Ionizing and nonionizing decays of superexcited acetylene molecules in the extreme-ultraviolet region

Abstract

Absolute measurements of the photoionization and photodissociation cross sections of C H h b d · .2 2 ave een rna e usmg contmuum monochromatized synchrotron radiation in the 53-93 nm region. The absolute photoabsorption cross section and photoionization quantum yield of C 2 H 2 have also been measured. The excitation spectra ofC, and H(Lyman-a) fluorescence have also been obtained. The obtained results have been compared with theoretical calculations. An unresolved problem of the spectral. interpretation concentrated on the (J * and 1T* shape resonances has been clarified by the ~tr~l~htforward demonstration of the photoionization quantum yield. The ionizing and nomomzmg decay processes of the superexcited C Z H 2 molecules have been discussed in view of the strong competition of autoionization and neutral dissociation. An overlapping nature of Rydberg states with the shape resonance is found to be important. 4142

Photoabsorption spectra in the continuum of molecules and atomic clusters

“…The experimental data are taken from Ref. [41,46]. Inset: An energy region of 12.5 < ω < 17.5 eV is magnified and the total oscillator strength (thick line) is decomposed into partial oscillator strengths associated with different occupied valence orbital, 2σu (solid line), 3σg (dashed) and 1πu (dotted).…”

Interaction of photons with molecules - cross-sections for photoabsorption, photoionization, and photodissociation

“…Acetylene Figure 6 shows recent measurements of the photoionization quantum yield of acetylene using SR combined with a thin metal foil window. Also shown are previous measurements using discharge lamps or electron beams as a virtual photon source [17]. In the energy range of [17] 18-24 eV, the yields obtained by using the virtual photon source are considerably larger than those obtained with SR as a real photon source.…”

“…Also shown are previous measurements using discharge lamps or electron beams as a virtual photon source [17]. In the energy range of [17] 18-24 eV, the yields obtained by using the virtual photon source are considerably larger than those obtained with SR as a real photon source. The yields obtained in the lower energy range by using different methods agree fairly well.…”

“…6 indicate the neutral dissociation of a superexcited acetylene molecule predominantly competing with autoionization. Figure 7 shows the photoabsorption cross-sections of acetylene [17], the structures of which are assigned to Rydberg series converging to each of the ionic states, (3σ g ) -1 , (2σ u ) -1 , and (2σ g ) -1 . Combining the photoionization quantum yields and the photoabsorption cross-sections, the cross-sections for the total ionization (σ ι ) and for non-ionizing decay processes (σ δ ) are obtained as shown in Fig.…”

“…Excitation spectra of fluorescence from excited fragments produced in the dissociation of a superexcited acetylene molecule have been observed [17]. According to the emission spectra of excited fragments which may be produced from a superexcited acetylene molecule, band-pass filters were chosen to disperse the total fluorescence.…”