Photofragmentation of tetrahydrofuran molecules in the vacuum-ultraviolet region via superexcited states studied by fluorescence spectroscopy

Abstract

Photofragmentation of tetrahydrofuran molecules in the vacuum-ultraviolet region, producing excited atomic and molecular fragments, has been studied over the energy range 14-68 eV using photon-induced fluorescence spectroscopy. Excited hydrogen atoms H(n), n = 3-11, have been detected by observation of the H α to H ı lines of the Balmer series. The diatomic CH(A 2 ), CH(B 2 − ) and C 2 (d 3 g ) fragments, which are excited to low vibrational and high rotational levels are identified by their A 2 → X 2 r , B 2 − → X 2 r and d 3 g → a 3 u emission bands, respectively. Dissociation efficiency curves for CH(A 2 ) and H(n), n = 3-7, have been obtained in the photon energy ranges from their appearance thresholds up to 68 eV. The appearance energies for CH(A 2 ) and H(n), n = 3-7, have been determined and are compared with estimated fragmentation energy limits in order to discuss the possible fragmentation processes. In the present studies, superexcited states of tetrahydrofuran are found, which dissociate into the above excited atomic and molecular fragments.

Superexcited states in the vacuum-ultraviolet photofragmentation of isoxazole molecules

“…The dispersed fluorescence spectra of isoxazole were measured using an experimental set-up that was described in detail in [8]. Briefly, a monochromatized photon beam provided by the beamline crossed the effusive beam of the sample molecules emanating from a hypodermic needle.…”

Interactions of protons with furan molecules studied by collision-induced emission spectroscopy at the incident energy range of 50–1000 eV

“…It is visible from Figure 5 that values of this ratio obtained for protons are much higher than that for the C + and O + cations. The enhancement of hydrogen peaks in the present experiment cannot be explained by fragmentation of the target molecule itself, because on one hand the formation of the CH radicals is minor as compared to other impact systems [14,15,[25][26][27][28][29][30] and on the other hand the production of the excited hydrogen atoms from neutralized protons, due to electron capture mechanism, is energetically the most favored channel [15].…”

“…Also fluorescence spectrum measured in the studies of electron impact excitation of furan [25] presents pronounced intensity of the diatomic CH fragments formed in the A 2 Δ, B 2 Σ − and even C 2 Σ − electronic states and the C 2 fragments in the d 3 Π g excited state. Present results of fragmentation of furan molecule may also be compared to the photon [26][27][28], cation [15] and electron [29,30] impact fragmentation of other five-and six-membered heterocyclic molecules. Again in contrast to present measurement all these studies demonstrated major fragmentation of the target molecules into several different atomic and diatomic fragments.…”

Electron impact excitation of methane: determination of appearance energies for dissociation products

“…Motohashi et al observed in their electron impact excitation experiments with methane an exponent of 4.5 ± 0.2 for the Balmer series [20] in agreement with [32]. In contrast, the exponential factors of the Balmer hydrogen series for dissociation of larger molecules like furan, tetrahydrofuran and isoxacole [34][35][36] yielded values much closer to the theoretical value (between 3.2 and 3.74). The dependence of the Balmer line intensities on n as obtained in the present experiment is presented in figure 4.…”