT Failures for Torsional Barriers

“…[31] Other studies showed that relative energies between two torsional conformations of methyl vinyl ketone cation predicted using popular B3LYP [17] or CAM-B3LYP [32] functionals do not match experiment. [33] MAE, S b In this study, we explain the source of the DFT torsional barrier error and propose a simple method to improve various carbon-carbon torsional barriers, including long polymers. First, we create a carbon torsional barrier (CTB) dataset consisting of 279 torsional barriers with various functional groups attached to carbon atoms.…”