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Absorption coefficients of acetylene, propyne and 1-butyne were measured by a photoelectric technique in the region 1050–2000 Å. Two or three Rydberg series accompanied by vibrational bands were observed in the spectrum of these molecules. The photoionization curves and the Rydberg series yielded the same ionization potential: 11.41, 10.36, and 10.18 eV for acetylene, propyne and 1-butyne, respectively.
Nakayama et al. (1964) studied this question.