On the electronic structure of methyl butyrate and methyl valerate

Abstract

We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere. Graphical abstract

Photoionization of Two Potential Biofuel Additives: γ-Valerolactone and Methyl Butyrate

“…The ground-state TPES of MB consists of a single broad band (Figure a) due to an abundance of low-frequency vibrational modes, the rich configuration space of MB, and the, in part, large geometry change upon ionization. The ionization energy of MB has been studied several times − and reported as 9.95 ± 0.05 eV in a previous PEPICO study, whereas a calculated value of 9.977 eV has been given by Śmiałek et al However, the absence of a vibrational progression due to the large geometry change upon ionization makes it impossible to assign the origin transition with the help of a double harmonic Franck–Condon simulation of the ground-state band. Published ionization energies have often been found to be in error in such cases, for instance in ethanol or in diethyl ether, , as the onset of the photoelectron spectrum only represents a likely upper limit to the adiabatic ionization energy.…”