Valence and Ionic Lowest-Lying Electronic States of Isobutyl Formate Studied by High-Resolution Vacuum Ultraviolet Photoabsorption, Photoelectron Spectroscopy, and Ab Initio Calculations

Abstract

The highest resolution vacuum ultraviolet photoabsorption spectrum of isobutyl formate, C5H10O2, yet reported is presented over the energy range 4.5-10.7 eV (275.5-118.0 nm) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series observed in the photoabsorption spectrum have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl formate and are compared with a newly recorded photoelectron spectrum (from 9.0 to 27.0 eV). The value of the first ionization energy was determined to be 10.508 eV (adiabatic) and 10.837 eV (vertical). New vibrational structure is observed in the first photoelectron band, predominantly resulting from C-O and C═O stretches of the molecule. The photoabsorption cross sections have been used to calculate the photolysis lifetime of isobutyl formate in the upper stratosphere (20-50 km), indicating that the hydroxyl radical processes will be the main loss process for isobutyl formate.

Electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations of ethyl acetate

“…The first band, shown in Figure 2, with a maximum cross section of 0.19 Mb, has been identified as the transition from the terminal oxygen in-plane lone pair (n O1 ) to the first π antibonding molecular orbital (π*(C=O) ← n O1 19a )(1 1 A ← 1 1 A ). The calculated value of the oscillator strength, 1 × 10 −3 , is comparable with the values obtained for the previously analysed esters [11][12][13]. The position of the maximum cross section of this band also agrees well with the value given by others, obtained from the spectrum of the liquid sample, i.e.…”

“…1). In our previous studies on the related compounds of ethyl formate [12] and isobutyl formate [13] it was shown that a proper assignment of the spectroscopic features is obtained using calculations on a single conformer. Therefore, in the present study theoretical computations are only performed on the trans-trans conformer.…”

“…The only available studies of this molecule concern its first ionisation energy that was obtained either through electron impact mass spectrometry [4][5][6] or conventional photoelectron measurements [7][8][9] and PIPECO spectroscopy [10]. The absolute photoabsorption cross sections of ethyl acetate presented here are needed for modeling studies of the Earth's atmosphere and radiationinduced chemistry of esters, and, together with the results on previously analysed members of this class: methyl formate [11], ethyl formate [12] and isobutyl formate [13], will help to understand the chemistry of esters and their electronic state spectroscopies.…”

Photoelectron and threshold photoelectron valence spectra of pyridine

“…The apparatus was described previously in detail [25] and a specific description of the operation in the threshold mode was also provided [26]. Although it was primarily designed to be used for measurements of noble gases and small, diatomic molecules, it was recently proven that it may also be used for measurements on more complicated systems, such as pyrimidine and of its heavier derivatives [27] or esters [28,29].…”

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

“…The only previous studies of this molecule concern its first ionization energy [1]. The absolute photoabsorption cross sections of isobutyl acetate presented here are needed for modeling studies of the Earth's atmosphere and radiation-induced chemistry of esters, and together with the results on previously analysed members of this class: methyl formate [2], ethyl formate [3], isobutyl formate [4] and ethyl acetate [5], help to understand the chemistry of esters and their electronic state spectroscopies.…”