Valence shell electronic spectroscopy of isoprene studied by theoretical calculations and by electron scattering, photoelectron, and absolute photoabsorption measurements

Abstract

The first ab initio calculations (vertical energies and oscillator strengths) are reported for the neutral electronic transitions of isoprene (2-methyl-1,3-butadiene), CH(2)CHC(CH(3))CH(2). The VUV photoabsorption spectroscopy of the molecule is presented in the energy range 4.6 to 10.8 eV (270-125 nm) with the highest resolution yet reported above 6.05 eV, revealing new spectral features. Valence and Rydberg transitions have been assigned in accordance with the theoretical results and the associated vibronic series have been analysed. The absolute photoabsorption cross sections at energies below 6.89 eV have been used to calculate the photolysis lifetime of isoprene in the upper stratosphere (20-50 km). Electron energy loss spectroscopy (EELS) measurements have enabled further photoabsorption cross sections to be derived in the range 9-28 eV. The first ab initio calculations have been carried out to determine excitation energies to the lowest energy ionic states of isoprene. The calculations are compared with the He(i) photoelectron spectrum (8 to 17 eV) and new vibrational structure is observed in the first photoelectron band.

Temperature-dependent rate coefficients for the reactions of the hydroxyl radical with the atmospheric biogenics isoprene, alpha-pinene and delta-3-carene

“…Evident from Fig. 1 is the good agreement between this discrete value (the red star) and the literature spectrum from Martins et al (2009), who reported σ isoprene = 1.29 × 10 −17 cm 2 molecule −1 . Taking into account potential systematic errors from e.g.…”

“…6), consistent with results from this work. A similar re-evaluation using cross sections from Martins et al (2009) does not change the rate coefficients from our study.…”

“…(2) to yield values of B with a high degree of precision (two standard errors were generally less than ±2 %). Systematic errors from unwanted radical chemistry were unlikely, since isoprene absorbs only weakly at the photolysis wavelength (σ = 1.18 × 10 −19 cm 2 molecule −1 at 248 nm from Martins et al 2009), whilst the use of low [OH] ensured that losses of OH by reaction with itself or with products from (R1) or (R5) could be disregarded in this analysis. Nonetheless, test experiments were conducted using an invariant [isoprene] = 3.2 × 10 14 molecule cm −3 whilst photolysis laser fluence, and thus radical concentrations, was varied by a factor of 15.…”

The use of isoprene as a novel dopant in negative ion atmospheric pressure photoionization mass spectrometry coupled to high‐performance liquid chromatography

“…In this study, we primarily evaluated the potential of monoterpenes including limonene, α‐pinene, and p ‐cymene and their structural unit, isoprene, as dopants for APPI. According to data available on photoabsorption cross sections, these species absorb the VUV photons from the krypton lamp as effectively as toluene and do not have positive electron affinities . Moreover, these compounds are natural compounds ubiquitous in nature and are considered less hazardous .…”

Capturing multireference excited states by constrained-density-functional theory

“…We summarize in Table I excitation energies computed with τ XCDFT along side with available benchmark data [36][37][38][39][40][41]. We find that the performance of τ XCDFT is comparable with XCDFT [7].…”