Isobutyl acetate: electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations

Abstract

Abstract. The high-resolution vacuum ultraviolet photoabsorption spectrum of isobutyl acetate, C 6 H 12 O 2 , is presented here and was measured over the energy range 4.3-10.8 eV (290-115 nm). Valence and Rydberg transitions with their associated vibronic series have been observed in the photoabsorption spectrum and are assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. The measured photoabsorption cross sections have been used to calculate the photolysis lifetime of this ester in the Earth's upper atmosphere (20-50 km). Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl acetate and are compared with a photoelectron spectrum (from 9.5 to 16.7 eV), recorded for the first time. Vibrational structure is observed in the first photoelectron band of this molecule.

Photoelectron spectroscopy of a series of acetate and propionate esters

“…The molecular structure of acetate esters is presented in Figure 1 (1-4a). In all cases, in accord with previous studies of formate [5,6,7] and acetate [9,8] esters, the highest occupied molecular orbital (HOMO) in the neutral ground state is localized largely on the terminal oxygen in-plane lone pair (n O1 ), as seen in Figure 1 (1-4b). For methyl acetate the HOMO is (16a') 2 , for isopropyl acetate -(20a') 2 , for butyl acetate -(25a') 2 , and for pentyl acetate -(28a') 2 .…”

“…Electronic excitation of these compounds have been described with aid of quantum chemistry calculations. Combining our findings with data obtained for those esters that have been studied previously: methyl formate [5], ethyl formate [6], isobutyl formate [7], isobutyl acetate [8], ethyl acetate [9], methyl butyrate and methyl valerate [10] we can draw some conclusions on the influence of the increase in the alkyl and aryl group on the ionization energy of ester molecules.…”

On the electronic structure of methyl butyrate and methyl valerate

“…4). Such feature has not been observed previously for other ester molecules [8][9][10][11][12]. This series may be an additional vibrational mode, such as a series of C-C skeletal stretching, already seen here as ν d associated with the ν a mode.…”

“…Previously we have reported our findings on methyl formate [8], ethyl formate [9], isobutyl formate [10], ethyl acetate [11], isobutyl acetate [12] and some acetates and propionates [13]. Here we present our findings on a further two methyl esters: butyrate and valerate.…”

Dynamics of systems on the nanoscale

“…The high-resolution vacuum ultraviolet photoabsorption spectrum of isobutyl acetate, C 6 H 12 O 2 , measured over the energy range 4.3-10.8 eV, is presented in [6]. Valence and Rydberg transitions with their associated vibronic series have been observed and are assigned in accordance with new ab initio calculations of the excitation energies and oscillator strengths.…”