Conformational Structures of Neutral and Cationic Pivaldehyde Revealed by IR-Resonant VUV-MATI Mass Spectroscopy
Pivaldehyde, which is an unwanted by-product released with engine exhaust, has received considerable research attention because of its hydrocarbon oxidations at atmospheric temperature. To gain insight into the conformer-specific reaction dynamics, we investigated the conformational structures of th...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2022-11-01
|
| Series: | International Journal of Molecular Sciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1422-0067/23/23/14777 |
| Summary: | Pivaldehyde, which is an unwanted by-product released with engine exhaust, has received considerable research attention because of its hydrocarbon oxidations at atmospheric temperature. To gain insight into the conformer-specific reaction dynamics, we investigated the conformational structures of the pivaldehyde molecule in neutral (S<sub>0</sub>) and cationic (D<sub>0</sub>) states using the recently invented IR-resonant VUV-MATI mass spectroscopy. Additionally, we constructed the two-dimensional potential energy surfaces (2D PESs) associated with the conformational transformations in the S<sub>0</sub> and D<sub>0</sub> states to deduce the conformations corresponding to the measured vibrational spectra. The 2D PESs indicated the presence of only the <i>eclipsed</i> conformation in the global minima of both states, unlike those in propanal and isobutanal. However, comparing the IR-dip VUV-MATI spectra from two intense peaks in the VUV-MATI spectrum with the anharmonic IR simulations revealed the correspondence between the <i>gauche</i> conformer on the S<sub>0</sub> state and the measured IR spectra. Furthermore, Franck–Condon analysis confirmed that most peaks in the VUV-MATI spectrum are attributed to the adiabatic ionic transitions between the neutral <i>gauche</i> and cationic <i>eclipsed</i> conformers in pivaldehyde. Consequently, electron removal from the highest occupied molecular orbital, consisting of the nonbonding orbital of the oxygen atom in pivaldehyde, promoted the formyl-relevant modes in the induced cationic <i>eclipsed</i> conformer. |
|---|---|
| ISSN: | 1661-6596 1422-0067 |