Ionic fragmentation of the isoprene molecule in the VUV energy range (12 to 310 eV)

Abstract

a b s t r a c t Isoprene, C 5 H 8 , is a biogenic volatile compound emitted from plants and animals, playing an important role in atmospheric chemistry. In this work, we have studied the ionic fragmentation of the isoprene molecule induced by high energy photons (synchrotron radiation), both at the valence (12.0, 14.0, 16.0, 18.0, and 21.0 eV) and carbon 1s edge (270 and 310 eV, respectively, below and above edge) energies. The ionic fragments were mass-analyzed using a Wiley-McLaren time-of-flight spectrometer (TOF) and single (PEPICO) and double ionization coincidence (PEPIPICO) spectra were obtained. As expected, the fragmentation degree increases with increasing energy. Below and above the carbon 1s edge, the fragmentation patterns are quite similar, and basically the same fragments are observed as compared to the spectra following valence-shell ionization. Stable doubly-charged ions were not observed. A PEPIPICO spectrum has shown that the main dissociation route for doubly-ionized species corresponds to the [CH 3 ] + /[C 4 H 2-5 ] + ion pair. Intense fragmentation of the isoprene molecule has been observed following valence shell and core electron ionization. The observance of basically the same fragments when moving from valence to inner-shell suggests that basically the same fragmentation routes are present in both cases. All doubly (or multiply)-charged cations are unstable, at least on a microsecond scale.

Kinetics for the Reactions of Ar+, O2+, and NO+ with Isoprene (2-Methyl-1,3-butadiene) as a Function of Temperature (300–500 K)

“…Two comparisons to the branching can be made. The first is to photodissociation experiments at energies (results in last row of Table ) comparable to the O 2 (12 eV photon and 12.1 eV reaction) and Ar (16 eV photon vs 15.8 eV reaction) ionization energies . For the 12 eV processes, the results line up reasonably well.…”

“…The first is to photodissociation experiments at energies (results in last row of Table 1) comparable to the O 2 (12 photon and 12.1 eV reaction) and Ar (16 eV photon vs 15.8 eV reaction) ionization energies. 35 For the 12 eV processes, the results line up reasonably well. The main products are the parent (C 5 H 8 + ) and loss of an H atom (C 5 H 7 + ) in about equal amounts with both experiments finding ∼6 to 8% of C 4 H 5 + (loss of CH 3 ).…”

“… a Uncertainties in the rate constants are ±25% absolute and ±15% relative, and the uncertainties for the product branching are as listed. b Photodissociation at 12 eV and 16 eV for comparison to electron transfer energies of 12.07 and 15.8 eV for O 2 and Ar. c Assumes lowest energy cyclic structure of the cation. d Calculated using the G4 method. …”

“… b Photodissociation at 12 eV and 16 eV for comparison to electron transfer energies of 12.07 and 15.8 eV for O 2 and Ar. …”

Ionization and Fragmentation of DCOOD Induced by Synchrotron Radiation at the Oxygen 1s Edge: The Role of Dimer Formation

“…This beamline has a monochromator with spherical diffraction gratings, which selects photons with energies between 250 and 1000 eV and energy resolution of E /Δ E = 1000, for 100 μm slits. The spectrometer allows to collect the PEPICO and PEPIPICO techniques. , The PEPICO and PEPIPICO spectroscopy has been widely used in recent studies − ,− to determine the fragmentation pathways of different molecular species that are single and doubly ionized.…”