Abstract R-matrix calculations using the Quantemol-N expert system on the photoionisation of acetylene, ethylene, methanol, and dimethyl ether for photon energies ranging from near-threshold to 40 eV were performed and reported here. Partial low-energy photoionisation cross-sections have been calculated for ionisation out of the two outermost valence orbitals (1πu and 3σg) leading to the X2Πu and A² g^+ states of the C₂ H₂^+ ion, four valence orbitals (1b3u, 1b3g, 3ag, and 1b2u) corresponding to the X2B3u, A2B3g, B2Ag, and C2B2u states of the C₂ H₄^+ ion, four ionic states (2a″ − 1) 2A″, (7a′ − 1) 2A′, (6a′ − 1) 2A′, and (1a″ − 1) 2A″ of CH3OH, and at last exclusively for the ionisation from the first valence orbital (2b1) of dimethyl ether. We have presented high-resolution cross-section data near the photoionisation threshold for the first time. These cross-sections are computed by incorporating electron correlation effects and large resonance structures, which have not been included in previous studies. We also did the calculations using different active spaces and target states to see if the current results were consistent and how they changed when the model was changed. Our best results, compared with available experimental and theoretical data, find reasonable agreement that confirms the reliability of our calculations. It is worth noting that previous studies have not fully accounted for autoionisation, multichannel coupling, and correlation-polarisation, which may be the reason for the slight variations in the results.
Mahla et al. (Thu,) studied this question.
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