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Published January 1982 | public
Journal Article

Photoexcitation and ionization in acetylene

Abstract

Theoretical studies are reported of photoexcitation and ionization processes in the acetylene molecule. The calculations performed employ Franck—Condon and static-exchange approximations, and implicitly invoke vibrational and rotational closure. Detailed comparisons with recent spectral assignments, electron-impact excitation studies, and total and partial-channel cross-sectional measurements indicate that the theoretical results provide a useful first approximation to the complete dipole excitation/ionization spectrum of C_2H_2. The calculated discrete spectra are seen to include contributions from virtual 4σ_g(n/σ^*) and 1π_g(π^*) orbitals, which appear an valence interlopers in the 1π_u→ nsσ_g, 2σ_u → nsσ_g, 1σ_u → nsσ_g and 2σ_u → ndπ_g, 1σ_u → ndπ_g Rydberg series, respectively, in good accordance with spectral measurements. By contrast, the 3σ_u(σ^*) virtual valence orbital gives rise to prominent diabatic resonance features above threshold in the 3σ_g → kσ_u, 2σ_g → kσ_u, and 1σ_g → kσu cross-sections, results that are in good quantitative accordance with corresponding experimental studies. Prominent features in the measured (1π_u^(−1))X^2Π_u partial cross-section, which is in good accordance with the present values, are attributed to autoionization 2σ_u → 1π_g(π^*) and 4σ_g(n/σ^*) intravalence transitions.

Additional Information

© 1982 Published by Elsevier B.V. Received 10 July 1981. It is a pleasure to acknowledge the support of the U S-Latin American Science Program, NSF(OIP)-CNPq (Brazil), of the Foundation for the Advancement of Science of the state of Sao Paulo (FAPESP), of the National Science Foundation, and the Donors of the Petroleum Research Fund, administered by the American Chemical Society. The kind hospitality of G H F Diercksen at the Max Planck Institut fur Astrophysik, Garching, to P W L is also gratefully acknowledged.

Additional details

Created:
August 19, 2023
Modified:
October 25, 2023