Formation of hot hydrogen atoms from superexcited states of acetylene

The cross sections for the formation of the H(2p) and H(2s) atoms, σ2p and σ2s , respectively, in photoexcitation of C2H2 were obtained in an absolute scale for studying formation and decay of superexcited states in the extreme ultraviolet range. Several superexcited states of C2H2 including multiply excited states were found in the curve of the σ2p cross sections as a function of the incident photon energy. The same states seem to contribute to the variation in the σ2s cross sections as well, which can be ascribed to the non-adiabatic transitions between the 2p and 2s channels. The Σ/Π symmetry-resolved cross sections for the H(2s) atom formation, σ2sΣ and σ2sΠ , were also obtained on an absolute scale. The coupling between the Σu+1 and 1Π u states was found to be small.