Ion-pair formation from saturated hydrocarbons through photoexcitation of an inner-valence electron

Abstract

Ion-pair formation from the superexcited states of saturated hydrocarbons has been studied by negative-ion mass spectrometry using synchrotron radiation in the 15–35 eV photon energy range. Negative ion H− has been observed from CH4, C2H6, C3H8, n-C4H10, iso-C4H10, and neo-C5H12. The maximum cross section ranges from 1.6×10−21 to 1.0×10−20 cm2. Strong peaks observed in the photodissociation efficiency curve of H− are assigned as resulting from transitions to the Rydberg states formed by promotion of an electron in a carbon 2s-type molecular orbital. In contrast, the valence-Rydberg transitions from a carbon 2p-type orbital have little (C2H6) or no contribution [CH4 and CmH2m+2 (3≤m≤5)] to the H− formation. This difference can be interpreted as that the latter Rydberg states have short lifetime with respect to autoionization to lower ionic states on account of relatively large overlap between two carbon 2p-type orbitals involved in an electron exchange process.

Vacuum-UV negative photoion spectroscopy of CH4

“…The line positions and relative peak intensities agree well with those observed by Mitsuke et al [28,29]. The first peak at ca.…”

“…The formation of H − from CH 4 has previously been investigated in the energy range 12-27 eV by Mitsuke et al [28,29]. In this paper, we confirm the H − efficiency curve features that they detected, and extend the range of detection to higher energy.…”

“…at the slightly higher energy of 21.5 eV, the peak of the 4p Rydberg state [29]. Whilst the errors made in evaluating absolute cross sections are often underestimated in the literature, we do not believe that this major discrepancy can be explained by an accumulation of individual errors in the various correction factors described in Section 2.…”

Two Studies in Gas-Phase Ion Spectroscopy

“…These data are available in the literature for CF 4 [41], SF 6 [42,43], CH 4 [44], CH 3 X (X = F, Cl, Br) [45], C 2 H 4 [46], C 2 H 6 [47,48], C 3 H 8 [47], and the chlorofluoromethanes (CFCl 3 , CF 2 Cl 2 , CF 3 Cl) [49]. The present work is in excellent agreement with these earlier studies and in most cases the quality and quantity of data obtained have improved.…”

“…Indeed when charge transfer has been observed, the EA of the neutral reactant molecule is large; dissociative and nondissociative charge transfer has been identified in some reactions of O 2 -, O -, CF 3 -, OH -and F -with SF 6 (EA = 1.1 eV), SeF 6 (EA = 2.9 eV), and TeF 6 (EA = 3.3 eV) [46]. To put these values into context, the EA values of O 2 , O, CF 3 , OH and F are 0.45, 1.46, 1.82, 1.83, and 3.40 eV, respectively [47].…”